All conclusions reached in this document should be considered tentative pending receipt of public comments. Four chemicals have been identified as potentially qualifying for revision on the basis of new IRIS or OPP health assessments that could impact the MCLG. These are beryllium, chromium, oxamyl, and picloram. This tentative identification of chemicals potentially qualifying for revision was conducted independently of other considerations (e.g., analytical and treatment technology, magnitude of gain in health protection, data gaps, occurrence), which may influence the final selection of contaminants to be revised. Three chemicals, cyanide, di(2-ethylhexyl)adipate, and thallium, are high priority because of reproductive and/or developmental concerns. New IRIS health assessments of these chemicals have been initiated. The new risk assessments are expected to be completed in the 2004/2005 time frame for cyanide, 2003/2004 for di(2-ethylhexyl)adipate, and 2004/2005 for thallium (US EPA 2002b). New data have become available regarding the effect of fluoride on bone, and the contribution of various sources to total fluoride exposure. EPA plans to request NAS to conduct a review of these data. Table 5 provides the details of the review process applied to each of the 68 chemicals under consideration.