EPA-600/4-76-027
June 1976
Environmental Monitoring Series
RADIOIODINE PREDICTION MODEL FOR
NUCLEAR TESTS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service. Springfield, Virginia 22161.
-------
EPA-600/4-76-027
June 1976
RADIOIODINE PREDICTION MODEL FOR NUCLEAR TESTS
by
Stuart C. Black and Delbert S. Earth
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
LAS VEGAS, NEVADA 89114
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Support
Laboratory-Las Vegas, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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CONTENTS
Page
List of Figures iv
List of Tables iv
Introduction 1
Summary 5
Chemical and Physical Forms 13
Milk Secretion Parameters 13
Air sampler prediction 19
Forage prediction 22
Pre-event prediction 22
Dose Estimates 25
Inhalation Dose 27
Comparison with Other Studies 28
Other Radionuclides 33
Baneberry Data 33
References 35
111
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LIST OF FIGURES
Number Page
1 General pattern of iodine-131 secretion in milk
following ingestion 14
2 Peak iodine-131 concentration in milk from cows on fresh
feed versus open-field gamma exposure rate 17
3 Peak iodine-131 concentration in milk from cows on hay
versus open-field gamma exposure rate 17
4 Peak iodine-131 concentration in milk frow cows on fresh feed
versus integrated concentration of iodine-131 in air 19
5 Peak iodine-131 concentration in milk from cows on fresh feed,
corrected by filter-to-charcoal ratio 20
6 Peak iodine-131 concentration in milk from hay-fed cows versus
integrated concentration of iodine-131 in air 21
7 Peak iodine-131 concentration in milk versus distance
from surface ground zero 23
8 Cumulative does to a 2-gram thyroid from radioiodine in milk 33
LIST OF TABLES
Number Page
1 Radioiotline experiments 2
2 Physical data for radioiodine model 6
3 Milk data for radioiodine model 9
4 Measured parameters for radioiodine transfer to milk 14
5 Inhalation exposure calculations 15
6 Maximum iodine-131 in milk by event and distance 2
7 Comparison of values reported in the literature 29
8 Comparison of predictions for infinite dose to a 2-gram thyroid 30
9 Comparison of thyroid dose estimates in rads to a 2-gram thyroid 32
10 Data on thyroid dose calculations for short-lived radionuclides 33
iv
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INTRODUCTION
Early in 1963 an Ad Hoc Working Group met at the Nevada Operations Office
of the U.S. Atomic Energy Commission (AEC)* to consider the problems associated
with radioactive debris from nuclear tests. Of the long-range studies suggested
by this Group, the AEC assigned a portion of the responsibility and funds to
the U.S. Public Health Service (PHS). As a result, in 1963 the PHS started
planning and in 1964 initiated an investigation of the possible hazards to the
general human population that might be caused by the release of radioiodine
during testing of nuclear devices.
One of the principal objectives of the investigation was to obtain a more
precise definition of the air-forage-cow-milk pathway for transfer of radio-
iodine, including the development of a prediction model for this transfer. The
program was conducted at the Southwestern Radiological Health Laboratoryt be-
cause of its proximity to the Nevada Test Site and the desire to do field ex-
periments, with all their concomitant problems, during planned releases of
radioactive materials and thus obtain realistic data.
Concurrent with the field experiments, a series of controlled experiments
was conducted in which aerosols of known characteristics were used to contam-
inate various types of dairy cow forage with iodine-131. The controlled ex-
periments were conducted at a dairy farm managed by the Laboratory (Douglas
1967, Smith and Engel 1969) located in Area 15 on the Nevada Test Site.
A resume of the experiments conducted since this program started is shown
in Table 1. Results of these experiments were used to evaluate many of the
factors involved in constructing a prediction model for the transfer of radio-
iodine to man through the forage-cow-milk route. The factors considered in
designing these experiments included:
- Those affecting uptake by the cows
mode of exposure (inhalation, ingestion)
* tvpe of food (hay, fresh forage)
arrangement of feed (spread or baled hay, chopped or growing forage)
species of forage (Sudan grass, alfalfa, oats, barley)
physical form of contaminant (gaseous, particulate)
chemical form of contaminant (iodine, iodate, organic, etc.)
biqlogical availability (prepared aerosols, effluent from various
nuclear tests)
* Since January 1975 the U.S. Energy Research and Development Administration
t In December 1970, this PHS Laboratory became a part of the newly formed U.S.
Environmental Protection Agency (EPA) and was later renamed the Environmental
Monitoring and Support Laboratory-Las Vegas.
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TABLE 1. RADIOIODINE EXPERIMENTS
Release Type:
Name & Date of
Experiment
Controlled Releases:
Milkrun 8-11-65
(Shimoda et al., 1970)
Hayseed 10-4-65
(Earth and Seal 1966)
Alfalfa 6-21-66
(Stanley et al., 1969)
Rainout 9-29-66
(Douglas et al., 1971)
SIP 6-6-67
(Mason et al., 1971)
MICE 9-21-67
(Black et al . , to be
^published)
Cows
Per
Group
8
4
4
4
4
4
4
4
4
6
6
6
6
}
6
6
6
6
Type of
Exposure
Single oral
Inhalation
Ingestion
ii
"
Inhalation
Ingestion
"
11
Ingestion
Inhalation
Inhalation
plus inges-
tion
Inhalation
Ingestion
Type of
Forage
Uncontaminated
Spread hay
Spread green chop
Green chop
Uncontaminated
Spread hay
Spread green chop
Green chop
Spread hay
Green chop
Uncontaminated
Hay
Green chop
Uncontaminated
Hay
Green chop
Species of
_ Remarks
Forage
Used Nal with 126I and 131I
Used diatomaceous earth-131!
_... , f dry aerosol, 23-pm count
Axiax ca _ , . i .. »
median diameter (CMD)
Sudan
"
Used diatomaceous earth-131!
. _ lf dry aerosol, 2-ym CMD
Alfalfa-oats
11
Alfalfa Used water spray with Na131!,
169-ym droplets
Used diatomaceous earth-131!
. dry aerosol, 0.13-vim CMD
Hay in manger during contamina-
M tion
Gaseous 131l£
Alfalfa Inhalation + baled hay + hay
made from pasture
(Continued next page)
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TABLE 1. RADIOIODINE EXPERIMENTS - Continued
Release Type:
Name & Date of
Experiment
Cows
Per
Group
Type of
Exposure
Type of
Forage
Species of
Forage
Remarks
HARE 9-18-68
(Black et al., 1975)
Ingestion Green chop
Sudan
Alfalfa
Used diatomaceous earth- 13
dry aerosol, 0.6-ym CMD
Accidental Releases, using commercial dairies:
Pike 3-13-64 3 Ingestion Green chop
(Earth and Veater 1964)
Alfalfa- Balance of herd on baled hay;
barley pasture feed started 5 days
" after event
Pin Stripe 4-25-66
(Earth et al., 1969)
4 Ingestion Green chop Alfalfa
6 " Green chop + hay "
Balance of herd on hay
Fed green chop or hay inter-
mittently
Planned Releases*:
TNT 1-12-65
(Black et al., 1969)
Palanquin 4-14-65
(Black et al., 1971a)
Cabriolet 1-26-68
(Black et al., 1971b)
5
5
4
6
6
3
3
4
Ingestion
ii
Inhalation
Ingestion
ii
it
Inhalation
Ingestion
Spread hay Alfalfa
ii ii
Uncontaminated
Spread hay Alfalfa i
Spread green chop "
Spread hay "
Uncontaminated
Baled hay Alfalfa
Planned destruction of a
rocket reactor
Forage from location where
inhalation cows were placed
Hay from different location
Sacrificed for tissue distri-
bution
Only one station contaminated
(Continued next page)
* Other experiments were planned for Tory, Kiwi, NRX and NRX-A6 reactor runs and the Sulky cratering
event, but the amounts of radioactivity released were too small.
-------
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- Those affecting transfer to milk
variation among cows (percent
secretion in milk)
stable iodine intake
thyroid status
stage of lactation
single versus multiple intake
Inhalation exposure is referred to as
air uptake in this paper because concurrent
ingestion generally occurs when the cow
licks its muzzle, nares, or surrounding
objects.
