TECHNICAL NO'I K
ORP/CSD-75-4
PRELIMINARY FINDINGS
RADON DAUGHTER LEVELS IN
STRUCTURES CONSTRUCTED ON
RECLAIMED FLORIDA
PHOSPHATE LAND
i
01
C3
THE UNITED STATES
ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS
SEPTEMBER 1975
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Technical Note
ORP/CSD-75-^
PRELIMINARY FINDINGS
RADON DAUGHTER LEVELS IN
STRUCTURES CONSTRUCTED ON
RECLAIMED FLORIDA PHOSPHATE LAND
OFFICE OF RADIATION PROGRAMS
U.S. ENVIRONMENTAL PROTECTION AGENCY
SEPTEMBER 1975
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PREFACE
The Office of Radiation Programs 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 control necessary to protect the public health and the
environment. This report of preliminary study findings was prepared to expeditiously provide
Federal, State, and local agencies, as well as the public with information concerning a situation
that poses a potentially significant public health problem. Readers of this report are encouraged to
inform the Office of Radiation Programs of any omissions or errors.
W. D. Rowe, Ph.D.
Deputy Assistant Administrator
for Radiation Programs (AW-458)
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ACKNOWLEDGMENT
The Office of Radiation Programs gratefully acknowledges the contributions of the staffs of
its Criteria and Standards Division, the Radiation Office - Las Vegas, and the Eastern
Environmental Radiation Facility, as well as the staffs of the Florida Division of Health -
Radiological and Occupational Health Section and the Polk County Health Department. Without
the contributions of these professionals and the cooperation of the residents of Polk County, this
study would not have been possible.
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TABLE OF CONTENTS
PAGE
I. INTRODUCTION *
II. SUMMARY AND CONCLUSIONS 2
III. RADIOACTIVITY IN POLK COUNTY LAND, 3
IV. STUDY DESIGN RADON IN STRUCTURES U
V. APPLICABLE FEDERAL GUIDELINES 13
VI. STRUCTURE STUDY FINDINGS U
VII. HEALTH RISK ESTIMATE l7
VIII. RECLAIMED LAND USE 22
APPENDIX A. SURGEON GENERAL'S GUIDELINES
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LIST OF TABLES
PAGE
TABLE 1. PRELIMINARY FLORIDA RADON DATA 15
TABLE 2. PERCENTILE RANGE OF RADON DAUGHTER
LEVELS - (FLORIDA) 16
LIST OF FIGURES
FIGURE 1. PHOSPHATE DEPOSITS IN FLORIDA 4
FIGURE 2. URANIUM-238 DECAY SERIES 5
FIGURE 3. GENERAL ECONOMIC GEOLOGY OF
FLORIDA LAND PEBBLE DEPOSITS ^
FIGURE 4. RECLAIMED LAND RADIATION EXPOSURE 9
FIGURE 5. FRACTIONAL RADON EMANATION RATE
VERSUS DEPTH OF BARE TAILINGS 10
FIGURE 6. EXPECTED LUNG CANCER MORTALITY RELATIVE
TO NORMAL LUNG CANCER MORTALITY VERSUS
CUMULATIVE YEAR OF RADON DAUGHTER EXPOSURE 21
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I. INTRODUCTION
Naturally-occurring radionuclides such as uranium, thorium and their progeny, tritium,
carbon-14, and potassium-40 are ubiquitous in the environment. Certain geological deposits
contain relatively large concentations of uranium and thorium which are mined and milled solely
for their uranium content. In the western U.S., deposits of this nature generally average about 0.2
percent uranium. Other geological formations, such as marine phosphate deposits, contain
uranium (about .01 to .02 percent) in concentrations significantly greater than normal rock or soil
but in concentrations too low to be processed economically solely for uranium at this time.
While these naturally-occurring radionuclides are confined to the earth's crust, they are
covered with several feet of overburden which minimizes their impact on the biosphere except for
possible dissolution into groundwaters. However, the mining and processing of ores (such as
phosphate rock) strips away the protective overburden. This may present situations that
potentially increases the radiation exposure to the population from processing and mining wastes,
as well as finished and by-product materials.
The U.S. Environmental Protection Agency (EPA) has the mission of protecting public
health and the environment. In this regard, EPA's Office of Radiation Programs (ORP) is
conducting, with the assistance of several Federal as well as State agencies, a program to
evaluate the radiological impact of industries and activities which may cause potential increases in
population exposure due to the addition of naturally-occurring radionuclides into the biosphere.
The Office of Radiation Programs has initiated this effort by conducting a comprehensive study of
the release of radiation and radioactive materials directly and indirectly from the phosphate
industry, thusly the radiological impact of phosphate mining, processing, use, and related
activities of the industry are being assessed. In the study, determinations will be made on the
effectiveness of present standards and controls and in areas where such controls are deemed to
be insufficient, appropriate standards and guides will be developed. The overall study has been
sub-divided into tasks involving the evaluation of effluents, emissions, products, by-products, on-
site exposures and reclaimed land uses. Efforts are presently underway in all of these areas.
The purpose of this report is to present the preliminary findings from the evaluation of the
use of reclaimed land for construction of residential and other structures in the State of Florida,
particularly Polk County.
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II. SUMMARY AND CONCLUSIONS
To determine the significance of radium-226 in reclaimed land on the radon daughter levels
in structures built on the land, a limited field study was conducted. A sample of about 125
structures was selected in Polk County. About two-thirds of the structures were believed built on
reclaimed land and the remainder were believed not on reclaimed land. Track-etch films and TLD
air sampler techniques were used to measure radon daughter levels. In addition, gamma surveys
of each structure were made.
In general, the data from this study coupled with existing information indicates that
radium-226 concentrations in soil beneath structures significantly affects the radon daughter
levels within the structures. The data collected over a five-week period suggests that structures built
on reclaimed land have radon daughter levels significantly greater than structures not built on
reclaimed land.
The health risk associated with the presence of increased concentrations of radon and its
daughter products is difficult to assess. Although epidemiological data indicate a substantial
increase in the incidence of lung cancer among uranium miners exposed to concentrations of
radon daughters, use of these results to estimate the potential risk in this case is difficult. Despite
uncertainties in health effects at relatively low levels of exposure, it is prudently assumed that
living in a structure with elevated radon daughter levels increases an occupant's risk of lung
cancer proportionate to the levels within the structure and the number of years of exposure.
Continuous exposure to the highest level measured (0.2 working levels) for ten years may
increase the normal risk of lung cancer for an occupant of the structure by a factor of about two.
