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PUBLIC HEALTH CONSULTATION

Y-12 WEAPONS PLANT CHEMICAL RELEASES INTO EAST FORK POPLAR CREEK
OAK RIDGE, TENNESSEE


BACKGROUND AND STATEMENT OF ISSUES

The U.S. Department of Energy (DOE) requested that the Agency for Toxic Substances and Disease Registry (ATSDR) address health-related issues associated with the Y-12 Weapons Plant at the Oak Ridge Reservation. Specifically, ATSDR was asked to comment on the health threat posed by past and present chemical releases, primarily mercury and polychlorinated biphenyls (PCBs), from the Y-12 Weapons Plant, which have contaminated East Fork Poplar Creek.

The Oak Ridge Reservation is a U.S. DOE research, development, and production facility that began operating in Oak Ridge, Tennessee, in 1943 [1]. Originally, it was part of the Manhattan Project; one of its primary missions was to separate uranium-235 (235U) from other isotopes of uranium (i.e.,234U and 238U) for production of nuclear weapons materials. The Oak Ridge Reservation is on 37,000 acres of federally owned land. The site is partially fenced; access is further restricted by 24-hour, on-site security guards. The Oak Ridge Reservation consists of three major operating facilities: the Y-12 Weapons Plant, the Gaseous Diffusion Plant (K-25), and the Oak Ridge National Laboratory (X-10). The facilities were built in different valleys and are separated from each other by high ridges, which are considered buffer zones. There is no other buffer zone between the Oak Ridge Reservation and the city of Oak Ridge. The Oak Ridge Reservation is bounded on the north and east by the city of Oak Ridge (population 28,000), and on the south and west by the Clinch River. Portions of the Oak Ridge Reservation are in a flood plain [2]. In 1989, the Oak Ridge Reservation was listed on the U.S. Environmental Protection Agency's Exiting ATSDR Website National Priorities List.

The city of Oak Ridge is in both Anderson and Roane counties and lies in a valley between the Cumberland and southern Appalachian mountain ranges. The city is bordered on the east by the Clinch River [2]. Except for the city of Oak Ridge, land within 5 miles of the Oak Ridge Reservation is predominantly rural, and used for residences, small farms, and cattle pasture. Since 1943, the city gradually has been built around the Oak Ridge Reservation; the nearest residence is about 0.25 mile from the Y-12 Weapons Plant [2].

Between 1950 and 1963, the DOE Y-12 Weapons Plant used mercury in a lithium separation process [3]. In a DOE study conducted in 1983, Oak Ridge officials estimated that 330 metric tons of mercury were released into the environment; of that total, 110 metric tons were lost to the East Fork Poplar Creek [3]. The study concluded that DOE could not account for an additional 750 metric tons of mercury used during that period [3]. Releases of mercury to the creek contaminated instream sediments, and periodic flooding contaminated flood plain soils along the creek. The flood plain width ranges from 5 to 500 meters.

Land uses along the flood plain are residential, commercial, and recreational (schools, baseball diamonds, tennis courts, running tracks). Furthermore, the city of Oak Ridge used creek sediment as fill material on sewer belt lines throughout the city, and residents used the sediment to enrich private gardens [4]. In 1983, the State of Tennessee publicly disclosed that sediment and soil in the flood plain of East Fork Poplar Creek were contaminated with mercury [4]. That same year, an Oak Ridge Task Force was established to collect data and evaluate the long-term public health effects of contamination in the vicinity of Oak Ridge [5]. The task force initiated the remediation of surface and subsurface soils, identified as requiring immediate removal, from public and private lands within the City of Oak Ridge. Remediation of contaminated soil at the Civic Center and junior high school was completed in 1985.

East Fork Poplar Creek originates from within the Y-12 plant boundary. The creek flows through the city of Oak Ridge for about 12 miles before it ultimately converges with Poplar Creek near K-25 [2]. A number of small tributaries flow into the creek. The East Fork Poplar Creek is classified by the State of Tennessee for fishing, recreation, irrigation, livestock watering, and wildlife use [6]. The creek appears to be too shallow for swimming, although some areas, particularly those near the confluence with Poplar Creek, are suitable for wading and fishing. The Tennessee Department of Environment and Conservation issued a fishing advisory for East Fork Poplar Creek that warns the public to avoid eating fish from the creek and to avoid contact with the water [6]. In 1992, some of the advisory signs along the creek were replaced, and additional signs were posted to warn the public about contaminated surface water and fish [7].

