Public Health Assessment Public Comment Release
In addition, although trespassing appears unlikely in the vicinity of the site, we estimated
exposure doses for 10-year-olds who might regularly trespass on the site and be exposed to the
maximum concentrations above. Details of the assumptions used in performing these
calculations can be found in Appendix A. The estimated exposure doses for children and adults
of
arsenic, copper, iron, DDT, aldrin, dieldrin, and heptachlor epoxide were below noncancer
health guideline values and resulted in a less than 1 in 10,000 excess cancer risk, and these doses
are therefore not expected to result in any adverse health effects.
For further evaluation of Aroclor 1260 and dioxins/furans/PCBs, the average concentrations in
surface soil were calculated because the long-term exposure would be to an average
concentration rather than the maximum. These contaminants were evaluated in
two ways: 1)
Aroclor 1260 exposure was used to estimate risk using PCB toxicologic information, and 2) the
TEQ for dioxins, furans, and dioxin-like PCB congeners (weighted for toxicity and summed)
was used to assess risk using toxicologic information for 2,3,7,8-TCDD. Aroclor 1260 surface
soil concentrations ranged from less than 0.036 ppm to 1,700 ppm in 67 samples collected at and
in the immediate vicinity of the site. The average Aroclor 1260 was 89 ppm. Eleven of the
surface soil samples also were analyzed for dioxins, furans, and specific PCB congeners. TEF-
corrected \ concentrations in soils were summed to obtain the TEQ of total dioxin-like
compounds. The TEQs in surface soil samples ranged from 0.00005 ppm to 0.06 ppm, and the
average was 0.01 ppm as 2,3,7,8-TCDD.
Exposure to Aroclor 1260 in Surface Soil
Because Aroclors are mixtures of both dioxin-like and non-dioxin-like PCB congeners, summing
the risk associated with both the Aroclor and with individual congeners included in the TEQ
could overestimate risk by accounting for the dioxin-like PCB congener risk both individually
and within the risk estimates for Aroclor. However, because the mass of dioxin-like PCB
congeners is only about 2% of that of Aroclor, correcting the Aroclor concentration by
subtracting out congener concentrations had a negligible effect on both the average concentration
of Aroclor and on the calculated risk. Therefore, ATSDR proceeded with the evaluation using
the uncorrected Aroclor value.
The average Aroclor 1260 concentration in surface soil is 89 ppm, which results in an average
estimated doses of 0.00014 mg/kg/day and 0.00009 mg/kg/day for child trespassers and adult
workers, respectively. The chronic-duration minimal risk level (0.00002 mg/kg/day) is derived
from an animal study that found a lowest observed adverse effect level of 0.005 mg/kg/day [5].
The child dose is more than 30 times smaller than this level, and the worker dose is more than 50
times smaller. In addition, the actual exposure to Aroclor in surface soil would probably be
smaller than estimated because access is restricted so that trespassing is highly unlikely, most of
the site is paved, and workers most frequently access areas of the site that are paved. ATSDR
considers adverse noncancer health effects from exposure to soil unlikely.
Aroclor 1260 is a probable human carcinogen. The contribution from soil exposure to theoretical
excess cancer risk for a 25-year exposure period to an adult is about 6.5 in 100,000. Although
this is a low cancer risk, it contributes to risk from multiple pathways, which will be addressed
later.
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