It must be emphasized that the findings presented in this report are preliminary and require
substantial additional study before overall definitive levels can be ascertained. Further, additional
investigations should be performed to better evaluate the background levels in areas with
phosphate rock underground and areas without phosphate deposits. Nevertheless, based on
these findings, consideration should be immediately given to providing the State of Florida with
the recommendation that continued, use of reclaimed land for construction of new structures be
discouraged.
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III. RADIOACTIVITY IN POLK COUNTY LAND
In 1973, over 91 percent of the U.S. phosphate mine rock production came from Florida
with the remainder coming from Tennessee and several western States (1). Figure I illustrates the
primary Florida phosphate deposit areas. Florida land-pebble phosphate deposits are
characterized by pebbles and fine phosphatic sand dispersed in a nonphosphatic sandy clay. This
matrix, varying in thickness from I to 50 feet but averaging about 16 feet, is covered by an
overburden of quartz sand and clay that averages 20 feet in thickness (2).
The standard mining practice in the Florida land-pebble phosphate fields is to strip the
overburden and mine the phosphate matrix with draglines. Electric-powered walking draglines
with 35 to 49 cubic yard buckets work in cuts varying from 150 to 250 feet in width and from a few
hundred yards to a mile or more in length. The cuts are from 50 to 70 feet deep. Overburden is
stacked on unmined ground adjacent to the initial cut by means of a dragline, until successive cuts
allow it to be cast into adjacent mined-out cuts. As each cut is stripped of overburden and then
mined, the ore is stacked in a suction well or sluice pit that has been prepared on unmined ground.
High pressure water is used to produce a slurry of about 40 percent solids from the matrix. This
slurry is then pumped via pipe to the washer plant. In this manner, a typical operation will mine
about 400 acres of land per year, remove 13 million cubic yards of overburden, and mine 9 million
yards of matrix per year.
Water is used in the beneficiation process, in addition to being used as a transportation
medium. Both fresh water from deep wells and reclaimed water from slime settling ponds are used
by the phosphate industry. Approximately 10,000 gallons of water are necessary to produce one
ton of marketable phosphate rock. As the mining progresses, mined-out areas are used for the
disposal of tailings and slimes, in addition to overburden. Approximately one ton of slimes and one
ton of sand tailings must be disposed of for each ton of marketable phosphate rock produced.
Some of the sand tailings ana* overburden is used to construct retaining dams in mined-out areas,
behind which phosphatic clay slimes settle and dewater.
Beneficiation methods differ slightly and are dependent on screen analysis of the feed; the
ratio of washer rock to flotation feed; the proportions of phosphate, sand and clay in the matrix;
and equipment preferences. Through a series of screens, in closed circuit with hammer mills and
log washers, the matrix is broken down to permit separation of the sand and clay from the
phosphate-bearing pebbles. Three concentrations of marketable phosphate rock are produced: a
3/4-inch by 14-mesh pebble, a coarse 14 by 35-mesh fraction, and a fine 35 to 150-mesh fraction.
The washed, oversize pebble fraction is a final product. The minus 14 plus 35-mesh fraction is
called the coarse feed from which a coarse concentrate is obtained by gravity and flotation
processes. The tailings or waste from this fraction is used in dam construction or land reclamation.
The minus 35 plus 150-mesh fraction is processed through a flotation section to recover a fine
concentrate. The waste, a clay slime, is impounded in areas that have been mined.
Uranium is present in the phosphate matrix at varying concentrations which average about
100-150 ppm (about 70-IIO picocuries natural uranium per gram of matrix). The uranium is
generally in equilibrium with its decay products at least through radium-226. This means that for
each curie (3.7x10" disintegrations per sec) of the parent radionuclide, there is one curie of the
daughter radionuclides also present. The decay scheme of uranium-238 is shown in Figure 2.
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LEGEND
Northern land-pebble district
Hardrock district
Central land-pebble district
?0 40 60 10
Sole, miles
Figure 1 Phosphate deposits in Florida.
(From Bureau of Mines Circular 8653, Economic Significance of the
Florida Phosphate Industry)
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FIGURE 2
URANIUM 238 DECAY SERIES
ATOMIC WOT.
ELEMENT
ATOMIC MO.
HALF-LIFE
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Radioactivity is also present in parts of the overburden. Figure 3 illustrates the general
geological structure throughout much of the Florida land pebble district. A "leach zone" which is
about five feet thick and covers much of the pebble deposits contains uranium in concentrations
comparable to that of the matrix. Other portions of the overburden are expected to also contain
some radioactivity, although not in as high concentrations (3). The radioactivity is generally
associated with the phosphate compound structure since the uranium replaces the calcium in the
apatite. Consequently, the marketable ore and slimes contain most of the phosphate. One-third of
the phosphate originally contained in the matrix remains in the slimes. The remainder is primarily
in the marketable rock.
Soil throughout the United States typically contains between 0.15 - 2.8 pCi radium-226 per
gram, a highly radiotoxic member of the uranium decay series. Consequently, we would anticipate
that Florida soils within several feet of the surface would normally contain about this
concentration of radium-226 in areas that have been undisturbed by mining. However, anomalies
might be observed in areas where surface waters may have exposed phosphate deposits or
where such deposits are very close to the surface.
Since matrix and leach zone material are expected to contain about 40 pCi of radium-226
per gram, it is reasonable to expect that the radium concentrations in soil taken from reclaimed
land sites to range between less than one to 40 pCi per gram depending upon the presence of
either low activity overburden soil, leach zone material, matrix, sand tailings, or slimes. However,
since all of these materials are blended together at most reclaimed land sites, an average soil
activity of about 20 pCi per gram might be expected assuming 50 percent dilution of high activity
material. One analysis has been made of reclaimed land soil showing a radium-226 concentration
of 16 pCi per gram. Although this suggests about a 50 percent dilution, additional sampling must
be conducted before definitive values of radium-226 concentrations in several reclaimed land
soils can be ascertained with any reliability.
The presence of radium-226 and its daughters in soil presents a potential source of gamma
exposure to individuals living or working above the soil. However, of much greater interest is
exposure arising from the release of radon-222; a noble gas daughter of radium-226. This decay
product has a 3.85 day half-life. It may diffuse through the soil into the atmosphere, where the
radon-222 levels are highly variable being influenced by several factors including precipitation,
barometric pressure, atmospheric thermal stability, and time of day.
Some measurements have been made by the State of Florida, Division of Health of
atmospheric radon-222 levels in Polk County. Although atmospheric radon-222 levels are of some
interest, of greater concern to public health importance is any buildup of radon in the air within
closed structures constructed on reclaimed land.
