FIELD DOCUMENTS AND WORK PLANS 1987

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Marley Cooling Tower Page 3 The only exposure which exceeds an AI is the chromium exposure which exceeds the AIC (acceptable intake -- chronic) for Cr VI. There would be a potential for chronic toxicity from chromium if all of the Cr is Cr VI. If 308 or less of the Cr is Cr VI, there would be no exceedance. Even this possibility is based on lifetime soil exposure by ingestion and dermal absorption, which assumes that all of the soil that gets onto the skin is as contaminated as the maximally contaminated sample taken at Marley Cooling Towers. These are extremely conservative assumptions. Realistically, there is not likely to be a chronic toxicity problem from chromium, unless the contamination is much more widespread than is apparent from the present evidence, and unless all the Cr in the sample is Cr VI. Arsenic -- Carcinogenicity The analysis identified arsenic, but did not discriminate whether the elemental form or an inorganic salt or organic compound is present. Elemental arsenic is relatively non-toxic (oral TDLo for man is 7857 mg/kg) because it is poorly absorbed. Arsenic trioxide is very toxic (oral LD50 for man is 1.4 mg/kg) because it is well absorbed. The health-conservative assumption would be that all the arsenic is present as arsenic trioxide. However, according to Bob Schlag, it is much more likely to be arsenic pentoxide, because this is the form of arsenic which has been used on site. The maximum concentration of arsenic found in a soil sample at Marley is 253 ppm. Based on a lifetime exposure to soil with this concentration, and based on a CAG unit risk of 15 (mg/kg.d)-1, the lifetime excess cancer risk would be 4 X 10(-2) , or 4 per 100. Exposure Unit Risk Risk Arsenic .18 mg/d 15 (mg/kg.d)-1 4 x 10(-2) This is a very high risk, but the assumptions are extremely conservative. The basic assumption is that all the soil ingested or adhering to the skin during the lifetime of the individual would be contaminated with the amount of arsenic found in the soil sample at Marley with the highest arsenic concentration. In reality, this soil contamination is probably very localized, and no one would be exposed exclusively to soil with the maximum concentration of arsenic. If the estimate of exposure were reduced by a factor of 1,000, then the risk would be 4 X 10-5 which is low but still significant. The exposure would have to be reduced by a factor of 40,000 to get down to the 1 X 10-6 risk level. At present we simply do not have adequate information on which to base any reasonable estimate of the exposure. Chromium -- Carcinogenicity If one were to assume that all of the chromium onsite is in the form of Cr VI, and that contamination is widespread at levels equal to the maximum detected, and further assuming that carcinogenic risk determined from inhalation exposure data is valid for estimating risk due to oral and dermal exposure, one might estimate a high level of exposure and calculate a high cancer risk from chromium.