Actinides in Deer Tissues at the Rocky Flats Environmental Technology Site 

Andrew Todd, M.S., U.S. Fish and Wildlife Service 

Mark Sattelberg, M.S., U.S. Fish and Wildlife Service 

Introduction

The Rocky Flats Environmental Technology Site (Rocky Flats), operated by the U.S. 

Department of Energy (DOE), is a former nuclear weapons research, development, and 

production facility located northwest of Denver, Colorado, USA. Historical site activities 

included the fabrication of components for nuclear weapons from plutonium, uranium, 

beryllium, and stainless steel, and support activities included chemical recovery and 

purification of recyclable transuranic actinides. In 1992, the mission of the Rocky Flats 

site changed from weapons production to environmental cleanup and closure. Cleanup 

and remediation is being completed by the DOE under oversight by the U.S. 

Environmental Protection Agency (EPA) and the Colorado Department of Public Health 

and Environment (CDPHE). 

By mandate of the Rocky Flats National Wildlife Refuge Act of 2001 (P.L. 107-107), at 

site closure, portions of the site will become the Rocky Flats National Wildlife Refuge to 

be managed by the U.S. Fish and Wildlife Service (Service). Transfer of property is 

contingent on EPA certification that cleanup and closure activities have been completed, 

and that all monitoring and maintenance activities are operating properly and 

successfully. 
The majority of the Rocky Flats site has remained undisturbed since its acquisition by the 

Federal Government and provides habitat for many wildlife species, including abundant 

populations of mule and white-tailed deer, and seasonal populations of elk [1]. 

According to the National Wildlife Refuge System Improvement Act of 1997 (P.L. 105-

57), hunting is one of six wildlife-dependent priority public uses that must receive 

enhanced consideration in Service Refuge planning and management. Given that Rocky 

Flats ungulates have had access to actinide-contaminated areas [2], measurements of 

actinides in a range of tissues were needed to provide important information regarding 

potential human consumption risks, and resultant compatibility of incorporating hunting 

as a recreational use on the Refuge. 

The Service conducted this study to determine concentrations of selected actinides in 

relevant Rocky Flats ungulate tissues. Further, these analytical results were used to carry 

out a series of conservative, risk-based calculations to define human risk associated with 

ingesting these tissues. 

Methods

Study Area 

The Rocky Flats Environmental Technology Site is a 6,240-acre property located 

approximately 16 miles northwest of Denver, Colorado, and is bordered by Boulder, 

Broomfield, and Jefferson counties (Figure 1). Vegetation communities at Rocky Flats 

include unique xeric tallgrass prairie and tall upland shrubland, along with riparian 
woodland, riparian shrubland, wetlands, mesic mixed grassland, xeric needle and thread 

grassland, reclaimed mixed grassland and ponderosa pine woodland [3]. 

Field Collection 

Deer tissues were collected on the Rocky Flats site on December 8th, 2002, during a 

Chronic Wasting Disease (CWD) study conducted by the Colorado Division of Wildlife. 

Twenty-six resident deer were culled to test for CWD, and at this time, USFWS 

biologists and one Rocky Flats ecologist harvested lung, liver, kidney, muscle and bone 

tissues from the carcasses. Control tissue samples were obtained on February 4th, 2004 

from a mule deer killed by a vehicle at the Rocky Mountain Arsenal National Wildlife 

Refuge (RMA). All tissues were rinsed with distilled water to remove any surface 

contamination, and were subsequently individually weighed, labeled, and double bagged. 

Bulk tissues remained frozen in a secure, sealed freezer (-10°C) at the RMA until July 6th, 

2004 at which point sub-samples were processed, packaged in ice, and shipped overnight 

to General Engineering Laboratories (GEL) in Charleston, SC for laboratory analyses. 

Additional sub-samples were re-sent on July 21st, 2004 due to laboratory error. 