Soil, sediment, surface water, and groundwater data from a summary of the East Fork Poplar Creek Remedial Investigation Phase IA were evaluated during development of this health consultation. Environmental samples were collected for DOE by Science Applications International Corporation and Radian Corporation [8]. Samples were analyzed for volatile and semivolatile organic compounds, pesticides, PCBs, metals, and radionuclides (americium-241, cesium-137, cobalt-60, neptunium-237, uranium-234, uranium-235, uranium-238) [8]. Groundwater samples were analyzed for strontium-89, strontium-90, and total radium [8].

Soil samples were taken from three transects across the creek in the National Oceanic & Atmospheric Administration (NOAA), Bruner, and Sturm areas known to be contaminated with mercury [8]. Six locations (three on each side of the creek), were sampled at 20-meter intervals along each transect [8]. Composite soil samples were collected from 0- to 12-inch depths at each location along the transects [8]. Nine sediment samples were collected along the East Fork Poplar Creek bottom from the Y-12 Weapons Plant to the confluence of Poplar Creek [8]. The concentration ranges of contaminants in sediment and in soil from all three locations are shown in Table 1. Elevated levels of mercury were found in a few soil and sediment samples from all three areas. A mercury speciation study of the East Fork Poplar Creek flood plain soil showed the distribution of mercury is 84-98% inorganic (mercuric sulfide), 3-8% elemental, and 0.003-0.01% organic (methyl mercury) [9].

Twenty-two shallow monitoring wells (5-15 feet deep) along East Fork Poplar Creek are sampled quarterly [8]. Groundwater samples collected from monitoring wells during Phase IA contained total metals, dissolved metals, and volatile organic compounds (VOCs) (see Table 2) [8]. Omitted from Table 2 are a few semivolatile organic compounds and pesticides that were detected in only one sample. The monitoring wells will be sampled until remediation at East Fork Poplar Creek is completed [10].

Information on the geologic and hydrogeologic characteristics of the creek, survey data on groundwater use along the creek, and private well water sampling data were not provided to ATSDR. It is unlikely, however, that private wells draw groundwater from shallow aquifers along East Fork Poplar Creek. There is no evidence that groundwater from shallow aquifers along the creek is used for domestic purposes. Most Oak Ridge residents use the municipal water system, which receives raw water from the Clinch River (Melton Reservoir) upstream of the DOE reservation. DOE treats the water supply at Pine Ridge. Therefore, there is no apparent health risk for residents who use municipal drinking water.

Five grab surface water samples were collected from East Fork Poplar Creek; contaminants found were not at levels of public health concern.

ATSDR evaluated a summary of ambient air data from the East Fork Poplar Creek Remedial Investigation; samples were collected from three flood plain locations (NOAA, Lysimeter, and Minit Chek) with known mercury soil contamination (up to 3,000 milligrams per kilogram [mg/kg]) [11]. Ambient mercury concentrations ranged from 5.9 to 10.9 nanograms per cubic meter (ng/m3) using short-term monitoring (minutes to hours) [11]. Long-term monitoring (days to weeks) samples found mercury in the ambient air over a 10-week period at levels ranging from 3.1 to 12.4 ng/m3 [11]. The air monitoring data indicate that mercury levels in the ambient air at the three locations are not of public health concern.

ATSDR evaluated a summary of the November 1990 and May 1991 fish data (from East Fork Poplar Creek) compiled by the DOE Biological Monitoring and Abatement Program. The sampling data show that fish in the creek are contaminated with mercury and PCBs [12]. The concentrations of mercury and PCBs in fish fillet samples ranged from 0.08 to 1.31 ppm and from less than 0.01 to 3.86 ppm, respectively [12]. No information was provided about radionuclide contamination of fish.

In preparing this health consultation, ATSDR has relied on the information provided in the referenced documents. We assume that adequate quality assurance and quality control measures were followed regarding chain of custody, laboratory procedures, and data reporting.

