Comparative Risk and Exposure Analysis
Evaluation of Relative Risk to PAH Compounds in Soil. At the request of counsel and on behalf of a confidential client, Dr. Smith compared the carcinogenic risk posed by polycyclic aromatic hydrocarbon (PAH) compounds in Superfund site soils requiring remediation with that posed by PAH compounds identified in two common over-the-counter shampoos containing coal tar. The carcinogenic risk posed by PAH compounds in Superfund site soil was determined using information and methodologies contained in a US Environmental Protection Agency (EPA) Record of Decision (ROD) for the site. Carcinogenic risk posed by site soils was determined using the provisional US EPA Estimated Order of Potency (EOP) approach and an earlier approach that assumed all site PAH compounds have the same potency as benzo[a]pyrene (BaP). Dr. Smith estimated the carcinogenic risk posed by PAH compounds in two brands of over-the-counter shampoo containing coal tar using U.S. EPA methodologies and default exposure factors. The result suggested that either: 1) PAH compounds in these shampoos pose 4-orders of magnitude (10,000-times) greater risk than PAH compounds requiring remediation in Superfund site soils; or 2) US EPA methodologies for determining carcinogenic risk of PAH compounds are seriously flawed.
Evaluation of Relative Carcinogenic Risk for Several Threshold Carcinogens. Dr. Smith evaluated the relative carcinogenic risk posed by three threshold carcinogens: dioxin, arsenic, and benzene and compared these carcinogenic risks to an over-the-counter analgesic, acetaminophen (paracetamol). Dr. Smith estimated the cancer potency of acetaminophen using a linear low-dose, non-threshold, method for extrapolating carcinogenic risk to low levels of human exposure. Dr. Smith compared the cancer potency estimate for acetaminophen to that published by the US EPA for dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin), arsenic, and benzene. Although the relative carcinogenic potency of acetaminophen is lower than any of the other compounds, it poses a greater cancer risk. Excess lifetime cancer risk (ELCR) associated with a dose of 500 mg acetaminophen per week posed more than 100-times the cancer risk associated with the allowable amount of dioxin, 1 part per billion (ppb), in soil and 4- to 7-orders of magnitude higher cancer risk than that posed by typical exposure to the maximum allowable concentrations of arsenic or benzene in drinking water.
Evaluation of Relative Exposure to Estrogenic Compounds in Surface Waters. Dr. Smith compared the concentration and relative estrogenic potency of several synthetic compounds, dicofol, DDT and its metabolites DDD and DDE, methoxychlor, lindane, chlordane, dieldrin, and endosulfan, with levels of natural estrogen in surface waters. Dr. Smith determined the percent contribution of natural estrogen and synthetic estrogen-like compounds historically detected in the Chesapeake Bay watershed to total estrogenic activity in these surface waters. The amount of natural estrogen, derived solely from chicken farms within this watershed, contributed the majority of the estrogen-like activity to surface water. Additional agricultural and human sources, such as municipal sewage treatment facilities, are likely to contribute even more natural estrogen than Dr. Smith estimated comes from area chicken farms. In contrast, Dr. Smith demonstrated that the total of the highest ever recorded concentrations of synthetic estrogenic compounds account for less than 1 percent of the estrogenic activity of surface waters within the Chesapeake Bay watershed. This suggests that U.S. EPA efforts focused on regulating synthetic estrogenic compounds is inappropriate.