Evaluation of the hazard quotient method for risk assessment of selenium

Environmental contamination with selenium from industrial and agricultural sources has poisoned fish and wildlife at several locations in the United States. Monitoring and risk assessment activities are currently being conducted by many state and Federal agencies. The U.S. Environmental Protection Agency (EPA) recommends a hazard quotient (HQ) method (waterborne concentration divided by the national water quality criterion) to assess the toxic threat of individual waterborne elements, including selenium. An evaluation of the EPA HQ method was conducted by comparing it to a recently published protocol (Protocol) for selenium assessment. Hazard estimates obtained using HQ were found to be invalid because the EPA water quality criterion is outdated, and the procedure uses mean rather than maximum waterborne concentrations. The HQ method seriously underestimates hazard and could lead to risk management decisions that would not protect fish and wildlife from selenium toxicity. The Protocol method provides an accurate assessment because it evaluates hazard by examining multiple exposure pathways on a site-specific basis. Until a revised (lowered) national water quality criterion is available, the EPA HQ method should not be used for selenium. Even then, with the availability of the Protocol, HQ analysis should be restricted to data sets where water is the primary or sole source of information on environmental concentrations of selenium.