Actinide Analyses 

As the primary edible portions of the deer, all muscle and liver tissues were analyzed for 

all actinide isotopes of concern (241Am, 238Pu, 239,240Pu, 233,234U, 235,236U and 238U). A 

subset of harvested lung, kidney, and bone tissues were analyzed for select actinides to 

obtain information regarding relative accumulation in non-edible tissues. In total, 90 

tissue samples were analyzed for Plutonium isotopes; 27 muscle, 27 liver, 6 kidney 
(composite), 15 lung, and 15 bone samples. Seventy-five sets of Americium isotopic 

analyses were completed; 27 muscle, 27 liver, 6 kidney (composite), and 15 lung 

samples. Uranium analyses were conducted on 75 samples; 27 muscle, 27 liver, 6 kidney 

(composite), and 15 lung samples. 

Analytical methodology was derived from a source method from the U.S. Department of 

Homeland Security Environmental Measurements Laboratory Methods Manual HASL 

300 U-04-RC, and uses similar principles of radiochemical separation and counting [4]. 

All samples were digested, if necessary, and aliquoted. Transuranic elements were 

scavenged by co-precipitation with iron hydroxide, and the resultant precipitates were 

dissolved, and separation of elements was accomplished through the use of extraction 

chromatography and ion exchange resins. Elements were then prepared for measurement 

of radioactive isotopes by co-precipitation with Neodymium fluoride. Neodymium 

fluoride precipitates were trapped on filters, mounted on stainless steel disks and placed 

in a partially evacuated chamber for the measurement of isotopic alpha emissions. 

These analyses were performed according to GEL method-specific quality control 

requirements, including proper instrument calibration, and the use of method blanks, 

matrix spikes, sample duplicates, and tracer recovery. 

Detection limits for analyses were needed that were lower than standard soil and water 

radiochemistry methods, in order to detect actinide concentrations typical of tissue 
samples. To reach these levels, the laboratory used large sample sizes and longer count 

times. Calculations used to determine appropriate detection limits are presented below. 

Calculation of reportable limits based on potential human risks

In order to assure that detection limits were set sufficiently low to detect tissue 

concentrations of potential human concern via an ingestion pathway, the following 

calculations were carried out for each actinide isotope: 

(1 ) (1) ( ) Risk Coefficient Sv

Risk Level Effective Dose Equivalent Sv = 

( )

( ) (2) ( ) −1 ⋅ = Effective Dose Equivalent Unit Intake Sv BqEffective Dose Equivalent Sv Radioactivity Bq

Bq

pCi

g

kg

Edible Tissue Mass kg

Radioactivity Bq Tissue Concentration pCi g 1

27

1000

1

( )

( ) (3) ( )

1 ⋅ = × × −

Input values and resultant dose calculations are presented in Table 1. 

Following these calculations, maximum detection limits required for analytical analyses 

were established as follows: Isotopic Americium, 0.001 pCi/g; Isotopic Plutonium, 0.002 

pCi/g; Isotopic Uranium, 0.02 pCi/g. These calculated values also serve as Report 

Thresholds (RT) for this study (Table 3). 
Results

Contaminant analyses 

In total, of the more than 450 individual isotopic analyses that were conducted on Rocky 

Flats deer tissue samples, 17 resulted in actinide concentrations measured above method 

detection limits (Table 2). 

241Am was detected in select lung, muscle, and kidney tissues of Rocky Flats deer, and 

was also detected in kidney and liver tissues of the control deer from the Rocky Mountain 

Arsenal. Both measured isotopes of plutonium (238Pu and 239,240Pu) were detected only in 

select bone samples from Rocky Flats deer. Uranium isotopes (233,234U, 235,236U and 238U) 

were detected in select liver and muscle samples of Rocky Flats deer, and were also 

detected in liver tissue of the control deer. 

Radiological Risk Assessment

In order to predict potential radiological risk resulting from ingestion of edible deer 

tissues from Rocky Flats, a highly conservative estimate of risk was conducted. 

