Challenging an agency’s assessment of scientific research in court is typically seen as a fool’s errand. The courts may keep the regulatory state on a close leash where matters of constitutional law are concerned, and will give challenges regarding the proper interpretation of statutes a fair hearing before (usually) deferring to the government’s view. But an agency has to go seriously off the rails before the courts will second-guess its assessment of the scientific record underlying a regulation.
That’s what makes EPA’s super-expensive Mercury and Air Toxics Standards (MATS) rule so interesting: the agency’s own assessment of the scientific research shows there was no good reason to regulate in the first place. The Supreme Court is now reviewing EPA’s decision to plow ahead regardless, irrespective of the costs of doing so.
Power plants emit trace amounts of mercury, and mercury poses a risk to human neurological development when pregnant women consume fish tainted by it. But, as EPA has explained, mercury deposition in the United States “is generally dominated by sources other than U.S. [power plants].” In fact, the agency’s figures show that those plants are responsible for only about one half of one percent of airborne mercury.
Common sense would therefore suggest that reducing or even eliminating emissions from U.S. plants could have little or no appreciable effect on public health. And EPA actually agrees, finding that “even substantial reductions in U.S. [power-plant] deposition…[are] unlikely to substantially affect total risk.”