USDOE remediation site case study

USDOE remediation site case study

Environment International, Vol. 22, Suppl.1,pp.8243S249,1996 Copyright 01996 Elsevier Science Ltd Printed in the USA. All rights reserved 0160-4120/96...

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Environment International, Vol. 22, Suppl.1,pp.8243S249,1996 Copyright 01996 Elsevier Science Ltd Printed in the USA. All rights reserved 0160-4120/96 $15.00+.00

Pergamon

PI1SO160-4120(96)00114-6

USDOE REMEDIATION

SITE CASE STUDY

Isabel M. Fisenne Environmental USA

Measurements

Laboratory, U.S. Department of Energy, New York, NY 10014-4811,

EI 951 l-359 A4(Received 2 November 1995; accepted 6 December 1995)

The uranium concentration ranges of important pathway matrices for the United States are compared with off- and on-site ranges at the Femald Environmental Management Project (FEMP). Empirically established uranium uptake factors for humans are linked with the National Council on Radiation Protection and Measurements (NCRP) recommendations on limits for exposure of the public to ionizing radiation. The maximum effective dose equivalent (EDE) to the local population is derived from the USDOE interim drinking water guideline and consideration of the inhalation and ingestion pathways for diet and local soils. The maximum effective dose equivalent estimates calculated for the inhalation and ingestion of uranium from local sources in the environs of the FEMP would be considered negligible under the individual risk level (NIRL) concept developed by the NCRP. However, empirical site data and risk modeling based on these data are necessary to meet 01w6 HWW s~i~ttceLIP USDOE mission objectives at FEMP and other remediation sites. copyright

INTRODUCTION releases was one of the first issues addressed by the USDOE. In 1990, the USDOE, Environmental Measurements Laboratory (EML) was tasked with preparing ‘white papers’ on some radionuclides released to the environment from the nuclear complex operations. For uranium, a single site was selected and modeled as a case study to estimate the risk to the public from past releases. The Feeds Materials Production Center, now the Fernald Environmental Management Project (FEMP), located in Fernald, Ohio, was chosen for this study. The facility is in southwest Ohio, some 29 km northwest of Cincinnati. The area of the facility is 425 ha of which the production area occupies 55 ha. There are few residences in the rural area immediately adjacent to the facility. A population of 14 300 resides within 8 km of the site. Further from the plant, there are larger communities and light industry. Cincinnati’s population is

The U.S. Department of Energy (USDOE) and its predecessor, the U.S. Atomic Energy Commission, oversaw as part of their mission the development of facilities for the production of nuclear materials for military and civilian applications. The nuclear complex was largely concerned with the mining, milling, and fabrication of uranium for these applications. The changes in world politics, huge material stockpiles, and heightened environmental concerns of the public caused the USDOE to cease production operations at most of its facilities in the complex. The USDOE mission emphasis was then placed on the remediation of sites to reduce or eliminate the known and documented releases of persistent materials to the environs. These materials could include inorganic, organic, and radioactive materials, either known or perceived to confer a risk to humans and/or the environment. Uranium is a heavy metal and mildly radioactive. As such, the public perception of risk from uranium

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I.M. Fisenne

-450 000 and -2.6 million persons live within SOkm of the FEMP. CHARACTERISTICS URANIUM

AND CONCENTRATIONS

OF

Primordial uranium consists of three isotopes, 238U and 234U from the Uranium Series and235 U from the Actinium Series. The characteristics of naturally-occurring uranium are shown in Table 1 (Browne and Firestone 1986). Table 2 shows the ranges of uranium concentrations in various matrices found within the continental U.S. (NCRP 1984; 1987a) compared to the concentrations on- and off-site at the FEMP (FMPC 1989). In the past, the majority of the uranium analyses were performed fluorimetrically (the mass of uranium and not the activity was measured), and the tabled data are presented here in the reported units. In nature, disequilibrium between 234Uand 238Umay exist due to alpha particle recoil from the decay of 238U which increases the availability of 234U for transport through geological processes. Thus, the 234U/238Uactivity ratio in seawater may reach 1.14, while the activity ratio in fresh waters covers a wide range (~1 to >3). The 234U/238U activity ratio in soils range from 0.6 to 1. Because fluorimetric uranium analyses are performed at the FMPC, the activity ratio of the 234U/238U is not available but may be inferred to approach naturallyoccurring abundances based on two factors. The mix of uranium materials processed at the FMPC over its operational lifetime is nearly that of the natural abundances and some isotopic uranium analyses have been performed which yield values close to the natural abundances. URANIUM