In many experiments, a deliberate
effort was made to obtain high levels of
contamination. For example, when contami-
nating hay for feeding experiments, the
hay was unbaled and spread out on plastic
sheets to allow maximum deposition of
activity. For fresh forage feeding, the
contaminated forage was cut fresh daily
(green chop) and fed rather than allowing
the cows to graze. Feeding green chop
(dry-lot feeding practice) is the most
common procedure used by dairies in the
Great Basin area. The forage plot at the
dairy farm had an average yield, for this
period, of about 1.5 kilograms fresh weight
per square meter. The cows' stable iodine
intake was approximately 250 milligrams
per day estimated from periodic measure-
ments of feed. To insure a realistic herd
average, cows in all stages of lactation
as well as high and low producers were
used in the experimental groups. Thus a
given experimental group might have cows
in which only 2 to 3 percent of the in-
gested radioiodine was transferred to milk
during the experimental period as well as
cows with transfers of 20 to 30 percent.
Since the amount of forage consumed
by the cow will affect some of the meas-
ured parameters, all of the results used
in this report have been adjusted mathe-
matically by using standard ingestion
data, based on the observed feeding hab-
its of the 26-cow dairy herd, and the
actual milk secretion curves of the indi-
vidual cows during each experiment.
-------
The standard ingestion data were: fresh forage 24 kilograms per day
in two feedings, or high quality hay 18 kilograms fresh weight per day in
two feedings.
Grain intake for either of the above regimens was 3.5 kilograms at each
milking or 7 kilograms per day. The amounts fed were based on the schedules
recommended by Morrison (1959). The dairy farm was operated as a Grade A dairy
with above-average veterinary care and with meticulous records on each cow.
For comparison with other dairy cow studies, the following characteristics of
the herd, which consisted of both grade and registered Holsteins, are listed.
Herd Characteristics Average
Number of milking cows 18
Days in lactation 271
Milk produced (liters/day) 21.5
Cow weight (kilograms) 585
Feces output, 218 samples (kilograms/day) 34.2
Urine output, 218 samples (kilograms/day) 25.7
The results obtained from the experiments listed in Table 1 are shown in
Table 2 (physical data) and Table 3 (milk data). These results are the founda-
tion of the prediction procedures which are outlined in subsequent sections of
this report. Where appropriate data are available, results from the Off-Site
Surveillance Program* conducted by this Laboratory are included. Dashes in the
tables indicate that data were not available.
SUMMARY
Over a 5-year period, 14 major experiments were conducted to investigate
the air-forage-cow-milk system for transfer of radioiodine. The experiments in-
cluded controlled releases using prepared aerosols, planned releases during
Plowshare cratering tests, and releases due to accidental venting of underground
nuclear tests. Two or more groups of dairy cows, three to six cows per group,
were used in each experiment to study the effect on radioiodine transfer of such
factors as: the mode of exposure, the type and state of forage fed, the type of
aerosol, and variations in feeding practices. In each experiment, measurements
were made of the total radioiodine intake and output in milk of the cows, the
concentrations in forage and milk, the gaseous and particulate air concentrations,
the open-field gamma exposure rate and the deposition per unit area.
The mean values of the experimental data are assembled in this report and
are used to develop the parameters for a standard milk excretion pattern for
dairy cows and to develop predictive equations for radioiodine. The resultant
equations, for predicting the infinite dose to a 2-gram thyroid caused by
* A program conducted for the Nevada Operations Office of the U.S. Energy
Research and Development Administration (SWRHL 1970, WERL 1972)
-------
TABLE 2. PHYSICAL DATA FOR RADIOIODINE MODEL
Exposure Route:
Name and Cows
Date of Per
Experiment Group
Hay:
Pike
03/13/64
Palanquin
04/14/65
TNT
01/12/65
Cabriolet
01/26/68
Buggy
03/12/68
Schooner
12/08/68
Hayseed
10/04/65
Alfalfa
06/21/66
Rainout
09/29/66
SIP
06/06/67
3
3
6
3
5
5
4
4
4
4
4
4
4
4
4
4
6
6
Distance
(mi.)
84
84
2.85
3.5
1.5
0.75
2.8
10
10
10
10
46
43.5
29
136
Peak
Y-dose
Rate1
(mR/h)
0.1
0.06
2xl04
17
9.0
2.9
31
252
252
64
64
100
34
14
0.58
Dose
Rate Planch.2 Air3 F/C1*
@ 6h (yCi/m2) (yCi-s/m3) Ratio
(mR/h)
0.08
0.05
2,300
2
1.05
0.34
3
25
25
6.2
6.2
55
30
7
0.68
206
1.5
1.04
18.2
18.2
3.1
3.1
6.43
1.93
0.39
3.13
4.66
24.6
1.63
264
3.5
ND
ND
9.92
52
52
7.9
7.9
3.2
2.0
1.5
323
333
5.6
157
3.4
0.11
1.43
14.6
14.6
6.6
6.6
6.4
4.1
13.7
4.9
3.5
0.33
3.2
Particle5 Peak
Size Forage
(ym) Concen.
(nCi/kg)
0.6
0.6
0.6
0.6
0.6-0.9
0.6-0.9
0.6-0.9
23
2
169 (drop)
0.13
1.3
0.65
26,000
385
5.1
1.6
68.4
452
121
57
20.7
56
19
4.3
405
640
9,800
79.8
Teff in
Forage Days
(days) Fed
8
24
2.4 6
4.0 6
6.2 8
0.5
6.8 8
0.5
8.2 10
10.5 10
7.9 10
6 =
6.5 8
3.6 7.5
0.5
(Continued next page)
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TABLE 2. PHYSICAL DATA FOR RADIOIODINE MODEL Continued
Exposure Route:
Name and Cows
Date of Per
Experiment Group
flay:
MICE
09/21/67
Green Chop:
Pike
03/13/64
Palanquin
04/14/65
Pin Stripe
04/25/66
Hayseed
10/04/65
Alfalfa
06/21/66
Rainout
09/29/66
SIP
06/06/67
MICE
09/21/67
HARE
09/18/68
Milkrun
08/11/65
6
6
3
3
6
4
6
4
4
4
4
6
6
6
3
3
8
Peak Dose
Distance Y~^ose Rate Planch.2 Air3
(mi.) Rate1 @ 6h (yCi/m2) (yCi-s/m3)
(mR/h) (mR/h)
0.66 132
0.66 132
84 0.1 0.08
84 0.06 0.05
2.85 2x10** 2,300 206 264
63 1.6 1.1 21.7
54 0.38 0.28 6.6
3.13 323
3.13 323
4.66 334
4.66 334
24.6 5.6
1.63 157
0.66 132
1.25 87.5
1.43
F/C"
Ratio
0.12
0.12
3.4
3.0
1.9
4.9
4.9
3.5
3.5
0.33
3.2
0.12
1.0
1.0
Particle5 Peak
Size Forage
(yin) Concen.
(nCi/kg)
gas 2 , 110
gas 102
4.7
1.7
45,400
56
18
23 1,900
23 2,700
2 260
2 3,400
169 (drop) 21,000
0.13 1,130
gas 2,630
0.6 1,030
0.6 775
118yCi
T .... in
eff
Forage
(days)
5.9
2.2
5.3
5.3
-
4.9
4.0
3.6
-
2.1
4.5
4.1
4.0
2.4
3.8
Capsule
Days
Fed
10.5
3
4
14
14
4
6
3
9
8
10
8
5
5
1
(Continued next page)
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.TABLE 2. PHYSICAL DATA FOR RADIOIODINE MODEL Continued
oo
Exposure Route:
Name and Cows Peak
Date of Per Distance y~d°se
Experiment Group (mi.) Rate1
(mR/h)
Air Uptake:
Palanquin . 4
04/14/65 8 Xl°
Hayseed .
