EPA last regulated a chemical under the Toxic Substances Control Act (TSCA) § 6, which provides for regulation of existing as opposed to new chemicals, in 1989. This 28-year hiatus may be coming to an end, with the proposal of three rules in the month before the inauguration of President Trump. While the new Administration may never adopt the proposed rules, the approach to implementing § 6 that they reflect should be of great concern to formulators, chemical manufacturers and manufacturing industry generally.
Going forward, it is important that new approaches to the accepted EPA methodology for cancer risk assessment be developed. This methodology is based on models developed to assess cancer risk from ionizing radiation. Under this linearized non-threshold model, radiation is always considered harmful, there is no safe exposure and biological damage caused by ionizing radiation (essentially the cancer risk) is directly proportional to the amount of radiation exposure to the human body (response linearity). The scientific basis for applying these assumptions to low-level radiation is under review by the Nuclear Regulatory Commission (80 Fed. Reg. 35870 (June 23, 2015), and consideration of the direct applicability of this approach to low-dose chemical carcinogenesis is long overdue. More narrowly, the circumstances in which non-linear or threshold mechanisms may account for increased cancer incidence in high-dose cancer bioassays, and species differences in metabolism and pharmacokinetics, need to be carefully evaluated and, where relevant, taken into account in EPA's cancer risk assessments.