TOXICITY

The toxic effects from uranium exposure are based entirely on its characteristics as a heavy element. Inferential material on radiation effects has been obtained from animal experiments and comparison with human exposures to radium isotopes. Reviews of the uranium literature dealing with experimental studies in animals and humans have been published by Gindler (1973), Tannenbaum (195 l), and Voegtlin and Hodge (1953). All uranium mixtures, natural, depleted or enriched, are considered chemical toxins that may result in nephrotoxic effects. The majority of the uranium deposited in the kidney is removed with a biological halftime (Tb) of 6 d and the remainder with a 1500-d

half-time (ICRP 1979). No permanent effects have been observed in any exposure case. Accidental occupational exposures resulting in urinary uranium concentrations of 2 mg L“ caused transient albuminuria in workers. It has been suggested that damage is avoided at concentrations of ~3 ug g-’ of kidney (Voegtlin and Hodge 1953). OCCUPATIONAL PUBLIC

LIMITS AND LIMITS TO THE

The American Conference of Governmental Industrial Hygienists compiled the occupational exposure limits for the inhalation of uranium (ACGIH 1991), based only on the chemical effects. In contrast, the International Commission on Radiological Protection (ICRP) has developed the annual limit on intake (ALI) for ingestion and inhalation of uranium compounds based solely on the radiation doses received by tissues and organs of the body (ICRP 1979; 1991). The ICRP occupational limits are summarized in Table 3. The ICRP limits are on an annual basis and fully recognize that the chemical toxicity of uranium presents a greater risk to workers than the radiation dose (ICRP 199 1). Only two countries have established intake limits for uranium in drinking water by the public. The Ministry ofNational Health and Welfare set the Canadian limit at 20 ug L-’ of water (Ministry of National Health and Welfare 1978; 1980). The current U.S. Environmental Protection Agency (USEPA) limit is 8 pg L-’ of water (USEPA 1976). The USEPA formed a committee of experts for advice on a revision of the drinking water standard for uranium. The committee recommended a uranium limit in drinking water of 100 pg L-‘, which included a safety factor of 50 to 150 to prevent kidney damage for chronic ingestion of uranium from this source (Wrenn et al. 1987). The USEPA is suggesting an increase in the current limit to 20 pg U L-’ of water based on the potential for carcinogenesis (U.S. Federal Register 1991). The USEPA suggested interim guideline for uranium in drinking water appears overly conservative in light of the ICRP’s AL1 for workers and the recommendations of their own experts. RELEASES TO THE ENVIRONMENT

FROM FMPC

The airborne releases from FMPC are estimated to be between 2 x lo3 and 6 x lo3 kg of soluble uranium. The majority of the material remained on-site and within 1 km off-site. At 1 km, the U concentration in soil is 2.5 times that ofthe background concentration of

3 ug g-‘.

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USDOE remediation site case study

Table 1. Characteristics of natural uranium. Natural abundance

Half-life (vears)

Nuclide

Type of emission

Energies IMeV)

Uranium series 238~

4.438 x IO9

99.2745

Alpha

4.147 (23%), 4.196 (77%)

234~

2.454 x 10’

0.0055

Alpha

4.724 (28%), 4.776 (72%)

7.037 x lo*

0.72

Alpha

4.216 (6%), 4.364 (1 l%), 4.395 (55%), 4.597 (5%), others

Actinium series 235~

1 pg of naturally-occurring

uranium = Ba

Nuclide

% of a-activitv

238~

0.0123

48.25

234~

0.0127

49.5

235~

0.0006

2.25

Total cl-activity 0.0256 Table 2. Uranium concentration ranges for the continental U.S. and FEMP. Continental Matrix

U.S. (NCRP 1984; 1987a) Ranges

Air

0.2 x lo” - 2.4 x 10m5pg mm3

Diet

1.3 - 7.3 pg d-’

Drinking water

0.03 - 10 pg L-1

FEMP (FMPC 1989) Matrix

Range off-site

Ranpe on-site

Air

ND- 1.1 x 10-2pgm-3

ND - 7.0 x 10e2yg rnT3

Diet

Within range listed above

NA

Monitoring

0.1 - 303 pg L-1

0.1 - 23 pg L-’

Surface

0.5 - 2.0 /Jg L-1

0.4 - 1170 pg L-1

Great Miami

0.9 - 4.2 /_g L-’

NA

2 - 9 yg g-’

4 - 105 kg g-’

Water

Soil Notes: ND = not detected NA = not applicable.