Table 1. Concentration Ranges of Contaminants in East Fork Poplar Creek Soil and Sediment

Contaminant

Soil Concentration Range - ppm

Sediment Concentration Range - ppm

Acetone
*
*
Aroclor-1248
*
0.05 - 2.2
Aroclor-1254 0.1 - 3.0
*
Aroclor-1260 0.09 - 3.8 0.1 - 2.8
Arsenic 1.1 - 15.1 2.9 - 17.6
Barium 36.0 - 454.0 42.2 - 740.0
Cadmium 0.36 - 41.3 0.5 - 46.0
Chromium 9.4 - 112.0 36.2 - 119.0
Cobalt 1.8 - 25.7 9.4 - 28.0
Copper 4.1 - 361.0 7.6 - 313.0
Lead 11.8 - 155.0 12.8 - 113.0
Manganese 25.6 - 1,740.0 464.0 - 27.6
Mercury 0.06 - 1,010.0 10.0 - 2,240.0
Nickel 3.7 - 174.0 13.5 - 275.0
Vanadium 13.5 - 44.9 19.9 - 67.0

Data from reference [8]
ppm - parts per million (mg/kg - milligrams per kilogram)
* - Below contract-required detection limits


Table 2. Concentration Ranges of Contaminants in Shallow Groundwater Along East Fork Poplar Creek

Contaminant

Total Concentration Range - ppb

Dissolved Concentration Range - ppb

Arsenic 1.5 - 76.4 1.0 - 21.9
Barium 0.5 - 3150 15.1 - 1110
Cadmium 1.5 - 75.1 1.5 - 6.3
Chromium 2.0 - 268.0 2.0 - 35.5
Cobalt 2.5 - 144.0 2.5 - 110.0
Copper 1.5 - 6320 1.5 - 108.0
Lead 1.0 - 299.0 0.5 - 9.2
Manganese 0.5 - 21,000 0.5 - 27,600
Mercury 0.1 - 280.0 0.1 - 26.1
Nickel 3.5 -657.0 3.5 - 160.0
Vanadium 1.5 - 225.0 2.0 - 191.0
PCBs
*
 
Acetone 2.0 - 14,000  
Chloroform 2.0 - 125.0  
Tetrachloroethene 1.0 - 125.0  

Data from reference [8]
ppb - parts per billion (µg/L - micrograms per liter)
* - Below contract-required detection limits


DISCUSSION

The East Fork Poplar Creek Phase IA data evaluated for this health consultation indicate that the creek's soil, sediment, groundwater, surface water, air, and fish are contaminated with various chemicals. However, only mercury in soil and sediment, and PCBs and mercury in fish are at levels of public health concern. The maximum levels of mercury in soil and sediment were 1,010 and 2,240 ppm, respectively. In addition, the concentrations of certain contaminants (See Table 2) in the shallow groundwater are of public health concern, but there is no evidence that shallow groundwater along East Fork Poplar Creek is used for drinking water or other domestic purposes. Other contaminants, including radionuclides found in soil, sediment, surface water, and fish, were not found at levels of public health concern.

The primary routes of exposure to contaminated soil and sediment are unintentional ingestion and excessive dermal exposures [13]. People, particularly children, who fish, play, or walk along East Fork Poplar Creek and the flood plain may be exposed to mercury through ingestion of soil from inadvertent hand-to-mouth activities and by dermal contact with soil. Exposure to mercury in the sediments would occur primarily through dermal contact, possibly by ingestion.

Mercury has three valence states and is found in the environment in various inorganic and organic compounds and as elemental mercury [14]. The state and form in which mercury is found in the environment depend on a number of factors. Volatile forms are expected to evaporate to the atmosphere; solid forms partition to soil and to the water column [14]. The severity and type of toxic effect resulting from exposure differs for each form of mercury.

The inorganic form of mercury, mercuric sulfide, makes up 84-98% of the mercury in the contaminated East Fork Poplar Creek soil [9]. Mercuric sulfide is insoluble in water and strongly adsorbs to soil [14]. The primary route by which people might be exposed to mercuric sulfide at the creek is ingestion of contaminated soil. Following ingestion, absorption of inorganic mercury compounds across the gastrointestinal tract is low in both people and animals. Oral absorption of a dose of inorganic mercury salts has been estimated to be less than 7% [14]. Absorption of inorganic mercury via inhalation and dermal exposures can occur; however, no quantitative data are available [14]. Inorganic mercury salts accumulate primarily in the kidney, but are distributed to the liver, erythrocytes, bone marrow, intestine, and skin.

