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Emerging Regulatory Issues
EPA Letter to the CRE
July 12, 2000
Mr. Jim Tozzi Dear Mr. Tozzi: This letter responds to your May 19 communication to Susan Wayland concerning cancer hazard descriptors and definitions. You are troubled by the lack of consistency among authorities regarding such classification systems and suggest that EPA's proposed cancer hazard position on atrazine be based on policy and not science. It is erroneous to think that all hazard classification systems and definitions should be the same. There are a number of different cancer hazard classification systems that haven been developed by various authorities here in the U.S. and abroad. Although there are elements in common, there are definite differences in purpose. For instance, the classification system used by the International Agency for Research on Cancer strives to summarize the scientific information bearing on the carcinogenicity of agents drawing from the published literature. Regulatory agencies, like EPA, rely on all relevant information including unpublished industry and other studies. In addition, regulatory risk assessments incorporate various science policy default positions which are often public health protective. Assessments also may be conducted at different times, which can lead to inconsistencies in classification among authorities. The hazard descriptors used by EPA in its 1986 guidelines include the groupings- "human," "probable human," and "possible human" carcinogen. Operationally, there were many problems with the application of the classification system. When the Agency proposed revisions to its cancer assessment guidelines in 1996 (and made further revisions in 1999), many changes were made to incorporate evolving and current scientific developments and practices. We purposely changed the names of the hazard classes and rearranged them to be more useful. The "possible human" category from the 1986 guidelines was removed. In working through examples of different chemicals, we recognized that "possible human" designations of the past might now be called "likely," "suggestive," "inadequate," or "not likely" according to the proposed guideline; the actual designation would depend upon the nature of the data base and the mode of action information. We have yet to finalize the guidelines, but have stated that in the interim the Agency will explore the use of the proposed guideline in some cases to gain experience with their applications. This is the same practice that was employed when we proposed guideline revisions in 1984, which were then finalized in 1986. EPA called atrazine a "possible human" carcinogen under the 1986 assessment guidelines based on mammary tumors in one rat strain. Since that determination, the registrant has performed a significant amount of research to elucidate the mode of action underlying tumor development. Although some questions remain, the Agency thinks that atrazine may still pose a cancer hazard for humans and proposed to call it a "likely" carcinogen under the 1996 proposed guidelines based upon scientific and science policy considerations. As you are aware, the Scientific Advisory Panel did not concur with the Agency's proposal at its June 27-29 meeting. For further information concerning the process used with atrazine, consult the response to your June 15 letter signed by Larry Dorsey. In summary, we neither expect nor desire that all authorities should use the same hazard classification descriptors and definitions because of the differences in purpose and assessment practices. In addition, the classification of atrazine has been based upon the existing science and proposed science policy positions. Our draft evaluations on atrazine will be subject to peer review through the Scientific Advisory Panel. Sincerely,
Steven K. Galson, M.D., MPH |
