-------
143
The mass fraction of the contaminant in the horizontal flux
was defined by Travis to be
£ - mS + mNS (188)
h p hAxAy + mg + mNg
Where fr, = mass fraction of contaminant, dimensionless .
m~ = mass of suspendible contaminant in surface layer
of depth h, gms .
mNS = mass on non-suspendible contaminant in surface
layer of depth h, gms.
p = density of native soil, gms/cm3
AxAy = area of grid cell, cm2
h = depth of credible surface layer, cm.
To account for the weathering process, Travis suggested two
methods, one of which decreased effectively the amount of contam-
inant by means of a "weathering-in" function such as described by
Anspaugh, et al. (1973). To follow this suggestion, it may be of
some use to consider first the total mass of contaminant, m^ +
m>,c> which can be related to total concentration per unit area,
SA, by
mS + mNS
S.AxAy
Where S. = total concentration per unit area, uCi/cm2
(assumed to be near the surface, top few cm)
AxAy = area of grid cell, cm2
acp = specific activity, yCi/gm.
Note, however, that all the parameters mentioned above are
independent of time. Referring to the source mentioned by
Travis, it can be recalled that the "weathering-in" function
mentioned in this regard was that described by a half-time of 38
113
-------
144
days, pertaining to the material decrease in availability to the
resuspension process, not to erosion by saltation and creep.
Furthermore, to apply this function to equation (188), the
surface concentration S (t) of pollutant would have to be con-
3.
sidered, not the total concentration per unit area, S., which
would signify that the depth h, to be realistic, would have to be
extremely small, which may lead to unrealistically high values of
fr, , approaching fr, = 1 in the extreme case of a "just-deposited"
material. Conceptually, this would indicate that the soil cannot
retain any significant amount of pollutant, the latter being able
to move about the grid in a manner reminiscent of hockey pucks on
ice. Making the questionable assumption that the weathering
half-times described by Langham, Anspaugh and others apply to all
erodible material and not just the resuspendible fraction still
does not relieve the modeler of the need of postulating mixing
depth h, the magnitude of which would be such as to make the
results "reasonable," but cannot be known "a priori" in the
strictly analytical sense.
The other alternative offered by Travis to account for
weathering was to make the thickness h time-dependent, and
increasing it as the pollutant penetrates further into the soil,
with time. However, as shown previously, this penetration occurs
very rapidly during the initial time period immediately after
deposition and then remains practically stationary. In order for
weathering to proceed in a manner similar to that described by
Anspaugh, fr, would have to include a decreasing exponential term
e~Xt, which, h being the variable of concern, would be roughly
equivalent to have h increase exponentially, in a manner dictated
by e . This behavior of h would be extremely unrealistic.
The import of the preceding discussion can best be gaged by
examining the vertical flux term, Fy. As expressed in the
present model, F is a function of F^ and friction velocity u *.
114
-------
145
p/3
- 1] (190)
„
U
where
C , C, = constants, defined by Gillette to be
v n
2 x 10"10 and 10"6 , respectively.
P = mass percent of suspendible particles
= 100 (°AxAy h f + m
u (QAxAy h + ms +bm
where f = mass fraction of suspendible
soil particles
The mass fraction of suspendible contaminant particles in the
vertical flux can be calculated by the ratio
«;
fr = - ^ - (191)
h f + m
By following the development of F fr from equations (18 8)
through (191) and the intervening discussion, it can be seen that
the weathering effect on resuspendible particles is meant to be
incorporated by means of a similar weathering effect on the total
erodible mass and horizontal flux F, , F being proportional to
F, . Since Travis' model does not provide, apparently, any
efficacious or realistic way of achieving this time dependence,
it would follow that the weathering effect cannot be included, at
present, in the model as described (Travis, 1975). This repre-
sents a drawback of the present model.
Using the vertical flux F as a source term for a "Gaussian
Puff" model of an instantaneous point source diffusing in three
dimensions, the concentration of pollutant at any position
(x,y,z) may be obtained by
115
-------
146
(x-x ) (y-y )
'3/2 I" 1^-20-*-
FyfrvAXAyAt asp(2-rT) e x y
where
C(x,y,z,t) = concentration of pollutant, yci/cm3
a ,a ,a = dispersion coefficient, cm
.A. y z*
x ,y ,z = position of puff center, as cloud moves
>— • v- L-
downwind
Multiplying this equation by 1/fr aCD will provide the total soil
V or
concentration in air at the corresponding locations. Travis
estimated that ground level concentrations from this Gaussian
Puff model should be correct within a factor of 3.
As the cloud drifts downwind, material is lost from it at a
rate determined by the deposition velocity V,. At present, the
model assumes this deposition velocity to be equal to the ter-
minal velocity, V .
g
V
d - p -a (193)
where V = gravitational settling velocity, cm/sec
&
D = particle diameter, cm
g = gravitational constant,
= 980.665 cm/sec2 at sea level.
3
p = density of particle, gms/cm
= 11.4 gm/cm3 for Pu02
p = density of air, gms/cm
cl
= 0.0012 gms/cm at 20°C, 1 ATM
y = viscosity of air, gm/cm-sec
= 0.000181 gms/cm-sec at 20°C, 1 ATM
116
-------
1*7
As Travis pointed out, this equation is in error when small
particles are considered, due to the influence of surface and
wind characteristics on the deposition process. Consequently,
the model may miscalculate air concentrations of pollutant,
particularly when particles of respirable size (<3 ym) are
considered.
It should be recalled that Travis's model prime intent was
the description of contaminant redistribution, not that of
resuspension. Consequently, and in view of the lack of proper
weathering terms and deposition velocities applicable to small
particles, the conclusion must be made that the model in present
form can best be used for short times after deposition, provided
that the mass fractions of suspendible and non-suspendible
pollutant can be accurately identified, and for particles above a
certain, as yet unidentified, minimum size.
117
-------
148
CONCLUSIONS
Having reviewed the salient characteristic of each model,
commented on possible drawbacks, and added interpretations that
may be, hopefully, of some assistance to the-modeler, several
generalizing statements appear to be in order.
In viewing model disadvantages, it becomes apparent that all
the models discussed have a common characteristic - that of
failing to identify, at a realistic (finite) source, the progres-
sively diminishing portion of the contaminated soil that may be
resuspended.
In gaging models advantages, the possible specific applica-
tions of each model must be considered. Suggesting the use of
one model to the exclusion of all others is an arduous task,
inasmuch as each model has features to recommend it, originating
from the conditions by which the model was developed and the
purpose of the model development. The simplest models should
have greater applicability, whereas more complex models should
gain in accuracy. In describing the relevant features of each
model and conditions for the model use, the author has opted for
a tabular presentation, suggesting the conditions for "best"
applicability of each, with the qualification that these condi-
tions are not restrictive (Table 15).
The intervening Table 14 separates the various models into
groups, on a somewhat arbitrary basis, depending on what derived
parameters, principles, or influencing conditions were applied of
greatest significance in the model, in the author.1 s interpreta-
tion.
118
-------
TABLE 14. BASIC GROUPING OF RESUSPENSION MODELS, ACCORDING TO
MAIN CONCEPTS EMPLOYED OR DERIVED FROM THEIR USE
RESUSPENSION FACTORS
Langham's model
Kathren's model
Anspaugh's model
u
M 2
Cd O
W t-T
X en
tn PH
O P-c
21 i— i
H Q
RESUSPENSION RATIOS
Horst's model
Amato's model
Healy's model
Gillette and
Shinn model
Mass loading
model
Slinn's model
Travis' model
Healy and
Fuquay model
WIND/ERODIBILITY EFFECTS
o en
*"7l *Tl
RESUSPENSION RATES
Sehmel and
Orgill model
s-. m
H-I n
2 -3
-------
TABLE 15. MAIN FEATURES OF RESUSPENSION MODELS AND CONDITIONS TO WHICH THEY ARE BEST APPLICABLE
ISJ
O
Model Main Features of Model
Langham's Model The airborne concentration of pollutant C(t) (time dependent)
is calculated through use of a "resuspension factor" Rp (constant)
and the "surface contamination available for resuspension" Sa(t) (time dependent),
expressed as an exponential decay function, with an initial value S (0),
the rate of decay being set by an "exponential coefficient, product of time t
and an "attenuation coefficient" A. (constant)
Kathren's Model The airborne concentration of pollutant C(t) (time dependent)
declines exponentially at a rate set by a coefficient which is product of time t
and an "air concentration attenuation factor" X. (constant)
The initial value of airborne concentration C(0)
is related to the surface concentration S (constant)
through a "resuspension factor" Rp (constant)
Anspaugh s Model The airborne concentration of pollutant C(t) (time dependent)
is related to the "total concentration per unit area" [regardless of depth] Sa (constant)
through a "resuspension factor" Rf(t) [time dependent)
expressed as an exponentially declining function, with an initial value R£(O) (constant)
and a rate of decline given by exp [-0.15// day x ^t]
until a final value is reached of Rf(~) (constant)
Stinn's Model The resuspension factor Rr»
calculated on the basis of several measureable parameters,
expressed as soil erodibility £,
fraction of horizontal flux at samples height, r
mean wind velocity u,
depth to which contaminant has penetrated into the soil, s
Conditions to which Model is best applicable
1. Uniform distribution of pollutant
2. over large (ideally "infinite") areas
3. for relatively fresh contamination
4. for short time spans
For use with Rp = lO^m'1, 5. under conditions of moderate activity
(Langham's suggested value 6. in lightly vegetated areas
Same conditions as above 1 through 4
For use with Rp = lO'^m'1(value used by Kathren),
add 5 under conditions of extreme activity.
Conditions 1, 2, and 6 above, plus
3. Following an "instantaneous" release or release of short duration
4. for times t > tf- 4 days ( 100 hours) where t » "model" time
t = time since release
S, for short time spans following deposition, i.e., for fresh contamination
6. for aged contamination (where Rf(t) Rf
HT'm"1)
(little documentation exists for Rr(t) behavior during "intermediate" periods)
1. Uniform distribution of pollutant
2. for aged sources
3. for contaminated areas of finite size, Ag.
4. at distances downwind from the contaminated area such that
-------
TABLE 15. MAIN FEATURES OF RESUSPENSION MODELS AND CONDITIONS TO WHICH THEY ARE BEST APPLICABLE (Continued)
Model
Mass Loading Model
Sehmel and Of gill Model
Gillete and Shinn Model
Main Features of Model
The airborne concentration of contaminant C,
product of "average mass loading" AML,
times the specific ground activity A
The airborne concentration of contaminant C
expressed as function of wind velocity u
elevated to the 2.1 power
The "dust flux" F and concentration C, at 1 meter height,
expressed as functions of friction velocity u*
elevated to a power f (empirically determined).
and a "reference dust flux" F (at u* = 1 m/sec)
Both F and y are represent graphically,
as functions of soil erodibility index I
(see, however, present author's discussion, eqn (15) and following)
Conditions to which Model is best applicable
1. For aged contamination
2. for specific land uses
3. over large areas
Strictly applicable to conditions and locality where model was obtained
1. At Rocky Flats, Station S-8
2. for West and Southwest winds
In a strict sense, the model predicts dust fluxes and concentrations,
applicable to contaminants if a proportionality between dust and
contaminant concentrations were established, in which case
the model would best be applicable under the following conditions:
1. over large areas
2. for aged contamination
3. for soils of low erodibility index I
Heaty and Fuquay Model'
tsJ
The airborne concentration of resuspended contaminant C(x,y,0) (location dependent)
is calculated through application of diffusion, depletion and
source expressions, described below:
A source rate, Q
function of mean wind velocity u,
related to: a surface concentration S (constant),
of a given contaminant of density f> (constant),
present as particles of a physical diameter d (constant),
through a "pickup coefficient" K (constant)
Source depletion rates, Q(x)/Q,
function of wind velocity u,
distance from source x,
Button diffusion coefficient C (constant),
atmospheric stability n (constant)
and a "coefficient of deposition" A (constant)
Atmospheric diffusion equations, C(x,y,0) (location dependent),
function of x, c, n, u (already mentioned above),
the "crosswind distance" y,
and a "reflection factor," R (constant)
1. For contamination sources of specific shapes, as developed by Healy and Fuquay:
a. point sources
b. line sources of great (ideally "infinite") length
c. areal sources of "infinite" crosswind extent but finite along wind direction
d. large (infinite") areal sources,
2. with surface contamination distributed uniformly,
3. with contaminant particles of a given diameter,
4. Sutton coefficients such that GZ - C,
5. at short distances from the ground.
6. for relatively small wind velocities,
7. for slight soil movement.
CJl
-------
TABLE 15. MAIN FEATURES OF RESUSPENSION MODELS AND CONDITIONS TO WHICH THEY ARE BEST APPLICABLE (Continued)
Model
Main Features of Model
Conditions to which Model is best applicable
Healy's Model
The airborne concentration of resuspended contaminant C(x,y,z) (location dependent)
is calculated through application of atmospheric diffusion, depletion and source
expressions as described below:
Source rates Q
related to surface contamination S (constant)
through & "resuspension rate" R£ (constant)
Source depletion rates, Q(x)/Q
function of the distance from source x
the Sutton diffusion coefficient C., (constant)
the average wind velocity u
the atmospheric stability n (constant)
1. For contamination sources of specific shapes, as developed by Healy:
^. point sources
b. line sources of great (ideally "infinite") length
c. areal sources of "infinite" crosswind extent but finite along wind direction
d. large ("infinite") areal sources
e. line sources with a Gaussian distribution of contaminant
2. with surface contamination distributed uniformly (excepting le above)
3, at "ground level" for cases lc, 13, and le
4. directly downwind from peak ground concentration in case le
?. for particles not much greater than 1.5 micrometers (physical diameter]
Atmospheric diffusion equations,
function of the variables x, C , n, u (mentioned above)
in addition to: the "crosswind distance" y
the elevation i
the Sutton diffusion coefficient C (co
the "reflection factor" R (constant)
Horst's Model
ro
The airborne concentration of resuspended contaminant C (t) (time dependent)
is calculated by applying a resuspension factor R_(constant)
to the total contamination per unit area S (t) (time dependent),
obtained through solution of two differential equations describing the rates
of change of the two quantified indicated below:
A surface contamination S (t) (time dependent)
affected by three terms, as follows:
1. a "rate of resuspended contaminant deposition"
related to resuspended contaminant concentration C (t) (time dependent)
[itself a function of the surface contamination S (t)
and a "resuspension factor" Rp (constant)],
through a "deposition velocity" V, (constant)
2. a "rate of surface contaminant soil fixation, '
related to the surface contamination S (t)
through a "fixation rate" A (constant)
3. a "rate of surface contaminant resuspension,
related to the surface contamination S (t)
through a "resuspension rate" R- (constant)
A total contamination per unit area S.(t), '(time dependent)
affected by two terms, as follows:
1. a "rate of resuspended contaminant deposition"
(with the same relationships mentioned in 1) above)
2. a "rate of surface contamination resuspension"
(with the same relationships mentioned in 3) above)
Solving these two equations results in a now explicit time dependence, t
1. Treshly deposited contamination
2. uniformly distributed
5. over large areas,
4. for low wind velocities
CJi
ro
-------
TABLE 15. MAIN FEATURES OF RESUSPENSION MODELS AND CONDITIONS TO WHICH THEY ARE BEST APPLICABLE (Continued)
Model
Main Features of Model
Conditions to which Model is best applicable
Amato's Model
A computerized model, calculating the "resuspension ratio" R ,,
as the ratio of airborne concentrations in an interval of finite width and "infinite" length i
due to "resuspension" of material deposited in preceding intervals, C
and to resuspension from the originally contaminated yround source interval, Cj
The "resuspended" airborne contamination in interval i, C
is obtained by suranation of contributions from preceding intervals j,
each providing at interval i an additional concentration C JS /(Oh
i J
i.e., the airborne soil contamination at i from interval j, Cs*
weighed by interval j's soil contamination S-,
the depth of penetration of contaminant into the soil h,
and the density of the soil p,
Ihe airborne soil concentration at interval i suspended from interval j, C§J
is obtained by means of a diffusion equation, including factors such as 1
resusrension flow rate q
distance between intervals j and i, x
Sutton coefficient C
Sutton coefficient Cz
stability coefficient n
deposition velocity V,
wind velocity u
elevation Z
1. For aged contamination [implying intijnate association with soil)
2. uniformly distributed with depth,
3. the depth not exceeding top centimeter of topsoil,
4. the topsoil consisting of material able to move in suspension,
but not in saltation or creep, i.e., extremely fine material,
S. uniformly distributed over the soil surface,
6. initially, over an area finite along wind direction and of
infinite extent in the "crosswind" direction.
The soil contamination
interval j, S
is obtained as summation from preceding intervals k,
of the soil contaminations in k from original source contamination >S,,
weighed by a resuspension flow rate Sr (mentioned previously),
a "fixation rate"A ,
and constants obtained from the particular solutions A.-* ,
to differential equations expressing rates of change of S.,
including h,p, qr, A (mentioned previously)
in addition to a deposition rate coefficient I).
and a "time of flight" from k to j T.
The "deposition rate coefficient "between k and j, I).
is obtained as function of qr, h, |0, V^, x, Cz> C , n, u
and, in addition, a "reflection factor" R
he "time of flight" between j and k, T.
:-s a function of the length of intervals L^
the number of intervals between k and j, n
and the wind velocity u
The resuspended airborne contamination at i, direct from source "1",
with C ^ in the diffusion model being replaced by Cg
with S^being replaced with S,
Oi
-------
TABLE 15. MAIN FEATURES OF RESUSPENSION MODELS AM) CONDITIONS TO WHICH THEY ARE BEST APPLICABLE (Concluded)
Model
Main Features of Model
Conditions to which Model is best applicable
Travis' Model
A computerized model, calculating airborne concentration CCx^y.z.t) (space, time dependent)
over any one grid cell of area x y of a two-dimensional grid system, as function of
the spatial coordinates x
the time t
the dijnensions of the grid cell Ax
Ay
the specific activity of the soil a^
P
of the mass fraction of suspendible contaminant in the vertical flux fr
[itself a function of the mass of suspendible contaminant M ,
the depth to which the contaminant has penetrated into the soil h,
the mass fraction of suspendible contaminant in the soil f ,
the density of the native soil p ,
and the area of the grid cell, AXAy],
and "the vertical mass flux" F
[the latter a function of the friction velocity u*,
the threshold surface friction velocity u. ,
the correlation constants C
1. For aged contamination,
2. with resuspendible fraction consisting of particles not over 20ttm in
diameter,
3. but sufficiently large to preclude turbulent transfer effects over-
shadowing terminal settling velocities,
4. not necessarily uniformly distributed,
5. over a large readily partitionable into planar cells,
6. with a recognizably uniform contamination in each cell
An alternative to condition 1) is in applying model to
la) fresh sources
Ib) for short time periods
the mass percent of suspendible particles, F
and the "horizontal mass flux" R]
The "horizontal mass flux" F, , is a function of
the effective surface friction velocity u
[function of observed surface shear r ,
surface soil moisture content a ,
density of surface airpa]
a reference surface friction velocity j
[function of a reference surface shear T ,
density of surface airfu (mentioned above)]
the already mentioned threshold surface velocity u
the soil credibility fraction x
[function of soil erodibility index I,
amount of regetative residue R,
surface roughness K,
and two constants a
b
The mass percent of suspendible particles P
depends on parameters p.Ax.Ay, h, f (already mentioned above)
and the mass of non- suspendible contaminant H^
Redistribution of contaminant along the ground is introduced through
the "mass fraction of contaminant in the horizontal flux" frh>
dependent on the same parameters that affect fry,
plus the "mass of non- suspendible contaminant" M^
Material loss from a cloud moving downwind is related to Vg,
gravitational settling velocity equated to 'Velocity of deposition" V
function of particle diameter D,
gravitational constant g,
density of particles p ,
density of airp^,
viscosity of air
-------
155
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PARAMETERS FOR ESTIMATING
THE UPTAKE OF TRANSURANIC ELEMENTS
BY TERRESTRIAL PLANTS
David E. Bernhardt
George G. Eadie
Formally Published as Technical Note ORP/LV-76-2
U.S. Environmental Protection Agency
Office of Radiation Programs - Las Vegas Facility
Las Vegas, Nevada 89114
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This report has been reviewed by the Office of Radiation
Programs - Las Vegas Facility, Environmental Protection Agency,
and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or
recommendation for use.
11
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PREFACE
The Office of Radiation Programs of the U.S. Environmental
Protection Agency carries out a national program designed to
evaluate population exposure to ionizing and non-ionizing
radiation, and to promote development of controls necessary to
protect the public health and safety. This literature survey
was undertaken to assess the available information of parameters
for estimating the uptake of transuranic elements by terrestrial
plants. Readers of this report are encouraged to inform the
Office of Radiation Programs of any omissions or errors.
Comments or requests for further information are also invited.
Donald W. Hendricks
Director, Office of
Radiation Programs, LVF
111
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CONTENTS
Page
INTRODUCTION 1
SUMMARY AND CONCLUSIONS 2
DEPOSITION ON PLANT SURFACES 4
Consideration of Particle Size 5
Deposition Parameters 7
RADIONUCLIDE UPTAKE FROM SOIL BY PLANTS 12
COMBINATION OF DEPOSITION AND PLANT UPTAKE 19
REDISTRIBUTION OF ACTIVITY WITHIN PLANTS 21
REFERENCES 22
APPENDIX A
Parameters for Atlantic-Pacific Interoceanic Canal Model 28
LIST OF TABLES
Number
1 SUMMARY OF PLANT DEPOSITION AND RETENTION PARAMETERS
2 SUMMARY OF PLANT UPTAKE OF PLUTONIUM
3 PLUTONIUM IN VEGETATION AND SOIL
Page
9
13
20
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INTRODUCTION
This report summarizes information from the literature
concerning parameters which can be used to estimate the transport
of transuranic elements through plants to man. The scope of the
report is limited to parameters for estimating the concentrations
of transuranics in terrestrial plants based on activity concen-
trations in soil and air.
There is only a limited amount of information specifically
concerning plant uptake of transuranics. In many instances it
has been necessary to use information based on other elements,
which interjects additional uncertainties due to the variance in
physical and chemical characteristics of these elements versus
the transuranics. Furthermore, most of the transuranic data
relates to plutonium; thus, this report focuses on plutonium.
Brown (1975) presents a bibliography of information concern-
ing plant uptake of americium. Americium has only received cur-
sory coverage in this review, although consideration has been
given to the differences between americium and plutonium in plant
uptake. Differences in the mobility and uptake of plutonium-238
and plutonium-239 are discussed. Papers concerning deposition
and retention of plutonium on reindeer lichens have been excluded.
Plant uptake results from root uptake and deposition of
contamination on above ground surface areas of the plant.
Although deposition or fallout on the plant may not actually be
taken into the plant tissue structure, Romney et al. (1975) and
Hanson (1975) note that it may be tightly bonded to the plant
microstructure and become essentially indistinguishable from
material in the plant tissue. Deposition on plant surfaces
occurs from both the initial contamination cloud and resuspension
of contaminated soil.
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SUMMARY AND CONCLUSIONS
The limited amount of available information is not adequate
to select precise parameters for estimating concentrations of
plutonium in vegetation due to root uptake and foliar deposition.
The existing data base is essentially non-existant for some
parameters, and shows significant variations for other para-
meters. Furthermore, much of the existing laboratory-generated
data is not directly applicable to the normal geographical and
climatological field conditions.
There is a significant variance in the estimates of the
particle size distribution for airborne plutonium. Estimates of
aerodynamic mean diameters appear to vary from sub-micrometer to
about 10 pm diameter particles. For given particle size distri-
butions, there are uncertainties in the deposition velocity,
vegetation interception factors, and retention parameters.
Furthermore, much of the experimental data appears to be for
particle-size distributions significantly larger than those
expected from normal nuclear reactor fuel cycle plant releases,
worldwide fallout, or resuspension. There is the additional
unknown feature in that specific plant deposition parameter work
has not been done with plutonium.
The plant deposition parameter information is summarized in
Table 1. These data imply a deposition interceptor factor
(F, pCi on vegetation per unit area subtended by the vegetation,
per pCi per unit area of ground) of about 0.2. Although the
measurement of this parameter is time dependent, the time after
deposition is generally not indicated in these studies. It
appears that the weathering half-life is short (hours to a day)
during the initial deposition period.
There is a significant range in the initial retention
estimates associated with the type of vegetation, and more
importantly, a variance-associated with the time after deposition
when the measurement is made. The intervening wind and precipi-
tation conditions are also of prime importance.
It is suggested that the initial retention and weather half-
life data should be treated as sets for each individual study.
That is, the individual parameters should not be averaged between
studies without a detailed evaluation as to common situations
(e.g., time of measurements and climatology). Prudence appears
to indicate choice of a weathering half-life of about 30 days for
time periods of about a week after deposition. For small plants,
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not prone to trapping particles, a retention factor of about 20
to 30 percent appears reasonable, but there is considerable
uncertainty in the data.
Plant uptake parameters are summarized in Table 2. Hanson
(1975) estimates the plutonium uptake by plants to be about 10-1*.
Others generally categorize it as about 10-3to 10-6 which
includes most of the data in Table 2. Romney et al. (1970) and
Neubold (1963) present data that show a definite increase in
plant uptake with successive crops. Romney's et al. (1970) data
indicate about an order of magnitude increase, from 1.9 x 10-5 to
14 x 10-5 over a 5-year period. This increase is generally
related to microorganism activity in the soil (Au (1974), and
Au and Beckert (1975)) and chelation by organics in the soil
(Romney et al. (1970)).
There is some indication that plutonium-238 is more mobile
than plutonium-239, but this has received only limited verifica-
tion. Cline (1967) reported that barley took up 50 times as much
americium-241 as plutonium-239. Romney et al. (1974 and 1975)
have also reported that americium-241 appeared to be more mobile
than plutonium.
Essentially all of the plutonium uptake studies are based on
laboratory experiments containing plutonium uniformly mixed
throughout the soil volume thereby increasing root contact.
Results therefore appear to be unrealistic for natural vegetation
where the deposited plutonium is largely limited to the upper
2 to 5 cm of soil, above the natural root mat. Therefore, the
laboratory results should be conservative for most natural plant
species growing in undisturbed or unplowed land; but, the uniform
distribution of the plutonium in the laboratory soil should be
representative of farm crops grown on plowed land.
Bloom et al, (1974) and Martin et al. (1974) report data
from Romney et al. (1974) indicating plant uptake from Nevada
Test Site field studies. A total plant uptake of about 0.3 is
inferred. They also estimate a total long-term uptake (20 years)
of about 0.3 by exponentially extrapolating Romney's et al.
(1970) 5-year study to 20 years. Romney et al. (1974 and 1975)
qualify the 0.3 uptake as being from both root uptake and deposi-
tion and they emphasize that deposition is the primary contrib-
utor, probably by several orders of magnitude.
There appears to be general consensus that deposited
plutonium is not taken up (by foliar absorption) into the plant;
rather, it is generally immobile.. This hypothesis is based on
limited information.
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DEPOSITION ON PLANT SURFACES
The following parameters are used in the deposition pathway:
- Deposition velocity: This may be given with raspect to
the ground surface or for vegetation. If the deposition
velocity for the ground is used, the plant intercept area
or factor must be used.
- Plant interception factor (F): Witherspoon and Taylor
(1969J defined F=WC°/m,
where:
W is the biomass of foliage in grams (dry weight)
per square foot of soil surface area (g/ft2").
C° is the quantity of radionuclide initially
intercepted per gram dry weight of foliage
(yCi/g).
m is the quantity of radionuclide deposited per
ft2 of soil surface area.
Thus, F is the ratio of radioactivity deposited on the
foliage to the radioactivity deposited on the ground
area inhabited by the foliage. The ratio has no units.
The product of the deposition velocity for the ground
surface and F is the initial effective deposition
velocity for vegetation.
- The initial retention factor, (f) , is the fraction of
radioactivity originally deposited that remains at some
time after deposition. This is usually given for one to
two weeks after deposition.
- The weathering or retention half-life (Tw) represents the
exponential decrease in the retention of deposited
activity rfter the initial one to two week period.
- The plant biomass of foliage (W) is given as grams dry
weight per square meter.
- The fraction of deposited activity that is actually taken
into the plant is denoted as (d).
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CONSIDERATION OF PARTICLE SIZE
The deposition velocity, plant interception factor, and
plant retention of deposited material are all a function of the
particle size distribution. The size distribution of airborne
particulates is related to the source of release. Particle size
distributions vary from the micrometer and sub-micrometer dia-
meter for nuclear fuel cycle plants and worldwide fallout to tens
of micrometers for near-in fallout and aged fallout in the soil.
High efficiency particulate air filters (HEPA) are used to
minimize releases from nuclear fuel cycle plants. HEPA filters
have removal efficiencies of 99.97 percent for 0.3 ym diameter
dioctyl phthalate smoke particles; thus, releases from most
nuclear installations are assumed to be in the sub-micrometer
size range (Burchstad (1967)). Moss et al. (1961) also report
mass median diameters of less than 1 ym for airborne plutonium in
working areas of a plutonium fabrication plant.
Klement (1965) indicates that particulates from nuclear
explosions are generally in the sub-micrometer range; but, they
may become attached to other material forming conglomerates of
10 ym or more (Gudiksen and Lynch (1975), and Nevissi and Schell
(1975)). Generally, worldwide fallout is classed in the microm-
eter to sub-micrometer diameter size.
The size distribution of resuspended material is dependent
on both its original size and composition, and on the material to
which it becomes conglomerated within the soil. Bretthauer
et al. (1974) analyzed particles from air samples at the Nevada
Test Site (NTS) and observed plutonium-bearing particles from
less than 0.5 to 17 ym in diameter. The composition of the
particles ranged from plutonium, uranium, and oxygen (several
micrometer) to silicate and organic particles (about 10 ym). The
geometric mean particle diameter was about 1.5 ym.
Volchok et al. (1972) report data from two studies of
airborne particulates around the Rocky Flats Plant in Colorado.
The initial study, based on particles on particulate filters,
indicated a mean diameter around 10 ym. This study was poten-
tially biased by the lack of analysis sensitivity for particles
below 0.5 ym. Results from six cyclone and elutricator samples
(run time of about 50 hours) indicated median diameters of about
5 ym.
Tamura (1974 and 1975) reports on the particle size
distribution of plutonium in NTS soils. One to ten percent of
the activity was found in the 0 to 5 ym diameter soil fraction;
whereas, about 60 percent (up to 90 percent for several samples)
of the activity was found in the less than 53 ym size. Romney
et al. (1975) indicate that the micro-structure of many species
of vegetation is adept at capturing particles of these size
ranges. The bond between the vegetation and these particles is
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186
apparently so tenacious as to make it almost impossible to
distinguish the material from that actually taken up into the
plant.
Bloom et al. (1974) assume a particle size of 10 ym for
plutonium in air, which leads to a value of about 5 cm/sec for
the deposition velocity. These values are used in their environ-
mental plutonium model.
Bagnold (1945) and Chepil (1945a,b,c,d) indicate that over
90 percent of the wind movement of soil is by surface creep and
saltation. These phenomena occur at heights below 1 meter above
the ground surface and are not observed on standard air samples.
Surface creep and saltation are connected with movement of soil
particles of tens to hundreds of micrometers in diameter. Thus,
they include movement of the soil size fraction that contains the
majority of plutonium (Tamura (1974 and 1975)). Furthermore,
vegetation can retain particles of this size class, (Romney
et al. (1975)).
In summary, various investigators recommend a range of
particle sizes for airborne plutonium. Particle material from
original source terms is generally in the micrometer to sub-
micrometer class. Plutonium in soil (limited data, mostly from
NTS) appears to be predominately associated with particles
between 20-50 ym in diameter (Tamura (1974 and 1975)). The
limited information from Bretthauer et al. (1974) and Volchok
et al. (1972) indicate that the mean diameter of resuspended
plutonium particles is less than 10 ym, probably around 5 ym.
Much of the activity deposition on plants with foliage near the
ground, would appear to result from surface creep and saltation
associated with the larger diameter particles (10 to 100 ym)
versus resuspended material.
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DEPOSITION PARAMETERS
Witherspoon and Taylor (1969) present data for simulated
fallout on pine and oak trees, using cesium-134 as a tracer. The
initial fraction (F) of the simulant fallout (88 to 175 ym
diameter particles) intercepted and retained by foliage was
higher in the oak tree (0.35) than in the pine tree (0.24).
After 1 hour, the broad-leaved oak lost about 90.5 percent of the
initial deposition, while the pine loss was only about 10 percent,
corresponding to initial retention factors of 0.095 and 0.90,
respectively. Weathering half-lives (Too) due to wind, rain, and
all other environmental factors were determined to be 25 and 21
days for the oak and pine trees, respectively, for the period
from 7 to 33 days after initial fallout deposition.
Witherspoon and Taylor (1970) present data for five crops
using simulated fallout with rubidium-86 as a tracer. Two sizes
of quartz particles (44 to 88 ym and 85 to 175 urn diameter) were
used on squash, soybean, sorghum, lespedeza, and peanuts. For
the size range 44 to 88 ym, the fraction of fallout initially
intercepted (F) ranged from 0.075 for the small-leaved lespedeza
to 1.248 for the squash. Interception factors (F) greater than
unity were obtained for squash and soybean plants. Such plants,
which have bush-like structures, have large exposed surface areas
available in many different interception planes. The average
fraction intercepted (F) for the smaller diameter particle size
range was 0.587, which was about 2.5 times greater than F for the
larger particle size range.
Fisher (1966) predicts a theoretical decrease in the deposi-
tion velocity on pasture grass with decreasing particle size in
the 20 to 0.1 i>m range. It would appear that using Witherspoon
and Taylor's data for the 44 to 84 ym range would be conserva-
tive, but there is limited information on which to base this
hypothesis.
Witherspoon and Taylor (1970) also studied particle reten-
tion. Losses from plant foliage due to wind removal (during the
first 12 hours postdeposition) ranged from 3 to 35 percent
(average--21.1 percent) for the 44 to 88 ym particles. During
the same period, losses for the larger particle size ranged from
9.5 to 26 percent (average--15.8 percent). For the 12- to
36-hour period postdeposition, losses ranged from 1.2 to 33.5
percent (average--15.4 percent) for the smaller size simulant and
ranged from 7.7 to 34 percent (average--21.6 percent) for the
larger size simulant. Therefore, during the first 12 hours of
postdeposition, when the wind speed averaged 0.5 mph and there
was no rainfall, the plants lost an average of 18.5 percent of
the initial deposition. This corresponds to an average value of
the initial retention factor (f) of 0.815. Losses for the next
24 hours also averaged 18.5 percent. From 1.5 to 7 days post-
deposition, the plant retention dropped from 63 percent to
about 33 percent. This decrease was largely related to 0.25
7
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188
inches of rain on the sixth day. Retention dropped to 7.9 per-
cent of initial deposition during the second week, after a heavy
rainfall of 1.33 inches. Another intense rainfall caused a sharp
decrease in fallout retention to 3.3 percent, which slowly
decreased during the remainder of the experiment.
The weathering half-lives (Tu) for the 44-84 urn particles
were 26 days for the 14- to 28-day postdeposition period and 84
days for the 28- to 56-day postdeposition period. During the
entire 56-day study period, the weather half-lives (Tw) ranged
from 2.09 to 272.8 days for the 44 to 88 pm particle size; and
1.33 to 56.5 days for the 88 to 175 ym particle size. This
experimental data indicates that large differences in initial
interception existed between plant species for different particle
size distributions, but that these differences become insignifi-
cant after about 1 week of exposure to environmental influences
such as wind and rain.
Witherspoon and Taylor (1970) report values for the activity
per dry gram of foliage, per activity per unit area of soil for
the five crops. These values range from 0.01 to 0.2 ft2/g (10 to
200 cm2/g). The biomass values (W), in grams of dry foliage per
square meter of soil (dried at 100°C for 24 hours), ranged from
20 for lespedeza to 120 for soybeans. These data- are for 6-week-
old plants at the time of deposition. The plants were planted
the last of May in the Oak Ridge, Tennessee, area. All of the
foregoing values are summarized in Table 1.
Concentrations of iodine-131 and strontium-89 on plants
contaminated by fallout from Project Sedan at the Nevada Test
Site were reported by Martin (1965). Examination of the fallout
deposited on foliage indicated that most of the activity was due
to particles less than 5 urn diameter, with virtually no retained
particles greater than 44 ym diameter. The observed effective
half-lives for iodine and strontium on the vegetation corres-
ponded to .weathering half-lives (Tto) of 17 and 28 days.
Russell (1965) presents a review of interception and
retention of airborne material by vegetation. Based, on data from
Milborn and Taylor (1965) concerning strontium-89, Russell con-
cludes that on the average nearly one-quarter of the deposited
fallout material is initially held on edible leaf tissues. An
equal quantity may be associated with the basal tissues. The
studies of Milbourn and Taylor also indicate that 50 percent of
the radioactivity present on the edible herbage per unit area is
usually lost in about 14 days. The fraction of initially depos-
ited fission products lost from cabbage plants in a 28-day period
ranged from 0.83 for cesium-137 to 0.90 for ruthenium-106
(Middleton and Squire (1961)). Data were also presented which
indicated that washing cabbage leaves in water could remove from
10 to 36 percent of the deposited contamination (average of 24
percent). Middleton and Squire also concluded that the extent
of radionuclide absorbtion into leaves was of little importance
8
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TABLE 1. SUMMARY OF PLANT DEPOSITION AND RETENTION PARAMETERS
Reference
Witherspoon & Taylor (1969)
Witherspoon & Taylor (1969)
Witherspoon & Taylor (1970)
Witherspoon & Taylor (1970)
Witherspoon & Taylor (1970)
Levin et al. (1970)
Levin et al . (]970)
Martin (1965)
Martin (1965)
Russell (1965)
Russell (1965)
Russell (1965)
Plant Foliage Initial
Interception Biomass Retention
Factor F (g,dry/m2) Factor
0.35 0.095
0.24 0.90
0.075 to 1.2 20-120 <0.1@ 2 wk
20 lespedeza ^0.8@ 12 hr
120 soybeans ^0.3@ 1 wk
0.25 540 fruits
3500 leaves
^0.5
^0.17
M).10
Weathering Half-Life
Half-Life Pertinent
(Days) Period (Days)
25 7 to 33
21 7 to 33
26 14 to 28
14
17
28
Comments
88 to 175 urn particles,
oak trees
88 to 175 urn particles,
pine trees
44 to 88 ym particles,
6-wk old plants
Fallout, 1-131
Fallout, Sr-89
Cabbage, Cs-137
Cabbage, Ru-106
Bloom et al. (1974)
Bloom et al (1974)
Martin et al. (1974)
Milbourn & Taylor (1965)
5 cm2/g
0.14
5 cm2/g
0.14
30
30
14
F factor divided by
biomass.
Assume biomass of
289g/m2
Project Sedan Sr-89
09
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190
compared to the retention of activity on the leaves.
Levin et al. (1970) discuss the choice of parameters for
dose model calculations for the proposed nuclear applications in
the construction of an interoceanic canal. The information they
present is oriented to South America and general fallout of mixed
fission products. Thus, the information has limited applica-
bility to conditions in the United States. A summary of their
parameters is given in Appendix A. Several of the more pertinent
values are:
--Fraction of the element in plant edibles which comes from
leaves (due to foliar deposition) of 0.05. This value
apparently relates to fruit type plants.
--W, biomass of plant edibles of 540 g/m2 (dry weight).
Biomass of plant leaves 3500 g/m2.
--Growth-rate coefficient for plant edibles of 0.05 day-1
or half-life of 14 days.
--Weathering elimination rate for plant leaves of 0.05
day-1 or 14-day half-life.
--F, Fraction of fallout intercepted by plant leaves of
0.25.
The weathering elimination rate (Aco) was estimated to be
0.05 day-1 based on a Too of 14 days. The fraction of fallout
intercepted by plant leaves was 0.25. For most fission products
the fraction in the plant edibles which comes from leaf contami-
nation was estimated to be 0.001. The fraction in plant edibles
which comes from the root uptake of contaminants in soil was 1.0.
These values are estimates influenced by natural weathering
conditions and decontamination due to washing and food prepara-
tion.
Bloom et al. (1974) review the literature values to obtain
parameters for use in their transport model. Based on fission
product fallout data, they postulate the following half-lives:
Half-Life Time Increment
(Days) (Days)
1.4 0-5
20 5 -15
30 15 -30
130 30 -60
Bloom et al. (1974) note that such parameters as inter-
ception, retention, and retention half-life are dependent on the
time after deposition when these factors are measured. Given
this, they select an interception factor (units of cm2/g dry
weight) of 5 and a weathering half-life of 30 days. This
interception factor (in units of cm2/g) is equivalent to the
unit-less interception factor (F) divided by the plant biomass
10
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191
(W) in g/cm2. Bloom et al. (1974) refer to the studies by Miller
and Lee (1966) of interception factors (cm2/g) for fallout from a
volcano eruption. Values of the interception factor vary by a
factor of two (from 47 to 96 cm2/g) between low and high (greater
than 90 percent) relative humidity. Miller and Lee (1966) note
that these values were based on samples collected immediately
after deposition. Notation of time after deposition may explain
the discrepencies with nuclear fallout data reported by Martin
(1965). Martin (1965) reported values from 1.9 to 11.1, with an
average of 3.7 cm2/g. For relative comparison purposes, Bloom's
et al. (1974) factor of 5 cm2/g can be converted to the unit-less
factor by assuming a biomass of 289 g/m2 (Martin et al. (1974)),
resulting in an F value of 0.14.
Martin et al. (1974) uses parameters similar to those of
Bloom et al. (1974). Several of the recommended parameters are:
interception factor of 5 cm2/g; weathering half-life of 30 days
(based on nonvolatile particulates on shrubs); and a desert plant
dilution growth rate of 36 g(dry)/m2-year. A biomass value of
289 g/m2 is referenced (Bamberg (1973)).
11
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192
RADIONUCLIDE UPTAKE FROM SOIL BY PLANTS
The uptake of radioactive material from soil by plants is
generally expressed as a discrimination factor pCi/g (dry weight)
of plant per pCi/g (dry weight) of soil. Variations of this
parameter include the discrimination factor between soil and the
roots or the edible fruits of the plant. The discrimination
factor is also given for uptake from hydroponic solutions. Table
2 summarizes the plant uptake of plutonium studies discussed
below.
The depth basis of the soil concentration presents an
inherent uncertainty in the discrimination factor. The majority
of fallout plutonium is normally found in the top two-to-five cm
of soil. Thus a 10-cm depth soil sample will only contain
essentially one-half the concentration of plutonium as a 5-cm
depth sample (i.e., the 10-cm sample is diluted with uncontamina-
ted dirt). It appears that most discrimination factors are based
on a 5-cm depth soil sample.
Several investigators have indicated an increase in the
discrimination factor with time (Romney et al. (1970); Price
(1973); Francis (1973)). The extent of and reasons for this
increase are uncertain. It is generally related to either the
chronological increase in depth penetration of plutonium in soil
and/or the increased availability of plutonium with time.
The increased penetration is related to alternate freezing -
thaw.ing, and wetting - drying of the soil; earthworm activity;
agriculture practices; possibly changing plutoirium
solubilization; and physical translocation downward through the
soil by the root hair system of plants (Wildung and Garland
(1974)). Wildung and Garland (1974) noted that plutonium from
surface soil was translocated down to the roots of barley. This
may have special health pathway implications for root crops
directly consumed by man.
Chronological increases in the bio-availability of plutonium
are related to the natural chelation of plutonium by decaying
roots (Romney et al. (1970)). Au (1974) and Au and Becker (1975)
indicate significant uptake of PuOa by soil microorganisms,
specifically Aspergillus niger. Their experiments, conducted at
several values of soil acidity, indicate that microorganisms may
chronologically increase the bio-availability of Pu02 micro-
spheres .
12
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TABLE 2. SUMMARY OF PLANT UPTAKE OF PLUTONIUM
Reference
Discrimination Factor
(pCi/g dry plant: Time of
pCi/g dry soil) Measurement (Yrs)
Type Plant
Comments
Romney et al. (1970)
Garland et al. (1974)
Johnson et al. (1972)
Jacobson & Overstreet (1948)
Cline (1967)
Cline (1967)
Cline (1967)
Neubold (1963)
Nishita et al. (1965)
Rediske et al. (1955)
1.9xlO"5
4.1xlO-5
4.4xlO"5
7.1xlO"5
14 x 10~5
4.4xlO"5
15 x 10"5
1 x 10"7
200 (roots)
0.8 to 4xlO~3Aerial portion
2xlO"6to 10"3
Av 6.4x10""
10""
2 x 10"5
4.5xlO"6
0.4 (roots)
0.25 (roots)
0.2 (roots)
Am-241 50xPu-239
0.003 for Am
2 x 10""
1 x 10""
Factor 4 increase
10""
9 x 10""
1/3
root
1/365
1/365
1/365
Ladino Clover Pu-239 from NTS soil
Barley Pu(NO-,)4 100 uCi/g in soil, toxic effects
Barley Pu(N03)4 10 uCi/g in soil
Barley seeds
Barley roots, activity may not have been taken up
Used Pu02
Pu(N03)4
Barley
Barley Pu"+
Barley Pu3+
Barley PuO?2
Barley Pu"+
Barley Pu022+
Barley
Alkaline Ephrata fine sandy loam
Pu acid soil
Pu alkaline soil
Ryegrass Pu in acid soil
Ladino clover Pu Fallout
Barley Pu"+
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194
Earth (1975), Raabe (1973), Hakonson and Johnson (1973), and
Patterson et al. (1974) report data inferring that plutonium-238
is more soluble than plutonium-239, and possibly more bio-
logically available. Raabe et al. (1973) report that the
dissolution rate for plutonium-238 dioxide monodispersed par-
ticles in an in. vitro laboratory system was nearly two orders of
magnitude greater than for plutonium-239. Hakonson and Johnson
(1973) report changes in the plutonium-238 to plutonium-239 ratio
for the Trinity Site, New Mexico. Twenty-three years after the
nuclear detonation, the plutonium isotopic ratios varied from
0.05 for soil, 0.10 for plants, to 1.0 for mammals. Brown and
McFarlane (1975) are conducting experiments with several plant
species and soils to determine uptakes for plutonium-238 and
plutonium-239.
Hanson (1975) notes that the increased availability of
plutonium-238 may result from the chelating action resulting from
more intimate contact of plant roots with the plutonium particles
(plutonium-238 versus plutonium-239); transport of plutonium by
individual cells; or a combination of such mechanisms by which
plutonium-238 may be absorbed differently than plutonium-239.
The higher specific activity of plutonium-238 versus plutonium-
239 is also potentially related to possibly different isotopic
effects.
Data indicating differences in the transfer or isotopic
ratios for plutonium-238 and plutonium-239 should be critically
evaluated. Plutonium-236, which is often used as an analytical
tracer may contain plutonium-238 as a contaminant. This error
can be corrected by analyzing tracer blanks. Furthermore,
sources of purer plutonium-236 are now available. An additional
problem results from the similarity of the americium-241 and
plutonium-238 alpha energies, 5.49 and 5.50 MeV, respectively.
Incomplete separation of americium in sample processing or delays
in counting after sample processing (i.e., amercium-241 ingrowth
from plutonium-241) can result in erroneously high indications of
plutonium-238 content. Generally, these pitfalls are not
present, but their potential must be recognized.
Plant uptake of plutonium from soil has been reviewed by
Bloom et al. (1974), Hakonson (1975), Hanson (1975), Price
(1973) , and Francis (1973). The general consensus is that
short-term uptake is minimal, but that increased chronological
uptake due to natural chelation and other mechanisms presents an
uncertain picture and some cause for concern.
Romney et al. (1970) studied the transfer of plutonium-239
from soil to plants for ladino clover. These crops were grown
under glasshouse conditions on contaminated soil for five years.
Total crop yields increased each year. The plant-to-soil
discrimination factor for the first year was 1.9xlO-5 pCi/g of
dry plant per pCi/g of dry soil. The factor increased to 14x10-5
for the fifth year, for a five year average of 6.3x10-5. The
14
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195
soil was a one-to-one mixture of Yolo soil and soil from Area 11
of the Nevada Test Site contained in 60-liter containers (filled
volume 50 liters), with a surface area of 0.12 m2. The soil was
uniformly contaminated with a plutonium-239 concentration of
1.62x10-s dis/min-g. Romney et al. speculated that some of the
yearly increase in plutonium uptake was related to increased
development in the root system. They maintained the root system
provided more intimate contact of the roots with plutonium.
Additional studies showed increased plant uptake of plutonium
from soils where DTPA chelating agent was added.
Garland et al. (1974) report results for barley and soybean
plants grown in soils containing Pu(N03)4. The split-root
technique was used to study the uptake and distribution of
plutonium in the plant tissue. The distribution of plutonium was
determined in the tops and roots of soybeans (Glycine max) after
50 days of growth, and barley (Hordeim vulgare") after 27 days of
growth. Slight increases in the total plant uptake were related
to increasing the volume of soil in the test plots for both
above-ground and root tissues of barley. But the height of the
soil column appeared to be a more important variable. Since the
plutonium was uniformly mixed in the soil column, increased
uptake from a taller soil column probably relates to the
increased contact between roots and soil.
Garland's et al. (1974) experiments were conducted with
concentrations of 10 and 100 yCi/g of plutonium-239. But the
elevated concentration of 100 yCi/g did not result in a marked
increase in uptake versus the 10 yCi/g soil. The respective plant
uptakes (dry weight, 60°C for 24 hours) for barley were 4.4xlO-5
and 15.5x10-5. The plants in the 100 yCi/g soil showed toxicity
symptoms until the root systems were established in the nutrient
solution below the soil. Plants grown in the two concentrations
were indistinguishable at the time of harvest. If the observed
toxicity is concentration dependent, Garland et al. (1974)
indicate that the previously reported results of Wildung and
Garland (1974) , indicating an inverse relationship between uptake
and soil concentration, may have been due to toxic effects on the
roots.
Garland et al. (1974) reported that the distribution of
plutonium activity in the plant roots of barley averaged 17.1
percent and 4.79 percent (percent of total plant activity) for
two different plutonium activity soils (0.05 and 10 yg plutonium
per yg soil). Therefore, the average root content was 10.95
percent, with the remaining plant activity in the above-ground
parts of the plant (outer sheath, leaf blades and new growth).
Both the barley and soybean plant studies indicated that
plutonium, once in the plant, was rather mobile, with leaf tissue
containing 5 to 10 times the plutonium activity of that in the
stem tissue. After 100 days of growth, the barley seed had an
activity corresponding to a concentration factor of less than
1x10-7 of the soil content.
15
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196
Johnson et al. (1972) reported the results of an experiment
to test the active transport of plutonium by plant roots. Barley
plants were grown in a nutrient media containing soluble
23 9Pu(N03) i,. The barley plant roots were removed at various time
intervals, washed and analyzed for plutonium-239 content. A
tentative concentration factor from solution to roots of approxi-
mately 200 was observed. Although the roots were washed after
removal from the nutrient media, it is possible that much of the
plutonium was only associated with exterior surface contamination
of the roots and was not assimilated by the roots.
Johnson et al. (1972) conducted another,experiment where
barley plants were allowed to mature and the root and aerial
portions were removed and separately analyzed. The ratio or
fraction of the concentration of plutonium in the aerial portion
of the plants, as compared to the root portion of the plants,
ranged from O.SxlO-3 to 4xlO-3 (average of 2xlO-3)for plants
grown in Pu02 solutions. The ratio for plants grown in Pu(N03)lt
solutions ranged from 2x10-6 to 1x10-3, with an average of
6.4x10-^ These ratios are similar to those reported by Romney
et al. (1970). This indicates that either the plutonium was not
taken up into the roots, or there is a significant discrimination
factor preventing the transfer of plutonium from roots to the
above-ground parts of the plant.
Menzel (1965) reviewed the literature concerning the soil-
plant relationships of radionuclides. This review was limited to
experiments where the radioactivity was in a soluble form when
added to the soil and where radionuclide concentrations were low
enough so that there were no toxic effects. In summary, Menzel
classed plutonium in the bottom of the lowest category (that is,
less than 0.01 (ratio of dry weights of plant and soil acti-
vity)).
Francis (1973) reviewed the mobility of plutonium in soil
and its uptake by plants. The following items are based on
Francis1 review:
1. Jacobson and Overstreet (1948) studied the. trans-
location of plutonium in barley (one of the original
plutonium plant uptake studies of barley plants in
calcium-bentonite clay suspensions). Over a 24-hour
period, the fractional translocations to leaves, were
10-4 for Pu022'+, 2xlO-s for Pu"+, and 4.5xlO-6for
Pu1**. The respective values for the roots were 0.4,
0.25, and 0.2.
Rediske et al. (1955) noted the discrimination factor
(ratio of dry weight of aerial portion of plants to
soil) increased from 10-1* to 10-3, with pH changes
of 7 to 4.
16
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197
2. Wilson and Cline (1966) studied the uptake of
plutonium-239 by barley from three soils. The soils
were Ephrata fine sandy loam, a slightly alkaline soil;
Milville silt loam, a calcareous soil; and Cinabar silt
loam, a moderately acid forest soil. Plutonium uptake
from the acid soil was more than three times greater
than from the calcareous soil. A 0.IN nitric acid
solution removed 0.64 percent of the plutonium,
approximately one-thousand times more than that taken
up by barley. This shows that common soil extracting
methods do not provide a reliable indication of
potential plant uptake.
3. Cline (1967) reported that the uptake of americium-241
into foliar portions of barley was fifty times that of
plutonium-239. The barley was grown in Hoagland's
nutrient solution.
4. Unpublished work of Buckholz et al. does not show a
chronological increase in the discrimination factor for
alfalfa after four years of growth. The study was
conducted in a plutonium contaminated soil associated
with the 1966 Palomares Spain accident. This is at
variance with the results of Romney et al. (1970).
Price (1973) reviewed several studies concerning plant and
animal uptake of plutonium. The following studies were not
reported by Francis (1973) :
1. Nishita et al. (1965) studied the uptake of fallout
plutonium in ladino clover (Trifolium respens I,.). The
discrimination factor was lO-1* (yCi/g plant per iaCi/g
soil, probably dry weights).
2. Rediske et al. (1955) noted that Puk+ becomes associ-
ated with root surfaces exposed to culture solutions.
The quality of sorption to root surfaces is linear with
respect to concentration of the solution, whereas, the
leaf concentrations had a curvilinear relationship.
The uptake into shoot tissues of tumbleweed from
solution cultures was slightly less than for beans,
barley, or tomatoes. The discrimination factor for
barley was 9x10-"*, based on the Neubauer test. This
was considered to be an overestimate for what would be
expected under field conditions.
3. Cummings and Bankert (1971) used culture pots for
plutonium-238 uptake studies for nine soils. The
results for plutonium-238 were lower than those for
cerium-144 and promethium-147. The fractional uptake
(total activity in plants divided by total soil
activity) for plutonium varied from 7 to 280x10-8.
17
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198
4. Cline (1967) reports discrimination factors of 0.003
for americium-241 from alkaline (Ephrata lime sandy
loam) and acid (Cinabar silt loam) soils. The
plutonium factors were ZxlO-1* (acid soil) and 1x10-
(alkaline soil).
5. Neubold (1963) reported that although plutonium uptake
by perennial ryegrass (Folium perenne L.) was low, it
did increase over a 2-year study span,"Tor several
different soils. There was a 4-fold increase for an
acid soil.
Price (1973) indicates the following ranking for decreasing
uptake by plants from soil: curium, americium, and plutonium.
Neptunium uptake probably resembles that of plutonium.
Hakonson (1975) reviewed pathways for plutonium into terres-
trial plants and animals. Several investigators have noted higher
plutonium concentrations in native grasses than for forbs,
shrubs, or trees (e.g., Hakonson and Johnson (1973) and
Whicker et al. (1973)). This may be related to the morphological
structures of the plants and their ability to intercept and
entrap airborne material. Russell (1966) has noted that the
heads of grains serve as an excellent trapping device for depos-
ited material. On the other hand, the physical structure of root
systems of grasses and their position within the soil/plutonium
profile may be favorable for root uptake of plutonium by grasses.
Bloom et al. (1974) present an environmental transport model
with associated parameters. A soil to plant discrimination
factor of 0.313 (pCi/g of dry vegetation per pCi/g of wet soil)
is recommended. This factor is based on the indications of
increases of plant uptake with time (e.g., Martin's et al.
(1974) estimates from data from Romney et al. (1974)). The
Romney et al. (1974) values are based on results from the Nevada
Test Site, 20 years after deposition. Martin et al. (1974)
further justified the value of 0.313 by estimating the uptake at
20 years from Romney's et al. (1970) data. In essence, Martin
et al. (1974) exponentially extrapolated Romney's et al. (1970)
5-year study to 20 years.
Romney et al. (1974 and 1975) emphasize that the high dis-
crimination factors are not solely related to root uptake,
rather, they are a result of deposition with limited root uptake.
Romney et al. (1975) estimate the root uptake to be 10-3 to
10-\ Thus, it appears Bloom's et al. (1974) and Martin's
et al. (1974) assumptions are in error.
18
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19
COMBINATION OF DEPOSITION AND PLANT UPTAKE
Romney et al. (1974 and 1975) reports data on the total
plutonium and americium-241 concentrations in vegetation for
several areas of the Nevada Test Site. These data are compared
on a pCi/g (dry and ashed) basis to soil concentrations. The
vegetation results are based on a sample of foliage, and exclude
the root mat. Romney et al. (1975) estimated that for Area 13
only 1/1600 of the plutonium-239 inventory was in the vegetation.
The ratio of foliage to soil values averaged about 0.08, and most
of the values (several hundred) fell within 0.02 to 0.16.
Romney et al. (1974) reported values for the total amount of
plutonium-239 on foliage versus the soil concentration. The pre-
liminary results for vegetation were based on the ashed weight.
The average values (pCi/g ashed vegetation per pCi/g dry soil)
were 1.0, 1.7, and 5.1 for Atriplex canescens, Atriplex confer-
tifolia, and Eurotia lanata, respectively.The average value was
2.24.Romney's plant-to-soil ratios are apparently all based on
the plutonium concentration in the top 5 cm of soil.
Colorado State University (1973) reported data on the
plutonium-239 inventory for the Rocky Flats, Colorado, area. The
data is based on plant distributions from the Pawnee National
Grassland. The soil accounted for 99.464 percent of the
plutonium-239 in the top 2 cm of soil. Standing vegetation
accounted for 0.058 percent, litter for 0.180 percent, and roots
(surface to two cm depth) accounted for 0.298 percent of the
total activity on the test plot. Considering the litter as part
of the standing vegetation, the foliage would then account for
0.238 percent of the total activity, comparable to the root
content of 0.298 percent. The total plant content would be 0.536
percent.
Whicker et al. (1973) reported plutonium concentrations for
various terrestrial ecosystems in the Rocky Flats environs. In
the top 3 cm of soil, fifty-nine percent of the plutonium-239 was
found in the soil fraction of less than 0.5 cm in diameter.
Additionally, 39 percent of the soil activity was found to be
below the 3 cm depth. Two-tenths percent was associated with the
surface litter and detritus, 1.3 percent with roots, and 0.06
percent with standing vegetation. Considering the litter as part
of the standing vegetation, the foliage would then account for
0.26 percent of the total activity, compared to the root content
of 1.3 percent. The total plant content is 1.56 percent, corres-
ponding to a concentration factor of 0.0156, due to both
19
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201
deposition and soil uptake. The root, foliage, and soil data
from Whicker (1973) are summarized in Table 3.
TABLE 3. PLUTONIUM IN VEGETATION AND SOIL
(Whicker (1973))
Plant
Western
Wheatgrass
Cheatgrass
Prickly
lettuce
Salsify
Biomass
Dry Weight
(g/m2)
32
10
2
9
Average Cone.
In Roots
(dpm/g)
247
294
157
13
Average Cone.
In Standing
Plant (dpm/g)
30
112
13
13
Average
Standing Veget.
Cone:
Soil cone.*
0.00125
0.0467
0.00542
0.00542
0.0015±0.02
* Vegetation concentration in dpm/g divided by average soil concentration of
2397 dpm/g. Based on soil sample of 0 to 3 cm depth and particles less
than 5 mm. Dry Weights.
Schultz et al. (1974) report a proposed study of plant
uptake of plutonium and americium. The study will include
several soils and several chemical forms of the elements.
Results have not yet been published.
20
-------
201
REDISTRIBUTION OF ACTIVITY WITHIN PLANTS
There appears to be very little absorption and redistribution
of deposited plutonium within plants. There is, however, only a
limited amount of published information.
Russell (1965) reviewed several studies concerning inter-
ception and retention of airborne material. He concluded that
the absorption of deposited material was of limited importance
compared to the retention of activity on foliar surfaces.
Aarkrog (1975) studied the uptake of deposited fission
products on wheat and barley crops. Radionuclides such as
strontium-90, ruthenium-103, and cerium-144 were generally
immobile. Whereas, zinc-65, iron-55, cesium-137, cobalt-60, and
manganese-54 were more readily translocated to the seeds.
Levin et al. (1970) estimate that only 0.1 percent of the
radioactivity in plant edibles comes from the leaves (for rela-
tively immobile elements). Essentially all of the activity in
the plant edibles is related to root uptake. The parameters
listed in Appendix A (Levin et al. (1970)) are for the inter-
oceanic canal project and are assumed to relate to fruits, nuts,
etc., -- not to leafy edibles.
21
-------
202
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26
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2C7
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Health Physics. 19:493-499
27
-------
Is)
oo
Appendix A
Parameters for Atlantic-Pacific
Interoceanic Canal Model
(LEVIN et al., 1970)
Parameter
FA
S01
£43
f42
f
F
Parameter Definition
Average fallout concentration on a
watershed, uCi/cm*
Initial specific activity of the
radionuclide in the fallout, MCi/g
element
Fraction of the element in plant
edibles which comes from leaves
(dimension less)
Fraction of the element in plant
edibles which comes from the soil
(dimension less)
Ratio of runoff water to total
rain water (dimensionless)
Ratio of the amount of radionuclide
Values Used
-
~
0.05 (P&C)(a)
0.001 (P&C)
1.0 (P&C)
0.001 (P&C)
0.9 (P&C)
4.0 x 10"5 (P&C)
Remarks
These values are classified and thus are
not available
These values are classified and thus are
not available
For mobile elements H, P, I, and C
For all other elements than H,P, 1, and C
For all elements except carbon
For carbon
Infiltration is 10 percent of rainfall
reaching ground surface
For all elements except hydrogen; calcu-
References
-
"
Martin (1969)
Martin (1969)
Kazmaier (1569)
Kazmaier (1969)
Charnell et al (1969)
Charnell et al (1969)
dissolved in surface water to the
total amount present on the soil
surface (dimensionless)
0.3 (P&C)
lated from reference dataC1)
For hydrogen; calculated from reference
data(b)
Charnell et al (1969)
r
r
u
W4
*W4
Average rainfall rate, cm/day
Unit rain, cm
Dry biotnass of plant edibles, g
dry weight/cm2
Fraction of water in plant edibles,
g water/ g fresh weight
0.636 cm/day (P)
0.596 cm/day (C)
2.5 cm (P&C)
0.054 g/cm2 (P&C)
• 0.70 g/g (P&C)
Estimated from mass rainfall curves
Estimated from rainfall curves
Defined by reference^)
Calculated from reference data^ ^
Estimated average water content from
reference data
Charnell et al (1969)
Charnell et al (1969)
Charnell et al (1969)
Traaseau (1926)
Wu Leung and
Flores (1961)
to
o
OP
-------
Appendix A (continued)
Parameter
Parameter Definition
Values Used
Remarks
References
XB7
AM
Density of water, g/cm3
Biological elimination rate coefficient
of element from freshwater fish, day"1
1.0 g/cm3 (P&C)
0.055 day'1 (P&C)
Biological elimination rate coefficient
of element from animals, day'1
Biological elimination rate coefficient
of element from marine fish, day'1
Growth-rate coefficient for plant
edibles, day"1
d C.
*8 - ^r>'c4
Weathering elimination rate coefficient
from plant leaves, day'1
Fraction of fallout intercepted by
plant leaves (dimensionless)
Biotnass of plant leaves, g dry weight/
cm2
Average fallout concentration on the
marine fallout area, pCi/cm^
Total amount of radionuclide initially
present in the canal channel and rubble,
uCi
Ratio of the amount of radionuclide
dissolved in the canal water to the total
amount present in the canal channel and rubble
(dimensionless)
0.1 day"1 (P&C)
0.02 day"1 (P&C)
0.05 day"1 (P&C)
0.05 day'1 (P&C)
0.25 (P&C)
0.35 g/cm2 (P&C)
4.