10/04/65
Alfalfa
06/21/66
SIP
06/06/67
MICE
09/21/67
Dose
Rate Planch.2 Air3
@ 6h (yCi/m2) (yCi-s/m3)
(mR/h)
2,300 206
3.13
4.66
1.63
0.66
264
323
334
157
132
F/C"
Ratio
3.4
4.9
3.5
3.2
0.12
Particle5 Peak T in
Size Forage _ Days
/ % Forage _ *
(ym) Concen. . , . Fed
, ^,. ., . (days)
(nCi/kg)
23
2
0.13
gas
1-y^dose-rate measured 3 feet above ground
2-Deposition on planchets
3-Integrated air concentration
4-Activity on filter divided by activity on charcoal
5-Count median diameter of the aerosol
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TABLE 3. MILK DATA FOR RADIOIODINE MODEL
Exposure Route:
Name and Peak
Date of Milk
Experiment (nCi/liter)
Hay:
Pike
03/13/64
Palanquin
04/14/65
TNT
01/12/65
Cabriolet
01/26/68
Buggy
03/12/68
Schooner
12/08/68
Hayseed
10/04/65
Alfalfa
06/21/66
Rainout
09/29/66
SIP
06/06/67
0.07
0.03
2,260
17.3
0.18
0.16
0.841
3.37
1.06
0.66
0.14
1.20
0.354
0.084
0.063
29.8
47.4
196
3.15
Percent
of Dose
in Milk
-
9.6
12.7
7.4
22.6
2.16
1.19
2.77
1.36
-
3.94
2.88
2.59
6.3
15.2
4.5
-
1st
T
eff
(days)
_
-
6.2
5.0
5.7
2.9
11.9
-
-.
-
-
63
30
38
2.7
8.2
2.5
2nd 3rd
T T -
eff eff I
(days) (days)
_ _
- -
0.94 3.12
- -
1.7
1.2
1.7
0.78
0.61
0.92
0.68
0.75
0.68
0.74
<1 3.0
0.9
0.9 5.6
1.05
Peak Milk
Peak Forage
0.054
0.046
0.087
0.045
0.035
0.098
0.012
0.0074
0.0088
0.011
0.0069
0.021
0.019
0.020
0.074
0.074
0.02
0.04
Time t
- to Peak J<
' (days) E
1
_ B
-
2.5
4.0
2.0
2.0
2.0
5.6
-
8.0
-
9.6
10.0
4.6
1.4
0.8
1.1
-
Average
lilk Remarks
'reduction
[liters/day)
_
-
13.9
16.3
15.5
16.6
20.1
17.8
19.2
15.1
18.7
19.1
16.7
13.7
20
21.3
20.4
21.9
Baled hay
Baled hay
Spread hay
Spread hay
Spread hay
Spread hay
Baled hay
Baled hay
Baled hay,
feeding
Baled hay
Baled hay,
feeding
Baled hay
Baled hay
Baled hay
Spread hay
single
single
Spread hay, bagged
immediately
Spread hay, 131i-
labeled Nal in water
Spread hay
feeding
, single
(Continued next page)
-------
TABLE 3. MILK DATA FOR RADIOIODINE MODEL Continued
Exposure Route:
Name and
Date of
Experiment
Hay:
MICE
09/21/67
Green Chop:
Pike
03/13/64
Palanquin
04/14/65
Pin Stripe
04/25/66
Hayseed
10/04/65
Alfalfa
06/21/66
Rainout
09/29/66
SIP
06/06/67
Peak
Milk
(nCi/liter)
137
17.8
0.42
0.07
2,700
4.8
1.4
38.5
75.8
26.2
237
1,572
68.4
Percent
of Dose
in Milk
11.5
-
-
-
5.6
10.4
4.9
2.0
2.1
14.8
12.5
6.1
7.6
1st 2nd 3rd
m m m
eff eff eff
(days) (days) (days)
4.5 0.75 2.8
1.1
3.8
4.0
*
16.0 1.05 3.3
5.6 1.0
4.0
2.3 <1
3.0 <1 3.0
1.5
2.5 0.9
7.9 0.86 5.1
5.2 1.2 3.2
Peak Milk
Peak Forage
0.065
0.174
0.089
0.041
0.060
0.086
0.078
0.020
0.028
0.10
0.07
0.075
0.061
Time Average
to Peak Milk
( days ) Production
(liters/day)
3.7 19.2
19.2
10.5
5.8
3.0 16.0
2.0 20.1
3.0 16.7
2.0 24.5
2.4 21.0
2.0 28.1
1.2 23.6
1.7 17.8
1.6 22.5
Remarks
Hay baled from con-
taminated pasture.
(Considered same as
green chop)
Inhalation + baled
hay
Jersey cows, 1 feed-
ing/day alfalfa-bar-
ley green chop
Sudan, spread green
chop
Sudan, fresh green
chop
Alfalfa-oats, spread
green chop
Alfalfa-oats , fresh
green chop
Alfalfa, fresh green
chop
Alfalfa, fresh green
chop
(Continued next page)
-------
TABLE 3. MILK DATA FOR RADIOIODINE MODEL - Continued
Exposure Route:
Name and Peak
Date of Milk
Experiment (nCi/liter)
Green Chop:
MICE
09/21/67
HARE
09/18/68
Milkrun
08/11/65
Air Uptake:
Palanquin
04/14/65
Hayseed
10/04/65
Alfalfa
06/21/66
SIP
06/06/67
MICE
09/21/67
151
21.6
50.8
500
1,200
0.58
2.2
1.17
3.6
Percent 1st 2nd 3rd peak Milk
,_..,, ef f ef f ef f Peak Forage
in Milk /,.,,.,,.
( days ) ( days ) ( days )
8.5 7.1 0.74 3.9 0.058
3.6 4.5 0.85 3.7 0.021
7.2 0.74 3.8 0.066
8.6 0.61
1.3
0.8
0.9
1.1
0.8 2.81
Time Average
- to Peak Milk
&
(days) Production
(liters/daj
2.0
2.0
4.0
0.2
2.25
0.4
0.9
1.6
0.7
19.4
25.1
23.4
23.1
17.6
21.0
25.8
20.1
21.9
Remarks
0
Alfalfa, fresh green
chop
Sudan, fresh green
chop
Alfalfa, fresh green
chop
Given single capsule
containing 131I + 126I
Evidence of some in-
gestion
-------
ingestion of iodine-131, are divided into two major categories, post-event and
pre-event, and are estimated to be accurate to a factor of 2 or less. The
equations are:
Post-event predictions
For cows on hay
D^ = 0.042(mH/h) (1)
D^ = 0.014(IAC) (2)
For cows on fresh forage
Dm = 0.37(mR/h) (3)
Pre-event predictions
For cows on fresh forage
D = 1500 (kt) (S)-1-32 (5)
OO
For cows on hay
D = 176(kt) (S)-1'32 (6)
00
where D = infinite dose in rads
00
mR/h = peak gamma exposure rate, or the H+6 hour rate (extrapolated
backward) if the peak occurs later than H+6 hours
IAC = integrated air concentration in curies times seconds per
square meter ( Ci-s/m }
F/C = iodine-131 activity on the filter divided by that on charcoal
kt = fission yield in kilotons vented to the atmosphere
S = distance from surface ground-zero in miles
If the fresh forage is Sudan grass, then the results from equations 3, 4
and 5 may be divided by 3. Equations 5 and 6 apply if no concentrating effect
occurs (rainout, etc.). If a concentrating effect is present, it is suggested
that the results be increased by a factor of 10.
Comparison of the results obtained by use of the above equations with the
results obtained by other authors indicated good agreement among them. However,
the data in this report permit a better prediction by including corrections for
the type and state of the cow forage, and by including equations for pre-event
predictions.
Data on the short-lived radioiodines (the 132, 133, and 135 isotopes) were
collected in several studies. These isotopes, in fresh fallout, increase the
dose to a 2-gram thyroid by 38 percent if cows are ingesting contaminated fresh
forage and by 12 percent if ingesting contaminated hay. The dose delivered by
these radioiodines would be decreased by 90 percent if the milk consumption
were to be delayed for 4 days after the nuclear event. Inhalation of activity
during cloud passage (passage of the airborne effluent) could increase the
dose to an infant by a maximum of 6 percent if the cows were on fresh Treed and
30 percent if the cows were on hay.
12
-------
A test of the equations developed herein, using data collected following
the accidental venting of the Baneberry event*, indicated that a reasonably
accurate prediction of peak iodine-131 concentration in milk was possible.