Uncertainty values were calculated as a function of counting efficiency error, peak area 

error, isotopic abundance error, systematic error and sample calculated activity. Samples 

which yielded detectable quantities of any radioisotope were organized (Table 3), and 

experimental uncertainty values were added to measured results to produce a high-end 

estimate of tissue concentration. These values were compared with calculated report 

thresholds. Out of a total of 454 isotopic analyses, two (2) yielded detectable 
concentrations of an actinide isotope of concern that, with the uncertainty value added, 

exceeded the pre-calculated report threshold (Table 3). 

All liver and muscle tissues which yielded detects were utilized to back-calculate risk 

values associated with the ingestion of these tissues. As detailed above, uncertainty 

values were added to reported detection values to give a high-end estimate of tissue 

actinide concentrations. Bone, lung, and kidney tissues were not included in this analysis 

because they are not considered edible tissues for the purposes of this study. The same 

calculations that were used in the methods for setting detection limits were utilized in this 

analysis. A value of 2.3 kg was used as an approximate weight of edible organ meat 

(liver) from a 60 kg deer, while a value of 28 kg was utilized for the edible weight of 

muscle tissues. On the basis of these conservative assumptions, the actinide risk 

associated with consuming the edible organ meats of an adult deer on Rocky Flats is 

presented in Table 3. The highest risk calculated in this exercise was attributable to 

241Am in the muscle tissue of deer 38-189-53, with tissue concentrations translating to a 

6.76 x 10-8 risk level. This level of risk corresponds with a 1:14,700,000 increased 

chance of cancer resulting from ingestion of 28 kg of muscle tissue. If this same 

individual consumed this same amount of deer tissue yearly, throughout his / her lifetime 

(70 yr), this would result in a 4.73 x 10-6 risk level, or a 1:210,000 increased chance of 

cancer. This risk level falls within the U.S. EPA’s acceptable risk range of 1x10-4 and 

1x10-6 [5]. 
Discussion / Conclusions

The extremely low levels of actinides present in ungulate tissues at Rocky Flats are likely 

the result of low levels across a majority of the site’s surface soils, very low soil to plant 

actinide transfer rates [6,7], and low gastrointestinal adsorption rates [8]. Though 

actinide specific, terrestrial animal assimilation of actinides from the gastrointestinal tract 

is assumed to be less than 0.01% [9]. 

Historical studies of actinide levels in deer tissues at Rocky Flats, although limited in 

both number and scope, have yielded similar results to those detailed in this study. The 

findings from these studies are presented in Table 4. In summary, plutonium analyses 

conducted on tissues from eight (8) Rocky Flats Region deer demonstrated tissue 

plutonium (238Pu and 239,240Pu) concentrations near or below detection limits [10]. 

Similarly, a total of 12 tissue samples from Rocky Flats deer were analyzed for 

plutonium isotopes in 1992, and all tissues had activities below detection limits [2]. 

The risk levels presented in Table 3 are the result of highly conservative assumptions and 

calculations, and as such, likely overestimate the risk associated with ingestion of Rocky 

Flats deer tissues. For instance, a hunting program at the future Rocky Flats National 

Wildlife Refuge would be highly controlled, limiting take of animals to a few weekends, 

and a few individuals, per year [3]. Further, estimates of the consumable mass of an 

average deer used in this study are higher than predicted in comprehensive investigations 

of mule deer carcasses [11]. Finally, as analytical results are only slightly higher than 

detection limits, it is probable that several could be considered non-detects, given the 
equal magnitude of the uncertainty. The control samples in this study qualitatively 

support this possibility, as tissues obtained from a site not contaminated with actinides 

yield detectable concentrations of select actinides of the same magnitude as samples from 

the Rocky Flats site (Table 2). Analysis of control samples in a historical study of Rocky 

Flats deer tissue actinide concentrations demonstrated similar results, with 2 of 9 tissue 

analyses indicating detectable concentrations of Pu239,240 in deer from uncontaminated 

regions (Table 4). The uptake of background concentrations of actinides stemming from 

fallout deposition following weapons testing could serve as an alternative explanation for 

the presence of detectable concentrations of actinides in off-site deer [12]. 