0 x 10'3 (P&C)
0.3 (P&C)
Listed in reference
Geometric mean calculated from reference
data by method outlined by Bloom et al
(1970)
Geometric mean calculated from reference
data
Estimated from turnover rates for
anchoveta
Arithmetic mean calculated from reference
data by method outlined by Bloom et al
(1970)
Calculated from reference data^ '
Highest value selected from reference
data(S)
Calculated from reference data*-")
These values are classified and thus are
not available
These values are classified and thus are
not available
For all elements except hydrogen^1'
For hydrogen
Weast and Selvy (1967)
Templeton et al (1969)
Brungs (1967)
Boroughs et al (1956)
Polikarnpov (1966 a&b)
Kevern (1966)
Miser and Nelson (1964)
Friend et al (1965)
Golley et al (1969)
Lowman et al (1970)
Malavolta et al (1962)
Transeau (1926)
Jacob and von Uexkull
(1963)
Martin (1965)
Nishita et al (1965)
Middleton (1960)
Transeau (1926)
Essington (1969)
Essington (1969)
to
C5
-------
Appendix A (continued)
Parameter Parameter Definition
B Net flow rate of water through the
canal channel, cm3 /day
H Horizontal extent of the marine fall-
out field in the direction perpen-
dicular to the current, cm
Z Horizontal extent of the marine fall-
our field in the direction parallel
to the current, cm
K Turbulent diffusivity in the verti-
cal direction, cur/day
V Volume of water in the canal
channel, cnr^
V Speed of ocean current, cm/day
o
2
3
1
1
1
1
7
9
1
2
2
1
3
.83 x
.62 x
.85 x
.20 x
.11 x
.11 x
.4 x
.26 x
.0 x
.52 x
.19 x
.0 x
.0 x
Values Used
1014 cm3 /day (P)
1011 cm3/day (C)
107 cm (P-Pacific
107 cm (P-Atlantic
107 cm (C-Pacific
107 cm (P-Pacific
106 cm (P-Atlantic
side)
side)
side)
side)
side)
106cm (C-Pacific side)
106 cm2 /day (P&C)
1015 cm3 (P)
1015 cm3 (C)
106 cm/day (P)
106 cm/day (C)
Estimated
Estimated
Estimated
Estimated
Estimated
Estimated
Estimated
Estimated
Estimated
Estimated
Estimated
Estimated
Estimated
from
from
from
from
from
from
from
from
from
from
from
from
from
Remarks
reference
reference
reference
reference
reference
reference
reference
reference
reference
reference
reference
reference
f
References
data
data
dataU)
data
data
data
data(J)
dataU)
data
data
data
data
, . ( 1 )
'
Harleman (1967)
Harleman (1967)
Ferber
Ferber
Ferber
Ferber
Ferber
Ferber
(1968)
(1968)
(1968)
(1968)
(1968)
(1968)
Pritchard et al
(1966)
Harleman (1967)
Harleman (1967)
Lowman
Lowman
et al (1970)
et al (ic
170)
(a) P designates value used for Panama (Route 17). C designates value used for Colombia (Route 25).
(b) The quantity F was calculated as follows: ,
w j.
F =
Li
where or is the fractional soil porosity, 0.3
and 1C is the distribution coefficient of the rainwater between the soil surface and surface water, 1 for
all other elements.
(c) If the interflow layer has a thickness of 7.5 cm (Odum, 1967) and a porosity of 33 percent, then the amount of
this interflow layer is the unit rain (2.5 cm).
hydrogen, and 1.0 x 10^ for
rain required to saturate
to
-------
Footnotes for Appendix A (continued)
(d) The quantity W, was calculated as follows:
_ rdry weight plant edible-. .-No. plants -
4 plant 2
r cm
r216g plant edible-, rI.O x IP4 plants 2.471 x 10'6 acres -
W4 ~ L plant J X L acre x cn)2 J
(e) Reference data described the growth of tropical plants. Pineapple, sugar cane, rice, and bananas were some of the foodstuffs for which
growth rate data were reported. „ ,„.
(f) The quantity k was calculated as follows: k = —^
where T is the environmental half-life of a radionuclide on leaves.
T was assumed to equal to 14 days for all radionuclides on fallout-contaminated plants in humid regions.
(g) Tne relative percentage of fallout intercepted by plants in the environs at NTS (Nishita et al, 1965), from 8 percent to 15 percent at the
Maralinga Test Site for close-in and far-out fallout, respectively, (Nishita et al 1965), and up to 25 percent retention near NTS
(Middleton, 1960).
(h) The quantity W-j was calculated as follows:
,dry weight plant leaves, no. plants
W3 = ( plant > X ( cm2 >
_ ,140 g leaves, ,1.0 x 10 plants 2.47 x 10' acre,
W3 * pl^t ' X ( acre X 2 }
cm
(i) The quantity FC was calculated for all elements except hydrogen as follows: FC = 100 Fw .
(j) This quantity is dependent upon the orientation of the fallout patterns over the marine fallout area. As no fallout is expected over the
Atlantic side of Route 25, no values are listed for the Atlantic side of Route 25.
(k) This quantity is the value used for both the Atlantic and Pacific sides of Route 17.
(1) This quantity is the value used for the Pacific side of Route 17.
-------
213
A MODEL TO ASSESS POPULATION INHALATION EXPOSURE
FROM A TRANSURANIUM ELEMENT CONTAMINATED LAND AREA
Christopher Nelson (1)
Robert Davis (2)
Ted Fowler (2)
June 1978
U.S. Environmental Protection Agency
Office of Radiation Programs
(1) Environmental Analysis Division
(2) Criteria and Standards Division
Washington, D.C. 20460
-------
214
CONTENTS
Page
Introduction 1
Summary and Conclusions 2
General Model Description ^
Dispersion Equation 6
Calculation of Air Concentration Resulting From Resuspen-
sion of Material at Source and Subsequent Population
Inhalation Exposure 9
Discussion on the Derivation of the Air Concentrations
X,, X', .... X , Resulting from the Secondary Resuspension
1 /
of Contaminated Material
Calculation of Air Concentration X, Resulting from the
First Secondary Resuspension of Contaminated , ,-
Material 13
Calculation of the Population Inhalation Exposure PE^(r,t)
Resulting from Air Concentration X-(r,t) 20
Calculation of the Total Infinite Population Exposure
PET(»,») 21
Environmental Dose Commitment 24
Parameter Selection 27
Resul ts 29
Appendix I: Derivation of X/Q vs Distance Relationship
for a Ground Level Release 48
Appendix II: Solutions to Selected Integrals and
Differential Equations 55
Appendix III: Summary of Equations 60
References 65
-------
215
Introduction
Land areas contaminated with radioactive material will cause
radiation exposure when the material is resuspended from the ground
and dispersed by wind action to populated areas where it is inhaled or
ingested. To assess the overall impact of such a contaminated area on
the surrounding population, requires a summing of all individual doses
over the entire time the material is capable of exposing the popula-
tion; this is the environmental dose commitment.
A model is proposed that estimates the population inhalation
exposure, as a function of time and distance, that results from a
single source of radioactive contamination. This permits the estima-
tion of the environment dose commitment from the inhalation pathway.
Population inhalation exposure, as used in this report is the
integrated air concentration multiplied by the number of persons
exposed to this concentration, and has units of person Ciyr/m . A
method is described to convert population inhalation exposure to an
environment dose commitment, which then may be used to estimate the
number of potential health effects.
The model calculates the air concentration resulting from the
resuspension and dispersion of material located at the source and away
from the source. These air concentrations are then integrated over
time and area and multiplied by a population density to get the
population inhalation exposure.
-------
216
The model provides a basis for determining the importance of
specific physical parameters and how changes in these parameters
affect the population inhalation exposure. Its use is intended only
to scope the magnitude of radiological impact on the surrounding popu-
lation from a land area contaminated with radioactive material. The
model is generic and is not directly applicable to a specific site
because of the use of many simplifying assumptions.
Summary and Conclusions
A model is proposed for use in estimating the population
inhalation exposure in the environs of an area contaminated with
radioactive material. One use of this model is that the user can
determine by sensitivity analysis, which parameters greatly affect the
population inhalation exposure. Several simplifying assumptions were
used in the model, such as uniform meteorology, uniform population
density, point source approximation of an area source, constant depo-
sition velocity, and constant resuspension rate and soil sink transfer
rate. Also atmospheric dispersion versus distance is represented by a
power function and a source depletion model is employed. These
assumptions place strict limitations on the use of this model to
specific sites.
To illustrate the i^se of the model, sample calculations were
performed using selected parameter values. A comparison is made of
two sets of parameter; which differ only in the value of the resuspen-
sion rate, selected to represent typically observed initial and
-------
217
equilibrium rates. This, in effect, brackets the population
inhalation exposure which would have been derived if the model used a
time-dependent resuspension rate. The sample calculations use a 1
Curie Pu-239 source term as a reference level.
The following is a summary of the important results obtained for
the sample calculation performed in this report. The use of parameter
values, other than the ones used in this report, can result in differ-
ent conclusions.
1. A high resuspension rate results in a greater population
inhalation exposure than a low resuspension rate.
2. When a high resuspension rate exists, the population
inhalation exposure is much greater from the secondary resuspension of
contaminated material located away from the source, than the exposure
from the initial resuspension of material located at the source.
3. For a low resuspension rate, the population inhalation expo-
sure from the initial resuspension of contaminated material located at
the source is much greater than the exposure from the secondary
resuspension of material located away from the source.
4. For a high resuspension rate, most of the population inhala-
tion exposure is delivered within the first year after a contaminating
event, while for a low resuspension rate it takes 100 years for most
of the exposure to be delivered.
5. The distance from the source within which most of the
population inhalation exposure is delivered is dependent on deposition
-------
218
velocity. For a doubling of the deposition velocity the distance
within which most of the exposure occurs decreases by more than
sixty-five per cent.
General Model Description
Figure 1 depicts the events considered in this model. The source
is assumed to consist of a single radionuclide with an initial activ-
ity of 1 Curie. The contaminating event is assumed to occur as a
ground level release, thus there is no initial airborne plume of
material to consider. Contaminated material at the source is resus-
pended and dispersed resulting in an air concentration, X-. Some
fraction of this airborne contamination deposits on the ground, which
also resuspends resulting in an air concentration X.. Material from
air concentration X. partially deposits on the ground, and
resuspends resulting in air concentration X_ and so on. Resus-
pension of contaminated material at the source will be called initial
resuspension. Resuspension of material located outside the original
source will be called secondary resuspension.
The model calculates, as a function of time and distance from the
source, air concentrations, X0 and X., and the respective
population inhalation exposures, PE~ and PE,. The total popula-
tion inhalation exposure, 2PE^, due to the sum of air concentrations,
2X , is also calculated.
n
For sources consisting of several radionuclides, the population
inhalation exposure is calculated separately for each radionuclide and
multiplied by its activity and summed.
-------
219
DEPOSITION
RESUSPENSION
V 1
I
r
I
1 i
MM
>
r
4
^
1
1
>
r
k
J
1
1
1 1
1 I
* 4
1
1
I •
M M M
i * t r j j
t * + + v +
I*
:
—*
*o
X,
x2
*n
POINT SOURCE
FIGURE 1
where:
Q = activity of point source (Ci)
r = distance from point source to receptor (m)
Xn = air concentration at distance r and time t resulting from
Ci
dispersion of resuspended material from source (~~T)
m
X = air concentration at distance r and time t resulting resu-
,Ci,
spension of material on ground at r (~~o")
m
X = air concentration at distance r and time t resulting from
resuspension of material deposited on ground from X _.
(— )
m
X_ = £ X ' = the air concentration at distance r and time t due to sum
Ci
of initial and secondary resuspension (~o)
m
PE- = population inhalation exposure due to air concentration
X_ (person -- -• - sec)
m
PE1 - population inhalation exposure due to air concentration
v / Ci %
X.. (person - — r - sec)
m
PE^ = population inhalation exposure due to air concentration
v / Ci ,
X (person -- «• - sec)
m ci
?£„, = £ PE = total population inhalation exposure (person -- «• - sec)
m
-------
220
Resuspension of contaminated material is the only physical
process used to describe the movement of contaminated material from
the soil to the air. Selected resuspension rates are assumed to be
constant with time and distance.
The model was prompted by the recent concern about transuranium
element soil contamination around several nuclear facilities in the
United States. In general, only relatively small areas are involved,
with population centers being fairly distant from the contamination
(>1 km). Where larger areas were intially contaminated, the popula-
tion centers are much farther away. Since the model's main purpose is
to assess the total radiological impact over large areas, the area
source is approximated by a point source. Where there is a small or
no population near the source the point source approximation is
satisfactory, considering the overall accuracy of the model.
Dispersion Equation
The air concentration of a radionuclide at a distance r from a
continuous ground level point source is found by calculating the
atmospheric dilution factor using a Gaussian diffusion equation which
is a function of wind speed, Pasquill stability category (determines
horizontal and vertical diffusion coefficients), and elevation of
receptor.
If the source rate term, Q, is known, the air concentration is:
X - (-)Q (l)
-------
22!
where X = air concentration at distance r (Ci/m )
X/Q = atmospheric dilution factor at distance r (s/m )
Q = source rate (Ci/s)
Another method of determining the air concentration downwind from
a source is from an equation for X/Q which is only a function of
distance. The former Atomic Energy Commission has presented data on
atmospheric dilution factors versus distance for a ground-level
release for 17 nuclear power sites situated near rivers, lakes, and
seacoasts. An equation which relates X/Q as a function distance can
be empirically derived from this data (see Appendix l). This
relationship is:
f(r) - (f>r ~£ (2)
Q Q n n
where r = normalizing distance (m)
(7) = value of X/Q at r = rn (s/m3)
Q n
-£ = slope of X/Q vs r on log-log plot
r = distance from source to receptor (m)
Equation (2) is valid only for those distances where data exist
for X/Q. It also not account for depletion of material as plume is
dispersed. The deposition of material on the ground can be accounted
-------
222
for in two ways, either by considering depletion of material from the
plume as it is dispersed, or by depletion of the source rate term Q.
Both methods yield the same result. A depletion correction factor
based on depletion of the source term is (see Appendix I):
*d
3- = exp [-(—)] (3)
Q rd
• d •
where Q /Q = depletion correction factor
Q = depleted source rate (Ci/s)
(2-£)r * 2-1
r = depletion distance = [ - - — ] (m)
n
v
-------
223
Calculation of Air Concentration Resulting from Resuspension of
Material at Source and Subsequent Population Inhalation Exposure
Three loss mechanisms involved with the depletion of the point
source activity are considered in this model. These are: resuspen-
sion of contamination from the ground, transfer of
contaminated material from the soil surface to a soil sink, and radio-
logical decay. Each loss mechanism is represented as an exponential
decay with a specific decay constant and each is assumed to be
independent of time. Thus the variation of the point source activity
with time is:
Q(t) = Q exp(-Att) (5)
where Q(t) = activity of point source at time t (Ci)
Q = initial activity of point source (Ci)
t = time (s)
A = total decay constant = X + X + A, (s )
*• L O Q
A = resuspension rate (s )
A = transfer rate of contaminated material from
8 _1
soil surface to soil sink (s )
A, = radiological decay constant (s )
-------
224
Equation (5) assumes there is no addition of contaminated
material to point source thru time. The quantity of the source activ-
ity, Q(t), which may potentially result in an inhalation exposure to
an individual is that amount being resuspended, which is:
Q(t) - XrQ(t)
= XrQ exp(-Att) (6)
•
where Q(t) = rate at which' the source activity is
being resuspended and available for
dispersion (Ci/s)
The air concentration, XQ, of a radionuclide at a distance r
from the source and at time t is the product of the atmospheric dilu-
tion factor and the source emission rate, that is:
Yd
(7)
Substituting equations (4) and (6) into equation (7):
xj(rft) = X-Q&r (f-)"1 «P[-(f-> " ] exp[-A t] (8)
u r Q n n d
where X_ (r,t) = the air concentration of a radionuclide at
a distance r from the source and at time t
taking into account depletion of the plume.
The subscript 0 denotes the air concentration
10
-------
225
due to dispersion of contaminated material
from the point source.
Using polar coordinates, (r,6), the differential population
inhalation exposure, dPE~, in area dA at a radial distance r + dr
from the point source and at an angle from a reference radial line
is the product of the air concentration XQ and population
density p in area dA during the time dt.
dPEQ = XQ pdtdA (9)
The total population inhalation exposure in area A and at time t
is obtained by integrating equation (9) over area and time.'
At,
PEQ = / / XJj pdtdA (10)
where
dA = rdrd0 (see Fig. 2)
p - population density
PEQ = population inhalation exposure due to contaminated
material resuspended from the source
From Fig. 2, dA = rdrd6 , substituting into equation (10)
27r fc2 r2
PE0(r,t) = / / / pXJjrdrdtdG (11)
v v-* JL •*
1)
-------
FIGURE 2
226
Assuming symmetry about the point source and uniform population
density:
PEQ(r,t) = 2irp
l rl
Xjj rdrdt
(12)
d .
Substituting equation (8) for XQ into equation (12)
PEn(r,t) =
u
r Q n
(— ) exp[-(— )
n d
exp[-Att]drdt
(13)
12
-------
227
Integrating over time and distance and simplifying gives: (see
Appendix II for complete integration steps):
PE0(r,t)
-exp(-Xtt2)]
Evaluating equation (13) over the following limits, r, = 0,
°° and t = 0, t ~ M , gives:
PEn(»,-) = (~-) (15)
u d t
PE^C00,00) is referred to as the infinite population inhalation
exposure. Integration over infinity is performed for mathematical
convenience and represents a plateau for the population inhalation
exposure. The plateau exposure is actually reached in a relatively
short time and distance depending on the values of parameters used.
Equation (14) can be evaluated over various times and distances to
determine when and where the plateau exposure is achieved.
13
-------
228
Discussion on the Derivation of the Air Concentrations X. ,
X0 X , Resulting from the Secondary Resuspension of
/ n 1
Contaminated Material
Calculation of the air concentrations, X1, X« .... X ,
due to the secondary resuspension of contaminated material requires a
prior determination of a soil surface concentration equation. The
material in XQ deposits at a rate equal to w. = V.XQ,
where V, is the surface specific deposition velocity. This
deposited material results in a soil surface concentration denoted
as fi.. . The material that is a part of fi. resuspends to give an
air concentration X . The material X.. , as it is dispersed,
deposits on the ground at a rate equal to u>_ = V.X.. . This
deposited material is a source term which results in a soil surface
concentration denoted as ft-. The material that is a part of 12-
resuspends to give an air concentration X_. The air concentra-
tions X_ .... X are similarly derived. The total soil
surface concentration at any point r from the original source is equal
to the sum of the soil surface concentrations, ft.,ft_ .... ft .
Note that ft is decreased by radiological decay and transfer to a
soil sink. The actual air concentration at any point r is equal to
the sum of air concentrations, Xn, X, .... X . This
u l n
model does not calculate the actual soil and air concentrations at any
point r. Only the soil surface concentration fl, and the air
concentrations XQ and X. are calculated. The result for the
-------
229
air concentration X« is shown but is not calculated in this
report. The population inhalation exposures PE~, resulting from
XQ, PE , resulting from X , and PE (»,») resulting from
SX are calculated.
n
Calculation of Air Concentration X Resulting from the First Secondary
Resuspension of Contaminated Material
X.(r,t) represents the air concentration at distance r and
time t resulting from the first secondary resuspension of contaminated
material. The material which is resuspended is that deposited from
air concentration XQ. This deposited material is represented by
the soil surface concentration fi-. Determining X1 requires
calculation of the soil surface concentration,fi., as a function of
time and distance.
The soil surface concentration, fl,, at distance r and time t is
increased by the deposition of contaminated material from Xn; it
is decreased by resuspension of the deposited contamination, by trans-
fer of the contaminated material from the soil surface to a soil sink,
and by radiological decay. The importance of each loss mechanism
depends largely on the value of its decay constant.
The deposition rate of contaminated material from air concen-
tration X~ to the soil surface is:
-------
230
The rate of change with time and distance of the soil surface
concentration, fl ., can be expressed as:
(17)
decrease in soil increase in soil
surface concentration surface concentration
The total decay constant, X , is equal to X + A + X,.
t IT S Q
Since we are interested in the air concentration which results
from a soil concentration at a distance r, equation (17) is changed
from a partial differential equation to an ordinary differential
equation by holding r constant and solving equation (17) with respect
to time. The solution may be found in Appendix II. The result is:
n-(r,t) = V 0$r £-> * exPt-(f-)~£l texp[-A t] (18)
1 a r Q n n d
The time when the maximum soil surface concentration is reached
can be calculated by setting the first time derivative of equation
(18) equal to zero and solving for time t-
2-£(-X t)-X texp(-A t)]
c
Q n n
Let A = VdArQ& (^-)~£ e*p[-(f-)2-£]
Q n n d
then:
—~ [A-AXtt][exp(-Xtt)] (19)
16
-------
231
Setting equation (19) equal to zero and solving for t, the
maximum soil surface concentration, fl,. , is reached when:
= i_ (20)
max ^t
Now that the soil surface concentration as a function of time and
distance is known, the air concentration, X. can be calculated.
To calculate X.(r,t), the source rate, which is equal to
X fi.A, is multiplied by the depleted atmospheric dilution
equation X /Q and integrated over area and time. In general
terms this is:
(21)
Equation (4) shows that X /Q is a function of distance r and
equation (18) shows that QI is a function of distance r. When these
terms are multiplied the result becomes very difficult to integrate
explicitly. The following section presents a method by which the
integration of X (r,t) becomes simplified.
Consider a disk of radius R uniformly contaminated with a soil
2
surface concentration ft. (Ci/m ) located at a distance r from the
original source. See Figure 3. The source rate Q from this disk is
the product of the soil concentration, 12., resuspension rate, X ,
17
-------
232
POLAR COORDINATES
FIGURE 3
and the area, A, of the disk. The incremental source rate in area dA
is:
dQ
(22)
The air concentration, X,, at the center of this disk is the
area integral of the source rate times the depleted atmospheric dilu-
tion factor, X /Q , given in equation (4). Remember fl. is now
assumed to be constant.
2ir R ...
1 0 0 r 1 Q rn rn
(23)
Symmetry is assumed, thus the integral for d9 is equal to 2n.
Integration over distance r was performed earlier in a similar
18
-------
233
calculation and the solution may be found in Appendix II, part A. The
result is:
X? = =*-i. [l-exp(- f-)2~*] (24)
d d
For a disk radius R > r,, the depletion distance, the term
R 2—a
exp[-(—) ]approaches zero, thus the air concentration becomes:
rd
, An..
x = ^ (25)
Equation (25) gives the air concentration at the center of a disc
which is uniformly contaminated. Equation (18) gives the variation of
the soil surface concentration fi with time and distance., Substi-
tuting equation (18) for fl, in equation (25) gives:
X?(r,t) = A2 Q(f) (f-)~* exp[-(f-)2~£] texp[-A.t] (26)
r Q rn rn d C
The validity of the uniformly contaminated disk assumption may be
examined by looking atfi..(r,t) plotted as a function of distance
(equation 18). The soil surface concentration, n.(r,t) is an
exponential function of distance r. This says that for points close
to the source the soil surface concentration drops rapidly with
distance and for points far from the source fi1(r,t) decreases less
rapidly. The uniformly contaminated disk assumption becomes more
19
-------
234
valid the further one gets from the source. The model is mainly
interested in the total population inhalation exposure and not so much
with the variation of exposure with distance from the source. Any
overestimate and underestimate with distance of the air concentration
is averaged out because of the uniform population density assumption.
Calculation of the Population Inhalation Exposure, PE-(r,t)
Resulting from Air Concentration X..(r,t)
The population inhalation exposure, PE., due to air concen-
tration X, is derived the same way PEn was calculated. That is:
2ir 2 r2 .
PE1(r,t)=/ / / pX,rdrdtd6 (27)
0 t, r, X
Assuming symmetry and uniform population density,
PE1(r,t) = 27rp / -/ xjrdrdt (28)
Substituting equation (26) for X. in equation (28);
r Or ^ -f r(7~) exp[-(J-)2 £J . (2g)
Q n tx ^ d rd
texp[-Xtt]drdt
20
-------
235
Integrating over time and distance and simplifying gives: (see
Appendix II for complete integration steps).
PE1(r,t) =
d d
X t + 1
(30)
At + 1
(~~ - )exp(-Att2)]
Xt
Evaluating equation (30) for r, = 0, r, = °° and t, = 0,
t_ = 0° gives:
A 2
PE1 (»,») = **(•£•)
-1 V
d t
(31)
Calculation of the Total Infinite Population Inhalation Exposure
PET(»,»)
Previous sections have calculated the population inhalation
exposures due to the initial resuspension of material at the point
source and from the first secondary resuspension of material at
distance r that originated from the point source, i.e., PE0 and
PE,. The material at distance r which deposited from air concen-
tration X, is also available for resuspension and results in air
concentration X The material associated with X^ is
21
-------
236
dispersed and deposited, and re suspends as X- and so on. For
each of the air concentrations X , there is an associated popula-
n
tion inhalation exposure, PE . The summation of all the population
inhalation exposures, 2 PE , gives the total population inhalation
n
exposure, PE .
A simple expression for the total infinite population inhalation
exposure, PE C00,00) can be derived. Equations (16) and (31) for
PEQ C00,00) and PE, C00,") respectively show that PE.. (°°,°°)
A
differs from PEn («,°°) by a factor of - — , i.e.:
0 X
A A 2
PE0(«,co) = £&(_£) PEl(»,-) = *&(-£)
d t d t
The air concentration X_, is derived by the same method as
X was determined except fl. becomes O* an<* the deposition
rate becomes «„ = V ,X, . The infinite population inhalation
exposure, PE- (m,°°~) is the integral of the air concentration
X9(r,t) multiplied by the population density. The result is:
PE2(-f.) =f() (32)
d t
Each air concentration, X , results in an infinite
population inhalation exposure, PE , which differs from the previous
A
exposure, PE ,, by a factor of ~- . Therefore the total infinite
A
population inhalation exposure is:
22
-------
237
PE,,
F f« 00} = &(-±) + P^r—1 + £S(-JL}' + + P3(_Z)
V ' ' V/X/+V/X; V/A/ +"--+V/X/
d t d t d t d t
i fia^ (33)
j=l d t
Equation (33) is a geometric series, which stated in a more
general form is:
n . m,.. n-l+itK ....
Z arJ = ar (1-r ) (34)
1-r
J=m
When r
-------
238
Environmental Dose Commitment
Environmental dose commitment is defined as "the sum of all doses
to individuals over the entire time period the material persists in
the environment in a state available for interaction with humans" and
has units of person-rem. "It is calculated for a specific release at
a specific time and is obtained by summing the person-rem delivered in
each of the years following release to the environment until dose
increments are inconsequential by other means" (l).
The environmental dose commitment resulting from the inhalation
pathway in this model is calculated by multiplying the total infinite
population inhalation exposure by an annual breathing rate and a dose
conversion factor, i.e.:
Environmental Dose Commitment (person-rem) = (37)
Total Infinite Population Inhalation Exposure (person - —=• - yr) x
m3
Breathing Rate (—) x Dose Conversion Factor (——r)
The total infinite population inhalation exposure, designated as
PE-O^j00), is directly obtained by integrating over all distance and
time, the air concentration X (r,t) multiplied by the population
density, P . The annual breathing rate gives the total volume of air
inhaled by a person in one year. The dose conversion factor converts
the activity of a radionuclide inhaled into a dose, and is dependent
on many parameters, such as organ of interest, radionuclide inhaled,
24
-------
239
activity mean aerodynamic diameter (AMAD) of particles inhaled, and
biological residence time in organ.
The environmental dose commitment can also be calculated for a
period of time less than that stated in equation (37). For example, a
100 year environmental dose commitment is determined by calculating
the population inhalation exposure committed over a 100 year period
and substituting this value for the total infinite population inha-
lation exposure in equation (37).
The environmental dose commitment may be used to calculate the
cumulative potential health effects that result from a release of
radioactive material into the environment by multiplying the environ-
mental dose commitment for each organ by a dose-risk conversion
factor. Dose-risk conversion factors are derived for somatic and
genetic risk, and are dependent on the organ of interest, radio-
nuclide, and age category of person, usually child or adult.
The following sample calculation illustrates the conversion of
population inhalation exposure to an environmental dose commitment.
The calculation will determine the environmental dose commitment for
the pulmonary region of the lung as the result of inhaling Pu-239
particles. The pulmonary region of the lung is considered the organ
at greatest risk for the inhalation of Pu-239 particles.
Equation (37) requires data for 3 parameters to calculate the
environmental dose commitment, the total infinite population inha-
lation exposure, the annual breathing rate of a person, and a dose
25
-------
240
conversion factor. From Table 2, the total infinite population
inhalation exposure for parameter set #1 (see Table 1), is 8.5x10
person-Ci yr/m . The annual breathing rate is assumed to be that of
3
standard man and is equal to 8395 m /yr (2).
The dose conversion factor (DCF) is calculated using the
following equation:
ET fa
DCF = 7.38xlO"2 —£— „. ?"* . (38)
m pui inhaled
where:
E = effective energy of disintegrations MeV/dis
T = effective half-life of radionuclide in organ days
i_i
f = fraction of inhaled particles reaching organ
cl
m = mass of organ grams
The effective energy of Pu-239 disintegrations is 5.15 MeV/dis (3).
The effective half-life of Pu-239 in the lung is equal to the bio-
logical half-life since the radiological half-life of Pu-239 is so
long. Thus the effective half-life of Pu-239 in the lung is 300.4
days assuming the Pu-239 particles to be a class Y compound (4). The
fraction of Pu-239 particles inhaled reaching the pulmonary region of
lung is .23, assuming the Pu-239 particles have an AMAD of 1 micron
(5). The mass of the pulmonary region of the lung is 570 grams (2).
Substituting these parameter values into equation (38) gives:
570 pCi inhaled
26
-------
241
DCF = .046 , . = 4.6xl07 rad
pCi inhaled ' Ci inhaled
If a quality factor of 20 is assumed (9), the dose conversion factor
Q
becomes 9.2x10 rem/Ci inhaled. From equation (37), the environ-
mental dose commitment is:
EDC = (8.5xlO~U person - -^ - yr)(8395 2-)(9.3xl08 .Tfm )
r 3 J yr Ci inhaled
yr
EDC = 656 person-rem
Equation (38) is applicable only for an acute intake of
radioactive material. This calculation assumed that the exposure,
?£„(«>,°°), occurs as the of an acute intake. Figure 5 shows for
parameter set #1 that PE (°°,°°) is reached within one year. If the
total infinite population inhalation exposure is committed over a
period of greater than one year, the acute intake assumption is not
valid and the dose conversion factor must be derived for a continous
intake situation.
The use of the phrase "infinite dose" is used in the same
context as "infinite exposure" whose meaning is explained on page (13).
Parameter Selection
Table 1 presents the values of parameters selected to illustrate
exposure calculations using the model. Parameter values selected are
27
-------
Table 1
Parameter Values Used To Illustrate Model
2*2
Set //I
Set //2
Xr = 10
X = l.OlxlCf7 s'1
L
&_.
r
Xt = l.OlxlO'9 s'1
CX1
Q
X
s
Ad
Vd
Q
r
n
1km
a
rd
P
= 10-9 s-1
= 10-12 a'1
= 0.01-
s
= 1 Ci
= 1000 m
= 2.5xlO~6 ^j
m
= 1.43
= 9595 m
0 -, , _-5 persons
— L . /XXU ^
m
-------
2*3
intended to correspond to typically observed values in the field, but
are not indicative of any particular site. Two calculations are made
differing only in the value of the resuspension rate, X • and
therefore the total decay constant, X • The high resuspension rate
represents an area recently contaminated or an area being mechanically
disturbed, while the low resuspension rate represents a typical aged
source. Current data indicates that the resuspension rate is a
function of time, but this model does not take into account the time
dependence of the resuspension rate; it is assumed that the resuspen-
sion rate remains constant throughout time and also distance.
The model also depends on values chosen for the transfer rate of
contamination from soil surface to the soil sink, population density,
deposition velocity, half-life of the radionuclide of interest, and
the source strength. The transfer rate from the soil surface to the
soil sink was taken from the report ORNL-4992 (6), while the popu-
lation density used is that of the continental United States during
1970. Deposition velocity is a complex parameter dependent on the
meteorology of the site, and particle-soil surface aerodynamic
properties (7). The value selected for the deposition velocity is one
typically found in the field and is assumed to be constant with time
and distance.
Since this model is addressed to transuranium element
contamination, in particular Pu-239, radiological decay will generally
not be of any consequence in calculating population inhalation expo-
sure. The source strength is arbitrarily taken to be 1 Ci of Pu-239.
28
-------
244
For source activities greater or less than 1 Ci and for different
radionuclides, the population inhalation exposure calculated for each
radionuclide are multiplied by their respective activities and summed
to get the total population inhalation exposure. The specific para-
meter values of the dispersion equation used in this model are
discussed further in Appendix I.
Results
Table 2 gives the population inhalation exposure, PE^00,00) ,
integrated over distance, r = 0-»°°, and time, t = Q-*00. When the
resuspension rate is high (10 s ), the exposure PE. from the
first secondary resuspension is almost equal to the exposure, P£Q
from the initial resuspension. The sum of PEQ and PE» is a factor
of 51 lower than the total exposure indicating that subsequent
resuspension after the first secondary resuspension is a significant
contributor to the total infinite population inhalation exposure for
the high resuspension rate.
For the low resuspension rate (10 s ) the exposure PE-.
from the initial resuspension is a factor of 100 higher than the
exposure, PE., from the first secondary resuspension. The sum of
PE_ and PE, is just about equal to the total exposure indicating
that secondary resuspension is not much of a contributor to the total
infinite population inhalation exposure for the low resuspension rate.
The total infinite population inhalation exposure, PE^O30,00),
is a factor of 10 higher for the resuspension rate of 10"' s~*
-11 -1
as compared to the resuspension rate of 10 s , with all other
29
-------
parameters equal. If a time dependent resuspension rate was used in
this model instead of a constant resuspension rate, the total infinite
population inhalation exposure would be expected to lie between the
exposures resulting from the resuspension rates of 10 s and
10 s , assuming these are the initial and final resuspension
rates.
Table 3 presents the population inhalation exposure as a function
of time integrated over the distance r=0->«. The high resuspension
rate results in most of the population inhalation exposure being
delivered within the first year after a contaminating event, while for
the low resuspension it takes 100 years after a contaminating event
for most of the population inhalation exposure to be delivered.
Figure 4 is a plot of the values in Table 3.
Table 4 gives the distance within which the fraction X of the
total infinite population inhalation exposure is delivered for various
deposition velocities. Even though the total infinite population
inhalation exposure is obtained by integrating over infinite distance,
95% of the exposure is delivered, for example, within 66 kilometers
for a deposition velocity of 0.01 m/s. Doubling the deposition
velocity decreases the distance within most of the infinite population
inhalation exposure occurs by more than sixty-five per cent.
Tables 5 and 6 presents the air concentration as a function of
distance at various times after a contaminating event, taking into
account depletion. For the high resuspension rate the air concen-
tration, X., resulting from the first secondary resuspension is
30
-------
246
greater than the air concentration, X0, resulting from the
initial resuspension of the contaminated material. Within 10 years
both air concentrations drop to very small levels. For the low
resuspension rate the air concentration, X,., resulting from the
initial resuspension is much higher than the air concentration
resulting from the first secondary resuspension. After 50 years both
air concentrations are still within a factor of 10 of the levels
occurring after one year. Figures 5 and 6 are a plot of the values in
Tables 5 and 6.
Tables 7 and 8 gives air concentration as a function of time at
various distances, taking into account depletion. For the high
resuspension the air concentrations essentially drops to zero, while
for the low resuspension rate the air concentrations drop only by a
factor of 100 after 100 years.
Table 9 gives the soil concentration fl. resulting from
deposition of material originating from source as a function of
distance, 1 year and 10 years after a contaminating event. The high
resuspension rate has a 10 year soil concentration much lower than the
1 year soil concentration greater than the 1 year soil concentration.
See Figures 7 and 8.
Tables 10 and 11 presents the soil concentration,fl1, as a
function of time at various distances. The maximum soil concentration
is reached in 0.31 years for the high resuspension rate and in 31.43
years for the low resuspension rate. See Figure 9.
31
-------
Table 2
Infinite* Population Inhalation Exposure
247
PEO(-,»)
PET(»,»)
Parameter Set #1 Parameter Set #2
(person - Ci - y) (person - Ci - y)
8.5x10
nr
-11
8.4x10
-11
8.6x10
-9
8.5x10
-13
8.4x10
-15
8.6x10
-13
* Refers to integration over all distance and time, 95% of exposure
occurs within 66 km from source for both parameter sets and levels
stated above reached in ly and lOOy for parameter sets 1 and 2
respectively.
32
-------
2S8
Table 3
Accumulated Population Inhalation Exposure* As A Function Of Time
Parameter Set #1
Parameter Set #2
PE
o
PE
PE
0
(y) ,- Ci . , Ci
(person - y) (person r
Ci
m
m
y) (person 3 ~ y)
m
PE,
, Ci
(person --
- y)
m
0.01
0.1
1
10
25
50
100
250
500
1000
2.7xlO
~12
2.3xlO
~n
S.lxK
11
8.5X10
""11
4.2xlO
~U
3.4xlO
~12
6.9xlO
~U
8.4xlO
~U
2.7x10
2.7x10
2.7x10
2.3x10
4.7x10
6.8x10
8.1x10
8.5x10
.-14
-13
-13
4.3x10
-22
4.2x10
-20
4.2x10
-18
3.4x10
-16
1.6x10
4.0x10
-15
-15
6.9x10
-15
8.4x10
-15
PEQ(t) = (
d t
- Afct2)]
A 2
PE1(t) = ^(~) [l-(Att2+l)exp(
d t
^integrated over all distance.
33
-------
2*9
.s
u
c
UJ
-------
250
Table 4
Distance Within Which The Fraction X of Accumulated Exposure
X
.05
.10
.25
.35
.45
.50
.60
.75
.90
.92
.95
.98
.99
.999
.9999
Is Delivered
V =0.02 -*
d s
16
55
320
649
1,153
1,495
2,440
5,044
12,286
14,450
19,494
31,134
41,449
89,421
139,843
1
r n f -i \ I^""""A/
As A Function Of Vd
r2 (m)
V =0.01 -**
d s
52
185
1,078
2,190
3,891
5,044
8,231
17,018
41,449
48,751
65,768
105,038
139,841
284,817
471,799
V ,=0.005 -***
d s
177
625
3,638
7,387
13,128
17,017
27,767
57,413
139,833
164,469
221,877
354,359
471,771
960,868
1,591,675
r2 =
= 2,844m, £=1.43
= 9594m, £=1.43 *** r = 32,370m, £=1.43
35
-------
251
Table 5
Air Concentration* As A Function Of Distance-Parameter Set #1
r
(m)
1,000
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
xj(ly)
(%
m3
7.8xlO~15
1.4xlO"16
3.1xlO~17
1.2xlO~17
5.5xlO~18
3.0xlO~18
1.7xlO"18
l.lxlO'18
6.9xlO~19
— 1 Q
4.6x10
3.2xlO~19
xjJdOy)
<%
3
m
2.8xlO~27
_OQ
4.9x10 *
-29
1.1x10 *
4.2xlO-30
2.0xlO~~3°
l.OxlO'30
6.1xlO~31
3.8X10'31
2.4xlO~"31
1.6xlO~~31
l.lxlO'31
xjdy)
(%
v 3'
m
2.5xlO~14
4.4X10'16
9.8xlO~17
3.7xlO~17
1.7X10'17
9.4xlO~18
5.4xlO~18
3.4X10'18
2.2xlO~18
l.SxlO'18
l.OxlO'18
xj(10y)
(%
v y
m
8.8xlO~26
1.5xlO~27
3.5xlO~28
1.3xlO~28
-29
6.2x10
-29
3.3x10
-29
1.9x10
-29
1.2x10
7.7xlO-30
5.2X10'30
3.5X10'30
(T>r (7-)
Q n n
-(^-) *]exp[-Att]
d
2 £
X?(r,t) = A -K (f-) *exp[-(f-) ]t exp[-X t]
1 r Q rn rn d
*corrected for deposition from plume
36
-------
252
10"
15
.E
o
cc
t-
H
LU
o
z
o
o
cc
Q
LJU
I-
III
_l
0.
UJ
O
i-16
1C'
17
10
•19
>t=1.01x
N{j=0.01m/i
Q-1 Ci
10,000 20,000 30,000 40,000 50,000 60,000 70,000
DISTANCE (m)
AIR CONCENTRATION VS. DISTANCE - PARAMETER SET * t
FIGURE 5
37
-------
Table 6
Air Concentration* As A Function Of Distance-Parameter Set #2
253
r
(m)
1,000
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
xjdy)
(~)
m
1.8xlO~17
3.2xlO~19
7.7xlO-20
2.7xlO-20
1.3xlO-2°
6.9xlO~21
4.0xlO~21
2.5xlO-21
d
(-3)
m
1.4xlO~17
2.4xlO~19
5.5xlO-20
2.1xlO-20
9.5xlO~21
5.2xlO~21
3.0xlO~21
1.9xlO~21
xj(ly)
1.6x10
1.1x10
7.4x10
r21
-21
-22
1.2x10
8.1x10
5.6x10
-21
-22
m
3.9x10
6.8x10
1.5x10
5.8x10
2.7x10
1.5x10
8.5x10
5.2x10
3.4x10
2_.3xlO
1.6x10
-18
-20
-20
-21
-21
-21
I
-22
-22
-22
m
5.8x10
1.0x10
2.3x10
8.7x10
4.1x10
2.2x10
1.3x10
7.9x10
5.1x10
3.4x10
-21
-22
-23
-24
-24
-24
-24
-25
I
-25
-25
m
4.4x10
7.7x10
1.7x10
6.5x10
3.1x10
1.6x10
9.6x10
5.9x10
3.8x10
2.6x10
~2°
-22
~24
~24
m
6.1x10
1.1x10
2.4x10
9.1x10
9.3x10
2.3x10
1.3x10
8.3x10
5.3x10
3.6x10
-20
-21
-22
-23
-23
-23
-23
-24
-24
-24
Q n n
Q n n
*corrected for deposition from plume
38
-------
254
CO
.E
o
HI
CJ
H
O
CJ
Q
LU
[-
01
_l
0.
LU
Q
0.01 m/$
Q-ICi
6 = 2.7 xlO"5 persons
2
10
10'21 ..
10"
22
10,000 20,000 30,000 40,000 50,000 60,000 70.000
DISTANCE (m)
AIR CONCENTRATION VS. DISTANCE - PARAMETER SET * 2
FIGURE 6
39
-------
255
Table 7
Air Concentration* As A Function Of Time
At Various Distances-Parameter Set #1
t
(y)
0.01
0.1
1
10
25
50
100
250
500
1000
r=l,000m
1.8xlO~13
l,4xlO~13
7.8xlO~15
2.8xlO~27
4.9xlO~48
-------
256
Table 8
Air Concentration* As A Function Of Time
At Various Distances-Parameter Set #2
t
(y)
0.01
0.1
1
10
25
50
100
250
500
1000
r=l,000m
1
1
1
1
8
3
7
6
2
2
.9x10 17
.9xlO"~17
.8xlO-17
.4xlO"17
.exlO"18
.9xlO"18
.8xlO~19
.6xio"2:L
.3xlO-24
.8xlO"31
xdfe
V 3}
m
r=10,000m
3.3X10'19
3.3xlO"19
3.2xlO"19
2.4xlO"19
1.5xlO~19
6.8xlO~2°
l!4xlO-2°
-22
1.2x10
JfL
4.0x10 °
4.9xlO~33
r=20,000m
7 . 5x10
7.5x10
7 . 3x10
5.5x10
3.4x10
1.5x10
3.1x10
2.6x10
9.1x10
1.1x10
-20
-20
-20
-20
-20
-20
-21
-23
-27
-33
r=l,000m
6.
6.
5.
4.
6.
6.
2.
5.
3.
8.
OxlO~23
OxlO~
8xlO-21
4xlO-2°
7x10-2°
IxlO-20
5xlO-2°
2xlO-22
6xlO-25
8xlO-33
m
r=10,000m
1
1
1
7
1
1
4
9
6
1
.IxlO-24
.OxlO"23
.OxlO"22
7xlO"22
;2xio-21
.IxlO-21
.4xlO"22
.IxlO-24
.9xlO"27
.5xlO-33
r=20,000m
2
2
2
1
2
2
9
2
!
3
.4x10 25
.4xlO"24
.3xlO-23
.7xlO-22
-22
.7x10
-22
.4x10
.8xlO-23
.IxlO-24
4xlO"27
!5xlO-34
*corrected for deposition from plume
41
-------
257
Table 9
Soil Concentration As A function Of Distance
Parameter Set #1
Parameter Set #2
(m)
1,000
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
J^UOy)
m
2.5x10
4.4x10
9.8x10
3.7x10
1.7x10
9.4x10
5.4x10
3.4x10
2.2x10
-9
-11
r12
-12
-12
-13
-13
-13
-13
m
8.8x10
1.5x10
3.5x10
1.3x10
6.2x10
3.3x10
1.9x10
1.2x10
7.7x10
-21
-22
-23
I
-23
-24
-24
-24
,-24
-25
^(ly)
fCi.v
m
-12
n1(ioy)
5.8x10
1.0x10
2.3x10
8.7x10
4.1x10
2.2x10
1.3x10
7.9x10
5.1x10
-13
-14
-15
-15
-15
-15
-16
-16
4.4x10
7.7x10
1.7x10
6.5x10
3.1x10
1.6x10
9.6x10
5 - 9x10
3.8x10
m
-11
I
-13
-13
-14
-14
-14
-15
-15
-15
n n
-A tj
42
-------
-10
u
tc.
t-
z
111
u
o
u
10
-11
258
10
-9 ..
PARAMETER SET *
Af« 10-7 s-1
VlO'V1
Xd=iO-12S'1(Pu-239»
A,' 1.01 x 10-7 S'1
vd =0.01 m/i
Q-1CI
S' 2.7 x 10''persom
10Y < 10-21
-13
10,000 20,000 30,000 40,000 50,000 60,000 70,000
DISTANCE (m)
SOIL CONCENTRATION VS. DISTANCE - PARAMETER SET * 1
FIGURE 7
43
-------
259
-------
260
Table 10
0.01
0.1
0.2
0.3
0.4
0.6
0.8
1
10
20
50
100
500
1000
Soil Concentration As A Function Of Time
At Various
Distances-Parameter Set
//I
m
r=l,000m
5.8xlO"10
4.4xlO~9
6.3xlO~9
6.9xlO~9
6.7xlO~9
5.3xlO~9
3.7xlO~9
2.5xlO~9
8.8xlO~21
-------
261
Table 11
(y)
0.01
0.1
1
10
20
35
40
50
100
250
500
1000
Soil Concentration As A Function
At Various
Distances-Parameter
Of Time
set n
V%
m
r=l,000m
6.0xlO~14
6.0xlO~13
5.8xlO~12
4.4xlO~1:L
6.3X10"11
6.9xlO~n
e.yxio"11
e.ixio"11
2.5X10"11
5.2xlO~13
3.6xlO~16
-23
8.8x10 J
r=10,000m
l.lxlO"15
l.OxlO"14
l.OxlO"13
7.7xlO~13
l.lxlO'12
1.2xlO~12
1.17xlO~12
l.lxlO~12
4.4xlO~13
9.2xlO~15
6.4xlO~18
1.5xlO~24
r=20,000m
1.2xlO~18
1.2xlO~17
1.2xlO~16
8.9xlO"16
1.3xlO~15
1.4xlO~15
1.36xlO~15
1.2xlO~15
5.0xlO~16
l.lxlO"17
7.4xlO~21
1.8xlO~27
(max) occurs at t
= 31.43y
46
-------
282
CM
.£
c3
cs
z
o
LU
o
z
o
13
PARAMETER SET * 2
10 "S" (Pu-239)
-\t= 1.01 x 10 -9S-1
0.01
Q= 1 Ci
10
16
.01
1 10
TIME (YEARS)
SOIL CONCENTRATION VS. TIME
FIGURE 9
1000
47
-------
263
APPENDIX I
Derivation Of X/Q Vs. Distance Relationship For A Ground Level Release
The former Atomic Energy Commission in its draft environmental
statement for Appendix I, 10 CFR 50, (8) presented data on average
annual atmospheric dilution factors, — , versus distance, r, at a ground
Q
level release height for 17 nuclear power reactor sites situated on
rivers, lakes, and seacoasts. The data, plotted on a log-log graph,
showed a linear relationship between the atmospheric dilution factor and
distance. The general equation describing this line is:
log y = mlog x + log b (1)
- loggb = mlogex
log(} =
eb
y = bxm (2)
where m = slope of the line
b = value of y at X = 1
For a specific case: (see Fig. 1)
brm (3)
where
X
• = average annual atmospheric dilution factor
r = distance
m = slope
48
-------
Fig. 1
loge(X/Q)2
264
Ioge(r1) loge(X/Q)1
Ioge(r2) loge(X/Q)2
loge(r)
The slope of the line in Fig. 1 is:
m =
M- lose(x/Q)2 " Iose(x/Q):
AX Ioge(r2) - Ioge(r1)
loge{(X/Q)2/(X/Q)1>
m
loge{(X/Q)1/(X/Q)2}
log (r^r,)
(4)
let m = -£
In equation (3), b is calculated for distances other than r=l as
follows. Select some arbitrary normalizing distance, r , and determine
the corresponding X/Q value, (X/Q) , from Fig. 1. At r=r equation
(3) becomes:
n
(X/Q)
(b)
n
n
49
-------
265
or (b) = (-) r£ (5)
r v«'r n
n Q n
Substituting equation (5) into equation (3):
A. / \ S&\ A* ™>
T(r) = (7) r r
Q Q n n
7 = (T)
-------
266
•d
The depleted source term Q is derived as follows:
Assume the deposition rate, w(r) , at a distance r to be:
-------
Substituting into equation (8) and separating variables:
Q Q n n
Integrating over 0 to r and 0 to 2ir
r ^A Y r 2ir o
/^=- *r V, / / r(^-)-£ drdG
0 Q Q n a 0 0 n
logeQ(r) - loge Q(0) = - d
Q
let Q(0) = Q
Q(r) = Qd
2-£
Q nrn
let r = t
Q n
Therefore:
2-fi, Q r r
n n
267
52
-------
288
Substituting into equation (9)
,Q , ,1 .2-H 2-£
<>--<- r
and
f- = exp[-(^-)2 £] (10)
Q d
Substituting this into equation (8), the depleted X/Q equation
becomes:
~ (r) = & (^)'£ expt-Cf-)2^] (11)
Q Q n n d
In equation (10), r, represents a deposition distance, when r=r,,
•d
-^— has decreased by a factor of — or 37%.
Q e
The AEC data presented in reference (8) can be used to obtain an
expression for the undepleted X/Q as given in equation (6).
-(r) = (-) (f-)
Q Q n n
let r = 1 km
n
— at 1 km varies from 2 to 3x10 —
Q m
assume — at 1 km = 2.5x10 ^
m
53
-------
269
- at 160 km varies from 1.5 to 2.1x10 -^r
• J
0 m
X ~9 s
assume — at 160 km = 1.8x10 —_
Q m
The slope of the line is:
m = -St,
loge (160}
log {2.5xlO~6/1.8xlO 9}
loge(160)
a = 1.43
and (-), . = 2.5x10 6 ~
• 1 km J
Q m
Therefore:
-(r) = 2.5x10 6 r"1'43 (12)
This equation is the result of averaging the average annual
atmospheric dilution factors for rivers, lakes, and seacoasts sites.
It is valid only for those distances for which data was presented,
i.e., .1 km
-------
270
Appendix II
Solutions To Selected Integrals And Differential Equations
A. Integration of Equation (13)
t2 T2 -H 2-SL
PEQ(r,t) = 2TrpArQ(*)r / / r(-|-) exp[-(^-) Jexp[-AttJdrdt
Q n t, r, n d
Integrating over r first:
r2 -I 2-1 r2 !-«, 2-1
/ r(—) exp[-(—) ]dr = / £—r exp[-(J-) ]dr
IT t , ^X/ t i
r.. n d r.. r d
1 In
By substitution:
2-H
let u = r
du = (2-£)r1~i!'dr
2-£
U0 = rd
The new limits of integration are:
2-1
L
2-1
ul = rl
U2 = r2
Therefore:
2-£
du - - - -— exp(
.
2-£ r (2-4)r 0 r 2-£) r
-, n n JL
2-t
UQ r , u ,,r2
-^ - t-exp(- — )]
r £(2-Jl) U0 r, ^
n 1
55
-------
271
r. 2-1
r (2-5,)
n
r, 2-1
(-±)
PEn(r,t) now becomes:
2-1
PEn(r,t)
U
Qrn
(-
r
2-H
(-
r
2-St,
n
exp(-A t)dt
L
Integrating over t:
exp(-A t)dt =
Also r, * = [(
d
J -
d Q rn
27rV
(-)
Q rn
_
Substituting in the time integration and the result of r , and
simplfying gives:
A r 2—
PE(r,t) = ^(^-Hexpt-^i)
d t d
2— Si
Q
B. Solution to Equation (17)
or
This linear first order differential equation is solved, with
respect to time, by use of an integrating factor u(t), where:
t
u(t) = exp[J p(x)dx]
56
-------
272
l t
and y = • .- . [ J u(s)p(s)ds + c] c = constant
where y is the solution of y + p(t)y = g(t)
l(r,t) = VdXg(r,t)
substituting equation (8) for X_
-a 2-a
u (r,t) = VrQ(.}r (r~~} exP[~^>
Q n n d
Therefore:
-£ 2-£
let A = V A Q£) (^-) exp[-(f-) ]
Q n n d
^(r.t) + Atfi1(r,t) = A exp[-Xtt]
The integrating factor u(t) is:
t t
u(t) = exp[/ p(x)dx] = exp[/ Xfcdx
u(t) = exp[Att]
and
, t
[/ u(s)g(s)ds + c]
2— a
X fl (r,t) = VdArQ()r (-)
Q n n d
= exp[-Att][J exp[AttJ(A exp[-Att]ds + c]
t
= exp[-Xtt][/ Ads + cj
57
-------
,t) = Atexp[-Att]
= 0 therefore c = 0
^ (r,t) = Atexp[-Xtt] substituting for A
-Si 2-1
fl^r.t) = VrQ(-}r (|-) exp[-(f-) ]texp(-Att)
Q n n d
C. Integration of Equation (29)
273
fc2 r2 -a
2-a
PE. (r,l
-^
Q n t. r. n
-) exp[-(f-) ]texp[-A t]drdt
L t- L-
Integrating over r first and using result of part A in this Appendix
2 -H 2-£
r(-) exp[-(-) ]dr =
rn n
1
r~'(2-Jl)
n
ri
(-
PE.. (r,t) now becomes:
2-X,
PE^r.t)
rx 2-Jl
r2 2-fc 2
C—) ] / texp(-Xfct)dt
Integrating time integral by parts:
/udv = uv - Jvdu
58
-------
/ texp(-Att)dt let u = t du = exp[-Att]dt
1
du = dt v = — exp(-A t)
C2 , .
, .
texp(-A t)dt = - f- exp(-X t) + — / exp[-A t]dt
h
X "t>L "t"lj X
Combining terms:
/ texp(-Xtt)dt = (~
tl t
X t + 1 At + 1
(~^4 - )exp(-Att1) - (-— - )exp(-Xtt2)
X A
2-a
Substituting in the time integration and the result of r. and
d
simplifying gives:
r 2-A r, 2-SL
PE (r,t) =
d d rd
X t + 1 X t + 1
)exp(-Xtt1) - (-- - )exp(-Xtt2)]
59
274
-------
275
Appendix III
Summary of Equations
XJj(r.t) = ArQ(^)r (f-
Xn(r,t) = depleted air concentration at distance r and
time t resulting from dispersion of resuspended
Ci
material from source (~~)
m
(2) X?(r,t) = A2 Q(V £-) £ exp[-(^)2~*-] texpf-A t]
J- r _ L *- ^-j L.
Q n n d
X^r.t) = depleted air concentration at distance r and time
t resulting from resuspension of material that
deposited out from X- (—^-)
m
^ ' rt
PEQ(r,t) = ^(^)
d t
PE»(r,t) = population inhalation exposure due to air
concentration XQ (person - —TT - s)
m
60
-------
(5)
PE0(-,-) =f(f)
d t
„(<*>, °°) = the infinite population inhalation exposure,
/ Ci -v
r = 0 -*», t = 0 -*» (person - —_• - s)
m
pQA* TI 2-1 r2 2-t
1 r>t Vd 6XP rd 8XP rd
At + 1 At
-—
- )exp(-Att2)]
Xt Xt
PE (r,t) = population inhalation exposure due to air
concentration X (person -- r- - s)
m
<6> PV-S-, - ^
d t
..^,00) = the infinite population inhalation exposure
r = 0 -*», t = 0 -*« (person -- - s)
276
m
-------
(7)
277
d d s
PE (°°,<>°) = the infinite total population inhalation
exposure due to all resuspensions, r = 0 -*°°,
Ci
t = 0 -*» (person -- r - s)
in
ft1(r,t) = VdXrQr (-)- exp[-(^-)-] texp[-X tj
Q n n d
!l.(r,t) = soil surface concentration at distance r
Ci
and time t (—j)
m
(9) 1,
r2 = rd[-Jln(l-X)]2~£
r_ = the distance from the point source within which
the fraction X of the pop. exposure is delivered (m)
62
-------
(ID
278
(10) x = l-exp[-(—
r
X = fraction of population inhalation exposure delivered
within distance r,.
2-9.
n
r , = a depletion distance, when r = r , the atmospheric
dilution factor -*—(r) has decreased by a factor of
Q
l/e or 37% (m)
Q = activity of point source (Ci)
r = distance from receptor to point source (m)
(_) = value of —(r) at r = r (—5—)
Q rn Q n m
r = normalizing distance (m)
A = resuspension rate (s )
A - transfer rate of contaminated material
s
from soil surface to soil sink (s )
63
-------
279
A = radiological decay constant (s )
A = A + A + A , (s'1)
t r s d
2
p = population density (persons/m )
V = deposition velocity (m/sec)
64
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280
References
1. "Environmental Radiation Dose Commitment: An Application to the
Nuclear Power Industry" (EPA-520/4-73-002) U. S. Environmental
Protection Agency, Office of Radiation Programs, Washington, D.C.
(June 1974).
2. ICRP Publication 23, 1975, "Report of the Task Group on Reference
Man," Pergamon Press, New York.
3. Sullivan, R. E., "Plutonium Air Inhalation Dose (PAID)," Technical
Note ORP/CSD-77-4, U. S. Environmental Protection Agency, Office
of Radiation Programs, Washington, D.C. (June 1977).
4. ICRP Publication 19, 1972, "The Metabolism of Compounds of
Plutonium and other Actinides," Pergamon Press, New York.
5. Strom, P. 0. and Watson, E. C., "Calculated Doses from Inhaled
Transuranium Radionuclides and Potential Risk Equivalence to Whole
Body Radiation" (IAEA-SM-199/114), International Atomic Energy
Agency.
6. Killough, G. G. and McKay, L. R. (compiled by), "A Methodology
for Calculating Radiation Doses from Radioactivity Released to the
Environment" (ORNL-4992) Oak Ridge National Laboratory, Oak Ridge,
Tennessee (March 1976).
7. Oksza-Chocimowski, G. V., "Resuspension Models Review," Technical
Note ORP/LV-76-11, U. S. Environmental Protection Agency, Office
of Radiation Programs, Las Vegas Facility, Las Vegas, Nevada
(July 1976).
8. "Draft Environmental Statement - Concerning Proposed Rulemaking
Action: Numerical Guides for Design Objectives and Limiting
Conditions for Operation to Meet the Criterion "As Low As Practi-
cable" For Radioactive Material in Light-Water-Cooled Nuclear
Power Reactor Effluents," U. S. Atomic Energy Commission,
Directorate of Regulatory Standards (January 1973).
9. ICRP Publication 26, 1977, "Recommendations of the International
Commission on Radiological Protection," Pergamon Press, New York.
65
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281
THE PHYSIOLOGICAL BASIS
OF TRANSURANIC ELEMENT
DOSE ESTIMATES
Neal S. Nelson, D.V.M., Ph.D.
February 1978
U.S. Environmental Protection Agency
Office of Radiation Programs
Criteria and Standards Division
Washington, D.C. 20460
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283
THE PHYSIOLOGICAL BASIS OF TRANSURANIC
ELEMENT DOSE ESTIMATES
Despite extensive literature reviews, scientific information on the
biological properties of transuranium elements in humans is sparse and
the medical prognosis following inhalation or ingestion of these
substances is uncertain. Because of the care taken in handling
Plutonium by those groups who work with it and the length of the latent
period before cancer develops, little information is available or likely
to become available in the near future on the biological effects of
plutonium in man. The basis for establishing metabolic parameters in
humans is even less promising, since experiments using hospitalized
patients are no longer performed.
HUMAN STUDIES
In 1945-46, 18 hospitalized persons were injected with tracer
amounts of plutonium (1). Fifteen of the patients were 45 years of age
or older. However, three had bone disorders, either fractures or
cancer; three had liver disorders, two had kidney disorders, and the
rest had other conditions which may have affected their metabolism of
plutonium. Only about six of the persons studied provided reasonable
data in that they were "normal" for most of the metabolic parameters
examined (1) .
To some extent supportive studies on metabolism of plutonium have
been done using other groups of humans, but, because members of these
other groups were accidentally exposed and the initial dose is not known
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284
with any degree of accuracy, about the only information available from
these groups is confirmation of trends of metabolism and effective half-
lives. The accidentally exposed groups are being followed both for the
metabolic information and for information on possible health effects.
The groups being followed to develop information on the long-term
or latent effects of plutonium exposure in man include:
1. Groups presently studied at Los Alamos Scientific
Laboratory (2)
a. The UPPU* group, 25 men exposed during 1944-45 with
relatively large doses, (exposed primarily by inhalation; about 75% have
one or more maximum permissible body burdens (3)).
b. A group of 42 men exposed during the Manhattan Project
(1943-1946), (exposed primarily by inhalation; have less than one
maximum permissible body burden (3) .
c. A group of 190 early and current plutonium workers, (about
75% exposed by inhalation, 25% through wounds; about 20% have one or
more maximum permissible body burdens (2)) .
2. The United States Transuranium Registry
The U.S. Transuranium Registry was established in 1968 to
protect the interests of workers, employees and the public by serving as
a national focal point for acquisition and provision of information
about the effects of transuranic elements on man. in October 1975, the
Registry had identified 9063 transuranium workers and obtained autopsies
*UPPU is an acronym of: U = Pronoun; P = Urinate; Pu = Plutonium.
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285
on 53 of them. Of the workers identified, about 60% have burdens less
than 5% of maximum permissible body burdens (4) . Thus, the data base
for the effects of plutonium in man is less than 10,000 exposed persons,
most of whom were only nominally exposed and most of whom are alive
today.
As Thompson (5) has pointed out, the histological changes at the
cellular level that have been observed in man following plutonium
exposure cannot be qualitatively related to health consequences.
Therefore, we know nothing directly about effects of plutonium in
humans. Thompson (5) suggested since we have no useful data on human
plutonium effects, it is useful 1) to extrapolate from plutonium effects
in animals to plutonium effects in man or 2) to extrapolate from
nonplutonium radiation effects in man to plutonium effects in man. He
felt that not only was there "ballpark" agreement between human and
animal data, where direct human data could be compared to experimental
animal data, but also that plutonium data from animals could reasonably
be extrapolated to man.
In 1976, Thompson (6) reiterated his plea for use of animal data
suggesting that it is unlikely that anything useful about dose effect
relationships will be learned from humans exposed to plutonium. He
stated, however, that it is worthwhile to continue to study human
exposure cases to obtain information on metabolism and to insure that
there are no "surprises" in the biological effects of plutonium in
man (6).