If a 30-kg child played four days a week for 10 years in the East Fork Poplar Creek flood plain soil containing the maximum concentration of contaminants reported, only the estimated ingested exposure dose for inorganic mercury exceeds the ATSDR oral minimal risk level (MRL) of 0.002 mg/kg/day [14]. The MRL is an estimate of daily human exposure to a contaminant below which noncancer health effects are considered unlikely. No apparent increases in carcinogenic risk or in noncancer health effects are expected from oral exposure to other contaminants in the soil. Long-term exposure to soil at this site containing mercury at concentrations of 1,010 ppm may result in body burdens of mercury that could result in adverse health effects.

The mercury in the contaminated East Fork Poplar Creek soil consists of up to 8% elemental mercury [9]. Elemental mercury is a liquid, but readily vaporizes with increases in temperature. At East Fork Poplar Creek, volatile chemicals such as elemental mercury are expected to evaporate to the atmosphere during excavation. Once inhaled, 80-100% of elemental mercury vapors are absorbed through the lungs into the systemic circulation; however, elemental mercury is poorly absorbed through dermal and oral routes [15].

Depending on their solubility, organic forms of mercury adsorb to particulates or are transported in the water column. The mercury in the East Fork Poplar Creek soil is less than 0.01% organic mercury [9]. The most common organic form of mercury, methyl mercury, is soluble, mobile, and quickly enters the aquatic food chain [14]. Methyl mercury biomagnifies in fish on the order of 10,000 to 100,000 times the concentration found in ambient waters [14]. The primary routes of exposure to organic mercury at East Fork Poplar Creek would probably be ingestion of contaminated fish and, to a lesser extent, soil. Organic mercury is readily absorbed orally [14]. Retention and excretion studies have shown that approximately 95% of an oral dose of aqueous methylmercuric nitrate is absorbed across the gastrointestinal tract [14]. Exposure to a number of forms of mercury in the soil, sediment, and fish by multiple routes -- ingestion, inhalation, and dermal contact -- would result in an increased exposure dose and an increased risk of noncancer health effects.

Mercury poisoning can be cumulative and may take weeks, months, or years to produce a recognizable clinical effect [16]. Adverse health effects of long-term exposure to low levels of organic and inorganic mercury are primarily kidney damage and central nervous system (CNS) effects [14]. The kidney is the organ most sensitive to the effects of ingestion of inorganic mercury salts and inhalation of elemental mercury. Renal effects have been seen in people following chronic oral exposure to inorganic mercury salts and in rats and mice following acute (less than 14 days), intermediate (15-365 days), and chronic (greater than 365 days) oral exposure to inorganic mercury salts [14]. Severe effects on the kidney have been seen in people following chronic and acute occupational inhalation exposure to elemental mercury vapors [14]. Effects on the kidney include increased urine protein levels and, in more severe cases, a reduction in the glomerular filtration rate, which is a sign of decreased blood-filtering capacity.

The CNS and peripheral nervous system are also target organs for elemental, organic, and inorganic mercury. Neurologic and behavioral disorders in people have been seen following long-term ingestion and dermal application of inorganic mercury-containing compounds such as teething powders, ointments, and laxatives, as well as pesticides containing organic mercury [14]. Limited human and animal data are available on dermal exposure to mercury. However, acrodynia (pink disease) occurs in children dermally exposed to inorganic mercury compounds. Acrodynia is a complex neurologic syndrome characterized by fine postural or action tremor of the face or extremities, lack of muscle tone, sensitivity to light, general rash, and hypertrichosis. Information on neurotoxicity in people following oral exposure to organic mercury comes from reports of people who have ingested contaminated fish and fungicide-treated grains [14]. Organic forms of mercury are known neurodevelopmental toxins. Human and animal studies indicate that organic mercury, particularly methyl mercury, and elemental mercury vapor cross the placenta to the fetus [14]. Although maternal milk may contain only 5% of the mercury concentration of maternal blood, neonatal exposure to mercury may be greatly increased by nursing [15]. Severe brain damage has been seen in infants following prenatal exposure via maternal ingestion of methyl mercury in bread and fish [14]. No abnormal reproductive or anatomic effects have been seen in infants exposed prenatally [14]. The CNS is likely to be the most critical target organ for elemental mercury vapor. Acute, intermediate, and chronic exposure to mercury vapor may elicit consistent and pronounced neurologic effects. The neurologic syndrome commonly seen as a result of chronic mercury toxicity is characterized by common CNS symptoms, including irritability; fatigue; anorexia; tremors; dementia; memory loss; impaired peripheral vision, hearing, taste, and smell; sleeping disorders; and unsteadiness of gait and limbs [14] [16].