Radon-222 that diffuses up through soil also readily diffuses through concrete slabs and
other construction materials. Within a structure, the principal route of removal is by ventilation or
leakage through the structure's walls, window frames, etc., where there exists a concentration
gradient. Radioactive decay of the material as a removal process is generally small compared to
ventilation and leakage. Radon-222 is probably not in equilibrium with its daughters in most
situations within structures. Consequently, the level of radon and its daughters in a structure is
primarily dependent upon the rate at which it diffuses into the structure and the rate at which it is
removed by ventilation, leakage, and decay. Clearly, if ventilation is low, the radon and daughters
6
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FI6URE 3
GENERAL ECONOMIC GEOLOGY OF
FLORIDA LAND PEBBLE DEPOSITS
SURFACE
ui
Q
DC
tr
UI
g
LEACH ZONE
MATRIX
BEDROCK
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have the potential to significantly buildup within a structure. Figure 4 depicts the movement of
radon and daughters into a structure. The impact of ambient environmental radon levels is
expected to be only a fraction of the contribution originating from diffusion through the ground.
However, data is lacking to quantify this fraction and further information is needed.
Different seasons of the year with various environmental conditions, such as thermal
inversions, etc., may have a pronounced effect on the residence time of radon and its progeny in
structures. This variable should also be investigated.
The depth of soil containing the elevated radium-226 is believed to be significant in
determining the radon-222 source term (release rate) at the surface. The amount of radon
diffusing into the environment from the soil is limited by several factors, including the time needed
to diffuse from its position of origin to the surface. Since radon-222 has a half-life of 3.85 days, this
significantly affects the depth from which it can contribute to environmental concentrations.
Figure 5 illustrates the theoretical fraction of maximum exhalation versus the depth of the
material (4). This graph was based on uranium mill tailings parameters but should generally
approximate the situation with respect to reclaimed land. Radon generated at a depth of about ten
feet or more does not significantly contribute to atmospheric levels. Consequently, it is the
radium-226 concentration within the first ten feet that determines the amount of radon emanating
into the environment. A slab foundation provides an additional barrier to the diffusing radon-222,
thus effectively making the contributing soil depth less than ten feet. Specific quantification of this
effective depth requires investigation under field conditions.
8
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FIGURE 4
RECLAIMED LAND RADIATION EXPOSURE
f
AIRBORNE RADIOACTIVITY
LUNG EXPOSURE
(RADON DAUGHTERS)
f
1
§
e
1
EXTERNAL GAMMA 1
WHOLE BODY EXPOSURE < 1
2 1
j
' '
S
o
CONCRETE
1
FLOOR
1
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1.0
0.8
0.6
OO
0.4
0.2
FIGURE 5
FRACTIONAL RADON EMANATION RATE VERSUS
DEPTH OF BARE TAILINGS
I I I I \
000 (PCi/m2-s)=1.6 CRa(pCi/g)
8
DEPTH OF TAILINGS (X) (FEET)
10
FROM SCHIAGER, K.J., ANALYSIS OF RADIATION EXPOSURE ON OR NEAR
URANIUM MILL TAILINGS PILES, RADIATION DATA AND REPORTS, VOL. 15,
NUMBER 7, JULY 1974.
10
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IV. STUDY DESIGN RADON IN STRUCTURES
To determine the significance of radium-226 in reclaimed land on the radon daughter levels
in structures built on the land, a limited field study was conducted. A sample was selected of
structures believed built on reclaimed land and structures believed not built on reclaimed land. All
structures selected for study were within Polk County and except for the variable of the study (i.e.,
reclaimed versus non-reclaimed land), were selected as randomly as practicable. The overall
sample size was approximately 125 structures with two-thirds of them being reclaimed land sites
and the remainder non-reclaimed land sites. This limited study was not intended to evaluate radon
levels in all structures throughout the county but rather to give us a perspective of the problem if
one existed and thereby point the way to further evaluation, if needed.
Two techniques were employed for measuring the radon daughter levels within structures,
track-etch films, and TLD air samplers. The track-etch badge consists of a one-half inch by one
inch plastic chip which is coated with cellulose nitrate. As radon and its decay products (radon
daughters) are formed, alpha particles are produced. When the alpha particles strike the cellulose
nitrate a record of its passage is made. The badges are each numbered and two of the badges are
usually mounted on a cardboard card which can be positioned on a wall. The badges are left in
place from six months to a year and collected. The badges are then dipped in a caustic solution
(NaOH). This process is called etching and the alpha particle's passage becomes an etched
track. These tracks are visible with the use of a light microscope.
Each badge, after etching, is read by a technician using a light microscope with a calibrated
field. The number of tracks observed is recorded and the tracks per square millimeter (T/mm2)
can be calculated. This value is then compared to a calibration curve and the working level hours
(WL-h) associated with the number of tracks observed is obtained. The WL* is then calculated
using the number of hours the badge was in the sampling location.
The badge has the advantage of being a passive dosimeter. That is, it is put in place and
picked up, but no maintenance is required during the sampling period (no moving parts).
The badge, however, has the disadvantage of measuring or recording the alpha energy
given off by radon, as well as polonium-218 (radium A) and polonium-214 (radium C). Since the
alpha energy from radon is not a portion of the alpha energy used to determine the WL (the radon
daughters and not the radon-222 itself, are the prime contributors to adverse health impact), the
system must be calibrated so that the complement from radon can be substracted.
In the survey of structures 'built on reclaimed phosphate tailings, 85 were placed in
structures believed to be built on reclaimed land and 40 were placed in structures built on non-
reclaimed land. Structures surveyed consisted primarily of private dwellings; however, local health
department buildings and a few office buildings were also surveyed.
* WL - The working level is defined as the potential alpha energy from the short-lived daughters of radon
which will produce 1.3xlOs MeV in one liter of air.
11
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Only one-half of the track-etch film is mailed to the lab for analysis, the other half is retained
for backup checks and analysis, in the event that the other half is damaged or lost. A portion of the
track-etch films presently in place are to be read after six-months exposure and the remainder
after 12-months exposure.
The air sampling system used by the Environmental Protection Agency, Office of Radiation
Programs (EPA/ORP) was developed by Colorado State University, Fort Collins, Colorado. It is
known as the Radon Progeny Integrating Sampling Unit (RPISU) and utilizes the detection
techniques of thermoluminescent dosimetry (TLD).
The air pump is located inside two pieces of polyvinyl chloride (PVC) pipe. The PVC pipes
are of different diameters and the area behind the pipes is filled with sound deadening material.
The pump is attached to a sampling head which is located outside of the pump housing. This
sampling head, which is actually a hypodermic syringe filter holder, contains the TLD's. The filter
head is made up at the EPA facility in Las Vegas, Nevada, and packaged in a small 3" x 5"
envelope. This envelope also provides space for the entry of the necessary field data.