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286
ANIMAL STUDIES
The literature on plutonium and the transuranic elements is
voluminous. Starting with some of the earliest reviews of the subject
(7-9) and speciality symposia (10) and continuing until the present (11-
19) the emphasis has been primarily on animal experiments as the source
of data on metabolism and hazards of plutonium. The data, based on
animal studies on the distribution and metabolism of plutonium, have
been summarized in ICRP-19 (20) and used by some to calculate doses in
rads. The ICRP recommends that the numerical values derived for
plutonium deposition in the various organs be applied to all
transuranics. At best this is only a first approximation since the
metabolic characteristics of the transuranics do differ.
A comparison of the organ distribution of plutonium in several
species of mammals indicates that the soluble plutonium distribution
estimates of 45% in the skeleton, 45% in the liver, and 10% in soft
tissues proposed some years ago in ICRP-19 (20), are more likely to be
43% in the skeleton, 34% in the liver, 5% in bone marrow and 19% in soft
tissues and excreta (21,22). In addition, on the basis of animal data,
the distribution of soluble americium and curium would be estimated as:
skeleton - 35% and 25%, liver - 57% and 60%, bone marrow - 4% and 3%,
and soft tissue and excreta - 4% and 12%, respectively (21).
The Agency employs both animal and human data bases in deriving
health effects estimates for plutonium, using extrapolation 1) from
animals to man and 2) of nonplutonium radiation effects to plutonium
effects in man. Animal data are used primarily to estimate distribution
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287
factors and retention parameters, and to relate these to the sparse
human data. Following the NAS-BEIR Committee recommendations, human
data are used primarily for dose-response conversion estimates (23).
EPA has noted that as the Nuclear Regulatory Commission pointed out (24)
there are great difficulties in extrapolating dose-response data between
strains of the same species and even greater difficulties extrapolating
between species. Therefore, the Agency agrees that major reliance on
human dose-response data appears to be the most prudent course. Since
there are so little data on transuranic element metabolism in man,
extrapolation must be made from animal data. But, the extrapolation
must be on the basis of what is observed in several diverse species
rather than in a single species.
MODELS FOR TRANSURANIC DOSIMETRY
Inhalation
The model currently used by the EPA Office of Radiation Programs
for estimating deposition and retention of inhaled transuranics in man
is the ICRP Task Group on Lung Dynamics [TGLD] model (25) as modified by
ICRP Publication #19 (20).
In this model, three chemical classes of compounds are considered
based on the rate of elimination from the lung; Class Y compounds in
years, Class W in weeks and Class D in days. Class Y compounds include
-------
28f
carbides, oxides, hydroxides and lanthanide fluorides.* Class W
compounds include nitrates, carbonates and lanthanide halides and
phosphates. Class D compounds include all highly soluble materials.
Information is not available on all plutonium compounds, but the ready
hydrolysis of uncomplexed actinides suggests that no actinide compound
would be in Class D.
The parameters used by the TGLD for estimating fractional
deposition within regions of the lung for particles of differing
"activity median aerodynamic diameter" (AMAD)** are based on a 30 year
old adult standard male, breathing through the nose at a rate of 15
respirations per minute and with a tidal volume Of 750 cm3, 1450 cm3 or
2150 cm3. Retention expected in the lungs would be:
Lung -- For inhaled Class Y compounds, 13.8% of the inhaled
material is retained in the pulmonary region of the lung, with a 500 day
half-life. For Class W compounds, the 13.8% of the inhaled material is
retained with a 50-day half-life. In the tracheobronchial region of the
lung clearance half-times are 0.2 days or less; in the nasopharyngeal
region they are 0.4 days or less (20).
*Rapid translocation of curium oxide from the dog lung suggests the
possibility of exceptions to this Class Y retention for some actinide
compounds.
**The Aerodynamic Diameter (AD, Aerodynamic Equivalent Diamter) is
defined as the diameter of a unit density sphere, which has the same
settling speed under gravity as the particle being described. The
Activity Median Diameter (AMD) is the diameter of the particles at the
median of the log normal distribution of the radioactivity in an
aerosol. The AMAD, then is the diameter of a unit density sphere having
the same settling properties under gravity as the AMD particles.
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289
Lymph Nodes — About 3.H% of the Class Y material deposited in the
lung is translocated to the thoracic lymph nodes and retained with a
half-life of 1000 days. In Class W, 1.15* of the deposited material is
retained with a half-life of 50 days (20) .
The ORP inhalation code PAID (26) is based on the Task Group on
Lung Dynamics model with appropriate adjustments for continuous intake
of airborne radioactive materials. The PAID code employs ICRP-23
estimates of eight hours at rest (tidal volume 500 cm3) and eight hours
each of "light" and nonoccupational activity (tidal volume 1250 cm3) as
the basis of calculations (27) .
The burden, q
-------
29G
The cumulative organ burden is then defined as
rT
Q (t) = / q(t)dt
•*o
In principle, this cumulative organ burden can be used with
appropriate dose-conversion factors to calculate the annual dose rate to
the organ in rad per year. The annual organ dose rate in turn can be
used to estimate health effects, e.g., malignancy in either terms of
individual risk or population risk. In actual practice the uncertainty
in such risk estimates makes these calculations, at best, only estimates
of expected response.
Ingestion of Inhaled Transuranics
Some of the inhaled transuranics will be cleared from the lung via
the mucus escalator, swallowed, transported to the GI tract just as if
they had been ingested. The calculation of transport from the lung to
the GI tract indicates that about 92% of inhaled Class Y material will
enter the GI tract, and about 8195 of Class w material. Table I lists
the relative disposition of inhaled material by region for a nominal
1.0 M AMAD aerosol, assumed in reference 25.
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291
Distribution of Transuranics in the Body
The material which has been transported into the blood stream will
distribute in the organs of the body. ICRP estimates the following
distributions:
Skeleton — 45% of the transuranics in the circulatory system is
expected to deposit in the skeleton and be retained with a half-life of
about 100 years (20). In the case of very stable, biologically inactive
complexes of plutonium (e.g., plutonium-DTPA) as little as 10% may
deposit in the skeleton.
Liver — 45% of the transuranics in the circulatory system may be
deposited in the liver and retained with a half-life of 40 years (20).
As in the case of the skeleton only 10% of stable, biologically inactive
complexes may deposit in the liver.
Soft Tissues — About 7% of the plutonium in the circulatory
system may be deposited in soft tissue in the spleen, ovaries, uterus,
testis, and adrenal glands. [From data in references 1 and 28, the 10%
in soft tissue and excreta estimated by ICRP (20) may be divided into 7%
and 3%, respectively.] Plutonium deposits are retained for extended
periods with half-lives of 1500 days or longer. However, there are no
ICRP estimates of percent deposition in these tissues.
Gonads -- Richmond and Thomas reported that in five animal species
0.03% of plutonium was transferred from blood to gonads (29). The MRC
review of plutonium toxicity concluded 0.05% was transferred to gonads
(18). These observations postdate the ICRP review (20) and should be
used.
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292
Excreta — About 3% of the plutonium is located in urine and
feces, primarily in feces (see soft tissues above). There is evidence
that higher specific activity isotopes, e.g., 237Pu and 23epu, are
translocated more rapidly than 23«Pu. This difference probably reflects
the reduced amount of polymeric material in high specific activity
radionuclides.
In making estimates of the distribution of transuranics, attention
is paid both to the chemical form and particulate size of the element
administered. However, little emphasis is given to the question of
whether the element was in monomeric or polymeric form. Although this
question may influence dose-response estimates, there are little data
about the chemical and physical form of transuranics in environmental
situations.
In addition, it is known that particles up to 75 p diameter can
pass fairly rapidly and easily into the circulatory system after
ingestion by the process of persorption (30). Macrocolloids of
polymeric transuranics could be absorbed in a similar manner.
Likewise, inhaled particulates are considered to be transported to
the lymphatic system by being transported there by macrophages or
penetrating the alveolar membrane physically by endocytosis or
pinocytosis (31). The particulates are then carried through the
lymphatics to lymph nodes or other sites or dumped into systemic
circulation through the thoracic lymph duct. Support for this concept
is found in the report that za^PuOg particulates with a mass median
diameter of 0.3 pm and a geometric standard deviation of 1.6 were
10
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293
identified in a tracheobronchial lymph node removed from an
occupationally exposed worker (32). The particles to which the worker
may have been exposed had mass median diameters of 0.28 to Q.U5 pm and
geometric standard deviations of 1.4 to 1.6 (32). These observations
strongly suggest that some particles are transported directly to local
lymph nodes after inhalation without changing their characteristics much
from those of the inhaled aerosol.
Since macrocolloid or other particles probably reach systemic
circulation after inhalation or ingestion of transuranics, it is
reasonable to use human health effects data based on other multivalent,
colloid formers, i.e., thorium and polonium. This is particularly true
when considering the health effects in specific organs such as the
liver.
11
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295
Table I
Disposition of Inhaled Transuranics (25)
Inhaled Class Y Compounds (1.0 >jm AMAD)
Region
Nasopharyngeal
Tracheobronchial
Pulmonary
Total
Percent
Deposition (D)
29
8
23
Percent Transported to
Blood GI Tract Lymph Nodes
60
0.23
0.08
1.15
1.46
28.71
7.92
18.10
55.03
3.45
3.45
Inhaled Class W Compounds (1.0 |jm AMAD)
Region
Nasopharyngeal
Tracheobronchial
Pulmonary
Total
Percent
Deposition (D)
29
8
23
60
Percent Transported to
Blood GI Tract Lymph Nodes
2.9
4.0
3.45
10.35
26. 1
4.0
18.4
48.5
— —
1.15
1.15
12
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295
Ingestion of Transuranics
Absorption of transuranics from the GI tract has been estimated in
the past to be 10-* percent for insoluble forms such as Pu02 and 3x10~3
percent for more soluble forms (20). However, the absorption has been
shown to be much greater for strongly acid solutions and chelated forms
of plutonium (up to about 2%) and in younger animals (possibly a factor
of 100 increase in absorption) (20).
Recent reports suggest that organically bound transuranics are more
easily transported across the gut than inorganic forms. More Pu in milk
was absorbed than was Pu from Pu-citrate solution (33). This was
particularly true in nursing animals which absorbed up to 3.2 percent of
ingested Pu in milk, 1000 times the ICRP estimate of the absorbed
fraction (33). In studies at Battelle Northwest Laboratory,
biologically incorporated (protein bound) Pu was absorbed up to 10 times
as readily as Pu in Pu-nitrate, while absorption of similarly prepared
Np was only about 1/10 to 1/20 of that seen with Np-nitrate (34).
Earlier, Sullivan and Crosby (35) had shown that rats given single
oral doses of transuranic isotope absorbed from 0.1 percent to 0.01
percent of nitrates and oxides in the case of adults and 0.5 percent to
5 percent of nitrates and oxides (except Pu oxides) in the case of
neonates.
At the request of the Agency, scientists at Battelle-Pacific
Northwest Laboratory estimated the absorption of transuranic elements
from the gastrointestinal tract. They concluded that for oral
administration a prudent estimate for radiation protection purposes
13
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296
would be that persons one year of age and older would absorb: 0.1
percent of all inorganic transuranics except 239pu and 2*°Pu oxides;
0.01 percent of 239Pu an(j a*opu oxides; and 0.5 percent of biologically
incorporated transuranics (36). Infants (less than one year of age)
would absorb 10 percent of all transuranic elements except 2*9Pu and
2*opu oxides; and 1 percent of 23»Pu and 240pu oxides (36) .
While these estimates have a large degree of conservatism and are
more than an order of magnitude greater than current ICRP estimates,
they are supported by other observations. In particular, a review of
gonadal deposition of actinide elements reported that, following
intravenous injection of plutonium (citrate or nitrate), gonadal
deposition in the pig was about 2x10-*; following ingestion about 3x10~6
(29). This suggests absorption of a fraction about 10~2 of the amount
ingested, in the case of beagles, the fraction of plutonium deposited
in the gonads following intravenous injection was about 4x10-*,
following ingestion about 8x10~* (29), again indicating about 10~2 is
transferred through the gut wall. These observations support use of the
Battelle estimates rather than those of ICRP.
The current ingestion model used by ORP is patterned after the four
compartment model of ICRP-2 (37), but neglects the one-hour time delay
in the gastrointestinal tract. This model is combined with the lung
model and used both for the ingestion pathway and as part of the
inhalation pathway for those lung subcompartments clearing through the
gastrointestinal tract (26).
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297
Skin Contamination
The case of skin contamination as a route of exposure for
transuranics can be neglected unless the skin is not intact. Even if
the skin is damaged, there are not enough data to make a quantitative
estimate of the rate of amount of absorption of environmental
transuranics. However, this mode of exposure is believed at present to
be a relatively unimportant pathway for the case of interest here.
PROBLEMS IN DOSIMETRIC MODELING FOR TRANSURANIC ELEMENTS INHALATION
Inhalation
The physical, physiological, and biological assumptions used in the
models for dosimetry and metabolism used in toxicologic studies of the
transuranics have some problem areas.
To some extent the ICRP Task Group on Lung Dynamics (TGLD) model
(25) employs parameters that maximize dose estimates in its assumptions
for exposure by inhalation. To this extent it is conservative. The
model assumes tidal volumes of 750 cc or 1450 cc for resting and light
work, respectively, which are adequate for an adult male. Values for
adult females are of the order of 340 cc or 660 cc, and for childr-en
they drop as low as 17 cc or 33 cc in the sleeping newborn (27,38). In
this respect, the model provides estimates of exposure which are
somewhat higher than would be expected in a general population. This is
compensated for in part by the decreased organ mass for children and
women which leads to higher average organ dose.
15
-------
The TGLD model uses other assumptions which are not conservative:
1. The model uses a respiratory rate of 15 respirations per
minute. For a heterogenous aerosol the percentage of deposition varies
with breathing rate. The minimum level of deposition occurs at 15 to 20
respirations per minute and increases on either side of this value (39).
Deposition rates in hard workers, or in sleeping or sedentary
individuals would be higher than the model predicts.
2. The Task Group, as Mercer points out, used a Findeisen
anatomical lung model, which underestimates airway branching and
therefore impaction sites (10). This will lead to overestimation of
pulmonary deposition and underestimation of tracheobronchial deposition
during mouth breathing (40).
3. The pulmonary lung is not treated as a single compartment but
rather as a series of parallel tubes so that clearance by a given
pathway is arbitrarily independent of other clearance routes.
4. No provision is made in the model for the known regional
distribution of inhaled material within the lung. Bates, Ball and Bryan
have shown that, in the upright individual, the distribution and rates
of wash-in and wash-out gases are different by about 40% between the
upper and lower lobes of the lung, indicating a similar difference in
regional airflow (41). This has profound implications in that it
affects the distribution of inhaled aerosols both for settling and for
diffusion within alveoli.
16
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299
5. The model is based on laminar flow in tubes at a constant rate,
per the calculations of Findeisen and Landahl (25) . A summary of the
assumptions in the model that need refining include (39):
a. The pattern of airflow during respiration is not constant,
but goes from zero to some maximum and then returns to zero.
Information is needed on the effect of this pattern on deposition.
b. Airflow in the lung may be a mixture of laminar and
turbulent flows. The extent of this phenomenon and its effect on
deposition should be investigated.
c. The bulk of new air does not mix volumetrically with lung
air. Nondiffusible particles (>0.5p) will penetrate only as far as the
new air goes, while finer particles (<0.5>j) will be able to penetrate
the depths of the lung by diffusion similar to that of a gas molecule.
This has implications for distribution of alveolar versus respiratory
bronchiolar deposition of particles and subsequent clearance by mucus.
d. The respiratory tree is not composed of circular tubes but
irregular cross-section tubes which are often corrugated or folded over.
The effects of these irregularities on turbulence and deposition are not
known.
e. The effects of respiratory excursions (coughs) on
respiratory clearance cannot be assessed. This is probably an important
route of transport where the mucus escalator is impaired due to smoking,
etc.
While the lung model is considered to be accurate enough for
standard setting purposes, problems peculiar to plutonium distribution
17
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300
and retention are not settled. There is evidence that the higher
specific activity isotopes of plutonium (230Pu, 237Pu) have a different
distribution pattern in the body than 239Pu after translocation (42,43).
In general, the zsopu resembles injected monomeric 239Pu* in its
distribution pattern after translocation from the lung. When 239Pu is
translocated from the lung, the pattern of distribution within the body
is similar to that of injected polymeric 239Pu.** This suggests that
the 23epu is dissolving and being transported as a Pu-transferin complex***
within the body while the 239pu is being engulfed and transported as
particulate material (44) .
It has been suggested that the more rapid translocation of 238Pu
relative to 239Pu aerosols deposited in the lung is due to the effect of
the specific activity on local chemistry after deposition; that is, the
higher activity 23epu produced enough radicals in its aqueous
environment (lung mucus or parenchyma) to influence local chemistry and
the rate of dissolution of the particle (45). Regardless of whether
these arguments are correct or not, separate models should be developed
for each plutonium isotope based on observed and expected differences.
*Monomeric plutonium is in the form of single molecules of the plutonium
compound, not a large number of particles aggregated.
**Polymeric plutonium is a form where a number of molecules of the
plutonium compound aggregate together as colloid.
***Transferin is the serum protein which binds iron as an iron-
transferin complex to transport the iron throughout the body. It also
appears to be involved in transport of transuranic elements.
18
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301
The available estimates of half-times for the translocation of
plutonium from alveolar deposits and from lymph nodes are subject to
considerable uncertainty. The data on retention, particularly in lymph
nodes are based on animal experiments at relatively high levels of
exposure which impaired local histology and physiologic processes.
Therefore, it may not adequately reflect transport in humans exposed
environmentally.
Much of the environmentally distributed plutonium is in the form of
very small sub-micron particles weakly attached to larger dust particles
(46). Unfortunately, the TGLD models does not address the question of
extremely small particles bound to 1.0 p (or larger) particles. This
question should be addressed since plutonium which escapes through high
efficiency particulate filters is a source of environmental
contamination.
Ingestion
The recent studies of transuranium element uptake following
ingestion suggest that earlier estimates may be in error. Sullivan and
Crosby found (3<»,35) that 10~3 to 10~4 of a single ingested dose of
transuranics is absorbed from the gastrointestinal tract. This is at
variance with the ICRP estimate of 3x10~s to 10~6 (20) derived from
chronic feeding studies. The estimate of 10~3 to 10-* is supported
indirectly by data on gonadal deposition of transuranium elements. In
the data reviewed by Richmond and Thomas (29) the ratio of gonadal
deposition following ingestion of transuranics to that following
19
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3G2
intravenous injection ranges from about 10~2 to 1d~3. This implies
absorption of about that fraction from the gastrointestinal tract.
The question of the fraction of ingested transuranium element
absorbed from the gastrointestinal tract as a function of age of the
subject and chemical form ingested should be resolved to a greater
extent than it is today. An adequate answer may change dose and risk
estimates by an order of magnitude or more.
Distribution and Retention
Dose models currently employed must extrapolate animal data on
distribution and retention of transuranium elements to man. While the
general lack of data in man demonstrates adequate radiation protection
efforts, it does force extensive use of animal data. The animal data
usually encompass only one or two ages, one or two routes of
administration, and one or two chemical forms of the element in a given
sex and species. Often the studies are not directly comparable and it
must be assumed that differences in age, sex, or chemical form of the
element cause negligible differences in distribution or retention.
As was pointed out earlier (Animal studies) what data are available
on different transuranium elements show that each has its own
distribution pattern (13,22). In addition, when sexes or several
species can be compared, distribution is often species and isotope
specific (22).
Superimposed on these uncertainties in the distribution of
transuranium elements is the uncertainty in retention. Most studies
20
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3C3
have been done in short-lived animal species. However, retention half-
times in man are estimated at 40 years or 100 years (20). In a rodent
with a two-year lifespan an element with a i» 0-year half time would decay
about H% and an element with a 100-year half time about. 2%. Such
variations are less than counting error and individual variation. Even
in canines with a 15-year lifespan, decay would be only 16% and 10%,
respectively.
It is obvious that more data on man are needed for all actinide
elements. Perhaps a solution to the distribution question may come from
autopsy series of environmental and occupational exposures and for the
retention problem from accident cases or tracer studies. Perhaps
additional studies in animals scaled to duplicate specific human
experiences for which there are data would strengthen confidence in the
extrapolations from animal to man now made so blithely.
Genetics
One of the greatest uncertainties in health effects estimates for
transuranium elements relates to the estimate for genetic effects. Not
only do the estimates of percent of administered nuclide deposited in
gonads from blood have a range of 10~* to 10~3 (18,29), but the
estimates are almost entirely for males. In addition, what data are
available in man from environmental exposure do not agree well with the
data from occupational exposure or animal studies (see Annex 3, Section
3.2).
21
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304
The internal distribution of the transuranium elements in tha
testes has been reported for mice (47), rats (48), and Chinese hamsters
(49). The preferential deposition of plutonium along the peritubular
membrane produces an inhomogeneous dose distribution. The inhomogeneity
factor was 2.5 for mice, 1.6 for rats and 1.0 for Chinese hamsters
(47-49). There is no information on what it might be for man or other
species.
There is little published information on inhomogeneity factors for
ovaries. There is no good information on distribution from blood to
ovary, retention in ovary or testes, nor RBE for alpha emitters in the
ovary or testes (although some recent work suggests an RBE for testes of
20 or more).
The uncertainty in genetic risks from exposure to transuranium
elements is quite high, probably orders of magnitude. Studies to
identify retention, distribution, inhomogeneity of dose, and cytogenetic
effects adequately are urgently needed to determine if somatic or
genetic effects constitute the primary hazard of exposure to
transuranium elements.
22
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305
REFERENCES
1. Durbin, P.M. (1972). Plutonium in Man: A New Look at the Old Data,
pp 469-530 in Radiobiology of Plutonium, B.J. Stover and W.S.S.
Jee, editors, the J.W. Press, University of Utah, Salt Lake City,
Utah.
2. Richmond, C.R. (1974). Human Experience as Related to Plutonium,
pp 87-96 in Plutonium Information Meeting, Los Alamos, NM,
CONF-740115, U.S. Atomic Energy Commission, Oak Ridge, TN.
3. Voelz, G.L. (1975). What we Have Learned About Plutonium from
Human Data, Health Physics 29:551-561.
4. Norwood, W.D. and C.E. Newton, Jr. (1975). United States
Transuranium Registry Report, July 1, 1974 to October Jj^ 1975,
HEHF23, Hanford Environmental Health Foundation, Richland,
Washington.
5. Thompson, R.C. (1974). Implications with Respect to Protection
Criteria, pp 271-289 in Plutonium and Other Transuranium Elements;
Sources Environmental Distribution and Biomedical Effects,
WASH-1359, U.S. Atomic Energy Commission, Washington.
6. Thompson, R.C. (1975). Animal Data on Plutonium Toxicity, Health
Physics 29:511-519.
7. The Biology of the Transuranic Elements (1962). R.C. Thompson,
editor, Health Physics j}:561-780.
8. Thompson, R.C. (1967). Biological Factors, pp 785-829 in The
Plutonium Handbook, Vol. 2f O.J. WicJc, editor, Gordon and Breach,
New York.
9. Delayed Effects of Bone-Seeking Radionuclides (1969). Mays, .C.W.,
Jee, W.S.S., Lloyd, R.D., Stover, B.J., Dougherty, J.H., and G.N.
Taylor, editors. University of Utah Press, Salt Lake City, Utah.
10. Problems in Plutonium Toxicology (1970). Buldakov, L.A.,
Lyubchanskii, E.R., Moskalev, Yu.I., and A.P. Nifatov, editors.
Translated by A.A. Horvath, edited by R.G. Thomas, LF-tr-41,
Lovelace Foundation, Albuquerque, NM.
11. The Biological Implications of the Transuranium Elements (1972).
Thompson, R.C. and W.J. Eair, editors. Health Physics 22:533-954.
12. Radiobiology of Plutonium (1972). Stover, B.J. and W.S.S. Jee,
editors, the J.W. Press, University of Utah, Salt Lake City, Utah.
23
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30 f
13. Uranium, Plutonium, Transplutonic Elements (1973). Handbook of
Experimental Pharmacology XXXVI, Hodge, H.C., Stannard, J.N., and
J.B. Hursch, editors, Springer-Verlag, New York.
14. A Radiobiological Assessment of the Spatial Distribution of
Radiation Dose from Inhaled Plutonium (1974). Bair, W.J.,
Richmond, C.R., and B.W. Wachholz, WASH-1320, U.S. Atomic Energy
Commission, Washington.
15. Plutonium and Other Transuranium Elements; Sources, Environmental
Distribution and Biomedical Effects (1974). WASH-1359, U.S. Atomic
Energy Commission, Washington.
16. Hot Aerosol Particles Associated with Industrial Atomic Energy
(1975) by A.V. Bykhovskii and A.M. Zaraev Atomizdat, Moscow, 1974,
translated ERDA-tr-65, U.S. Energy Research and Development
Administration, Washington.
17. Plutonium - Health Implications for Man (1975). J.W. Healy,
editor. Health Physics 29:441-632.
18. The Toxicity of Plutonium (1975). Medical Research Council, Her
Majesty's Stationary Office, London, England.
19. The Health Effects of Plutonium and Radium (1976). W.S.S. Jee,
editor. The J.W. Press, university of Utah, Salt Lake City, Utah.
20. ICRP Publication 19 (1972). The Metabolism of Compounds of
Plutonium and Other Actinides, Pergamon Press, New York.
21. Ellett, W.H., Nelson, N.S., and W.A. Mills (1976). Allowed Health
Risk for Plutonium and Americum Standards as compared to Standards
for Penetrating Radiation, pp 587-601 in Transuranium Nuclides in
the Environment, International Atomic Energy Agency, Vienna,
Austria.
22. Durbin, P.W. (1975). Plutonium in Mammals: Influence of Plutonium
Chemistry, Route of Administration, and Physiological Status of the
Animal on Initial Distribution and Long-Term Metabolism, Health
Physics 25:^95-510.
23. BEIR Report 1972. The Effects on Populations of Exposure to Low
Levels of Ionizing Radiation, Report of the Advisory Committee on
the Biological Effects of Ionizing Radiations, National Academy of
Sciences, Washington, D.C.
24. Nuclear Regulatory Commission (1976). Natural Resources Defense
Council, Denial of Petition for Rulemaking, sections c-3 and C-4,
Federal Register 41:15371-15379 (April 12, 1976).
24
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3C7
25. TGLD (Task Group on Lung Dynamics) (1966). Deposition and
Retention Models for Internal Dosimetry of the Human Respiratory
Tract, Health Physics J2:173-208.
26. Sullivan, R. (1977). Plutonium Air Inhalation Dose (PAID),
Technical Note, ORP/CSD-77-4, Office of Radiation Programs, U.S.
Environmental Protection Agency, Washington, DC 20460-
27. ICRP Publication 23 (1975). Report of the Task Group on Reference
Man, Pergamon Press, New York.
28. Durbin, P.W. and N. Jeung (1976). Reassignment of Distribution of
Plutonium in the Human Body Based on Experiments with Non-Human
Primates, pp 297-313 in The Health Effect of Plutonium and Radium,
W.S.S. Jee, editor. The J.W. Press, salt Lake City, Utah.
29. Richmond, C.R. and R.L. Thomas (1975). Plutonium and Other
Actinide Elements in Gonadal Tissue of Man and Animals, Health
Physics _29:241-250.
30. Volkheimer, G. (1974). Passage of Particles Through the Wall of
the Gastrointestinal Tract, Environ. Health Persp. ^:215-226.
31. Leeds, S.E. (1976). The Pulmonary Lymphatics and Radiation, pp 36-
^5 in Radiation and the Lymphatic System, ERDA Symposium Series 37,
U.S. Energy Research and Development Administration, Oak Ridge, TN.
32. Mdnroy, J.F., Stewart, M.W., and W.D. Moss (1976). Studies of
Plutonium in Human Tracheo-bronchial Lymph Nodes, pp 54-58 in
Radiation and the Lymphatic System, ERDA Symposium Series 37, U.S.
Energy Research and Development Administration, Oak Ridge, TN.
33. Finkel, M.P. and W.E. Kisieleski (1976). Plutonium Incorporation
through Ingestion by Young Animals, pp 57-69 in The Health Effects
of Plutonium and Radium, W.S.S. Jee, editor, The J.W. Press,
University of Utah, Salt Lake City, Utah.
34. Sullivan, M.F. and A.L. Crosby (1976). Absorption of Transuranic
Elements from Rat Gut, pp 91-93 in Pacific Northwest Laboratory
Annual Report for 1975. Part J Biomedial Sciences, BNWL-2000, Pt.
1, Battelle-Pacific Northwest Laboratories, Richland, Washington.
35. Sullivan, M.F. and A.L. Crosby (1975). Absorption of Uranium-233,
Neptunium-237, Plutonium-238, Americium-241, Curium-244, and
Einsteinium-253 from the Gastrointestinal Tract of Newborn and
Adult Rats, pp 105-108 in Battelle Pacific Northwest Laboratories
Annual Report for 1974, BNWL-1950, Battelle-Pacific Northwest
Laboratories, Richland, Washington.
36. Bair, W.J. and R.C. Thompson (1977). Letter communication.
25
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37. ICRP Publication 2 (1959) . Report of Committee 11 on Permissible
Dose for Internal Radiation, Pergamon Press, New York.
38. Spector, W.S. (1956). Handbook of Biological Data, W.B. Sanders,
Co., Philadelphia, PA.
39. Hatch, T.F. and P. Gross (1964). Pulmonary Deposition and
Retention of Inhaled Aerosols, Academic Press, New York.
40. Mercer, T.T. (1975). The Deposition Model of The Task Group on
Lung Dynamics: A Comparison with Recent Experimental Data, Health
Physics 21:673-680.
41. Bates, D.V., Ball, W.C., and A.C. Bryan (1964). Use of Xenon-133
in Studying the Ventilation and Perfusion of the Lung, pp 237-247
in Dynamic Clinical Studies and Radioisotopes, AEC Symposium Series
#13, U.S. Atomic Energy Commission, Oak Ridge, TN.
42. Bair, W.J., Willard, D.H., Nelson, I.e., and A.C. Case (1974).
Comparative Distribution and Excretion of 237Pu and 239pu Nitrates
in Beagle Dogs, Health Physics 27:392-396.
43. Morin, M., Nenot, J.C., and J. Lafuma (1972). Metabolic and
Therapeutic Study Following Administration to Rats of 23epu Nitrate
- a Comparison with 239Pu, Health Physics 23;475-480.
44. Durbin, P. (1973). Comments at the Third International Congress of
the International Radiological Protection Association, Washington.
45. Craig, D. (1973). Comments at the Third International Congress of
the International Radiological Protection Association, Washington.
46. Nathans, M.W., Reinhart, R., and W.D. Holland (1976). Methods of
Analysis Useful in the Study of Alpha-Emitting and Fissionable
Material-Containing Particles, pp 661-674 in Atmosphere-Surface
Exchange of Particulate and Gaseous Pollutants, ERDA Symposium
Series 38, R.J. Engelman and G.A. Sehmel, Coordinators, Energy
Research and Development Administration, Oak Ridge, TN.
47. Green, D, Howells, G.R., Humphreys, E.R. and J. Vennart (1975).
Localization of Plutonium in Mouse Testes, Nature .255:77.
48. Taylor, D.M. (1977). The Uptake, Retention and Distribution of
Plutonium-239 in Rat Gonads, Health Physics 32:29-31.
49,
Brooks, A.L., Diel, J.H., and R.O. McClellan (1976). The
Distribution, Retention and Cytogenetic Effects of 239pu citrate in
the Testes of the Chinese Hamster, pp 399-403 in Inhalation
Toxicology Research Institute Annual Report, 1975-1976, LF-56.
Lovelace Foundation, Albuquerque, NM (1976).
26
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309
ACUTE TOXICITY OF
TRANSURANIUM ELEMENTS
Neal S. Nelson, D.V.M-, Ph.D.
February 1978
U.S. Environmental Protection Agency
Office of Radiation Programs
Criteria and Standards Division
Washington, D.C. 20460
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311
ACUTE TOXICITY OF TRANSURANIC ELEMENTS
Although plutonium and transuranics are reported to be extremely
radiotoxic, the magnitude of toxicity is closely related to the route of
administration. There is no evidence that transuranics can compare with
highly toxic chemical or biological agents when the route of
administration is by injection (1,2). Following ingestion or
inhalation, the toxicity of transuranic elements is probably comparable
to that of the most toxic materials known.
The first consideration of transuranic element toxicity should be
for acute responses following relatively massive exposures to the
material. Such responses may be characterized as peracute, acute, or
subacute.
Peracute Toxicity
For purposes of discussion peracute toxicity will refer to the case
when the endpoint, death, occurs within hours of exposure.
1. Inhalation
There is no substantive evidence that inhalation of transuranic
elements will cause death in hours due to radiotoxicity. Undoubtedly,
air concentrations of transuranic element aerosols sufficiently high to
cause death by smothering can be estimated. However, the same
concentration should then be effective for even an inert aerosol.
Inhalation of many chemicals and biologic agents in the mg/kg range or
less will kill in hours (1,2,3,4).
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2. Ingestion
Tentative evidence of peracute toxicity associated with massive
oral doses of plutonium was reported by Sullivan and Thompson in 1957
(5). They found that 50% of rats given an oral dose of 93 mCi/kg of
plutonium nitrate died within one day. The dose would be about 18 mCi
per rat, equivalent to 294 mg of z^'Pu or 600 mg of 239pu (N03)4. If
this dose does cause peracute toxicity, and is scaled up to a 70-kg man
on the basis of body weight, the oral doses associated with peracute
radiation lethality following ingestion by man would be: 239pu - 106
grams, zaapu - 375 mgf z«iAm - 2.45 grams, and 24*cm - 95 mg. If the
mass of the gastrointestinal tract rather than the body weight was used
in developing the scaling factors, the respective oral dose estimates
would be: 23»Pu - 48 grams, Z3spu - 170 mg, 2*iAm - 1.11 grams, and
2**Cm - 13 mg. Many chemical and some biological agents when
administered orally are fatal at levels of pg/kg (1,3,4).
Sullivan and Thompson (5) doubted that this peracute response of
rats to plutonium nitrate was due to radiation injury. Sullivan, et al.
(6), showed that an ingested beta emitter, Ru-106, could cause acute
lethality. However, they did not see any deaths in less than four days
after exposure. The possibility of acute nitrate toxicity has also been
considered, but the question of peracute nitrate toxicity is complicated
by the differences in the blood enzyme methemoglobin reductase between
species and ages. The young adult appears to have the highest reductase
activity, adults have less, and very young animals only limited activity
(7). Sheep reduce methemoglobin mere rapidly than pigs or horses (7).
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The only specific estimates of nitrate toxicity in rats appear to
be those of Wright and Davidson (8) who found that the LD50 for
intravenous injection of nitrate is 3.152 g/kg (800 mg/kg of nitrate-
nitrogen); and Druckrey, et al. (9), who reported that 443 mg/kg (100
mg/kg of nitrite-nitrogen) of nitrite fed to rats in drinking water
caused growth inhibition and shortening of lifespan.
On this basis, the 300 mg of nitrate in the 600 mg of plutonium
nitrate given to each rat would not be expected to be the cause of
peracute death reported by Sullivan and Thompson (5). Until some better
evidence is available, the cause of death cannot be attributed to
nitrate toxicity.
The toxicology of nitrates is confused by the toxicology of
nitrites. In the production of methemoglobinemia, conversion of
hemoglobin in red blood cells to methemoglobin which cannot transport
oxygen in the blood, the controlling factor appears to be the rate of
conversion of nitrate to nitrite since nitrite seems to be the agent
causing the methemoglobinemia (7,10,11). While anoxia develops as a
consequence of methemoglobinemia, the exact mechanism of cause of death
is not known (12). Normally 1 to 2% of total blood hemoglobin is
methemoglobin (7). Methemoglobin concentrations of 30 to 50% lead to
anoxic symptoms but are compatible with life (7,12). Death occurs at
methemoglobin concentrations of 50 to 80% of total blood hemoglobin
(7,12).
Conversion of 10% of hemoglobin to methemoglobin is estimated to be
caused by 1 mg/kg of nitrite and 2 mg/kg of nitrate in infants less than
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314
three months of age. A 10% concentration of methemoglobin in the blood,
considered the upper limit of the subclinical range, is generally
regarded as of no medical importance (7). Burden (13) estimated the
maximum permissible dose of nitrate as 53 mg (12 mg nitrate-nitrogen) in
a 3 kg infant and 1.062 g (240 mg nitrate-nitrogen) in a 60 kg adult.
Above these levels appreciable methemoglobinemia may occur.
The lethal dose of nitrite has been estimated at 20 mg/kg in the
adult (10) and of nitrate at about 120 mg to 600 mg per kg in the adult
(13). Acute methemoglobinemia with cyanosis, vomiting, abdominal pain,
etc., has been observed in children after sodium nitrate doses of 100 to
400 mg and in adults after doses in excess of 150 mg (11). Peracute
death, in minutes, has been observed after doses of nitrite exceeding 1
gram. The death appears to be due to cardiovascular collapse and shock
(11). So it is probable that peracute transuranic i.itrate radiation
death could not occur in man; peracute nitrate toxicity would probably
occur first. However, since the peracute lethality following massive
oral doses of plutonium nitrate in the rat is not due to nitrate
toxicity, the possiblity remains that there is a transuranic element
toxicity which is as yet unidentified. While radiotoxicity is a
possibility, so is a direct heavy metal toxicity.
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Acute Toxicity
For purposes of discussion, acute toxicity will refer to the case
when the endpoint, death, occurs in days, usually less than 60 days,
post exposure. If 50 percent of those exposed die in 30 days, the
associated exposure is called the LD50/30. If 50 percent die in 60
days, the associated exposure is called the LDSO/60-
1. Inhalation
Thompson (14) estimated that with an LDSO/30 for 23«PU-citrate;
in rats of 70 /jCi/kg, in mice of 70 fjCi/kg and in dogs of 20 pCi/kg
following intravenous injection, a minimum estimate of the internally
deposited dose which would be an LDSO/30 was 10 pCi/kg. Based on this
LDso/30 internal deposit of 10 MCi/kg in animals, the LD50/30 for a 70
kg man would be 700 pCi, i.e., 10 mg of 2"Pu or 40 pq of 238Pu. This
is roughly 80 mg of 23«Pu or 230 pg of 238Pu inhaled.
Since curium and americum require a dose about 22% greater than
239pu to cause 50% lethality in 30 days (15), the approximate doses in
man which might produce an LD50 30 are: 241Am or 24*Cm, 854 pCi
deposited or about 264 jjg of 2**Am and 10 jjg of 2**Cm. This would be
roughly 2. 1 mg of 241Am or 80 fig of z**Cm inhaled, if the same scaling
used for plutonium is applied.
If the estimated dose is scaled according to the amount of isotope
per gram of lung, the dose required to produce an LDSO/30 would be
greater. Using the data from Durbin (15), Thompson (16) and Wacholz (1)
the estimated doses for an LDSO/30 are 11.25 to 19.44 ^Ci/gram of lung
in the rat and 10 yCi/gram of lung in the dog. If 10 fiCi/gram of lung
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316
is used as the LDSO/30 estimate, the dose required in man is 1000
This is equivalent to about 14 mg 239Pu, 60 jig 238Pu, 380 pg 24lAm or
14 pg 2«*Cm deposited in the lung; 112 mg 239Pu, 480 tig Z38Pu, 2.04 mg
2*»Am or 112 pg of 2**Cm inhaled.
While these doses are lethal to 50% of the exposed animals in 30
days, curves shown by Buldakov, et al. (17) , indicate that early
mortality following an LD50,30 dose of plutonium may start within five
days after the exposure in rats,
2. Ingestion
Acute ingestion toxicity has not been reported as a radiation
response following ingestion of transuranium elements. Buldakov, et al.
(17), did observe 50% mortality in 99 days in rats fed 50 pCi/kg of
239Pu-citrate per day. Acute ingestion toxicity in a 70-kg man would,
on this basis, require daily doses in excess of 50 mg 239Pu, 0.2 mg
23epu 1.1 mg 24iAm, or 41 jjg 2**Cm; with perhaps half that much required
if the mass of the gastrointestinal tract is used rather than total body
mass.
Subacute Toxicjty
For purposes of discussion, subacute toxicity will refer to the
case when the endpoint, death, occurs more than 60 days but less than
many years post exposure.
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1. Inhalation
Large doses of inhaled transuranics will probably cause
fatalities in weeks to a year or so past exposure. The major cause of
death will probably be radiation induced pneumonitis and pulmonary
fibrosis. Baeza, et al« (18) , in a small number of patients, found
about 25% developed radiation pneumonitis after x-ray doses of 1500 to
2000 rads given across a two-week period. This will be used as a lower
estimate of the radiation dose that will cause death due to radiation
pneumonitis and fibrosis.
In animal experiments with inhaled 239PuO2 both rats and dogs could
be killed by pulmonary fibrosis (19).
Species Total Lung Dose Administered whole Body
Dose (rads) Lung
Rat 20,000 0.7 pCi/g 3.0 MCi/kg
Dog 1600-1UOOO 0.3-0.2 nCi/g 0.2-1.U
Based on these data, the subacute toxicity for inhaled transuranics
in man should start at 30 yCi lung dose. This would be about 490 jig
23»Pu, 1.7 Mg 238puf 9.2 pg 2*»Am or 0.4 pg 2**Cm.
2. Ingestion
Subacute lethality following ingestion has not been reported.
Any effects anticipated would be delayed effects (cancers).
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318
CONCLUSIONS
The whole question of peracute, acute and subacute effects of
transuranics in man as outlined above is highly speculative. The
extrapolations from animals to man may or may not have validity because
of other competing factors including mass transport phenomena. However,
since human data are not, and hopefully will not become, available,
extrapolation of animal data is the best method to estimate the order of
magnitude of human risk.
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8. Wright, M.J. and K.L. Davison (1964). Nitrate Accumulation in
Crops and Nitrate Poisoning in Animals, Adv^ Aqron. 16; 197-247.
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13. Burden, E.H.W.J. (1966). The Toxicology of Nitrates and Nitrites
with Particular Reference to the Potability of Water Supplies,
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in Plutonium Information Meeting, Los Alamos, CONF-7U0115, U.S.
Atomic Energy Commission, Cak Ridge, TN.
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Transplutonium Elements, pp 739-896 in Uranium, Plutonium,
Transplutonic Elements, Handbook of Experimental Pharmacology
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Plutonium Handbook, Vol. 2, O.J. Wick, editor, Gordon and Breach,
New York.
17. Buldakov, L.A., Lyubchanskii, E.R., Moskalev, Yu.I., and A. P.
Nifatov (1969). Problems in Plutonium Toxicology, translated by
A.A. Horvath, edited by R.G. Thomas, LF-tr-11, Lovelace Foundation,
Albuquerque, NM (1970).
18. Baeza, M.R., Berkley, H.T., Jr., and C.H. Fernandez (1975). Total
Lung Irradiation in the Treatment of Pulmonary Metastases,
Radiology 116;151-154.
19. Bair, W.J., Ballou, J.E., Park, J.F. and C.L. Sanders (1973).
Plutonium in soft Tissues with Emphasis on the Respiratory Tract,
pp 503-568 in Uranium Plutonium, Transplutonic Elements, Handbook
of Experimental Pharmacology XXXVI, Hodge, B.C., Stannard, J.N.,
and J.B. Hursch, editors, Springer-Verlag, New York.
10
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321
INHALATION AND INGESTION MODELS FOR HUMANS
EXPOSED TO RADIOACTIVE METERIALS
Robert E. Sullivan, Ph.D.
February 1978
U.S. Environmental Protection Agency
Office of Radiation Programs
Criteria and Standards Division
Washington, D.C. 20460
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323
INHALATION AND INGESTION MODELS
INTRODUCTION
The two primary modes leading to internal radiation exposure are
the inhalation and ingestion of radioactive materials. The estimation
of organ burden and exposure, as well as of the resulting dose rates
and doses, due to uptake by these pathways, is relatively complicated
and requires the adoption of mathematical models which depend on many
parameters.
A. Inhalation
Industrial hygienists have recognized for many years that the
inhalation of an aerosol carrying radioactive nuclides was a
potential mechanism for damage to the respiratory tract as well as a
possible pathway for the translocation of inhaled radioactive material
to other internal organs. The complexity of the biological phenomena
which govern transmission and elimination of such material makes
consideration of potential health effects due to the inhalation of
radioactive materials extremely complicated. Even a first order
analysis of the process must consider the factors enumerated below:
1. The fractional deposition of inhaled material in the
respiratory tract depends on properties of the aerosol - size and mass
distribution, chemical form and charge - as well as on the
physiological characteristics - surface properties, configuration, and
breathing rate - of the lung.
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324
2. The duration and extent of the exposure* depends on the
biological and physical mechanisms which transport the deposited
material within the body. These include the various clearance paths,
the nuclide half-life, the chemical form, solubility, and the degree
of retention in each organ of interest.
3. The dose depends on the time integral of the activity in the
organ, the organ mass, the emitted energy, and the fraction of the
energy absorbed by the organ tissues. For alpha emitters, this
absorbed fraction is assumed to be unity. At present, the organ mass,
breathing rate, and clearance times in the PAID code (see below)
correspond to a 30 year old working male. Specific parameters are
given in the text.
In some cases, H, the dose equivalent in rems can be found by
multiplying the dose (rads) by quality and modifying factors as
defined in ICRU supplement 19. In the case of lung tissue, a
modifying factor has yet to be established for particulate sources of
alpha radiation. Therefore, provisionally, 1 rad (a, lung) is
equivalent to 10 rem. In actual practice the risk can be calculated
in terms of rad (a, lung) and the use of the dose equivalent becomes
irrelevant.
4. The health effects depend on type of radiation, site of
energy deposition, susceptibility of the organ to radiation damage,
and specific type of health effect considered. Since the mechanisms
*The time integral of the activity is given the name exposure in
TTDD D<3TM~»-t- Jilfl
ICRP Report #10.
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325
by which somatic and genetic damage are inflicted are incompletely
understood, accurate stipulation of the degree and number of health
effects is also subject to unquantifiable uncertainties.
B. Ingestion
The ingestion of radioactive material represents another
pathway for internal radiation exposure. While description of this
pathway is generally considered to be simpler than for inhalation,
due to the direct deposition of all the ingested material into the
gastrointestinal tract, treatment of the balance of the biological-
physical processes involved suffers from many of the same
limitations discussed above for the inhalation mode.
For ingestion, the critical transfer mechanism appears to be
the absorption of radioactive materials into the systemic blood.
Values for this fraction have been studied in animals and, to a very
limited extent, in man but are still subject to large uncertainties
which strongly affect projected doses to internal organs. As a
consequence, the health effects predicted will be subject to
uncertainties until more detailed data are available.
C. Models
Reasonable estimates of internal radiation doses due to
inhalation and ingestion require that a consistent model for both
the respiratory and gastrointestinal tracts be employed. While a
large amount of theoretical and experimental work on such models has
been done, the most widely accepted models have been those developed
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326
by members of the respective International Commission on
Radiological Protection (ICRP) task groups.
The ICRP Task Group on Lung Dynamics (TGLD) has proposed a
model for the respiratory tract which has been well documented and
the parameters suggested for use in the model have been extensively
reviewed and, to some extent, improved in later ICRP publications
(Morrow, 1966), (ICRP, 1972). Details of this model are given by
Morrow with the revised parameters collected by the ICRP.
Therefore, only a brief outline of the model is presented here. The
ICRP TGLD proposed model comprises three major compartments: the
nasopharyngeal, the tracheobronchial and the pulmonary, as shown in
Figure I, taken from ICRP Report #19 (ICRP, 1972).
FIGURE I
BONE
LIVER
OTHER
^—
1 /
J
X
BLOO
(J)
\
-7
(c)
\
s
(o)
(i
IkU
H
NAS.OPHARYNGEAL
REGION
D4< ,
1
)
TRACHEOBJ
REGI
ION
ON
) '
/
PULMONARY
Ih) 13
rf i
i/lPH
CHIAL
c.
REGION
T.
(d)
•7
(g)
G.I.
TRACT
fl
-------
327
Each of these major compartments is divided into subcompartments,
corresponding to various transfer mechanisms, which are treated as
essentially independent processes. In addition, the associated
lymph nodes are appended to the pulmonary compartment in one of the
transfer chains. Direct deposition through inhalation is only to
the three major compartments with the fractional deposition to each
a function of the aerosol properties. Subsequent transfer and/or
clearance is governed by the parameters specified for each
subcompartment, as shown in Table I (ICRP, 1972).
TABLE I
AMI:NI>:;O CONSTANTS KIR UM; wim TGI.M CU;AKANC:I; MODEL
Region
N-l'
T-3
P
L
I'alhwaj
(a)
(b)
(c)
(d)
(c)
(0
(s>
(h)
(i)
Compound class
(0)
0.01 cl/0.5
0.0 1 d/0.5
0.01 d/0.95
0.2 d/0.05
0.5 cl/0.8
0.5 ci/0.2
0.50/1.0
(\V)
0.0 1 d/O.I
0.4 d/0.9
0.01 d/0.5
0.2 d/0.5
50d/0.15
1 cl/0.4
50 d/0.4
50 d/0.05
SOU/l.O*
(Y)
0.01 -(1/0.0 1
0.4 d/0.99
0.01 d/0.01
0.2 d/0.99
500 d/0.05
1 d/0.4
500(1/0.4
500 d/O.I 5
1000 d/0.9
Ultimate disposition in this model is to the systemic blood or to
the gastrointestinal tract.
The ICRP gastrointestinal tract (GIT) model is documented in
(ICRP, 1959). The model comprises a four compartment, as shown in
Figure II, tract consisting of the stomach, small intestine and
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328
lower and upper large intestine. Parameters for this model are
given by the ICRP, (ICRP, 1959).
FIGURE II
Although both models are described exhaustively in words,
neither of the ICRP groups has given mathematical descriptions for
these processes. This lack has led to some confusion in attempting
to calculate doses and effects using the models. For the present
treatment, several of the previous analyses have been reviewed and
discrepancies in the equations compared with the "official" verbal
descriptions of the models. While some ambiguities may remain, the
present treatment has attempted to reconcile the ICRP descriptions
with the governing equations used in the EPA code "Plutonium Air and
Ingestion Dose (Sullivan, 1977).
The PAID code calculates the dose from each radionuclide in a
two-member chain. Such mother-daughter chains are of particular
interest in the dosimetry of transuranium elements because some have
a short half-life mother, e.g. curium-242, and others have a beta
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329
emitting parent and an alpha emitting daughter, e.g. Pu-241.
Complete equations for two-member chain analysis are given in
Reference 8. The description here is confined to single
radionuclides. This allows a simpler mathematical development. The
extension of the LaPlace transform analysis, outlined below, to the
chain problem is straightforward.
D. The Respiratory-Gastrointestinal Tract Model
The code used by the Environmental Protection Agency (EPA)
corresponds to descriptions of the physiological processes as
contemplated by the originating ICRP groups. In addition, an
attempt has been made to keep the resulting mathematical
relationships as simple and understandable as practicable. To this
end, the respiratory and gastrointestinal tract models have been
coupled as outlined below:
The ICRP TGLD lung model implicitly assumes that the
physiological processes associated with each subcompartment operate
independently. Thus, a general equation governing the behavior of
any member, either subcompartment or organ, in a chain of members
connected in series may be written as:
q£(t) = S£(t) - Vl£(t) (
where q = the organ or subcompartment burden in the Hth organ
(curies)
S n = the source term for the &th member (curies)
A. = the total, or effective, decay constant for the
Xi
radionuclide in the £th member (yr )
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330
The source term will vary, depending on the position of the member
in the chain. The only direct deposition in the lung is through
inhalation and is to k major compartments; nasopharyngeal,
tracheobronchial, and pulmonary. These major compartments are
further divided into £ subcompartments, and their associated
pathways, (a) through (h), see Figure 1. For these subcompartments,
the source term will be:
where
D, = deposition fraction for the kth compartment
f = fraction of D, translocated through pathway Si
and where I may be a quantity (curies) for acute intake or a rate
(curies/year) for constant continuous intake, Table II.
TABLE II
Breathing Rate - Male Adult ICRP Report #23 (ICRP, 1975)
Minute Volume Duration
(liters/minute) (hours/day)
Light Activity 20.0 16
Resting 7.5 8
4
Average Daily Intake = 2.3 x 10 liters.
For ingestion, the initial compartment is the stomach and the source
to this member is:
S = I
where, again, I may be either the annual intake in curies for
continuous ingestion, or a quantity (Ci) for an acute intake.
8
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331
For succeeding members of the chain, the only source is
material transmitted from the preceeding organ. All organs or
sub compartments inferior in position are presumed to have no initial
material content. Therefore, for all subsequent organs
where £-1 refers to the preceeding member and X is the biological
decay constant. It is obvious, from the last equation, that each
equation in the chain is coupled to all preceeding equations through
the source term.
Coupled equations of this type are most readily solved by using
LaPlace transforms. Application of the transform to Equation 1
VS) + q?
whence q£(s) = (g + ^ (3)
and q, is the initial burden (Churchill, 1944). The initial organ
burden for all organs inferior to the first, £>1, is set equal to
zero. Furthermore, the source terms for the first organ (or
subcompartment) are constant and their transforms will be:
IDkf£
S (s) = k
or ->- s
Sl(8) = I
To simplify the notation involved, let the constant part of both of
these be represented by I" and let any initial acute deposition,
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332
presumed to be present at t = 0, be represented by I . The
general equation then becomes, in transform space,
r
S = 8(8 X^ (s + V
for the first member of the chain. Using the transform of Equation
4 as the source in Equation 3, the equation for the second member
of the chain is seen to be
f2Xl I? Vl Zo
2 3(8 + A^CS + X2) (S + \^(B + X2)
from which it is obvious that the equation for each succeeding member
in the same series differs only by an additional factor
(s + A) and, of course, by modification of the coefficient by the
terms f^ and by X the transmission fraction to the second
organ and the biological decay constant of the first, respectively.
The general equation for the nth organ or subcompartment may then be
written as:
qn(s) = [ H f, A*? ] { - 5—^ - + — n - ° - > <6)
n £=i l A~1 s[ n (s + A )] [ n (s + A )]
i-1 £=1
where A is defined as 1 and the first term corresponds to the
continuous intake case and the last to the acute case. It is easily
noted that these terms differ only by the factor s in the denominator
of the first. A well-known theorem in transform theory states that
division of the transformed equation by s corresponds to integration
of the inverse transform between the limits 0 and t (Churchill,
1944). Therefore, the solution to the continuous intake case is the
10
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333
integral of the acute intake case. The time integral of the organ
burden equation is defined as the "exposure", Q (T), in ICRP, 1969.
The general equation for the exposure, in transform space, to any
organ is obtained by dividing both terms of Equation 6 by s.
^(s) = [ n f£ Ab ] {~2 + } (8)
Inverse transforms for equations of this form are readily found
using an extension of the Heaviside partial fraction expansion
(Churchill, 1944). Applying this expansion to the first term of
Equation 6 yields a general solution for the nth organ burden in the
continuous intake case:
IL n K1e~Ait
n i=l n
n(A.) -x± [ n (-A± + Xj)]
n b
where K. = n f A
1 1=1
and A is defined as 1.
For the acute case, corresponding to the second term of Equation
6, the removal of the s in the denominator is equivalent to
differentiation with respect to t (Churchill, 1944). Performing this
differentiation on Equation 9 yields the solution for the organ burden
for acute intake which is identical to Equation 9 if the first term is
i i
omitted and K. is replaced by K. -»• -A.I K. /I . Inverse
11
-------
304
transforms for equations containing repeated linear factors, while
somewhat more tedious to calculate, are still straightforward
(Churchill, 1944). The general solution to the first term of Equation
8 for the exposure is
KnT K.e"XiT
9
n(V -** [IU-A. + A.)]
where the indices run as in Equation 9. This solution may perhaps, be
more readily verified by conventional integration of the burden
solution, Equation 9. The solution for the exposure due to acute
intake then follows from the treatment outlined for the acute burden
but, as described above, is identical to Equation 9. For the lung,
the average dose is defined here as the average dose to the pulmonary
compartment (with a mass of 570 grams) which, for Class Y compounds,
receives the greatest dose. This dose can be used to determine an
upper bound on the risk of lung cancer. The dose rate and dose are
defined in terms of the organ (or subcompartment) burden and exposure
as: D(t) = 51.2 -- q (t) (11)
£% n
and D(T) = 51.2 -£- Q (T) (12)
Mn n
where
e = the absorbed energy (MeV) per disintegration for a
particular isotope and organ pair.
m = the mass of the organ (grams)
and the result is in rads (ICRP, 1968).
Finally, the health effects are estimated by multiplying the dose
for each organ by the number of effects expected per unit dose.
12
-------
335
E. Solutions for a Single Radionuclide
Due to similarities in each of the terms of Equations 9 and 10,
the solution for each succeeding organ may be found by iterating on
the previous solution. For example, consider the chain consisting of
the lung subcompartment , h, which transfers material to the lymph
nodes, i, and, thence, through the systemic blood, to a reference
organ, n. From Equation 9, the solution for the burden in the h
subcompartment, for the acute intake case, is:
qh(t) = ID5fh[e~V]
1 2
Representing the terms in this solution by H and H , the solution
for the lymph node is: „ _,
l , H . e i ,
^
r \ ^
q.(t) = f .
_ . h
and, using L for those terms, the solution for organ n is:
2 3 —X t
,,_,.,b Tl r _ L _ , __ L _ . __ e n _ -•
VU ~ n i L l(-X, + X ) (-X. + A ) + (-X + X,)(-X + X.)J
hn in nnnx
To simplify the coding as much as possible, the procedure
followed is to obtain the solutions for each subcompartment in a chain
by starting with the first and modifying succeeding ones as indicated
above. When the solutions for all the chains are found, they are then
summed to obtain the total doses for each major compartment or organ.
For ingestion, there is only one initial compartment, the
stomach, and, therefore, only one chain. Since, in the ICRP model of
the gastrointestinal tract, the only transfer of material to the blood
is accomplished in the small intestine, only the stomach and small
intestine ICRP compartments are built into the program. If results
13
-------
336
for the upper large intestine (ULI) and the lower large intestine
(LLI) are desired, they must be run as reference (user supplied)
organs.
Two additional modifiers for the equations must also be
considered. First, for material which is transferred through the
gastrointestinal tract, the additional fraction f, (transfer from
small intestine to blood) must be used as multiplier for organs
inferior to the small intestine. Second, for material transferred
through the systemic blood, the fraction f_ (fraction from blood to
reference organ) must be incorporated into the product of the
transmission fractions. These parameters are automatically inserted
into the chains by the program.
Solutions for the mother-daughter chains follow the same form as
those shown alone, but are of course more complex due to consideration
of the multiplicity of sources for the daughter radionuclide. The
daughter may be formed by decay of the mother radionuclide in a given
compartment or may enter that compartment due to decay in and
subsequent transfer from all previous compartments. The solutions are
complex, see Reference 8.
14
-------
337
REFERENCE
1. Morrow, Paul E., "Deposition and Retention Models for Internal
Dosimetry of the Human Respiratory Tract," 1966, Health Physics,
12, 1973.
2. International Commission on Radiological Protection (ICRP)
Publication 19, 1972 (New York: Pergamon Press).
3. International Commission on Radiological Protection (ICRP)
Publication 2, 1959 (New York: Pergamon Press).
4. Churchill, Ruel V., 1944, Modern Operational Mathematics in
Engineering (New York: McGraw-Hill).
5. International Commission on Radiological Protection (ICRP)
Publication 10A, 1969 (New York: Pergamon Press).
6. International Commission on Radiological Protection (ICRP)
Publication 10, 1968 (New York: Pergamon Press).
7. International Commission on Radiological Protection (ICRP)
Publication 23, 1975 (New York: Pergamon Press).
•
8. Sullivan, Robert E., "Plutonium Air Inhalation Dose (PAID)"
ORP/CSD Technical Note 77-4, July 1977.
15
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339
EVALUATION OF
SAMPLE COLLECTION AND ANALYSIS TECHNIQUES
FOR ENVIRONMENTAL PLUTONIUM
David E. Bernhardt
May 1976
Formally Published as Technical Note ORP/LV-76-5
U.S. Environmental Protection Agency
Office of Radiation Programs - Las Vegas Facility
Las Vegas, Nevada 89114
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340
PREFACE
The Office of Radiation Programs of the U.S. Environmental
Protection Agency carries out a national program designed to
evaluate population exposure to ionizing and non-ionizing
radiation, and to promote development of controls necessary to
protect the public health and safety. This literature survey was
undertaken to assess the available information concerning
sampling and analysis techniques for environmental concentrations
of plutonium. Readers of this report are encouraged to inform
the Office of Radiation Programs of any omissions or errors.
Comments or requests for further information are also invited.
n
^cvJ
Donald W. Hendricks
Director, Office of
Radiation Programs, LVF
This report has been reviewed by the Office of Radiation
Programs - Las Vegas Facility, Environmental Protection Agency,
and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommend-
ation for use.
111
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341
EVALUATION OF SAMPLE COLLECTION AND ANALYSIS TECHNIQUES
FOR ENVIRONMENTAL PLUTONIUM
ABSTRACT
Information concerning sampling and analysis techniques for
plutonium in the environment is presented and evaluated in this
report. Consideration is given to available techniques and their
applicability to various situations, sensitivities of the tech-
niques, and the validity and reproducibility of results.
Soil is the primary reservoir for plutonium in the environ-
ment but inhalation, with the resulting lung dose, is the primary
pathway for human exposure. This evaluation is therefore primar-
ily oriented toward sampling and analysis of soil and air, with
secondary consideration of other environmental media.
IV
-------
TABLE OF CONTENTS
Page
ABSTRACT iv
LIST OF FIGURES vii
LIST OF TABLES vii
INTRODUCTION 1
Objective 1
General Status of Techniques and Their Evaluation 1
DIRECT FIELD MEASUREMENT TECHNIQUES 4
FIELD COLLECTION TECHNIQUES FOR SOIL 10
Soil Sampling Techniques 12
Potential Sampling Errors 18
Bulk Density 18
Significance of Sampling Depth 20
Discrete Particulate Material 28
PARTICLE SIZE DISTRIBUTION OF PLUTONIUM IN SOIL 40
AIR SAMPLING TECHNIQUES 46
Physical Characteristics of Aerosols 47
Types of Air Samplers 49
Mass or Filter Type Samplers 50
Electrostatic Precipitation 51
High-Volume Cascade Impactors 51
Air Elutriator and Centrifugal or Cyclone Samplers 54
Combination Electrostatic Precipitation and Cascade
Impaction 56
Types of Filtration Material 56
Ambient Concentrations of Naturally-Occurring Alpha
Emitters 58
Analysis of Air Samples 59
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343
Page
SAMPLES ANALYSIS TECHNIQUES 61
Analytical Sensitivity 61
Sample Types 71
Review of Analytical Techniques 73
Sample Preparation and Dissolution 75
Chemical Separations 77
Electrodeposition 77
Sample Counting Techniques 79
Calculation of Sample Activity and Estimation of
Analytical Error 83
Discussion and Comparison of Techniques 84
Sample Size 86
Sample Dissolution 86
ANALYTICAL VARIATION AND REPRODUCIBILITY 91
SUMMARY AND CONCLUSIONS 99
REFERENCES 106
APPENDICES 116
A. Workshop Recommendations on bampiing and Analysis n6
B. Radionuclide Information 139
C. Frequency Distribution for Analyses of
80 Replicate Soil Samples 140
VI
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344
LIST OF FIGURES
Number Page
1 Correlation between plutonium concentrations
and FIDLER readings 8
2 Histogram of weight per unit area for 72 soil samples
from vicinity of Trinity, New Mexico (From Douglas,
EPA/ORP-LVF, unpublished data) 21
3 Cumulative frequency plot for a true value of 10 65
4 Histogram of blank or background plutonium-238
soil samples 70
5 Histogram of ratio of duplicate soil sample results
(LFE/MCL) from Enewetak 95
6 Histogram of ratio of duplicate soil sample results
(EIC/MCL) from Enewetak 95
LIST OF TABLES
Number Page
1 Sensitivities and Calibration Factors for
FIDLER Instrument 5
2 Estimated Correlations Between Laboratory Gamma
Scans for Americium-241 and Plutonium-239, -240,
and Between FIDLER Cpm of Americium-241 and
Plutonium-239, 240 7
3 Approximate Costs for Soil Sample Collection
and Analysis 10
4 Sample Collection Techniques 17
5 Percentage Plutonium Distribution in Soil as
a Function of Depth 23
6 Comparison of Surface and Profile Samples 26
7 Comparison of Plutonium Soil Sampling Data 28
8 Plutonium Particle Characteristics 29
vii
-------
345
LIST OF TABLES (Continued)
Number Page
9 Reproducibility of Analyses Using 10-Gram
Aliquots of Prepared Soils 31
10 Comparative Analyses of Plutonium-239 in Soil 34
11 Pertinent Statistics for Plutonium-239 Results from
Selected Sample Groups 36
12 Interlaboratory Comparison of Mound Laboratory and
EPA Results of Plutonium-238 in Soil and Sediment 38
13 Soil Mass and Plutonium Associated with Various
Particle Size Fractions of Soil 43
14 Soil Size Mass and Activity Fractions of Various
Investigators 44
15 Radionuclide Levels in Air Filters 58
16 Summary of MDA's for Plutonium in Environmental Samples 68
17 Plutonium in Blank and Low Level Samples 67
18 Minimum Detectable Concentration 72
19 Americium-241 Ingrowth into Plutonium Samples 84
20 Summary of Dissolution Techniques 85
21 Soil Leaching Experiment 87
22 Leaching Versus Fusion of Soil Samples 89
23 Leachability of Plutonium from Standard Soil No. 3 89
24 Plutonium Left in Vegetation Ash After Acid Leaches 90
25 Summary of Analytical Variability or Reproducibility 93
26 Variability of Analytical Results 96
27 Variability of Environmental Soil Sample Results 97
28 Summary of Variations Associated with Analytical
Results and Sampling and Analysis Results 104
Vlll
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341
ACKNOWLEDGMENT
The author gratefully acknowledges the assistance and
advice of numerous individuals in the preparation of this report.
