In Vitro Bioassays for Assessing Estrogenic Substances

This past summer, United States President Bill Clinton signed into law amendments to the Safe Drinking Water Act and Food Quality Protection Act that include clauses requiring the EPA to develop testing procedures for substances that “mimic” the effect of naturally-occurring estrogens. The act requires the testing of substances found in drinking water and all pesticide materials including both active and inert ingredients as well as substances that may have a cumulative or synergistic effect when combined with pesticides. Estimates indicate that this could require the testing of as many as 70 000 chemicals currently used in the United States. EPA, industry, and public interest groups are investigating strategies to develop screening tests by August 1998 in order to implement a program by August 1999 as mandated in the legislation. This review focuses on in vitro assays such as competitive ligand binding, cell proliferation, and estrogen receptor transcription assays, which are currently being used to identify and assess chemicals alleged to possess estrogenic activity. The advantages and limitations of each assay are discussed. The review concludes that complementary in vivo and in vitro assays are required to accurately assess the potential estrogenic activity of any chemical or complex mixture.