As presented, these risk levels are functional as indicators of maximum risk likely to 

result from human consumption of deer tissues from the Rocky Flats site under future 

management scenarios. Cleanup activities at Rocky Flats will continue until Site closure, 

at which point all surface soils will meet stringent, human-risk-based standards, as 

specified in the Final Rocky Flats Cleanup Agreement of 1996. As the cleanup at Rocky 

Flats concludes, levels of actinides in deer tissues may decrease, as contaminated surface 

soils will have been removed, resulting in fewer actinides available on the exterior 

surfaces of plants and/or assimilated into the plant itself. 

Acknowledgements

Support for this work was provided through an inter-agency agreement (DE-AI34-

02RFO2046) with the U.S. Department of Energy. We would like to thank Ward 

Whicker for his insight and comments on earlier drafts of this manuscript. We are also 
grateful to Michael Wedermyer and the Colorado Division of Wildlife for their support in 

the collection of tissue samples. 
Bibliography: 

1. Kaiser-Hill, LLC, 2001. Annual Wildlife Survey for the Rocky Flats Environmental 

Technology Site. Golden, CO. 

2. Symonds, K.K. and A.W. Alldredge, 1992. Deer Ecology Studies at Rocky Flats, 

Colorado: 1992 Progress Report. Colorado State University, Fort Collins, CO. 

3. U.S. Fish and Wildlife Service, 2004. Rocky Flats National Wildlife RefugeComprehensive Conservation Plan and Environmental Impact Statement. 

4. U.S. Department of Homeland Security, 1997. Environmental Measurements 

Laboratory Methods Manual HASL-300-U-04-RC, 28th edition. 

5. U.S. Environmental Protection Agency, 1991. Role of the Baseline Risk Assessment 

in Superfund Remedy Selection Decisions. OSWER Directive 9355.0-30. Memorandum 

from Don Clay to Regional Division Directors. 

6. U.S. Environmental Protection Agency, 1979. Plutonium-239 and Americium-241 

Uptake by Plants From Soil. Las Vegas, NV: U.S. Environmental Protection Agency, 

EPA-600/3-79-026. 

7. Hinton, T.G. and J.E. Pinder, III, 2001. Plutonium in the Environment. A. Kudo, 

Editor. Elsevier Science Ltd. Pp. 413-435. 

8. Agency for Toxic Substances and Disease Registry, 1990. Toxicological profile for 

plutonium. Atlanta, GA: U.S. Department of Health and Human Services, Public Health 

Service. 

9. Whicker, F.W. and V. Schultz, 1982. Radioecology: nuclear energy and the 

environment. CRC Press, Inc., Boca Raton, FL. 

10. Hiatt, G.S. 1977. Plutonium dispersal by mule deer at Rocky Flats, Colorado 

[masters’ thesis]. Fort Collins, CO, USA: Colorado State University. 

11. Field, R.A. et. al., 2003. The Mule Deer Carcass. University of Wyoming, 

Agricultural Experiment Station, B-589R. 

12. Hardy, E.P. et. al., 1973. Global inventory and distribution of fallout plutonium. 

Nature (241), pp. 444-445. 

13. ICRP. 1992. 1990 recommendations of The International Commission on 

Radiological Protection. Pergamon Press, Oxford, UK. 
14. U.S. Environmental Protection Agency, 1988. Limiting Values of Actinide Intake 

and Air Concentration and Dose Conversion Factors for Inhalation, Submersion, and 

Ingestion. Federal Guidance Report No. 11. Washington, DC: U.S. Environmental 

Protection Agency, EPA-520/1-88-020.
Figure 1: Location of the future Rocky Flats National Wildlife Refuge and 

surrounding communities. 

Table 1: Calculation of tissue actinide concentrations necessary for a 10-6 additional 

cancer risk, following human ingestion of all edible tissues from an average sized 

Rocky Flats deer. Detection limits are set approximately an order of magnitude 

lower than this calculated value. 