Special recognition is extended to Messrs. W. A. Bliss,
E. W. Bretthauer, J. W. Mullins, and Dr. P. B. Hahn of the
Environmental Protection Agency (EPA), Office of Research and
Development, Environmental Monitoring and Support Laboratory
(EMSL) in Las Vegas, Nevada. This facility was formerly known as
the National Environmental Research Center - Las Vegas (NERC-LV).
Recognition is also given to Drs. Guy L. Merrill, Jr. and Wes
Efurd of the Air Force McClellan Central Laboratory; Messrs. R.
Robinson and W. H. Westendorf of the Monsanto Research Corpora-
tion, Mound Laboratory, in Miamisburg, Ohio; and Mr. Eric Geiger
of Eberline Instrument Corporation.
Thanks are also extended to Dr. Gordon Burley, Ms. Mary K.
Barrick, and Mr. Thomas C. Reavey for their assistance in review
of drafts of the report. The indicated thanks to the above
individuals does not exclude gratitude to the many additional
people, some of whom are referenced in the text, who assisted the
author in compilation and evaluation of the information in this
report.
The author, although recognizing the assistance of many
people, accepts full responsibility for the content of this
report.
IX
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347
INTRODUCTION
OBJECTIVE
The objective of this report is to review and evaluate past,
present, and proposed environmental sample collection and analy-
sis techniques for the measurement of plutonium and associated
transuranic elements. Consideration is given to the various
available techniques, their applicability to various situations,
sensitivities of the techniques, and reproducibility of results.
Soil sampling appears to be the predominant technique for
assessing accumulative environmental levels of plutonium (AEC,
1974). Thus, emphasis in this review has been placed on soil
sampling and analysis, although consideration is given to other
media, especially air sampling. Air sampling is emphasized be-
cause of the predominance of the inhalation pathway for plutoni-
um. The review is largely based on published information from
nationally recognized laboratories, although some unpublished
data, which may include unintentional bias, is included.
GENERAL STATUS OF TECHNIQUES AND THEIR EVALUATION
There are several published intralaboratory evaluations of
analytical techniques (e.g. Chu, 1971; Bishop et al., 1971; Sill,
1971; Sill and Hindman, 1974). There are also several reports
containing limited data from interlaboratory comparisons (Krey
and Hardy, 1970; AEC, 1973; Sill and Hindman, 1974).- These
studies have largely dealt solely with analytical techniques for
soil samples, with limited consideration of the interaction
between sample collection and analytical techniques. Krey and
Hardy (1970) and Bliss (1973) present some data on the inter-
action of both collection and analysis, but there does not appear
to be any comprehensive evaluation of both collection and ana-
lytical techniques.
Most analytical cross-check programs intra- or interlabora-
tory are done with samples containing plutonium concentrations
significantly above background (roughly 0.05 pCi/g of dry soil
for a 5 cm depth sample). But, there are several limited groups
of data available for replicate analyses of samples containing
near-background plutonium levels. These are reported by Sill
(1971), AEC (1973), Krey and Hardy (1970), and Butler et al.
(1971).
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348
Much of the difficulty with the sampling and analysis of
soil samples appears to relate to the discrete particulate nature
of plutonium contamination under some circumstances. The poten-
tial refractory nature of plutonium, along with the potential for
producing refractory material during sample preparation aggra-_
vates the inherent difficulties and complexities of the analysis
(Sill, 1971; and Sill and Hindman, 1974).
Although there are considerable variations and potential
inadequacies in past techniques, and to a lesser extent in cur-
rent techniques, there is cause for optimism for improvements, or
at least standardization, in the near future. In May 1974, the
Atomic Energy Commission (now Nuclear Regulatory Commission-NRC)
issued Regulatory Guide 4.5, "Measurements of Radionuclides in
the Environment, Sampling and Analysis of Plutonium in Soil"
(AEG, 1974). This Guide outlined generally compatible and sup-
plementary collection and analysis techniques. In April 1974,
the Environmental Protection Agency (EPA), National Environmental
Research Center-Las Vegas (NERC-LV; now known as Environmental
Monitoring and Support Laboratory, EMSL) sponsored a workshop on
soil collection and analysis techniques. A summary of this
workshop (attached as Appendix A) and the tentative reference
method developed from it (Bretthauer et al., 1975) were issued in
1975.
The following paragraphs are extracted from the EPA criteria
for standard methods (EPA, 1973).
"Sampling is the removal from the environmental continuum of
a portion of the pollutant for detailed investigation. Sampling
involves containerizing a discrete volume of polluted air, water,
soil, or biological materials, or it may involve partitioning the
pollutant directly from these media into a filtering or absorbing
device or into another fluid (e.g., the absorption of the sulfur
dioxide pollutant in air into a solution of potassium tetra-
chloromercurate). Additionally, it includes those procedures
necessary to preserve the sample. In all of these sampling
methods, we must accurately know what fraction of the pollutant
passes from the environmental continuum into the sample. Stan-
dardization of the sampling method establishes the reproduci-
bility of this relationship. This relationship must be shown to
be stable or to follow predictable changes from the time the
sample is taken to the time the sample is worked up for analysis."
"Sample work-up consists of the preparation of the sample by
concentration of pollutant, removal of interfering substances,
etc., for the analytical procedures to follow. It must be estab-
lished that all pollutant losses during sample work-up can be
quantitatively accounted for and are reproducible within statis-
tically acceptable limits."
"Analytical methods are designed to give accurate estimates
of the true amount of pollutant remaining in the worked-up
-------
349
sample. The standardization procedure assures that these values
are reproducible within statistically-acceptable limits. The
value derived from the analytical method adjusted for predictable
losses in sampling and sample work-up gives the estimation of the
true concentration of the pollutant in the environmental con-
tinuum."
"The reference method is the best, readily available method.
Under most circumstances, it will be expected that the reference
method will be the method of choice of most user laboratories.
When other methods must be used for any reason, their equivalence
to the performance characteristics of the reference method must
be demonstrated to assure that data generated by their use is
equivalent to that generated by the reference method and that
statistically valid comparisons can be made between such data and
that generated by use of the reference method."
EPA started a standards distribution program for plutonium-
239 and americium-241 in December 1973 (EPA, 1974a). A plutonium-
239 cross-check program for water samples (<10 pCi/1) was initi-
ated in 1974 (EPA, 1974b).
A basic problem in most environmental monitoring programs is
inadequate coordination of the sampling and analytical programs.
This is exemplified by a field program where significant efforts
are made to obtain unbiased soil samples representative of the
sampled area. This sample may represent kilograms of material.
The analyst, in order to insure complete dissolution of the mate-
rial, analyzes a one- or possibly ten-gram aliquot of this
sample. If the plutonium contaminant is of a discrete particu-
late nature, replicates from this sample can vary by several
orders of magnitude (Bliss, 1973). Therefore, the objectives of
the monitoring program must be continually examined and reevalu-
ated.
-------
350
DIRECT FIELD MEASUREMENT TECHNIQUES
The most viable means of field measurement for plutonium
contamination appears to be the FIDLER (Field Instrument for
Detecting Low Energy Radiation) instrument developed by the
Lawrence Livermore Laboratory (Tinney et al., (1969). The FIDLER
uses a thin Nal or CaF crystal (Piltingsrud and Farr (1973)) and
photon pulse height discrimination to detect the 17-keV X-rays
from the progeny of plutonium, or the 60-keV gamma photon of
americium-241. Although the sensitivity of the FIDLER instru-
ment, ideally about 130 nCi/m2, is about two orders of magnitude
above ambient background levels of plutonium (nominally 1-2 nCi/nr
of plutonium-239, it provides significantly greater utility for
contamination surveys than the prior alpha detection survey
instruments.
Minimum sensitivities or calibration factors in terms of
pCi/m2 are generally not stated for most alpha survey meters
(Dummer, 1958). Survey instruments are generally only designed
for assessing the relative degree of contamination. Information
from general sources, including Dummer (1958) indicates a general
sensitivity, under ideal field conditions, of about 5-10 pCi/cm2
(50-100 nCi/m2). The response relationship is about 500 cpm per
100 nCi/m2. However, these relationships assume that the alpha
activity is essentially emitted from an infinitely thin layer of
contamination on a smooth surface. Further, the measurement is
made with a fragile mylar-windowed probe, which must essentially
be placed in contact with the surface. A layer of moisture (dew)
essentially will shield out the alpha particles. There are
problems of fracturing or contaminating the probe. Vegetation or
rocks make it very difficult to place the probe near the surface.
Measurements taken at one centimeter from the surface are in
error by roughly a factor of two (Dummer, 1958).
Table 1 presents sensitivities and calibration factors for
the FIDLER instrument. These values are based on a nominal
background of 200 cpm for the 17-keV region and 600 cpm for the
60-keV region. These values assume the background is known
within counting error variations. The 17-keV sensitivities
relate to a net background counting rate of 75 cpm, above the
background of 200 cpm. Thus, an uncertainty in background of 100
cpm, which is possible assuming the background was determined in
a distant contamination-free area, introduces a factor of two
error.
-------
TABLE 1. SENSITIVITIES AND CALIBRATION FACTORS
FOR FIDLER INSTRUMENTS
(1/16" Nal(Tl) crystal)
Nuclide
Energy Minimum
Region Sensitivity
(KeV) (nCi/m2)
Response Minimum
(cpm/nCi/m2) Sensitivity
Point Source
(nCi)
351
Plutonium- 2 38
Plutonium- 2 39
Americium-241
Americium-241
100% photon
100% photon
17
17
17
60
17
60
56
130
19
36
7
13
1.3
0.58
3.9
36
10.1
100
28
63
9.4
19
3.6
6.9
Lindeken et al. (1971) studied the background in the 17-to
60-keV energy region. He concluded that although the background
may vary by a factor of two in adjacent areas, the energy spec-
tral shape, or the percentage of the background per 10-keV
interval, varied by less than 5 percent. Thus, in the absence of
general fission product gamma fluxes, the background at about 80
keV (Compton continuum) can be measured within an area of suspec-
ted plutonium contamination, and the background in the 17- and
60-keV regions estimated. This technique can be used to supple-
ment or replace other background readings, to minimize the errors
associated with variations in background.
Piltingsrud and Farr (1973) report on a modified FIDLER-type
instrument using a CaF(Eu) crystal. The modified instrument is
amenable for field repair and costs less than the NaI(Tl)-type
instrument. A sensitivity value of about twice that for the
Nal(Tl) instrument is reported.
Tinney et al. (1969) report field tests for the NaI(Tl)-type
FIDLER at the Nevada Test Site. They estimated the actual
background to be 400 counts/min, with a corresponding sensitivity
of about 300 nCi/m2. It was noted that although alpha survey
instruments indicated a higher count-rate for selected point
sources, it was necessary to use the FIDLER to find these sources,
Furthermore, this field test indicated that for general contamin-
ated areas, the FIDLER cpm readings were roughly ten times the
alpha instrument readings, versus the theoretical ratio of about
-------
352
0.1. This indicates the poor efficiency of alpha monitoring in
the field (actual versus theoretical).
REECO reported (NAEG, 1971) that at NTS, with a depth-
dispersed source of plutonium-239, most of the 17-keV X-rays were
absorbed in the soil. Even using the americium-241 60-keV photon
required a correction factor of three. The use of the FIDLER
with a multichannel analyzer readout was also suggested for areas
with general fission product contamination.
Gilbert and Eberhardt (1974) present data for plutonium-239:
americium-241 ratios based on laboratory analysis for both
nuclides, and on plutonium-239 laboratory analysis versus FIDLER
estimates for americium-241 from NTS. The data are summarized in
Table 2, taken from Gilbert and Eberhardt. The data indicate a
change in the plutonium-239:americium-241 ratio by isopleth. The
isopleths were relative concentration lines determined by FIDLER
surveys. Except for the Clean Slate I and II sites, there is
good correlation between the plutonium and americium ratios
within the isopleths.
The ratios and correlation of the plutonium-239 to americium-
241 60-keV FIDLER readings are also given in Table 2. Although
the correlation improves with an increase in plutonium concentra-
tion, the correlation indicates there is little direct relation-
ship. Figure 1 presents scatter diagrams of the plutonium-239
versus americium FIDLER data.
Although the FIDLER is an effective instrument for mapping
general areas of contamination, its use as an accurate predictor
of plutonium concentrations in surface soils appears to be
limited, based on the NTS situation. Additonal field evaluations
are necessary for a more specific conclusion.
Stuart of EG and G reports (1971) the use of gamma spectros-
copy from an aerial platform for measurement of americium-241 in
soil.
Due to the disagreement between published values of half-
lives, and X-ray and photon yields for plutonium and americium,
various values are summarized in Appendix B.
In summary, although the minimum sensitivity for the FIDLER
is indicated as 130 nCi/m2 for plutonium-239, this relates to
only 75 cpm above minimum background values of 200 cpm. Given
the variability in background with values up to 400 cpm, or more,
extreme care has to be exercised to accurately assess net contami-
nation at 200 or even 500 nCi/m2. Without an accurate knowledge
of background, values at these levels would have uncertainties
approaching 50-100 percent. The data in Table 2 and Figure 1
indicate that even at 100 dpm/g (roughly 50 pCi/g or 500 nCi/m2),
there is limited correlation between the FIDLER results and
plutonium-239 radiochemistry results. Use of the 60 keV gamma
-------
TABLE 2. ESTIMATED CORRELATIONS BETWEEN LABORATORY GAMMA SCANS FOR
AM-241 AND PU-239-240, AND BETWEEN FIDLER CPM OF AM-241 AND PU-239-240
(from Gilbert and Eberhardt, 1974)
Lab Gamma Scans for
Am-241 vs Pu-239-240
FIDLER vs Pu-239-240
Area 13
Area 5
TTR
Isopleth
1 < 1000 cpm
2 1-5,000 cpm
3 5-10,000 cpm
4 10-25,000 cpm
5 25-50,000 cpm
6 > 50,000 cpm
1
5
Clean Slate I
Clean Slate II
Clean Slate III
Double Track
No. of
Samples
24
28
15
20
20
46
24
10
10
9
22
8
Estimated
Correlation
0.98
0.85
0.98
0.99
0.99
0.95
0.93
0.99
0.73
0.54
0.91
0.99
Average
Ratio ± S
12.6 ±
14.2 ±
9.4 ±
8.8 ±
8.8 ±
9.4 ±
11.9 +
10.9 ;
31.7 ±
37.0 ±
21.7 ±
28.7 ±
Pu/Am
.E. ttt
0.9
3.9
0.4
0.2
0.3
0.3
1.0
0.6
5.6
10.8
2.2
1.4
No. of
Samples
20
28
14
15
20
46
45
15
__
__
—
— «-
Estimated
Correlation
0.19t
0.33tt
0.5ltt
0.40tt
0.69tt
0.69tt
0.54t
0.76t
____
— __
....
tFIDLER 60-kev readings not corrected for background (correcting often resulted in negative
readings).
ttFIDLER 60-kev readings corrected for background.
tttThese are appropriate only if the Pu/Am ratio remains constant as the Am Value varies. See
text for further comments.
CO
CJ1
CO
-------
354
o>
250
200
150
100
50
AREA 13
ISOPLETH 1 MOOOCPM)
n = 20
CORRELATION = 0.19t
I
I
'INCLUDES DATA POINT
(4000 CPM, 671 dpm/g)
NOT SHOWN ON GRAPH
. I .
2000 4000 6000
FIDLER "'Am CPM (UNCORRECTED)
8000
AREA 13
ISOPLETH 2 (1.000-5,000 CPM)
600
600
400
a
N
r 300
200
100
n = 28
CORRELATION = 0.03 t
t INCLUDES DATA POINT (2400 CPM,
1280 dpm/g) NOT SHOWN ON GRAPH
I
I
1000 20OO 3000
FIDLER "'Am CPM (CORRECTED)
4000
Figure 1. Correlation between Plutonium concentrations and
FIDLER readings, (from Gilbert and Eberhardt,1974)
-------
355
from americium-241 for field measurements is not recommended
where the age of the material and the original percentage of
plutonium-241 is not known.
-------
356
FIELD COLLECTION TECHNIQUES FOR SOIL
The sampling or program mission and intended use of the
sample results is of utmost concern in defining the adequacy of
sampling techniques. The efforts and costs 'associated with
sampling as well as the costs of analyzing unnecessary samples
make it expedient to relate sampling techniques to the intended
use of the data. Table 3 presents approximate costs for sample
collection and analysis. The values for collection include
nominal driving times between sampling sites.
TABLE 3. APPROXIMATE COSTS FOR SOIL SAMPLE
COLLECTION AND ANALYSIS
Sample Collection
Surface Sample
Depth Profile
(3 to 5 samples)
Plutonium Analysis
1 gram by Dissolution
10 gram by Dissolution
10 gram by Fusion Tech.
Cost
$10-20
25-50
100.00
100.00
150.00
Man-hours
per Sample
2
4-5
There are three primary considerations in sample collection
1. Selection of the general area to be sampled; e.g.,
undisturbed, type and amount of vegetation, size of
rocks, etc.
2. Determination of sample depth.
3. Compositing material from an adequate sample area.
10
-------
357
Appendix A, the summary report from the NERC-LV workshop,
includes an extensive discussion of sampling techniques and
necessary considerations. AEG (1974) also discusses the cri-
teria.
The intent of sampling programs can generally be related to
one or more of five specific objectives:
1. Sampling for low levels, such as those associated
with world-wide fallout, to establish base line or
background concentrations. The deposition of the
contaminant is generally fairly uniform.
2. Sampling to determine the occurrence of a release
associated with a specific facility, or accident at a
specific location. The deposition levels and distribu-
tion may vary with direction and distance from the
point of release (Sill, 1971). This includes deter-
mining the inventory.
3. Sampling to determine the deposition during various
chronological periods of time. The objectives would
relate to surface samples or possibly samples from
various depths that had been covered at a specific
point in time.
4. Profile sampling to determine movement of material
through the vertical profile. The sampling technique
would be similar to general profile sampling, but
samples should not be composited and depths should
correspond to the soil horizons.
5. Sampling to determine quantities of source material
readily available for resuspension; i.e., normally the
surface one-eighth to one-half inch of soil.
Common sampling techniques are not oriented to resuspension.
Thus, pertinent comments and techniques are discussed in the next
section.
The required accuracy and sensitivity in conjunction with
the analytical sensitivity of results must also be considered
prior to selecting the sample collection techniques; e.g.,
dilution of the plutonium concentration in the surface layer by
soil with a lower plutonium concentration from deeper profiles.
The surface area represented by a sample and the allocation or
splitting techniques used to select the final aliquot that is to
be analyzed must be such as to meet the necessary resolution
between the results based on the sampling mission objectives.
Furthermore, the sampling parameters Cdepth and area) must be
such as to give reproducible results. Michels (1971), in an
analysis of data from around the Rocky Flats Plant concludes that
Poet and Martell's (1972) sampling techniques probably introduced
artificial variability in their results due to inadequate
11
-------
8
sampling depth. This made it difficult to differentiate between
plant and world-wide contamination.
SOIL SAMPLING TECHNIQUES
Two basic techniques are presented in AEC (1974). The
techniques are generally referenced to their developers; i.e.,
the HASL and NAEG techniques. They have similar philosophies,
and generally are supplementary in that they are applicable for
different soil types. The site selection criteria, outlined
below, are similar for both techniques:
1. Select general sample locations based either on general
areas around a site, average geographical distribution,
or on a random basis (random numbers referenced to a
geographical grid).
2. Pick undisturbed sites for actual sampling. This may
require abandoning certain sites if the selection of
general location is based on random numbers. Although
usually unacceptable, disturbed sites, blow sand, dams,
or recent landfill may be appropriate for certain
mission objectives.
3. Pick open, generally flat areas where there are no
nearby potential anomalies, such as near buildings or
trees. Also avoid stream beds, dry wash bottoms, and
hillsides.
4. Pick areas away from rock outcrops and with generally
uniform vegetation coverage. Try to insure that the
soil grain size is compatible with the sampling method.
5. Soil having high earthworm activity should be avoided
due to the abnormally high vertical mixing.
6. Locations should be roughly 120 m (400 ft) or more from
dusty roads or sites of previous construction.
The following items outline the HASL technique:
Surface Sample
1. Obtain surface samples by core technique. Any type of
sampling tool that can remove an intact plug (cookie
cutter-type instrument) is appropriate.
2. The surface sample depth should be 5 cm (2 inches).
The sample area should be 500 to 1,000 cm2 (about 0.5
to 1 ft2). In grass areas the vegetation should be
close-clipped and taken as a vegetation sample or
discarded.
Energy Research and Development Agency, Health and Safety
Laboratory, and Nevada Applied Ecology Group.
12
-------
359
5. It is suggested that the sample be composed of about 10
plugs from a 5-meter line transect. The line should be
located by reference to fixed landmarks.
4. The soil sampler should be pressed into the ground
without twisting or disturbing the grass cover or soil
surface.
5. The 5-cm depth is intended to include the soil of
maximum plutonium activity and most of the root mat in
areas covered with grass. In areas with a deeper root
mat, it may be necessary to take a deeper surface
sample to allow accurate estimation of the sample
depth.
Depth Profile
1. A 3.5-in. diameter auger may be used to take incre-
mental depth profile samples at the same locations
where the surface plug was removed. Ten cores should
be composited for a profile. The purpose of the
profile determines the number of profiles that should
be taken at a given location. Both the HASL and NAEG
techniques recommend compositing a number of profiles
(e.g., 10), but specific study objectives, such as
determination of the movement of plutonium through the
soil column, are best based on individual samples.
2. For the trench-type method, the vegetation, if present,
is closely clipped, and the sod layer removed from the
proposed trench area. A trench approximately 60 x
90 cm, and 60 cm deep is dug adjacent to the clipped
area.
3. A rectangular three-sided 15xl5x5-cm deep.pan is used
to take samples from the vertical wall of the trench.
4. A flat-bladed knife should be used to score the soil
around the edges of the pan to allow removal of a
sample having an accurate area.
5. The soil is removed from each side of the sampled area
to provide a flat shelf prior to each 5 cm depth
sampling increment.
6. The minimum profile depth should be based on analysis
of preliminary samples (roughly a minimum of 20 cm).
7. The sampling area for this type of profile is only
230 cm2, which provides a less representative deposi-
tion sample than does the surface sampling technique.
13
-------
3GO
Sample Preparation
1. Spread out and air dry sample for about 3 days. Break
up soil aggregates, and pull apart and cut up root mat.
Weigh the total sample.
2. Remove and discard rocks greater than about 2.5 cm
diameter. For gravelly soil, sieve through 10 mesh,
removing material greater than 2 mm. Crush and blend
s amp1e.
3. Spread sample and quarter. Take a three-kilogram
composite by taking small repetitive aliquots from each
quarter and pulverize or grind this subsample.
The following items outline techniques patterned after those
developed by the NAEG, but which were modified for the purposes
of the Regulatory Guide 4.5 (AEC, 1974).
The NAEG techniques and sampling philosophy are described by
Fowler, Gilbert, and Essington, "Sampling of Soils for Radio-
activity: Philosophy, Experience, and Results; ERDA Symposium
Series 38 (1974, CONF-740921.
The techniques were designed to be applicable to sandy
soils, but more importantly were designed to minimize the poten-
tial of sample cross-contamination that can occur with coring
techniques (smear of surface activity to subsurface sample). The
NAEG does not generally composite samples, and neither endorses
nor disapproves of transect sampling or compositing of samples.
The specifications for compositing samples are based on the
modifications of the NAEG techniques for the regulatory guide.*
Ring Method for Surface Samples
This technique can be used to collect either surface or
profile samples.
1. A 12.7 cm-ID x 2.5 cm-deep ring is pressed into the
soil. The soil inside the ring is removed with a
disposable plastic spoon.
2. The soil from the outside of the ring is removed, and
the ring is pressed down for another sample.
3. A surface sample is defined as a minimum depth of 5 cm.
A minimum number of five separate samples should be
taken along a straight line transect and composited for
analysis.
Changes made subsequent to the original publishing of this
report as ORP/LV-76-5 in 1976 (Reference Fowler, E. B. and
E. H. Essington, Sampling Soils for Transuranic Nuclides:
A Review: NAEG Symposium in Gatlinburg, TN, 1976, NVO-178).
14
-------
36!
Trench Technique for Surface or Profile Samples
1. Dig trench of convenient size, 15 to 25 cm deeper than
desired sampling depth.
2. Take samples from trench wall with three-sided rectan-
gular tray (10 x 10 x 2.5 cm deep).
3. Push the tray into the trench wall. Use a flat trowel
to close the open end of the tray.
4. Remove the soil around the tray down to the sampling
depth. Remove the sample.
5. A surface sample consists of soil taken from a minimum
depth of 5 cm.
6. A minimum of five samples should be taken from separate
trenches along a straight line transect. Composite the
samples for analysis.
General Comments
1. Samples should either be double bagged or placed in
cans.
2. Varying soil types require modification - Rocky soils
may require larger samples to minimize the errors
associated with sampling accurate areas and depths.
3. Locations should be identified by reference to fixed
landmarks.
4. Adding moisture (as a fine spray) to the soil may
minimize sampling problems.
Sample Preparation
1. Oven dry soil for 24 hr at 100°C. Weigh total sample.
2. Sieve sample to remove material greater than 0.6 cm.
(0.25 in.) diameter (1/4-in sieve). This excludes
rocks and most root material from further considera-
tion.
3. Rocks can be acid washed, with the wash solution added
to the solubilized soil sample.
4. Roots and vegetative material can be analyzed sepa-
rately.
5. The sample should be ground (ball-milled) and blended
prior to taking a representative aliquot for analysis.
15
-------
362
Table 4 summarizes collection techniques used by several
investigators.
The following points emphasize the similarities of the
various techniques and potential pitfalls:
1. Both the HASL and NAEG techniques have standardized on
a minimum depth for surface samples of 5 cm (2 in).
For most locations and situations the majority of the
Plutonium is in the top 3 to 5 cm. A sample repre-
senting a depth of less than 5 cm may not account for
the majority of the plutonium deposition (Krey and
Hardy, 1970). Furthermore, the fractional uncertainty
in the sampled depth is proportional to the sampled
depth (e.g., a 1-cm uncertainty is 1001 of 1 cm, but
only 201 of 5 cm). An unnecessarily large depth
results in diluting the higher surface concentrations
with (usually) relatively uncontaminated soil. This
increases the uncertainty in sample results. Mixing of
surface soil with subsoil can also result in a signifi-
cant scatter or variance in results, if uniform methods
are not used.
2. AEC (1974) emphasized that when sampling rocky soils,
modified techniques may be necessary. However, a
representative depth is more important than a repre-
sentative width. But as Bliss (1973) notes, the
measurement of the cross-sectional area is more impor-
tant than the measurement of the depth, because of the
direct dependence of the deposition calculations on the
area represented by the sample.
3. The AEC (1974)techniques emphasize the compositing of
a number (five) of small-area samples for a given site
to obtain a representative sample and a minimum sampled
area (0.5-1 ft ). This is not emphasized in many of
the techniques in Table 4. In fact, as noted in Table
4, Bliss (1973) only composites two samples per horizon
in depth profile samples. Bliss (verbal communication)
indicated that REECO ususally only takes one sample per
horizon. Moore, Office of Radiation Programs - Las
Vegas Facility (ORP-LVF) (verbal communication) noted
that probably only one sample per horizon was taken for
Enewetak.
Several potential uncertainties are associated with sample
preparation. These include:
1. Oven drying at 120°C versus air drying for several
days. The differences in the resulting weights (up to
roughly 10 percent) are present in the pCi/g values,
but should be accounted for in the pCl/m2 values.
16
-------
TABLE 4. SAMPLE COLLECTION TECHNIQUES
(Blanks indicate no information)
SURFACE SAMPLES
PROFILE SAMPLES
Reference
AEC Guide (1974)
AEC Guide (1974)
AEC Guide (1974)
AEC Guide (1974)
Bliss (1973)
Douglas (ORP-LVF)
Bliss (Verbal)
AEC (1973)
Corley, et al (1971)
Corley, et al (1971)
Kahn, 10/1/74
Little (1973)
Poet & Kartell (1974)
McClendon (1975)
Krey & Hardy (1970)
Krey & Hardy (1970)
WASH-1259 (AEC, 1973)
WASH-1259 (AEC, 1973)
WASH-1259 (AEC, 1973)
WASH-1259 (AEC, 1973)
WASH-1259 (/-EC, 1973)
WASH-1259 (AEC, 1971)
WASH-1259 (AEC, 197 3)
WASH-1259 (AEC, 1973)
WASH-1259 (AEC, 1973)
WACH-1,'59 (AEC, 1973)
WASH-1259 (AEC, 1973)
WAT,II-1259 (AEC, 1973)
Organization
(HASL)
(HASL)
(NAEG)
(NAEG)
NERC-LV/NAEG
ORP-LVF
REECo/NAEG
Enewetak
Han ford
Hanford
EPA/NEF Cinn.
Colorado State
University
3RP
RASL
HASL
LASL
SRP
Mound
Mound
Pantex
BocVy Fl n t,n
Sandia, Abq.
Argonne
Idaho, NETS
ORNL
Han ford
LLL
Technique
Core/Auger
Ring
Tray
Tray
Tray
Ring
Core
Shovel
Tape Cont.
Trench
Spatula
Core
Auger/Cope
Template
Core
Core
Core
Scrape
Core
Cor^
?
Core
Core
Core
Sample
Area
( cm2 )( in2 )
60
127
100
100
100
127
30 or 60
549 216
64
25
1000
45
62
930 144
44
62(?)
62
62
100
230 144
R7
79
46 7
Number of
Composites
10
5
5
10
10
=1
1 or 2
*1
4
1
10
10
1
5
10
10
=1
1
1
2
5
9
Sampled
Total Area Depth
(on2)(ln2) (omXin)
600 5
600 5
500 5
1000 5
1000 5
127 5
30 or 60 5 or 15
1.3 0.5
ilOO 1.6
2.5 1
100 3
1000 1
450 15
62(3 20
930 144 20
220 5
600( ? ) 5
600 30.5 12
0.3 1/8
=62 5.1
100 5
230 144 2.5 1
173 30
390 5
410 1
2.54 1
l;up to 25
Increments
Technique (cm)
Auger 0-30 total
Trench/Tray
Trench/Tray 2.5-5
Trench/Tray 2.5-5
Trench/Tray 2.5-5
Trench/Tray
Trench/Tray =5
Trench 3-21
0-0.3,
1.3, 2.5 ...
Core 0-5, 5-15,
15-22.5-30
Auger/Core 0-5, 5-20
Auger 0-5, 5-15,
15-22.5-30
Area Per Sieve
Sample Number of Total Area Size
(cm2)(in2) Composites (cm2)(in2) (cm)
62 10 600 <2.56
225 1 225 <2.5
100 5 500 <0.2
<0.2
100 2 200 <0.2
100 2 200
=100 =1 =100
100 1 100
25 4 100
=1000 1 =1000 <.05
45 10 450
62 10 600
10 600
CO
en
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-------
364
2. AEC (1974) refers to calculating field bulk density.
This apparently is an error in semantics because the
actual field weight is not obtained. Also, standard
soil sampling methods are not used to determine the
volume of hole from which the sample was taken.
POTENTIAL SAMPLING ERRORS
The available literature indicates that very few efforts
have been made to evaluate the adequacy of soil sampling tech-
niques. The following subjects will be treated in this section:
consideration of apparent inconsistencies in results based on
calculated bulk densities; consideration of plutonium depth
profiles; discrete particles; and comparision of actual ana-
lytical variations in several groups of results.
Bulk Density
Kaufmann (internal memorandum dated October 3, 1974,
ORP-LVF)*, noted that the tray/trench method was probably not
adequate for obtaining an accurate estimate of sample weight per
sampled area. This corresponds with a preliminary workup of data
by Douglas (ORP-LVF, unpublished data) for the 1973 Trinity Field
Study. Figure 2 shows a histogram of weight per unit area
sampled and calculated bulk densities (g/cm2). Histograms of
other samples from this study indicate similar distributions.
The maximum observed values from the Trinity study are equal to
the minimum bulk density indicated by Terzaghi and Peck (1968)
for uniform loose sand (1.43 g/cm3). The median values indicated
by Douglas for Trinity are roughly 30 percent lower than the
value indicated by Terzaghi and Peck. Bliss (verbal communica-
tion) also indicated that values of less than 1 g/cm3 have been
noted in the Nevada Test Site (NTS) EMSL work.
Kaufmann (verbal communication) indicated that although
valid values of about 1 g/cm3 are not impossible, they are
improbable. In nature they result largely from undisturbed
drying of a saturated soil, forming an unconsolidated matrix-like
material.
The American Society of Testing Materials soil sampling
method D-1556 (ASTM, 1964) specifies a minimum sample size of
1400 cm3 for soils with a maximum particle size of 12.5 mm or 0.5
inch diameter. Furthermore, the standard specifies a technique
for measuring the sample volume by refilling the sampled hole
with a measured weight of sand of known density.
The methods of Bliss (1973) and Douglas, which basically
follow the NAEG technique, only collect about 1,000 cm3 per
horizon for profile samples--actually only 250-500 cm3 per
sampling cut. Furthermore, the use of the tray disturbs the
actual sample and the surrounding area. Also, Bliss (verbal
communication) notes that the two samples for profiles (NTS) are
*ORP-LVF, Office of Radiation Programs, Las Vegas Facility
-------
365
usually taken immediately adjacent to each other. Thus, the soil
disturbed by the first cut is sampled in the next cut. Also, one
side of the tray is not confined by soil during the second cut.
There would appear to be inaccuracies associated with this type
of sampling methodology. The significance of these is hard to
assess, but could amount to 30 percent or more.
Inaccurate bulk densities do not necessarily affect the
results. The actual calculation is activity per unit weight
times weight collected, divided by area sampled. The pertinent
question relates to the representativeness of the grams of sample
to the sampled area. Minor variations in the sampled depth
probably have more affect on the interpretation of the results
than on the actual numerical values.
Terzaghi and Peck (1968) present information on compressi-
bility and the hysteresis loop after removal of the compression
force for soil. A force of about 10-20 pounds applied to a scoop
with frontal area of 50 cm2 (10 cm x 5 cm) may produce a change
in the void ratio (e) of up to about 10 percent of its value.
The void ratio is the ratio of the volume of voids to the volume
of soil substance. By relating the change in e to the change in
porosity, n, (n = e/l+e) , the change in the field bulk density of
the soil can be estimated.
If the cutting edges of the scoop are assumed to transmit
the force as a compression force to the total frontal area of the
scoop, the bulk density at the frontal interface of the scoop is
increased by roughly 5 percent. But part of the compressed soil
would be in the scoop, and the compression would be reduced with
distance from the scoop frontal interface. Thus, the maximum
reasonable error would be less than 5 percent. This error would
appear as a reduction in the actual amount of soil taken as a
sample.
The bulking of the soil, as it is disturbed by inserting the
scoop, tends to make it mound up in the scoop. Unless this is
recognized, the tendency would be to only take a deep enough
sample to fill the scoop, thus underestimating the volume sampled
by about 20 percent. Bulking can also cause losses of material
while taking the sample to be overlooked. Data from Terzaghi and
Peck (1968) indicate potential errors of up to about 20 percent.
The EMSL-LV program has incorporated the use of scoops
having an extra 2 cm length (10 cm sampling length, plus 2 cm for
bulking, etc.) to minimize bulking and compression errors.
Taking profile cuts adjacent to each other could result in
errors of roughly 10 percent, due to the disturbed nature of the
soil and thus reduced bulk density, even if extreme care is taken
in positioning the scoop on the open face of the second cut.
19
-------
366
All of these errors tend to minimize the amount of sample
actually obtained from an assumed area sample. This is appar-
ently illustrated by the histograms of apparent soil density for
the Trinity results as shown in Figure 2.
An experiment was conducted by EPA - Las Vegas staff to
obtain an indication of variations in the soil volume collected
by the scoop technique for depth profiles. Samples were taken by
three experienced teams from a 10-meter diameter circle of
relatively undisturbed desert. Two of the teams (A and B)
basically used the NAEG scoop profile technique. The third team
(C) used a displacement technique where the volume of soil
removed was measured by filling the hole with a known volume of a
standard density sand.
Team A actually took two side-by-side scoops (10 x 10 x 5 cm
deep) from a trench. Not only were the scoops taken side by
side, but a bench was not cleared off before going to the next
lower depth. Team B took a single scoop. A bench was not
cleaned off before sampling at the next depth.
Each team took four profiles. The only significant error
noted was the sampling depth. Team A sampled to a depth of
22.9 cm versus the design depth of 20 cm.
Team B sampled to depths of 21.6 to 22.23 cm. These depth
errors are equivalent to bulk density errors of about 10 percent.
However, assuming the errors were generally uniform and that the
actual sampling depths were measured, the bulk densities can be
corrected.
The average bulk densities (wet weight) for the four pro-
files for teams A and B were 1.70 and 1.62 g/cm3. Correcting for
the sampling depth gives values of 1.49 and 1.48 respectively.
These values compare well to the value of 1.53 g/cm9 for team C.
The standard deviation for all three sets of data was about
0.05 g/cm3, indicating overlap of the data.
An interesting speculation is that concern for bulking of
the sample and fear of not taking an adequate depth appears to
result in over-compensation. The sampling depth may be deeper
than expected.
Significance of Sampling Depth
The sample depth increment has a significant impact on
sample results, and is inherently related to the objectives of
the sampling program. This is just as true for results reported
as activity per unit soil mass as for those reported as activity
per unit area. Plutonium is deposited on the surface of the
soil. Through mechanical action, as well as water and earthworm
movement, etc., it is mixed through the upper soil layers, down
to 20 cm, or more. The relative concentration with depth varies
20
-------
387
20-1
15-
tn
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a.
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•-• '••..-'-
ill
15 4.
83 0.
1 -••'i;;i '
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1 weight, (grams)
a sampled, (cm2)
< density(gm/em3)
/A
depth
15 7.65
43 1.53
Figure 2. Histogram of weight per unit area for 72 soil samples
from vicinity of Trinity, New Mexico.
(from Douglas, EPA/ORP-LVF, unpublished data)
21
-------
388
within localities and from one geographical area to another.
Leopold et al. (1966), Colby (1963), EPA (1973a), Chepil (1945a,
b,c,d), Chepil (1946), and Chepil and Woodruff (1963) present
information on soil denuding, transport, and erosion as a result
of natural forces and of human land-use.
Data on plutonium soil profiles from numerous areas are
summarized in Table 5. These data include results from Savannah
River, Georgia; NTS, Nevada; Rocky Flats, Colorado; New York, New
York; and Trinity, New Mexico. The range of results, means, and
standard deviations are given for the various sites. This pre-
sentation inherently assumes the data are normally distributed.
This hypothesis has not been tested. Given the range and scatter
of the data, the summarization and treatment is presented only as
a trend or indication.
It is readily apparent that some of the groups of data, such
as those reported by Bliss (1973) for NTS are not normally
distributed. The data are inherently bounded by a value of 100
percent, and a value of the mean plus one standard deviation
exceeds the 100 percent accumulation in several instances.
It is difficult to obtain meaningful information from some
of the data because they are reported as pCi/g with no indication
of the bulk density of the soil. Since most investigations vary
the vertical increment with profile depth, each sample represents
an average of a composite over a different depth increment. The
variation of soil bulk density with depth further complicates the
comparison. Also, at depths below several centimeters, the
plutonium concentrations approach the minimum detectable activity
(MDA)* Given the detection of plutonium at the lower depths in
many profiles, it is apparent there is some plutonium down to
about 20 cm in most cases. Thus, the plutonium concentration
postulated for the MDA results (e.g., zero to the MDA) influences
estimates of the percent of plutonium for the various soil
strata. There is also the speculation that the observed concen-
trations of plutonium at lower depths may be due to cross-
contamination during sample collection, preparation, or analysis.
The following items discuss the groups of profile data in
Table 5.
1. Bliss (1973) presents profile data for the off-site
area around NTS. The data are reported in pCi/g of dry
soil and nCi/m2. Bliss reports values below the
detection limit as zero. Given a nominal detection
limit of 20 fCi/g (0.02 pCi/g), it can be seen that the
exclusion of values below the detection limit can have
a significant impact on the cumulative percent deposi-
tion for locations having deposition near background--
roughly 1 nCi/m2. For example, for the Furnace Creek-1
sample, the only detectable result in the profile was
*MDA (minimum detectable activity)
22
-------
TABLE 5. PERCENTAGE PLUTONIUM DISTRIBUTION IN SOIL AS A FUNCTION OF DEPTH
Location Reference
Nevada Test Bliss (1973)
Site NV^
Nevada Test Gilbert &
(1974)
Rocky Flats, Krey & Hardy
ro( i Q7o ^
Rocky Flats, Poet & Martell
Trinity Site, Douglas
New York Krey & Hardy
f-i +\r MY ( 1 Q7H ^
Waynes vi lie, Krey & Hardy
nu / n ovn ^
North Eastham, AEG (I974a)
Savannah AEG (I973a)
0-1 cm Depth
n* x* S* Range
TQ s? "3? o-i on#
0-2.5 cm Depth
n x S Range
i £,(-,
1 " S T
0-3 cm Depth
n x S Range
/ 1 QI ?n i (^ i nn^I
0-5 cm Depth
n x S Range
1 "3 Q7 7 QD QQ#
7 ^? "17 ?Q- Q1 ^
*i rtT 97 TQ "1 Hfl^
1 ftl
-| y 7
7 AT 7 /rt 7^^
0-15 cm Depth
n x S Range
41 99 5 76-100$
y 7Q ?? /A QS^!
72 Ql )
1. Depth intervals are missing from several profiles. The interval was
0-1.3 cm versus 0-1 cm. Deposition was calculated from the original
data by assuming a bulk density.
2. Most of the profiles indicated undetectable plutonlum levels below 15 cm.
3. Excludes two values of 38 and 46.6%. These values give x" = 90; S = 20.
*n = number of samples
*x = mean Pu in increment, as percent of total
deposition
*S = standard deviation
CO
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CO
-------
370
0.02 pCi/g. This then indicates 100 percent of the
activity was in the first centimeter of soil.
If it is postulated that all the samples contain 0.01 pCi/g
(about one-half the nominal MDA), the following profile is noted;
-
Depth
(cm)
0-
1-
3-
7-
15-
1
3
7
15
23
Bliss
(PCi/g)
0.02
0
0
0
0
Postulated
PCi/g
0.
0.
0.
0.
0.
02
01
01
01
01
Calculated
nCi/m *
0.
0.
0.
1.
1.
3
2
5
2
2
Postulated Bliss
Cum % Cum %
9
15
29
65
100
100
-
-
-
_
* Calculated by assuming soil density of 1 g/cm3 from
0-5 cm and 1.5 g/cm3 from 5-23 cm.
The postulated values differ from Bliss1 estimates, for this
extreme example, by over a factor of 10. If a level equal to the
MDA were postulated, the difference would be a factor of 20. The
assumption of zero for MDA values can easily account for vari-
ances of tens of percent in the cumulative deposition. With a
lower MDA, this effect would decrease.
The following items summarize specifics from Bliss (1973):
1. A large fraction of the total plutonium is generally in
the top centimeter of soil.
2. The top 5 cm of soil generally contains over 90 percent
of the detected activity.
3. Excluding one sample (Moapa-1), whose values are at or
near the MDA, 50 percent or more of the detected
activity is in the top 3 cm of soil.
Gilbert and Eberhardt (1974) summarize profile data from
Areas 5 and 13 on the NTS. The following observations can be
drawn from their data:
1. Thirteen of 15 profiles indicated over 90 percent of
the detected plutonium was in the top 5 cm for desert
24
-------
371
pavement areas. The other two areas gave values of 38
and 47 percent.
2. The average of the 13 values is given in Table 5. The
mean for all the values is 90 percent with a standard
deviation of 20 percent.
3. The averages for Areas 13 and 5 are similar. However,
if the two low values are included, the mean for
Area 13 is lower than that for Area 5. The two low
values also cause a large increase in the standard
deviation.
4. The authors conclude that most of the profiles have
greater than 95 percent of the plutonium in the top
5 cm. The actual data are not presented, so the
presence and treatment of MDA values cannot be
assessed.
5. The authors noted a trend toward a decrease in the
plutonium:americium ratio with depth.
Krey and Hardy (1970) present profile data for Rocky Flats,
New York City, and Waynesville, Ohio. The following points are
noted:
1. Only about 62 percent of the plutonium was found in the
top 5 cm.
2. As much as 60 percent was found below 5 cm.
Poet and Martell (1972) report data for the Rocky Flats
area. Their profiles generally extended to only 10 cm or less;
and several increments are missing in the reported data. Fur-
thermore, the data were only reported in units of dpm/g. The
data were transformed to units of nCi/m2 by multiplying by the
incremental depth of the sample and a postulated bulk density.
The density from 0-5 cm was assumed to be 1 g/cm3 (based on Poet
and Martell, 1972, and random estimates derived from Krey and
Harty, 1970). A density of 1.5 g/cm3 was used for samples below
5 cm (estimated from Krey and Hardy, 1970).
Table 6 (data from Poet and Martell, 1972) indicates general
uncertainties in the data as a result of the sampling techniques
for the profiles (fractions of a centimeter to a centimeter), the
previously mentioned transformation assumptions, point-to-point
variations, etc.
25
-------
372
TABLE 6. COMPARISON OF SURFACE AND PROFILE SAMPLES
Estimated cumulative
Profile deposition based on
Depth depth profile
Estimated deposition
based on I cm-deep
surface sample*
Location
J
K
I
(cm)
0-
0-
0-
0-
0-
0-
0.
1.
0.
1.
0.
0.
3
3
3
3
3
7
(nCi/m2) (nCi/m2 )
6.
14.
6.
4.
0.
0.
27
06 5.18
78
01 3.97
12
21 7. 75 (Taken prior
to profile)
0-0.7 plus
1.3-2.5
0.45
* Different data from profile sample
The variations between surface samples and profile samples
from similar depths range from over two to greater than an order
of magnitude. Poet and Martell (1972) note a large build-up of
soil from wind erosion at Site I subsequent to taking these
samples, which probably explains the apparent discrepancy for
that site. However, it should be emphasized that this was not
noted when the samples were first taken. This indicates the
problems in taking characteristic samples--hindsight helps.
The following items characterize the Poet and Martell data:
1. About 52 percent of the detected plutonium was found in
the first 1.3 cm of soil.
2. About 69 percent was found in the top 2.5 cm of soil.
3. About 83 percent was found in the top 5 cm of material.
Given the calculated standard deviations, the range and
limitations of the data, and the assumptions necessary
to transform the data, the value of 83 ± 231 for Poet
and Martell is considered similar (not statistically
different even at low probabilities) to the value of 62±
\1\ for Krey and Hardy.
26
-------
373
Data for the Trinity, New Mexico site are based on four
samples taken in November 1973. The data will be published in a
future ORP-LVF report. The concentrations ranged up to 1 pCi/g
and 47 nCi/m2.
Since actual MDA values were reported, the concentration was
postulated to be equal to the MDA. The percentage of total
deposition for 0-15 cm becomes 78 percent with a standard error of
16 percent. These values are essentially indistinguishable
statistically.
Data from the Savannah River plant were transformed from
pCi/g to nCi/m2 as indicated previously. All but one of the
profiles indicated values below the MDA for strata below 15 cm.
Thus, the first value below the detectable limit was set equal to
the MDA.
The profile from North Eastham, Mass. (AEC, 1974b) is from a
background location.
The most general conclusion that can be drawn from the
summary of profile data in Table 5 is that the initial phase of a
soil sampling program should include profile samples to charac-
terize the area. Further, 5 cm is a prudent minimum depth for
surface samples.
A non-weighted average of the values in Table 5 indicates
that 721 ± 18% (1 sigma) of the activity is above 5 cm. Given
the potential for bias in the various groups of data, a non-
weighted mean appears to be reasonable. If the values in the
table are weighted by the number of results represented by each
value, the average is 83 percent.
Table 7, taken in part from Krey (1974) compares some of his
data with that from Poet and Martell (1972). Krey notes that
Poet and Martell's data are generally low by a factor of 10.
This evaluation is based on Poet and Martell's data for the top 1
cm of soil, and Krey's data for a 20 cm sampling depth.
It should be noted that these data are very difficult to
compare due to the difference in sampling depth, and possibly
more importantly, Poet and Martell only report their data in
pCi/g. If a surface soil density of 1 g/cm3 (suggested by Poet
and Martell, and used by Krey for the comparison) is used for the
first 5 cm, and 1.5 g/cm3 for the 5 to 15 cm increment, some of
the Poet and Martell data can be related to the same general
depth used by Krey (1974). Three values are presented in Table
Poet and Martell (1972 and 1974) note that their objective
was to detect the recent deposition of plutonium and indicate an
inhalation hazard - thus their choice of a shallow sampling
depth. In any case, although the original data in Table 7
27
-------
314
indicate a significant disagreement between the two sets of data,
the data for similar sample depths are generally compatible.
TABLE 7. COMPARISON OF PLUTONIUM SOIL SAMPLING DATA
Poet and Martell Data Krey § Hardy Estimate
Site
A
B
C
I
J
K
L
M
N
V
V
W
Z
(nCi/m2) (nCi/m2) Profile
1 cm surface profile depth
sample data (cm)
5.8
10
61
0.41
0.26
7.7 3 14
5.4 15 10
4.0 11 2.5
0.52
1.7
6.0
1.4
2.4
0.15
0.84
(nCi/m2)
15
35
35
11
11
4
20
14
17
17
30
4
8
17
4
It appears, based on the comparisons in Table 7 of the Poet
and Martell and the Krey data, and the similar tabulation in
Table 6, that a 1-cm sample depth results in a large variation of
the data. This is reflected by the large standard deviation
noted in Table 5.
Discrete Particulate Material
Various authors (Poet and Martell, 1972, and Sill, 1971)
have related variations between samples to discrete particles,
whereas other authors relate variations to inadequate sample
collection and aliquoting techniques (Krey and Hardy, 1970 and
1974). Sill (1971) and Sill and Hindman (1974) emphasize the
limitation of various analytical techniques for complete
28
-------
375
dissolution of refractory plutonium particles. They not only
indicate concern with insoluble refractory material in the origi-
nal sample, but also with the formation of refractory material
during sample preparation. This section is only concerned with
the sampling implications of discrete particles. The analytical
implications will be dealt with in another section.
Plutonium contamination in the environment does not appear
to be in the form of discrete particles composed of plutonium
oxides. Rather, soil and air particles containing plutonium
appear to be composed of natural particles with plutonium oxides
generally dispersed in the particle or natural particles agglom-
erated with one or more plutonium oxide particles (Nathans and
Holland, 1971, and Bretthauer et al., 1974). The actual char-
acteristics of the particles is expected to vary depending on the
source of formation and release (e.g., plutonium in oil leaking
from drum at Rocky Flats, and explosive detonations at NTS).
Table 8 indicates characteristics for various size particles.
TABLE 8. PLUTONIUM PARTICLE CHARACTERISTICS
Diameter
Isotope (ym)
239Pu 0.1
1
1.5
2
5
pCi per
particle
0.000325
0.325
1.096
2.60
40.59
particle
per pCi
3076
3.077
0.912
0.385
0.0246
Particle per
gram of soil
for 0.1 pCi/g
308
0.308
0.091
0.039
0.0025
Particle per
930 cm2
@ 1 nCi/m2
286,000
286
84.8
35.8
2.29
JOPu 0.1
1
1.5
2
5
0.09
90.99
307
728
11,370
11.1
0.0110
0.0033
0.0014
8.8E-5
1.1
0.0011
0.00033
0.00014
8.8E-6
1021
10.2
0.30
0.13
0.00
Ettinger et al. (1967), Mishima and Schwendiman (1970),
Kelkar and Joshi (1970), Molen and White (1967), Sherwood and
Stevens (1965), Hunt (1971), Mishima (1964), and Kirchner (1966)
present data on particle size distributions expected and observed
around various types of plutonium operations and accidents. The
mean sizes vary from less than one to tens of micrometers
(Mishima, 1964, and Mishima and Schwendiman, 1970). The most
29
-------
376
probable geometric mean sizes for release appear to be around 1
micrometer, with geometric standard deviations of about 1.5 to 3.
Nuclear explosions apparently produce particles a few millimicro-
meters in diameter (Klement, 1965).
Although the agglomeration of plutonium particles to soil
and dust particles changes the basic size distribution, the
activity per aggregate particle should relate to the original
plutonium particle or particles. Thus, for samples near facili-
ties associated with plutonium releases, it is possible that the
contamination is composed of two or more particle size distribu-
tions (worldwide fallout and facility) with one of the distribu-
tions in the micrometer size range. Thus, as noted by Sill
(1971), the deposition near such facilities may be heterogeneous,
when viewed from one-, 10-, or even 100-g samples. Table 8 shows
the number of particles in a sample of given size.
If samples are based on a significant fraction of a 1000 cm2
area (929 cm2 per ft2) the homogeneity of plutonium deposition
within the area is less critical than is the homogeneity within
the sample aliquot taken for actual analysis.
Table 9 presents a set of results from Sill (1971). Geo-
metric means, X, and geometric standard deviations, S, have been
calculated for the various groups of data. The column on the
right indicates the ratios of the maximum to minimum values
for the 95 percent confidence range. The first two samples were
collected from an area that should have only been exposed to
global fallout. The values for the duplicate analyses reflect
expected analytical variations (Sill, 1971). It should be noted
that the background concentrations varied by a factor of two.
This could possibly relate to different sample depths, in which
case the deposition numbers (nCi/m2) might have less variance.
The third through seventh samples (Table 9) were collected
downwind of a facility where there was a known release. This is
evident in the observed plutonium concentrations and general
increase in the ratio of the 95 percent confidence limits, which
indicates more heterogeneous distribution. Sample 7, which was
43 miles downwind, is an exception to both the concentration and
heterogeneous distribution comments. Sample 4, although eleva-
ted, also indicates r fairly uniform distribution. Samples 8 and
9 are from another facility with a known release. The larger
range for Sample 8 is due to only one result. The general
scatter in the duplicate results for Sample 9 and the range in
the 95 percent lim cs reflect that it was collected near the
facility, apparent / in an area of heterogeneous deposition.
Many of the variations in Table 9 can be accounted for by
micrometer-size particles of Pu02._ The activity of plutonium
particles is proportional to the diameter cubed of the particle.
Thus, using data from Table 8, the high result for Sample 3
(Table 9) could have been due to about one 1-micrometer particle
30
-------
TABLE 9. REPRODUCIBILITY OF ANALYSES
USING 10-GRAM ALIQUOTS OF PREPARED SOILS
(From Sill, 1971)
Number
1
2
3
4
5
Measured
Pu-239
(dpm/g)
0.
0.
0.
0.
0.
0.
0.
0.
0.
1.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
110
116
112
101
111
060
050
054
063
59
56
94
68
62
56
57
044
077
042
055
±
±
±
±
±
+
+
+
+
+
+
+
+
+
+
+
±
+
+
+
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
009
010
012
008
008
007
007
008
007
04
02
03
03
02
02
02
006
008
005
010
Ratio of Upper
Location or t and Lower 95%
Type Sample In xa In S (95%) x Confidence Limits
General
General
2 miles
wind of
ity with
release.
2 miles
wind of
ity with
release.
16 miles
wind of
ity with
release .
Bkgd. -2.21 0.051 2.776 0.11
Bkgd. -2.87 0.104 3.182 0.056
down-
facil-
Pu -0.141 0.456 3.182 0.87
down-
facil-
Pu -0.540 0.054 4.303 0.58
down-
facil-
Pu -2.96 0.245 2.776 0.052
1.3
1.9
18
1.6
3.9
0.047 ± 0.006
CO
<5
-------
ro
TABLE 9. REPRODUCIBILITY OF ANALYSES
USING 10-GRAM ALIQUOTS OF PREPARED SOILS
(From Sill, 1971)
(Continued)
Number
6
7
8
9
Measured
Pu-239
(dpm/g)
0.079 ±
0.058 ±
0.071 ±
0.29 ±
0.051 ±
0.066 ±
0.056 ±
0.052 ±
0.071 ±
0.22 ±
0.051 ±
0.059 ±
0.35 ±
0.78 ±
1.73 ±
0.26 ±
0.009
0.008
0.009
0.01
0.007
0.009
0.006
0.006
0.008
0.02
0.007
0.006
0.02
0.04
0.04
0.01
Ratio of Upper
Location or t and Lower 951
Type Sample In xa In S (951) x Confidence Limits
17 miles down-
wind of facil-
ity with Pu -2.32 0.731 3.182 0.099
release.
43 miles down-
wind of facil-
ity with Pu -2.88 0.117 3.182 0.056
release.
50 miles down-
wind of facil-
ity with Pu -2.49 0.665 3.182 0.083
release.
100 yds. down-
wind of facil-
ity with Pu -0.524 0.852 3.182 0.592
release.
104
2.1
69
227
a The analytical error estimates have not been considered in
the statistical summarization of the data.
CO
-------
379
per gram, or a single particle having a diameter of about 2.5
micrometers in the total 10-gram sample, above the global back-
ground.
As part of the NAEG program, a set of 20 soil samples were
collected from Penoyer Valley, Nevada, about 20 miles northeast
of the NTS. The samples were split into duplicates and two
aliquots were taken from each duplicate. The scatter of results
from these 80 samples was such that the variations between the
four positions from an individual site and the 80 samples could
not be related to a rational explanation of sampling or analyti-
cal errors.
In an attempt to resolve this problem, portions of the
sample from one site were split for inter-laboratory analyses.
Table 10 shows replicate aliquot analyses of the sample by three
laboratories. Each laboratory used its standard analytical
method to analyze aliquots of less than 10-mesh desert soil.
Most of these data were published by Bliss (1973). Although the
sample preparation and analysis techniques vary somewhat between
the three labs, they are basically the same. The analyses were
all done by the basic acid dissolution technique (HCL, HF, and
HNO J. The specific techniques vary, in part, because of the
different sample sizes.
Although the geometric means from the different labs vary,
all of the 95 percent confidence levels (C.L.) have a significant
overlap. These data illustrate the dramatic decrease in the
ratio of the extremes of the 95 percent confidence range with the
increase in sample size.
The geometric mean and standard deviation for the 80 repli-
cate results, and the 95 percent C.L. estimates and their ratios
are given in Table 11. The mean and C.L. estimates and their
ratios include the values from Table 10. This would be expected,
since the group of 80 replicates is based on a sample from four
sites, whereas the interlaboratory samples came from one of the
four sites. A frequency distribution table and probability plot
for the 80 values is shown in Appendix C.
Means, confidence levels, and ratios of the C.L. are given
for three other groups of data in Table 11 (Bliss, 1973). The
samples from Baker, California and Kingman, Arizona and northwest
of NTS indicate background values and have much lower C.L. ratios
than the other two samples. The Baker and Kingman group of data
represents several sites, and thus would be expected to have a
larger range than the data from ^he location northwest of NTS.
33
-------
TABLE 10. COMPARATIVE ANALYSES OF PLUTONIUM-239 IN SOIL
Lab
EPA
Aliquot
Size (g)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Pu-239
(pCi/gm)
0.23
0.24
0.27
0.37
0.30
0.40
0.42
0.53
0.67
1.0
1.2
1.4
3.0
5.3
Ratio of Upper
Range and Lower 95%
In x In S x 95% C.L. Confidence Limits
0.405 0.952 0.67 0.085-5.21 61
(n = 14; t = 2.16)
REECo
10
10
10
10
10
10
10
10
10
10
0.66
0.90
1.3
1.4
1.5
2.0
2.6
3.3
4.4
5.2
0.646 0.674 1.9 0.415-8.76
(n = 10; t = 2.26)
21
CO
CO
CD
-------
TABLE 10. COMPARATIVE ANALYSIS OF PLUTONIUM-239 IN SOIL
[Continued)
Ratio of Upper
Aliquot Pu-239 _ _ Range and Lower 951
Lab Size (g) (pCi/gm) In x In S x 95% C.L. Confidence Limits
LLL
7 c; A f.
0.97-10.32 11
2.33-10.4 4.5
25
25
25a
25a
100
100
100a
100a
1.9
4.6
3.3
3.5
4.1
5.5
4.0
6.5
1.078
1.226
1.565
1.635
0.6312
0.0415
0.213
0.3374
2.9
3.4
4.8
5.1
a Aliquot received additional grinding and blending prior to analysis.
CO
OO
-------
382
TABLE 11. PERTINENT STATISTICS FOR Pu-239 RESULTS FROM
SELECTED SAMPLE GROUPS (from Bliss, 1973)
Location and Units of Activity
Baker, CA and Penoyer Valley Northeast of Northwest of
Kingman, AZ Replicate Site NTS (nCi/m2) NTS (nCi/m2)
(nCi/m2) (pCi/g)
No. of Results
In X
In S
X
Lower 951 C.L.
Upper 951 C.L.
Ratio :
Upper to Lower C.L.
27
0.068
0.869
1.071
0.188
6.086
32
80
0.053
1.336
1.054
0.0729
15.245
209
•100
1.881
1.261
6.557
0.527
81.638
155
35
0.584
0.572
1.793
0.571
5.627
10
The sample from northeast of NTS is at the extreme of or
above background. The Penoyer Valley results are generally
indicative of roughly 10 nCi/m2 or higher. Thus, both of these
samples appear to contain dispersed global fallout, plus rather
discrete NTS fallout.
The variation in the analyses of these samples is relatable
to a variance of one or several particles, of one to several
micrometer diameter, per gram of sample. The actual numbers
depend on the particle size and sample size of concern. The
potential variation in results for 1-gram samples is particularly
obvious. A single one-micrometer particle can cause a multiple
variance in results. This would give strong credence for taking
a minimum sample aliquot of 10 grams for analysis.
Little et al. (1973) present a limited amount of data for
soil grain size in the Ro.cky Flats areas and the percent of
plutonium associated with the various grain size increments. The
plutonium concentration, pCi/g, for two samples is inversely
proportional to the soil grain size, 0.1 to 5 mm. Tamura (1975)
presents similar data (see the end of this section).
The heterogeneous deposition of plutonium-238 presents an
even greater problem than for plutonium-239, because the specific
36
-------
383
activity of plutonium-238 is about 280 times that of plutonium-
239. Furthermore, the concentration of plutonium-238 in the
environment is normally much lower than that of plutonium-239.
Plutonium-238 background levels are roughly 1 fCi/g for soil
samples several cm deep (Krey and Hardy, 1970, and Robinson et
al., 1975). Thus, from Table 8 it can be seen that a plutonium-
238 dioxide particle of one micrometer diameter in a 10-gram
sample can give a value of 9 pCi/g, or four orders of magnitude
above background. Even a 0.1-micrometer particle in a 10-gram
sample gives a value of 9 fCi/g.
