Law360, New York (January 20, 2016, 11:20 AM EST) -- Selecting a toxicity value for use in setting regulatory limits raises questions "on the frontiers of science," which require a delicate balancing of the science with "policy judgments." Such calculations can well "lead to risk estimates that, although plausible, are believed to be more likely to overestimate than to underestimate the risk to human health and the environment."[1] Increasingly, such regulatory risk decisions may involve unarticulated, nontransparent agency practices and preferences. Because all the draft bills reforming the Toxic Substance Control Act (TSCA) contemplate increasing the number of substances whose risk will be assessed or reassessed, and other U.S. Environmental Protection Agency and state regulatory programs commonly utilize EPA reference doses (RfDs) and reference concentrations (RfCs), it is timely to reflect on what portion of these regulatory decisions should be science-based, what portion should be policy-based and whether the nontransparent application of agency lore is appropriate at all. This article uses EPA's development of an RfC for the noncancer effects from exposure to trichloroethylene (TCE) in air as a case in point....