UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, o.c. 20460 IPA-SAB-EHC-89-036 September 19, 1989 OFFICE fNE AOiM i wiS Honorable William K. Reilly Administrator U.S. Environmental Protection Agency 401 M Street, S.W. Washington, B.C. 20460 Subject! Science Advisory Board's preliminary review of mixture issues relating to, some Phase II drinking water regulations of the Office of Drinking Water Dear Mr. Reilly, The Halogenated Qrganics Subcommittee of the Science Advisory Board's Environmental Health Committee has completed its preliminary review of mixture issues relating to three contaminants for which regulations are currently being developed. This review was conducted early in the deliberations of the Office of Drinking Water (ODW) with the objective of providing them with some general directions for their thinking about the state of knowledge of the scientific background concerning how to estimate the health effects of complex chemical mixtures. The three contaminants of immediate interest to QDW were; polycyclie aromatic hydrocarbons, plasticiiers (including phthalates and adipate esters) and gasoline. This review was based on a briefing paper presented to the Subcommittee which met in Washington, D.C., November 9-10, 1988. The subcommittee reached conclusions resulting in suggestions for both the plasticizers and gasoline, some informal suggestions and comments were given at the meeting for all three contaminants. Regarding the plasticizers, the Subcommittee concluded that the health assessments for diethyl hexyl phthalate (DEEP) and diethyl hexyl adipate (DEHA) should be conducted separately, This suggestion is based on the lack of adequately defined mechanisms that would provide a rationale for treating these substances eguivalently. DEHP is classified as a group B2 carcinogen in the EPA weight of evidence scheme, while DEHA is tentatively classified as a group C carcinogen. Results from future mechanistic studies may necessitate reexamination of this recommendation. A thorough literature search might resolve the question of whether any additional phthalates or adipates should be of concern. ------- There was a clear agreement among the Subcommittee members that only a few of the many components of gasoline are of major health significance. Since benzene is invariably a component of gasoline, and is generally the most soluble component, and is a known carcinogen which is already regulated, and since there are no known synergistic or antagonistic effects betwefen the • components of gasoline/ the Subcommittee sugges€s that benzene is the most appropriate component for risk assessment. The toxicity of water soluble contaminants (xylenes, toluene, ethylbenzene, n- hexane) could be evaluated using EPA's mixtures guidelines. Gasoline additives, such as methyl tributyl ether, could be considered on an individual component basis. We appreciate the opportunity to conduct this particular scientific review. Since this is only preliminary advice, the Agency may wish to respond formally at this time or wait until the time of its proposed regulations for these contaminants. Sincerely, Raymond Loehr Chairman Executive committee Arthur Upton chairman ""Environmental Health Committee Martha Ri Vice-chairman Halogenated Organics Subcommittee ------- U.S. Environmental Protection Agency Science Advisory Board Haloganated Organios subcommittee November 9-10, 1988 Meeting CHAIRMAN Dr. John Doull University of Kansas Medical Center Kansas City, KS 66103 VICE CHAIRMAN Dr. Martha RadiKe University of Cincinnati Medical College Department of Environmental Health 3223 Eden Avenue, M.L.056 Cincinnati, OH 45267 CONSULTANT^ Dr. George T, Bryan Department of Human Onconolgy University of Wisconsin K4/528, Clinical Science Center 600 Highland Avenue Madison, WI 53792 Dr. James M. Gentile, Professor Biology Department Hope College Holland, Michigan 49423 Dr. Ronald D. Hood, Professor Department of Biology The University of Alabama P.O. Box 870344 Tuscaloosa, Alabama 35487-0344 Dr. Larry Kaminsky, chief Biochemical and Genotoxicology Laboratory Wadsworth Center for Laboratories and Research New York State Department of Health Albany, NY 12201 Dr. Curtis Klaassen Professor of Pharmacology and Toxicology University of Kansas Medical Center 39th and Rainbow Boulevard Kansas city, KS 66103 ------- SOiC-PASB TWO Dr. Eugene McConnell * Box 348-25 ' Route 6 Raleigh, N.C. 27613 Dr. Don E. McMiHian Chairman, Department of Pharmacology Mail 1638, University of Arkansas Medical Sciences 4301 West Markham street Little RoaJc, AR 72205 Dr. Myron Mehlman Director, Mobil Environmental & Health Science Laboratory P.O. Box 1029' Princeton, NJ 08540 Dr. Stephen Safe Department of Veterinary,Physiology and Pharmacology College of Veterinary Medicine Texas, _A & M University College"*Station, TX 77843-4466 Dr. Thomas Starr CUT P.O. Box 12137 Research Triangle park, NC 27709 Dr. Robert Squire 1515 Labelle Avenue Ruxton, MD 21204 Executive secretary - (for this meeting) Dr, K. Jack Kooyoorajian Environmental Protection Agency Science Advisory Board 499 South Capitol Street, S.W. Washington, D.C, 20460 Executive secretary Dr. C. Richard Cothern Environmental Protection Agency Science Advisory Board 499 South Capitol Street, S.W, Washington, D.c. 20460 ------- |