Robinson et al. (1975) report results of two programs where
samples were split between Mound Laboratory and EPA. The ratios
of the results of these programs are shown in Table 12. The
samples collected by EPA were split in the field. The samples
taken by Mound Laboratory were first dried and ground to less
than 20-mesh particle size. It is evident from Table 12 that the
samples split after mixing gave more comparable results than did
those which were split in the field.
37
-------
384
TABLE 12. INTERLABORATORY COMPARISON OF MOUND LABORATORY
AND EPA RESULTS OF PLUTONIUM-238 IN SOIL AND SEDIMENT
(From Robinson et al., 1975)
Samples Split in Lab
Code
EA1
EB1
EC1
EDI
EE1
EF1
EG1
EH1
Ell
EJ1
FA1
FE1
GA1
HA1
IA1
JA1
KA1
LAI
CE1
QE1
a Mean
b Mean
c Mean
Mound
fnCi/gl
0.0001 ± 0.0001a
<0.0001a
0.0029 0.0011
0.0009 ± 0.0004
0.425 ± 0.024a
1.03 ± 0.05C
0.0098 ± 0.0027
0.0238 ± 0.0053
<0.0001
0.0010 ± 0.0005
0.0094 ± 0.0026
0.0138 ± 0.0025b
0.0004 ± 0.0002
0.0047 ± 0.0016
0.0020 ± 0.0008
0.0007 ± 0.0004
0.0309 ± 0.0065
0.0096 ± 0.0027
0.0302 ± 0.0064
1.00 ± 0.09
of quadruplicates
of duplicates
of triplicates
EPA Ratio of Results
(nCi/g) Mound/EPA
0.00011b
0.00012b
0.0048
0.0011
0.440
1.13b
0.0108
0.026
0.00098
0.0011b
0.0085C
0.0181
0.00048
0.0051
0.0025
0.0007
0.027
0.0109
0.024
0.920
0.91
< 0.83
0.60
0.82
0.97
0.91
0.91
0.92
< 1.02
0.91
1.11
0.76
0.83
0.92
0.80
1.00
1.14
0.88
1.26
1.09
n^HT
3T=0.929
S=0.147
38
-------
385
TABLE
AND
Code
EPA-17
EPA-18
EPA-1
EPA -6
EPA-20
EPA-14
EPA-15
EPA-3
EPA-13
EPA -7
EPA-12
EPA -2
12. INTERLABORATORY COMPARISON OF MOUND
EPA RESULTS OF PLUTONIUM- 238 IN SOIL AND
(From Robinson et al., 1975)
(Continued)
Samples Split in
Mound
(nCi/g)
0.284 ± 0.035
0.280 ± 0.035
0.165 ± 0.023
0.0052 ± 0.0017
0.0011 ± 0.0005
0.0009 ± 0.0004
0.0009 ± 0.0004
<0.0001 ± 0.0001
<0.0001 ± 0.0001
<0.0001
<0.0001
<0.0001
Field
LABORATORY
SEDIMENT
EPA Ratio of Results
CnCi/g) Mound/EPA
0.047
0.060
0.230
0.0038
0.0019
0.00044
0.00096
0.00039
0.00010
0.00044
0.00019
0.00012
6.04
4.67
0.72
1.37
0.58
2.05
0.94
<0.26
<1.00
<0.23
<0.53
<0.83
n=12
S=l]84
ALGAE SAMPLES
EPA -9
EPA-21
0.111
0.0024
0.079
0.00088
1.41
2.73
n=2
T=2.07
S=0.93
39
-------
386
PARTICLE SIZE DISTRIBUTION OF PLUTONIUM IN SOIL
Although inhalation is generally considered to be the pri-
mary intake pathway for plutonium, soil is generally considered
to be the primary reservoir of environmental contamination*
Thus, there is a need to relate soil sample results to potential
or actual airborne concentrations. The first part of this
section has addressed techniques primarily intended to quantitate
the amount of plutonium in soil. Thus, the emphasis has been to
take samples of a reproducible and sufficient depth in order to
assess the total plutonium inventory. Sampling for resuspendible
plutonium requires different priorities and considerations.
Presently applied techniques include a one-eighth inch depth
sample by the State of Colorado, 1-cm depth samples by Poet and
Martell (1972), and techniques using sticky paper placed in
contact with the soil surface (Volcnok, 1971).
More recently, McLendon et al. (1975) published results
where a vacuum cleaner type instrument was used to collect the
resuspendible material from the area of the sample head. This
technique appears to have merit, but sample results have not been
directly related to air concentrations.
Johnson et al. (in press) proposed that the less than 5-
micrometer (density 11 g/cmj; i.e., 17 micrometer density
1 g/cm3)*size material that can be swept from the soil surface be
used as an indication of inhalation hazard. The sample fraction-
ation procedure includes breaking the soil down to basic discrete
particles. Thus, the technique would appear to reverse the
"weathering" effect that decreases the relative resuspendibility
of old versus newly deposited contamination (Anspaugh et al., 1975)
There presently is no accepted technique for measuring
resuspendible material from soil. However, data from several
studies allude to soil being associated with various particle
size fractions (Johnson et al., Little et al., 1973, and Tamura,
1975). Since resuspensiou is dependent on the soil particle
size distribution (Anspaugh et al. 1975), as well as other
factors, the size distribution of plutonium in soil is con-
sidered to be pertinent basic information.
The ORP-LVF obtained several samples from Rocky Flats to
independently investigate the size distribution of plutonium in
the soil. The samples were collected by the Rocky Flats Environ-
mental Research and Development Administration area office
several hundred yards downwind of the pad where the basic Rocky
Flats plutonium contamination incident originated. Although it
was originally presumed that the samples would contain less than
about 25 pCi/g of plutonium-239, they actually contained over 500
pCi/g. Thus, because of concern for laboratory contamination,
they received less extensive analysis than originally proposed.
*The use of a density of 1 g/cm is based on the definition of
the equivalent aerodynamic diameter. Conversions to equivalent
diameters in this section are based on the settling velocity
in air--see next section. .„
-------
387
A sample from about 35 miles downwind at the Trinity, New Mexico
site was also analyzed.
The Rocky Flats samples were collected in February 1976 from
the surface centimeter of soil, from an area of 2000 cm2. The
Trinity sample was collected in December 1974. It represented
the surface 2.5 cm of soil from an area of 2500 cm2.
Two Rocky Flats samples were partitioned into three separate
aliquots. The aliquots were further partitioned as described
below (the aliquots are denoted as A, B, and C in Table 13).
1. Dry sieve through 10-mesh sieve--Less than 2 mm
2. Wet sieve (not dried material) through 140-mesh sieve--
Less than 102 micrometer
3. Elute material from sedimentation column for a Stoke's
Law setting velocity of less than 3.37 x 10-3 cm/sec--
(10 micrometer at 1 g/cm3, or 6.1 micrometer at
2.65 g/cm3 ; Krumbein and Pettijohn, 1938)
The samples were prepared according to the general tech-
niques presented by Folk (1961). The following comments relate
to specific information on the sample preparation procedure:
1. Radiochemistry was performed on about 10-gram aliquots
of the samples.
2. The samples were not completely dried prior to sieving
(forms and increases the stability of conglomerates, Falk, 1961).
3- A solution of Calgon, sodium metaphosphate, was used as A
dispersing agent for the sedimentation separation (about
10 ml of a solution of 40 g/liter).
4. The material retained on the 10-mesh sieve was washed
with a solution of Calgon, and the wash included with
the less than 10-mesh material.
5. The material retained on the 140-mesh sieve during wet
sieving was then dry-sieved through the 140-mesh
sieve. Folk (1961) notes that the fines are partially
bound to the coarse material by moisture bonds during
wet sieving. The amount of material passing 140 mesh
was increased by 4 to 10 percent for the Rocky Flats
samples and 20 percent for the Trinity sample. This
material was not used in the mass balances or for
radiochemistry analysis.
41
-------
3C8
6. The "pipet aliquoting" procedure for determining the
total 'fraction of the sample less than 10 micrometer
was incorrectly done on oven-dried samples. Thus, the
results were anomolously low. The values for the total
sample fraction less than 10 micrometer are therefore
estimates based on multiple elutions from the settling
column. Various numbers of elutions indicated values
of up to 10 percent for the Rocky Flats samples. Based
on the material recovered, the total value is estimated
to be 20 percent.
7. The amount of the plutonium in the greater than 2-mm
size fraction was not determined.
The results of the study are given in Table 13. The size
fractions of less than 2 mm and 100 micrometers are based on the
sample that passed 10- and 140-mesh sieves, respectively. The
less than 10 micrometer size is passed on an equivalent aero-
dynamic diameter in air (density of 1 g/cm*).
The Rocky Flats soil had a smaller particle size distribution
than the Trinity sample. The size difference is also reflected
in the distribution of plutonium. About 50 percent of the
plutonium from the Rocky Flats samples was associated with the
less than 10-micrometer size versus about 10 percent for the
Trinity sample. The specific activity of plutonium in soil
(pCi/g) appears to be generally inversely proportional to par-
ticle size. The ratio of the concentration of plutonium in the
less than 10-micrometer fraction to that in the less than 2-mm
fraction (basic soil size) was about 2.4 versus 1.8 for the less
than 100-micrometer size fraction.
The radiochemistry results indicate good reproducibility for
the preparation and analysis procedures. The only anomalous
result appears to be the value of 1580 pCi/g for 1A (less than
100 micrometer). The other results for the various size frac-
tions are within the two-sigma counting errors.
The mass fractions also show reasonable reproducibility for
the sample preparation procedures. The mass of the less than 10-
micrometer size fraction varies because a varying number of
sedimentation runs were done for each sample. The fraction of
material in the less than 10-micrometer size range is based on
the maximum amount of material recovered (sample 2A) and a
subjective observation that about half of the available material
was recovered.
The results are compared to those of other investigators in
Table 14. In general, the Trinity results for mass fractions are
similar to those of Tamura (1975) for NTS (similar sandy soils).
The results of Johnson et al. show reasonable agreement with the
ORP-LVF results, especially considering the differences in the
treatment techniques. Johnson et al. used hydrogen peroxide to
42
-------
TABLE 13. SOIL MASS AND PLUTONIUM ASSOCIATED
WITH VARIOUS PARTICLE SIZE FRACTIONS OF SOIL
Mass and Activity of Material
Fraction of Material Passing 10 Mesh Sieve
Sample
and Units
Trinity (g)
(PCi/g)
(PCi)
Rocky Flats
1A (grams)
(PCi/g)
(pCi)
IB (grams)
(PCi/g)
(pCi)
1C (grams)
CpCi/g)
(PCi)
Rocky Flats
2A (grams)
(PCi/g)
(pCi)
2B (grams)
Greater
Than 2 mm
341
-
133'
-
-
140
-
-
169
-
-
93
-
-
88
Less Than
2 mm
1147 ,
1.3 ± 0.2b
1468
502
635 ± 91
3.19 ES
487
634 ± 94
3.09 ES
568
593 ± 83
3.37 E5
591
642 ± 95
3.79 ES
462
Less Than
100 pro
578
1.9 ± 0.10
1087
188
1580 ± 160
2.96 E5
178
1050 ± 130
1.87 ES
203
939 ± 113
1.91 ES
319
1030 ± 120
3.30 ES
213
Less Than Less Than
10 ^m 2 nun
34 1.0
2.0 ± 0.10
138a
(68)
46
1680 i 160
1.69 E5a
(7.73 E^)d
44
1730 t 190
1.69 E5a
(7.61 E**)d
20
1460 ± 160
1.66 E5a
(2.92 EI+)
71
1590 ± ISO
1.88 E5a ,
(1.13 E5)d
40
Less Than
100 ym
0.50
1.5
0.74
0.38
2.5
0.93
0.37
1.6
0.61
0.36
1.6
0.57
0.54
1.6
0.87
0.46
Less Than
10 uma
0- 06
1.5
0.09
0.2
2.6
0.5 ,
(0.2<*)d
0.2
2.7
0.6
(0.25)0
0.2
2.S
0.5
(0. 087)"
0.2
2.0
0.5 ,
(0.30)d
0.2
Samples not analyzed
2C (grams)
(pCi/g)
Rocky Flats
(pCi/gl
(pCi)
72
Average (grams)
490
838 ± 142
670 ± 100C
216
Other samples
1150 ± 300
38
not analyzed
1.0
1620 ± 120 i.o
1.0
0.44
0.43 i 0.07
1.8 ± 0.5
0.75 ± 0.18
0.2
0.2a
2.4 ± 0.3
0.5
* Six percent of the Trinity soil mass and 20 percent of the Rocky Flats soil mass were assumed to be in this size.
D Two sigma counting errors.
c Standard deviation.
d The value in parenthesis is the actual quantity of picocuries or fraction thereof recovered in the less than 10 urn fraction. See footnote a
and item 6 on page 42 of tne text.
En indicates 10m; e.g. E5=10S
CO
CO
CO
-------
TABLE 14. SOIL SIZE MASS AND ACTIVITY FRACTIONS
OF VARIOUS INVESTIGATORS
Investigator
Fraction of
Sample Tata] Sample
Location Greater than 2 mm
(mass basic)
Ratio of the sample mass and
plutonium concentration in the
less than 2 mm fraction which was
in the less than:**
100 11 m fraction 10 um fraction
(mass) (activity) ^mass) (activity)
Depth Ultrasonic
of sample Dispersion
( cm ) Used
Remarks
ORP-LVF
Tamura (1975)
ORP-LVF
Johnson et. al.
Little et. al. (1973)
Tamura (1975)
Tamura (1975)
Trinity
NTS #1
#1
#2
#2
Rocky Flats
RFP (4 samples)
(4 samples )
( 7 samples )
RFP ( 1 Bkgd. )
Rocky Flats
Rocky Flats
ORNL
Mound Lab
Ohio
0.
0.
0.
0.
0.
—
—
—
0.
0.
0
0
0
0
23
20
20
027
027
31
40
0.50
0.34
0.40
0.45
0.51
0.43i0.07
—
—
—
0.05
0.13
1
1
0.87
0.91
1.5
—
—
—
1.8 ± 0.5
—
—
—
1.8
•v 4
—
—
—
—
0.05
0.033
0.083
0.011
0.086
0.2 ± 0.1
0.28±0.12
0.25±0.04
0.36+0.09
0.49
—
—
0.30
0.38
0.30
0.37
1.5
—
—
—
—
2.4 ± 0.3
5 i 50**
3 ± 2rj%*
2 ± '>0%*
u6 *
—
—
—
—
—
—
2.5
5
5
5
5
1
surface.
dust
surface
dust
3
3
7.5
7.5
Core
Core
No
No
Yes
No
Yes
No
YesN
Yesl
Yes \
YesJ
No
Yes
No
Yes
Desert Pavement
Desert Pavement
Desert Mound
Desert Mound
4 Samples
< 17 um, Ig/cm ,
used.
H202 to break bonds '
Dry sieved, after
Dry sieved
Dry sieved
Flood plain silt
Flood plain silt
Silt
Silt
drying
' The Plutonium concentration in the total sample is not based on the sample of material. Rather it is based on Johnson's et. al.
adaption of isopleths from Krey and Hardy (1970).
The values were estimated by dividing the average plutonium
in soil concentrations, for given areas, for particles less than
5 micrometers in diameter (density 11 g/cm ) from Johnson et al.
by the plutonium concentration in the total soil estimated from
isopleths that Johnson et al. adopted from Krey and Hardy (1970).
The error term is the standard deviation from averaging the
results.
The reference to a 17 um diameter relates to the equivalent
aerodynamic diameter in air.
**Mass refers to the mass fraction of material (i.e., g/g).
Activity refers to the ratio of plutonium concentrations (i.e.,
pCi/g:pCi/g).
CO
to
CD
-------
391
destroy any organically-bonded conglomerates, and ultrasonic
mixing to further destroy conglomerate bonds. The intent of the
ORP-LVF treatment was to preserve the basic conglomerates that
would not disperse in a water suspension.
The results of Little et al. (1973) indicate a relatively
small fraction of material in the less than 100-micrometer size
class. This may be due to the difference in samples, or to oven-
drying the sample (which stablizes the conglomerates) and dry
sieving versus wet sieving the sample at 140 mesh.
The results of Tamura (1975) from Mound Laboratory, Ohio and
Oak Ridge National Laboratory (ORNL) are for silt samples. Thus,
it was expected that a large fraction of the material would pass
140 mesh.
45
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332
AIR SAMPLING TECHNIQUES
Inhalation is the primary human intake pathway for pluto-
nium; thus air sampling data are the preferred environmental data
for inhalation exposure evaluation. In order to assess inhala-
tion hazards from soil sampling, it is necessary to postulate
factors for resuspension and atmospheric transport of plutonium.
Air sampl'ing provides direct evaluation of atmospheric concentra-
tions of plutonium from airborne releases prior to deposition,
and a direct measure of resuspended material. Furthermore, soil
samples only provide results for discrete points within poten-
tially heterogeneous areas--whereas air sample results indicate
the average concentration for plutonium over a general area.
Air sample results are not always generally applicable to
human exposure or even to actual atmospheric concentrations of
the sampled material. For plutonium, the emphasis is on the
particulate material. Thus, there are the concerns of:
a. Isokinetic sampling--sampling at the air stream
flowrate so that the particle size distribution of the
sample is representative of that in the atmosphere.
b. The air sampler face velocity or linear flowrate
should be representative of human biophysical
parameters. If the sampler inlet configuration and
linear flowrate are not properly designed, the sampler
will not obtain a sample of the representative
particle-size distribution inhaled by man. Intake and
deposition within the respiratory tract is dependent on
the equivalent aerodynamic particle-size distribution
of the inhaled material.
c. If the sampler is of the filtration type, the filtra-
tion material must be such as to provide retention of
the airborne material at the sampling flow-rate. The
dust-loading pressure drop characteristics of the
filtering material must be considered also.
d. The sampler must be properly located so that it obtains
a representative sample of the atmosphere, i.e., not on
the leeward side of buildings or hills.
Given the above comments, it becomes apparent that a random
air sample does not necessarily provide all necessary hazard-
assessment information. Sampling parameters must be defined.
46 .
-------
393
There are several reference works on aerosol-sampling
technology (Mercer, 1973). Thus, this section will not attempt
to discuss the physics of aerosols. This section will focus on
aerosol-sampling techniques pertinent to assessing airborne
concentrations of plutonium. The emphasis will be on techniques
designed for adequate flowrates and sampling times for assessing
environmental concentrations (less than 0.1 fCi of plutonium per
cubic meter of air). A minimum detection level of about 20 fCi
is required on the final separated sample. Assuming a chemical
yield of 50 percent, and given the uncertainties in sample
analysis, a reasonable minimum required activity in the sample is
80 fCi. The necessary sampling rate is equal to the minimum
required sample activity divided by the product of air concentra-
tion and sampling time. Thus, assuming an air concentration of
0.05 fCi/m3, a sample volume of 1600 cubic meters is necessary.
Therefore, for a flow-rate of one cubic meter per minute, the
sampling time required is 1600 minutes, or about one day.
Work by Bagnold (1954) and Chepil and Woodruff (1963),
referenced by Anspaugh et al. (1975) and Buck et al. (in press),
indicates that saltation and surface creep account for the
majority of airborne soil movement. These processes generally
include soil particles from 50-500 micrometers and 500-2000
micrometers, respectively. Thus, although these processes
generally move particles near the ground (within one meter), air
samples should be scrutinized to insure that they do not contain
large amounts of material above the respirable particle-size
range (5 to 10 micrometers).
The phenomena of resuspension is generally related to
particles ranging up to 50 micrometers. Thus, only a fraction of
windborne material related to resuspension is respirable, and
resuspension accounts for less than 10 percent of airborne soil
movement.
PHYSICAL CHARACTERISTICS OF AEROSOLS
The physical characteristics of airborne particles are
generally described by their aerodynamic characteristics. In
simple terms, the forces acting on a particle are proportional to
the density of the particle and the square of the diameter of the
particle for particles of the density and diameter of interest
for plutonium inhalation (Mercer, 1973; Morrow, 1966; and ICRP,
1972).
Deposition of plutonium-related particles greater than
10-micrometer aerodynamic diameter in the pulmonary section of
the lungs is essentially zero (Mercer, 1973 and Morrow, 1966).
The aerodynamic diameter relates to the equivalent diameter of a
particle with a density of 1 g/cm3 which responds similarly in
air streams to the subject particle.
47
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334
The terminal setting velocity of a particle can be described
as (Eisenbud, 1963) :
V = 0.003 pd2
Where V = velocity (cm/sec)
p = density of particle (g/cm3)
d = particle diameter (ym)
This equation is applicable for particles with streamline
motion (e.g., density less than 10 g/cm3 and diameter less than
50 ym or d less than HS/p1^). When the diameter of a particle
is less than the mean free path of gas molecules, Stokes' equa-
tion underestimates the terminal settling velocity. This can be
corrected for by using Cunningham's modification of Stokes1
equation (Eisenbud, 1963) :
Vc = Vs[l + (1.7A/l(Td)]
Where V = corrected velocity
V = Stokes ' Law velocity
X = mean free path of gas molecules ,
about 10*5 cm at sea level.
d = particle diameter, ym
The air entering the nose is actually deficient', with
respect to the ambient air, in particles having settling
velocities similar to the inhalation face velocity and normal
wind speeds. (ICRP, 1966). The inhalation face velocity is
(ICRP, 1966):
n rnn i 15 nose meter min 0 r ,
1500 ml x mI5- x^-g-jjp x x = 2.5 m/sec
The assumptions are:
a. Tidal or inspirational volume, 1500 ml
b. Inspiration rate, 15 per minute
c. Cross sectional area of nostril, 0.75 cm2 or
1.5 cm2 for nose.
48
-------
335
The above parameters correspond to a reasonable level of
activity, somewhat equivalent to industrial workers. Basal
metabolism is about 500 ml tidal volume with 12 respirations per
minute (Comroe et al., 1963). Mild to moderate activity would
relate to 750 cm3 and a respiration-rate of 15 per minute
(ICRP, 1966).
Air sampler face velocities vary over a wide range. A
volume of 1 1/min for a 1 cm diameter filter (0.785 cm2) relates
to a velocity of 0.21 m/sec (1 ft3 /min through a 1- in diameter
filter is 0.93 m/sec). Thus, for a nominal high volume sampler
(1 m3/min for an 8 by 10 inch filter having an effective filter
area of 7 by 9 inches), the face velocity is 0.41 m/sec. If a
4 in-diameter filter was used, the velocity would be about
2 m/sec.
A nominal wind velocity of 10 miles per hour is 4.47 m/sec.
Thus, it becomes apparent that it is difficult to sample
isokinetically with conventional filter-type samplers. The high
volume sampler only has a face velocity of 2 m/sec with a
4 in-diameter filter. Even the face velocity for the human nose
is about 2.5 m/sec, or the equivalent of 5 miles per hour.
Patty (1958) indicates that the air velocity drops to about
10 percent at one diameter from the face of an exhaust vent.
Thus, given the ratio of the diameters of air samplers and human
nostrils (generally 10 cm versus less than 1 cm, respectively),
air samplers with face velocities 0.25 m/sec generally should be
equivalent to the human nose. Furthermore, the settling velocity
of a 10 ym aerodynamic equivalent particle is only about
0.3 cm/sec; i.e., two orders of magnitude less than a sampler
face velocity of 0.25 m/sec.
The above does not resolve the problem of subisokinetic
sampling rates. If the sample face is oriented downwind, there
is a definite probability of unrepresentative sampling due to an
inadequate capture velocity. Sehmel (1973) has generally
resolved this problem by placing samplers on a pivot. The
sampler orientation is then controlled by a wind-oriented cowl,
so that the sampler is oriented into the wind.
TYPES OF AIR SAMPLERS
There are several techniques for obtaining samples of the
particulate material suspended in air. They include:
1. Mass air samplers where the air stream is drawn through
a filter medium.
2. Electrostatic precipitators where the particulates are
removed from the air stream by electrostatic force.
49
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396
3. Impactors which normally are used to segregate the
particulates into various size categories. Particu-
lates are impacted on various stages (size categories)
as a result of channeling the air stream around the
impaction plane.
4. Air elutriation sampling techniques separate particles
on the basis of the settling velocity. The differen-
tial of the settling velocity and the velocity of the
air current in which the particle is moving is used to
separate particles based on their size and density.
5. Aerosol centrifuges utilize the same principle as
elutriators, except centrifugal force is used in place
of gravitational force.
Many samplers utilize several of the techniques. Andersen
impactors use several impactor stages to segregate particles into
size fractions from 1 or 2 to 10 micrometers and a filter to
collect the smaller particles. The sampler may be designed to
exclude material over 10 micrometers. Some characteristics of
the various types of samplers are discussed below.
Mass or Filter-type Air Sampler
An air mover is used to draw air through a fibrous or
membrane-type filter. Although particle sizing can be done
either through optical or audioradiographic techniques, or by
using filter packs containing filters with different size pene-
tration characteristics, normally particle sizing is not done for
filter-type samples.
Filter-type samplers come in a large range of sizes; from
personnel monitoring devices having flowrates of liters per
minute, to the high volume samplers at about 1000 liters per
minute. Anspaugh et al. (1974) report on an ultra high volume
sampler capable of flowrates of 25,000 liters per minute. This
sampler was designed to obtain samples of resuspended dust over
short periods of time.
The principal parameters for filtration-type samplers are
the flowrate, face velocity, and the filtering medium. The
flowrate determines the volume of air sampled per unit time and,
thus, in part, dictates the sampling time, assuming the amount of
material collected is near the MDA.* The face velocity affects
not only the characteristics of the aerosol drawn into the
sampler, but also the fraction of material collected by the
filter. The decision concerning filtering material must be based
on face velocity, expected dust loading, proposed analytical
techniques, particle size retention requirements, and pressure
drop characteristics.
* MDA; minimum detectable activity, see Sample Analysis Techniques
section.
50
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337
E 1 e c t r o static Pr e c ip i t at i on
This is a two-stage process. First, the particles must be
charged in a unipolar ion field. In the second stage, a strong
electric field is used to precipitate the charged particles on a
suitable collection surface (Mercer, 1973). Collection efficien
cies of 99.9 percent can be obtained for particles of 0.2 to 0.7
micrometer mass median diameter; whereas particles around 0.2
micrometer are difficult to collect because of the small charge
retained by the particle. Because of design complexities and
power requirements , electrostatic precipitators are not used
commonly in environmental sampling.
Recently, the U.S. Environmental Protection Agency
laboratory at the Research Triangle Park in North Carolina has
participated in the development of an ultra high volume sampling
system. The system is capable of flow-rates of 26 m3/min. The
particulate material is segregated into respirable and non-
respirable material by use of an electrostatic precipitator and
other techniques.
Cascade Imp actors
Cascade impactors are composed of a series o'f impactor
stages and a final filter. The units of interest generally
provide several fractional steps for particles between 1 and
10 micrometers in diameter, with the final filter collecting
material less than 1 micrometer in diameter. Cascade impactors
have demonstrated their ability to provide particle-size distri-
butions, based on the equivalent aerodynamic diameter, for
ambient levels of airborne particulate material.
A single impaction stage is composed of a plate with
precision-machined orifices followed by an impaction plate. The
impaction plate contains the orifices for the next stage. The
airstream 'flows through the orifice, and as it is impinged on the
impaction plate the airstream splits to go on through the adjoin-
ing orifices. The inertial qualities of the particles cause
those in the designed size spectrum to be impacted tin the impac-
tion plate, directly below the orifice. The deflected airstream
goes through the adjoining orifices. The orifices are of a
slightly smaller diameter than the previous stage. Thus, the
constant air volume, but smaller orifice diameter results in an
increased air velocity, with the resulting impaction of the next
size smaller particles on the following impaction plate.
Mercer (1973) presents a detailed account of the theory of
impaction units. There is not a discrete cutoff of particle size
increments with each stage. Mercer (1973, Figure 6.36), illus-
trates the general fractionation that occurs. The hypothetical
aerosol is assumed to be made up of unit density particles with a
geometric mean diameter of 10 micrometers and a geometric
51
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338
standard deviation of 2. The effective cutoff aerodynamic
diameters (ECAD) are 16, 8, 4, and 2 micrometers.
It generally is assumed that all particles collected on a
given stage have aerodynamic diameters larger than the ECAD for
that stage. A stage not only does not collect all particles
above the ECAD, but collects some particles smaller than the
ECAD. Some material is assumed to be collected that is not
collected, and some material assumed to be passed by a stage is
actually retained. These are about equal for each stage. Thus,
the actual mass per stage is approximately correct. The differ-
ences in the mass for a stage generally are less for round jets
than for rectangular jets (Mercer, 1973, p.234). The ECAD is the
diameter for a particle which has a 50 percent probability of
retention on the subject stage.
In addition to errors resulting from non-ideal design there
are several potential sources of error. These include wall loss
of material, disaggregation of particles, and rebound and re-
entrainment of deposited material.
Wall losses refer to the retention of impacted material in
the impaction stages other than at the intended impaction area.
Mercer (1973, p.235) reports wall losses ranging from 14 percent
to 2 percent for high sample volumes for a low volume sampler
(i.e. , 0.05 to 0.15 1/min).
Wall losses result from non-laminar flow between the stages.
However, the wall losses can be extenuated by rebound and/or re-
entrainment of the impacted material. Mercer(1973, p.236) notes
rebound is a serious problem if the collection surfaces are not
coated with a soft layer to cushion the impact of particles (e.g.,
if the impactor plate is used as the collection medium versus
using a filter for collecting the impacted material). He also
notes that both rebound and re-entrainment put an upper limit on
the amount of material that can be collected on a stage without
degrading the operation of the instrument.
Sehmel (1973) defines wall loss as the amount of material
associated with the walls directly above the stage of interest,
divided by the amount of activity on the stage of interest. He
reports wall losses for the Andersen 2000, Inc., Model 65-100,
20 ft3/roin, high volume unit for stage loadings between about 50
and 200 mg. The losses vary from about 1 percent at 50 mg/stage
to 5 to 20 percent at 200 mg/stage.
Sehmel (1974) provided additional information on the wall
losses for the Andersen 2000 Inc., unit. He noted the following:
1. There appears to be no direct relationship between
interstage losses and stage loading.
52
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339
2. The data indicate wall losses of up to 20 percent.
Operations during dust storms would undoubtedly result
in higher wall losses.
3. The average particle size in the interstage material
(wall loss) for each stage was much larger than should
have been present for the respective stages. Appar-
ently, some nonrespirable particles work their way
through the various stages. This tends to give results
that are conservative (i.e., there is more respirable
material indicated as being present than actually is
present in air).
There appear to be only two high-volume impactors available
through commercial sources. The Andersen 2000 Inc. is based on
20 ft3/min flow rate (566 1/min). The unit has four stages with
cutoffs at 7.0, 3.3 , 2 , and 1.1 micrometers, with a backup
filter for material less than 1.1 micrometers (Burton et al.,
1973). The unit is about 30 cm in diameter and can be matched to
high-volume air samplers. The operation of the unit has been
reviewed by Burton et al. (1973) and Sehmel (1973, 1974). In
addition to the previously indicated information, Burton et al.
(1973) note that some types of fiberglass filters are prone to
absorb atmospheric acid gases. Thus, the total mass amount of
collected material cannot be directly related to a mass air
sample result for a single sample. Apparently, fiberglass
filters with a pH adjusted to 6.5 largely resolve the problem.
Tech Ecology, Inc. markets a 5-stage cascade impactor
designed for a flow rate of 40 ft3/min (1,130 1/min). Tech
Ecology model 252 has size cutoffs of 8.2, 3.5, 2.1, 1.0, and 0.5
micrometers, with a final filter for less than 0.5 micrometers.
The unit is rectangular and fits the standard 8 x 10-inch
high-volume filter holder. The impactor orifices are rectangular
slits 12.5 cm long. An advantage of the design is the small
amount of filter paper (about 170 cm2) that has to be analyzed
for results from each stage. There appear to be no published
reports evaluating this unit.
Sehmel (1973) reports results of a study with the impactor
facing into the wind, and with the impactor face pointed vertic-
ally up or down. About 50 percent more material was collected
with the sampler pointed up versus down. The results with the
sampler oriented into the wind, with a wind directed cowl, fell
between the upward and downward oriented sampler, and were
considered to be the most valid of the three sets of results.
The data were obtained usine Andersen 2000 Inc. samplers. The
flowrate was 20 ft3/min (570 1/min), and the linear velocity for
the 6-in (15-cm) diameter cowl was 0.54 m/sec (1.2 miles/hr).
53
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3GG
Air Llutriator and Centrifugal or Cyclone Samplers
Air elutriators and cyclones utilize similar processes. The
settling velocity of the particle is used to fractionate material
in elutriators, whereas cyclones utilize centrifugal force con-
cepts. Both systems generally are used in two-stage samplers.
The elutriator and cyclone stages are used to remove the non-
respirable material from the air stream. The respirable material
(less than several micrometers in diameter) is collected on a
filter in the second stage.
The fractionated particulate material passed by the cyclone
generally relates to the definition of respirable material desig-
nated as the Los Alamos Scientific Laboratory (LASL) criterion.
The horizontal elutriator passes material which relates to the
criteria of the British Medical Research Council (1961J. The
LASL criteria resulted from a meeting called by the Atomic Energy
Commission, Office of Health and Safety, at Los Alamos in 1961.
Thus, the term AEC criteria is also used. The American Confer-
ence of Governmental Industrial Hygienists set forth a slightly
revised version of the LASL criteria (Federal Register, 1969).
These criteria, are summarized by AIHA (1970) and Ettinger
et al. (1970) .
Air elutriation is a process of particle separation based on
the settling velocity of the particle. This process may be done
on either a horizontal or vertical plane—thus horizontal or
vertical elutriators. Both techniques are based on the compari-
son of particle settling velocities and the velocity of the air
stream transporting the particle.
In vertical elutriators, the particles are carried upward in
a diverging air stream until they reach a point in the air stream
at which their settling velocity equals the vertical component of
the diminishing air velocity. Vertical elutriators have been
used for size-fractionation of powders, but have received little
use as air samplers (Mercer, 1973, p. 192).
In horizontal elutriators (HE), the particle settling
velocity is normal to the transporting air velocity. The air
stream passes through a horizontal duct. The distance from the
duct inlet at which particles fall out is inversely proportional
to their settling velocity or aerodynamic particle size. The
size distribution of material along the path length of the duct
varies, thus indicating the potential for obtaining an indication
of the size spectrum.
The vertical dimension of the inlet air duct of a HE is
generally a significant fraction of the total vertical fall
height. Thus, particles entering at the lower level of the duct
have a reduced fall height, compared to particles entering the
upper part of the duct. Thus, there is a general spread of the
54
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60]
size distribution along the horizontal length of the HE. Mercer
(1973) indicates that a sharp cutoff can be obtained with a
properly designed HE. Wright (1954) indicates the comparison of
the actual and theoretical retention values for the 100 1/min
Hexhlet instrument. The following retention values generally are
obtainable (Wright, 1954; AIHA, 1970; and Mercer, 1973):
Particle Size Percent Retention
(micrometers) (In HE)
1 %2
<2 10
5 50
7 100
Lippmann (1970) describes various HE's. Although most of
the units operate in the liter-per-minute category, Wright (1954)
presents data on the Hexhlet unit, designed for 100 1/min. The
design was subsequently revised to 50 1/min. Shanty and Hemeon
(1963) discuss a unit designed for a flowrate of 1250 1/min.
Lippmann (1970) notes it is generally difficult to collect
the material from HE units for analysis. In many designs, it
apparently is difficult to clean the HE adequately, to prevent
future samples from being contaminated by re-entrained material.
A preference for cyclone separators is noted.
Centrifugal or cyclone samplers (CS) separate particles
based on their centrifugal force (i.e., mass and diameter, or
equivalent aerodynamic diameter). They are more flexible than
HE's in that they can be operated in any position. Thus, small
cyclones have been developed as personnel monitors. Lippmann
(1970) indicates a listing of CS's, most of which are in the
liter-per-minute flowrate range, although one unit with a turbine
blower is rated at about 1000 1/min. Volchok et al. (1972)
report results from the Rocky Flats, Colorado area using a 100
1/min CS described by Lippmann and Harris (1962).
*
The design parameters on a CS are critical. Ettinger et al.
(1970, Table 4) indicates the change in the cyclone retention
with flowrate for a one-half inch unit. Lippmann (1970) reports
that most of the cyclone calibrations prior to about 1970 were in
error. The errors were due to an overestimate of particle sizes,
as a result of the microscopic measurement technique used.
Apparently the disagreements range up to a factor of two in
flowrate for describing a given size cutoff. Given this, the
data presented by Ettinger et al. (1970, Table 4) would indicate
roughly up to a factor of two error in cyclone retention for 2-
micrometer particles.
55
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402
Combination Electrostatic Precipitation and Cascade Impaction
Henry and Mitchell (1975) present data on a high-volume
sampler developed for EPA, Research Triangle Park, North Caro-
lina. The sampler is designed for 28 m3/min (1000 ft3/min). It
contains impaction stages designed for particles greater than 3.5
micrometer and 1.7 to 3.5 micrometer. The final stage, for less
than 1.7 micrometer particles, is an electrostatic precipitator.
There does not appear to be any published information evaluating
the operation of the unit.
TYPES OF FILTRATION MATERIAL
Many of the characteristics and limitations of filtration
samplers relate to the filter medium. Based on their physical
structure, filters can be classified as either fibrous mats or
porous membranes. Filters have varying particle size retention
characteristics, and the characteristics of a given filter are
dependent on the airstream face velocity. Other considerations
include dust loading and associated pressure drop, and the
presence of trace materials (e.g., uranium, thorium, and radium)
in the filter material.
The theory of fibrous mats is discussed by Mercer (1973,
p.115). Fibrous filters are made of cellulose fibers, plastic
fibers, glass fibers, and other materials including asbestos.
The filter performance is closely related to the diameter of the
fibers, with the smaller diameter fibers having better collection
properties. Collection of particles on filters is not solely a
sieving phenomena; rather, it is due to electrostatic forces,
interception, impaction, and diffusion.
Most common filters, fibrous or membrane, have adequate
particle collection efficiencies for air sampling; however, it
has been noted that Whatman 41 cellulose fiber filters have a
fairly low efficiency (70 to 80 percent) at low face velocities
of 20 to 30 ft/min (about 0.13 m/sec or 0.28 mi/hr). This is
equivalent to a flowrate of about 2 ft3/min (60 1/min) through a
4-inch (10-cm) diameter filter.
Unpublished information from a study by Eadie, ORP-LVF
provides data on the dust loading and pressure drop properties of
several filters. Tests were conducted on 4-in (10-cm) diameter
Whatman 541, Acropor, Gelman Type E Glass Fiber, and Microsorban
filters at initial flow rates of about 10 ft3/min (280 1/min).
The results indicate that the glass fiber and Microsorban filters
had better dust loading properties than the other filters. Glass
fiber filters showed a 30 percent decrease in flow rate with a
filter load of 260 mg. Microsorban indicated less than a 10
percent decrease in flow rate with a load of 200 mg, the highest
load used on the Microsorban tests. Conversely, Whatman 541
paper indicated a 60 percent flow rate decrease with a dust load
of 200 mg or less.
56
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403
The filter composition affects the difficulty and precision
of radiochemistry analysis. The ease of wet or dry ashing
Whatman paper always has made it a favorite with chemists. The
difficulty of dissolving fiberglass filters and the associated
trace elements put in solution have provided difficulty for
radiochemical analysis. Even with refined techniques, the EPA's
Las Vegas analytical laboratory has found about 80 in2 (500 cm2)
to be the maximum amount of fiberglass material to be amenable to
plutonium chemistry analysis.
Microsorban, a polystyrene fibrous mat material, is very
amenable to radiochemistry. If dried and heated for several
hours at increments of 100°C to 350°C, it can be white-ashed to a
powder at 600°C. When put in solution, it essentially has zero
residual (Golchert, Argonne National Laboratory, Personal commun-
ication, Feb. 1975).
Filtering materials contain numerous trace elements. These
elements include uranium and thorium progeny, and many metals
(especially in the fiberglass filters). The amounts and vari-
ances of the trace elements significantly effect the sensitivity
of monitoring low levels of these trace elements in air. Table
15 indicates values determined by ORP-LVF for some, of these
contaminants in several filters.
The analyses for many of the radionuclides are incomplete.
However, it is evident that most of the filter materials contain
varying amounts of radium-226, uranium and thorium. Admittedly,
some of the variation may be due to analytical or counting error,
but many of the results were based on a composite of four fil-
ters.
Golchert, in a private communication on Feb. 11, 1976, noted
that Argonne National Laboratory has detected concentrations of
4 to 18 fCi of thorium-232 and 2 to 8 fCi of uranium-238 per 780
cm2 of Microsorban. These relate to average values of about
1 fCi and 0.5 fCi, respectively of thorium-232 and uranium-238
(1 fCi total uranium) for a 4-inch diameter (10-cm) Microsorban
filter. These values are significantly lower than the radium-226
values given in Table 15.
Given several assumptions, these trace contaminants can be
related to equivalent air concentrations. Assuming a sampled
volume of 2000 m3 (1.4 m3/min for 1 day), a contamination level
of 0.2 pCi/filter is equivalent to an air concentration of 0.1
fCi/m3. This is about one-fifth of the nominal radium-226
ambient concentrations (see section on natural activity).
57
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494
TABLE 15. RADIONUCLIDE LEVELS IN AIR FILTERS (ORP-LVF)
pCi per Filter
Filter
Material
Whatman 41
Whatman 541
Number
of
Samples
4
2
Ave
(g)
0.62
Weight
. Range
1.06
0.62 1.01
Ra-226 U-238 Th-230
Ave Range Ave Range Ave Range
0.16 1.82
0.30 1.28
Th-232
Ave Range
Gelman Glass
Fiber 7 0.52 1.04 0.26 1.96 0.085 6.15 0.18 1.63 0.013 2.00
Microsorban 5 1.47 1.05 0.17 3.73
Acropore 5 0.41 1.02 0.90 5.7
Millipore 1 1.7 0.1 --- <0.01
* The range is the ratio of the highest result to the lowest result.
There appears to be minimal, if any, plutonium contamination
in air filter materials. Thus, these contaminants are somewhat
academic for sampling related solely to plutonium. But their
presence should be recognized in determining methods for plu-
tonium analysis and when considering gross alpha measurements.
The variance of filter weights has to be recognized if the
specific activity of the material on air samples is to be deter-
mined. Mercer (1973) notes that cellulose fiber filters are
prone to collect moisture from humid air. At 100 percent
relative humidity, a cellulose filter may gain 17 percent weight,
compared to its dry weight, versus 0.1 percent for fiberglass
filters.
AMBIENT CONCENTRATIONS OF NATURALLY-OCCURRING ALPHA EMITTERS
The ambient concentration of plutonium-239 in air is roughly
30 aCi/m3. This is significantly below the standard concentra-
tion guide of 10 CFR 20 for individuals in the general population
which is 60,000 aCi/m3.
Ambient concentrations of the naturally- occurring alpha
emitters range over several orders of magnitude. Values vary
from yearly averages of 100 aCi/m3 of total uranium, about
30 aCi/m3 of thorium-238 and 232, and 50 aCi/m3 of thorium-230
(AEC, 1974a) to 2000 aCi/m3 of polonium-210 (AEC, 1973a).
58
-------
405
Based on information in the previous section, roughly
100 aCi/m3 of the various nuclides could be accounted for by
contamination in the filter material, depending on the filter
material used and volume of air sampled per quantity of filter
material.
By way of illustration, the total gross alpha activity on an
air filter result could be roughly 0.9 pCi under the following
conditions . Assuming a sampling rate of 1 m3/min, a sampling
time of 100 minutes, and an estimated nominal ambient background
of 4000 aCi/m3, the gross alpha value is comprised of 0.5 pCi
from natural contaminants in the filter and 0.4 pCi of activity
collected during the sampling period.
The gross alpha estimate is somewhat greater than the
average gross alpha estimates from Argonne National Laboratory
(ANL), Illinois, 2,500 aCi/m3 (AEC, 1974a); Rocky Flats,
Colorado, 5,000 aCi/m3 (AEC, 1973a); and Los Alamos, New Mexico,
1,000 aCi/m3 (AEC, 1973a). The above gross alpha results are
based on longer run times (days); thus, the filter contamination
becomes less significant (estimated at 5,000 aCi/m3 in our
hypothesized value). Also, the ANL and Los Alamos results are
based on Microsorban filter material, which has a contamination
value lower than the postulated value. In addition to these
factors, the hypothesis of the gross alpha air concentration was
based on higher-than-normal values of natural radionuclides in
the atmosphere. Even with the noted conservative assumptions,
the postulated ambient gross alpha estimate of 9,000 aCi/m3 is
significantly below the plutonium-239 concentration guide of
60,000 aCi/m3.
ANALYSIS OF AIR SAMPLES
Analysis of air samples generally is equivalent to the
analysis of soil samples, plus considerations of the sampling
medium if a filter is used. The medium generally does not pre-
sent unusual problems, except in the case of fiberglass filters.
Most membrane filters, Microsorban, and cellulose fiber filters
generally can be wet or dry ashed to a low residual. The spe-
cific activity of naturally occurring uranium and thorium radio-
nuclides in air samples generally is similar to their specific
activity in soil (Golchert, ANL, personal communication, February
1976).
Plutonium in air samples stems from both resuspended soil
and fallout. In areas with an air concentration of about
30 aCi/m3 from atmospheric fallout and deposition on the soil of
less than 10 - 30 nCi/m2 (i.e., about 10 times background), the
plutonium concentration in air is largely a result of atmospheric
59
-------
406
fallout.a Thus, the particulate material on air filters has a
higher specific activity than that in soil. The information on
sample analysis in the following section is applicable to air
samples.
a. Douglas, ORP-LVF personal communication, February 1976 and
A. Hazle, Colorado State Department of Health, personal
communication, February 1976.
G. Merrill (Air Force McClellan Central Laboratory, verbal
communication, May 3, 1976) indicated that using plutonium
isotopic ratios from mass spectrometry, a contribution from
resuspended Trinity contamination (up to tens of percent)
could be detected in the data from Douglas.
60
-------
407
SAMPLE ANALYSIS TECHNIQUES
In many situations it appears that the analysis of samples
is not integrated with the philosophy of collection of the
samples and the objectives of the overall program. Plutonium in
soil, as well as in other media such as animal tissue, exemp-
lifies this situation, because of its potentially heterogeneous
distribution. The objectives of the program may dictate com-
positing up to ten discrete soil samples, to insure a sample
representative of the sampled location. The total sample,
composed of several kilograms, may be milled and mixed, with only
a small aliquot taken for the actual analysis. This aliquot may
vary from as small as one gram (EMSL-EPA, Las Vegas prior to
January 1975) to about 100 grams (Krey and Hardy, 1970). The
aliquot size for analysis is related to the difficulties of
dissolution of large quantities of soil, and for fusion tech-
niques the limitations and costs of the required analytical
apparatus.
In most instances, the analyst follows the philosophy of
taking an aliquot which he thinks can be adequately analyzed.
The potential presence of discrete particulate plutonium in the
sample, and the probability of obtaining a representative frac-
tion of the material in the aliquot, may not be addressed.
The problem of adequate sample size also relates to some
biological samples, such as bovine livers, kidneys, and bones,
etc., where it may not be convenient to analyze the whole sample.
Consideration of the heterogeneous structure of organs is neces-
sary if analyses of aliquots of the organs are to be meaningful.
ANALYTICAL SENSITIVITY
Analytical sensitivities are generally related to the
counting error (Johns, 1975; Sill, 1971; Krey and Hardy, 1970;
Chu, 1971; and Eberline, 1974). In many instances, the minimum
detectable activity (MDA) is defined as a value which is equal to
the 2-standard deviation (SD) or 95 percent confidence level
(C.L.) value (e.g., 20 fCi ± 20 fCi). Such results are normally
presented as less than values (e.g., <20 fCi).
The use of a value of less than the 2-SD value results in
the significant probability of an erroneous statement. If one
believes in the validity of the counting error, there is only a
50 percent probability that the value is less than the 2-SD value
61
-------
408
(e.g., <20 £Cij. In order to have a 95 percent confidence level
statement, a value of the mean plus 2-SD should be used.
Eberline Instrument Corporation (1974) uses another fairly
standard technique of three times the background counting error.
This gives an MDA somewhat less than the 2-SD equal to the mean
technique. But, as in the 2-SD technique the statement of a less
than value has a 50 percent or greater probability of being in
error.
Robinson et al. (1975) considered the range of background
samples for plutonium-238 and the variation of results for low
concentrations. The objective of the study was to assess the
inventory above the baseline or background level near the Mound
Laboratory, Miamisburg, Ohio. Aliquots of a sediment sample from
50 miles upwind of the plant were used for background determina-
tions. The reported gross concentrations in the background
samples (no system background subtracted) ranged from 0.000 to
0.765 pCi/g with a mean of 0.077 ± 0.040 (1-SD for 50 values).
The minimum detectable level was set at 0.1 pCi/g. Using 0.1
pCi/g and recognizing that background values ranged up to 0.8
pCi/g, the sample results were reported as less than 0.1 pCi/g or
the actual result for values above 0.1 pCi/g. Blank background
values were not subtracted from the results. Actual plutonium-
238 background values for this area were reported to be 0.0002
pCi/g for 30 cm (12 in.) depth cores, or roughly 0.002 pCi/g for
the top 5 cm (2 in.).
Although the results of Robinson et al. are not directly
applicable to studies at background levels, the concept of using
the variation in low level results, versus the counting error, to
define the MDA has merit.
The sensitivity of analytical procedures is inherently a
function of five parameters, some of which are reasonably fixed,
but several of which can be varied. The parameters are:
1. Sample size: The sensitivity depends on the total
amount of activity present. Thus, ideally the sensi-
tivity of a 10-gram sample is one-tenth of that for a
1-gram sample. The acid dissolution and fusion tech-
niques tend to have a nominal maximum of about 10 grams
of sample. The ease of analysis, size of vessels and
quantities of interfering elements generally result in
the analysist's preference for a sample smaller than 10
grams. 7 ie size refers to the dry weight of soil, or
weight of ash for biological samples.
2. Radiochemical yield: The yield is not an independent
variable. Mullins (EMSL-LV, verbal communication,
Feb., 1975) noted that although yields of 90 percent
plus were obtainable with 1-gram soil samples, the
yield for 10-gram samples had been about 50 percent,
62
-------
409
although there was hope for improving it. The drop in
yield is due to the interference from the increased
quantities of elements such as calcium and iron. Thus,
the 10-gram samples are only the equivalent of 5-gram
samples, or less, but there is still the benefit of
obtaining a more representative aliquot. There is an
additional uncertainty with low yields, due to the
uncertainty in the yield determination. A measured
recovered activity divided by a yield of 90 percent
(with an uncertainty of 10 percent) has a much lower
uncertainty than a value divided by 50 ± 101 or 20 ±
101. There is the additional uncertainty related to
the conventional propagation of error techniques
(Parrott, 1966 and Pugh and Winslow, 1966). The
simple technique for the square root of the sum of the
squares of the coefficient of variation only applies
for the division of parameters if the coefficient of
variation is at most 20 percent, and preferably less
than several percent. If the error term for the
denominator is large, the limits are much more diffi-
cult to calculate, and they are not symmetrical around
the mean (Finney, 1971).
3. Counting efficiency: Optimally 50 percent for 2ir
geometry, but generally about 20 percent for alpha
spectroscopy.
4. Background counting rate: The background error and
sample counting error are propagated by the square root
of the sum of the squares. The background for alpha
spectroscopy is generally low (counts per hour or less)
and stable enough that backgrounds and/or blanks are
only run about once a week or less. Thus, there is the
potential for actual errors in the blank count that is
used to correct the sample gross count to a net count,
'if the chamber is contaminated.
5. The counting time for both the sample and background or
blank impacts the sensitivity as a result of the
counting error calculation. The counting error or
standard deviation is generally assumed to fit the
normal distribution with the variance equal to the
total counts (i.e., standard deviation equal to the
square root of the total counts). Thus, doubling the
counting time reduces the percentage counting error by
the square root of 2 (100 counts ± 10, versus 200
counts ± 10/2~). Counting times for low-level alpha
analyses are normally 1000 min. (Johns, 1975).
Most calculations of counting error and thus statistics
(e.g., Johns, 1975) assume the applicability of the normal
distribution. Nuclear disintegration or counting statistics are
basically described by the binominal distribution (Evans, 1955,
63
-------
and Jarett, 1946). It is only through generalizations and
assumptions that the normal distribution is applicable. The
basic assumption of concern for low level determinations of long
half-life radionuclides is the accumulation of sufficient counts
for the transition from the Poisson to the normal distribution.
The minimum value normally stipulated is 20 counts, below which
the Poisson is too skewed to be approximated by the normal (Evans
and Jarett). Jaffery (1960) stipulates a value of 100 counts.
For a mean of 20 counts, the mode of the Poisson is 19
versus the mean and mode of 20 for the normal (Jarett, 1946).
Figure 3 is a cumulative frequency plot for a mean of 10 events.
The cumulative 50 percent point for the Poisson is about 9,
versus 10 for the normal distribution.
Most of the minimum detectable activities (MDA)* are associ-
ated with net sample counts of about 10 above a background count
of 0 to 5 - where both counting times are about 1000 minutes.
Equation 1 indicates the calculation for the probability, P,
of x events occurring for the Poisson distribution, where m is
the true value
x **
P(x) = m exp-m (1)
Equation 2, using the same nomenclature, indicates the
probability P (x) for the normal distribution
P rvi - 1 exp-(x-m)2/2m
r ^AJ - ("91
(2 Trm) 0.5 L^J
For an assumed mean or true value of m = 2, the probability
of occurrence of a value of two is similar for the two distribu-
tions (i.e., 27.41 for the normal, versus 27.11 for the Poisson).
But, the probability values of one or three occurring differs by
about 20 percent for the two distributions (the values for the
normal distribution are integrated between x plus and minus one-
half) .
It is difficult to assess the full impact of the limitation
of the assumptions in using a normal distribution. But for
samples near the MDA, if results related to counts of 10 or less
events are used, it appears that the errors in the counting error
statements and in actual results could be several tens of percent,
For these purposes MDA is used as a general term to indicate
the defined detection limit. No attempt is made to distin-
guish between the original sample, a prepared sample, or
curies versus counts.
** exp-m = e
64
-------
18
14
12
i/»
i—
Z
UJ
u 10
u.
o
2 8
Normal
P o i s s o n
3
Z
0.01 0.1 0.5 1 2 5 10 SO 90 99
PROBABILITY OF LESS THAN NUMBER OF EVENTS OCCURRING
Figure 3. Cumulative frequency plot for a true value of 10.
-------
412
Johns (1975) presents equations for calculating the
plutonium-239 activity in a sample and the associated counting
error. The calculations use the ratio of the plutonium-236
tracer added to the sample to the recovered plutonium-236, rather
than an actual detector efficiency.
The counting error equation is a propagation of error of the
square root of the sum of the squares of the coefficients of
variation for the following parameters:
- Sample count for plutonium-239
- Reagent blank count for plutonium-239
- Sample count of plutonium-236 tracer
- Reagent blank count for plutonium-236 tracer
This results in a rather complete analysis of the counting
error for a sample. For samples near the MDA, the sample count
is probably around 10, and thus has the previously noted limita-
tions of not being normally distributed. The same is true for
the background or blank count for all analyses. Thus, the error
term may not be truly representative by up to tens of percent for
the two values.
In talking to personnel from various laboratories, it was
discovered that some do not subtract an instrument background and
few subtract a reagent blank background. The significance of
errors associated with these practices depends on the level of
sample activity, as well as the degree of possible contamination
of the counting instruments, reagents, laboratory glassware, and
tracer solution. Given the potential for errors, it is prudent
not only to subtract background, but also to run reagent blanks
containing the tracer, and use this blank as the background.
A general review of the effects of various actual numbers
would indicate a potential for a misrepresentation of the error
term by up to 30 percent for values near the MDA (assumed to be
about 10 counts). The calculations indicate a nominal MDA of
about 20 fCi/sample; assuming 1000-min count time, high chemical
yield (about 90 percent), and low background (0-5 counts in 1000
min). Consideration of the assumptions indicates that the actual
MDA varies from sample to sample, if it is based on counting
error. Thus, single values are only nominal estimates based on
representative results.
Sill (unpublished document) presents a counting error
evaluation which includes several additional factors. Although
Sill included error estimates for the tracer standardization and
for correcting the tracer for decay since standardization, these
errors are a small part of the total error. The error associated
with the sample count accounts for well over 90 percent of the
66
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413
total error for his estimate. Furthermore, the potential error of
assuming the background is zero overshadows the contributions
from these other errors.
MDA's from several organizations are summarized in Table 16.
Many authors do not report MDA's, and many that do, report them in
terms of their specific sampling and analysis parameters (e.g.,
pCi/g or nCi/m2 for soil, or pCi/m3 for air). The basic MDA for
plutonium analysis by alpha spectroscopy is based on the amount
of plutonium present on the electroplated sample and the count
time. Inclusion of the chemical yield and sample size results in
secondary MDA's.
Another approach for evaluating the MDA is to consider
results of samples that contain essentially no plutonium. Table
17 from Krey and Hardy (1970) presents results from two samples,
one collected prior to 1945 and the second collected from a depth
of 90 cm in 1970. The analyses were performed on 100-gram
samples and the counting errors are only one standard deviation.
Thus, the minimum numbers 0.0001 to 0.0003 dpm per gram relate to
10 to 30 fCi per sample (e.g., 0.0001 dpm/g x 103 fCi/2.22 dpm x
100 g/sample x 2 sigma = 10 fCi per sample).
The results for the Woodcliff Lake sample are surprisingly
high. Krey and Hardy note the probable cause as contamination,
either during collection or analysis. Two of the TLW values are
noted as suspect.
TABLE 17. PLUTONIUM IN BLANK AND LOW-LEVEL SAMPLES
(From Krey and Hardy, 1970)
Sample
Laboratory
dpm per
Plutonium-239
gram
Plutonium-238
Pre-bomb
(Collected before 1945)
ii
ii
it
ii
Woodcliff Lake, N.J.
(Collected below 90 on
in March 1970)
ii
H
ii
* Suspect value
HASL
IPA
IPA
TLW*
TLW
IPA
IPA
TLW
TLW
TLW
0.0003 ± 100%
0.0001 ± 100%
0.0001 ± 100%
0.0196 ± 7%
0.0001 ± 1001
0.0046 ± 7%
0.0043 ± 6%
0.0071 ± 9%
0.0468 ± 5%
0.0055 + 25%
0.0002 ± 100%
0.0001 ± 100%
0.0001 ± 100%
0.0054 ± 14%
0.0001 ± 100%
0.0001 ± 100%
0.0001 ± 100%
0.0009 ± 53%
0.0001 ± 100%
0.0002 + 100%
67
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TABLE 16. SUMMARY OF MDA'S FOR PLUTONIUM IN ENVIRONMENTAL SAMPLES
Investiqator
Denham and Waite (1974) Survey3
Johns (1975)
Poet and Martell (1972)
AEC (1973a), Sedlet et al. (ANL)
Robinson et al. (1975)
E. Geiger (Eberline Instrument
CT> Corporation Verbal 5/7/75)
Krey and Hardy (1970) (estimated
by Bernhardt)
Smith and Black (1975)
McDowell et al. (1973)
Majors et al. (1974)
McBryde (McClellan, Verbal, 1975)
Church(1974) REECo et al.
Definition Basic MDA
of MDA fCi/sample
... *3»pu
239pu
*-<2a 20
Only report
1 a error
x±2a -\-5(?)
x±2a 20
MO-55
x±la 20
Sample=Bkgdc 140
x>la(?) 20
15,000
x>la 0.06-6
•V300.000
Soil Air
Sample Sample
fCi/g Size fCi/mJ Size
(g) (m3)
3 (0.03-500) 10"3 (5xlO:"-0.1)
3 (0.4-30) 5xlO"3 (10" -0.1)
20 Ig
4 lOgb
10-" 25-60xl03
100 10
10
(liquid scintillation, alpha spectrometry)
(Gamma spectrometry for 21flAm)
(Mass spectrometry with sophisticated and
3,000 100
2!llAm in soil
Water Tissue
Sample Sample
fCi/1 Size fCi/g ash Size
(1) (g/ash)
5 (0.5-50)
10 (0.5-50)
0.1 45
0.5 10
routine chemistry)
a. Summary paper of AEC Contractor techniques. Single value is considered typical; numbers in sample size column indicate the range.
b. Present yield on 10-gram samples is only about 50%.
c. Sample countrate equals background countrate.
-------
415
A possibly unfair conclusion would be that "zero" for these
samples ranged from 10 to 55 fCi per sample, assuming the two TLW
samples can be excluded, which probably would not be the case for
unknown samples.
Robinson et al. (1975) report 50 values for a background
sample which should have contained only 0.2 fCi/g of plutonium-
238. Their values range from 0 to 765 fCi/g, based on a 10-gram
sample (no background subtracted). The standard deviation for a
single result is a counting error of 40 fCi/g. Two times the
counting error, 80 fCi/g, essentially is equal to the average of
the 50 results, 77 fCi/g. Based on their analysis, they picked
100 fCi/g as the minimum reporting value for reliable results.
This relates to an MDA of 1000 fCi per sample (100 fCi/g x lOg).
The intent of the reported project was to assess plutonium-238
contamination significantly above the background level of 0.2
fCi/g for a 12-in core.
Figure 4 is a histogram of Robinson's et al. data. It can
be seen that 20 percent of the values (blank or background) are
above the MDA of 100 fCi/g.
The optimum MDA, assuming essentially zero background, 1000-
min counts, and ignoring the limitations of the statistical
assumptions, is about 10 fCi. Practically, a more reasonable
minimum is 20 fCi. The value of 20 fCi relates to about
3 x ID'13 g of plutonium-239 or 1 x 10"15 g of plutonium-238.
Malaviya (1975) indicates a theoretical capability for mass
spectrometry of 10"18 g.
In summary, there are several means of defining the sensi-
tivity of analyses, or minimum detectable activity. The tech-
niques that give the lowest MDA's that are reasonably valid are
based on the 2- or 3-sigma counting error. The EMSL-LV technique
(Johns, 1965), defines the MDA value as the mean value equal to
the two-sigma error. Others sometimes use three times the
background counting error, which generally gives results similar
to Johns (1975). In most instances when mean sample results are
below or equal to the MDA, they are expressed as less than the
MDA.
It should be recognized that most less than values are only
a 50 percent probability statement. That is, 50 percent of the
time the statement is wrong. A reasonable minimum MDA is about
20 fCi per sample; i.e.,the counting error is 100 percent at the
2-sigma or 95 percent confidence level. A more realistic MDA
statement , given the limitation of the statistical assumptions,
would be less than 20 fCi plus 1- or 2-sigma, i.e., 30 or 40 fCi
per sample. These values are in essence per sample planchet,
after electroplating. If the chemical (tracer) yield is only 50
percent, the values actually are 40, 60, and 80 fCi per original
s amp1e.
69
-------
416
Natural Background
Selected as MDA
100 200 300 400
f C i Pu-238 per gram of soil
238
Figure 4. Histogram of blank or background ' Pu soil samples
70
-------
(til
Table 18 converts the sample MDA into MDA's for various
environmental samples. It is evident from the table that present
analytical techniques can detect plutonium at concentrations well
below the standards.
SAMPLE TYPES
The chemical and physical characteristics of samples in part
determine the dissolution technique for getting the plutonium in
solution for analysis, and the steps in the analysis that are
necessary to remove elements that interfere with subsequent steps
in the analysis, especially electroplating. The various refrac-
tory compounds of plutonium, and the generally low solubility of
many plutonium compounds, requires emphasis on the complete dissolu-
tion of the sample material to assure dissolution of any associ-
ated plutonium. If there is residual sample material, there is
concern that there may be plutonium in the residual. Sill et al.
(1974) and Sill and Hindman (1974) indicate that non-fusion
techniques may leave up to 40 percent of refractory plutonium in
the undissolved residual.
The refractory nature of plutonium in the sample is related
to several factors, including the following:
1. History of the source of the plutonium in the sample
and its particle size distribution. For example, Rocky
Flats and global fallout plutonium generally are
amenable to leaching techniques (Krey and Hardy, 1970),
while plutonium from many of the NTS tests appears to
be in the form of generally insoluble discrete parti-
cles .