During operation, air is pulled through the sampling head and the particulate material
containing the radon daughters is trapped on a one-half inch filter. A TLD (CaRDy) is located in
the airstream directly before the filter and the alpha energy from the decay of the radon daughters
is recorded by this TLD. A second TLD separated from the first by a stainless steel washer is also
located in the filter head. The first TLD is referred to as the alpha (a) TLD and the second the
gamma (y) TLD.
The filter head is placed on the sampler and the starting sampler information consisting of
the reading on a running time meter, a location number, date and time, and airflow (measured by a
calibrated rotometer) is filled in on the envelope. The sampler is usually left in place for one week.
Information on date, time, and flow rate at cut-off is entered on the envelope. The envelope with
the filter head is then returned to Las Vegas. The head is taken apart, the TLD's read out on a
Harshaw TLD reader, a data form completed and sent for computer analysis, and finished printout
containing the calculated working level (WL) is retrieved.
The working level is calculated by providing a working level-liter/nanocoulomb (WL-1 /nC)
conversion factor for the TLD reader, nC readout for gamma and alpha TLD, the running time of
the sample, the on and off air flow rates and the number of the rotometer used.
The net nC value is obtained by subtracting the gamma TLD nC (background gamma
radiation) from the alpha TLD nC (alpha decay energy plus background). This value multiplied by
the conversion factor and divided by the corrected air balance produces the WL value average for
the period of exposure.
Since gamma levels give a rapid indication of the presence of anomalous radioactivity and
further, might be used as a surrogate for measured radon levels in future work, gamma levels were
measured at each structure visited and a map of the structure drawn indicating the various
radiation levels. Sodium iodide scintillators (Ludlum Model 12S) were used to make these
measurements.
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V. APPLICABLE FEDERAL GUIDELINES
There are no Federal radiation protection guidelines specific to radium-226 in soil or radon
daughter levels in structures. Recommendations of the former Federal Radiation Council*
published in 1960 established annual limits of 500 millirems to an individual in the general
population and 170 millirems to an average member of a suitable population size. However, it
should be kept in mind that these limits specifically excluded natural background radiation, and
therefore their applicability is not completely straightforward. Since exposures resulting from
reclaimed land use are a direct result of man's alteration of the natural environment, they are not
natural background; thus the FRC guidelines could be generally applicable to the incremental
difference above normal background levels. In applying these guidelines, however, it is strongly
emphasized that there are large uncertainties in deriving dose estimates for radon daughters.
A second relevant Federal guide is the U.S. Surgeon General's Guidelines for remedial
action in Grand Junction, Colorado. A copy of these is included as Appendix A. These guidelines
were developed in light of the FRC guides and information derived from uranium mine studies for
use in establishing remedial action criteria for structures having uranium mill tailings under or
around them. The guidelines include criteria for external gamma levels or indoor radon daughter
levels. However, it must be emphasized that the Surgeon General's Guidelines are specific to the
Grand Junction situation and should not be interpreted to be directly applicable in this or any other
case.
The present Federal guideline for exposure of uranium miners to radon daughters is
4 WLM** per year as recommended by the Environmental Protection Agency in May I97I (5).
Although this occupational exposure guideline is not directly applicable to the situation of
population exposure due to structures on reclaimed land, comparison of the levels observed in
structures to the uranium miner standard could provide a perspective of the significance of the
levels in the structures studied.
When the Environmental Protection Agency was established by Reorganization Plan No. 3 in 1970, the
Federal Radiation Council was vested in EPA.
** A working level month (WLM) is defined as exposure to IWL for 170 hours (a working month). Continuous
exposure to radon daughters at I WL for one year is aqual to about 50 WLM.
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VI. STRUCTURE STUDY FINDINGS
Although work is continuing in an effort to define the gamma radiation, radon and radon
daughter levels in Polk County, investigations to date indicate that these levels are highly variable
depending upon the existence of phosphate related material. In areas where no phosphate
material is present, the total gamma radiation background is generally quite low, approximately 5
to 7 microroentgens per hour (jiR/hr) and is about twice this range in areas where some
phosphate rock is probably near the surface. Generally on known reclaimed land areas, levels of 2
to 10 times this range were observed, i.e., gamma radiation levels in the range of 10 to 80 juR/hr.
Radon daughter levels in structures in background areas were generally about .004 WL These
radon daughter levels may not be valid in structures built on land where phosphate rock is near the
surface.
To date, data on radon daughter levels from only five weeks of TLD air pump sampling are
available. This data is listed in Table 1. The structures studied are listed in decreasing order of
observed radon daughter concentrations. Structures that were believed to be on reclaimed land
are noted with the symbol R. All other structures were believed not to be on reclaimed land. The
highest radon daughter level measured was 0.2 WL. If thfs structure had that level continuously
over a year, the resultant exposure would be about 10 WLM. However, it must be emphasized that
these findings are preliminary and radon daughter levels must be determined for a period of a year
before overall conclusions can be drawn regarding the specific annual exposure within a
structure. Seasonal variations including more open window ventilation in spring and fall could
have an impact on the levels observed over a period of one year.
Using the Surgeon General's Guidelines as an evaluation tool, the levels from Table I were
arranged in Table 2 according to their percentile ranking with respect to the Guidelines. It is clear
that as a group, structures on reclaimed land had greater radon daughter levels than structures
not on reclaimed land.
If we assume that structures on reclaimed land will have radon daughter levels greater than
0.01 WL and structures not on reclaimed land will all have radon working levels below .01 (i.e.,
about 2.5 times a background level of .004 WL), we find three structures out of twelve on
reclaimed land and two structures out of nine on non-reclaimed land that are contrary to the
assumption. One of the structures built on reclaimed land that had levels below .01 WL was
observed not to have air conditioning. Consequently, since this structure has had its windows
open during the study period, the excellent ventilation probably kept the radon daughters levels
down. No plausible explanation for the lower observed levels in the other two structures is known
at this time. Of the two structures on non-reclaimed land that exhibited levels greater than .01 WL,
one was observed to have elemental phosphorous slag alongside the structure. Since this slag
contains about 50-60 pCi per gram of radium-226, radon from this material may be contributing to
the levels observed in the structure. However, because of the gamma levels observed in these
two structures (i.e., greater than 10/uR/hr), there may be phosphate rock near the surface under
them which is providing a source of radon for the structures. Clearly, these factors need further
study to better explain the observed anomalies.
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TABLE 1
PRELIMINARY FLORIDA RADON DAUGHTER DATA
LOCATION NO.
RADON DAUGHTERS (WL)
INSIDE (/uR/hr.i
AVG. (HIGt
OUTSIDE (pR/hr.)
