(CASAC) Peer Review of EPA's Integrated Science Assessment

The Panel was impressed by the way the preceding chapters’ information wassummarized in a series of tables that effectively collated the textual materials, tables, andfigures from the preceding chapters as well as the wealth of data contained in theappendices. The conclusions regarding causality with regard to short-term exposures arereasonable. A better discussion is needed on the range of exposures at which effects areobserved in the clinical studies and the much lower range at which effects are observed inthe epidemiological studies. In addition, the importance of identifying susceptiblesubgroups of subjects, and estimating the contribution of these groups to population shiftsin response characteristics may be a task for the REA, but that document should beinformed by a discussion of this issue in the ISA.The larger question is whether the additional research carried out in the last 10years has led to a substantial change in the scientific basis for making decisions regardingthe basis for setting standards for SO 2 . Although the ISA answers this questionaffirmatively, the final chapter should be organized to answer all of the policy-relevantframing questions introduced in Chapter 1. The answers to these questions wouldgreatly improve the usefulness of this document as a scientific prelude to the Risk andExposure Assessment.With respect to the entire ISA, there remains the longstanding issue associatedwith the Clean Air Act's single pollutant approach to analysis and rulemaking. In the realworld, we breathe complex mixtures of multiple pollutants, thus isolating the effects of asingle pollutant requires simplifying assumptions that depart from real world phenomena.With SO 2 in particular, the reality of having to adjust for the possible confoundingcontributions of other pollutants makes definitive determinations of assigned causality achallenge.In closing, the CASAC is pleased to provide the Agency with advice andrecommendations in the development of this ISA for Sulfur Oxides, which is afundamental part of the new NAAQS review process. We look forward to providingadditional advice as the Agency completes the NAAQS review process for sulfur oxides.Sincerely,/Signed/Dr. Rogene HendersonChairClean Air Scientific Advisory CommitteeEnclosuresvi