2. Sample preparation techniques, such as firing to remove
soil organic matter, can produce refractory plutonium
(Sill and Hindman, 1974). Sill and Hindman indicate
that temperatures of about 700-1000°C produce refrac-
tory plutonium.
3. The nature of the sample material, particularly soil
samples, can have an impact on the dissolution. Lime-
stone and coral are largely calcium carbonate and can
be dissolved rather readily with nitric or hydrochloric
acid (AEC, 1973; Wessman et al., 1974; and E. Geiger,
Eberline Instruments Corporation, verbal communication,
May 6, 1975). The amount of calcium in a limestone or
coral soil can produce interferences in a fusion-type
technique. Iron oxides also are less prevelent in
limestone and coral, resulting in less interference
from iron.
4. Most soils are composed of from 50 percent to 80
percent sandstone. Thus, there is a large amount of
undissolved residual material from leaching techniques,
71
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TABLE 18. MINIMUM DETECTABLE CONCENTRATION
AIR SAMPLES
10 cfm - 1 day
10 cfm - 3 day
10 cfm - 7 day
40 cfm - 1 day
40 cfm - 3 day
WATER SAMPLES
1-liter
5- liter
SOIL
1-gram
10- gram
100- gram
a. IfCi/m3 =10"
b. An MDA of 40
SAMPLE
VOLUME
400 m3
1 ,200 m,
2,800 m3
1 ,600 m3
4,900 mj
1-liter
5^-1 i ter
1 gram
10 gram
100 gram
15 uCi/cc.
fCi is the
- MINIMUM DETECTABLE CONCENTRATION
UNITS * BASED ON SAMPLE MDA OF (
fCi/m3,xlOl5uci/cc
fCi/m3,xlOl5uci/cc
fCi/m3,x!015uCi/cc
fCi/m3,xlo]V:i/cc
fCi/m3,x-1015uCi/cc
fC1/lorlo!SuC1/ml
fCi/lorlo'^uCi/ml
fCi/g
These values are n fCi/m
same as the MDA for 20 fCi
20 fCi
0.050
0.017
0.007
0.013
0.004
20
4
20
2
0.2
or n x 10"15
with a 50%
40 fCi'D
0.10
0.03
0.014
0.025
0.008
40
8
40
4
0.40
uCi/cc.
chemical yield. A yi
POPULATION
i INDIVIDUAL)
RPG3-
60
60
60
60
60
5 x 105
5 x 106
r
ield of about
RATIO:
20 fCi MDA/RPG
0.0008
0.0003
0.00012
0.00021
0.00007
4 x 10"6 ,
0.8 x 10"°
100% has
been assumed. The MDA's are for 20 or 40 fCi per original sample quantity.
There are no Federal Standards for Pu in soil. Colorado stipulates 2 dpm or about 1 pCi/g.
are those from 10CFR20, for the most limiting form.
The RPG's
00
-------
£19
with a potential for retained plutonium. Furthermore,
there is the potential for plutonium oxide to occur in
a siliceous matrix.
5. Liver and kidney samples present analysis problems
analogous to or worse than soils because of the pre-
sence of heavy metals, other than plutonium. Due to
various interference mechanisms, chemical yields at
times are close to zero (J. Mullins, EMSL-LV, verbal
communication).
6. In essence, analysis of air samples presents the same
difficulties as the analysis of soil samples. The
plutonium on air filters is associated with essentially
the same material, with possibly a smaller particle
size distribution, as the plutonium in soil (e.g., 0.05
pCi/g x 100 ug/m3 = 0.005 fCi/m3, roughly one-tenth of
ambient air background). The air sample filtering
material may present additional analytical difficulties
(e.g., fiberglass air filters are difficult to dissolve
and have metals that interfere with the analysis of
plutonium).
REVIEW OF ANALYTICAL TECHNIQUES
As in most areas of life, there are few absolute generaliza-
tions that can be applied to plutonium analytical techniques.
Recognizing this, but also recognizing a need for categorization,
plutonium analytical techniques may be divided into three basic
techniques for getting the plutonium in solution and four tech-
niques for plutonium quantification.
The techniques for placing the plutonium in solution are:
1. Leaching: The technique generally is related to that
of (or represented by) Chu (1971). The basic technique
is to leach plutonium from the sample with HN03 and
HC1. The sample generally is digested for several
hours at boiling temperatures. The technique has the
advantage of being able to treat large soil samples,
nominally 100 g, but up to 1000 g or more. Also, the
technique is less likely than other techniques to
dissolve interfering elements along with the plutonium.
A significant volume of residue remains after the
leaching. The technique can be conducted by normal
radiochemistry technicians. The disadvantage is the
potential for not having dissolved all the plutonium,
or having it in an available chemical state.
2. Acid dissolution: This technique can be considered an
advanced acid leach. The basic difference is the use
of additional HF (the leach technique may use some HF)
and the increased digestion and treatment to the point
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where essentially the whole sample is placed in solu-
tion, with only minimal residue. Hydrofluoric acid has
the ability to dissolve silica, and also increases the
solubility of refractory oxides, forming fluoride
complexes (Sill et al., 1974). The technique generally
is amenable to sample sizes of 10 to 15 grams of soil
or ash, although the implementation of the technique is
easier with 1-g samples. Mullins (EMSL-LV, verbal
communication) notes that the treatment of 10-g samples
requires the use of professional personnel, or
increased supervision of technicians. The increased
dissolution of the sample results in increased dis-
solution of interfering metals. There is an increased
probability of dissolving refractory plutonium, but
there is still some uncertainty about complete dissolu-
tion and chemical availability of the plutonium
(Mullins, verbal communication, January, 1975, and Sill
and Hindman, 1974). The EMSL-LV method generally is
representative of this technique (Johns, 1975).
3. Fusion: Sill (1969) and Sill and Williams (1969) have
developed the basic technique of a pyrosulfate fusion
for placing uranium and the transuranium elements in
solution. The tentative EPA Reference Technique is
essentially identical to this method, Hahn et al. (in
press). Furthermore, this technique is used to check
the efficiency of other techniques (Sill et al., 1974).
This method generally is limited to 10-to 15-g samples
because of available equipment size limitations.
Furthermore, the method requires a high degree of
technician proficiency, generally professionals.
Sill et al. (1974) present a summary of the concept of
several analytical techniques. The following discussion is based
on their review.
Basically, analysis can be broken down into the following
phases:
1. Sample dissolution and addition of tracer.
2. Chemical separations to isolate desired elements from
interfering elements through precipitation, volitali-
zation, and ion-exchange.
3. Electroplate (or by other means) place sample on
planchet or metallic disk (or place in solution for
liquid scintillation).
4. Count sample by appropriate technique, such as alpha
pulse height analysis.
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5. Calculate sample activity and estimate analytical error
term, based on tracer yield and blank or background
count rate.
Church et al. (1974), Majors et al. (1974J , and Gilbert and
Eberhardt (1974) report data on americium-241 analysis by gamma
spectrum analysis. Values for plutonium-239 can be estimated
from assumed or calculated plutonium-239/plutonium-241 ratios,
based on radiochemistry. Gamma spectrum analysis for americium-
241 essentially requires no sample preparation or radiochemistry.
The sample is dried and placed in a standard container. Given
the relatively low gamma energy (60 keV) and photon abundance,
the sensitivity of the method is not adequate for ambient con-
centrations. The sensitivity is about 100,000 fCi per sample,
plus or minus about a factor of five depending on the other gamma
emitters present and the counting time. The technique is amen-
able to samples of roughly 100 grams (e.g., sensitivity roughly
1000 fCi/g or 1 pCi/g). Piltingsrud and Stencel (1973) present
similar information for phoswich detectors.
Each of the five analytical steps are discussed in detail
below.
Sample Preparation and Dissolution
Sample preparation usually consists of drying the sample at
about 100 to 120°C. This normally is the weight basis for
reporting results. The difference in weight between air dried
(Krey and Hardy, 1970) and oven dried weights may range up to 15
percent (Bliss, EMSL-LV, verbal communication). If there is a
significant amount of organic material and roots, the sample is
then heated in a muffle furnace to 400°C (Sill et al., 1974) or
to 600°C or more; or the material may be burned off with a blow
torch, (Bishop et al., 1971). Sill et al. (1974) and Sill and
Hindman (1974) express the concern that the high temperatures
will increase the refractory nature of the plutonium. This can
affect dissolution for silica soils, but apparently does not for
coral-type soils.
Many authors recommend sieving the samples subsequent to
ball milling them (e.g., Sill et al., 1974 and Krey and Hardy,
1970). Gilbert (verbal presentation at May 1975 NAEG meeting)
noted a disparity between sieved and non-sieved aliquots of
groups of samples. Gilbert's comments were not conclusive, but
indicated a concern for sieving. Possibly a disportionate amount
of fines containing plutonium are electrostatically bound to the
larger particles.
The following discussion of sample and plutonium dissolution
primarily relates to soil samples. However, subsequent to
dissolution or combustion of the filter, it also can be related
to samples of airborne particulates. The dissolution of ashes
from various biological samples is similar.
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Most of the techniques are based on dissolving the sample in
concentrated hydrochloric and nitric acids. The digesting times
and temperatures vary. One of the most significant variations
between techniques is the amount and concentration of hydrofloric
acid used. Hydrofloric acid is recognized for its ability to
dissolve silica, the predominant material in most soils.
Hydrofluoric acid is used to dissolve and break down the
silica and soil matrix. The "dissolution" versus leaching
processes call for an excess of HF. The leaching processes use
little, if any, HF. The HF also acts as a catalyst for breaking
down the plutonium and getting it into ionic form in solution.
Sill et al. (1974) and Sill and Hindman (1974) stress the
difficulty and necessity of getting the plutonium into a mono-
meric, ionic form. Plutonium is prone to forming colloids and
complex ions. Thus, dissolution alone is not sufficient--it must
be in ionic form. Mullins (EMSL-LV, verbal communication) notes
that sometimes the miscellaneous heavy metals in liver or kidney
tissue can form complexes with the plutonium tracer, resulting in
a zero tracer yield. Emphasis must be placed on insuring that
the sample and tracer are in chemical equilibrium; e.g., the same
ionic state.
It is important that the tracer be added at the right time.
If tracer is added to an empty beaker, it may bind to the beaker.
The resulting low yield does not reflect the recovery of sample
plutonium. Also, if tracer is added too late in the process, the
yield will not reflect plutonium losses prior to the tracer
addition. In any case, there is always uncertainty as to whether
the tracer truly interacts with the plutonium in the sample. The
probability is that the tracer may exhibit a yield higher than
that of the sample plutonium. But it is possible that the tracer
plutonium may also be lost while the sample plutonium is still
tied to the sample, thus indicating a yield lower than that
achieved for the sample plutonium.
Sill et al. (1974) recommend a combination potassium fluor-
ide and pyrosulfate fusion subsequent to the previously indicated
acid treatment to ensure the complete dissolution of the sample
and associated plutonium. They note that sodium carbonate or
hydroxide fusions do not guarantee complete dissolution, and that
the necessary subsequent steps often result in yields of less
than 50 percent to as low as 2 percent.
The anhydrous potassium fluoride fusion (in a platinum dish)
is used to insure the complete dissolution of siliceous material.
The pyrosulfate fusion is used to insure complete dissolution of
nonsiliceous materials, especially high fixed oxides (plutonium)
along with the volatilization of hydrogen fluoride and silicon
tetrafluoride. Except for a small amount of barium sulfate, the
pyrosulfate cake resulting from the fusions can be readily
dissolved in dilute HC1.
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Sill et al. (1974) recommend that the fusion technique be
used to check undissolved residuals from other dissolution tech-
niques, resins, and various laboratory equipment. They emphasize
the validity of checking residuals versus relying on tracer
yields or duplicate analysis by the fusion technique.
Chemical Separations
Sill et al. (1974) precipitate the alpha emitters (radium
through californium) with barium sulfate. The various elements
are extracted from the solution through control of valence states
and solvent extraction. There are several steps where care must
be taken to prevent the hydrolytic precipitation of plutonium,
the carry-over of iron or quadrivalent cerium with plutonium,
and subsequent electrodeposition interference.
Sill et al. (1974) note that for soil samples, calcium is
the worst source of interference for the barium sulfate precipi-
tation, because of its relatively high concentration (^3%) in
most soils. If the calcium present in 10 grams of soil precipi-
tates as calcium sulfate and is filtered off, it probably will
carry most of the alpha-emitter ions with it. The acidity of
solution can be increased by the addition of HC1, but this
affects the barium sulfate precipitation. Apparently, these
losses are acceptable for plutonium up to a value of about 5
percent calcium in a 10-gram soil sample. A dissolution of the
initial barium sulfate precipitate with reprecipitation is
necessary to remove small quantities of calcium and other ions
which would interfere with electrodeposition and alpha resolution
from the deposited sample.
Sill et al. (1974) note various modifications for recovery
of the alpha emitters other than plutonium. The basic method is
oriented to plutonium.
Sill et al. (1974) report the activity associated with
sample residuals and the various pieces of analytical hardware.
This data can be used to assess sources of cross-contamination
and critical points where sample activity may be lost.
Talvitie (1971) describes the basic method for ion exchange
separation of the elements. The technique emphasizes the separa-
tion of iron to prevent interference during electrodeposition of
plutonium. Talvitie's method is used by Johns (1975).
Bentley et al. (1971) describe the LASL solvent extraction
technique. The plutonium is extracted into di-2-ethylhexyl
orthophosphoric acid (MDEPH).
Electrodeposition
Electrodeposition generally is used to produce the uniform,
essentially weightless, deposition needed for alpha spectroscopy.
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The sample must be essentially infinitely thin to minimize self-
absorption, or energy degradation, of the alpha particles.
Evaporation of solutions on a hot plate does not produce an
adequately uniform deposit (Talvitie, 1972). Several alternative
techniques include liquid scintillation counting as described by
McDowell et al. (1973), and co-precipitation of plutonium with
trace amounts of lanthanum carrier (Lieberman and Moghissi, 1968,
and Butler et al., 1971). Mass spectrometry also eliminates the
need for electrodeposition, but equipment and personnel require-
ments generally are beyond the resources of most laboratories.
Most laboratories utilize alpha spectroscopy after electro-
deposition of the sample. Although electrodeposition entails
inherent problems, it generally results in a higher quality alpha
spectrum than liquid scintillation or plutonium co-precipitation.
These alternate techniques, along with mass spectroscopy, will be
discussed at the end of this section.
There are several basic potential problems associated with
electrodeposition. One basic problem in all radiochemistry
procedures is residual contamination of equipment from prior
sample analysis. This is especially true with electrodeposition
equipment. Talvitie (1972) describes a technique based on
disposable electrodeposition cells to minimize this problem.
This process is used by EPA/EMSL (Johns, 1975).
Changes in the electrolyte pH during electrodeposition and
various elements, such as iron, interfere with electrodeposition,
increase the thickness of the deposit, and result in low and
variable yields. Talvitie (1972) describes recovery from 1M
ammonium sulfate at pH 2 in a period of about 40 minutes. It is
recommended that the iron content be less than 0.1 mg.
Puphal and Olsen (1972) describe recovery from ammonium
chloride-ammonium oxalate electrolyte over about 50 minutes.
They discuss the use of a chelating agent to reduce -the inter-
ference of some cations, and fluoride to alleviate the interfer-
ence from iron, aluminum, thorium, and zirconium. But they noted
that the presence of even microgram quantities of rare earths can
cause serious interference if fluoride is added.
Sill (verbal, EPA/NERC-LV Workshop, now EMSL-LV, April 3,
1974) notes that using methyl red as a pH indicator prior to
electroplating results in the possible formation of plutonium
hydroxide. Although the pH is corrected prior to electroplating,
the plutonium hydroxide may not dissociate and go back into
solution. Thus, Sill recommended using thymol blue as the
indicator. Hahn et al. (in press), Johns (1975), AEC (1974), and
Sill and Hindman (1974) use thymol blue.
Sill et al. (1974) note that subsequent to reasonable
dissolution, electrodeposition is by far the step with the great-
est potential for loss of the sample. Electrodeposition of
electropositive elements such as the actinides depends on
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deposition of hydroxides by hydroxyl ions produced electrolyti-
cally at the cathode. All metal ions forming insoluble hydrox-
ides may be expected to electrodeposit to some extent, degrading
the sample plate and thus the alpha spectra. Furthermore, if
precipitates are formed during pH adjustments, the element being
determined may coprecipitate more effectively than if it were
alone and therefore not be available for electrodeposition. This
is especially worrisome with high pH's around 4.8 to 6 (i.e.,
methyl red) which is the justification for recommending the use
of thymol blue (pH 1.2 to 2.8). Sill et al. (1974) recommend
using the salmon-pink end point of thymol blue (pH 2.0).
Sample Counting Techniques
There are four basic counting techniques: Alpha counting of
solid samples, liquid scintillation counting of alpha particles,
gamma counting for americium-241 (estimate of plutonium-239), and
mass spectrometry.
Various types of alpha counters can be used for gross alpha
counting. Lieberman and Moghissi (1968) propose a plutonium
method with separations appropriate for gross alpha counting.
But as in all gross counting techniques, there is the potential
for error as a result of inadequate separation. Bains (1963)
notes that ambient-level samples, purified to the extent of about
one net count per hour, often contain sufficient natural activity
to affect low level results. Bains concludes that spectrometry
is needed for low-level alpha work.
Sill and Hindman (1974) and Hahn et al. (in press) suggest
standardizing tracer in 2-tr alpha counters prior to standardizing
alpha spectrometers. The need for cross checking electrodeposi-
tion samples (standardization), due to the uncertainties, with
standards made up from solutions evaporated on counting disks is
stressed. Alpha spectrometers are only calibrated as a general
cross check, because normally sample activity estimates are
derived from the observed tracer counts versus the amount added
(i.e., yield and counter efficiency are considered in a single
parameter).
Due to the degradation of alpha particles in the electro-
plated source, and the separation distance between sample and
counter, alpha spectrometers normally operate at 20-30 percent
efficiency (Mullins, verbal, February 1975, and Sill and Olson,
1970). Sill and Olson (1970) and experience at EMSL-LV (Mullins,
verbal, February 1975) stress the need to consider potential
detector contamination from alpha-active daughter products of the
sample activity. The concern for contamination relates to the
alpha recoil of nuclides, possibly in connection with the vola-
tility of nuclides. Polonium-210 appears to present the greatest
hazard. Preheating the plate prior to counting appears to
minimize the problem.
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Alpha spectroscopy is only appropriate for analyzing the
Plutonium isotopes of mass 236, 238, 239, 240, and 242. The
isotopes plutonium-236 and -242 normally are not found in the
environment in significant quantities, and are used as tracers.
The alpha energies of plutonium-239 and 240 are so close together
they cannot be distinguished by alpha spectroscopy. Plutonium-
241 is a beta emitter, and thus, although it is the plutonium
isotope normally present in the environment in the largest curie
quantities, it cannot be determined by the normal plutonium
quantitation techniques. Plutonium-241 quantities normally are
estimated from assumed isotopic ratios, from the estimated
ingrowth of its progeny americium-241, or by mass spectroscopy.
McDowell et al. (1973) describe a liquid scintillation
method for low-level alpha counting. The method has the advan-
tage that electrodeposition, with the associated problems of
various interferences, is excluded. But due to the inherently
higher background of the liquid scintillation counter, its normal
sensitivity is higher than that for solid state alpha spectros-
copy. The increased background of liquid scintillation is
partially offset by the increased counting efficiency.
McDowell et al. (1973) indicate an alpha counting efficiency
of 100 percent with energy determination capability of ±0.1 MeV.
The MDA for Pyrex sample tubes is reported as 1 dpm (0.5 pci-
whereas for quartz sample tubes the level is reduced to 0.3 dpm
(0.14 pCi). If pulse shape discrimination is used, a value of
0.02 dpm or 10 fCi appears attainable.
The normal system background is reported as 1 cpm. This can
be reduced to 0.3 cpm by using quartz sample tubes. Pulse-shape
discrimination, which requires sample deoxygenation can reduce
the background to 0.01-0.05 cpm.
It appears that the sensitivity or MDA has been set equal to
the background. Assuming the sample and background counting
times are equal, this is equivalent to an MDA where the two-sigma
error is equal to or less than the MDA.
Energy discrimination or resolution is such that plutonium-
236 tracer and plutonium-239 can be counted simultaneously.
McDowell et al. (1973) indicate that background can be determined
simultaneously from adjacent channels (away from actual channels
of interest). Although this alleviates the need of separate
background determinations, it has the potential error of over-
looking separation errors, and background due to reagent or
equipment contamination. It also is noted that if uranium is not
separated from plutonium, impurities in the scintillator may
cause overlap of the uranium-234 and plutonium-239 peaks. The
uranium-238 peak can be used to estimate the uranium-234 inter-
ference.
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McDowell et al. (1973) note that iron and other metals do
not interfere with liquid scintillation counting, since electro-
deposition, the point of interference, is not necessary. Thus,
simpler, less time-consuming separation steps may be used (1 hour
versus 10 or more hours), and the uncertainties and potential
yield reduction associated with electroplating is eliminated.
McDowell et al. (1973) indicate that even with uranium in
108-fold mole excess over plutonium, quantitative separation and
recovery can be obtained. In summary, it appears that liquid
scintillation counting can be used to quantitate plutonium at
ambient concentrations, but the equipment and techniques are more
sophisticated than normally available at most laboratories.
Lieberman and Moghissi (1968) and Butler et al. (1971)
describe a technique using trace amounts of lanthanum to co-
precipitate plutonium. The essentially weightless precipitate is
collected on a membrane filter and is amenable to alpha spectro-
scopy analysis. There is some degradation of the alpha spectrum,
but apparently most samples can be quantitated easily. If there
is too much mass in the precipitate, it can be dissolved and
purified. Robinson et al. (1975) report cross-check results
between the EPA laboratory in Montgomery, Alabama*which uses this
technique and Mound Laboratory. The results show good reproduci-
bility. The co-precipitation technique apparently has received
only limited use, but appears to have definite utility, either
for those who do not have electrodeposition capability or who
would prefer an alternate technique.
Mass spectrometry (MS) provides isotopic data not available
from alpha spectroscopy (AS) (plutonium-240 and -241) and it also
has greater potential sensitivity than AS. In essence, it is
based on counting the number of atoms of a given mass. Thus, its
sensitivity, if converted to pCi/g, is greater for long half-life
nuclides than for short half-life nuclides, because more mass is
present for a given curie quantity. Mass spectroscopy often is
used only to determine isotopic ratios, but if a tracer is used,
it can be used to quantitate results. It often is used to
supplement alpha spectrometry results.
For the long half-life isotopes of plutonium, MS has the
potential for several orders of magnitude sensitivity greater
than AS. For the present day optimum state of the art, as
practiced by the McClellan Air Force laboratory, the routine
sensitivity of MS is about an order of magnitude greater than AS
sensitivity.
Mass spectroscopy is based on determing the number of atoms
of a given mass number. Thus, just as in AS, chemical separa-
tions are necessary to remove interfering elements. These
interfering elements may be either elements with isotopes of the
mass of interest (e.g., uranium-238 and plutonium-238) or iso-
topes that can be combined with the MS filaments to provide
•K
Eastern Environmental Radiation Facility (EERF).
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interfering mass units. Thus, more sophisticated chemistry (not
justified for routine samples) can be used to increase the
sensitivity by roughly an order of magnitude.
The sensitivity of MS for plutonium-238 is less than that
for AS. This is because of the short half-life of plutonium-238
and interference from traces of uranium-238. Also, because of
the short half-life of plutonium-236, plutonium-242 is the
preferred tracer. The present state-of-the-art routine sensiti-
vity for MS is about 10-13 g of plutonium (Merrell, Air Force
McClellan Central Lab, verbal communication May 1975). This can
be reduced to about 10-15 g with special chemistry techniques.
The value of 10-13 g is equivalent to 6 fCi of plutonium-239.
Isotopic ratios determined by MS often can be used to
determine the source of environmental contamination. Evaluations
by Krey (1976) and Krey et al. (1975) illustrate the utility of
isotopic ratios, in conjunction with quantitative results, to
distinguish the source of contamination.
Americium-241 can be quantitated by either gamma counting
with Nal(Tl) wafers (Majors et al.,1974) or Ge(Li) semiconductor
detectors. Quantitation is based on the 60-keV photon.
Plutonium-239 may then be estimated based on the plutonium-239/
americium-241 ratio determined from radiochemistry analysis of a
selected number of samples. The sensitivity of the americium-241
method is dependent on the associated gamma emitters in the
sample and the counting time. Brady (REECO, verbal presentation,
NAEG, May 1975) indicated a plutonium-239 sensitivity of about
50 pCi/g based on a plutonium-239/americium-241 ratio of ten.
This relates to an americium-241 sensitivity of about 500 pCi/g.
Brady noted the plutonium/americium numbers agreed within about
50 percent with chemistry numbers. The complications of
plutonium-239:241 ratios and americium-241 ingrowth time have to
be considered.
Piltingsrud and Stencel (1973) report on an X-ray measure-
ment technique for the low-energy X-rays from plutonium-239 and
americium-241. The detector is based on a sandwich of a Nal(Tl)
crystal backed by a Csl crystal. The two detectors have differ-
ent pulse rise times, thus photons interacting with both detec-
tors can be discriminated from low energy photons (X-rays)
interacting with the Nal detector. The sensitivity is about
20 pCi/g for 500 g samples - 10,000 pCi per sample (plutonium-239
+ americium-241).
The detector does not distinguish between plutonium-239 and
americium-241 or other low energy X-ray emitters. However,
except for plutonium-238 contamination (normally lower than
plutonium-239), most of the X-rays would be from plutonium-239
and americium-241.
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Calculation of Sample Activity and Estimation of Analytical Error
The calculations are based on multiplying the measured
sample activity by the ratio of the known amount of added tracer
to the recovered tracer. The counting errors generally are based
on propagation of the normal error based on the observed sample
and background counts (Johns, 1975).
There are several potential sources of error (not statis-
tical) associated with the various techniques. These include:
1. Use of plutonium-236 tracer, which has a relatively
short (2.85-year) half-life. Thus, the standard tracer
solution should be corrected for decay subsequent to
calibration, and recalibrated periodically.
In past years plutonium-236 contained a small amount of
plutonium-238 contamination. Thus, any initial cali-
bration error would be compounded with time due to the
relative increase of the plutonium-238 fraction, due to
plutonium-236 decay. The plutonium-238 contamination
must be subtracted from plutonium-238 results for
samples traced with plutonium-236. Furthermore, the
plutonium-236 tracer solution should be purified
periodically to prevent interference from the progeny--
uranium-232, thorium-228, and subsequent progeny
(Sill, 1974).
2. Americium generally is separated from plutonium prior
to analysis. The separation factor generally is
several orders of magnitude, so although the americium-
241 alpha is similar in energy to the plutonium-238
alpha, there should be little problem. But due to the
presence of plutonium-241, americium-241 ingrowth must
be considered. Mullins (EMSL-LV, February 1975) notes
that samples generally are counted within one month of
separation.
Table 19 indicates various plutonium-238:americium-241
ratios. It is evident that americium-241 ingrowth
cannot be ignored completely for normal plutonium
isotopic ratios.
3. Enough tracer should be added to produce a small
counting error for yield estimates. But there is some
uncertainty in the necessary amount due to varying
yields. Furthermore, if there is too much plutonium-
236, its peak can interfere with the plutonium-239
alpha peak. This can be compensated for by using blank
reagent samples, including tracer, for background
determinations. Sill (1974) and Johns (1975) suggest
about 10 dpm per 10-gram soil sample.
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TABLE 19. AMERICIUM-241 INGROWTH INTO PLUTONIUM SAMPLES
Activity Ratio a Time After Ci Am-241 b Activity Ratio
Pu-241:Pu-238 Separation per Gram Pu-238:Am-241
Cdays) Pu-241
166 00 0
166 30 0.013 51
166 60 0.038 17
166 90 0.065 10
166 120 0.15 4
a Assume plutonium-241 is 0.5% by weight or 891 by activity of
environmental plutonium at the time of release. Assume the
weight percent has decayed to 0.251 (about 15 years).
Assume the plutonium-239: plutonium-238 activity ratio is
35. Thus, per gram of plutonium, there is 110.3 Ci/g x
0.251 = 0.276 Ci of plutonium-241 and 0.0614 Ci Pu-239/g x
95% x 1 Pu-238/35 Pu-239 = 1.67 x 10-3 Ci of plutonium-238.
(Putzier, 1966; Krey and Hardy, 1970, and Del Prizzo et al.,
1970) .
b Putzier, 1966, Figure 13.
4. The separation of polonium from samples should be
considered. The alpha from polonium-208 tracer and
polonium-210 may interfere with plutonium-239.
5. The background measurement technique and time interim
between background measurements can be a source of
error. The background from reagents, glassware, and
the tracer should be assessed. The potential for
contaminating counters (especially from polonium) in
part indicates how often backgrounds should be taken.
Grouping together of samples of similar activity
levels for analysis minimizes the potentials for errors
due to contamination.
DISCUSSION AND COMPARISON OF TECHNIQUES
Table 20 summarizes the dissolution techniques used by
various organizations and investigators. As indicated in the
previous sections, assuming a representative sample is taken for
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TABLE 20. SUMMARY OF DISSOLUTION TECHNIQUES
Reference
Sample Dissolution Method
Type Acid
Leach Diss. Fusion
Comment
Church et al. (1974)
Johns(1975)
Krey & Hardy(1970)
Major et al.(l974)
Talvitie(1971)
Silland Hindman(1974)
Sill etal.(1974)
Hahn (in press)
AEC(1974)
Toribara et al.(1963)
Markussen(1970)
Chu(1971) HASL tech.
Essington (1973) LASL
Bokowski(1971)
Soil
Soil
Soil
Vegetation
Soil, Air Filters
Soil
Soil
Soil
Biological Samples
Environmental
Samples
Soil
Soil
Soil
Biological Samples
Coralline Soils
Biological Samples
Soil
Bains(1963)
AEC(1973)
Keough and Powers(1970)
Bentley et al.(1971)
Lieberman &Moghissi(-1968)Environmental
Samples
Corley et al.(1971) Soil
Butler et al.(1971) Soil
Wessman et al.(1971) Soil
Bishop et al.(1971J Soil
x
x
REECO, NTS
ESHL
Rocky Flats et al.
NTS checked residual by fusion
x KF & pyrosulfate fusion
x KF & pyrosulfate fusion
x Tentative Reference Method
x Carbonate & bisulphate fusion
x K pyrosulphate,
Thule samples
Proposes using HF and HNO,
on siliceous material
Modified HASL/LASL
Rocky Flats, Dow Chem.
Repeats HF-HNO- step
5 times
Leach plus HF.
Enewetak
LASL
x Alkali fusion
Hanford
x Study of fusion techniques
(after Chu, 1971)
May use 1 ml of HF in
leach
85
-------
432
analysis, the primary analytical concern is dissolution of the
sample. Other prime concerns relate to consideration and removal,
if possible, of interfering elements and ions (calcium, iron,
etc.)- This interference is of less concern than dissolution,
because generally it is reflected by low tracer yields and is
thus accounted for.
Analysis of samples by liquid scintillation counting or mass
spectrometry eliminates the need for electrodeposition, the
analysis step that has the greatest potential for interference
and loss of plutonium (Sill and Hindman, 1974). Liquid scintil-
lation tends to be less sensitive, without using special tech-
niques, than solid-state alpha counting. Thus, although it has
potential and possibly should be investigated, it will not
receive further consideration in this section.
Mass spectrometry has several virtues for plutonium anal-
ysis, including providing information on isotopic ratios and
improved sensitivity. But due to its limited use for quantita-
tion of environmental plutonium samples, the high sensitivity for
plutonium-238, and the expense for organizations to initiate this
type of analysis, it will not receive further consideration.
Furthermore, it entails the same concerns about dissolution of
the initial sample as alpha spectrometry. Also, it has its own
unique problems of separation and removal of interfering sub-
stances (iron, uranium, and hydrocarbons).
Sample Size
Sample size considerations, based on analytical sensitivity
and the representativeness of the sample have been discussed
previously. The analytical sensitivity generally is inversely
proportional to the sample size (e.g., sensitivity in pCi/g is 10
times higher for a 1-gram sample than for a 10-gram sample).
However, the increased amounts of interfering substances in large
samples may decrease the chemical yield and thus the relative
benefit of large samples. The discrete or heterogeneous nature
of plutonium in samples limits the minimum size for analysis
aliquots, depending on the acceptable variability of sample
results. This potential variability has been discussed pre-
viously, but the actual situation will depend on specific sources
of contamination and samples.
Sample Dissolution
A basic aspect of sample analysis is getting the plutonium
into solution. This not only applies to soil samples, but to
vegetation and biological samples. Butler et al. (1971) report
results of leaching techniques on two soil samples, one spiked
with plutonium-238 (possibly plutonium-239), and one contaminated
by an accidental release of plutonium-239. These results are
summarized in Table 21.
86
-------
433
TABLE 21. SOIL LEACHING EXPERIMENT
(From Butler, et.al. 1971)
Leach
Solution
Water
4^-HCl
12N[ HC1
IN. HF
28N. HF
4N HC1 , IN. HF
Sample Activity
Based. on Fusion
Analysis (dpm/g)
UOO-pSoiked
witii Pu, heateu
to 550°C
1700— Spiked
with238Pu, heated
to 550°C
1700— Spiked
with238Pu, heated
to 550°C
1700— Spiked
with 238Pu, heated
to 550°C
1700— Soiked
with 238Pu, heated
to 550°C
1700— Soiked
with 23°Pu, heated
to 550°C
Percent of
Activity in
Leached Fraction (a)
0
92
92
0
9
43
4N. HC1
4N HC1 , IN. HF
4N HC1 , 2N. HF
0.57 ± 0.40— soil (b)
contaminated with 2-"Pu,
heated to 550°C
0.57 ± 0.40— soil (b)
contaminated with 239Pu,
heated to 550°C
0.57 ± 0.40— soil (b)
contaminated with 2J9Pu,
heated to 550°C
39
87
> 100
a. One-gram sample boiled in 10-ml volume of leach solution, and allowed to
digest for 1 hour. Results based on average of two samples. The two
samples varied by less than about 10% except for the 2BH_ HF, in which
case they differed by a factor of 2.75.
b. Based on analysis of 21 1-g samples. Leach samples are based on treat-
ment of 20-g samples with 200 ml of solution.
87
-------
434
Table 22 indicates a comparision of leaching and fusion
results from Bishop et al. (1971) of Mound Laboratory and a
result from a cross check between laboratories reported by Sill
and Hindman (1974). Table 23 reports data from Sill and Hindman
(1974) for several different leaching conditions for plutonium
fired at various temperatures.
Chu (1971) reports results for three sets of samples ana-
lyzed by the leach technique (HCL/HN03) and sodium carbonate
fusion for both plutonium-238 and -239 (six results). The ratio
of the leach:fusion results varied from 0.74 to 1.46, with four
of the values being below one. The mean of the ratio was
1 ±0.24 (1 sigma). It should be noted that Sill et al. (1974)
and Butler et al. (1971) report difficulties (e.g., incomplete
recovery) for sodium carbonate fusions.
Essington (1973) reports data for analysis of a soil sample
spiked with plutonium (any heat treatment not indicated). The
results indicate that the former LASL acid leach technique
(10-g sample) only recovered about 64 percent of the plutonium-
239,based on the EPA/NERC-LV method (Johns, 1975) and the mod-
ified LASL leach procedure (includes HF and NaHS03).
Majors et al. (1974, p. 107) discuss the solubility of
plutonium-239 and americium-241 associated with desert vegeta-
tion. It is not certain how the plutonium is bound to the
vegetation. Although some may be taken up systemically, the
major fraction appears to be particulate material deposited on
the vegetation (Romney, verbal presentation, NAEG, May 1975).
Thus, the majority of the plutonium on vegetation probably is in
the same form as plutonium in soil, although possibly associated
with less siliceous material. The fraction of plutonium remain-
ing in vegetation ash after an acid leach is given in Table 24.
The fraction of plutonium removed from soil (apparently also
vegetation and probably air) samples by acid leaching is vari-
able. Values from various investigators range from less than 50
percent to 100 percent. The validity of the 100 percent value
may be questioned, since it is not based on the analysis of the
leach residual. Also, it was based on a sodium carbonate fusion
versus the technique of Sill et al. (1974).
In summary, it appears acid leaching may recover only
roughly 60 percent of soil-related plutonium, depending on the
source term. Acid dissolution, using HF may recover all of the
plutonium, but prudence would indicate that samples and/or
residuals should be checked by Sill's et al. (1974) pyrosulfate
fusion technique.
88
-------
435
TABLE 22. LEACHING VERSUS FUSION OF SOIL SAMPLES
Technique
HN03 leach of Pu-239
sample heated to 1000°C
(Sill and Hindman, 1974) ,
Bishop et al. (1971).
Sample
Activity
(dpm/g)
35
35
Percent Activity
Leached
From Sample
17
24
Percent of
Activity Found
in Residue
81
78
Pu-238 in soil (a)
Bishop et al. (1971) (b)
Bishop et al. (1971) (b)
Bishop et al. (1971) (c)
Sill and Hindman (1974)
0.04 ± 0.008
0.17 ± 0.03
1.59 ± 0.31
26 ±22
35
97.5 ± 18
114
103
53
27
± 36
± 15
± 18
No HF used
(3 determinations)
Ta)Error based on 8 replicate analyses, 1-sigma error
(b) Error based on 6 replicate analyses, 1-sigma error
(c) Error based on 11 replicate analyses, 1-sigma error
The residual of 8 of the aliquots were checked for plutonium-238. The
small amount of material found in the leach residual indicates that the
sample activity estimate, 26 dpm/g was biased or incorrect, possibly
because of discrete particulate material, and the sample size for fusion;
10 g versus 20 or 50 g for leaching. The analysis of residuals infers
the leaching recovery was 93 percent versus 53 percent.
Table 23. Leachability of Plutonium from Standard Soil No.3a
(from Sill and Hindman,1974)
Heat
treatment
2 hours at
110°C
1 hour at
700 °C
4 hours at
1000°C
4 hours at
1000°C
4 hours at
1000°C
4 hours at
1000°C
Plutonium
standard
High"
Low'1
High"
Low'1
High"
Low"
High'
Low
High"
Low"
High'
High''
Acid Soluble
dpm gram
29.2 ±0.5
0.452 ± 0.018
19.0 ± 0.3
0.256 ± 0.013
5.8 ± 0.1
0.071 ± 0.005
17.6 ± 0.2
15.4 ± 0.1
0.281 ± 0.015
19. 2 ±0.2
18.5 ± 0.2
98 0 ± 1.6
89.9 ± 3.6
63.8 ±1.0
50.9 ± 2.5
19.5 ± 0.3
14.1 ± 0.9
59.1 ± 0.7
51.7 ± 0.4
55.9 ± 2.9
644 ± 0.7
62.1 ±0.7
Residue
dpm gram
0 89 ± 0 04
0.024 ± 0.004
11.4 ± 0.3
0.246 ± 0.012
23.4 ± 0.2
0.422 ± 0.013
12. 0± 0.4
14.2 ± 0.3
0.224 ± 0.011
9.9 ± 0.2
10.9 ± 0.2
%
3.0 ± 0.1
4.8 ± 0.8
38.3 ± 1.0
48.9 ± 2.3
78.5 ± 0.7
83.9 ±2.5
40.3 ± 1.3
47.7 ± 1.0
44.5 ± 2.1
33.2 ± 0.6
36.6 ±0.6
Total
dpm gram
30.1 ± 0.5
0.476 ± 0.018
30.4 ± 0.4
0.502 ± 0.018
29.2 ± 0.3
0.493 ± 0 014
29.6 ± 0.5
29.6 ± 0.3
0.505 ±0.019
29.1 ± 0.3
29. 4 ±0.3
%
101.0 ± 1.6
94.7 ± 3.4
102.1 ± 1.4
99.8 ± 3.5
98.0 ± 0.8
98.0 ± 2.7
99.4 ± 1.6
99 4 ± 1 . 1
100.4 ± 3.6
97.6 ± 1.0
98.7 ± 1.0
" Calculated values are 29.8 ± 0 1 and 0 503 ± 0.003 dpm gram ol 239Pu lor the high and low standards, respectively. " Ten grams of soil was boiled
for 2.5 hours with 100 ml of aqua regia.' Ten grams of soil was simmered in a platinum dish for 2 hours with 95 ml of concentrated nitric acid and 5 ml of
48% hydrofluoric acid " Ten grams of soil was moistened with concentrated nitric acid and evaporated to dryness with 40 ml 48% hydrofluoric acid in
about 1 hour. *' Ten grams of soil heated to near boiling for 16 hours with 100 ml of either 95-to-5 or 50-to-50 of concentrated hydrofluoric acid and 8M
nitric acid
89
-------
436
TABLE 24. PLUTONIUM LEFT IN VEGETATION ASH AFTER ACID LEACHES*
(From Majors et al., NVO-142, 1974)
Plutonium in Leach Plutonium in Residue Plutonium in Residue
(dpm/g ash) (dpm/g ash) (Percent of Total)
118
47
151
44
63
231
354
69
54
174
284
326
355
22
19
37
0
3
66
249
3
0
20
5
0
6.2
16
29
20
0
5
24
41
4
0
10
2
0
2
* Leached with HN03-HC1 and H202.
90
-------
437
ANALYTICAL VARIATION AND REPRODUCIBILITY
Gilbert and Eberhart (1974) present data on within-lab
replicate sample variation. The samples are from the NAEG NTS
program. Thus, some of the variation probably is due to the
discrete particulate nature of the plutonium in the soil. This
data reflects a range in the coefficient of variation (sigma
divided by the mean) for replicates of 0.23 to 0.93.
Butler et al. (1971) report plutonium cross-check results
from aliquots of five standard soil samples. Three aliquots of
each sample generally differed by less than 10 percent. The
individual values and their means generally were within 10 per-
cent of the known values. The fusion method, after Sill et al.
(1974), was used for analysis of the 5-g samples.
Butler et al. (1971) also report the analysis of 21 one-gram
replicates of an environmental sample. The sample was taken near
a nuclear facility about one year after an accidental particulate
release. The contaminated area had been covered with about 12
inches of fresh dirt during the year prior to sample collection.
The sample was dried, muffled at 550°C, and thoroughly mixed
prior to taking the one-gram aliquots. The fusion results indi-
cated a range of 0.25 to 1.72 dpm/g with a mean of 0.57 ± 0.40
(1 sigma) dpm/g. As indicated in Table 21, acid dissolution of
20-g samples with 4N HC1 and 2N HF actually indicated slightly
higher and more uniform results.
Chu (1971) and Krey and Hardy (1970) report interlaboratory
results related to the HASL Rocky Flats study. The sample sets
include aliquots of two samples which essentially should have
been zero and several interlaboratory comparisons of different
techniques. These data are given in Table 17.
Bishop et al. (1971) reports seven replicate analyses of a
soil sample by the fusion technique. The sample was prepared by
Sill, after the methods of Sill and Hindman (1974).
Sill and Hindman (1974) report data on an interlaboratory
cross-check of their standard soil. This group of data include
a comparison of duplicate analyses from seven laboratories by
different techniques.
Data from AEC (1973) for the Enewetak cross-check calibra-
tion program include interlaboratory analysis of coral soil.
There are five groups of data.
91
-------
438
These various sets of data, including similar data from
Table 12 are summarized in Table 25. a The data include the
number of samples, sample size, the mean of the results, (x) , the
standard deviation, or error, based on the averaging of the
results (S), the coefficient of variation, (CV), (the standard
deviation divided by the mean), and the coefficient of variation
at the 95 percent confidence level (CL) based on the
t-distribution (e.g., multiplied by 3.182 for 3 degrees of
freedom). The actual percent analytical error also is presented
(x-u/ii) , that is, the difference of the mean from the standard
value divided by the standard. Missing data are indicated by
horizontal lines. The data are based on analyses of duplicate
samples made up from spiked samples, and analyses of actual
environmental samples. The emphasis on data selection was to use
data sets illustrating analytical variability versus sampling or
aliquoting variability. However, selection of data sets for this
intent is admittedly subjective. The data from Bliss (1974) and
Gilbert and Eberhardt (1974) probably largely reflect sample
inhomogeneity versus analytical variations. The data from Bliss
(1974) illustrate the reduction in result variability with the
increase in sample size.
The data from Sill and Hindman (1974) come from two sources.
The first two entries are from an interlaboratory calibration
test using the standard soil. The other entries are from efforts
to determine analytical sensitivity and sample homogeneity. The
samples are based on various dilutions of the standard soil with
uncontaminated soil.
Several observations can be drawn from the data in Table 25.
There is a large range in the coefficient of variation (at 95
percent confidence level) in the various sets of data; it ranges
from as low as 1 to 2 percent for Sill and Hindman1s (1974)
evaluation of the variance of analysis of standard soils, to
hundreds of percent for duplicate analyses of 1-gram aliquot
sizes of soils near NTS or interlaboratory analysis of soils with
close to zero plutonium levels (Krey and Hardy, 1970). The
nominal minimum 95 percent CV is about 10 percent where values of
up to 30 to 40 percent are common.
The counting error reported by the various authors (not
shown) generally is much lower than the sample result CV.
Although the values were similar for Sill and Hindman1s (1974)
sample variance studies, the sample averaging CV generally was a
factor of two or more greater than the counting CV.
The actual data sets can be obtained from the respective
references or a request to Mr. David Bernhardt, Environmental
Protection Agency, Office of Radiation Programs, Las Vegas
Facility, P. 0. Box 15027, Las Vegas, Nevada 89114.
92
-------
TABLE 25. SUMMARY OF ANALYTICAL VARIABILITY OR REPRODUCIBILITY
Reference Analytical
Technique
Sill and Hindnan (1974) Fusion
Mixed
Fusion
Sill (1971) Fusion
H II
AEC (Enewetak), (1973) Leach
ii ..
Gilbert and Eberhardt (1974) Acid dissolution
Butler et al. (1971) Fusion
H II
Fusion ' *
"
M
Bishop et al. (1971) Fusion
Krey K Hardy (1970) Leach
Bliss (1973) see
Table 10) Acid dissolution
ii ii
Robinson et.al. (1975)
Comments
Himber of Sample
Samples size
(grams)
Triplicate analyses by Idaho Falls lab 3
Triplicate analyses by 7 labs; 21
1 excluded
Analysis by Idaho Falls Lab 6
9
5
6
6
9
6
Ambient Soil by Idaho Falls 6
4
3-4 interlab analysis of coral soil 5
4
3
5
4
5 - Labi standard solution 8
Analyzed by LASL 34
" 9
'*
'5
23
12
5
(Analyzed by EPA(EERl) 3
Cross check samples 3
3
3
3
of Leach a KF Dissolution 3
and to^CO, Fusion 3
2
2
4
4
Mound Lab-Soil Std.
Pre-1945 Sample; 3 Labs 5
Excludes anom. frort above 4
Sample from below 90 cm, 5
Excludes anomalous result from above 4
Aliquots of EPA 14
a single Rielo 10
sample from ILL 4
near «TS LLl 4
Replicates of Background
10
0.5-10
10
10
10
1
10
10
1
10
10
10-50
"
5
5
5
5
5
—
..
.-
1
10
25
100
Mean,
(dpm/g)
35.2
34.1
32.6
0.64
29.5
29.1
29.4
0.503
0.553
0.11
0.057
17.16
0.51
0.49
2.09
0.45
1276
"*
15.77
0.031
2.43
16.34
0.50
342
1612
8.07
0.63
1.7
0.42
4.5
0.004
0.00015
0.014
0.0054
1.095
2.326
3.325
5.025
--
Plutoniun-239
Error. Analytical
S Error,
(dpm/g) J-I.A.
(per cent)
0.12
1.19
0.24
0.057
0.11
0.51
0.26
0.0088
0.043
0.005
0.0059
1.57
0.062
0.047
0.66
0.57
39
0.15
0.001
0.13
0.65
0.04
50
15
2.10
0.16
0
0.06
0.29
--
0.009
0.0001
0.018
0.0013
1.419
1.53
1.109
1.198
—
1.2
2.0
0.36
5.9
0.94
2.4
1.7
0.2
10.0
„
..
"
""
""
..
__
0.55
0
8.6
4.8
5.7
..
--
-.
..
"
CV
S/x
(per cent)
0.33
3.5
tt 74
9.0
0.37
1.8
0.9
1.7
7.7
5.02
10.3
9.2
12.1
9.9
31.6
12.7
3.1
69
81
Gf}
ea
26
33
0.97
3.2
5.1
3.9
8.1
15
1
26
26
—
13.6
6.4
--
215
67
136
23
130
66
33
24
"
CV at
95% CL,
St/x
(per cent
..
7.3
1.9
20.7
1.0
4.5
2.3
4.0
19.9
12.9
32.8
25.4
38.4
41.8
87.7
40.4
7.3
135 .
187 1
194 >
122 (
9?
4.2
13.9
22.1
17
35
64
4
11?
331
0
44
20
598
212
377
74
260
149
106
76
"
Plutonium-238
Number of Sample Mean, Error, Analytical
Samples Size * S Error,
(grams) {dpm/g) (dom/g) S-w ^
) (per cent)
3
15
6
5
6
6
-.
—
..
..
..
Probably reflect
discrete particulate
matter and sample
inhomogeneity
3
._
3
3
3
—
2
4
4
6 1
5
4
5
..
, Data treatment i
-. by log nortnai.
i probably related
particulate natu
SO 10
0.55
KOI
0.51
0.44
0.46
0.46
-_
—
--
0.34
--
_-
--
6.57
33.6
0.18
0.23
0.11
0.)7
36.8
0.0012
0.00013
0.00028
n Table
Range of
to disc
re of PI
0.077
0.056 5.5
0.44 75
0.02 0.6
._
0.026 4.8
0.070 0.7
0.15 1.1
__
..
--
..
--
--
0.055 32
-.
--
0.65
3.2
0.04
-_
0.26
0.11
0.12
2.43 1.1
0.0024
0.00005
0.00035
10
data
rete
utonium contamination
0.123
CV
S/i
(per cent)
10
43
3.2
5.6
15
3.3
--
—
--
--
"
16
--
.-
-_
"
10
9.4
2?. 9
—
1T6
100
70
6.6
200
40
125
160
CV at
95X CL ,
St/x
(per cent)
43
92
8.1
16.4
40
6.6
„
--
--
--
--
_^
--
—
--
69
—
—
--
--
43
41
98
—
1476
318
223
17
555
127
346
3ZO
CO
CO
-------
Figures 5 and 6 are histograms of ratios of results from the
AEC (1973) Enewetak program. The ratios represent the results
for samples split between the Air Force McClellan Central Labora-
tory (MCL) and either the Eberline Instrument Company (EIC) or
the Laboratory for Electronics, Environmental Analysis Laborator-
ies Division (LFE).
The histograms of the data indicate that the LFE/MCL ratios
(Figure 5) are centered around one. AEC (1973) concluded, based
on a log normal treatment of the data (geometric mean of 1.02)
that the average was not statistically different from zero (95
percent confidence).
The data in Figure 6 indicate the EIC/MCL data are centered
about 0.8. The geometric mean, excluding the lowest value of
less than 0.1, is 0.85, and indicates statistically significant
bias.
The interlaboratory calibration indicated that the EIC value
was 94 percent of the average of the other laboratories and 95
percent of the average of MCL. The LLL:MCL ratio was 0.96. The
calibrations of these laboratories may not have all been indepen-
dent. The intent of this discussion is to indicate the varia-
tions, not which laboratories were correct.
Robinson et al. (1975) report data from 20 samples split
between Mound Laboratory and EPA/EERF. These data indicated a
Mound:EPA average ratio of 0.93 ± 0.12 (1 sigma).
Table 26 contains data extracted from Table 25 which are
related primarily to analytical variability. The values have
been catagorized by the relative level of activity in the sample.
Table 27 includes data that generally are related to both samp-
ling and analytical variability.
The lowest sample value in Table 26 (Krey and Hardy, 1970,
0.00015 pCi/g) indicates the greatest variation. This is indica-
tive of analysis near the MDA. The one-sigma counting error for
these results was 100 percent of the mean. Assuming a 100-gram
sample and roughly 75 percent tracer yield, the counted sample
would have contained about 10 fCi (0.00015 pCi/g x 103 fCi/pCi x
100 g x 0.75). This sample should have been zero, since it was
collected prior to 1945. The value of slightly above zero may
relate to minor sample handling or analytical contamination (data
given in Table 17).
The data from Robinson et al. (1975) reflect the variability
of low level results and the importance of instrument and reagent
blank background. The results are based on gross counts with no
background subtraction.
Other than the previously discussed "zero" sample in Table
26, the coefficient of variation values show a limited
94
-------
10-
0.6
0.8
12 ] 4
RATIO OF RESULTS
—I—
1.6
Figure 5. Histogram of ratio of duplicate soil sample results
(LFE/MCL) from Enewetak, (Data from AEG,1973))
0.8 1.0
RATIO OF RESULTS
Figure 6. Histogram of ratio of duplicate soil sample results
(EIC/MCL) from Enewetak, (Data from AEG,1973)
95
-------
TABLE 26. VARIABLIITY OF ANALYTICAL RESULTS
VD
Reference
Krey and Hardy (1970)
Bulter et al. (1971)
Sill and Hindman (1974)
"
Robinson et al. (1974)
Bulter et al . (1971)
"
Sill and Hinchian (1974)
"
"''
Biship et al. (1971)
AEC (1973) Enewetak
Number Sample
Technique of Samples Size
(g)
Leach - 3
Fusion - 1
Fusion - 1
Fusion - 1
Fusion - 1
Fusion - 1
Fusion - 1
Fusion - 1
Fusion - 1
Fusion - 1
Fusion - 1
Fusion - 1
fusion - 1
Mixed - 7
Fusion - 1
Fusion - 1
Leach - 5
labs
lab
lab
lab
lab
lab
lab
lab
lab
lab
lab
lab
lab
labs
lab
lab
labs
4
3
6
9
9
3
3
3
3
6
6
5
6
21
3
6
3
__
5
1
10
10
5
5
5
5
1
10
10
10
0.5-10
10
1
_.
Plutonium-239
Mean Difference CV at Number
(pCi/g) From True Value 95% CL of Samples
(per cent) (per cent)
0.00015
0.031
0.55
0.50
0.64
0.50
2.43
15.77
16.34
29.1
29.4
29.5
32.6
34.1
35.2
1278.
67
0
10
0.2
5.9
5.7
8.6
0.6
4.8
2.5
1.7
0.9
0.36
2.0
1.2
3.1
212
14
7.7)
4.0 >11±9«
21 J
35
22
4.2
17
4.5-1
2.3
l.ol 2±2%
1.9 7 (exclude
7.3 1 7%)
0.33J
7.3
4
—
—
—
—
50
—
--
3
—
6
6
5
6
15
3
6
--
Plutonium-238
Sample Difference CV at
Size (pCi/g) From True Value 9535 CL
(g) (per cent)
0.
10 0.
0.
0.
0.
0.
0.
1.
0.
36.
00013
077
34
46
46
44
51
01
55
8
40
--
32
0.7
1.1
4.8
0.6
75
5.5
1.1
127 %
320 %
69 %
40 %
8.6%
16 %
8.1%
92 %
43 %
17 %
US
*>
to
-------
TABLE 27. VARIABILITY OF ENVIRONMENTAL SOIL SAMPLE RESULTS
ID
Reference
Krey and Hardy(1970)
Krey and Hardy(1970)
Krey and Hardy(1970)
Krey and Hardy (1970)
Butler et al.(1971)
Robinson et al.(1975)
Chu(1971)
Chu(1971)
Sill(1971)
Sill(1971)
AEC(1973)Enewetek
AEC(1973)Enewetek
AEC(1973)Enewetek
8Hss(1973)
Bliss(1973)
Bliss(1973)
Bliss(1973)
Chu(1971)
Chu(1971)
AEC(1973)Enewetah
Chu(1971)
AEC(1973)Enewetah
Chu(1971)Rocky Flats
Chu(1971)Rocky Flats
Eberhart & Gilbert(1974)
Eberhart & Gi lbert(1974)
Eberhart & Gilbert(1974)
Eberhart & Gilbert(1974)
Eberhart & Gilbert(1974)
Eberhart & Gilbert(1974)
FhPrhart & Gil hert(1974)
Technique
Leach-3 labs
Leach-3 labs
Leach-3 labs
Leach-3 labs
Fusion
Mixed
Mixed
Fusion-1 lab
Fusion-1 lab
Leach-3 or 4
Leach-3 or 4
Leach-3 or 4
Accid Cissol
Accid Dissol
Accid Dissol
Accid Dissol
lab
lab
lab
Leach or Fusion
Leach or Fusion
Leach 3 or 4
lab
Leach or Fusion
Leach 3 or 4
lab
Leach or Fusion
Leach or Fusion
Accid Dissol
Accid Dissol
Accid Dissol
Accid Dissol
Accid Dissol
Accid Dissol
Accid Dissol
lab
lab
lab
lab
lab
lab
lab
Type Sample
Pre-1945
"(above + 1)
Sample below 90 cm
"(above - 1 )
Amb. Soil
Background
Amb. Soil
Amb. Soil
Ambient Soil
Ambient Soil
Coral Soil
Coral Soil
Coral Soil
Near NTS
Near NTS
Near NTS
Near NTS
Amb. Soil
Amb. Soil
Coral Soil
Amb. Soil
Coral Soil
Amb. Soil
Amb. Soil
NTS Soil
NTS Soil
NTS Soil
NTS Soil
NTS Soil
NTS Soil
NTS Soil
Number
of Samples
4
5
5
4
21
4
2
4
6
4
4
4
14
10
4
4
2
4
5
3
5
3
3
24
9
15
15
23
12
5
Sample
Size
(g)
--
--
—
--
--
—
10
10
10-50
10-50
10-50
1
10
25
100
--
--
10-50
--
10-50
—
--
—
--
--
—
—
—
Mean
(pCi/g)
0.00015
0.004
0.014
0.0054
0.57
0.42
0.63
0.057
O.l'l
0.45
0.49
0.51
1.095
2.326
3.325
5.025
1 .7
4.5
2.09
8.07
17.16
342
1612
—
—
--
—
—
::
Plutonium-239
CV at
95% CL
212%
598%
377%
74%
1447.
44%
331%
33%
13%
40?
42%
38%
280% i
149% }
106% }
76% }
0%
20%
89%
112%
2558
64%
4%
135% }
1 87% j
200% j
124% j
122% }
57% j
92% j
Number
of Samples
—
—
—
—
—
50
--
—
--
—
—
--
--
Aliquots
probably
Sample
Size
(q)
—
—
—
—
10
--
--
--
--
--
--
--
of same
reflect
Plutonium-238
Mean CV at
(pCi/q) 95% CL
0.00013
0.0012
0.00028
0.00028
0.077
0.11
--
127%
555%
346%
346%
320%
318%
sample,
discrete particulate
non-homogeneous nature of NTS
related Pu contamination
--
—
—
—
—
—
—
Probably
—
—
—
—
—
—
--
reflect
0.23
0.17
0.18
6.57
33.6
discrete
1476%
223%
98%
43%
41%
particulate nature of
NTS related Pu contamination
-------
444
relationship to relative levels of sample activity. Observing
only Sill and Hindman's (1974) data, the values below 1 pCi/g
appear to have about five times the variation of the values above
29 pCi/g average of 11 ± 9% versus 2 ± 21 at 1 sigma). The
respective geometric means and geometric standard deviations are
x = 91, s = 2.3 and x = 1.5, s = 2.7 respectively. However, this
is a limited amount of data (only two concentration classes) from
which to make a conclusion. There are not sufficient results
from interlaboratory studies to conclude that they have more
variance than intralaboratory studies, although there is an
indication of this.
The data indicate more uncertainty in the plutonium-238
results than in the plutonium-239 results. Excluding the "zero"
result, the means of the percentage uncertainties for concentra-
tions around 1 pCi/g or less are 37 ± 31 percent for plutonium-
238 versus 11 ± 9 percent for plutonium-239.
The first four entries in Table 27 are for the above-
mentioned pre-1945 sample, and a sample collected in 1970, at a
depth of 90 cm. Both samples were analyzed by three laborator-
ies. In both instances the same laboratory presented results
about an order of magnitude above the other laboratory's results.
Upon request, the sample was re-analyzed with lower, but still
elevated, results. The disparity is the reason for the assess-
ment for both four and five samples.
It is possible that the soil sample from 90 cm was contamin-
ated by natural movement of plutonium. However, Krey and Hardy
(1970) note that it is probably more likely that the sample was
contaminated during collection and handling. This implies the
difficulties of handling and collecting samples of grossly
different levels of contamination without minor cross contamina-
tion occurring. The associated problems are the basis for the
recommendation that samples of various stratified activity levels
be collected and analyzed separately.Minor crosscontamination
from one sample can grossly affect the results of a sample of
much lower activity.
98
-------
445
SUMMARY AND CONCLUSIONS
This report has considered both field instrumentation and
sampling and analyses techniques for assessing environmental
plutonium concentrations. The report has centered primarily on
soil and air sampling techniques and plutonium-238 and -239
analytical techniques. However, much of the information applies
to the transuranic elements in general and to other types of
samples.
Field instrument techniques are not sensitive enough to
assess the ambient environmental levels (roughly 1 nCi/m2 or less
than 1 pCi/g in soil). The FIDLER's sensitivity is indicated as
about 130 nCi/m2, but the variabilities associated with field
work indicate uncertainties at even 200 to 500 nCi/m2 (roughly
50 pCi/g), and the need for confirmatory radiochemistry analyses.
Several refinements can be made in using the FIDLER, but
basicially it is a survey instrument, not an instrument for
quantitating concentrations.
There are several photon counting techniques that allow
direct estimation of americium-241, and to a limited extent,
plutonium-239 (X-rays), with associated estimates of plutonium-
239. The general sensitivities range roughly from 1 pCi/g for
americium-241 to 20 pCi/g for plutonium-239.
There are six basic sources of error or variation in rela-
tion to plutonium and other transuranic analysis of environmental
samples. These are sampling technique (soil), sample size,
sample dissolution, inadequate chemical equilibrium between
sample plutonium and the tracer, interfering elements, and quanti-
tation of results.
SAMPLING TECHNIQUE (SOIL)
Items to be considered in sampling programs include:
1. Sample representative of stated conditions; i.e.,
stated depth and area for soil samples. The area
sampled should be sufficient to account for minor
inhomogeneity.
2. Sample of pertinent depth; i.e., adequate depth to
measure total inventory (if that is the objective) and
appropriately limited depth to prevent unnecessary
99
-------
446
dilution of contaminated layer for deposition or
resuspension studies.
3. Generally, it is recommended that samples should
represent an area of about 1000 cm2 (1 ft2). The
variance associated with this or smaller areas has not
been quantitated, and would be source-dependent.
Sampling errors for a sample of 1-cm depth or less are
estimated to be up to 50 to 100 percent. The sampling
error for a 5-cm depth (100 cm2) are estimated to be
limited to about 20 percent. The estimate of 20
percent is based on soil mechanics theory (Terzaghi and
Peck, 1968) and a ORP-LVF field experiment.
SAMPLE SIZE
The potential for plutonium contamination to exist as
discrete particles results in a potential variation in sample
results of up to several orders of magnitude (roughly 95 percent
C.L.) depending on the sample size analyzed and the particle size
of the plutonium contamination. The ratio of the upper and lower
limits, at the 95 percent confidence level, for 1-gram aliquots
of samples is roughly a factor of 10 or more, based on a log-
normal distribution (see Table 11). It appears this ratio may be
reducible to about 2 (Sill, 1971 data, Table 9) by using 10-gram
samples. The ratio is reduced further, at least for less homo-
geneous samples, by using 25-gram and 100-gram samples.
Michels (1971) evaluated two groups of data for the Rocky
Flats, Colorado area. Using a log-normal distribution, he
divided the data of Krey and Hardy (1970) into two distributions.
One, for global fallout, had a geometric mean of about 2 nCi/m2;
the other, generally relatable to Rocky Flats contamination, had
a geometric mean of about 15 nCi/m2. He notes that the data of
Poet and Martell (1972) range somewhat lower (units of nCi/m2)
than those of Krey and Hardy. This probably is due to the more
shallow sample depth, 1 cm, versus 20 cm for Krey and Hardy
(1970). Furthermore, the data cannot be split reasonably into
the two distributions, possibly because of the increased variance
associated with shallow sample depth and small sample aliquot
size (10-g versus 100-g for Krey and Hardy).