CHEMICAL AND PHYSICAL FORM
The predominant physical forms of iodine in air are the gaseous and par-
ticulate forms, and their ratio can vary widely. This ratio has some effect
on deposition and will be discussed later in this report. The particulate
forms include iodides and iodates, among others, some of which were bound to
particles at the time of formation and others which were adsorbed on particles
at later times. The gaseous forms include l£, HI and organic iodides. The
relative proportions of the gaseous forms have not been measured under field
conditions. However, only the organic forms vary drastically in deposition
(Bunch 1968) and these are minor constituents of fallout clouds.
It would appear that the chemical form of the iodine might affect its
metabolism. However, the literature contains reports of studies with iodates
in grazing animals and with methyl iodide (CHsI) in man which suggest that
chemical form is unimportant. To investigate this more fully, a study of milk
secretion of iodine-131 in diary cows following ingestion of four different
chemical compounds was conducted (Bretthauer et al., 1962). The results
indicate no difference for iodine secretion in milk following oral administra-
tion of sodium iodide (Nal) , gaseous iodine (12) , methyl iodide (CH^I) or
sodium iodate
It would thus be possible to ignore chemical or physical form in the
studies reported here with the proviso that if organic iodides are ever present
as the predominant chemical form in a fallout situation, then deposition and
the resultant forage-cow-milk transfer will be less than those calculated in
this report.
MILK SECRETION PARAMETERS
The milk secretion of radioiodine, following multiple ingestion of forage
contaminated by a single event, follows a general pattern as shown in the semi
log plot, Figure 1. The concentration of the radionuclide in milk first in-
creases to a peak value, then apparently decreases biphasically, unless the
duration of intake is short; then a component (12) appears more prominently
as shown in the figure.
This T2 component appears when the supply of contaminated feed is short
(10 to 12 days or less) or when uncontaminated feed is substituted for con-
taminated feed as a countermeasure, as was done in the Pin Stripe event (Barth
et al., 1969).
* Baneberry was an underground nuclear test of less than 20 kilotons yield
conducted at the Nevada Test Site on December 18, 1970.
13
-------
o
H
-P
rt
M
4J
0)
O
§
O
H
g
EP
3'
Time (days)
Figure 1. General pattern of iodine-131
secretion in milk following
ingestion
The values for the various por-
tions of the curve in Figure 1 plus
other measured parameters are shown in
Table 4. These data suggest little
difference between spread hay or fresh
pasture as contaminated forage relative
to the transfer of radioiodine to cow1s
milk. The principal difference is in
the amount of activity that accumulates
on the two types of forage. When ex-
posed to the same radioactive cloud,
the concentration in growing pasture
(microcuries per kilogram fresh weight)
is five to six times the concentration
attained in spread hay.
TABLE 4. MEASURED PARAMETERS FOR RADIOIODINE TRANSFER TO MILK
(Mean ± Standard Error)
Parameter
Time of peak (days)t
TX (effective Tjg in daysV
TZ (effective Tig in days)"""
Ta (effective Ti^ in days) '
Teff on forage (days)
Peak cone, in milk v
peak cone, in forage
Secretion in milk (%)
Cows Fed
Green Chop
(9)*
2.2 ± 0.2
4.7 ± 0.5
0.97 ± 0.07
3.7 ± 0.3
4.2
0.068
8.9 ± 1.3
Cows Fed
Spread Hay
(8)
2.2 ± 0.4
4.2 ± 0.7
1.0 ± 0.1
3.6 ± 0.7
6.5
0.069
8.5 ± 1.5
Cows Fed
Baled Hay
(7)
4.2 ± 1.0
36 ± lot
0.8 ± 0.08
6.6§
0.024
2.4 ± 0.4
Air Uptake
Exposure
14)
0.6 ± 0.2
0.9 ± 0.1
* The number of experiments averaged. Each experiment was an average for three
to six cows.
t These parameters are labeled in Figure 1.
T This value is an artifact caused by uneven distribution of activity in the
hay as fed to the cows. The Teff cannot be longer than the 8.05-day half-life
of iodine-131.
§ The total hay for the three Schooner groups was chopped and stored in an
enclosure. The data were not used for this Teff.
The data for the groups of cows fed baled hay (Table 4) are based on ex-
periments conducted during three cratering events (Cabriolet, Buggy and Schooner)
They show a striking difference from the other feeding regimens in that the
percent of iodine-131 secreted in milk is 2 to 2.8 percent for cows fed baled
hay as compared to 7 to 10 percent for the other cases. This is probably due
14
-------
to the chemical or physical state of the debris released by these Plowshare*
events which apparently caused the radioiodines to be less biologically
available.
Air uptake represents a relatively minor mode of exposure for dairy cows.
In four experiments where air uptake and ingestion were compared, the peak
radioiodine concentration in milk following multiple ingestion (using maximum
values) was 22 to 110 times the peak concentration following air uptake.
Further, the continued ingestion of contaminated forage, following a single
deposition of radioactivity, would accentuate this difference in exposure.
Some calculations using the air uptake data are shown in Table 5f These
calculations assume approximately 100 liters per minute as the respiratory rate
for the cow (Altman and Dittmer 1964) and they assume that this minute volume
times the integrated air concentration (IAC) gives the cow exposure. The rela-
tively high percent of the calculated exposure which is secreted in the milk
suggests that inhalation was not the sole method of intake in these experiments.
TABLE 5. INHALATION EXPOSURE CALCULATIONS
Value
No.
1
2
3
4
5
6
7
8
Calculated Value
Integrated Air Concen-
tration (yCi-s/m3)
Minute volume (m3/s)
[1x2] Total exposure (nCi)
Peak milk cone. (nCi/liter)
[4-5-3] % in milk at peak
Total in milk (nCi)
[6-5-3] Total as % exposure
Particle size (pm)
Hayseed
323
0.0017
550
0.58
0.11
13.4
2.4
23
Alfalfa
334
0.0017
570
2.2
0.39
190
33
2
Sip
157
0.0017
270
1.17
0.43
54
20
0.13
Mice
132
0.0017
220
3.6
1.64
177
80
Gas
The data from Tables 2 and 3 can be used to develop predictive models for
nuclear tests or accidents but, for maximum utility, such a prediction also re-
quires an estimate of the amount or percentage of radioactive materials which
may be released to the atmosphere. Ignoring this for the moment, a post-event
estimate of the peak radioiodine concentration in milk can be made rather quick-
ly with certain monitoring techniques, as described below. Once the estimate
of peak concentration is made, the parameters from Table 4 can be used to es-
timate the time-course of radioiodine concentration in milk. With these data,
* Plowshare is the U.S. Energy Research and Development Administration program
for developing peaceful uses of nuclear explosives.
15
-------
and assuming an average milk consumption and thyroid uptake, an estimate of
human thyroid dose can be made as shown later in this report.
The earliest measurement that can be taken of a contaminated area is the
1-meter gamma exposure rate in milliroentgens per hour (mR/h), usually made
with Geiger-Mueller beta-gamma survey meters. Next in time is the integrated
air exposure measured by air sampling equipment. Obtainable concurrently, but
subject to large sampling error, is the concentration of radioiodine in
vegetation.
SURVEY-METER PREDICTION
This prediction of estimated radioiodine levels in milk can be made quick-
ly, using survey-meter measurements, but it is fraught with errors. The rela-
tionship of iodine-131 deposited to the total gamma activity deposited changes
with time because of the mixture of decay rates present in the radioactive
material deposited. This mixture varies with fractionation in the cloud and
with the fusion to fission ratio of the nuclear explosive device. The deposi-
tion in a given area can be highly variable because of micrometeorology, the
presence of structures, and the terrain. Furthermore, the survey-meter meas-
urement must be made in the immediate area of interest, as the measurement can
change drastically with distance.