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I.M. Fisenne

Table 3. ICRP annual limit on the intake of 238Uby workers. Annual limit of intake Intake

Inhalation

Ingestion

Solubility class

Bq

Soluble - D

9x I04

7.3

Moderately insoluble - W

1 x 104

0.8

Insoluble - Y

6x lo2

0.05

Soluble - D

9x 105

65

Moderately insoluble - W

3x lo6

242

Water for residential and industrial uses is drawn from private wells bored into an underground aquifer. Elevated concentrations of uranium were detected in some off-site wells. Water runoff from the waste storage and production areas infiltrated the aquifer. Most of the storm water runoff has been confined by a retention basin. Hamilton et al. (1994) state that a contaminated groundwater plume with two distinct areas has been identified. The off-site southern plume contains peak concentrations of 450 pg U L-‘. The background concentration in off-site wells near the facility is 1 pg L-‘. Their report is not clear as to whether any residential wells have been identified in excess of the USEPA interim guideline limit. For the purpose of this report, it is assumed that any residential well containing uranium concentrations in excess of the USEPA guideline have been closed for human consumption. This does not exclude the possibility that water from wells with uranium concentrations in excess of the USEPA guideline can be used for agricultural or industrial purposes. ESTIMATION OF URANIUM UPTAKE AND DOSE TO THE PUBLIC

In a non-occupational setting, the major intake route for the naturally-occurring uranium isotopes by humans is ingestion of diet and drinking water. Metabolic balance studies in humans have shown that the major fraction of the ingested uranium isotopes is excreted via the intestine, most probably unabsorbed (Spencer et al. 1990). The results of these metabolic balance studies for long-term chronic uranium intakes indicated that the gastrointestinal uptake of the uranium isotopes from diet is extremely small. Further, about 5% of the uranium in ingested water is absorbed into blood and excreted in urine. Blood is the vehicle for uranium transport and removal from the body organs.

g

With the long-term chronic intake of uranium, the metabolic model describing uranium in blood reduces to: Q=P/C where, Q = amount of uranium in blood (pg); P = input of uranium from GI uptake (pg d-l); C = coefficient for the removal of uranium from the blood by urinary excretion (d-l). Organ burdens of uranium can be estimated from a known daily chronic intake assuming that water is the significant pathway. Uptake factors for uranium in humans have been estimated for lung, liver, kidney, and bone (Spencer et al. 1990). The uptake factor is defined as: pg U kg-’ in tissue/pg U d-’ in water and the estimates for these soft tissues and bone at steady-state conditions (chronic intake) are: Lung

Liver

Kidney

Bone

4.9

2.0

4.3

24

These factors and alpha radiation dose factors (Fisenne et al. 1988) can then be linked with the National Council on Radiation Protection and Measurements (NCRP) recommendations on limits for exposure of the public to ionizing radiation (NCRP 1987b; 1993) to derive guidelines for the maximum intake of uranium. NCRP RECOMMENDATIONS FOR PUBLIC EXPOSURES TO IONIZING RADIATION (1987b; 1993) The NCRP recommendations

exposures are:

for non-occupational

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USDOE remediation site case study

Table 4. Maximum

EDE from drinking water.

Dose factor (mSv y-l per

pg U d-’

Tissue-weighting

EDE at DOE

Tissue

in water)

factor (W,)

guideline (mSv y-r)*

Lung (pulmonary)

5.3 x 10-z

0.06

0.32

Liver

2.2 x 10-z

0.05

0.1

Kidney

4.7 x 1w2

0.05

0.22

Bone

2.7 x 1O-2

0.01

0.08

Total

0.8 mSv y-’

* The estimated EDE is based on an assumed water consumption of 1.4 L d-‘, and a uranium concentration of 75 pg L-’ of drinking water.

1) Effective dose equivalent (EDE) limit, continuous or frequent exposure: 1 mSv ye’ (0.1 rem y-l); 2) EDE limit, infrequent exposure: 5 mSv y-’ (0.5 rem y-l); 3) Remedial action recommended when: >5 mSv y-’ (>0.5 rem y-l). Recommendations 1 and 2 are the sum of external and internal exposures exclusive of natural background and medical exposures. Recommendation 3 includes natural background but excludes internal and medical exposures. MAXIMUM TRATIONS