AVG. (HOG)
98R
110R
107R
105R
94R
76R
172
103R
169
51 R
118R(NoA/C)
50R
170
175
84R(No A/C)
112R
134
176
180
135
136
.2013
.1050
.1011
.0737
.0410
.0302
.0247
.0234
.0218
.0105
.0100
.0071
.0057
.0053
.0052
.0048
.0042
.0039
.0036
.0002
.0002
.2083
.1169
.0277
.0252
.0041
1
.0254
.0030
20 (24)
12 (15)
15(16)
10(13)
12(15)
16 (16)
13(15)
9(10)
10(10)
9(10)
7(7)
12 (15)
7(10)
4( 4)
27 (28)
9 (11)
3( 5)
4( 5)
( 4)
3( 3)
4 (4)
36 (40)
26 (50)
40 (50)
25 (35)
35 (40)
25 (35)
19 (60)
10 (12)
13 (18)
(14)
17 (40)
(70 in road)
5 ( 8)
4 ( 5)
35 (40)
22 (26)
3 (4)
6 { 7)
(6)
3 (4)
4(4)
1. R-BELIEVED TO BE ON RECLAIMED LAND.
2. THESE GAMMA MEASUREMENTS HAVE NOT BEEN CORRECTED FOR BACKGROUND WHICH
IS ABOUT 5-7/iR/hr.
3. HIG - HIGH INSIDE GAMMA
4 HOG - HIGH OUTSIDE GAMMA
15
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TABLE 2
PERCENTILE RANGE OF RADON DAUGHTER LEVELS [FLORIDA)
AUGUST 1975
RECLAIMED LAND .05 WL : 33.3%
.05 =» X a .01 WL : 41.7%
«= .01 WL : 25.0%
NON-RECLAIMED LAND (n=9)
S .05 WL : -0-
.05 =» X a .01 WL : 22.2%
*= .01 WL : 77.8%
TOTAL (n=21)
a .05 WL : 19.0%
.05 S X > .01 WL : 33.3%
«= .01 WL : 47.7%
16
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VII. HEALTH RISK ESTIMATE
Internal and, to a lesser extent, external sources of ionizing radiation may cause adverse
health effects to occupants in areas of high radium and radon concentrations. The dose due to
external sources is primarily from radium daughter products that emit gamma rays capable of
penetrating all tissues of the body. Penetrating radiation can cause somatic and genetic effects in
humans. Somatic effects which might be expected include leukemia and solid tumors, such as
bone, breast, and lung cancers. Genetic effects will appear as congenital defects in the children of
exposed parents. Internal exposure will be due primarily to alpha particles from radon daughter
decay products, the chain of radionuclides that follow radon-222 in the uranium radium decay
series. The radon daughters deposit in and irradiate parts of the lung, particularly the basement
membranes of the bronchial airways. The expected response to this irradiation is an increase in
lung cancers (6).
Risk Estimates for External Radiation
*
In the case of external penetrating radiation, data presented in the NAS-BEIR report
provides the following estimates (6):
200 estimated excess cancer deaths/106 man-rem
200 estimated excess nonfatal cancers/106 man-rem
200 excess congential abnormalities per rem/IO6 live births.
These estimates are based on the assumption that the number of health effects observed
at relatively high doses and dose rates can be extrapolated linearly to the low levels of radiation
usually found in the environment.
External exposure to natural background radiation in Florida is about 65 millirem per year,
except in regions containing anomalous sources (7). The annual population dose from natural
external background radiation is 65,000 man-rem per year per million exposed persons. Based on
the uncertain but prudent assumption that there is no threshold dose necessary to induce
radiation carcinogenesis, an estimated 13 cancer fatalities annually could be attributed to a total
population dose of 65,000 man-rem.
Risk Estimates for Internal Radiation
The lung cancer risk from inhaled radon and its daughter products is almost all due to the
radon daughters which cause over 95 percent of the dose delivered to the bronchial tree, rather
than radon itself. Almost all of the relevant clinical experience is based on the increased cancer
incidence experienced by uranium miners who were exposed to radon in an occupational
environment quite different from residential situations. There is a possibility that these miners may
also have been exposed to other carcinogens (not related to radiation) in their work which
increased the incidence of observed lung cancers. On the other hand, the dose to critical lung
tissues from a given concentration of radon daughters may be less for miners than for persons
exposed in more normal environments. The BEIR Committee estimated that the dose to miners is
17
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a factor of two less that that received by other persons, due to the miners occupationally induced
chronic bronchitis which increased the thickness of the mucous layer overlaying the basement
membrane of the larger bronchi (6). Because of the short range of alpha particles in tissue, the
bronchial dose is a sensitive function of the distance they penetrate (8).
An additional factor acting to reduce the dose to miners from a given radon daughter
concentration is that miner's exposure to radon daughters is usually expressed in a unit used for
monitoring purposes, namely "working level." This unit does not take into account the difference
in concentration of the various radon daughters or the presence of radioactive ions not attached
to dust particles. Such unattached ions have an increased probability of residence in the bronchial
tube and therefore deliver a greater dose. Since the concentration of the unattached ions is very
low in mines because of the high dust loading, the dose to miners from radon daughters may be as
much as a factor of four lower than in a "clean air" environment (8). Therefore, the risk estimates
given below, based on uranium miner experience are likely to be low. To a residental population,
the dose and the resultant cancer incidence may be several times larger (4 to 8) because of
cleaner (less dust loading) ambient air and deeper alpha particle penetration into the bronchial
membrane.
Cancer risks from exposure to radon daughters are usually quantified relative to working
level month which is the cumulative exposure over a period of time. A working level month
corresponds to a 170 hour exposure to radon daughter concentration of one working level, since
for miners an 8-hour workday is assumed. Residential occupancy may be up to 24 hours per day.
Therefore, a full year's exposure to one working level corresponds to about 50 working level
months.
Although the lung cancers observed in uranium miners occur most frequently in highly
exposed persons, not all of the clinical experience is based on heavily exposed persons. In
particular observations of uranium miner populations in Czechoslovakia, where, on the whole,
radon daughter concentration in mines is lower than in the U.S., have provided a source for risk
estimates at relatively low exposure levels. Sevc and Placek found excess lung cancer in Czech
miners after exposure of less than 100 working level months (9). These exposures extended over
as long as 40 years, indicating that effects may occur at exposure rates as low as 2 to 2.5 working
level months per year. Their study is not complete, some miners are still alive, and additional
follow-up may disclose lung cancers related to even lower exposures.
In 1973, Vaskov reported that in miners and workers in radon mineral baths, exposed to
0.036 to 3.2 WLM per year, there was an increase in the number of abnormal cells (metaplastic
and dyskariotic) found in the sputum compared to similar workers not exposed to radon (10). The
exact significance of such abnormal cells in sputum is not known, but they are often precursors of
lung cancer. These observations strengthen the case for suspecting that lung cancers may be
adverse sequelae even to rather low concentrations of radon and its daughter products.