From the data in Tables 2 and 3, log-log plots were made of the 1-meter
gamma exposure rate versus peak milk activity. The exposure rate (mR/h) values
used in the graphs included peak measured values, estimated peak values, H+24*
extrapolated or measured values, and H+6 extrapolated or peak values. The best
relationship was obtained when the peak exposure rate (or mR/h at H+6 if the
peak occured later) was plotted against peak milk concentration, as shown in
Figures 2 and 3. The H+6 value was determined by extrapolating back from meas-
ured values using observed decay data, where possible, or by use of the t~ *
function. The peak exposure rate at a location usually occurs during cloud
passage so some "shinet" is measured, but this becomes less important with dis-
tance . .Also shown in these figures are data from the Off-Site Surveillance
Program'. The data for cows-fed green chop compare favorably witlrours (Fig-
ure 2); however, the off-site data-for cows fed hay differ greatly, the peak
milk concentration-being about 100 times that derived from our data. The
dashed lines on each side of the best-fit line are a factor of 2 deviation
from that line.
* H+24: notation meaning 24 hours after detonation; H+6 denotes 6 hours after
detonation; D+2 denotes 2 days after detonation; etc.
1" "Shine" is radiation measured from radioactivity at a distance rather than
from radioactivity close to the measuring instrument or that in which the in-
strument is immersed. Shine would not be a measure of inhalation exposure
or deposition.
t A program conducted by the EPA's Environmental Monitoring and Support Labora-
tory-Las Vegas for the U.S. Energy Research and Development Administration. It
monitors radioactive contamination off the Nevada Test Site as described in peri-
odic reports available through the National Technical Information Service.
16
-------
10'
10''
a
10-'
10-'
OUR DATA
O OFF-SITE DATA
/
/&/
/*//
,y/
-'/''
<'%
/ NOTE: ARROWS INDICATE ESTIMATED PEAK IN MILK
X IF GREEN CHOP HAD BEEN FED ON DAY OF VENTING.
ID''
10'1 10° 101 10*
DOSE RATE AT PEAK OR H+6 (mR/h)
10'
Figure 2. Peak iodine-131 concentration in milk from cows on fresh feed
versus open-field gamma exposure rate
10'
10"
o
ffi
10"'
OUR DATA
O OFF-SITE DATA
/
-10T2
103
10" 10° 10' 102
DOSE RATE AT PEAK OR H+6 (mR/h)
Figure 3. -Peak iodine-131 concentration in milk from cows on hay versus
open-field gamma exposure rate
17
-------
From these figures, the equations for estimating the peak milk concentra-
tions from 1-meter gamma exposure rate measurements are:
for cows on fresh feed
nci/liter = 4.0 (mR/h) (7)
for cows on hay
using off-site data nCi/liter = 1.4(mR/h) (8)
using our data nCi/liter = 0.014 (mR/h) (9)
For cows on fresh feed or hay, then, this very convenient method for es-
timating the contamination can be used with equation (7) or (9) to predict the
peak iodine-131 concentration in milk within a factor of 2.
The great difference between the two sets of data for hay-fed cows is
difficult to explain completely, but there are several factors which may con-
tribute to it. The majority of the data are based on survey-meter readings
of less than 0.1 mR/h where the accuracy is very poor, and most of the read-
ings were taken near roads where the vegetation may have been less dense than
on the farms. Furthermore, most readings were taken in the area of, rather
than at, the locations where milk was collected.
Also, our data were obtained from the cratering tests (Cabriolet, Buggy,
and Schooner). The activation products in the fallout from Schooner would in-
crease the exposure rate (mR/h) without a concomitant increase in radioiodine.
For the other two tests, the experimental stations were so close to the crater
(3.2 to 16 kilometers) that larger particles, which would not stick to the hay,
would contribute to the exposure rate but not to the radioiodine in milk.
Because the data for green chop are relatively good, it is possible to
derive an appropriate equation for cows fed hay. As mentioned in the discus-
sion of milk secretion parameters, the peak concentration in growing pasture
is 5 to 6 times the peak attained in spread hay exposed to the same cloud.
Also, the milk-to-forage ratios differ by a factor of 2.9 (0.07 for green chop
and 0.024 for hay). Thus, the peak concentration in milk from cows on fresh
feed should be about 14 times the peak value for cows on hay. Therefore, a
reasonable estimate of the peak milk concentration for cows on hay can be ob-
tained by dividing equation (7) by 14.
nCi/liter = ~-(mB/h)
= 0.29 (mR/h) (10)
This factor of 14 can be partially substantiated with data from the
Palaquin report (Southwestern Radiological Health Laboratory 1970). Of the
dairies located in the areas of maximum deposition/ there were three using
pasture and three using hay, all located about 208 kilometers downwind. The
average peak milk concentration was about 8 times higher for cows on pasture.
At 480 to 510 kilometers (300 to 325 miles) downwind, the average peak milk
concentration at 5 locations using pasture was about 10 times that from cows
at 12 locations using hay. ^*
18
-------
AIR SAMPLER PREDICTION
After cloud passage, if an air sampler has been operating in the area,
the peak iodine-131 concentration in milk in that vicinity can be estimated by
use of the integrated air concentration (IAC). This is obtained by adding the
iodine-131 activity on the prefilter to that collected on charcoal and dividing
the sum by the sampling rate in cubic meters per second (m3/sec) . The IAC has
the dimensions of curie-seconds per .cubic meter (Ci-sec/m3).
The estimate of peak milk concentration again depends on the proximity of
the air sampler to the dairy farm, the ratio of gaseous to particulate iodine,
and other factors. Since iodine can be determined by gamma spectrometry, the
data should be better for our purposes than the data obtained by use of gamma
survey meters. The data on IAC versus peak iodine concentration in milk for
cows on fresh feed are plotted on log-log coordinates in Figure 4. The best-fit
line and factor-of-2 deviation lines are also shown in the figure. The equation
1.25
for the line is nCi/liter = 0.17(IAC)
increase in milk concentration with IAC.
suggesting a greater than linear
103'
10'
o
d 10'
2
ID
Q.
10°'
10T1
OUR DATA
O OFF-SITE DATA
10"
10° 10' 102 103
INTEGRATED AIR CONCENTRATION (pCi-s/m3)
10'
Figure 4. Peak iodine-131 concentration in milk from cows on fresh feed versus
integrated concentration of iodine-131 in air
19
-------
To explain this, it had been noted in earlier experiments that the gas-
eous to particulate iodine ratio in the contaminating cloud had some effect on
the forage-cow-milk transfer (Earth et al. 1969). This may be due to the vari-
ation in deposition velocity (Vg) between the two species, since Vg for gaseous
iodine is much less than 1 centimeter per second, while for particulate iodine
it is 1 or larger, occasionally reaching tens or hundreds.
Consequently, for those cases where the data were available, the iodine-131
activity on the prefilter was divided by that on the charcoal cartridge of the
air sampler to obtain a filter-to-charcoal ratio (F/C). The F/C is assumed to
correlate with the particulate-to-gaseous iodine makeup of the cloud and is
therefore used to adjust the IAC data. The revised data are plotted in Figure 5.
The best-fit line is now a linear fit to the data (exponent of IAC is 1).
103'
10*'
I
o
=! 10'-
10°'
10-'
OUR DATA
O OFF-SITE DATA
10-'
I I I
10° 10' 10* 10'
IAC/(FILTER TO CHARCOAL RATIO)-pCi-S/m3
104
Figure 5. Peak iodine-131 concentration in milk from cows on fresh feed (IAC
corrected by the filter-to-charcoal ratio)
This revised plot appears logical, as one would expect the peak concen-
tration of iodine-131 in milk to vary directly with the integrated air concen-
tration of iodine-131. Two of the points in Figure 5, representing the group
average data from a gaseous iodine experiment (MICE, Tables 1 through D suggest
that the F/C correction does not apply for a gaseous aerosol. One could also
20
-------
postulate a failure of this correction at the other extreme, i.e., iodine on
particles too large to be picked up by the air sampler but which would easily
be ingested by the cow.
Using air sampler data, then, an estimate of peak milk concentration for
cows on fresh forage can be made by use of:
peak nCi/liter =
(11)
Similar data for cows on hay are shown in Figure 6. In this circumstance
the correction for the filter-to-charcoal ratio (F/C) did not improve the fit,
perhaps because hay is more like an inert collector than is fresh forage. The
equation for the line is:
peak nCi/liter = 0.1(lAc)
(12)
The coefficient, compared to Equation 10, indicates the peak concentra-
tion in milk from feeding hay is one-eighth of that from feeding fresh forage
rather than the one-fourteenth calculated for the survey meter prediction
(page 18). The difference is probably due to the inaccuracies in the hay data
and to the use of the F/C correction factor.
