U.S. Environmental Protection Agency, 26 W. Martin Luther King Dr., Cincinnati, OH 45268

A -- STUDIES OF CHEMICAL MIXTURES (BREAST MILK, MIXTOX, AND QSAR) SOL SOL-3G0031 DUE 101997 POC Hans Schellhas, Fax: 513-366-2107 E-MAIL: U.S. EPA -- Cincinnati Contracts Management Division, schellhas.hans@epamail.epa.gov. The US EPA intends to negotiate on a sole source basis with the Department of Vetinary Medicine of the University of Illinois for the assessment of exposure characteristics and toxic properties of residues of pollutants detected in human breast milk, and of chemical mixtures and individual disinfectant byproducts (DBPs) detected in drinking water through an analysis of their toxic properties and chemical structures and utilizing the data base generated by Female Rat Endocrine Disrupting Assays (FREDA). . The National Center for Environmental Assessment-Cincinnati (NCEA-CIN) has recently developed the Breast Milk Pathway chapter of the document on the Methodology for Assessing Health Risks Associated with Multiple Exposure Pathways to Combustion Emissions. In addition, the NCEA-CIN is working on Structure Activity Relationships of DBPs and is developing a data base on binary mixture interactions called MIXTOX. The contractor shall review the entire chapter on the breast milk pathway of the document for significant omissions, errors or misrepresentations of fact or interpretation and make appropriate revisions. The contractor shall review the MIXTOX data base which NCEA-Cin is currently developing and recommend chemicals for this evaluation. In addition, the contractor shall advise as to the comprehensive toxicological implications for the first round of priority binary-paired chemicals currently being evaluated for the Mixtox database The significance of the binary pair comparisons shall be evaluated from a toxicological perspective on the various endpoints of concern and acute and chronic health implications. The contractor shall examine the Mixtox data base and advise on the next round of chemicals that should be evaluated for input into this data base. The contractor shall also review and advise on information available on chemicals that have additive or synergistic activities in mixtures. In all these activitites the contractor shall use the data base generated by Female Rat Endocrine Disrupting Assays (FREDA). The contractor shall likewise review and advise on the comprehensive toxicological implications of QSAR findings on DBP chemicals now being evaluated in terms of their potential human health toxicological endpoints. The contractor shall also advise on the next round of DBP chemicals to be evaluated under the QSAR models in order to determine metabolic interactions that are likely to be impacted by the various combinations of mixtures for their potential toxicological implications. Recommendations will be needed on what course of action will be needed to fully utilize this research tool in the mixture research agenda. The basis for sole source negotiations is the contractor's current knowledge, expertise and experience specifically required for this project. Prof. Hansen is the only scientist who has contributed original work using Female Rat Endocrine Disrupting Assay (FREDA), a short term in vivo assay, on the PCBs and associated chemical environmental pollutants on their endocrine and other toxicological activities. He is the innovator of the FREDA assay. All other assays on these compounds are in vitro assays. In vitro assays cannot be utilized for quantitative risk assessment. Only the data from in vivo bioassay, like FREDA, can be utilized for quantitative risk assessment of these endocrine disrupting neurotoxic pollutants. Prof. Hansen has used the required Chemical QSAR approach for predicting the endocrine and associated toxic effects of compounds, using the FREDA, present in certain Superfund sites. NCEA-CIN requires Prof. Hansen's scientific methods for evaluating the MIXTOX data base and QSAR for DBPs. Prof. Hansen is the only scientist who has the knowledge and expertise on the FREDA and the pollutants of interest as required for this project. THIS IS NOT A REQUEST FOR PROPOSALS. Sources wishing to be considered must submit documentation to the office identified above, which establishes the ability and necassary requirements to perform the work described above. Documentation may be sent via facsimile to Hans Schellhas at 513-366-2107. Documentation must be submitted within 15 days of publication of this notice. (0276)

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