Assumptions
ATSDR reviewed the fish and shellfish data as presented in the Draft Remedial Investigation
Report Manchester Annex Superfund Site, Manchester, Washington, Volume 1 J-4191-08,
March 1996. We selected contaminants to present in this following tables based on their
persistence in the environment, their toxicity, and their ability to bioaccumulate in fish and
shellfish. We calculated estimated exposure doses and estimated cancer risk values using the
following assumptions. Although the calculations below and in Tables A-1 and A-2 imply a
certain amount of precision, they are estimates using a range of values that include several safety
factors. When there is uncertainty, we over-estimate rather than under-estimate risk by a factor
of 10 to 1,000. Thus, our recommendations are highly protective of the public's health.
Estimated Exposure Dose and Cancer Risk from Consumption of Seafood from Clam Bay
Meals were assumed to be 0.228 kg (approximately 8 ounces) and comprised of either
intertidal or subtidal species, none combined.
Maximum concentrations were used to represent an assumed maximum exposure. Data
did not reflect any outlying values. Several values were elevated. We chose the
maximum rather than the average or geometric mean because there were only two
sampling events.
We used a standard adult body weight of 70 kg (154 pounds) for "employee" category
and 80 kg (176 pounds) for the subsistence consumer based on discussions with Richard
Brooks of the Suquamish Tribe.
For arsenic, we used 10% of the maximum concentration of arsenic actually detected in
shellfish tissue which represents the toxic inorganic form9,10,11,12,13.
ATSDR's comparison dose for arsenic is based on FDA's tolerable total intake for
inorganic arsenic (0.130 mg/person/day). We divided this value by 70 kg to get the
comparison dose for an 70 kg employee (1.86E-03) and 80 kg for the subsistence
consumer (1.62E-03) 9. The estimated comparison dose for the subsistence consumer is reported in the table.
We used the PCB values in shellfish as reported by Hart Crowser in 1996 and not that
reported by NOAA 1995. Because NOAA did not obtain total PCB values using the
recommended PSEP (Puget Sound Estuarine Protocol) methods, their values were
substantially different than those reported by Hart Crowser.
EPA's cancer slope factor of 2.2 (mg/kg/day)-1 for Aroclor 1254 was assumed for total
PCBs14.
For PAHs, we used total Toxic Equivalency Factor (TEF) approach which relates the
cancer slope factor of individual compounds to benzo(a)pyrene in order to derive a total
TEF value for the mixture of PAHs in each shellfish sample. EPA's cancer slope factor
of 7.3 (mg/kg/day)-1 for benzo(a)pyrene was assumed.
We derived a comparison dose for lead by using FDA's provisional tolerable total intake
level of lead and various research studies which relate blood lead levels and dietary lead
intake for pregnant women15,16,17,18,19,20. We used FDA's estimated dietary effect level of
0.250 mg/day divided by 80 kg to give an estimated dose for a corresponding blood lead
level of 10 ug/dL. Then we divided this by 4, which provides a safety factor and also to
account for transference of maternal blood lead to the fetus15,19.
0.250 mg/day
80 kg
-:- 4 = Comparison Dose for lead
In subtidal species, PAHs and PCBs were not detected above the laboratory detection
limits. We represented them in Table A-1 as DL, but did not assign a value. Assigning
these data values could misrepresent a level of risk.
For Dioxins, a Cancer Slope Factor of 156,000 was use to estimate cancer risk based on
the HEAST Tables.
Soil Exposure Estimates from Landfill and Fire Training Area
Average concentrations were used to represent the most likely exposure since data
showed a few random "hot spots" in soil.
We used a standard adult body weight of 70 kg (154 pounds) for workers who would be
exposed.
Highly conservative frequency of exposure for workers to soil was assumed to be
intermittently at 3 out of 7 days per week for an assumed 10 years.
The following table was not available in electronic format for conversion to HTML at the time of preparation of this document. To obtain a hard copy of the document, please contact:
Agency for Toxic Substances and Disease Registry
Division of Health Assessment and Consultation
Attn: Chief, Program Evaluation, Records, and Information Services Branch
E-56
1600 Clifton Road NE, Atlanta, Georgia 30333
The following table was not available in electronic format for conversion to HTML at the time of preparation of this document. To obtain a hard copy of the document, please contact:
Agency for Toxic Substances and Disease Registry
Division of Health Assessment and Consultation
Attn: Chief, Program Evaluation, Records, and Information Services Branch
E-56
1600 Clifton Road NE, Atlanta, Georgia 30333