OUR DATA
O OFF-SITE DATA
10
10-' 10° 10' 102
INTEGRATED AIR CONCENTRATION (pCi-s/m3)
103
Figure 6. Peak iodine-131 concentration in milk from hay-fed cows versus inte-
grated concentration of iodine-131 in air
21
-------
FORAGE PREDICTION
Another relatively quick method of estimating the peak milk concentration
is by a measurement of iodine-131 concentration in forage. This measurement,
together with the milk-to-forage ratios from Table 4, yield the following
estimates:
for fresh forage or spread hay
peak nCi/liter = 0.07(nCi/kg) (13)
for baled hay
peak nCi/liter = 0.024(nCiAg) (14)
The equations for predicting the peak milk concentrations for cows on
fresh feed apply if the .pasture consists of alfalfa, oats, or barley, or a
mixture of these. If the fresh feed is Sudan grass, however, the peak will be
about one-third the value obtained with the equations. Supporting evidence
for the latter was published in 1972 (Moss et al. 1972).
The principal difficulty with forage concentration measurements is in ob-
taining a. representative sample. Baled hay presents an especially difficult
problem. The majority of the data in Figure 6 are based on use of upper outside
bales of hay from stacks and thus yields a maximum estimate for this type of
feeding. Hay spread on the ground or in open troughs would have a higher con-
tamination, while bales in the interior of a stack would be less contaminated.
PRE-EVENT PREDICTION
This type of prediction was left until last because of the many uncertain-
ties connected with a given event. These include the ratio of fission yield to
total yield, the released fraction of fission activity, the degree of fractiona-
tion, and unpredictable concentrating factors such as rainout or washout.
Starting with the Palanquin event, the maximum observed iodine-131 con-
centrations in milk were tabulated with the distance from surface ground zero
(SGZ) for each event. Assuming these maximum values were on or near the path
of maximum fallout, it should be possible to correlate peak milk concentration
with distance. All the milk values were normalized by dividing them by the
announced total yield of the event. The log-log plot of the results is shown
in Figure 7. The line fit to the five values from Palanquin can be described
by Equation 14.
uci/liter-kt = 2.3(S)~1'32 (15)
where S = miles (1 mile = 1.609 kilometers) from surface ground zero
A parallel line, shown as a dashed line, appears to fit some of the data from
other field events.
*»
The wide scatter of the points can be reduced by use of two obvious
22
-------
103'
o
Q
LLJ
>- 10°
I
3
2
z
ffi
10'2-
10'3
= NOT ON HOT LINE
Ql=SNOW OUT EFFECT
B=BUGGY
C=CABRIOLET
Pl= PALANQUIN
S=SCHOONER
10°
10' 10* 103
DISTANCE FROM SGZ (mi.)
104
Figure 7. Peak iodine-131 concentration in milk versus
distance from surface ground zero (normalized
for yield)
corrections. The first correction is to standardize the type of feed through
use of the factor of 14, calculated previously, to correct hay data to fresh
forage data. The second correction is for the fraction of the activity actually
released. This is most easily done by using estimates of the cloud burden of
iodine-131 in curies and converting to kilotons of fission by use of the factor
1.25 x 10 curies per kiloton (iodine-131 from uranium-235 fission). For the
Schooner event, the peak milk concentration in nanocuries per liter (nCi/liter)
corrected for fresh feed is 1.20 x 14, which equals 16.8, and the cloud burden
assuming the iodine-131-to-tungsten-181 ratio is 0.16 and using the upper
estimate of total tungsten-181 in the cloud as reported by Anspaugh et al. (1969)
is calculated to have been 0.133 kilotons. Thus, the normalized value, in
nCi/liter-kt, becomes 16.8 -r 0.133, which equals 126.
23
-------
For lack of cloud burden data for the other cratering tests, assume the
same fractional release applies. Thus, the two "hot-line" stations for Schooner,
at 74 and 402 kilometers (46 and 250 miles) from surface ground zero, can be
used to locate the line for which the slope was set by the Palanquin data which
were only assumed to be on the "hot-line." For the underground ventings (Pike
and Pin Stripe) the published data on the total activity which escaped (Allen
1971) can be related to kilotons of fission, although probably only the volatile
fraction escaped, leading to normalized data which are too high. The raw and
corrected data are shown in Table 6.
With these corrections, the adjusted prediction equation becomes:
(-132)
UGi/liter-kt = 17(S)S (16)
This equation applies to cows eating green chop or pasture on farms in the path
of maximum deposition from a fallout cloud.
The radioiodine concentration in milk would be increased by rainout or
washout. For example, the snow-out effect in the Cabriolet data increased the
concentration in milk by a factor of 4 (data from Mountain View Farm in Table
6). Studies of iodine-131 fallout in South Africa from French tests (VanAs and
Vleggaar 1971) indicate that wet deposition increased the iodine-131 concentra-
tion in milk by a factor of 2. A summary of other published data suggests
wet/dry deposition ratios ranging from 1.8 to about 10 (Black and McNelis, to
be published). It would thus appear that increasing the radioiodine concentra-
tion, as calculated by the foregoing equations, by a factor of 10 would be a
reasonably conservative action for estimating the effect of precipitation on
deposition of radioiodine from a tropospheric cloud during the first few days.
DOSE ESTIMATES
The predictive data just described can be used to derive dose estimates
for the iodine-131 in thyroid glands which results from drinking contaminated
milk. The equation from the International Commission on Radiation Protection
Report Number 2 is used to calculate the infinite dose from a given quantity
of iodine-131 in the thyroid. This equation for infinite dose, inrads, is:
DOO = 74(qf2) (ZEF(RBE)jTeff rads (17)
where qf2 = fraction of body burden in the thyroid
ZEF(KBE)n = energy absorbed per disintegration, in MeV
Teff = effective half-life of the isotope in the organ of
interest, in days
A good summary of thyroid parameters is given in a paper by Wellman et
al. (1969). If we assume the effective half-life in the thyroid to be 7.1 days,
the energy loss per disintegration as 0.21 mega-electron-volts (MeV), and an
24
-------
TABLE 6. MAXIMUM IODINE-131 IN MILK BY EVENT AND DISTANCE
to
tn
Event Name . , ,
(feed type)
(kt)
Palanquin 4.3
(fresh)
.
Cabriolet 2.3
(hay)
Buggy 5 . 4
(hay)
Schooner 35
(hay)
Pin Stripe low
(fresh)
Pike low
(fresh)
Farm Name
EPA
EPA
Martin
Boggio
Pasquale
EPA
River Ranch
Mt. View
EPA
Pohlsander
EPA
Lund
Boyd Schena
Schofield
Habbart
Distance
From SGZ
(km) (mi)
4.5
4.5
217
472
483
4.5
435
441
16
467
74
219
402
101
135
2.8
2.8
135
293
300
2.8
270
274
10
290
46
136
250
63
84
Peak 131I in Milk _. . Peak 131I
Cloud
(nCi/liter)
2700
2300
11
4.1
5.5
0.84
0.16
0.63
3.37
0.55
1.20
0.063
0.10
4.8
0.82
(nCi/liter-kt)
625
535
2.56
0.95
1.27
0.365
0.070
0.274
0.624
0.102
0.0342
0.0018
0.00285
(Corrected* Corrected*
nCi/liter-kt) (kt) (nCi/liter-kt)
625
535
2.56
0.95
1.27
5.10
0.97
3.83
8.74
1.43
0.555 0.133 126
0.028 6.6
0.045 10.5
0.0172 280
0.0064 124
* Corrected for type of feed
t Curies of 131I divided by 1.25 x io5
t Corrected for cloud burden and type of feed
SGZ = Surface Ground Zero
-------
infant thyroid mass of 2 grams, then the equation becomes:
ft- = 74pf9 (0.21) (7.1)
= 55.2 rad/yCi (18)
The dose commitment to the infant thyroid can be calculated by using
Equation 17 with the data in Table 4. The assumptions used to estimate the
dose are:
1. Child drinks 0.7 liter per day, 0.35 liter from each milking;
2. First milking occurs 0.2 days (4.8 hours) after initial
ingestion by the cow;
3. Negligible decay between milking and consumption;
4. Buildup between initial ingestion and peak concentration has
an effective half-life of 1 day;
5. Fraction of ingested iodine in the thyroid is 0.3;
6. A peak activity in the milk of 1 microcurie per liter; and
7. Peak activity in milk occurs 2.2 days after initial ingestion
and effective half-life is 4.7 days during continued ingestion,
with cows on fresh feed.