Fish from East Fork Poplar Creek also contained elevated levels of PCBs. PCBs are widely distributed environmental pollutants commonly found in the blood and adipose (fat) tissue of the general population [17, 19]. PCBs bioaccumulate in fish and animal tissues. PCBs are classified as probable human carcinogens by the U.S. Environmental Protection Agency. PCBs (Aroclor-1254, Aroclor-1260) have been shown to produce liver tumors in mice and rats following intermediate and chronic oral exposure. Studies suggest that Aroclor-1254 induces gastric adenocarcinomas in rats.

Mercury and PCB concentrations found in fish fillet samples from East Fork Poplar Creek were below levels that cause acute adverse health effects by ingestion. However, frequent and long-term ingestion of contaminated fish from the creek could result in an increased risk of adverse effects on the CNS and kidneys and a moderate increased risk of developing cancer.

Other potential exposure pathways associated with the contaminated soil at the East Fork Poplar Creek are the food chain and soil excavation. Cattle and wildlife grazing in the creek's flood plain may bioaccumulate contaminants through ingestion of soil, plants, or animals that bioconcentrate contaminants. Furthermore, it is possible that contaminants in the soil may bioaccumulate in and accumulate on vegetables, especially root vegetables, grown in the creek's contaminated soil. The public health implications of exposure to contaminants in the soil via the food chain cannot be evaluated without additional information about the cattle, wildlife, and vegetable crops in the East Fork Poplar Creek flood plain.

Excavation of soil and sediments along East Fork Poplar Creek may result in the release of mercury vapor from the soils, especially as the ambient air temperature increases. Such releases may increase ambient air levels of mercury vapor, which could pose a health risk to unprotected workers and the public. As previously discussed, exposure to mercury vapor may cause pronounced neurologic effects [14].


CONCLUSIONS

From the available information and the summary of Phase IA data provided, ATSDR has reached the following conclusions:

  1. In some locations along East Fork Poplar Creek, mercury levels in soil and sediment pose a threat to people, especially children, who ingest, inhale, or have dermal contact with contaminated soil, sediment, or dust while playing or fishing along the creek's flood plain.

  2. Fish fillet samples collected from East Fork Poplar Creek contain mercury and PCBs. There is no acute health threat to people who eat the fish. However, if people frequently ingest contaminated fish from the creek over a prolonged period, there is a moderate increased risk of adverse effects to the CNS and kidneys, and of developing cancer.

  3. ATSDR does not have enough information on groundwater use along East Fork Poplar Creek to comment on the contamination of groundwater in shallow, private wells along the creek. However, the contamination detected in wells along the creek poses no threat to people who receive their drinking water from the municipal water supply.

RECOMMENDATIONS

  1. Determine the depth of mercury contamination and the extent of its horizontal migration in the East Fork Poplar Creek sediment and flood plain soil.

  2. As an interim action, until permanent remedial action is implemented, advise the public of contaminated soil and sediment at the creek by posting signs or restricting access to areas with elevated soil and sediment concentrations of mercury.

  3. Continue the East Fork Poplar Creek fish advisory. Ensure that a sufficient number of signs are posted, especially at the confluence of Poplar Creek, to warn the public of the presence of contaminated fish in the creek.

  4. Continue monitoring fish from East Fork Poplar Creek for mercury and PCBs.

  5. Conduct a survey of well water use along the East Fork Poplar Creek flood plain.

  6. Sample groundwater from shallow private wells near East Fork Poplar Creek for PCBs, total and dissolved metals, and volatile organic compounds.

  7. Monitor the ambient air for mercury during excavation of the East Fork Poplar Creek sediments and flood plain soil.

When additional information and data become available (e.g., completed remedial investigation), ATSDR will further evaluate the site.