EDE AT USDOE

GUIDELINE

CONCEN-

The EDEs for the three soft tissues and bone have been calculated for the USDOE interim drinking water guideline (45 to 75 ug U L-l), operable in 1990, using a water consumption of 1.4 L d-‘, the tissue uptake factors (Spencer et al. 1990), and the tissue weighting factors (NCRP 1993). Using the higher uranium concentration in water would yield an intake of 100 pg U d-’ from water (Table 4). The EDE values calculated in Table 4 are for the USDOE guideline limit and are not based on measured concentrations of uranium in private wells. For the USEPA interim guideline of 20 pg U L-‘, both the ingestion estimate and the EDE would be reduced by a factor of 3.8. In terms of the nephrotoxic limit of 13 ug g-‘, a steady-state intake of 100 pg U d-’ would result in a kidney concentration of 15% of the limit. The uranium concentration in the kidney, based on the USEPA interim guideline, would represent -4% of the nephro-

toxic limit. There may be other modifying conditions, including a reduction in the tissue uptake factors for high concentrations of uranium, particularly in the case of acute ingestion (Wrenn et al. 1988). The NCRP states: “A maximum annual EDE limit of 5 mSv (0.5 rem) is recommended to provide for infrequent annual exposures (NCRP 1987b; 1993). This recommendation is made because annual exposures in excess of this limit, to a small group of people, need not be regarded as especially hazardous, provided they do not occur often to the same groups.” The inhalation and ingestion routes for the intake of uranium from local soils have also been considered following the guidance given in NCRP Report No. 116 (NCRP 1993). Considering the uranium in air at the maximum of the USDOE guideline, 0.14 pg U rnT3of air (100 x lo-l5 pCi mL-‘), a dust loading of 200 ug mm3would imply local soil concentrations >700 ug U g-’. This is nearly a factor of 100 greater than the off-site soil concentrations of uranium within 1 km of the facility. As a more realistic but conservative approach, it is assumed that the soil concentration is 7 pg U g-’ of soil, and the particulate concentration is 200 pg me3 of air, resulting in an air concentration of 0.035 pg U mm3.Again as a conservative measure, the uranium was assumed to be Class Y (retained for years; the majority is more probably Class W, retained for weeks). For the chronic inhalation situation, the pulmonary lung EDE estimate would be co.005 mSv y-l. For the dietary intake, it is assumed local vegetable, fruits, and milk are the important pathways for increased ingestion of uranium. Hamilton et al. (1994) performed

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I.M. Fisenne

pathway analyses for these food items assuming irrigation with the groundwater. No numerical information was given in that report. In the present report, it was assumed that the fruits, vegetables, grass, and silage for the dairy animals was grown in soil irrigated with the highest off-site concentration, 450 ug U L“. It was also assumed that this concentration of uranium filled the entire soil pore space and was available for root uptake. The NCRP states that: “Plants take up the radionuclides in soil water, but are selective in so doing” (NCRP 1984). The closest approximation of these conditions were a set of greenhouse experiments in which tobacco plants were grown in soil containing a known, added amount of *l’Pb (Tso and Fisenne 1968). Nearly 98% of the *“Pb remained in the soil, ~1.5% was found in the roots, and 10.5% was found in the stem and leaves. Combining these percentages with the assumed equilibriumuraniumconcentration in soil water and the consumption of the food products mentioned above, the estimated dietarv intake of uranium would be double the measured value of 1.2 pg de1 for the standard U.S. diet (Fisenne et al. 1987). The sum of the EDE for the lung, liver, kidney, and bone surfaces due to the increased dietary intake would be
CONCLUSIONS

The EDE estimates presented were intended as a worst-case scenario for the exposure of the public at a specific restoration site. The estimates maximizing present exposure conditions lead to risk estimates of a fatal cancer which are small. The estimates derived here are only for uranium and for an adult population. They do not include possible additional exposures from other radionuclides released into the environment. The most important route of exposure to uranium would be through drinking water obtained from wells in the aquifer. Some off-site contamination of the aquifer has occurred, but additional uranium contamination is unlikely.

REFERENCES

d

THE NEGLIGIBLE

INDIVIDUAL

RISK LEVEL (NIRL)

The maximal EDE estimates for inhalation and ingestion intakes from water- and soil-derived uranium should be considered under the negligible individual risk level (NIRL) concept. This concept, introduced by the NCRP in 1987, offered a criterion for assessing exposures to the public, exclusive of natural background and medical exposures in terms of practical risk management. “A NIRL is defined as a level of average annual excess risk of fatal health effects attributable to irradiation, below which further effort to reduce radiation exposure to the individual is unwarranted. The NIRL is regarded as trivial compared to the risk of fatality associated with ordinary, normal societal activities and can, therefore, be dismissed from consideration” (NCRP 1987b; 1993). As noted above, the NCRP recommendation for continuous or frequent exposure to the public is an EDE limit of 1 mSv y-’. Summing the EDEs calculated for the inhalation and ingestion of uranium at maximized or quideline concentrations yields ~1 mSv y-‘. This emphasizes the assertion that the principal hazard from natural uranium is derived from its characteristics as a heavy metal.

