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.