The EPA’s new rule to limit mercury emissions is projected to be the single costliest regulation in U.S. history, with compliance costs of more than $10 billion per year. But does the science back up the EPA’s regulations?

Though the EPA predicts this costly new regulation will produce billions in health benefits, most of these health benefits don’t actually come from regulating mercury. In fact, limits on mercury only account for $4 million of the total estimated benefits for the final rule. Instead most of these benefits come from a side effect of imposing limits on mercury emissions—fewer particulate matter emissions. Because the rule doesn’t actually target what it claims to regulate, the rule has been criticized by many, including the former administrator of the Office of Information and Regulatory Affairs, Susan Dudley.

Secret Evidence

The EPA has also declined to make available the data upon which it based its new mercury emissions rule. Writing in the Wall Street Journal, Rep. Lamar Smith (R-TX) pointed out that, “Yet more than 99% of the EPA’s health-based justifications for the rule are derived from scientific research that the EPA won’t reveal. Taxpayers are supposed to take on faith that EPA policy is backed by good science.”

Aspects of the mercury rule are currently undergoing challenges in the federal court system. In a recent argument session before the D.C. Court of Appeals, Reuters notes that “some judges questioned whether the EPA ‘artificially skewed the data’ used to set mercury limits by basing them on the best performing power plants rather than a wider sample.”