The infinite dose for 47 days (10 half-lives) under the above assumptions
is 91 rads. This dose changes directly with any change in thyroid uptake,
effective half-life, peak concentration, or milk consumption.
From the calculated dose, the following data can be derived: buildup
phase gives 11.9 percent of the dose, and total intake is 7.66 times the peak
intake.
For cows on baled hay, the assumptions are the same except for the seventh
which becomes:
7a. Peak activity occurs 4.2 days after initial ingestion and
decreases thereafter with an effective half-life of 6.5 days
during continued ingestion (assuming the effective half-life
in milk equals that in hay).
Under these conditions, the infinite dose for 65 days of ingestion is
144 rads. Because of the longer time to the peak and the longer effective
half-life, 23 percent of the total dose is acquired during the buildup phase,
and the total intake is 12.4 times the peak intake. Thus, for equal peak milk
concentrations, the thyroid dose is 1.6 times greater if the cows are fed con-
taminated hay rather than contaminated green chop. For a given contaminating
event, though, the peak activity in milk from cows on green chop would be about
14 times that from cows on hay, and the infant thyroid dose would be about 9
times larger.
The infinite dose for continued ingestion of contaminated milk can be
combined with the equations previously derived to yield predictive dostf equa-
tions for the child with a 2-gram thyroid as follows. In these equations,
26
-------
mR/h refers to the net survey-meter reading in milliroentgens per hour 1 meter
above ground, IAC and F/C are derived from air sampler data, and kt is the
predicted cloud burden of fission products in kilotons.
1. For cows on fresh feed:
D^ = 91(10-3)(4)(mR/h)
= 0.37(mR/h) rads (19)
H. = 91(10-3)0.8(|A§)
= 0.072(1^) rads (20)
Deo = 91(17)(s)-1-32
= 1500(s)~1>32 rad/kt (21)
2. For cows on hay:
D^ = 144(10~3)(0.29)(mR/h)
= 0.042(mR/h) rads (22)
Da, = 144 (10~3) (0.1) (IAC)
= 0.014(IAC) rads (23)
D^ = 144(1.22) (s)~K32
= 176 (s)"1'32 radAt (24)
where rad/kt = rads per kiloton fission in the cloud
s = distance along the hot-line, in miles
The equations based on mR/h and IAC can be used at any location as long
as the type of cow feed is known and the mR/h value used is the peak value or
the value extrapolated back to H+6, whichever is greater. The two equations
based on distance and fission yield, Equations 21 and 24, are more restrictive.
They predict doses on the "hot-line" only and only for dry deposition with no
meteorological concentrating factors. Also, for any of the equations, cows
being fed fresh Sudan grass will transfer less iodine to milk, so the results
obtained by use of the equations may be divided by 3.
INHALATION DOSE
With these equations developed, the relative magnitude of inhalation ex-
posure can be readily ascertained. Assume an effluent cloud passes over a dairy
27
-------
farm where an infant resides, and assume an air sampler measures an integrated
air concentration of 1.0 microcuriei-second per cubic meter with activity
in the filter equal to the activity on the charcoal. Also, assume that the
infant is breathing at the rate of 15 liters per minute, or 2.5 x io-lf cubic
meters per second (m3/s), and that deposition in the lung is 100 percent with
100 percent absorption.
The inhalation dose, in millirads (mrads), then becomes:
(1.0 yci-s/m3)(2.5 x 10"* m3/s)(0.3 uptake) = 75 pCi in thyroid
(75 pCi)(55.2 rad/yCi) = 4.1 mrads
The ingestion dose calculated from Equation 19 would be:
°-072(f7§) = 0.072(1)
= 72 mrads
Therefore, under maximized conditions, inhalation adds about 6 percent
of the dose caused by ingestion for cows on fresh feed and about 30 percent of
the dose caused by ingestion for cows on hay. If deposition in lung and absorp-
tion is assumed to be less than 100 percent, then these calculated additional
doses would be even smaller percentages of the ingestion dose.
COMPARISON WITH OTHER STUDIES
A review of the literature indicates that many studies have been conducted
on this subject, although very few have used data from actual field situations.
Some of the published data are shown in Table 7. In general, there is no wide
divergence in most of the parameters tabulated, although some of them differ
significantly from the results reported here.
The effective half-lives for pasture, green chop, and milk reported in
this paper require some comment. The pasture values were obtained by use of
hand-cut samples from undisturbed pastures. Since pastures in the region are
irrigated regularly and require scheduled applications of fertilizer, it is
possible that growth may be more rapid, leading to dilution of the activity and
a shorter effective half-life. On the other hand, green chop for cow feeding
is generally cut only once a day, so loss of activity by growth of plants and
physical dislodgement for that single day is minimized. This would result in
a slightly longer effective half-life for the green chop and is reflected in
the effective half-life for milk of 4.7 days. The 4.2-day effective half-life
for pasture might have been observed in the milk had the cows been allowed to
graze.
A comparison of some of the published dose-prediction equations with
those developed in this report is shown in Table 8. There is general agreement
of most items, which is somewhat surprising considering the variability of the
28
-------
TABLE 7. COMPARISON OF VALUES REPORTED IN THE LITERATURE
to
Reference
Tamplin 1965
Sasser and Hawley 1966
Booker 1958
Thompson 1965
James 1964
Knapp 1963
Comar et al. 1967
Lengemann and Comar 1964
Garner et al. 1960
Hawley et al. 1964
Marter 1963
Hull 1963
Pendleton et al. 1963
Ekman et al. 1967
Stigall and Leary 1966
Burton et al. 1966
Soldat 1965
This report
Time to
Peak
(days)
2-5
2-3
1.5-2
4.25
4
3
2-3
1-3
2
9
2-5
5
2
3
2.2
Teff
Pasture
(days)
5.5±0.7
4.9
5±1
5
4.9
5
3.5
5
4
4.2
Teff
Milk
(days)
4-6
4.7
1.9
5
5
4-5
5.8
6
5
4.7
. Ratio of
.," Peak Milk to
Milk _ , _
Peak Forage
12.8 0.06-0.76
0.09
3.0 0.009
4-24
5.7-10.8
4.7 0.112
0.36-0.042
0.07
0.302
0.18
0.07
8.9 0.07
Remarks
Review of previous 1 iterature
Gaseous iodine release
Windscale release
Review of previous literature
Calculation vs . measured milk
mR/h vs. peak milk activity
Oral doses
Multiple oral doses
Multiple oral doses
Gaseous iodine release
Savannah release
Brookhaven data
Utah studies
Sprayed on pasture
Prediction equations
Summary data
Gaseous from separation plant
-------
TABLE 8. COMPARISON OF PREDICTIONS FOR INFINITE DOSE TO A 2-GRAM THYROID
w
o
Dose Dose from Dose from Total Dose Dose x 3 l 1 in
Reference from 1 yCi/liter 1 yCi/m2 Divided by Prior Milk or Remarks
1-m y* Peak Milk on Forage Dose from to Peak Forage
(rad) (rad) (rad) Peak Milk (%)
James 1964 15.6R0 179
Knapp 1963 (4. 4-16. 4) R0 128
Comar et al. 11
1967
Marter 1963 240
Pendleton et 224 13
al. 1963
Stigall and 436 15
Leary 1968
Burton et al. 340 48
1966
Tamplin and 3Ro
87.5Ro nCi per liter
(26-96) RQ nCi per liter
33
Used 45% uptake
l.SRo yci per m2
O.IRo UCi per m2
Fisher 1966
Burton 1966
Stocum 1968
Soldat 1963
Federal Radiation
Council #5, 1964
This report:
Fresh feed 0.37Rp
Hay 0.042Rp
58
156
143
91
144
85
11 8
7
7 8
25
Used 22% uptake, 0.62
liters per day
4.1 Used 50% uptake, 1
liter per day
20-25
12 4Rp nCi per liter
23 0.29Rp nCi per liter
* Gamma exposure rate measured 1 meter above ground; RQ = mR/h at 24 h;
= peak mR/h
-------
data which form the basis of the equations. The differences, for the most part,
are due to the assumptions for effective half-life in milk, milk consumption,
and thyroid parameters used in making the thyroid dose calculations. The
assumptions used in this paper are based on more recent data.