Particle Size Distribution of Plutonium In Soil
Soil samples from Rocky Flats, Colorado, were partitioned
into size categories of less than 2 mm, 100 micrometer, and 10
micrometer diameters. The mass fractions based on the soil less
than 2 mm in diameter were 43 percent and 20 percent, for the
less than 100-micrometer and 10-micrometer (density 1 g/cm3)
diameter partitions, respectively. The plutonium-239 concentra-
tions (pCi/g) for the 100-and 10-micrometer fractions were 1.8
and 2.5, respectively, times the concentration in the less than
2 mm fraction. These results are in general agreement with those
of other investigators.
100
-------
447
SAMPLE DISSOLUTION
Sill et al. (1974) and Sill and Hindman (1974 indicate that
non-fusion techniques may leave up to 40 percent of refractory
plutonium in the undissolved residual for siliceous soils.
Butler et al. (1974) further note that sodium carbonate fusions,
etc. are not as successful as Sill's et al. (1974) potassium
fluoride and pyrosulfate fusions. Furthermore, it is not suffi-
cient to get plutonium into solution only, but it must also be in
the monomeric ionic state. Failure to obtain proper chemical
equilibrium (ionic state) between the sample plutonium and the
tracer gives invalid results, which may be either high or low.
Although acid leaching is adequate in some instances (Krey
and Hardy, 1970, and Chu, 1971), it may recover only up to about
60 percent of the plutonium in siliceous soils. Acid dissolution
with HF appears to recover more of the plutonium, but still has a
potential for incomplete recovery. It would appear to be prudent
to check insoluble residuals and complete samples with Sill's et
al. (1974) fusion technique. Hahn et al. (in press) and
Bretthauer et al. (1975) have proposed this technique as the
tentative EPA standard method.
INTERFERING ELEMENTS
Various elements (e.g., fluorine, calcium, iron, uranium,
etc.) can interfere with the various separation techniques and
stages in the preparation of actinide samples for counting. It
is common, and would appear to be necessary, to use tracers
(e.g., plutonium-236 or -242) for radiochemistry determinations
(other tracers for other elements). Thus, although all of the
sample plutonium may not be recovered, the fraction lost, other
than from incomplete dissolution, generally is accounted for.
Thus, any inaccuracies result in low (lack of dissolution of
sample plutonium) results. However, there are two additional
considerations. If the plutonium tracer is placed in an empty
beaker, it may bond to the beaker and be partially lost. The
sample plutonium would be recovered nominally. Furthermore, some
techniques (spills and bubbling or spattering) may result in some
loss of tracer prior to dissolution of the sample plutonium.
The second consideration is the effect on analytical sensi-
tivity of low tracer yields. This is difficult to quantitate,
but a yield of 10 percent has more potential uncertainty than a
yield of 100 percent. Plus there is the increased counting error
associated with the lower count rates of low recoveries.
Sill et al. (1974) note that the electrodeposition step is
the point of greatest potential plutonium loss (reduced yield) in
the procedure for alpha pulse height analysis. This is due
partially to the potential for plutonium co-precipitation with
other elements or the general formation of insoluble or non-
electroplatable plutonium. There is the additional problem of
101
-------
448
uranium or other elements being included in the electroplating
and forming a non-weightless plate, with associated alpha self-
absorption. Although liquid scintillation counting and co-
precipitation of plutonium with trace amounts of lanthanum
present alternatives to electrodeposition, electrodeposition
appears to be the technique preferred by most laboratories.
QUANTITATION OF RESULTS
The quantitation of results is done by alpha spectroscopy of
an essentially weightless sample or liquid scintillation, or mass
spectrometry. All of these techniques require radiochemical
treatment prior to final analysis. They each have their unique
interference problems. Although mass spectrometry is inherently
and, at the present state of the art, more sensitive than alpha
spectrometry, there is interference from hydrocarbons, and
because of the high specific activity of plutonium-238 and
interference from uranium-238, the sensitivity for plutonium-238
is poor. Mass spectrometry has the advantage in that it provides
isotopic ratios for plutonium-239,-240, and -241 and thus can
often be used to relate contamination to specific sources, even
when the plutonium-239 contributions are similar.
There are several means of defining the sensitivity of
analyses, or minimum detectable activity. The techniques that
give the lowest MDA's that are reasonably valid are based on the
two or three-sigma counting error. The NERC-LV technique (Johns,
1965) , defines the MDA value as the mean value equal to the two-
sigma error. Others, (Eberline) sometimes use three times the
background counting error, which generally gives results similar
to Johns (1975). In most instances when mean sample results are
below or equal to the MDA, they are expressed as less than the
MDA.
It should be recognized that most less than values are only
a 50 percent probability statement. That is, 50 percent of the
time the statement is wrong. A reasonable minimum MDA is about
20 fCi per sample; i.e., the counting error is 100 percent at the
2-sigma or 95 percent confidence level. In essence, these values
are per sample planchet, after electroplating. If the chemical
(tracer) yield is only 50 percent, the values per original sample
are doubled.
Variation of Results
An indication of the variance associated with the analysis
of samples and with both sampling and analysis is presented by
the data summarized in Table 28. These.data are summarized from
the presentations in Tables 26 and 27. The variance of results
is presented in terms of both normal and log-normal distribu-
tions. This is not to imply that the data fit these distribu-
tions, rather, they are used as tools to summarize the data.
102
-------
449
The data in Table 28 illustrate that the variation of
environmental soil sample results is much greater than just the
analytical variation. The variance associated with sampling and
analysis for samples equal to or less than 1 pCi/g is more than
twice that associated with just the analysis of samples. There
are mixed groups of data and the categorizations may be subjec-
tive, but the majority of the various data sets clearly indicate
that sampling and analytical error, or just analytical error,
exceed the counting error by several factors. Consideration of
the data compiled in Tables 25, 26, and 27 indicate that vari-
ances of less than 20 percent are the exception, rather than the
rule, even for results significantly above ambient concentra-
tions .
The following points become evident:
1. Analytical results for 10-gram samples at ambient
plutonium-239 levels (less than 1 pCi/g) can be expec-
ted to have (95 percent confidence) coefficient of
variation of about 10 percent plus or minus a factor of
two. Plutonium-238 results can be expected to have a
coefficient of variation of about 30 percent, plus or
minus a factor of two or three.
2. Reasonably homogeneous soil samples (10-gram) can be
expected to have a 95 percent confidence level coeffi-
cient of variation (CF/95 percent) of about 50 percent
plus or minus a factor of up to four (one-sigma).
3. Soil samples characteristic of NTS, presumably with
discrete particulate material, appear to be character-
ized with a coefficient of variance of over 100 percent
plus or minus a factor of about two. The size of the
sample aliquot affects the variation.
4. Data reported by Bliss (1974) exemplify the decrease in
variability of heterogeneous samples with an increase
in the sample size that is analyzed. The CF/95 percent
decreased from 280 percent to 76 percent for 1-gram and
100-gram samples, respectively. This is between a cube
and fourth-root relationship.
5. Plutonium-238 soil sample results at ambient levels
indicate extreme variability, although only limited
data were available.
It should be recognized that the above conclusions are based
on normal and log-normal treatments of the data. No tests have
been made concerning the applicability of these treatments.
However, the statements are not intended to be statistically-
proven hypothesis, rather they are indications of trends and
categorizations of the data.
103
-------
o
TABLE 28. SUMMARY OF VARIATIONS ASSOCIATED
WITH ANALYTICAL RESULTS AND
SAMPLING AND ANALYSIS RESULTS
Data Averaged
Analytical Results
1. Plutonium- 239, <_ IpCi/g
2. Plutonium-239, <_ IpCi/g
Average of 95 Percent CL
Coefficient of Variation (Percent)
Normal
Average
49
16
Distribution
Standard Error
81
12
Log Normal
Geometric
Mean
20
13
Distribution
Geometric
Standard Deviation
4.0
2.3
Kreg & Hardy Excluded
3. Plutonium-239, ^ 30 pCi/g
4. Plutonium-238
Sampling and Analysis Results
1. Plutonium-239, <_ IpCi/g
2. Plutonium-239,
Other than NTS
3. Plutonium-239, NTS
4. Plutonium- 239, Bliss, NTS
4. Plutonium-239
Gilbert & Eberhardt (1974) NTS
5. Plutonium-239, all
6. Plutonium-238
3
74
110
76
140
150
130
130
330
3
95
110
86
64
90
50
190
440
1.9
39
72
39
130
135
120
62
185
3.0
3.4
2.8
4.1
1.6
1.8
1.5
3.6
3.1
-------
There does not appear to be adequate in-depth data for a
rigorous evaluation of analytical and sample result variability.
Data of this type probably can be obtained through specially
designed intralaboratory and interlaboratory studies.
The results from Tables 26 and 27 contribute confirmation to
the previous conclusions.
The following items summarize some additional pitfalls and
concerns that must be considered in evaluating environmental
data:
1. Low chemical or tracer yields are indicative of diffi-
culties or interferences in the analysis. Prudence
would seem to indicate reduced confidence in low yields
(roughly defined as below 50 percent, or especially 20
to 30 percent") . Low yields can occur because of loss
of tracer prior to dissolution of sample plutonium,
etc.
2. Sample aliquoting procedures can result in nonrepre-
sentative results. Lung, liver, kidney, etc. samples
are not homogeneous. If sections are taken for anal-
ysis (especially pertinent to large bovine organs),
care must be taken to take representative fractions.
3. Gonads, lymph, etc. produce very small samples, resul-
ting in limited sensitivity.
4. Soft tissues produce variable ash weights depending on
the time and temperature of ashing. Results reported
per gram of ash are thus variable. Wet tissue weights
also are effected by dehydration, depending on packing
techniques.
105
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452
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113
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46(i
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114
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461
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115
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APPENDIX A
EMSL
WORKSHOP RECOMMENDATIONS
ON
SAMPLING AND ANALYSIS
Summarized by
Dr. Bernd Kahn
and
E. B. Fowler
116
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463
WORKSHOP RECOMMENDATIONS ON ANALYTICAL PROCEDURE
Dr. Bernd Kahn Analysis Report April 3, 1974
It is my impression Chat the consensus was as follows:
1. EPA should consider two analytical procedures:
a. The HSL (Idaho Falls AEC Health Services Laboratory)
fusion method.
b. A total dissolution with HNO.-HF. (Several versions
available, some more promising than others. For example, a
Los Alamos Scientific Laboratory method which is also the AEC
Regulatory Guide Method. More detailed method descriptions,
error evaluations and definitions of limits are available and
should be obtained from the different laboratories.)
2. In addition, references should be made in the EPA Reference
Method to procedures that have special advantages, for example,
for processing large samples or numerous samples. The applica-
bility of using these latter methods should be confirmed by
comparison with the above cited reference methods.
3. The proposed reference methods should be tested independently
by EPA before recommending them.
4. The 10 gram sample size appears to be appropriate, but
required minimum detectable levels should be arrived at by the
EPA to determine if the 10 gram samples are indeed sufficiently
sensitive.
5. The major contribution to the variability of results is
believed to be the occurrence of "hot" particles. It is desirable
that studies be undertaken to check the influence of sample size in
this variability. Guidance should be presented in the Reference
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Method to assure that samples will be sufficiently large to
minimize variability for the particle size expected at the
location from which the methods will be used.
6. Methods should Include thorough discussions of the principles
and purposes of each of the procedural steps; guidance for mini-
mizing errors, identifying the sources of the errors and calcu-
lating the magnitude of the errors; and specify a quality assurance
program, including a program for minimizing cross contamination.
7. Th« importance in using sufficient plutonium tracer for achieving
high precision should be indicated. Both Pu-236 and Pu-242 are
satisfactory if they are sufficiently pure.
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5/74
EBF
COMPILATION FROM THE EPA APRIL WORKSHOP
SOIL SAMPLING
Discussions relating to soil sampling consisted of four
parts: (1) presentation of papers, (2) panel discussion, (3) group
discussion to fix objectives, and (4) a synopsis of group conclusions
******
Sampling for two general types of mission for radioisotope
measurement were identified:
A. Sampling for low levels of radioisotopes such as that
associated with worldwide fallout, specifically for preoperational
environmental surveillance or the establishment of a base line prior
to the installation of a facility; and
2. Sampling to determine levels of radioisotope dispersal due
to release associated with accidental incidents, testing, or rou-
tine plant emission.
Although the above two are different in some respects, a basic
sampling procedure will apply to both situations. In the above two
situations there can be permutations such as an abbreviated survey
to locate areas for more intensive sampling in case (1) , or in
case (2) an abbreviated survey to determine whether a suspected
release has occurred and if it has, its possible extent.
Further, in case (1) , pre and post operational surveys will be
required to determine and document the effect or lack of effect
of operations on the environment. Case (2) may require an inven-
tory either immediately after or at some 'period of months or even
years after an incident.
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466
It can be argued that continuous air monitoring is sufficient
for industrial plant environs; this may be especially true since the
predicted plant of the future is a plant of "zero emission".
However, since the soil is an integrator and is relatively stable
with respect to air it is a desirable matrix for programs involving
extended sampling.
With the above factors in mind, the following recommendations
are made relative to the establishment of an on-going soil
sampling program. It is recognized that some of the permutations
referred to will negate certain recommendations, however, any sampling
protocol, even the simplest, should fall within the boundaries
set forth herein.
The boundaries which define problems associated with a sampling
program are outlined in Fig. 1; the objectives to be met are listed
in Fig. 2.
The objective of any sampling method is to obtain a representa-
tive sample. The following outline is set forth as a guide to accom-
plish that objective. In the connotation used here, sample prepara-
tion is included as a part of the sampling scheme.
Let us assume an extended sampling program which could entail
four phases;
1. pre-operation or base line,
2. operational or environmental surveillance,
3. operational incident or release,
4. post release monitoring and inventory.
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Fi gure 2
OBJECTIVES
I. Define Mission
A. What is. the purpose
1. Pre-op survey
2. Confirm trends
3. Determine inventory
(routine operation or accident)
B. What nuclides
C. What degree of precision is to be considered
1. Number samples/location
2. Number anal./sample
3. Cost
4. Analytical sensitivity
II, Choice of Analytical Method
A. Dependence on sample type and size
B. Degree of confidence greater than that defined
in mission definition
III. Sampling Methods
A. HASL Method
B. NAEG Method
IV. Choice of Sample Preparation Method
A. Dependence on analytical method
B. Define excludable material
D. Consider need for special treatment
121
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BOUNDARY CONDITIONS
Figure 1
DEFINE MISSION
Q
U
CHOICE OF ANALYTICAL METHOD
CHOICE OF SAMPLING METHOD
CHOICE OF PREPARATION METHOD
****
CROSS-CONTAMINATION
W
W
SAMPLE ACTIVITY LEVEE
a
ALTERNATE SAMPLE POINTS OR SAMPLING METHODS
w
.J
SOIL PARTICLE SIZE DEFINITION
SAMPLING STRATIFICATION
O
O
SUBSAMPLE SIZE
****
O
Z
H Q
D D
OB
W 10
CO
SAMPLE SIZE WITH RiiSPECT TO THE PARTICLE PROBLEM
SOIL STRUCTURE & CONSTITUENTS
•ANALYTICAL PROCEDURE WITH RESPECT TO THE PARTICLE PROBLEM
122
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489
-3-
A basic requisite to such an extended sampling program relates
to the final product, i.e. data reduced to a form that is communi-
cable and meaningful. Statistical advise at all stages of such
an extended sampling program is a must. The rationale for
statistical advice is two-fold (1) communication of results on a
common base,and (2) legalistics of today demand numbers which
cannot be refuted.
The sampling program may be nonbiased or biased. A statistically
designed program requiring random sampling would be considered
nonbiased; an extended sampling program should fall into this
category. An abbreviated survey might be biased -and could serve
an immediate "need to know". It might be acceptable under those
conditions or as a starting point or base for a nonbiased extended
survey.
Figures 1 and 2 outline the parameters which must be defined
in an approach to an acceptable sampling procedure; they will be
discussed in detail.
I. Define the Mission
A. What is the reason for the sampling program?
1. In the assumed case of an extended sampling
program, the reason for sampling will change with
time, however, a first requirement will be the
establishment of a base line, the pre-operational
survey. The survey should be both extensive and inten-
sive in that future trends and conclusions may be
based on the initial findings. A well-planned, random
sampling scheme will be valuable in the determination
123
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470
-4-
of an initial "inventory". Aside from test, accident,
or discharge site, the concentrations of radionuclides
found is expected to be low.*
2. A second purpose is that of defining or confirming
trends. Any trend will be related to the base line.
It is probable that a larger number of samples will
be required during early operational experience and
that samples will be taken at greater frequency.
Complete documentation as in '(1) above will prevent
a resampling of previous points.
3. A third purpose is that of determining an
inventory particularly associated with and after an
accidental emission. In case (1) and (2) above,
a surface sample only might be required, however for
inventory purposes, profile samples will be necessary
to assure that the highest practical percentage of a
radionuclide has been accounted for.
It is recognized that resuspended soil could have been or may
become a part of the soil sample, however, the separate sampling
of that fraction is a special case and is not considered in this
discussion.
B. What radionuclides are being 'sought and what is the
physical nature of the dispersed material? Plutonium
*Drainage areas, low spots, areas of heavy vegetation, and denuded
areas should be noted. The basic survey should be as completely
documented as possible.
124
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471
is considered the nuclide of prime importance,
however, the sampling scheme is applicable to many
radionuclides, including other transuranics as
well as uranium. Radionuclides of interest in the
future might include the noble gases and tritium,
though proposals stated here do not consider such
special cases.
The physical nature of the dispersed material
will dictate the sampling design in that particulate
material widely dispersed will produce "hot" and
"cold" samples whereas an emission of material in
a soluble form will result in samples more nearly
uniformly distributed in extent of activity. Further,
the analytical niathod of choice may be dictated by the
physical nature of the material, e.g. a refractory
oxide as opposed to material deposited from solution.
The degree of solubility of the nuclide, hence
transport through the soil profile will dictate the
need for profile samples and their depths hence the
sampling scheme should consider the chemistry of
the nuclide being sought as well as the purpose for
which samples are taken.
C. What is the acceptable degree of precision?
The acceptable degree of precision is probably a
management decision, however, it is related to the defined
purpose for sampling. Certainly the need to determine
125
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472
post-incident inventory would require a high degree of
precision if a material balance is to be attempted.
For the following discussion, several terms should
be defined; it should be pointed out that some
definitions may be redundant; they are given here for
explanatory reasons :
1. Sample
That discrete mass removed from a single sampling
point.
2. Sampling point
The defined volume from which a discrete sample is
removed.
3. Sampling location
A volume delineated by a section of a gri'' by an
isopleth or by other means which may define a
supposed commonality i-of activity) to the enclosed
population.
4. Sampling area.
The area of experimental interest whose boundaries
are defined by the mission. It may be a small
area, say 10 x 10 feet associated with a spill or
as in the case of worldwide fallout, it is the
surface of the earth.
In considering the degree of precision,
the following should be factored into a decision.
a. The number of samples taken at a location.
Certain factors will dictate this number;
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473
they may be knowledge of the problem,
previous sampling results, field instrument
survey, or others.
b. The number of analyses per sample.
Heterogeneous distribution of particulate
matter which varies in size will dictate
replication to establish "within sample"
variation. Once established, replication
on a given percentage of samples should
be practiced to confirm the presence or
absence of change.
The more nearly homogeneous the sample,
the fewer the replications which will be
required.
c. Cost.
It is obvious that the greater the number
of samples taken and the greater the number
of analyses performed, the more precise
is the resultant number. Cost will affect
the number of samples taken and the number
of samples analyzed; a compromise is naces~
sary. The extent of the compromise will be
dictated by the mission.
Gilbert (1) has given the following
guidance relating the above factors.
127
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-8-
S. / C,
M _ * — V 7^
opt sp V C2
where: C, = cost of taking and pre-
paring one sample from
field
C2 = cost of alalyzing one
aliquot
s = standard deviation relat-
v ing to variation in the
field position, and
s = standard deviation relating
a to Variation within a given
soil sample.
The relationship does consider cost
and standard deviation and forms one basis
for consideration of the degree of precision.
d. Analytical sensitivity
The adoption of a common analytical method
would represent the ideal. In the absence
of an ideal situation, the realistic
approach is to choose only those methods of
analysis which have been shown to yield
comparable results and sensitivities. The
mission will dictate the sensitivity required
in that short cuts in a method may yield
results less precise but acceptable to the
mission. Such a case might arise when a
few samples are taken downwind after a sus-
pected emission as a first check to determine
128
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475
-9-
"whether and to what extent". Certainly
high analytical sensitivity is desired
in the determination of a "most practi-
cable inventory".
II. Choice of the Analytical Method
A. The possible analytical methods of choice will be deter-
mined by the group reviewing that problem. However, the
choice will be dependent on certain characteristics of
the sample. It is also true that characteristics of the
sample may dictate minor modifications associated with
analyses. As an example, a low organic soil may be
digested without pretreatment whereas a high organic soil
becomes more amenable to analyses if an ignition step
Is incorporated to remove organic matter.
The sample size will also relate to the method chosen.
The presence of a heterogeneous population of particles
dictates replication of analyses or analysis of large
samples. The fusion of large samples presents many
problems not the least of which is the need to purify
from large volumes of salts.
It is also true that the degree of sensitivity desired
suffers when very small samples are analyzed.
B. The degree of confidence associated with the analytical
method should be higher than that defined for the mission.
Although the statement may seem redundant, it is a
129
-------
476
-10-
point often overlooked. Sample should be subjected to
the analytical procedure and the "degree of confidence"
determined and related to that defined in the mission.
Since the sample cannot be changed, the analytical
procedure may require modification.
III. Sampling methods
A. Two methods for sampling soils for radioactive constit-
uents have been used with success; these are the HASL
method ' based, on the work of Alexander ' and the
NAEG method developed for the sampling of dry, sandy
soils. The NAEG method lends itself more readily to
true random and profile sampling; it does have the dis-
advantage of requiring more time per sample than does
the HASL method. The mission will determine tha method
more nearly applicable.
The recently prepared draft guide AEG Regulatory
4.X is also suggested as a reference.
B. Important points related to the sampling of soils for
radionuclide content are as follows:
1. As stated, the prime purpose is to obtain a representa-
tive and discrete sample hence classical methods,
such as conservation auger, do not apply.
2. Cross contamination of samples must be avoided; cross
contamination will bias final results, especially
profile samples taken for the purpose of determining
an inventory.
130
-------
3. Volume and area of samples must be known precisely
as factors in the calculation of overall aerial
concentration.
IV. Choice of sample preparation method
Sample preparation is considered a part of sampling in
this discussion; it relates to both the sampling method and
the analytical method of choice. The cost of analysis
(C2, page 3) is markedly effected by preliminary preparation;
the purpose of the mission will dictate to some extent the
sophistication of the preparation method employed. The best
sample is the total sample, however the cost of preparation
will dictate screening and/or aliquoting in many cases.
A heterogeneous particle size population will be present
in certain types of emissions, e.g. fires or explosions.
(41
Using the method of Leary it has been calculated that
239-240
a spherical particle of Pu°2 ' ^4 microns in diameter,
would assay at 86/000 d/m. In an actual analysis of one
gram aliquots from the same sample, activities ranging from
that level to 6 d/m/g were found.(5)
There is no known state of the art technique which will crush
particles of those sizes to a uniform size and distribute
them homogeneously throughout the soil matrix.
A prerequisite to sample preparation is the determination
of a standard dry weight (105-110°C for 24 hours or to constant
weight) on a known vaolume related to a known area.
A. Preparation of the sample is dependent upon the analytical
method of choice. The ideal aliquot to be analyzed will
represent the entire sample, hence the aliquot taken
131
-------
418
-12-
should not contain stones or pebbles which will drop from
the spatula and thus bias the sample. If stones and
pebbles are present as such, the dissolution process will
be extended and the cost increased. A pulverizing or
flouring of the sample is most effective in reducing it
to a form most amenable to analyses. However, in this
respect samples with detectable activity must be processed
in a dry box provided with an adequate air cleaning system;
the treatment will produce fines (which have been shown to
contain a high percentage of plutonium); the fines will be
lost to the filters and the results biased.
A further point relates to crass contamination. A
pulverizing mill used to prepare higher activity samples
must be dismantled and decontaminated between samples;
this is a costly procedure.
B. Definition of Excludable Material
The problems associated with A above can be solved in
part by nested or contained mechanical sieving within an
enclosure. With a single sieve, two fractions will be ob-
tained that passing, and that not passing. That passing
will comprise the sample for analyses; that not passing is
designated excludable material. Excludable in this sense
connotes excluded from the primary "to be analyzed"
sample. There remains to define the screen size and treat-
ment of the "excludables".
A 10 mesh screen size for preliminary separation is
132
-------
acceptable. Root mat, large organic pieces, stones; pebbles/
etc., which will not pass are removed from the sieve and
weighed. Root mat and other organic detritus which is
a definite part of the soil matrix (i.e., below soil
surface level) should be added to the less than fraction
and that fraction weighed.
The excludable rocks, stones, etc., may pose a problem;
it has been shown that a very small percentage (less than
3%) of total activity is associated with this material
and hence may be discarded. However, a confirmation of
"negligible percentage" may be desirable in which case
the material may be acid washed and the washings added to
the less than fraction or analyzed separately; if the
washings are added, a second drying and weighing should be
performed to obtain final weight of the "less than" fraction
and to prepare it for following steps.
It is probable that some samples will contain above
ground vegetation. Although this is part of the "collection
system", it is not part of the soil system. The mission
will define whether the total collector or the soil alone
is of importance. In either case, it is recommended that
vegetation be removed as a separate sample at ground level.
Results of analyses can be weighted and combined if re-
quired.
C. The fraction passing 10 mesh is to be blended, mixed or
ball milled; ball milling is recommended.
135
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£30
-14-
The NAEG procedure employs one (1) gallon paint
cans protected by an outer brass sleeve. The pro-
tocol designates ball milling to the point where
about 90% of the sample will pass a 100 mesh
screen. The mission, cost/ and analytical pro-
cedure will dictate the extent of ball milling.
The sample is screened (100 mesh) and the- weights
of material passing and not passing are recorded.
The less than 100 mesh material is the sample used
for analysis. Drying at 110°C for 24 hours will gen-
erally brittle most material to the extent that it will
ball mill properly/ however/ certain root material will
not pulverize. The mission will determine the relative
importance of root mat; if important, the organic detritus
removed from the 10 mesh screen can be weighed/ ignited/
and the ash added to the sample being prepared for ball
milling. The importance of base stem absorption
-------
481
-15-
D. Need for Special Treatment
A need for special problem or special study samples
is not a unique occurrence and is noted here-only to
alert the reader that on-site decisions may be required
to modify either the sampling or preparation procedure
or both. The mission as well as physical conditions of
the sampling point will determine factors which can be
considered for modification. It is strongly urged that
the boundaries set forth in Fig. 1 be used to guide the
sampling.
V. Addendum
A. Controllable Variables
1. Analytical results are no better than -the samples
submitted; it is iinportant to control all variables
which can be controlled.
a. The NAEG sampling protocol presents guidance to
minify possible cross-contamination; the added
effort required is minimal.
b. Sample activity level can be controlled best by
instrumental survey in the field to delineate
those which are relatively "hot" or "cold" and
thus alert the analyst to the aliquot size required
for good statistics.
A second approach involves a screening of
samples in the laboratory by means of GeLi scan
or other appropriate instrumental survey.
The GeLi scan for
135
-------
-16-
241
Am (60 keV) is especially helpful'in the ab-
*\ A "\
sence of fission products if Pu forms a part
of the radionuclide population; it is of little
value in the presence of significant levels of
fission products. Americium-241 x 10 has been used
to indicate a possible plutonium concentration.
However, the factor of 10 is variable and of ques~
tionable value in cases where plutonium concentra'-
tion is low, hence the technique is limited to
certain emission problems. However, the above can
in certain conditions guide the analyst as to
aliquot size.
c. Alternate Sampling Points - An initial statistical
design for random sampling should consider the
possibility that a sampling point cannot be used
such as extended rock outcrop, hence some alternate
random numbers should be available to be chosen
should the need arise.
d. Soil Particle Size Definition - The size of soil
particles which can be effectively sampled and
meaningfully analyzed is limited. This item is
closely related to "c." above. A sampling point
consisting of one to two inch stones is of ques-
tionable value; a second set of random numbers
should be available for such events if dictated
by the mission.
Sampling Stratification
In the case of plutonium distribution (provided
241
Pu is present) a FIDLER instrument set to detect
136
432
-------
483
-17-
241
the Am 60 keV energy peak is of value in delineating
stratification and assigning a range of levels to be
expected.. Such an initial separation assists the
analyst in grouping samples of like activity, reduces
possibility of serious cross-contamination of samples
in the field and guides the statistician in designing
the sampling scheme. Other means of stratification
may be used such as grass vs areas of brush or dry
runs or creek beds vs upland.
3. Subsampling or Aliquot Size.
The aliquot size necessary to obtain some relatively
constant level of activity per unit volume or per
final plate for counting can be determined within
reasonable limits by a GeLi scan as previously out-
lined. The activity per gram in many samples may be
so low as to require a volume of soil too large to be
accommodated by the analytical procedure and meet
the suggestion of constant level of activity per plate.
A relatively constant activity per unit volume or per
plate simplifies counting (sample changing) and reduces
gross cross-contamination possibility when lower level
samples follow much higher level samples.
B. Certain Variables Require Further Study; In a Sense, These
are Uncontrolled Variables at Present.
It has been pointed out that the distribution of
particles relates to sample size. The distribution is
one of size of particles as well as aerial distribution.
In the cases of an emission or an inventory oriented
137
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484
-IB-
mission, initial distribution or change in distribution
with time are unknown. Investigation to define a
representative sample under such conditions will be
desirable.
The effect of soil structure and constituents on
the representativeness of samples is unknown. Do
particles per s_e transport through the soil profile;
what is the chemical nature of the radionuclide in
the soil constituents on transport, for example, the
effect of organic matter on "solubility", chelation,
or even insolubilizing of radionuclides? These
questions are unanswered.
Such questions relate directly to profile sampling
for inventory.
Are the analytical procedures equally effective
with respect to all particles and their possible
chemical states or forms? What sampling, preparation,
and analytical methods apply to glassy material such
as trinitite?
Are there conditions under which highly resistant
forms (to chemical analyses) are produced — and thus
not accounted for? Tracer recoveries will not provide
the answers.
138
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Appendix 6
Radlonucllde Information
«o
Half Specific Weight X of Predominant
Life Activity Nucllde In a Particles
Ref. Nucllde (vrs) (C1/q) Weapons Hat. (MeV) (X)
(1)
2
2
3
4
1
5
*
4
Pu-236 2.85 520
2.85
Pu-238 86
86
89.6 16.
86.4 17.
Pu-239 24
24
1) 24
5)
2
4
1
5
2
4
1
5
2
24
Pu-240 6
6
6
Pu-241
,000
.400
.400
,440
,600
,540
.580
17.
0.
0.
0.
0.
13.2 113
14.8
112.
3 Am-241
4
6
1
5
2)
4) Pu-242 380
1
S
(2
387
379
References
13.2
433
462
433
433
,000
,000
.000
'• LedererMn
2. Budn1tz[19
3.
0.
0.
0.04
8
4
34
062 94.5
0613
93.34
227 S
226
6
0.5
2
0.58
22
00391
0039
0.04
S
5
5
5
5
5
5
5
4
5
S
5
4
.50
.50
.50
.16
.14
.16
.16
.16
.9
,57
.48
.49
.90
71.9
72
72.2
72.0
72.5
73.0
76
75.5
0.004
85.3
85
76
10 - 20 keV
keV X keV
13.6 4.60
17-keV
13.6 1.74
17-keV
13.6 1.55
17-keV
14 16
17-keV
17-keV
14 12
17
17
band:
17.0
17
band:
17.2
17
band:
17.4
17
band:
band:
17.8
X-Rays Gamma Rays
20 - 30 keV 20-30 keV 55 - 65 keV
X keV X keV X keV X keV X keV X keV X
4.31 20.2 0.58 43.5 0.04
13 45 0.034
10.55
1.63 20.2 0.22 band: 3.59 38.6 0.04 46.2 0.001 51.6 0.025 56.8 0.001
2.9 band: 2.9 39 0.003 53 0.007
39 0.001
4.9 band: 4.9
1.86 20.2 0.39 band: 3.8
10 44 0.01
10
15 20.82.0. 26.33.1' 43.40.01 59.538.4
37 26 2.7 43 0.06 60 37
37.6 26.4 2.5 43.4 0.07 59.6 35.9.
43.4 0.07 59.5 35.3
37.6
13 20.8 3 26.3 2.5 59.6 36
7§rs)
3. Poston(1975)
4. Putzier{1966)
5. Tlnney et. aj.(1969)
6. Nagnusson(1957)
CJ1
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486
APPENDIX C
TABLE C-l. FREQUENCY DISTRIBUTION TABLE FOR 80 ALIQUOT
RESULTS ON REPLICATE SOIL SAMPLES
FROM PENOYER VALLEY, NEVADA
Interval
0. -
1.1 -
2.1 -
3.1 -
4.1 -
5.1 -
6.1 -
7.1 -
8.1 -
9.1 -
10.1 -
11.1 -
12.1 -
13.1 -
14.1 -
15.1 -
16.1 -
17.1 -
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
Midpoint
0.5
1.5
2.5
3.5
4.5
5.5
6.5
7.5
8.5
9.5
10.5
11.5
12.5
13.5
14.5
15.5
16.5
17.5
Frequency
46
10
5
2
3
2
3
3
0
1
0
2
2
0
0
0
0
1
Cumulative
Frequency
46
56
61
63
66
68
71
74
74
75
75
77
79
79
79
79
79
80
Percent
Cumulative
Frequency
57.5
70
76.3
78.8
82.5
85
88.8
92.5
92.5
93.8
93.8
96.3
98.8
98.8
98.8
98.8
98.8
100.
Range of Data: 0.15 - 18.0 pCi/g
Interval Width: 1.0 pCi/g
140
-------
100-
487
10-
ex
A
0.1-
10 20 30 40 50 60 70 80
CUMULATIVE PERCENTAGE
90
98
Figure C-l.- Probability plot of replicate samples,
Penoyer Valley, Nevada.
141
-------
489
TECHNOLOGY AND COSTS FOR CLEANING UP LAND CONTAMINATED
WITH PLUTONIUM
C. Bruce Smith
Janet A. Lambert
April 1978
U.S. Environmental Protection Agency
Office of Radiation Programs
Technology Assessment Division
Washington, D.C. 20460
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£31
PREFACE
The Office of Radiation Programs (ORP) of the Environmental
Protection Agency carries out a national program designed to evaluate
public health impact from ionizing and nonionizing radiation, and to
promote development of controls necessary to protect the public health
to the environment. This report provides the technical information
necessary for ORP to evaluate the environmental aspects concerning the
costs and technology of cleaning up plutonium contaminated land. This
document is part of the supporting documentation for the Federal
Radiation Guidance for the cleanup of plutonium contaminated land areas.
David S. Smith
Director
Technology Assessment Division (AW-459)
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492
TABLE OF CONTENTS
I. INTRODUCTION,
A. Purpose 1
B. Summarization 2
(1) Technology 2
(2) Costs 3
II. TECHNOLOGY 4
A. Removal 4
B. Stabilization 6
C. Restriction of Land Use 6
D. Special Techniques 7
E, Procedures for a Project 7
III. COSTS 9
A. Removal, Stabilization, and Restriction of Land Use 9
B. Special Techniques 10
C. Plutonium Cleanup Experience 11
D. Economic Losses Resulting from Pu Decontamination 11
Projects
APPENDIX A - Eases for Costs in Table 2 12
Part 1 - General Information 12
Part 2 - Discussion of Specific Techniques 28
APPENDIX B - Special Techniques 37
Part 1 - Technology 37
Part 2 - Costs 39
TABLES
Table 1 - Plutonium Decontamination 40
Table 2 - Decontamination Costs 41
Table 3 - Adjustment Indexes 42
Table 4 - Summary of Techniques and Costs 44
Table 5 - Plutonium Cleanup Experience Costs 45
Table 6 - Uses for Stabilizers and Approximate Costs 46
to Apply to Acre
Table 7 - Value of Crops (per Acre) in 1973 47
Table 8 - Value of Forests (per Acre) in 1974 48
REFERENCES 49
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493
I. INTRODUCTION & CONCLUSIONS
A. Purpose
Plutonium contaminated* land areas can have an adverse impact
on man if the plutonium is resuspended in the air (inhalation pathway)
or if the plutonium is concentrated in plant life (direct ingestion by
man or ingestion of animals that feed on the plants). Usually, the
primary potential radiological hazard to man from land areas
contaminated with plutonium results from the resuspension of the
plutonium in the air as a particle. If the plutonium is plowed under,
then the primary potential radiological hazard may be through ingestion
of plant material. To reduce the potential radiological environmental
impact on man, three general techniques normally can be utilized:
removal of the plutonium from the land surface area, stablization of
the plutonium on the land, or restriction of the use of the
contaminated land. The purpose of this paper is to discuss the
technological feasibility and the unit costs of employing these
techniques or of utilizing several special techniques.
It is important to note that the Environmental Protection Agency is
currently involved in developing environmental criteria for radioactive
disposal and standards for the management of high-level radioactive
waste. In addition, standards may be prepared for other forms of waste
in the future. Many of the decisions regarding what must be done to
meet these criteria and standards may not be made for several years.
Currently guidance for cleaning up plutonium contaminated lands is
reaching final development. However, the acceptable methods for
cleaning up contaminated land and disposing the wastes have not been
determined at this time. This determination will probably result from
a cost-benefit analysis for each individual site. However there may be
some types of disposal that will not be considered acceptable for waste
removed from any contaminated site. In light of the uncertainty of
acceptable waste disposal techniques for wastes removed from
contaminated sites and facilitie's, this paper does not intend to select
acceptable cleanup techniques nor compare the pros and cons of various
cleanup techniques except on the basis of general costs. In this
respect, there may be several techniques evaluated which may eventually
be determined unacceptable as a result of future standards development.
With regards to the environmental criteria applicable to all
radioactive waste, it has been recognized that there is great need to
place a limit on the time period in which reliance can be placed on
institutional controls. In applying this consideration to the subject
of this paper, it is emphasized that reliance on institutional controls
such as fences and guards cannot be found acceptable for long periods.
The length of an acceptable period has not been determined at this
* Land areas are "contaminated" with plutonium if the resulting
environmental impact of the area exceeds any Federal regulation
or guidance.
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writing but has been proposed as 100 years by EPA. Placing a time
Limit on institutional controls implies that the site or facility will
evenutally revert to unrestricted use which, in turn, involves the many
unresolved issues related to decommissioning. Thus, the use of
institutional controls merely delays implementation of decommissioning
standards and/or criteria. However, this delay can be quite effective
for reducing environmental and public health risks in those cases
involving shorter-lived radioactive materials.
The decision to apply any cleaning techniques to plutonium
contaminated land areas should be based on Federal regulations and
guidance and on a net improvement in the environment. The levels of
radioactivity requiring clean-up or those to which the clean-up should
proceed, as well as the aspect of control over the contaminated land
areas are not addressed in this paper. The paper also does not address
the clean-up of urban or industrial areas (our focus was on farmland,
arid and semi-arid open land, prairies, mountainous areas, and forests)
nor does it attempt to define or recommend which techniques could, or
should be used, on the different kinds of land areas. Instead, the
paper presents a discussion of the available techniques for plutonium
clean-up projects since each project site will vary relative to a large
number of critical factors which significantly affect the costs and
effectiveness of the various techniques. Some of these factors are
physical in nature (such as the terrain, remoteness, climate, weather
conditions, type of environment, use of the land, existence of
vegetation, type of vegetation, type of soil). Other considerations
are the restraints of surveying the area (which can cause delays) and
the necessity for worker protection during clean-up (type clothing,
respirators). These factors relate to the type and quantity of
contamination. If there is any significant external radiation exposure
to the workers, the costs and difficulties with performing effective
clean-up operations may increase significantly.
B. Summarization
1. Technology. For any project, each of the general
techniques - removal, stabilization, restricted use - will involve
several or all of the following steps (or procedures): (a)
radiological support, (b) stabilization, (c) removal, (d) packaging,
(e) transportation, (f) ultimate** disposal, and (g) restoration. The
technology of and relationships of the techniques and the procedures
are discussed in Section II. In summary, the procedures that may be
employed with existing technology are:
(a) Radiological Support - A survey team employing such
instruments as alpha survey instruments, and FIDLERS, or lab-
oratory type instruments used in the field.
** The term "ultimate" means the resulting fate of the land at the
conclusion of the specific technique. Other measures concerning
the land may be required in the future and are discussed in the
appropriate sections.
-------
- 3 -
Cb) Stabilization - Plowing, application of
chemicals, vegetative cover, soil, sewage sludge, asphalt, or
foam.
(O Removal - Harvesting crops, removing vegetation and
trees, scraping soil, vacuuming soil, flooding land.
(d) Packaging - Containerization of vegetation, soil, or
solidified wastes.
(e) Transportation - Transport soil on or near the contam-
inated land area or transport containerized material to a wao,e
burial ground or a Federal Repository.
(f) Ultimate* Disposal - restriction of land used; retention
of the soil onsite (stabilization, concentration of soil as windrows,
mounds, or in trenches); burial or storage at waste burial grounds,
the Federal Repository.
(g) Restoration - application of soil, fertilizer,
stabilizer, seeds, seedlings, shrubs.
2. Costs. There are several general techniques that can
be utilized to reduce the environmental impact of an area contamin-
ated with plutonium. A representative sample of the most often applied
techniques is summarized in Table 4 along with their range of costs
and average costs, and the advantages and disadvantages of each. A
discussion of the costs is presented in Section III. Generally, the
average^costs (normalized to 1974 dollars) are:
(a) Restriction of land use $1100/acre
(b) Stabilization $2400/acre
(c) Soil removal, onsite retention S4800/acre
(d) Soil removal, offsite disposal
or storage at:
(1) a waste burial ground $145,000/acre
(2) the Federal Repository $515,000/acre
* The only truly "ultimate" disposal technique is elimination of plutonium
contaminated soil by extraterrestrial means or transmutation. If any of
the other disposal techniques are used, then it is always possible that
additional measures may be taken in the future to restrict the land use
or dispose of the contaminated soil.
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436
-4-
II. TECHNOLOGY
The potential environmental impact of plutonium deposited on
land areas may be reduced by a number of methods. Almost all of the
methods can be categorized as one of three general techniques - removal
of soil, stabilization of the land area, and restriction of the use of
the land. In utilizing any one of these three techniques, several or
all of the following seven procedures or steps may be necessary -
radiological support, stabilization, removal, packaging, transportation,
ultimate disposal, and restoration. The approach taken in this evalua-
tion is to present (1) a general discussion of the three techniques;
(2) a discussion of the seven procedures or steps; and C3) a discussion
of their relationship with the three techniques. Also a discussion will
be presented of several special techniques that are not generally appli-
cable to projects involving the reduction of the radiological environ-
mental impact of Pu contaminated on land areas. Finally, a short dis-
cussion of the effectiveness, advantages, and disadvantages of the
techniques will be provided.
A. Removal
Removal includes options such as raking and grubbing out
vegetation, stripping the top layer of soil by scraping, vacuuming,
flooding, or applying a polyurethane foam cover (or other chemical
cover) that removes the top layer of soil when the foam is removed.
Disposition of the contaminated soil and materials thus collected
will depend on factors such as quantity of materials; contamination levels;
local demography; meteorological and hydrological characteristics; land
value; and land usage. Hauling will generally be required to dispose of
contaminated soil offsite. The soil would have to be placed in containers
or enclosed hauling vehicles prior to hauling. Local conditions permitting,
however, burial may be preferable on or near the site (these methods are
discussed under the stabilization section;.
After an area is contaminated with plutonium, initially the
''bulk of the plutonium would be expected to reside very near the surface
of the soil, on vegetation, on litter layer, etc. The distribution of
plutonium also depends on the method of its release (airborne or liquid)
* A description of the packaging requirements for plutonium contaminated
soil are outside the scope of this paper. Current regulations for pack-
aging are contained primarily in 10 CFR Part 71 and 49 CFR Parts 171
through 189.
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£97
-5-
and thus it may not always reside near the surface of the land. As
weathering occurs and the area is disturbed by the forces of nature,
part of this plutoniura will be carried from the area, part will be
distributed on the soil surface, and part will penetrate into the soil.
The exact movement and distribution of the plutonium in the soil after
weathering is very dependent upon climate, type of soil, and time
elapsed before removal begins.
Raking and grubbing to remove vegetation and mulch will have
variable effects depending on the time span since the plutonium was
deposited on the land. As time passes, new vegetation replaces the old,
new layers of thatch cover the old., and the plutonium is leached into
the soil and removed from the land by weathering effects (such as wind
or rain) so that removal of surface cover becomes less effective as a
plutonium decontamination technique. The plutonium will also be dis-
tributed throughout the soil profile via root translocation and
decomposition of the dead root material. This decomposition may also
increase the uptake of plutonium by plants.
Removal of several inches of soil by scraping with graders,
scrapers, or bulldozers is one of the most widely used methods of
decontaminating an area. However, large industrial vacuum cleaners
equipped with high efficiency particulate filters (HEPA) may be
effective in decontaminating sandy soils or plowed land.* These vacuum
cleaners have not actually been used to remove soil from land areas,
thus their success can only be conjectured. Smaller vacuum cleaners
may be useful devices where small areas are involved and the amount of
loose surface material will not unduly load the equipment. Generally,
a combination of the collection and removal techniques mentioned plus
plowing the land will provide optimum results (see the discussion in the
stabilization section).
Polyurethane foam, which is applied by spraying, has been used
successfully on small areas.2 After setting, it is sectioned and re-
-moved. The top layer of soil, along with small rocks and detritus,
adhere to the underside of the foam and are removed with the foam. Since
this technique is experimental and also very costly, it would probably
not be used extensively as a soil removal technique at this time.
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B. Stabilization
Stabilization includes techniques such as plowing the land to
cover the top soil layer, scraping the soil into trenches, contouring
the land in windrows or mounds (this is also a removal technique),
covering the land with soil or vegetation, and applying chemical sta-
bilizers to the land area. It should be noted that usually stabilization
is only a short term solution which may often require a more permanent
clean-up technique in the future. Plowing can be used to invert the
contaminated top soil to place it beneath a cover of subsoil; thus,
providing a covering to prevent resuspension and also to achieve dilution.
It has the disadvantage, however, that subsequent removal operations,
should they be required, would be rendered much more difficult because
of rearrangement and dilution. Normally the dilution afforded by plowing
would place the area in unrestricted use. Thus, future clean-up efforts
or surveillance of the area would not be necessary.
Scraping the land into windrows or mounds has been used to
minimize the dispersion of radioactive contamination by wind action.
Windrowing could be accomplished by first scraping (blading) the top surface
of the soil and detritus into parallel rows. Soil below the top layer is
then bladed over the contaminated material to form windrows. Mounds are
formed by pushing the soil into large piles. Then, a clean earth cover or
chemical stabilizer can be applied to fix the plutonium. Establishment of a
vetetative cover, controlling access to the mounds, and using other
limitations on land use can be employed to maintain the integrity of the
windrows or mounds. The long term integrity of the windrows and mounds
are very dependent on the effectiveness of the stabilizers to prevent
erosion of soil or resuspension of plutonium while the vegetative cover
gains a foothold. If the Stabilizers are not effective, then the expense
of an alternative technique will also be incurred. The soil can also be
scraped and deposited in trenches. The trenches can then be covered with
uncontaminated soil by backfilling. The problems associated with this
technique are similar to the problems with windrows or mounds except the
contaminated soil will net be as susceptible to the wind and rain erosion.
C. Restriction of Land Use
Restriction of the contaminated land can often be accomplished
by- placing a. chain link fence (with or without barbed wire at the top) ,
signs to warn people, and a temporary guard service (if the area is
reasonably sized). It should be noted that restriction of land use is
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only a temporary solution. Thus, either additional maintenance costs
or a more permanent clean-up technique may be required in the future.
This technique by itself would not prevent resuspension of the plu-
tonium but would be useful to prevent access by people and animals.
The initial cost of the fence is not prohibitive; however, a 24 hour
per day guard service plus the maintenance of the fencing will be a
continuing expense that can be expensive if maintained for many years.
If fencing is continued for a long period of time, the land is relegated to
a non-productive status. Fencing may be effective if the activity levels
of the contaminated area are not very high and the land can not be used
for any worthwhile purpose (e.g., remote areas where land is either not
fertile or not easily accessible). It should be realized that other
decontamination techniques may have to be utilized in the future if
permanent fencing is either not feasible, ineffective, or impractical.
It should also be stressed that there may be an adverse psychological
impact upon the population of scattering fenced areas around the country-
side, perhaps with armed guards.
Restriction of the use of some types of contaminated land can
be done by changing the use of the land. For example, farm land,
commercial forests, or any type of land can be bought by the Federal
Government and relegated to a. non-productive status; national parks
can be closed; land can be rezoned; and crops can be purchased by the
Government. The costs of farmland, tree forests, and crops are dis-
cussed in Section III-D under Economic Losses. However, an exhaustive
analysis of this technique is not included in this paper.
D. Special Techniques
Several techniques that may not be utilized very often for
varying reasons are discussed in Appendix B, Part 1. They are
stabilization by application of asphalt or sewage sludge, decontaminating
snow covered areas, flooding as a soil removal technique, and taking other
preventive type measures.
E. Procedures for a. Project
The seven procedures (Indicated in the first paragraph of Section
I'll are discussed in detail in Appendix A, Part 1. Table 1 presents the
relationship of these seven procedures Cfirst column) to stabilization
(decontamination techniques I) and removal (decontamination techniques II
and III£. The stabilization techniques that are indicated in Table 1 are
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plowing, application of chemical or vegetative stabilizer, and application
of a soil cover of two different depths. The only procedures that are
utilized for stabilization techniques are radiological surveillance,
stabilization, vegetative removal (where appropriate), fencing (optional},
a guard service (optional), and restoration (mainly for erosion control).
The removal techniques that are indicated are scraping soil into
windrows, mounds, or trenches, vacuuming soil into trenches, and vacuuming
or scraping soil with offsite disposal at waste burial grounds or the
Federal Repository. Removal with onsite disposal of the soil (decontamina-
tion technique III on Table 1) includes all the procedures.
Restricted use of the land (not included in Table 1) would involve
radiological surveillance, stabilization (optional), vegetative removal
(where appropriate), fencing, and a guard service (optional). A discussion
of restricted use of the land by fencing is presented in Appendix A, Section
F, Part 1.
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III. Costs
The costs presented throughout this report, unless indicated
otherwise, are normalized to 1974 costs.12,13 j^e regionai variances
of labor and material costs for construction jobs in large cities in
the United States are presented in Table 3. The average costs, and
their ranges, presented for the various techniques and procedures
should be considered as general guides since the costs for a specific
project are dependent on a variety of parameters such as weather con-
ditions, terrain, soil conditions, accessibility of the site, age of
the Pu, moisture in the area, type of vegetation, use of the land,
and many other parameters. Because the cost ranges are often very
large, average costs may not be very useful for a particular project.
Also for unusual projects the costs may even be outside the cost
ranges presented.
A. Removal, Stabilization, and Restriction of Land Use
The average costs, and the range of costs, for the removal
and stabilization techniques presented in Table 1 are presented in
Table 2. The bases for these costs for each technique, and the pro-
cedures listed under each technique, are presented in Appendix A,
Part 2. The sections in Appendix A, Part 2, are designated in the
same manner as the sections in Table 2. The costs for restricting
the use of land include radiological surveillance costs (See Appendix
A, Part 1, Section A), stabilization (optional costs not included in
this evaluation), and ultimate disposal costs being fencing and.a
guard service (optional costs not included in this evaluation).
On particular projects, the radiological surveillance costs
will vary depending on the time required to complete a decontamination
project and the activity levels of the contaminated land. The stabil-
ization techniques and stabilizers are dependent primarily on the ex-
tent of plutonium resuspension, availability of stabilizers, and the
type of soils. Vegetation removal techniques, or course, are primarily
dependent on the type and extent of vegetative growth, the activity
levels on the vegetation, and the clean-up techniques to be employed.
The requirements to package, transport, and dispose of the soil at a
waste burial ground or Federal Repository are dependent on the activity
levels of the contaminated soil that will be removed from the site for
offsite disposal. The primary parameters that affect restoration
techniques are the aridity of the area and the type of vegetation that
will be effective to prevent erosion and also adequately revegetate
the land. Soil removal costs are dependent on a number of factors,
such as land terrain, soil moisture and characteristics, site access-
ibility, removal equipment availability, weather conditions, depth and
distribution of plutonium in the soil, activity levels, equipment op-
erating efficiency, operator techniques, distribution and size of rocks.
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It appears that the soil type (e.g., sandy, clayey, tilled land, etc.)
determines the selection of the soil removal technique, and the
resultant soil removal costs, more than any parameter, except plutonium
activity levels. The low end of the cost-range for removal would apply
to sandy type soils and the high end of the range would apply to hard,
clayey soils.
The total average costs and their ranges for the techniques
previously mentioned are presented in Table 4. Except for the costs
for restricting the use of the land, the costs presented are ex-
tracted from the TOTAL PROJECT COSTS presented at the bottom of Table 2.
For restricting the use of the land, the costs are two fold - the
surveillance costs extracted from procedure or step 2 of Table 2
(average $600/acre and range $250 - $1100/acre) and the fencing costs
extracted from Appendix A, Part 1, Section F (average costs $500/acre
for a 100 acre site and range $100 - $2000/acre for the low range of
a 1000 acre site to the high range of a 10 acre site).
In summary, the average costs of each technique are:
1. Restriction of land use $1100/acre*
2. Stabilization (Techniques 1 and 2
of Table 2) $2400/acre*
3. Removal with onsite retention
(Techniques 4A, 4B, 4C, and 5
of Table 2) $4800/acre
4. Removal with offsite disposal or
storage
(a) Waste burial ground $145,OOO/acre
(b) Federal repository $515,OOO/acre
B. Special Techniques
The special techniques considered are application of asphalt
or sewage sludge as a stabilizer, decontamination of snow covered land,
flooding as a soil removal technique, and removing soil under a protec-
tive air shelter. A discussion of the costs of these techniques is
presented in Appendix B, Part 2. Also, a discussion of costs is pre-
sented for a 24-hour guard service (Appendix A, Part 1, Section F),
disposal of solid waste in the ocean (Appendix A, Part 1, Section F),
and application of polyurethane foam as a soil removal technique
(Appendix A, Part 1, Section B).
* These costs do not include on-going maintenance costs. A discussion
of these costs is presented in other sections of this report.
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C. Plutonium Clean-up Experience
The available cost data for actual plutonium decontamination
projects are presented as total project costs except for the proposed
Enewetak Islands project which ran to $70,000/acre.* The costs for
four of the projects ranged between $9,000 to $83,000 per acre for a
wide variety of projects, while three of the four projects ranged be-
tween $9,000 to $26,000 per acre. The Niagra Falls clean-up was not
plutonium related. The fourth project, the decontamination at Palomares,
Spain, included many extra costs and high transportation costs that
probably would not be included if similar decontamination were performed
in the United States. The fifth project (at Rocky Flats) involved man-
ual removal of soil under a small portable metal enclosure; thus, the
project was time consuming and costly. However, costs were not avail-
able for this project.
The costs for the four projects are presented in Table 5.
They have not been normalized to any particular year, but they are still
an adequate presentation of general cost ranges for decontamination pro-
jects. It should be realized that each of these situations was unique,
hardly representative of average land clean-up conditions and should not
be used as a basis for deriving average cost estimates.
D. Economic Losses Resulting from Pu Decontamination Projects
The loss of crops or use of the land as a result of a decontam-
ination project should also be considered in an economic analysis of Pu
clean-up efforts. Tables 7 and 8 present the potential economic losses
for farm crops during 1973 and for forest trees in the national forests
during 1974. The market value of farmland in the United States for 1974
averages about $310 per acre with a range of $65 - $2100 per acre as an
average value by state (48 states). in summary, the average losses
would be about:
crops $170/acre/year
forests (commercial) $2650/acre/year
farmland $310/acre
* See the references for details of the costs. The costs for Enewetak
are estimates since this is a future project. Costs are per cubic
yard (c.y.), assumed 538 c.y./acre of soil removed (4 inch depth).
The actual costs are estimated to be about $70,000 per acre for a 4
inch soil removal. A 4 inch removal is assumed throughout this report
for consistency. If a different soil depth is chosen, the cost can be
estimated directly. The Army Corps of Engineers indicated that these
costs are about a factor of 2.8 higher than the costs for decontaminating
the same land in the United States. °
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APPENDIX A. Bases for Costs in Table 2
PART 1. General Information: Section A-H*
Section A. Radiological Support**
The radiological surveillance costs are based on the assumptions
that a surveillance team consists of one health physicist (GS-13), five
monitors (technicians GS-7), and one electronics maintenance man. One
team can adequately utilize five alpha survey instruments and five FIDLERS
(Field Instrument for the Detection of Low Energy Radiation) during a
project. A work week consists of 12 hours/day, 7 days/week. The team
would be at the project a short time prior to decontamination procedures,
the entire time during the decontamination, and a short time after the
decontamination is completed. The costs of a survey team also include
the travel and per diem expenses and laboratory costs for analyzing samples.
The following indicates each of these costs for a 100-acre plot:
One Health Physicist @ 84 hours/week $868/week
Five Technicians @ 84 hours/week $536/week (each man)
One Electronics Maintenance Man @ $10/hour @ 84 hours/week $1060/week
Per Diem for Seven workers @ $25/day/worker, $l,225/week
Five FIDLERS @ $3,000 each, ten-year lifetime $l,500/year
Five Alpha survey instruments § $1,200 each for 10 years $600/year
Travel, one way .15/mile
Laboratory analysis, $100/sample @ 1 sample/acre (radiochemistry
analysis in field)
For a 1,000 mile trip, the costs per acre per week are calculated
to be $37/week/acre plus $300 travel for the project plus $100/
acre for sample analyses.
* Appendix A, Part 1, discusses the general procedures and costs for the
seven general techniques that are applicable to any decontamination
project. The techniques referred to in Part 1 are presented in Tables
1 and 2.
** Radiological support costs were based on the assumption that the survey
team consisted of individuals and equipment from EPA's ORP Las Vegas
Facility. If the iiuvey team does not come from EPA, then the costs
could be quite dif^^rent from those presented.
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It is estimated that projects ranging from one month to six
months will cost: $250 - $1100/acre with an average of $500/acre for
a three month project. These costs are indicated in Section A.I through
A.6B of Table 2, since radiological surveillance is common to all plu-
tonium decontamination projects of the same time period.
Section B. Stabilization
In most cases, experience with stabilization of contaminated
land areas has been confined to "test" sites and small research areas.
As a result, many of the stabilization techniques that have been con-
sidered are experimental. The success of specific stabilizers may well
vary where the concentration and source of contamination vary, or where
the land surface or climatic characteristics are dissimilar. In addition,
since the same techniques have not been tested on all surfaces, it is
difficult to accurately assess the advantages or disadvantages of any
particular method since general applicability has yet to be established.
It is possible that alternative methods or types of stabilization would
prove to be more successful for decontamination purposes.
The experimental nature of previous decontamination situations
also offers another important point for consideration. In most of the
experiments, the goal was to determine the effectiveness or benefit of
a particular technique or stabilizer — and not to determine costs. As
a result, in almost all cases, no records of cost had been maintained.
Inability to acquire accurate cost figures based on actual decontamination
experience necessitated development of cost figures based largely on as-
sumptions. Thus, it was not possible to verify these cost estimates or
the basic assumptions through comparison with empirical experience.
The types of stabilization methods experimented wit-h thus far
fall into five categories. These categories and their costs are pre-
sented in Table 6. The first type of stabilizer is only temporary, e.g.,
application of water. It is likely that water would be used following
a contamination incident to minimize the resuspension of plutonium par-
ticles until the seriousness of the event could be thoroughly evaluated
and a clean-up plan initiated. In situations where expediency is advan-
tageous in reducing potential exposures, water offers the desirable
characteristics of being readily accessible in most areas and thus en-
abling timely action to be taken. At the same time, it does not represent
any irreversible commitments as far as other clean-up operations are con-
cerned. Water can be applied to any type of soil with a similar degree of
success in preventing resuspension. The cost to apply water for a 0.3
inch depth4 will run about $220 per acre.16'42
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There are several ways water can be used and the amount of
water required depends on the effect desired. Distributing a fine
mist into the air several feet above the contaminated surface until
the surface is wet to about a depth of three tenths of an inch has
proven to be effective in holding down dust for an hour. (This
effective time will vary locally in response to differing climatic
conditions and evaporation rates). The efficiency for preventing
resuspension is about 50%, ranging from 20-90%.^il? Direct wetting
by hose also has a similar effective life, though the pressure of
the water in this case causes a mixing in the upper centimeter of
soil and thus would cause a somewhat more effective fixation of the
contamination.^ The obvious problem here is that unless other
measures are taken almost immediately, it becomes necessary to rewet
the contaminated area hourly or risk resuspension of plutonium activ-
ity.
Water can also be used to flood a contaminated area. At
least one inch of water may be applied (with care taken to divert
any runoff) to enhance natural weathering and leach the contaminant
into the soil, thus reducing the amount of contaminant available for
resuspension by almost 85%. >^ This use, while still only "temporary"
does not require the frequent reapplication of the wetting methods and
still is fairly inexpensive. It would be possible to effectively apply
the water spray to almost any unvegetated surface without being re-
stricted by the local terrain. Flooding on the other hand would be
more limited by the terrain since an essentially flat surface would be
necessary in order .to maintain standing water on the contaminated area.
It might even be necessary to construct low dikes around the perimeter
of the area to help contain the water.
There are several problems created for later clean-up efforts
when water is applied in the initial stages of decontamination. For
example, when the polyurethane foam is applied to a water saturated
surface, a component in the foam reacts with the water and tends to
form a void between the foam and the surface of the soil. A contam-
inated surface treated in this manner would not be stabilized securely;
thus, pick-up of the contaminated soil by the foam would be erratic.
This situation could be modified by allowing the soil to dry to a just-
damp state before application of the foam.
The amount of moisture left in the soil would also impact on
the success of several of the other stabilizers, although not as sig-
nificantly. Since most of the chemical stabilizers are mixed with
water when they are applied, a limited amount of excess moisture in
the soil can be compensated for by increasing the concentration of the
chemicals during application.*° An increase in concentration is not
effective, however, on saturated soils.
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Both the asphalt-like surfaces and soil can be applied over
moist earth. In these cases, heavy machinery is involved in applying
the surfaces and such machinery does not maneuver well in mud. Again
it would be necessary to allow the soil to dry out somewhat before
continuing with decontamination.
Flooding could complicate removal procedures (though not
seriously) if the flooding were repeated over an extended period of
time. Each subsequent flooding would leach the contaminant deeper
into the soil, possibly dispersing it deep enough to necessitate ad-
ditional passes of the removal equipment. Neither this problem of
leaching nor the problem of poor adherence due to high moisture content
are insurmountable.
A second type of stabilization that has been experimented with
seals the contaminant more permanently by covering the surface with a
layer of an impermeable substance, such as fast-cure road oil, or as-
phalt emulsion. In 'both cases, there is only limited information
available on their use as stabilizers.^ Both substances are reasonably
easy to acquire and both can be applied with conventional road-oil or
asphalt spray trucks.
At the Nevada Test Site, road oil was applied to soil to a
thickness of from one-half inch to two inches. The oil formed a crust
which maintained its integrity (while exposed to desert weathering) for
almost 5 years and would have required an additional thin coating after
that time for maintenance.^ The tests proved this technique as some-
what successful in a desert climate but there are two major drawbacks
with the use of rapid cure oil: its surface remains tacky for quite
some time after curing, and depending on the locale, it may be stocked
on a seasonal basis only, thus, it may not be readily available at all
times.
The fact that the surface remains tacky could cause problems
for animals particularly if they were to wander inadvertently into the
area. Although experience has indicated that animals tend to avoid
such surfaces, additional research should be conducted to see just what
effect an application of road oil would have on localized animal life.
