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

5. Revisions were made to better integrate findings from atmospheric sciences, ambientair data analyses, exposure assessment, dosimetry, and health evidence in Chapter 5.To what extent do these findings support conclusions regarding causality of SOxrelatedhealth effects at relevant exposures?RESPONSE: The big issue that needs more discussion is why the epidemiology showshealth effects associations at much lower concentrations than do the clinical studies. Theparagraph at the top of page 5-11 does discuss one likely explanation of this apparentparadox: the effects of the fact that “aerosol particles act as carriers and deliver sulfurcontainingcompounds more effectively to the lower respiratory tract”. However, morediscussion is needed here of the fact that this may well account for why epidemiologicalassociations are found at SO 2 concentrations well below where effects are documentedby clinical studies using pure SO 2 exposures.50