Toxicological Profile for Plutonium
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PLUTONIUM 177 6. POTENTIAL FOR HUMAN EXPOSURE 1969, and leakage of drums of plutonium contaminated cutting oil to soil onsite. Resuspension of contaminated soils during remediation activities resulted in most of the releases of plutonium at the RFETS. Soil samples collected at the RFETS during 1992–1994 were reported to range from 1.1 Bq/kg (30 pCi/kg) offsite to 57 Bq/kg (1,500 pCi/kg) onsite. Isotopic ratios of 240 Pu: 239 Pu increased from 0.055 onsite to 0.123 at 19 km east of the RFETS boundary. An isotopic ratio of 0.06 is associated with contamination from activities at the RFETS, whereas the world mean isotopic ratio due to fallout was estimated at 0.176 (Ibrahim et al. 1997). ATSDR examined surface-soil contamination from an industrial portion of RFETS known as the “903 Pad Area”, because multiple site reports indicate that off-site surface-soil contamination largely originated from this location (Agency for Toxic Substances and Disease Registry 2005). Surface soils in the 903 Pad Area were originally contaminated when industrial oils containing trace amounts of plutonium leaked from steel drums stored at the site between 1958 and 1968. Although DOE contractors remediated many of the highest priority waste sites to levels meant to be protective of workers and rural residents near the site, soil sampling activities in this area found 239,240 Pu levels as high as 457,000 pCi/kg (16,909 Bq/kg), which is nearly 10 times greater than the action level of 50,000 pCi/kg (Agency for Toxic Substances and Disease Registry 2005). The highest off-site concentration of 239,240 Pu observed during a remedial investigation was 6,500 pCi/kg (240 Bq/kg). A separate sampling study conducted in the 1990s at 42 locations adjacent to RFETS measured 239,240 Pu concentrations in soil ranging from 0.22 to 14.80 Bq/kg (5.9–400 pCi/kg) (Litaor 1999). In 1960 at the McGuire Air Force Base in New Jersey, a missile caught fire at the Boeing Michigan Aeronautical Research Center and the warhead partially burned and melted, releasing weapons-grade plutonium (WGP) to the local environment (Lee and Clark 2005). The WGP at this site consisted of mostly 239,240 Pu, with a small amount of 241 Pu and a negligible amount of 241 Am (Amercium-241) at the time of its manufacture. Soil samples (0–2 inches) were collected from this site in June 2000 and analyzed for various plutonium isotopes. Concentrations were 0.42–6.34 Bq/g (11–171 pCi/g) for 239,240 Pu, 0.010–0.110 Bq/g (0.3–3.0 pCi/g) for 238 Pu, and 0.33–8.17 Bq/g (8.9–220 pCi/g) for 241 Pu in soil samples with various particle size fractions. The soil fraction with the smallest particle size (75–147 µm) contained the highest concentrations of plutonium, which were about 4 orders of magnitude higher than fallout levels. Based on the activity ratios of 241 Pu/ 239,240 Pu and 241 Am/ 239,240 Pu in the samples, the origin of the plutonium isotopes was identified as WGP (Lee and Clark 2005). PLUTONIUM 178 6. POTENTIAL FOR HUMAN EXPOSURE Soil samples were collected in 2004 on and around the Hanford Site (DOE 2005c). Average 239,240 Pu concentrations in surface soil collected on the 100-N Area, near facilities and operations in the 200 and 600 areas, and near facilities and operations in the 300 and 400 Areas were 0.004, 0.35, and 0.03 pCi/g (1x10 -4 , 1.3x10 -2 , and 1x10 -3 Bq/g) dry weight, respectively. With the exception of the concentration from the 200 and 600 Areas, the soil concentrations in 2004 were similar to levels determined from 1999 to 2003. Average 239,240 Pu concentrations in surface soil collected near Hanford Site facilities and operations in the 200 and 600 Areas from 1999 to 2003 were reported as 0.08, 0.29, 0.10, 0.12, and 0.09 pCi/g (3x10 -3 , 1.1x10 -2 , 4x10 -3 , 4x10 -3 , and 3x10 -3 Bq/g) dry weight, respectively. An average 239,240 Pu concentration of 0.0033 pCi/g (1.2x10 -4 Bq/g) dry weight was reported in surface soil collected from a distant community in 2004 (DOE 2005c). Radionuclides, including 239,240 Pu, were detected in river sediment adjacent to and downstream from the Hanford Site during 2004. Maximum 239,240 Pu concentrations in Columbia River sediment collected from four sites near the Hanford Site ranged from 7.8x10 -4 to 0.011 pCi/g (2.9x10 -5 –4.1x10 -4 Bq/g) dry weight (DOE 2005c, 2005g). Median 239,240 Pu concentrations from two of these sites, where more than one sample was collected, were 0.0084 and 0.0078 pCi/g (3.1x10 -4 and 2.9x10 -4 Bq/g) dry weight. Median 239,240 Pu concentrations in sediment collected from 1999 to 2003 from six sites in the Columbia River near the Hanford Site ranged from 0.0016 to 0.0098 pCi/g (5.9x10 -5 –3.6x10 -4 Bq/g) (DOE 2005c). Concentrations of 239,240 Pu ranged from 0.006 to 0.80 pCi/g (2x10 -4 –3x10 -2 Bq/g) dry weight in soil collected from communities surrounding the Nevada Test Site in southern Nevada and southern Utah during the summer 1996 and spring 1997. The activity ratios of radiocesium to plutonium in the soil samples suggest that the Nevada Test Site had a significant contribution to plutonium levels in this area as compared to global fallout (Cizdziel et al. 1998). A study on radionuclide levels in west Cumbrian soils contaminated by low-level discharges from Sellafield reported 238 Pu levels detected at a range of 200–18,000 pCi/kg (8–670 Bq/kg) and 239,240 Pu levels detected at a range of 800–83,000 pCi/kg (30–3,100 Bq/kg) (Livens and Baxter 1988). Core samples of surface soil at the Maxey Flats facility, Kentucky, where radioactive wastes were buried, were reported to contain a mean concentration of 1.9x10 5 pCi/kg (7,000 Bq/kg) of 238 Pu and 2.2x10 4 pCi/kg (810 Bq/kg) of 239,240 Pu (NEA/OECD 1981). Maximum 239,240 Pu concentrations of 488 and 27,900 Bq/kg (1.31x10 4 and 7.54x10 5 pCi/kg) have been reported in composite (0–20 cm) and surface (0–5 cm) soil samples, respectively, collected in the vicinity of ground zero of the first thermonuclear explosions at the Semipalatinsk Test Site (STS) (Carlsen et al. Yüklə 4,8 Kb. Dostları ilə paylaş:
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