The total cost of the road oil and its application would be about $660
per acre.^
507
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There is even less information available on the use of asphalt,
but its use has been considered as a means of containing plutonium on a
temporary basis until contamination can be removed, or on a permanent
basis (up to 10 years).20 (This is discussed in the section on Removal).
In the first case, about 1/16-inch of asphaltic emulsion could be spread
at a cost of about $1,100 per acre.21 This treatment locks on the sur-
face and makes removal of the contaminated soil more efficient. In the
second case, the asphalt surface would be expected to have a longer life
and would be at least 1/2-inch thick. At one dollar per square yard20
for material and application costs, it would cost about $4,800 per acre
to pour the asphalt. In order to weatherproof the .surface, a sealer
would have to be applied at a cost of $0.05 per square yard22 bringing
the total cost to about $5,100 per acre.
Any area stabilized with asphalt would also require that
adequate drainage be provided. Since the finished surface is impenetrable
to water, any rain would tend to accumulate in low spots and then wash
over the surface in sheets. Gathering volume and momentum at the edge
of the asphalt, the flow could erode peripheral soil and undercut the pre-
pared surface, threatening its integrity. Prepared drainage would mini-
mize this concern and also allow for control and possible diversion of
run-off in the event that it became contaminated. The asphalt surface
would also be subject to the "road edge effect." As the-surface would
cr.ack with time, moisture would collect in the cracks where plants could
germinate and grow. With the maximization of plant growth, the surface
would be further destroyed, threatening the possibility of recontamination.
The road oil and the asphalt could be applied over small amounts
of certain vegetation and both prevent resuspension of plutonium over
fairly long periods of time. However, they are unsightly, and the areas
stabilized in such a manner will require constant surveillance since the
plutonium would be fixed underneath. Also, the surfaces covered would
remain useless while stabilized — unattractive to both plant and animal
life.
The third type of stabilizers are those loosely described by
the term "chemical binders." (Most of the tests that have been conducted
with such substances were conducted with specific brand name binders and
although these brand names are merely representative of the field, it
simplifies the following discussion by utilizing the brand names).
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Chemical binders are typically substances that were developed
commercially to be applied, along with seed and mulching material, on
bare soil or slopes to bind the surface and assist in erosion control.
They are diluted with water to the appropriate strength and applied in
a spray form by means of a hydroseeder or a tank truck equipped with a
spray bar.23 In their normal use, they would secure the soil surface
and the seed in place until the seeds can germinate and provide the
vegetative cover to prevent erosion by wind or water. The use of such
chemicals has become increasingly popular with construction companies;
thus, they are not difficult to procure. The time period after an ac-
cident that these chemicals could be procurred is highly dependent on
the area of the country (remoteness, proximity to a company's distrib-
ution network, etc.); however, they should be available at the site in
no more than a few days.
Because of the stabilization properties of these binders, they
have been considered for use in preventing resuspension of plutonium.
The chemicals can be applied without seed or mulching materials and at
different strengths to produce surfaces whose integrity vary with time.
The less concentrated application could be ideal for temporarily pre-
venting resuspension, while a stronger concentration may provide ade-
equate protection for up to five years.
The following are binders which have been tested successfully
as stabilizers for land contaminated by radionuclides other than plutonium.
(1) Geo-tech: A. clear non-toxic resin which when applied
penetrates about 1/4-inch into the soil. It binds the soil against
degradation by wind and water yet also allows moisture to pass through.
It will maintain its integrity even after exposure to foot traffic,
but begins to deteriorate after about one year if exposed to the sun.
No tests have been conducted beyond that length of time but some sources
feel it would only be necessary to reapply the binder every 5-10 years
to prevent resuspension of plutonium since this product is very effective
in controlling dust. The cost for materials and application of this
stabilization material would run about $520 per acre.4>24
(2) Norlig and DCA-70 were experimentally selected over similar
products to stabilize the Tuba City mine tailings. They penetrated 3/4-
inch and 2 inches respectively and became water insoluble after emplacement,
No time period was available for the integrity of these crusts (the initial
work was completed in 1969). The costs of these applications per acre are
about $240 and $440 respectively.25
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Other "binders" that could possibly provide useful stabilization
in plutonium decontamination efforts include:
(1) Dust Control Oil: Sales representatives tout a 90-95%
minimum efficiency of this product in reducing dust and preventing resus-
pension of a contaminant.-1 Several references indicate the range to be
70-90% with an average of about 85%.4>17 It does not form a hard surface,
and it can be plowed and revegetated after 3 or 4 years. Depending upon
the strength of the solution applied, dust control oil can cost between
$360 and $730 per acre to apply.21
(2) Petroset: A petroleum resin in a rubber base which penetrates
to a depth of 1/2-inch and will bind the soil for at least 9 months. Like
the Geo-tech, it allows moisture to penetrate and can be applied to either
encourage or discourage revegetative growth. Cost for application to an
acre is about $1,200.I6
(3) Polyvinyl Acetate: Sprayed with conventional equipment, it
penetrates 1/4-inch into the soil surface. This treatment protects the
surface from wind and water erosion and will last a year with some minor
deterioration from sunlight.1& Depending on the concentration of the
material that is applied, costs vary from $200 - $700 per acre.26
These chemical binders only represent a sample of many specific
brands and types commercially available. It appears that there are many
such chemicals which have properties applicable to the plutonium clean-
up problem - but further laboratory studies need to be conducted in order
to determine which would be most effective for this application.
The fourth type of stabilizer is unique in that it was tested as
a stabilizer but was also found to provide excellent scavenging character-
istics for contaminated soil. The stabilizer used was polyurethane foam
applied to test plots at Rocky Flats at a thickness of about 2 inches.
The foam encapsulated the rocks and debris on the surface and when removed,
85% of the contaminated soil was also removed.2
The foam is a special case — it adheres to a variety to sub-
strates; it can be used readily in a wide range of weather and topographic
conditions; it resists environmental decay for periods up to 2 years,2^
and it can pick up stones up to three inches in diameter. Polyurethane
is used as insulation in houses and other buildings so it is available,
though perhaps in limited quantities, in most areas of the country.
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Perhaps the major drawback about the foam is that its costs are much
higher than some of the other stabilizers. Of course, it was not
intended to be used as a stabilizer as the others are, but a price
quoted from a local polyurethane dealer puts the cost of the required
2-inch thick covering of polyurethane at 65$ a square foot or approx-
imately $28,000 per acre." This cost is prohibitive over areas as
large as an acre -- and estimates run that it would take 2 men at
least seven and perhaps as long as 12 days to apply it to a one-acre
land area.
A fifth type of stabilization involves the use of soil and/or
vegetative covering. This method would leave the contaminated area in
a generally more attractive and usable condition than any of the others,
and it would also serve as a restoration process. However, covering
an area with soil does not guarantee vegetative cover, especially in
arid regions. Generally, a soil cover of at least 4 inches would be
applied over the contaminated surface. This would limit resuspension
and would also provide a surface which could be readily revegetated, as
desired, once amendments (like lime) were applied. (Some amendments
appear to be capable of minimizing the uptake of plutonium by plants).^
In most areas, the revegetation process could be enhanced by the controlled
application of water to encourage plant growth. Surface occupancy
would be allowed only if continuing surveillance determined that the
underlying contamination was not brought to the surface by man-made or
natural disturbances.
The cost of soil cover is rather high, with loam running between
$1,500 and $3,300 per acre for a layer 4 inches in thickness, and topsoil
running from $3,300 to $5,700 oer acre for the same depth.28>29 Increas-
ing the thickness of the layer increases protection and reduces the risk
of resuspension, but is also proportionately more expensive.
In most cases some type of stabilizer will probably be applied
to a land surface after a plutonium-contaminating incident requiring
remedial actions. The "fixing" qualities of stabilizers allow the nec-
essary control over resuspension of the plutonium and provides time to
determine an appropriate clean-up plan. The stabilizer selected will be
determined by the nature of the incident and the specific decontaminatinn
benefits desired.
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Section C. Removal
Costs were estimated for two types of removal: (1) vegetation
or crop removal and (2) soil removal. For all the techniques analyzed,
vegetation removal would be optional depending on the type of area de-
contaminated, type of vegetative growth, concentration of contamination,
and extent of clean-up required. The plutonium removal efficiencies
vary considerably from 70% for raking mulch to about 30% for mowing or
harvesting.^ Vegetation removal costs were calculated for three general
categories: (1) clearing and grubbing non-wooded areas, (2) clearing
and grubbing slightly wooded areas, and (3) removing trees. Note that
clearing and grubbing for non-wooded areas includes mowing grasses, raking
mulch, flailing crops, harvesting crops, or using a combine. The costs
for these methods are generally at the low range of the costs that are
presented in Table 2. The costs include overhead and profit of about 25%
and hauling the debris offsite at about a 20-30% incremental cost. There
are no costs included for either incinerating the trees or for special
packaging of the vegetation or trees which are to be taken to a solid
waste burial ground or Federal respository. There has been no experience
with such contamination to indicate what type of disposal would be appro-
priate. If the trees are to be incinerated, it will be necessary to use
special particulate filters to prevent resuspension of plutonium. No data
was available on this procedure. These costs, on a per cubic yard basis,
are expected to be comparable to costs for packaging and transporting
contaminated soil. The costs for each type of vegetation removal are
assumed to be:
Technique Costs References
clearing and grubbing non-wooded $ 500/acre 30, 31, 32, 33, 34
areas
clearing and grubbing slightly $l,250/acre 32, 33
wooded areas
removing trees $2,000/acre 33, 35, 36
The ranges of data are large, as shown in Table 2; however, the
assumed costs are reasonable to categorize the costs since many factors
contribute to the costs of a specific project. Some of these factors are
type of undergrowth, size of trees and thickness of forrested area, terrain,
capability of using large machinery, contamination levels of land and
vegetation, and ultimate disposal of vegetation.
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Soil removal may be accomplished by using scrapers (towed
types, bulldozers, carryall scrapers, self-loading grader, etc.),
industrial sized vacuum cleaners (on plowed land or sandy soil),
and polyurethane foam. Scraping involves either (1) scraping the
soil into windrows or mounds, (2) scraping the land and carrying
or pushing the soil to trenches for burial, or (3) scraping the
land and picking the soil up for packaging and offsite disposal.
Industrial vacuum cleaners can be used in conjunction with HEPA
filters to remove the soil after it has been plowed or scraped
into windrows or mounds and have it either transported to a trench
for disposal or to be packaged for offsite disposal. The removal
efficiencies for scraping range between 60-100% with about a 90%
average. Scraping in combination with plowing and/or backfilling
have combined Pu removal efficiencies of about 98%.33,37
Polyurethane foam may be applied to some types of soil as a sta-
bilizer (as discussed previously). The soil particles are bound
to the foam and the foam can then be removed by a front end loader,
incinerated in a special Pu incinerator, and the contaminated ashes
packaged for offsite disposal.
The ranges of costs for scraping land can be below $100/acre
to as high as several thousand dollars per acre depending on many
environmental factors including moisture of the soil, weather, temp-
erature, terrain, type of equipment, availability of equipment,
access to the land, type of soil, contamination levels, number of
scraping passes necessary to remove contamination, number of rocks on
the land, etc. The assumed costs are given for calculational purposes
only but the general costs presented should be adequate to compare the
different techniques. The costs for just scraping 4 inches of soil are
around $200 - $600/acre,3>4>16>33>34>37-40 while the costs for scraping,
digging, and backfilling a trench are about $1,700/acre.32~j5'41'42
Using an industrial vacuum cleaner to remove soil followed by disposal
in a trench costs around $2,450/acre.2>32~35>41>42 Scraping plus
packaging the soil in containers as a preparation for transportation
and disposal offsite averages around $800 - $l,000/acre, with the over-
all range of costs of about $450 - $2,800/acre.1>3>4>16,33-35,37-42
Application and removal of polyurethane foam costs about $28,000/acre.
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Section D. Packaging
The plutonium contaminated soil that must be transported to a
waste burial ground or the Federal repository for ultimate disposal
must be packaged in lined containers (usually 55-gallon drums), loaded
and transported by rail and/or truck to a licensed burial ground. The
major items that enter into the overall packaging costs include the
cost of drums, freight charges, return of the trucks (or rail car) to
the project site, labor for loading and unloading, truck driver costs,
and capitalization.
The costs for packaging wastes for disposal at waste burial
grounds and the Federal repository ranged between $6.80/cubic foot to
$10.20/cubic foot including transportation costs for" a nominal 1200
mile round trip.43 The costs from reference 45 were for a 600 mile
round trip, but would still be in the same range for a 1200 mile round
trip. For a nominal removal of 4 inches of soil from an acre of land,
the cost becomes about $100,000 to $150,000 per acre. For calculation-
al purposes, it is assumed that the packaging costs for waste sent to
a waste burial facility is $100,000/acre and that the packaging costs
for waste sent to the Federal repository is $150,000/acrfe. For trans-
portation distances significantly larger than about 1,200 miles round
trip, the added costs are presented in Apeendix A, Part 1, Section E,
under Transportation.
Section E. Transportation
Transportation includes two types of mobilization: (1) moving
soil by a scraper or dump truck several thousand feet to form mounds of
soil or to a trench for burial and (2) transportation of containerized
wastes to the licensed waste burial grounds or the Federal repository.
Q) Moving soil by a scraper - Building mounds or transporting
soil to trenches requires more time and effort than scraping the soil
into windrows. For estimating the costs of a job requiring a haul,
the costs discussed under Removal, Section C of Appendix A, Part 1,
include the costs for a 1,000-foot haul.32"34 The costs for longer
hauls were extracted from this removal data for distances of 300 feet
to 5,000 feet. The range of data is greater than an order of magnitude,
mainly because it appears that the type of scraper and the actual haul
distance are very critical. (Large scrapers add smaller costs for
longer hauls and extra costs for the last few 1,000 feet is less than
the first few thousand feet). All the costs per acre were estimated
assuming a removal of 4 inches of soil, or 538 cubic yards, per acre,
The range of costs for a 1,000 foot haul are $80-$S80/acre with an
average of about $300/acre.
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(2) Transportation of containerized wastes - The costs for
packaging (Section D of Appendix A, Part 1) include a nominal trans-
portation distance of 1,200 miles. The extra transportation costs
would be included only if the distance were greater than 1,200 miles.
The costs range from $0.05/cubic yard/mile to $0.20/cubic yard/mile.32-34
For a removal of 4 inches of soil, or 538 cubic yards, per acre, the
range is about $27/acre/mile to 2108/acre/mile. The assumed value is
$0.10/cubic yard/mile or about $54/acre/mile. For each 100 miles, the
extra transportation costs would be $5,400/acre.
Section F. Ultimate Disposal
A plutonium contaminated area may be restricted from public
access by placing a fence around the area and establishing a 24-hour
guard service at the area for a short-term (a few years). A guard
service, however, is usually not necessary and is not a normal re-
quirement. Prior to fencing, the contaminated material may have been
stabilized by plowing, covered by vegetation, chemical stabilizer or
soil; or buried in a trench. Any contaminated activity left onsite
should be periodically monitored with the stipulation that it may be
necessary to secure the contamination in a better fashion at a later
date.
Contaminated soil that is transported offsite to a waste burial
ground or the Federal Repository must be packaged in containers. This
waste may be in a retrievable or non-retrievable form at the waste
burial ground and in a retrievable form at the Federal Repository. The techno-
logical bases and the bases for estimating the costs of these techniques
are discussed below.
(1) Fencing: The fences considered are 5 feet high, 6 feet high,
and 6 feet high with three strands of barbed wire at the top of a galvan-
ized or aluminum chain link fence. The costs range from about $4 - $8 per
linear foot for each of the fences.32"34 Assuming the land to be fenced
is a perfect square, the average costs are about $l,500/acre for a 10-acre
plot, about $500/acre for a 100-acre site, and about $150/acre for a 1,000-
acre plot. The ranges of costs are about $400 - $2,200 per acre for the
10-acre plot, $300 - $700 per acre for a 100-acre plot, and $100 - $225
per acre for a 1,000-acre plot. If a different geometry for the area is
selected, the costs will range by a factor of 0.89 for a circle to 1.06
for a rectangle with the ratio of the sides of 2:1.
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(2) Guard Service: A 24-hour guard service requires 5 guards
for full time at approximately $3.00 - $5.00/hour.45 At these assumed
costs, the annual costs will range from about $30,000 to about $57,000
per year depending on the area of the country. For a specific case in
Nevada, the annual costs for a contracted guard service is higher at
$100,000 for 3.8 man years per year.5^ Costs for guard service in
areas that are not as remote as the case in Nevada will not be as high.
If more than a single guard is required to be on duty (possibly due to
the size of the area), then costs will be proportionately higher. Also,
guard service cost at a specific site may be higher depending on higher
local wage rates, overtime rates, specialized vehicles, and personnel
that may be necessary, and other specialized restrictions.
(3) Waste Burial Grounds:•*! »52 Solid radioactive waste with
concentrations less than a Pu concentration of 10 nCi/gram are current-
ly being buried at State burial grounds, such as the State-licensed
ones in South Carolina, Nevada, Washington, Kentucky, New York, and
Illinois. The one time charge for storing non-retrievable containerized
wastes at these burial grounds range from about $0.50 - $2.00/cubic feet
with an average of about $1.35/cubic foot.46-50 The one-time charges
for retrievable wastes are est5.mated to be $3 - $5/cubic foot at these
burial grounds, with an assumed value of $4/cubic feet.44
(4) Federal Repository:51'5 Higher level (>_ lOnCi/gram) solid
waste may be shipped to the Federal Repository, which is in the develop-
ment stage. The outcome of this concept is dependent on rulemaking
actions by the Nuclear Regulatory Commission. The Energy Research and
Development Administration indicated the projected one-time charges to
range from $20 - $30/cubic foot with an assumed value of about $25/cubic
foot.47
The one-time charges for burial at the waste burial grounds and
acceptance at the Federal Repository include land costs, handling, re-
packaging, if necessary (for retrievable wastes), monitoring, inspection,
and perpetual care. It is not known at this time if the charges indi-
cated are adequate to defer all of the perpetual care costs of long-term
burial of plutonium contaminated soils. The charges are either current
charges or the best estimate of the costs.
The costs per cubic foot for storage is converted to costs per
acre by assuming that 4 inches of soil are removed on each acre of land,
or 538 cubic yards of soil are removed per acre.
-------
$/ft3 $/ft3 $/Acre
Type of Waste Burial Activity Level Range Average Assumed
Waste Burial Ground <10nCi/gram $ 0.50-$2 $ 1.35 $ 20,000
non-retrievable
Waste Burial Ground !OnCi/gram $20-$30 $25.00 $360,000
retrievable
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Section G. Restoration
A necessary consideration in any discussion of the costs of a
plutonium clean-up are the costs to restore the land after decontamina-
tion. These costs will vary, as do the costs discussed in other sections,
with terrain, climate, soil type, the degree of contamination and most
importantly with the desired end use of the land affected by the contam-
ination. However, generally these costs would be comparable to the costs
developed for recovery of coal strip-mined areas. Prior to restoration
experts in this area should be consulted to determine the type and ex-
tent of restoration to be applied at a specific site.
Experience with recovery of plutonium-contaminated land has been
limited primarily to "natural" restoration -- where man did not reestab-
lish soil or vegetative cover but left the disturbed land to recover as
best it could. More recently, the trend is toward restoring disturbed
land to its original condition or to some productive status.
There are two main goals for any restoration effort on contam-
inated land: (1) to merely restore the vegetation or ground cover so
that erosion does not occur or (2) to restore the surface so that both
man and animals can have unrestricted access to it. Again, the factor
determining which goal is selected will vary for every site, and it will
be desirable from a cost standpoint if the goals are established prior
to selection of a clean-up plan so that the decontamination can proceed
with that goal in mind.
Obviously, the method of decontamination will determine the
extent of the restoration procedures required. In those cases where
the soil has been removed, it will be necessary to apply a new covering.
The cost of a 4-inch soil covering, including delivery and distribution,
will run between $1,500 - $3,000 an acre for loam, averaging $2,400 per
acre, and $3,300 - $5,700 -for topsoil, averaging $4,500 per acre.4>2°>29> 31-34
These figures compare favorably with the cost of distributing an equal
amount of soil at normalized costs at Enewetak -- $2,530 per acre.30
Following a logical sequence, the land could be treated to
encourage revegetation. Lime and fertilizer could be added, at a cost
of $20 - $480 per acre (averaging $150 per acre),31>32-34 -^e i^nd could
then be seeded for $190 - $220 per acre (average $200 per acre).31,32
In some cases, one of the chemical binders discussed in the section on
Stabilization could be dispersed together with seed (at an additional
cost of about $600 per acre) to hold them in place and protect the soil
until a ground cover is established. 6
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Depending on the site, optional treatments might be selected.
Mulch may be applied with the seed and binder (at a cost of from $35 -
$190 per acre) to further protect the soil from erosion.31,32,34,58
Grasses or legumes could be planted instead of the seeds for $20 -
$220 per acre (averaging $100/acre).31>38 Seedlings could be planted
for $40 - $120 per acre (averaging $60 per acre).3° Shrubs could also
be substituted at a minimum installed cost of about $8.60 per shrub.
Depending on the shrub density desired, costs would likely run from
$860 per acre to $1,720 per acre.34
These costs and treatments apply under what might be called
normal circumstances. A very special case for restoration would be
desert conditions like those found at the Nevada Test Site. The
sparseness of soil, vegetative cover, and water severely complicate
the task of restoring a decontaminated area. Cost figures have not
been computed for such an effort; but, research has been conducted
to determine the most successful methods for restoring desert surfaces.
Generally, the researchers concluded that due to the problems involved
in such restoration, decontamination efforts which involve removal of
soil or vegetation in a desert situation should be very carefully
considered.4
As indicated in the section on Stabilizers, some stabilizing
techniques include steps also considered necessary for restoration.
There would be an obvious benefit from reduction of costs where the
requirements for both can be met in a single operation.
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APPENDIX A. Bases for Costs in Table 2
Part 2. Discussion of Specific Techniques*
I. Stabilization Only
1. Plowing
A. Radiological Surveillance - See Section A of Part 1.
B. Stabilization - First the area should be stabilized
with a short-term stabilizer to reduce resuspension of plutonium
to a minimum. The short-term stabilizer is the type used on ground
that has vegetation, i.e., unplowed land or ground that is not bare
soil. The costs of this type of stabilizer are discussed in Section
B of Part 1. Then, the land can be plowed by farm machinery to a
12-inch depth or with a large plow pulled by bulldozers or heavy
machinery to turn the top layers of soil under 3 feet of earth. This
3-foot depth should be sufficient to control uptake of plutonium by
plants. Also, the plowing should help dilute the plutonium and remove
plutonium from the surface of the land. The costs of a 3-foot plowing
are similar to those for plutonium scraping in Appendix A, Part 2,
Section 4A. A 12-inch plowing cost is in the range of a few tens of
dollar an acre and is, thus, an insignificant cost.
C. Removal - Vegetation removal may be necessary prior to
plowing. The types of removal that may be warranted are discussed in
Section C of Part 1. There will be no soil removed from areas to be
plowed.
D. Packaging - Not applicable. (See Section C of Part 1
concerning packaging of vegetation that has been removed from the land.)
E. Transportation - Not applicable.
F. Ultimate Disposal - Fencing in the plowed area may be
necessary if the area is heavily populated and if the public should
need to be excluded. The fence should also have the appropriate
radiation warning signs. The need for fencing would be dependent on
plutonium contamination and the effectiveness of the plowing operation.
*Appendix A, Part 2, discusses costs for the specific techniques
presented in Tables 1 and 2.
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Temporary fencing may be necessary for the time period before the
restoration procedures become effective. Guard service may also be
necessary if exclusion of the public from the plowed area is essential.
The costs of fencing and guard service are presented in Section F of
Part 1.
G. Restoration - As a minimum, restoration for the plowed
area would include fertilizing, seeding, and application of a short-
term stabilizer. The stabilization costs presented in Table 2 are for
the type of stabilizer that is used primarily for erosion control on
bare ground as indicated in Table 6. The stabilizer should be
adequate until vegetative growth becomes effective as a permanent
stabilizer. The stabilizers are discussed in Section B of Part 1.
The alternative restoration procedures that may be necessary
or desirable are mulching (instead of stabilization), starting a ground
coyer (instead of seeding), and placing seedlings or shrubs to aid in
returning the land to its original state or to an acceptable status.
Restoration costs are discussed in Section G of Part 1.
2. Chemical and/or Vegetative Stabilization
A. Radiological Surveillance - See Section A of Part 1.
B. Stabilization - As a preventive measure, a short-term
stabilizer may be applied before any decision is made concerning the
decontamination techniques to be employed. There are two types of
stabilization discussed: (1) vegetation plus chemicals and (2) Jong-
term (5 to 10 year life, as indicated in Table 6) chemical stabilization.
(1) Vegetation plus chemicals - A short-term stabilizer
that is used primarily on bare ground as indicated in Table 6
is applied to the contaminated area to allow the vegetative
ground cover to become effective. The short-term stabilizer
costs are discussed in Section B of Part 1 and the vegetative
ground cover costs are discussed in Section G of Part 1.
(2) Long-term stabilization - Chemical stabilizers that will
be effective in stabilizing the soil for a 5 to 10 year period
are applied. Reapplication may be necessary each 5 to 10 years
or the soil may be decontaminated in the future using a different
procedure. The long-term chemical stabilizer costs and types are
discussed in Section B of Part 1.
C. Removal - Vegetation removal may be necessary prior to
application of the stabilizers. The types of removal that may be
warranted are discussed in Section C of Part 1. There will be no
soil removed from the area to be stabilized by application of
vegetation and/or chemicals.
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D. Packaging - Not applicable. (See Section C of Part 1
concerning packaging of vegetation that has been removed from the
land.)
E. Transportation - Not applicable.
F. Ultimate Disposal - Permanent fencing for the stabilized
area would generally be more appropriate for this decontamination
procedure than for any of the other procedures or techniques. A
discussion of fencing and guard service is presented in Section l.F
of Part 2 and Section F of Part 1.
G. Restoration - Not applicable.
3A. Soil Cover as a Stabilizer - 4 inches of soil.
A. Radiological Surveillance - See Section A of Part 1.
B. Stabilization - The area to be covered with soil should
be stabilized with the short-term stabilizer as indicated in Table 6
that is used on land with vegetation. This reduces resuspension
prior to and during application of the soil. There are two choices
of soil - loam and topsoil, with loam usually being adequate for
most decontamination purposes. The costs of soil application are
directly proportional to the soil depth. Some types of land may
not be appropriate for placing a soil cover depending on soil, type,
terrain, moisture in the soil, etc. The costs of the soil, its
application, spreading, etc., are presented in Section B of Part 1.
If this type of stabilization is not effective, other methods may have
to be utilized at a future date.
C. Removal - Vegetation removal may be necessary prior to
application of the soil. The types of removal that may be warranted
are discussed in Section C of Paft 1. There will be no soil removed
from areas to be stabilized by application of soil.
D. Packaging - Not applicable. (See Section C of Part 1
concerning packaging of vegetation that has been removed from the
land.)
E. Transportation - Not applicable.
F. Ultimate Disposal - A discussion of fencing and guard
service is presented in Section l.F of Part 2 and Section F of
Part 1. Permanent fencing and guard service is probably not appro-
priate but temporary fencing may be used until restoration procedures
become effective.
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G. Restoration - The restoration procedures appropriate for
a 4-inch soil cover are identical to those discussed in Section l.G
of Part 2. Restoration costs are discussed in Section G of Part 1.
3B. Soil Cover as a Stabilizer - 12 inches of soil.
A. Radiological Surveillance - See Section A of Part 1.
B. Stabilization - The procedures are the same as those
presented in Section 3A.B. in Part 2 except 12 inches of loam are
spread or 8 inches of loam with 4 inches of topsoil are spread. The
extra depth of soil (8 inches extra) would be for added stabilization
for reducing resuspension of soil, and to reduce uptake of plutonium
by plants, thus allowing the land to be used productively. (The
choice of 12 inches of soil is primarily for calculational purposes.)
The costs of applying the soil are directly proportional to the depth
of the soil and are discussed in Section B of Part 1. If this type
of decontamination is not effective, other methods may have to be
used in the future.
C. Removal - Vegetation removal may be necessary prior to
application of the soil. The types of removal that may be warranted
are discussed in Section C of Part 1. There will be no soil removed
from areas to be stabilized by application of soil.
D. Packaging - Not applicable. (See Section C of Part 1
concerning packaging of vegetation that has been removed from the
land.)
E. Transportation - Not applicable.
F. Ultimate Disposal - The soil cover, after restoration
procedures become effective, should be sufficient in itself as
an ultimate disposal. Fencing and a guard service should not be
necessary since the soil covering would be about a foot deep; thus,
it is unlikely erosion could remove the entire soil covering.
G. Restoration - The procedures for restoring the land should
be identical to those discussed in Section l.G of Part 2.
II. Removal with Onsite Disposal
4A.Scraping into Windrows.
A. Radiological Surveillance - See Section A of Part 1.
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B. Stabilization - Prior to soil removal, the land should
be stabilized with a short-term stabilizer (as indicated in
Table 6) to reduce resuspension of plutonium to a minimum. The cost
of this type of stabilizer is discussed in Section B of Part 1.
The windrows are stabilized in the same manner as the
land in Section 2.B of Part 2 using long-term chemical stabilizers
or a combination of chemical and vegetative stabilizers. The long-
term chemical stabilizers may need to be reapplied every 5 to 10
years. If this technique is evaluated at a future date to be
unacceptable, the windrows may be scraped up and buried onsite or
transported offsite for burial. The costs of the stabilizers are
discussed in Section B of Part 1.
C. Removal - Vegetation removal will probably be necessary
prior to scraping the land into windrows. The types of removal that
may be warranted are discussed in Section C of Part 1.
Soil removal will be by a scraper, grader or dozer with an
angled blade to produce windrows that are assumed to be about 18 inches
high, and 3-1/2 feet wide at the base.19 The depth of soil removed
by scraping is assumed to be 4 inches. The costs will vary considerably
With the type of soil and the terrain. Soil removal is also discussed
in a little more detail in Section C of Part 1. The range of costs
range from less than $100 per acre for sandy soils with ideal conditions
to six or seven hundred dollars per acre for clayey hard soils during
adverse conditions. The average costs from the data available are
calculated to be about 200 dollars per acre except for sand (about 70
dollars per acre).3-4,16,33-35,37-40
D. Packaging - Not applicable. (See Section C of Part 1
concerning packaging of vegetation that has been removed from the land.)
E. Transportation - Transportation costs would be incurred
only if the windrows are pushed several thousand feet. The extra costs
for handling or pushing soil with a scraper are discussed in Section E
of Part 1.
F. Ultimate Disposal - A discussion of fencing and guard
service is presented in Section l.F of Part 2 and Section F of Part 1.
Permanent fencing and guard service would probably not be necessary,
especially after restoration procedures become effective.
G. Restoration - The windrows are stabilized with chemicals
and/or vegetation and are not usually restored further. The windrows
will cover approximately 50 percent of the land area. Thus, the
remaining land area would have to be restored by applying (1) a soil
cover of loam Cassume^ to ^e 4 inches) to replace the soil that was
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scraped, (2) short-term stabilizer to cover bare ground (as indicated
in Table 6), (3) fertilizer, (4) seeds, and probably (5) lime. The
restoration costs are based on restoring 50 percent of each acre
since 50 percent of an acre is covered with windrows and will not be
restored. The stabilizer is discussed in Section B of Part 1, and the
restoration procedures are discussed in Section G of Part 1.
4B. Scraping into Mounds
A. Radiological Surveillance - See Section A of Part 1.
B. Stabilization - Stabilization techniques for scraping
the soil into mounds are the same as those discussed for scraping the
soil into windrows in Section 4A.B of Part 2.
C. Removal - Vegetation removal will probably be necessary
prior to scraping the land to form mounds. The types of removal
that may be warranted are discussed in Section C of Part 1.
Soil removal would be by a scraper, grader, or dozer that can
either push or carry the soil a short distance to make mounds. It is
assumed that a nominal haul distance is 1,000 feet and the mound size
is 10 feet high with a base of 50 feet by 100 feet. The mound is
assumed to have sides that slope at a 45 degree angle and a flat
surface at the top that is 80 feet long and 30 feet wide. (The
shape and dimensions of the mound ware chosen for calculational
purposes to determine the surface area a mound would cover.) If
4 inches of soil are removed from the land, the mounds would require
only about 5 percent of the surface area per acre.
The range in costs for scraping and hauling the soil about
1,000 feet to form a mound were calculated to be about $150 to $1,640
per acre. The average cost is about $600 per acre.3-4,16,33-35,37-40
D. Packaging - Not applicable. (See Section C of Part 1
concerning packaging of vegetation that has been removed from the land.)
E. Transportation - The transportation costs indicated would
be incurred if the distance the soil must be hauled to the mounds is
greater than 1,000 feet. The extra costs for hauling (or possibly
pushing) the soil with a scraper are discussed in Section E of Part 1.
F. Ultimate Disposal - The procedures would be similar to
those used in Section 4A.F in Part 2.
-------
526
-34-
G. Restoration - The restoration costs only apply to the
area of land from which the soil is removed. This area is
calculated to be 95% of the original area since the mounds cover
about 5% of the land area. This calculation is based on the assumption
of the geometry of the mounds as presented in Appendix A, Part 2, Sec-
tion 4B.C. The techniques and procedures would be identical to those
in Section 4A.G in Part 2 except the costs would be calculated for 95%
of an acre instead of the 50% of an acre for scraping land into
windrows. More details on costs are presented in Section G of Part 1.
4C. Scraping and Hauling Soil into Trenches (includes a 1,000 foot
transport distance)
A. Radiological Surveillance - See Section A of Part 1.
B. Stabilization - Prior to soil removal, the land should be
stabilized with a short-term stabilizer (as indicated in Table 6) to
reduce resuspension of plutonium to a minimum. The cost of this type
of stabilizer is discussed in Section B of Part 1.
C. Removal - Vegetation removal will probably be necessary
prior to scraping the land. The types of removal that may be warranted
are discussed in Section C of Part 1.
Soil removal would be by a scraper, grader, or dozer that can
carry (or possibly push) the soil a short distance to the trenches.
The trenches are dug and backfilled by large earth moving machinery.
The soil removed from the trenches may be applied to the scraped land
to help defer the soil costs for restoration of the scraped land.
The costs of burying the contaminated soil include a 4-inch removal
of soil and a 1,000-foot haul (or possibly push) of the soil to the
trench. The range of costs is estimated to be $530 - $3.710 per acre
with, an average of about $1,700 per acre.3~4>16,33-35,37-40 If the
trenches are constructed near the scraped areas, about $300 per acre
in hauling (transportation) costs can be eliminated.^, 33,34
D. Packaging - Not applicable. (See Section C of Part 1
concerning packaging of vegetation that has been removed from the land.)
E. Transportation - The transportation costs indicated would
be incurred if the distance the soil must be hauled to the trenches
is greater than 1,000 feet. The extra costs for hauling or pushing
the soil with a scraper are discussed in Section E of Part 1.
F- Ultimate Disposal - Fencing and a guard service around the
scraped land or the trenches is probably not necessary since the
contaminated soil is buried.
-------
527
-35-
G. Restoration - Restoration procedures would be the same
as those discussed in Section l.G of Part 2 with one exception:
the soil from the trenches can be used to cover the scraped area;
thus, there is no cost of procuring the soil. An option may be to
add 2 inches of topsoil to promote vegetation growth.
5. Vacuuming with Disposal of the Soil in a Trench
The techniques and costs are similar for Vacuuming (with
trench disposal) and Scraping (with trench disposal) for all the
categories except for (1) stabilization and (2) soil removal.
(1) Stabilization - There is little available data concerning
stabilization prior to vacuuming. Temporary stabilizers used on bare
ground (as indicated in Table 6) are assumed to be adequate prior to
vacuuming. However, the use of stabilizers prior to vacuuming may
interfere with this process. The land area will probably require
plovring or discing to break up the stabilizer. Even water used as
a stabilizer might form a crust which can impede vacuuming.
C2) Soil Removal - There is limited information concerning the
use of an industrial vacuum cleaner for soil removal. Sand can be
picked up with a high efficiency and with ease.* Most other types
of soil should be shallow plowed (several inches depth) prior to
vacuuming to loosen the deep soil. Plowing (8-10 inches depth or
deeper) will move the contamination below grade thus reducing the
efficiency of -vacuuming. The efficiency for removal for these soils
is less than sand and is very dependent on the moisture content of
the soil.
The vacuum cleaner must have a HEPA filter for preventing plutonium
resuspension in the air. The vacuum cleaner would be mounted on a boom
on a flatbed truck. The soil removal costs of this technique
a 4-inch removal were calculated for plowing, vacuuming, building
a trench, and covering the trench. The range of costs were
estimated to be $910 - $5.100 per acre with the average assumed to
be about $2,500 per acre.
III. Removal with Offsite Disposal
6A § 6B. Scraping or Vacuuming
A. Radiological Surveillance - See Section A of Part 1.
B. Stabilization - For scraping, stabilization is the same
as that discussed in Section 4.C.B. For vacuuming, stabilization is
the same as that discussed in Section 5.
-------
528
-36-
C. Removal
(1) The soil is plowed, vacuumed, and deposited in
containers to be transported off site. This is discussed
further in Section C of Part 1.
An alternative method with a similar cost would
be to scrape the soil into windrows or mounds, pick up the
soil using an industrial vacuum cleaner, and deposit the soil
in a container to be transported off site. It may be easier and
more economical to pick up the soil with a scraper or a front
end loader to deposit 'the soil in containers. With either
method, it is very important to keep spillage of soil to a
minimum.
If the soil is picked up manually, rather than by a
vacuum cleaner, the costs for the pickup alone can range between
$2,000 - $6,000 per acre-33,34 for a 4-inch removal. Thus
Vacuuming seems to be economical, as well as fast.
^* Packaging - The packaging costs are discussed in Section D
of Part 1 for the Waste Burial Grounds and for Federal Repositories.
E. Transportation - The transportation of containerized soil
is discussed in Section E of Part 1.
F. Ultimate Disposal - Ultimate disposal is discussed for
the Waste Burial Grounds and the Federal Repository in Section F of
Part 1.
G. Restoration - The restoration of the land includes the
cost of materials (including 4 inches of soil) and their application
for a full acre. A discussion of the costs for restoration are
presented in Section G of Part 1.
-------
529
-37-
APPENDIX B. Special Techniques
Part 1 - Technology
There are several techniques not listed in Table 1 that may be
used for reducing the environmental impact of plutonium that has
been deposited on land areas. These techniques are generally used
for the reasons indicated below.
(1) Application of Asphalt: A surface treatment of asphalt
can be applied on small areas as a permanent stabilizer.5 This
type of surface would not be adequate as a parking area, but it
would effectively prevent resuspension of plutonium (100% efficient)
and for a number of years prevent vegetation growth (about 100%
efficient). This method probably would not be used because of the
high costs and the commitment of the land to a nonproductive status.
The stabilizer action and its costs are discussed in more detail in
Appendix A, Part 1, Section B.
(2) Sewage Sludge: Sludge may be applied to land as a fixation
stabilizer just as soil is applied (as described in Appendix A,
Sections 3A and SB of Part 2) or in lieu of restorative measures
requiring soil and vegetative applications. The savings in cost
would be the material cost of soil. However, this method would
only be applicable to areas where large quantities of sludge are
available and the land can be committed as a sewage sludge disposal
site.
(3) Snow: Decontamination of snow probably would involve
collecting and melting the snow, 'and then removing the plutonium by
evaporation or ion exchange, and disposal at a waste burial ground.
The solid waste would be about a factor of 100 smaller* than the
volume of snow scraped, which would significantly reduce the costs
of packaging and burying the waste. Thus, scraping the snow with
ultimate disposal at an approved waste burial site could be less
expensive than scraping and burying a similar volume of soil, even
though there would be additional costs for solidification or ion
exchange.
*Melting snow to water reduces the volume by about a factor of 8 to
12.12 present day techniques of solidification can reduce a volume
of contaminated water by a factor of 10 or more.45 Solidification
of the waste would then probably increase this volume by a factor
of 2 or more.
-------
530
-38-
(4) Flooding land areas with about an inch of water, combined
with collection of the water, removes loose soil and debris
containing Pu. This technique would result in large volumes of
contaminated water requiring disposal. Since many waste burial
grounds and the Federal Repository probably will not bury or store
liquids, the contaminated liquids would also require solidification.
Flooding might be useful, even though difficult, on mountainous
areas which are inaccessible to large earthmoving equipment. However,
for most land areas, flooding would not be acceptable because of the
generation of large volumes of contaminated water and the difficulties
of collection of the contaminated water.
(5) Air Shelters: A canvas type structure supported by air is
presently being utilized at the Idaho National Engineering Laboratory
to allow the excavation of solid waste burial drums during advserse
weather conditions. A similar type structure covering approximately
half an acre can be utilized during plutonium decontamination
operations to help prevent the wide disposal of plutonium contaminated
dust particles (i.e. resuspension) and/or to provide protection from
the weather. These shelters are large enough to allow the limited
movement and operation of scrapers, dozers, and other earthmoving
equipment within the structure. The structure can also be transported
from one area to the other so a reasonably large area (several acres
to several tens of acres) may be decontaminated. 5,56
(6) Other measures: Other measures to reduce the environmental
impact of plutonium deposited on farmland could possibly be (1) the
use of additives, such as lime or fertilizer, to reduce the entry of
radioactivity from soils into crops; (Note: Additives to reduce
plant uptake of plutonium were not specifically mentioned in the
literature. It should also be noted that there is no information in
the literature to indicate that plutonium in the forms which might
normally be distributed is taken up in growing crops to a significant
degree.) (2) growing crops that take up small amounts of plutonium;
or (3) treating of milk or other products during the processing stages
for removal of plutonium;^ (4) leaching out nlutonium contamination
from the soil by some chemical treatment method, and (5) selectively
screening contaminated soil so as to separate fine particulates from
stones and larger material.with the idea that most of the plutonium-
distribution will reside with the small particle fraction.
-------
531
-39-
Part 2 - Costs
(1) Application of Asphalt: See Appendix A Section B of Part 1
concerning costs of a surface treatment of asphalt.
(2) Sewage Sludge: Costs of hauling and spreading sewage
treatment plant sludge are calculated to range between about $200
-$3,800/acre/year. The sludge could be spread for several years.
The bases of these calculations are presented on page 9 and Tables
9 and 10 of reference 24.
(3) Snow: The costs for scraping, packaging, and disposing of
contaminated snow are assumed to be proportional to those for soil,
except the volume of solid waste per acre is assumed to be a factor
of about 100 smaller. These assumptions are made to present a ball-
park estimate and other costs such as demineralization or evaporation
of the melted snow are not included. The range of costs is estimated
by dividing by 100 the costs presented in 6A and 6B of the "typical"
project discussed in Appendix B. These costs are $900 - $5,100/acre.
C4) Flooding (1 inch of water): The costs to flood an acre of
land with 1 inch of water would be proportional to the costs for
applying water as a stabilizer (See Appendix A, Section B, Part 1) .
The costs of flooding would include radiological surveillance,
packaging (at $6.80 - $10.20 per ft3 or an extra $49,000 - $74,000/
acre, See Appendix A, Section D, Part 1), Ultimate Disposal and
Restoration. The costs for applying the water will be about (1.0/0.3)
$220/acre = $730/acre and a range of about $330 - $l,130/acre.16,42
The water that is collected would probably have to be solidified by
the same techniques.as used for melted snow, with disposal of the
solid material at a waste burial ground or the Federal Repository. As
an example of the disposal cost, assume that the water is encased in
concrete with an increase in volume of a factor of 2. The volume of
concrete would be 7260 ft . At a waste burial ground, the disposal
costs would be about $9800/acre for nonretrievable disposal, $29,000/
acre for retrievable storage, and about $182,000/acre for storage at the
Federal Repository. (See Appendix A, Section F Part 1). If the volume
of solid material is significantly less (as a result of using another
solidification technique), then the packaging and disposal costs can
also be reduced significantly.
(5) Air Shelters: The one time direct and indirect costs for an
air shelter, including anchor blocks is estimated to be about $170,000
(1975 dollars). This shelter can enclose about 22,500 square feet.
The costs to initially install the structure or to move and install
the structure near its original installation is about $49,000 (1975
dollars).56
-------
PRlS* TO 'IOWII
CONTROL!
Dttf H.OIHING-I:
ISuirtftIN) fO ii.
MIL* KttvEHf tHOSlOB
S-IOVItS HiTHHEAtfLICATlOW
SllLechl|» HHV
«*«AH.O* MUUS. IWILL INCLUM LOMH ACT1
StC* I.LOX 0 OUUS WIQMfHUVEl 0<*CTIVIT
TO TB1NCHIACAIH COSTS tO» TM[l flRST THOUSAND fl
SOIt ff-WHttff f "°" TREMCHIS SOIL HpftDVtD ft
KR*PtD*REA£-Uni°VADDi VACUUM ED AHEM
CJ1
CO
to
-------
B'BWS*
rsoirvaoS'Tat^vris
liOtiONIHG SW -IttW
CJ1
CO
CO
-------
534
-42-
TABLE 3
Adjustment Indexes*
Multiply the costs appearing in Table 2 by the following factors
to adjust for geographical differences:
Location
Albany, New York
Albuquerque, New Mexico
Anchorage, Alaska
Atlanta, Georgia
Austin, Texas
Baltimore, Maryland
Birmingham, Alabama
Bismark, North Dakota
Boise, Idaho
(Base) Boston, Massachusetts
Bridgeport, Connecticut
Buffalo, New York
Camden, New Jersey
Charleston, West Virginia
Charlotte, North Carolina
Chattanooga, Tennessee
Cheyenne, Wyoming
Chicago, Illinois
Cincinnati, Ohio
Cleveland, Ohio
Columbus, Ohio
Dallas, Texas
Denver, Colorado
DesMoines, Iowa
Detroit, Michigan
El Paso, Texas
Evansville, Illinois
Harrisburg, Pennsylvania
Hartford, Connecticut
Honolulu, Hawaii
Houston, Texas
Indianapolis, Indiana
Jackson, Mississippi
Jacksonville, Florida
Kansas City, Missouri
Lansing, Michigan
Las Vegas, Nevada
Little Rock, Arkansas
Los Angeles, California
Louisville, Kentucky
Labor
96
84
29
82
77
91
79
79
83
00
98
08
07
94
66
81
83
07
03
10
04
.75
.86
.87
1.21
.69
.89
.92
1.00
.92
.84
.89
.72
.85
1.07
1.01
1.04
.73
1.13
.95
Material
01
93
04
89
90
89
85
94
93
00
01
01
97
00
93
94
94
90
18
.88
.95
L.06
.89
.97
.96
.90
.94
.97
.98
1.02
.91
.94
.85
.95
1.05
.93
1.06
.86
.97
.94
1
-------
-43>-
535
TABLE 3
(continued)
Location
Madison, Wisconsin
Manchester, New Hampshire
Miami, Florida
Milwaukee, Wisconsin
Minneapolis, Minnesota
Mobile, Alabama
Nashville, Tennessee
Newark, New Jersey
New Orleans, Louisiana
New York, New York
Norfolk, Virginia
Oklahoma City, Oklahoma
Omaha, Nebraska
Philadelphia, Pennsylvania
Phoenix, Arizona
Pittsburgh, Pennsylvania
Portland, Maine
Portland, Oregon
Providence, Rhode Island
Richmond, Virginia
Rochester, New York
St. Louis, Missouri
Salt Lake City, Utah
San Diego, California
San Francisco, California
Savannah, Georgia
Seattle, Washington
Shreveport, Louisiana
Sioux Falls, South Dakota
Spokane, Washington
Springfield, Illinois
Springfield, Massachusetts
Syracuse, New York
Tampa, Florida
Topeka, Kansas
Trenton, New Jersey
Washington, D.C.
Wichita, Kansas
Wilmington, Delaware
Youngstown, Ohio
Montreal, Quebec
Toronto, Ontario
1
1
Labor
90
89
02
99
97
84
78
12
83
33
70
83
90
04
.98
1.04
.71
.94
.97
.71
1.06
1.04
.88
1.02
1.20
.77
.99
.76
.81
.91
.89
.98
.00
.88
.86
.09
.99
.92
.98
.99
1
.73
.94
1
Material
95
97
95
96
09
91
90
89
88
02
.94
.89
.97
.78
.95
1.14
.98
.95
.98
.95
1.03
.97
.94
.93
1.06
.94
.74
.86
.94
.94
.93
.99
1.00
.95
.98
1.02
.96
.97
.97
.94
.73
1.09
*1974 Dodge Guide^ for Estimating Public Works Construction Costs,
Annual Edition No. 6, McGraw-Hill Information Systems Company,
Princeton, New Jersey (1974)
-------
TABLE 4 SUMMARY OF TECHNIQUES AND COSTS
cosis/ A:
SECTION OF REPORT
ADVANTAGES
DISADVANTAGES
t RESTRICTION OF LANO USE
IF 1 ICING I
2 STABILIZATION
Ai CHEMICAL ANO. OR
VtGCTATIVE
Cl APPLICATION Of A
SOU COVER
3 SOU RtMOVAt WITH ONSITE
A SCRAP1 INTO WINDROWS
I, SCHl''! OR VACUUM INTO
4 Sim REMOVAL WITH OFFSITE
AFVENOIS B. PART II
TECHNIQUE 2 IN TABLE 1 AND 2
TECHNIQUES IA ANO IB IN TABLE
1 ANO 2
TECHNIQUES 4A OF TABLES
I'ANO 2
TECHNIQUES 4B. 4C ANO S OF
TECHNIQUES S> ANO (B OF
1100
2100
4.600 14 INCH COVER)
9.600 112 INCH COVCRI
3.600
5.200
125.000 IWASTE
NON RETRIEVABLE!
105 000 WASTE
BURIAL GROUND.
RETRIEVABLE!
515,0001'EOCRAl
REPOSITORY)
350-3300
500-3.000
2.400-7.500
5.400-14.000
1.600-6.300
2200- 10.200
110.000-100.000
150000-235.000
400000 600000
-INEXPENSIVE
-LAND IS NOT DISTURBED OR DEGRADED
-INEXPENSIVE
-EASY TO APPI Y
-DOES NOT DISTURB THE LAND
-LANO CAN BE PRODUCTIVE
-PREVENTS RESUSPENSION OF PLUTONIUM
-FLOWING TO A DEPTH OF 3 FEET AIDS IN REDUCING
PLANT UPTAKE OF PLUTONIUM
-OIlllIESTHE PLUTONIUM ACTIVITY
-IODN EFFECTIVE IN PREVENTING RE SUSPENSION
-LANOCANBE PRODUCTIVE
-ABOUT SO-. OF LAND IS ACTIVITY FREE (GENERALLY ABOUT
W\ EFFICIENCY FOR REMOVAL OF PL UTON >UMI
-ABOUT 60*. OF LAND CAN BE PRODUCTIVE
-RESUSPiNSION AND PLANT UPTAKE OF Pu IS SIGNIFICANTLY REDUCED
-FUTURE OE CONTAMINATION EFFORTS WOULD NOT BE DIFFICULT SINCE
ALMOST ALL OF THE ACTIVITY WOULD BC iTABILIZEO IN THE WINDROWS
-ABOUT 90'. (OR BETTER! OF THE ACTIVITY IS REMOVED FROM THE LANO
-HESUSPLNSION ANO PLANT UPTAKE OF Pu IS SIGNIFICANTLY REDUCED
-FUTURE DECONTAMINATION IF NECESSARY .WILL NOT BE DIFFICULT
(HOWEVER IT WUULO BE A LITTLE MORE DIFFICULT THAN THE
PREVIOUS CASE WHERE THE SOIL IS SCRAPED INTO WINDROWS)
COMPLETE REMOVAL OF CONTAMINATED SOIL FHOM THE AREA
BUHIAl GROUND IX RETRIEVABLE FORM THE SOIL MAY BE
REPACKAGE 0. IF NECESSARY. AND MAINTAINED IN HIGH IN
TEGHITY CONTAINERS)
NOT{ SOIL WILL POSSIBLY NEVER BE DEPOSITED
AI A FEDERAL REPOSITORY CURRtNT REQU.REMENIS ARE THAT
THE ACTIVITY CONCENTRATION BE AT LEAST IOoC./,..o. BEFORE
THE Pu CONTAMINATED SOIL IS DEPOSITED AT THE FEDERAL
REPOSITORY
-LAND IS NOT PRODUCTIVE WHILE RESTRICTED
-TECHNIQUES IS APPLICABLE FOB LOW ACTIVITY CONTAMINATE* ON! i
-REPLACEMENT OF FENCING IS NECESSARY AFTER 20 -30 YEARS
-DOES NOT PREVENT PLANT UPTAKE OF PLUTONIUM
-CHEMICALS MUST BE Rf APPLIED EVERY5 -10 YEARS UNLESS VICE TA» vE
COVEM IS ADEOUATE TO PREVENT FtESUSPENSION OF PLUTONIUM
-USED FOR RELATIVELY LOW ACTIVITY CONTAMINATION
-PLUTONIUM STILL REMAINS IN THE AREA
-USED ON LOW OR MEDIUM LEVEL ACTIVITY CONTAMINATION
-MODERATELY CXPENSIVE-THt MOST EXPENSIVE STABILIZATION TtCNMQUf
-OOESNOT PRE VENT PLANT UPTAKE 112 INCH SOU COVER SHOULO BE WORE
EFFICIENT IF PREVENTING PLANT UPTAKE THAN THE 4 INCH SOIL CO.E<
-MODERATE COSTS
-WINDROWS ARE STABILIZED BY CHEMICALS ANO OR VEGETATION
THUS. PROBLEMS ARE SIMILAR TO THOSE LISTED FOR 2. A ABOVE
-ACTIVITY STILL REMAINS ONSITE
-MODERATE COSTS
IN THE FUTURE
-ACTIVITY STILL REMAINS ONSITE
-LEACHING Pu INTO THE SOIL MAY BE A CONCERN WITH TRENCH DISPOSAL
-EXTREMELY EXPENSIVE
THUS INCREASING THE PROBABILITY OF AN ACCIDENTAL SPILL
c.
.£.
I
CO
<75
-------
-45-
537
TABLE 5
Plutonium Cleanup Experience Costs
Project
Total Cost
Acres
$/Acre
AEC Niagara Falls Sitea
Palomares, Spain*3
Nuclear Reactor Developmenta
Station at NTS
Enewetak Islands0
Rocky Flatsd
$ 88,000 (1972)
$50,000,000 (1966)
$ 100,000 (1965)
— (1976)
8-10
600
5
0.46
$ 8,800
$83,300
$20,000
$25,500*
Enewetak Islands Project
Estimated Costs for 1976°
Technique
Actual Costs
Costs Adjusted for
Continental U.S.
Costs Including
32% Overhead
Debrushing
Scraping (including
Stabilization)
Replacing Soil
Disposal
$l,700.00/acre
6.40/cubic yard
11.00/cubic yard
80. OO/ cubic yard
$/C.Y.
2.3
3.9
28.6
$/Acre*
$ 800
1,620
2,790
20,280
Totals
$ 97.4 /cubic yard
34.8
$25,500
*Costs in $/C.Y. were converted to $/Acre by assuming that 4 inches of soil were
removed or replaced. A 4-inch layer of soil is equal to 538 cubic yards of soil
per acre. Actual costs are estimated to be about $70,000 per acre. The Army
Corps of Engineers indicated that these costs are about a factor of 2.8 higher
than the costs for decontaminating similar land in the United States.
aFrom reference 4 of this report. Note: Radioactivity deposited on the land
was not Pu.
Kathren, Ronald L. Towards Interim Acceptable Surface Contamination Levels for
Environmental PuO. BNWL-SA-1510 (1968)
Reference 31 of this report.
dSummary Report of Soil Removal - Preliminary Excavations, C.E. Wickland,
Report presented at the Conference for Decontamination and Decommissioning
(D and D) of ERDA Facilities held in Idaho Falls, Idaho, August 19-21, 1975.
-------
TABLE 6. USES FOR STABILIZERS AND APPROXIMATE COSTS TO APPLY/ACRE
Temporary
(prior to any decon)
Water - $220 ($100-$340
Short-term
(prior to soil removal)
Asphaltic - $1100
Emulsion
Geo-tech - $ 520
oil
Petroset $1200
Polv vinvl -$7flO-<7nf)
Acetate
Short-term
(on bare soil as a
part of restoration)
s
\
N
"7
/
Norlig - $240
Long-term
5-10 years
Geo-tech $520
(with reapplication
every 5 years)
Soil Cover
i
i
DCA-70
$440
Range $200-$1200/acre
Average $700
Rapid Cure Road Oil
$660 (reapply after
5 years)
Range $200-$1200
Average $570
Range $520-$660
Average $600
4" Loam
Range
$1500 - $3300 -Average
$2400
4" Topsoil
Range
$3300 - $5700 -Average
$4500
Range $100-$340/acre
Average $220/acre
Loan Topsoil
Range $1700-4500 +$3500-6900
Average $3100 $5200 CJI
CO
GO
-------
-47-
TABLE 7
Value of Crops (per Acre)*
in 1973
539
No. Units/Acre
Crop
Corn
Wheat
Soybeans
Oats (grain)
Tobacco
Hay
All Crops (total U.S. Average)
Major crops - corn, soybeans, hay, wheat
Unit
$/Unit
$/Acre
91.4
31.8
27.8
47.0
1983.0
2.2
bushels
bushels
bushels
bushels
pounds
tons
2.37
3.82
5.65
1.09
0.90
40.60
217
121
157
51
1785
89
170
*U.S. Department of Commerce. Statistical Abstract of the
United States 1974 National Data Book and Guide to Sources,
Bureau of Census, Social and Economic Statistics
Administration, U.S. Department of Commerce.
-------
-48-
TABLE 8
Value of Forests Cper Acre)
in 1974*
540
Region
1
2
3
4
5
6
8
9
10
States
Montana, N. Idaho
Colo., Wyoming, S. Dakota
Ariz., New Mexico
Utah, S. Idaho, Nevada
California
Oregon, Washington
S.E. (Va. to Texas)
Lake States and N.E.
Alaska
Average for the U.S.
$/per 1000 Board Feet
46.16
12.65
62.85
72.78
83.36
124.35
50.76
17.21
15.26
88.14
# board feet per acre --
National average
Region 6 average
Maximum
$ per acre --
30,000
60,000
150,000
National average $ 2,644
Region 6 $ 7,461
Maximum (at $88.14/1000 board feet) $13,200
*U.S. Department of Agriculture.
Fourth Quarter and Fiscal 1974.
Timber Sold on National Forest,
Circular Memorandum, July 22, 1975.
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541
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References
1. Telephone conversation with R. E. Shaddock, VIP Corporation,
Streator, Illinois, on February 26, 1975.
2. U.S. Atomic Energy Commission, "Scavenging Contaminated Soil
with Polyurethane Foam," RFP-1949. Rocky Flats Division, Dow Chemical
USA, Golden, Colorado 80401.
3. U.S. Department of Agriculture in cooperation.with the
Atomic Energy Commission, "Research on Removing Radioactive Fallout
from Farmland," Technical Bulletin No. 1464, Agricultural Research
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E. M. Romney, University of California Laboratory of Nuclear Medicine
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90024 (September 1974).
5. Telephone conversation with a representative of Bituminous
Products Corporation, Washington, D.C., on March 3, 1975.
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7. U.S. Environmental Protection Agency. "Ocean Dumping Proposed
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Concerning Radioactive Wastes and Other Radioactive Matter. Referred
to in Annexes I and II to the Convention on the Prevention of Marine
Pollution by Dumping of Wastes and Other Matter. Revised Draft,
July 19, 1974.
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9. Trip report by Wayne R. Hansen, Ph.D. ATSB/TAD/ORP/EPA
to Hickara Air Force Base, Honolulu, Hawaii, for a meeting sponsored
by the Defense Nuclear Agency, Department of Defense (March 17-25, 1975).
1(X. Conversation with Bob Dyer, CSD/ORP/EPA on March 14, 1975.
11. Telephone conversation with the U.S. Weather Bureau,
Washington, D.C., (May 12, 1975).
12. Building Cost and price index roundup. 20 Cities: Construction
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13. U.S. Government Printing Office. Economic Report of the
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15. Telephone conversation with the District of Columbia Water
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16. U.S. Environmental Protection Agency. "Comparative Costs of
Erosion and Sediment Control, Construction Activities," EPA-430/9-73-016,
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17. U.S. Atomic Energy Commission. "Radiological Emergency
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18. Telephone conversation with Mr. William Clark, Marketing
Representative for American Cyanamid Company, Industrial Chemicals and
Plastics Division, Wayne, New Jersey (February 28, 1975).
19. Telephone conversation with Al Western, Radiation Safety
Field Superintendent, Reynolds Electrical and Engineering Company, Inc.,
Las Vegas, Nevada, on March 6, 1975.
20. Telephone conversation with a representative of Bituminous
Products Corporation, Washington, D.C. on March 3, 1975.
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543
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21. Telephone conversation with Don Hess of Standard Oil
Corporation of California, San Francisco, California, on
March 5, 1975.
22. Telephone conversation with TopCote Polyurethane
Application Company, Washington, D.C., April 1975.
23. Telephone conversation with Tom Hobbs, a representative
of Hydro Turf Co., Maryland, in March 1975.
24. U.S. Environmental Protection Agency. "Costs of Hauling
and Land Spreading of Domestic Sewage Treatment Plant Sludge,"
PB-227-005. Prepared by Walter F. McMichael, National Environmental
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26. Cost figures calculated from a price list and sales
brochure received from Mr. Clark on American Cyanamid Aerospray 70.
27. Telephone conversation with Dr. William Bright, Research
Office of Rocky Flats, Division of Dow Chemical Company, on
March 6, 1975.
. 28. Telephone call to R§W Construction Company, Washington, D.C.,
in March 1975.
29. Telephone conversation with a representative of Fairland
Excavating Co., Fairland, Maryland, in March 1975.
30. U.S. Department of Defense. Draft Environmental Impact
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31. U.S. Environmental Protection Agency. "Environmental
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32. 1974 Dodge Manual for Building Construction Pricing and
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544
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33. Building Construction Cost Data, 1971. 29th Annual Edition,
Robert Snow Means Company, Inc., Engineers and Estimators, P.O. Box G,
Duxbur/, Massachusetts
34. 1974 Dodge Guide for Estimating Public Works Construction
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35. Carter, R. P., Zimmerman, R. E., and A. S. Kennedy. Strip
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37. Department of Defense. "Radiological Recovery of Fixed
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41. Telephone conversation with the Guy E. Simpson Company, Inc.,
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42. Telephone conversation with Mr. Ed Northrup, Jr., of Northrup
and Johnson (Contractors and Equipment Suppliers), Washington, D.C.,
in March 1975.
43. Telephone conversation with Bruce Owens, Dow Chemical Company,
Rocky Flats Division, Colorado, on February 26, 1975.
44. Program for the Management of Hazardous Wastes, Final Report,
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Northwest Laboratories, Richland, Washington, 99352.
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545
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45. Telephone conversation with Government Services Administration,
Federal Protection Service Division, Technical Services Branch, on
March 18, 1975.
46. Telephone conversation with Landy Strongin^ New York State
Aeronautical Engineering and Space Authority on February 27, 1975.
47. Telephone conversation with Joe Work, ERDA on February 25, 1975.
48. Telephone conversation with Bud Hickman, Aerojet Nuclear
Company, on February 24, 1975.
49. U.S. Atomic Energy Commission. The Nuclear Industry 1974,
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active Wastes: Study of Commercial Operations and Facilities,
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51. U.S. Atomic Energy Commission, Proposed Changes to
10 CFR Part 20 Concerning Transuranium Waste Disposal, 39 FR 32921.
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53. Conversation with D. French, ERDA, at the Conference for
Decontamination and Decommissioning of ERDA Facilities at Idaho Falls,
Idaho, August 19-21, 1975.
54. U.S. Department of Agriculture. Farm Real Estate Market
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55. Telephone conversation with Dennis McMurtrey, Aerojet
Nuclear Company, in September, 1975.
56. Information sent with a memo from George Wehman, Director,
Office of Waste Management, Idaho Operations Office, ERDA, to
Bruce Smith,, Office of Radiation Programs, EPA, dated October 3, 1975.
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