This is a comparative study that evaluates various methods for reducing the number of chemicals of potential concern in baseline risk assessments. The methods of reducing the number of chemicals of potential concern that were evaluated are the indicator score method (OERR 1986), grouping of chemicals by class, evaluating frequency of detection, and the concentration-toxicity screening method (OERR 1989). The evaluation consisted of comparison of quantitative risk assessment results for four case studies. Seven quantitative risk assessments were completed for each case study, six using a reduced subset of chemicals of potential concern and the seventh using all of the chemicals of potential concern. The six subsets were determined by using each of the four methods separately and two combinations of the methods.
The estimated risks for the subsets of chemicals of potential concern were generally equal to or less than the risks for the entire set of chemicals of potential concern. Carcinogenic risks were decreased in ten of the twenty-three test cases. Each of these decreases was less than an order of magnitude (10 times). Also none of the decreases reduced the carcinogenic risks to less than 10-4. This is significant since 10-4 represents the excess lifetime cancer risk which generally warrants remedial action (OSWER 1991a). Noncarcinogenic hazard indices were also decreased in ten of the twenty-three test cases. However, the hazard indices remained above one, the level of concern (OSWER 1991a), in all cases.