The cancer risk from radon daughters is better expressed in terms of the percentage
increase in the expected cancer incidence, i.e., relative risk, rather than the absolute number of
cancers expected per working level month of exposure. However, the health characteristics of the^
population at risk are important in using a relative risk coefficient to estimate the risk from radon
exposure. The cancers occurring in uranium miners were in males and current incidence of lung
cancer in U.S. males and females are substantially different. Another factor is habitual cigarette
18
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smoking. Most of the observed lung cancers in both U.S. uranium miners and the U.S. population
occurs in smokers. Archer has indicated that from the study of U.S. miners, the absolute cancer
risk from radon among non-smokers may be a factor of 2 to 10 less than for cigarette smoking
miners (II). Although the relative risk coefficient for lung cancer from radon exposure is thought to
be relatively independent of smoking history, it is more meaningful when applied to groups having
comparable cancer incidence so that the true population at risk can be ascertained (12). For
example, in the South Atlantic States, lung cancer mortality (which differs only slightly from
incidence rates), is reported to be about 34 deaths per year per 100,000 persons for males and
4.6 for females (13). However, cigarette smokers are included in these totals and therefore a
further breakdown is desirable. From the Surgeon General's Report on the Effects of Cigarette
Smoking it is estimated that lung cancer mortality in the South Atlantic States is about 47 annual
deaths per 100,000 persons among smoking males; 5 deaths annually per 100,000 among non-
smoking males; 6 deaths annually per 100,000 among smoking females; and 3 deaths annually
per 100,000 among non-smoking females (13).
W. Jacobi has recently analyzed the combined results from the U.S. uranium miner
experience, as reported in the BEIR report and the Czechoslovakia experience (14). At cumulative
exposure less than a few hundred working levels, his analysis shows that: (a) the two sets of
observations agree quite well with each other even though the radon daughter concentration at
which the U.S. miners were exposed was much higher, (b) the excess of observed over expected
cancer mortality increases approximately linearly with the cumulative exposure, and (c) the
relative risk coefficient is "nearly equal for both groups," 0.9 percent for each working level
month. The 95 percent confidence band for this risk coefficient is +_ 0.3. Therefore, assuming the
risk coefficient is 0.9 percent per working level months, HO working level months cumulative
exposure would be expected to increase the observed lung cancer mortality by 100 percent, i.e.,
double the normal incidence.
It should be noted that most of these data are based on adult white males including
cigarette smokers and care should be used when applying this relative risk estimate to other
population groups. It would be desirable to apply these estimates to appropriate control groups by
multiplying the risk coefficient by the lung cancer incidence observed in homogenous groups
having the same characteristics and lung cancer mortality, i.e., non-smoking adult males, smoking
males, non-smoking adult females, etc. Without performing these comparisons the higher risk to
smokers will be underestimated and the risk to women, children, and non-smokers will be
exaggerated.
In using these risk coefficients and the linear nontnreshold hypothesis to project potential
health effects from radon daughter exposures, it is useful to consider the limited conclusions
reached by Jacobi in his study (14).
"Taking into account the limits of error in the presently, available
data for both groups therefore do not indicate the existence of a
practical exposure threshold above 100 - 200 WLM. The data also do
not allow a reliable, quantitative distinction between a linear or
nonlinear relationship between LC-incidence and cumulative radon
exposure. The mean regression lines indicate, that a linear
relationship in the considered exposure range cannot be excluded. At
19
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the present time the recommendation of an exposure limit should be
based therefore on the assumption of a linear exposure-risk curve.
It follows that the mean, relative risk coefficient is nearly
equal for both groups of uranium miners and results to a(rel) = 0.009
+_ 0.003 WLM'1, corresponding with a mean "doubling exposure" of
about IIO WLM. For comparison it should be noted, that the mean
natural background level of radon daughters in air leads to an
cumulative exposure of about 4-5 WLM during a lifetime of 70 years.
This means that only a few percent of the observed LC-mortality in our
population can be attributed to irradiation of the lung by inhaled radon
daughters, if a linear extrapolation down to these low exposure values
is generally accepted."
From the data in Table 1, the highest observed level was 0.2 WL. At this level, exposure for
one year would result in a radon daughter exposure of about 10 WLM. Over an eleven year period
this would result in a cumulative exposure of IIO WLM. Based on our assumptions, this cumulative
exposure could result in increasing the risk of lung cancer by a factor of two. Exposures to various
levels of radon daughters for differing time periods would modify the potential health risk in
proportion to the exposure levels and residence time. Figure 6 illustrates the estimated lung
cancer mortality relative to the normal lung cancer mortality for different radon daughter levels
and exposure periods.
20
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!2 -
5
CO
oc
5
UJ
tr
Q
IU
1-
i
5
IU
2
'
g
o
5
d
S
CM
d
11
3
o
5
d
S
CM
0
22
5
o
d
CM
d
33
t
o
t
d
Z
CM
d
44
CUMULATIVE YEARS OF EXPOSURE
FIGURE 6
TOTAL ESTIMATED LUNG CANCER MORTALITY RELATIVE TO NORMAL LUNG CANCER MORTALITY
AS A FUNCTION OF RADON DAUGHTER EXPOSURE LEVELS AND YEARS OF CONTINUOUS EXPOSURE
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VIII. EXTENT OF RECLAIMED LAND USE
To date, approximately 25,000 acres of phosphate mine land has been reclaimed in
Florida (2). Initial estimates from maps provided by the Polk County Health Department indicate
that about 20,000 acres have been reclaimed in Polk County and is used in the following
proportions:
USE PERCENTAGE
Residential 29
Commercial or Industrial 8
Farming 16
Grazing 41
Miscellaneous 6
The Polk County Health Department has initially estimated for us that between 500 and 1000
structures presently exist on reclaimed land within the county. Some of these structures have
existed for over twenty years, whereas others are presently under construction. From field
studies, we observed that generally the older structures, i.e., constructed over ten years ago were
of either crawl space or slab construction but generally did not have air conditioning, particularly
central air conditioning. Whereas newer houses and particularly those now being constructed are
on concrete slabs, possess a more airtight design, and have central air conditioning.
Consequently, it would be anticipated that radon daughter levels would be highest in the newer air
conditioned structures.
At the present, about 90,000 acres of land have been mined for phosphate rock (2). The
industry is currently mining about 4700 acres per year. If we assume that 40-50 percent of the
mined land can be potentially reclaimed (the remainder will be used to store slimes) and that the
Florida phosphate industry will continue for at least 30 years, these will be about 50,000 to 70,000
additional acres available for reclaiming. Further, if slime dewatering systems are developed,
slime ponds will not be needed and about 140,000 additional acres will be available for reclaiming.