A comparison of the dose estimates, using the equations developed here,
with those of Knapp (1963) and Tamplin (1966) for specific fallout situations
is shown in Table 9. From this comparison, it appears that Knapp's dose es-
timates are too conservative. The estimates derived in our paper are almost
identical to those of Tamplin. Marked differences in data are due to differ-
ences in cow forage. Tamplin's data apply to dairy cows on fresh forage, but
it is reasonable to assume the forage was hay in St. George, Utah, during March
when the Annie and Telsa detonations took place.
OTHER RADIOIODINES
The data and equations used in the preceding portions of this paper apply
to iodine-131. This is because iodine-131 was the easiest radioiodine to work
with both for nuclear test effluent and controlled contamination experiments.
However, the effluent from nuclear tests does contain other radioiodines, and
in some cases useful data can be derived from the gamma spectrometric analyses.
The data available are from the three cratering tests (Cabriolet, Buggy,
and Schooner) and from the accidental venting of Pin Stripe. These data and
some of the parameters used for dose calculation are shown in Table 10. The
cumulative dose to the infant thyroid from all radioiodine isotopes is shown
in Figure 8. The dose is increased by 38 percent if the cows are fed contami-
nated green chop and by 12 percent if the cows are fed contaminated hay. In
both cases, about 90 percent of this additional dose occurs in the first 4 days
after a nuclear test.
BANEBERRY DATA
After this paper was drafted, the Baneberry underground nuclear test
accidently vented. According to the published report* on this accident (Western
Environmental Research Laboratory 1972), the McCurdy Ranch near Springdale,
Nevada, had the highest reported iodine-131 concentration in milk. It is in-
formative to apply the equations developed in our paper to the situation at the
McCurdy Ranch.
The cows on this ranch were grazing a pasture at the farm. There were no
survey-meter readings taken during or shortly after the deposition of radio-
nuclide contamination. Furthermore, there were no air samplers operating there.
The available data were integrated air concentration data from Scotty's Junction
(about 23 miles northwest of the ranch) and Beatty (less than 10 miles south of
the ranch), Nevada. The sums of the air sampler data plus an estimate of missing
31
-------
TABLE 9. COMPARISON OF THYROID DOSE ESTIMATES IN RADS TO A 2-GRAM THYROID
u>
to
Location and Exposure Rate
Event Name , _- . ._..
(mR/h at H+24)
Alamo, NV
Small Boy 0.09
Caliente, NV
Small Boy 0.08
St. George, UT
Annie 13
Harry 26
Tesla 1 . 8
Zucchini 1 . 2
Peak or H+6 Knapp Tamplin ,^r^ f Estimate From
Exposure Rate Estimate Estimate ^?& f This Report
(mR/h) (rad) (rad) (rad)
0.61 0.4-1.5 0.27 Fresh 0.22
0.43 0.35-1.3 0.24 Fresh 0.16
69 57-213 39 Hay 2.9
4.1
138 115-427 78 Fresh 50
71*
9.5 7.9-30 5.4 Hay 0.4
1.8
6.4 5.3-9.6 3.6 Fresh 2.3
62t
Equation
Used
19
19
22
24
19
21
22
24
19
21
* Perez and Robinson (1967) in estimating iodine-131 thyroid doses from milk samples collected at St.
George, Utah, in 1953, obtain an estimate of 68 rad to the "standard" child thyroid.
t The high estimate obtained by using Equation 21, compared with that obtained from Equation 19 , suggests
that St. George was not on the "hot line" for this event.
-------
10'
10'
at
T3
CO
102
O
10''
10°'
10-'
I COWS FED GREEN CHOP
(COWS FED HAY
*«-
-162 rads
-123 rads
10°
i i
10' 102
TIME (days)
103
10'
Figure 8. Cumulative dose to a 2-gram thyroid from radioiodine in milk
(131I peak = 1 yci/liter with l32' 133' 135I in proportion; first
milking 0.2 d after deposition; 0.7 liters/d consumed; no delay
between milking and consumption)
TABLE 10. DATA ON THYROID DOSE CALCULATIONS FOR SHORT-LIVED RADIOIODINES
Isotope
Cows fed
132I
133-j-
135,-
Cows fed
132I
13 3I
135-
Time to Ratio to
Peak in 131I in
Milk Peak Milk
(days)
hay:
2
1
ND
green chop:
2
1
1st milking
3.1
2.1
ND
3.0
3.3
2.7
Teff in
Milk
(days)
2.25
1.0
ND
2.0
1.0
0.3
Teff in
Thyroid
(days)
0.1
0.84
0.28
0.1
0.84
0.28
Absorbed
Energy
(MeV)
0.59
0.49
0.48
0.59
0.49
0.48
Thyroid
Dose
(rads/yCi)
2.18
15.3
5.0
2.18
15.3
5.0
Total*
Dose
(rads)
3.7
11.7
2.0
5.5
20.8
2.1
* total dose to a child's 2-gram thyroid; 0.7 liters of milk ingested per day;
cows fed contaminated pasture continuously following a single contaminating
event
ND = no data available
33
-------
data, based on ratios, for the period of December 15 to 21, 1971 yield an IAC
value of 0.61 microcuries per second per cubic meter for Beatty and 2.03 for
Scotty's Junction. The filter-to-charcoal ratios were about 1 for both cases.
Because McCurdy's Ranch is about one-fourth the distance between the two, we
assume the IAC equals 1 microcurie per second per cubic meter. Because the
cows were grazing, we use Equation 10. Thus, we would predict:
peak nCi/liter = O.
= 0.8
Thus we calculated a peak concentration in milk of 800 picocuries per liter
which compares well with the 810 picocuries per liter measured.
The vegetation sampled at this ranch (rabbit bush and greasewood) had a
peak concentration of 2.9 nanocuries per kilogram which, using Equation 12 and
assuming the cow forage had the same concentration, would predict a peak con-
centration of 0.07(2.9) or 0.2 nanocuries per liter, a much lower value than
the 0.8 calculated above. This confirms the unreliability of most forage
sampling procedures.
34
-------
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-------
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38
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TECHNICAL REPORT DATA
/Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/4-76-027
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
RADIOIODINE PREDICTION MODEL FOR NUCLEAR TESTS
5. REPORT DATE
June 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Stuart C. Black and Delbert S. Earth
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
10. PROGRAM ELEMENT NO.
1AD606
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA-ORD Office of Monitoring
and Technical Support
15.SUPPLEMENTARY NOTES studies performed for the U.S. Energy Research and Development
Administration under Memorandum of Understanding AT(26-1)-539 were the basis for the
nodel described in this report.
16. ABSTRACT
Results of 14 experiments on the air-forage-cow-milk transfer of iodine-131
are summarized and used to develop prediction models for dose to the thyroids of
infants. The models are based on data from various types of nuclear tests together
with data from controlled experiments using contaminating aerosols. This provides
a realistic foundation for the predictions and for adjusting the predictions to
correct for some types of forage.
Equations developed from these studies can be used to predict within a factor
of 2 the infinite dose to a 2-gram thyroid from a single contaminating event where
cows continue to ingest contaminated forage and the subject drinks 0,7 liters of.
milk per day. This dose, in rads, is equal to 0.37 times the peak exposure rate
measured 1 meter above ground, or 0.07 times the integrated air concentration. For
wet deposition, it is suggested that the predicted doses be increased by a factor
of 10. An equation for pre-test prediction is also developed.
Short-lived radioiodines and inhalation during effluent passage have a
definite effect on the predicted doses.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Mathematical models
Nuclear explosions
Radioactive isotopes
Radiobiology
Weapons effects
Prediction models
Radioiodine
Thyroid dose
06 R, U
14 B
18 B, C, H
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
44
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
*GPO 691-428-1976
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