PREPARERS OF REPORT:

Robert L. Williams, Ph.D.
Toxicologist
Energy Facilities Assessment Section
Federal Program Branch
Division of Health Assessment and Consultation

Jack E. Hanley
Environmental Health Scientist
Energy Facilities Assessment Section
Federal Program Branch
Division of Health Assessment and Consultation


REFERENCES

  1. Wing S, et al. Mortality among workers at Oak Ridge National Laboratory: Evidence of radiation effects in follow-up through 1984. JAMA 1991;265:1397-1402.

  2. U.S. Department of Energy. Oak Ridge Reservation Environmental Report for 1988. Vol. 1: Narrative, Summary, and Conclusions. Oak Ridge, Tennessee: U.S. Department of Energy, Office of Scientific and Technical Information, 1989.

  3. U.S. Department of Energy. Mercury at the Y-12 Plant: A Summary of the 1983 UCC-ND Task Force Study. Oak Ridge, Tennessee: U.S. Department of Energy, 1983; Contract No. W-7405-ENG-26.

  4. Bashor B and Turri PA. A method for determining an allowable concentration of mercury in soil. Arch Environ Contam Toxicol 1986;15:435-38.

  5. U.S. Department of Energy. Environmental Restoration Program East Fork Poplar Creek: Phase 1B Sampling Analysis Plan for Soil, Sediment, and Water. Oak Ridge, Tennessee: U.S. Department of Energy, June 1992; Contract No. DE-AC05-900R21851.

  6. Agency for Toxic Substances and Disease Registry. ATSDR record of activity for telephone communication with Greg Denton, Tennessee Department of Environment and Conservation. January 26, 1993.

  7. Tennessee Department of Environment and Conservation. Letter to Robert C. Williams, Agency for Toxic Substances and Disease Registry, from Earl Leming, DOE Oversight Division, regarding posting East Fork Poplar Creek and Poplar Creek. August 21, 1992.

  8. U.S. Department of Energy. Letter to Robert L. Williams, Agency for Toxic Substances and Disease Registry, from Clayton S. Gist, Environmental Restoration Integration Branch, regarding the summary of East Fork Poplar Creek Phase 1A Data. August 21, 1992.

  9. Revis NW, Osborne TR, Holsworth G, Hadden C. Distribution of mercury species in soil from a mercury-contaminated site. Water, Air, and Soil Pollution 1989;45: 105-113.

  10. U.S. Department of Energy. Verbal communication from Mr. David Page, East Fork Poplar Creek Program Manager, to Robert L. Williams, Agency for Toxic Substances and Disease Registry. September 14, 1992.

  11. U.S. Department of Energy. Mercury in Ambient Air Over Flood Plain of East Fork Poplar Creek. Oak Ridge, Tennessee: U.S. Department of Energy, 1992; Contract No. DE-AC05-84OR21400.

  12. Oak Ridge National Laboratory. Letter to Robert Williams, Agency for Toxic Substances and Disease Registry, from G.R. Southworth, Biomonitoring Group Environmental Sciences, regarding PCB and mercury monitoring in fish in East Fork Poplar Creek and Bear Creek in Oak Ridge, Tennessee. July 30, 1992.

  13. Assessing the potential environment and human health risks of contaminated soil. Comments Toxicology 987;3-4:185-220.

  14. Agency for Toxic Substances and Disease Registry. Toxicological profile for mercury. Atlanta: ATSDR, December 1989; DHHS publication no. ATSDR/TP-89-16.

  15. Amdur MO, Doull J, Klaassen CD, ed. Casarett and Doull's Toxicology, The Basic Science of Poisons. 4th ed. New York: Pergamon Press, 1991.

  16. Haddad LM, Winchester JF. Clinical Management of Poisoning and Drug Overdose. Philadelphia: W.B. Saunders Company, 1983.

  17. Tryphonas H, Luster MI, Schiffman G, Dawson LL, Hodgen M, et al. Effect of chronic exposure of PCB (Aoclor 1254) on specific and nonspecific immune parameters in the rhesus (macaca mulatta) monkey. Fundam Appl Toxicol 1991;16: 773-786.

  18. Gilman AG, Goodman L. Goodman and Gilman's The Pharmacological Basis of Therapeutics. 6th ed. New York: Macmillan Publishing Company, 1980.

  19. Agency for Toxic Substances and Disease Registry. Draft toxicological profile for selected PCBs (Aroclor-1260, -1254, -1248, -1242, -1232, -1221, and -1016). Atlanta: ATSDR, 1991.


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