Consequently, a vast amount of land will be made available for societal use. The radiological
impact of this land must be considered when determining the activities for which it will be used.
22
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REFERENCES
(1) Stowasser, W.F., Phosphate Rock, 1973 Mineral Yearbook, preprint, Bur. of Mines, Dept of the
Interior.
(2) Wang, K.L, et at.. Economic Significance of the Florida Phosphate Industry, Information Circular
8653, Bureau of Mines, Dept. of the Interior, 1974.
(3) Cathcart, J.B., Economic Geology of the Fort Meade Quadrangle Polk and Hardee Counties, Florida,
Geological Survey Bulletin 1207,1966.
(4) Schiager, K.J., Analysis of Radiation Exposure on or near Uranium Mill Tailings Piles, Radiation Data
and REports, Vol. 15, Number 7, pp. 4II-427, July 1974.
(5) Radiation Protection Guidance for Federal Agencies, Environmental Protection Agency, Federal
Register, May 25,1971 (36F.R.9480).
(6) "The Effects on Populations to Exposure to Low Levels of Ionizing Radiation," Report of the
Advisory Committee on the Biological Effects of Ionizing Radation, Division of Medical Sciences,
National Academy of Sciences, National Research Council, November 1972, Washington, D.C.
20016.
(7) Natural Radiation Exposures in the United States, ORP/510 72-1, U.S. Environmental Protection
Agency, Washington, D.C. 20460.
(8) Ionizing Radiation Levels and Effects, Vol. I, United Nations UNSCEAR Report E.72.IX.18, New
York, New York.
(9) Sevc, J. and Placek, V. (1973), Lung Cancer Risk in Relation to Long Term Experinece to Radon
Daughters, pp. 129-136 in Health Physics Problems Internal Contamination, E. Bujdoso, editor,
Akademiai Kiado, Budapest, 1973.
(10) Vaskov, L.S., Comparative Clinical Studies on the Occupational Hazards from Inhaled Radon
Daughters in Workers of Non-uranium Mines and Mineral Waters, pp. 645-650 in Health Physics
Problems of Internal Contamination, E. Bujdoso, editor, Akademiai Kiado, Budapest, 1973.
(II) Archer, V.E., Gillam, J.D., and Wagoner, J.K. (1975), Respiratory Disease Mortality Among Uranium
Miners, Conference on Occupational Health Experience with Uranium, Arlington, Va., 1975. In Press.
(12) Lilenfeld, A.M., Morton, LL, and Kessler, I.I., "Cancer in the United States," Harvard University
Press, 1972.
(13) Smoking and Health, Report of the Advisory Committee to the Surgeon General of the Public Health
Service, U.S. Department of Health, Education, and Welfare, U.S. Government Printing Office,
Washington, D.C. 20402,1964.
(14) Jacobi, W. (1973), Relation Between Cumulative Exposure to Radon Daughters. Lung Dose and
Lung Cancer Risk, Noble Gases Symposium, Las Vegas, Nevada, 1973. in Press.
23
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APPENDIX
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DEPARTMENT OF HEALTH. EDUCATION. AND WELFARE
PUBLIC HEALTH SERVICE
WASHINGTON. D.C. 20201
Dr. R. L. Cleere *1*"*^. ;i
Executive Director
Colorado State Department of Health i... fj n
4210 E. llth Avenue "UL '-. 1S~J
Denver, Colorado 80220 ^
Dear Dr. Cleere:
\.
I am pleased to respond to your letter of January 29 in which you
asked Dr. M. W. Carter, Director of our Southwestern Radiological
Health Laboratory, for Public Health Service and/or U.S. Atonic
Energy Commission assistance in providing exposure guidelines appli-
cable to homes with high concentrations of radon progeny.
The enclosed graded recommendations for action have been developed
within the framework of existing Federal Radiation Council guidance
for occupational exposure to airborne concentrations of radon-and
its daughters (progeny). Also, graded action levels applicable to
external gamma radiation are included.
You will note in the accompanying Explanatory Notes that these
recommendations apply specifically to duellings constructed with or
on uranium mill tailings. Further qualifications in the Explanatory
Notes should be consulted before these recommendations are applied.
The specific information vMch your Department is developing on the
variability of radon daughter concentrations in dwellings and on
optimum control measures will be essential towards making those
decisions necessary in applying the recommendations.
These recommendations have been directed to the Atomic Energy
Commission for comment. Because of the urgency attached to your
receiving the recommendations as soon as possible, they have been
forwarded to you in advance of receiving AEC views and comments.
We will advise you of the AEC response when received.
Sincerely yours,
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RECOMMENDATIONS OF ACTION FOR RADIATION EXPOSURE LEVELS
IN DWELLINGS CONSTRUCTED ON OR WITH URANIUM MILL TAILINGS
External Gamma Radiation
Level
Greater than 0.1 mR/hr
From 0.05 to 0.1 mR/hr
Less than 0.05 mR/hr
Indoor Radon Daughter Products
Level
Greater than 0.05 WL
From 0.01 to 0.05 WL
Less than 0.01 WL
Recommendations
Remedial action indicated
Remedial action may be suggested
No action indicated
Recommenda tions
Remedial action indicated
Remedial action may be suggested
No action indicated
EXPLANATORY NOTES
1. These recommendations are written specifically for dwellings con-
structed on or with uranium mill tailings. This situation may involve
continuous exposure of members of the public to radon daughter product
activities and whole-body gamma irradiation levels in excess of the
t
background radiation levels found within dwellings in the area not con-
structed with or on uranium mill tailings.
-------
2. Although the-initial concern was the presence of radon daughter
product activities within these dwellings, preliminary surveys have
indicated that, in some instances, the gamma radiation levels were
of prime importance. Thus, recommendations are made concerning both
types of radiation. The recommendation applicable to a particular
dwelling will be determined by whichever type of radiation has the
higher level.
3. Three levels for action are recommended for both external gamma
and radon daughter product exposures. This graded system of actions
is proposed to allow latitude in the middle ranges for the judgment
of the on-site investigators.
4. The external gamma and radon daughter product levels proposed
constitute exposures which are in addition to the natural background
levels found within dwellings in the area not constructed on or with
uranium mill tailings. In the Grand Junction, Colorado, area these
levels are approximately 0.01 mR/hr (approximately 90 mrem/yr) and
0.004 Working Levels (WL) (approximately 0.2 CWLM/yr) respectively (1)
5. The expected health effects of concern will be different for the
two types of radiation, i.e., leukemia for whole body gantma radiation
exposure and lung cancer for exposure to inhaled radon daughter
products. This expectation is based, in part, on findings derived
from population studies such as the Japanese atomic bomb survivors
and uranium miners. These specific health effects are considered to
be mutually exclusive. The basis for this assumption is that the
expected radiation contribution to whole body exposure from inhaled
-------
radon and daughter products would be considerably less than the direct
exposure from external gamma radiation at the levels encountered in
the dwellings. Conversely, the external gamma radiation contribution
to the lung dose is considered to comprise a negligible additional
risk of lung cancer.