Isotope 

Risk 

Level 

Risk 

Coefficient* 

(1/Sv) 

EDE per unit 

intake** 

(Sv · Bq-1) 

Edible 

Tissue *** 

(kg) 

Dose 

Calculation 

(pCi · g-1) 

Detection 

Limit 

(pCi · g-1) 

239Pu 1 x 10-6 0.073 9.56 x 10-7 30.3 0.0128 0.002 

241Am 1 x 10-6 0.073 9.84 x 10-7 30.3 0.0124 0.001 

234U 1 x 10-6 0.073 7.66 x 10-8 30.3 0.1594 0.02 

238U 1 x 10-6 0.073 6.88 x 10-8 30.3 0.1774 0.02 

* The Risk Coefficient is needed to convert risk to effective dose. Value obtained from 1990 

recommendations of the International Commission on Radiological Protection [13]. 

** The sum of the effective dose equivalents to various tissues of the body, each multiplied by its 

weighting factor. Effective dose equivalent per unit intake provides an estimate of the lifetime radiation 

dose to an individual from radioactive material taken into the body through either inhalation or ingestion 

[14]. Values in the table are based on the most conservative, gastrointestinal absorption assumptions. 

*** An average deer was assumed to weigh 60 kg, of which approximately 28 kg is edible muscle tissue 

and 2.3 kg is edible organ meat (liver).
Table 2: Comparison of measured concentrations of 241Am, 238Pu, 239,240Pu, 233,234U, 235,236U and 238U in lung, liver, muscle, bone and 

kidney tissues of deer sampled at Rocky Flats and the Rocky Mountain Arsenal NWR (control). Data are expressed as pCi/g wet 

tissue. The reported mean value is calculated as the arithmetic mean of all detects for a specific isotope within that tissue.

241Am 238Pu 239,240Pu 233,234U 235,236U 238U 

Tissue Statistic RF Control RF Control RF Control RF Control RF Control RF Control 

Lung Mean 0.000358 Bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl 

 n 2/14 0/1 0/14 0/1 0/14 0/1 0/14 0/1 0/14 0/1 0/14 0/1  Max 0.000468 Bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl 

Liver Mean bdl 0.000384 bdl bdl bdl bdl 0.00673 bdl 0.00218 0.00192 bdl bdl 

 n 0/26 1/1 0/26 0/1 0/26 0/1 3/26 0/1 1/26 1/1 0/26 0/1  Max bdl 0.000384 bdl bdl bdl bdl 0.0125 bdl 0.00218 0.00192 bdl bdl 

Muscle Mean 0.000307 Bdl bdl bdl bdl bdl 0.0033 bdl bdl bdl 0.00409 bdl 

 n 4/26 0/1 0/26 0/1 0/26 0/1 1/26 0/1 0/26 0/1 1/26 0/1  Max 0.000458 Bdl bdl bdl bdl bdl 0.0033 bdl bdl bdl 0.00409 bdl 

Bone Mean n/a n/a 0.000623 bdl 0.000624 bdl n/a n/a n/a n/a n/a n/a 

 n n/a n/a 2/14 0/1 2/14 0/1 n/a n/a n/a n/a n/a n/a  Max n/a n/a 0.000642 bdl 0.000773 bdl n/a n/a n/a n/a n/a n/a 

Kidney Mean 0.000983 0.000252 bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl 

 n 1/5 1/1 0/5 0/1 0/5 0/1 0/4 0/1 0/4 0/1 0/4 0/1  Max 0.000983 0.000252 bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl 

n = number of detects / total number of samples analyzed bdl = below detection limits n/a = not analyzed 
Table 3: Comparison of Rocky Flats deer tissue samples having actinides measurements above detection limits with calculated 

Report Thresholds.

Deer ID Tissue 

Type 

Actinide 

Isotope 

Result 

(pCi/g) 

Uncertainty 

(pCi/g) 

Result + Uncert. 