ACGIH (American Conference of Governmental Industrial Hygienists). Guide to occupational exposure values-1991. 117. Cincinnati, OH: ACGIH; 1991. Brown, E.; Firestone, R.B., eds. In: Table of radioactive isotopes. New York, NY: John Wiley & Sons; 1986. Fisenne, I.M.; Perry, P.M.; Decker, K.M.; Keller, H.W. The daily intake of 234,235,23sU,228.230.232Thand 226,22aRa by New York City residents. Health Phys. 53: 127-l 3 1; 1987: Fisenne, I.M.; Perry, P.M.; Harley, N.H. Uranium in humans. Radiat. Prot. Dosim. 24: 127-131; 1988. FMPC (Feed Materials Production Center). Environmental monitoring annual report for 1988. FMPC Restoration Department Renort FMPC-2173: 1989. Femald. OH: FMPC Gindler, J.E. In: Hodge, H.C. Jr.; Stannard, N.; Hursh, J.B., eds. Handbook of experimental pharmacology: Uranium, plutonium, transplutonic elements. Chapter 2. Heidelberg, Germany: Springer-Verlag; 1973. Hamilton, L.D.; Holtzman, S.; Meinhold, A.F.; Morris, S.C.; Pardi, R.; Rowe, M.D.; Sun, C.; Anspaugh, L.R.; Bogen, K.T.; Daniels, J.I.; Layton, D.W.; McKone, T.E.; Straume, T.; Andricevic, R.; Jacobson, R.L. Pilot study risk assessment for selected problems at three U.S. Department of Energy facilities. Environ. Int. 20: 585-604; 1994. ICRP (International Commission on Radiological Protection). Annual limits on intake of radionuclides by workers based on the 1990 recommendations. ICRP Publ. 61. Oxford, UK: Pergamon Press; 1991. ICRP (International Commission on Radiological Protection). Limits for intakes of radionuclides by workers. ICRP PubI. 30. Part 1. Annals of the ICRP, 2, 102. Oxford, UK: Pergamon Press; 1979. Ministry ofNational Health and Welfare. Guidelines for Canadian drinking water quality. Ottawa, Canada: Health and Welfare; 1978. Ministry of National Health and Welfare. Guidelines for Canadian drinking water quality, update. Ottawa, Canada: Health and Welfare; 1980.

USDOE remediation site case study

NCRP (National Council on Radiation Protection and Measurements). Exposures from the uranium series with emphasis on radon and its daughters. NCRP Report No. 77. Bethesda, MD: NCRP; 1984. NCRP (National Council on Radiation Protection and Measurements). Exposure of the population in the United States and Canada from natural background radiation. NCRP Report No. 94. Bethesda, MD: NCRP; 1987a. NCRP (National Council on Radiation Protection and Measurements). Recommendations on limits for exposure to ionizing radiation. NCRP Report No. 91. Bethesda, MD: NCRP; 198713. NCRP (National Council on Radiation Protection and Measurements). Limitation of exposure to ionizing radiation. NCRP Report No. I 16. Bethesda, MD: NCRP; 1993. Spencer, H.; Osis, D.; Fisenne, I.M.; Perry, P.M.; Harley, N.H. Measured intake and excretion patterns of naturally occurring 234U 238U and calcium in humans. Radiat. Res.124: 90-95; 199;. Tannenbaum, A., ed. Toxicology of uranium. In: National nuclear energy series. New York, NY: McGraw-Hill; 1951.

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Tso, T.C.; Fisenne, I.M. Translocation and distribution of lead-210 and polonium-210 supplied to tobacco plants. Radiat. Botany 8: 457-462; 1968. USEPA (United States Environmental Protection Agency). National interim primary drinking water regulations. Report No. EPA570/9-76-093. Washington, D.C.: USEPA Office of Water Supply; 1976. U.S. Federal Register. 56: 33050; 1991. Voegtlin, C.; Hodge, H.C., eds. The pharmacology and toxicology of uranium compounds. Chapter 26. National nuclear energy series. New York, NY: McGraw-Hill; 1953. Wrenn, M.E.; Durbin, P.W.; Willis, D.L; Singh, N.P. The potential toxicity of uranium in water. J. Am. Water Works Assoc. 79: 177-184; 1987. Wrenn, M.E.; Singh, N.P.; Ruth, H.; Burleigh, D. Gastrointestional absorption of soluble uranium from drinking water. In: Proc. seventh international congress of the International Radiation Protection Association, Sydney, Australia. Vol. I.: 195-198; 1988. Sydney: Pergamon Press; 1988.