6 a. A Working Level (WL) is the term used to describe radon daughter
product activities in air. This term is defined as any combination
of short-lived radon daughter products in 1 liter of air that will
result in the ultimate emission of 1.3 x 10 MeV of potential alpha
energy (2). The numerical value of the WL is derived fron the alpha
energy released by the total decay through Ra C' of the short-lived
radon daughter products, Ra A, Ra B and Ra C, at radioactive equi-
ooo
librium with 100 pCi of *Rn per liter of air (3).
6 b. A Working Level Month (WLM) is the term used to express the
occupational exposure incurred in one working month of 170 hours by
a uranium miner laboring in an atmosphere containing radon daughter
products; i.e., one working month in a mine atmosphere containing
1 WL of radon daughter products equals 1 WLM.
i
6 c. Cumulative Working Level Months (CWLM) is the term used to
express the total accumulated occupational exposure to radon daughter
products in air; i.e., an air concentration of radon daughter prod-
ucts of 1 WL would, in one working month, equal 1 WLM, and in 1 year
or 12 months would equal 12 CWLM.
6 d. Since occupational exposures are based upon 170 hours per
month and continuous exposure involves approximately 170 hours per
-------
veek, then an occupational exposure to an air concentration of 1 WL
is equivalent to continuous exposure to 0.25 ML.
7* These recommendations are based on the assumption of a linear,
non-threshold dose-effect relationship. The lack of definitive
information precludes allowances for possible differences in radio-
sensitivity due to age, sex, or other biological characteristics.
8. No action is indicated when the external gamma exposure rate is
less than 0.05 mR/hr and the radon daughter product activity is less
than 0.01 WL since under conditions of continuous exposure these
levels would result in maximum annual exposures of approximately
400 mrem and 0.5 CULM, respectively. The maximum annual value of
400 mrem is less than the dose limits recommenced for an individual
member of the general public by the FRC (4) and ICRP (5) for whole
body exposure to external gamma irradiation.
The ICRP (5) recommends that the annual dose limit for members of
the public shall be 1/10 of the corresponding annual occupational
maximum permissible dose. The maximum annual value of 0.5 CWLM of
radon daughter product exposure is approximately 1/10 of the 4 CWLM
annual occupational exposure limit recommended by the FRC (6) for
implementation on 1 January 1971, and less than 1/20 of the annual
occupational exposure limit of 12 CWLM recommended for uranium miners
in the present FRC regulations (4).
9. Remedial action may be suggested in the case of external gair.raa
exposure rates of 0.05-0.10 mR/hr or radon daughter product activ-
ities of 0.01-0.05 WL since under conditions of continuous exposure
-------
these levels would result in maximum annual exposures of approximately
400-900 mrem and 0.5-2.5 CWLM. The upper limit of these ranges
exceeds the strictly applied recommendations of the FRC and ICRP for
exposures of an individual member of the public. However, this
extension seems justified in situations in which unforeseen exposures
have occurred, since as stated by ICRP (5) "in general it will be
appropriate to institute countermeasures only when their social cost
and risk will be less than those resulting from the exposure." It
is further stated by the ICRP (5) that vary low levels of risk are
implied in the dose limits for members of the public and that it is
likely to be of minor consequence to their health if the dose Units
are marginally or even substantially exceeded.
10. Remedial action is indicated at gamma exposures greater than
0.1 mR/hr or at radon daughter product activities greater than
0.05 WL. Under conditions of continuous exposure, these levels
would result in minimum annual exposures of 900 mrem and 2.5 CWLM.
All values above these would indicate the necessity for remedial
action, since at these levels the maximum annual exposures reconner.ded
by the FRC and ICRP for an(individual member of the public is exceeded.
11. With respect to the external gamma irradiation, from the esti-
mates published by ICRP (7), it can be interpolated that the annual
risk of leukemia under conditions of continuous exposure to 500 mrea
per year is an increased incidence of about 10 cases per year per
million persons exposed. The natural annual incidence of leukemia
for all ages is given by ICRP (8) as 10-100 cases per million persons.
-------
With respect to radon daughter product exposures, it has been estimated
by Archer and Lundin (9) that an exposure of 120 CW1.M to a group of
white adult males in the United States appears to approximately
double the normal lung cancer incidence which for this population is
about 2-3 cases per year per 10,000 persons. At an annual exposure
of 2.5 CWLM, 48 years would be required to reach 120 CWLM.
12. It is considered that implementation of these recommendations
for the various exposure ranges would make it highly unlikely that
any serious health effects would result from exposure to radon
daughter products or external gamma irradiation in this particular
situation.
13. It is suggested that remedial action be taken only after an
adequate number of measurements taken under a diversity of temporal
and climatic conditions have clearly established that the average
exposure is in excess of C.I mR/hr or 0.05 WL.
14. It is recognized that some time lapse will be inherent in
establishing that radiation levels in excess of 0.1 mR/hr or 0.05 KL
exist and in instituting corrective measures. However, it is con-
sidered that the additional health risks from continued exposure
over this time period are of lesser consequence than the economic
and social discomfitures of precipitous action.
y-;_Jefese.E. Steinfeld, M.D. / Date / /J
~^3tfrgeon General / / ./ / '
Public Healjeh Service
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References
1. Personal communication, Mr. Robert D. Siek, Colorado State
Department of Health.
2. U. S. Public Health Service Publication No. 494. Control of
Radon and Daughters in Uranium Mines and Calculations on
Biologic Effects, 1957.
3. Federal Radiation Council Report No. 8 Revised. Guidance for
the Control of Radiation Hazards in Uranium Mining, 1967.
4. Federal Radiation Council Report No. 1. Background Material for
the Development of Radiation Protection Standards, 1960.
5. Recommendations of the International CoiraiiLssion on Radiological
Protection. ICRP Publication 9 (1966).
6. Federal Register, Vol. 34, No..10 pp 576-577 (1969).
7. The Evaluation of Risks from Radiation. ICRP Publication 8 (1966)
8. Radiosensitivity and Spatial Distribution of Dose. ICRP Publi-
cation 14 (1969).
9. V. E, Archer and F. E. Lundin, Jr.: Radiogenic Lung Cancer in
Man: Exposure-Effect Relationship, Environmental Research JL,
370-383 (1967).
U.S. GOVERNMENT PRINTING OFFICE: 1975210-810:50
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