(pCi/g) 

RT 

(pCi/g) 

Above 

RT? 

Calculated 

Risk Level 

Rocky Flats Tissues 

38-189-34 Bone Pu-238 0.000603 0.000682 0.001285 0.002 No --- 38-189-39 Bone Pu-238 0.000642 0.000629 0.001271 0.002 No --- 38-189-39 Bone Pu-239,240 0.000475 0.000538 0.001013 0.002 No --- 38-189-44 Bone Pu-239,240 0.000773 0.000678 0.001451 0.002 No --- 38-189-39 Lung Am-241 0.000468 0.000375 0.000843 0.001 No --- 38-189-40 Lung Am-241 0.000247 0.000280 0.000527 0.001 No --- 

38-189-K5* Kidney Am-241 0.000983 0.000574 0.001557 0.001 Yes --- 

38-189-31** Liver U-233,234 0.00302 0.00224 0.00526 0.020 No 2.51 x 10-938-189-32** Liver U-233,234 0.00469 0.00261 0.0073 0.020 No 3.48 x 10-9

38-189-52 Liver U-233,234 0.0125 0.00926 0.02176 0.020 Yes 1.04 x 10-838-189-54 Liver U-235,236 0.00218 0.00191 0.00409 0.020 No 1.83 x 10-938-189-48 Muscle Am-241 0.000244 0.000276 0.00052 0.001 No 3.87 x 10-838-189-49 Muscle Am-241 0.000258 0.000292 0.00055 0.001 No 4.10 x 10-838-189-50 Muscle Am-241 0.000267 0.000302 0.000569 0.001 No 4.24 x 10-838-189-53 Muscle Am-241 0.000458 0.000449 0.000907 0.001 No 6.76 x 10-838-189-41 Muscle U-233,234 0.00330 0.00374 0.00704 0.020 No 4.08 x 10-838-189-34 Muscle U-238 0.00409 0.00400 0.00809 0.020 No 4.21 x 10-8

Control Tissue 

38-189-K6 Kidney Am-241 0.000252 0.000285 0.000537 0.001 No --- 

38-189-60 Liver Am-241 0.000384 0.000435 0.000819 0.001 No 5.01 x 10-9 38-189-60 Liver U-235,236 0.00192 0.00188 0.0038 0.02 No 1.70 x 10-9 

* Kidney sample 38-189-K5 is a composite sample, with kidney samples from deer 38-189-44, 38-189-45, 38-189-48, 38-189-49, and 38-189-54. 

**Tissues were involved in a laboratory fire during the ashing process, therefore, the reported values should be considered estimates of concentration. 

The other two samples involved in the fire (38-189-47 and 38-189-53) were non-detects. 
Table 4: Historical measurements of actinide concentrations in Rocky Flats deer tissue 

samples. 

Study Tissue Actinide n* Max (pCi · g-1) 

Pu-238 1/7 0.0146 Lung Pu-239,240 5/7 0.0150 

Pu-238 0/6 bdl** Liver Pu-239,240 0/6 bdl** 

Bone Pu-238 0/7 bdl** 

(metacarpal) Pu-239,240 1/7 0.0150 

Pu-238 0/1 bdl** Muscle Pu-239,240 0/1 bdl** 

Pu-238 0/9 bdl** 

Hiatt, 1977 

Control*** Pu-239,240 2/9 0.0191 (liver) 

Pu-238 0/3 bdl** Lung Pu-239,240 0/3 bdl** 

Pu-238 0/4 bdl** Liver Pu-239,240 0/4 bdl** 

Pu-238 0/4 bdl** 

Symonds, 1992 

Bone (Rib) Pu-239,240 0/4 bdl** 

*- n = number of detects / total number of samples analyzed 

**- bdl = below detection limits 

***- Control tissues in this study were sampled from 1 lung, 3 livers, and 5 bones from 5 control deer 

outside of the Rocky Flats area. Detects occurred in the liver tissue sample of deer C1, and in the 

bone tissue sample of deer C4.