On March 16, 2011, the United States Environmental Protection Agency (EPA) issued a proposed rule that would place new limits on emissions of toxic air pollutants from coal- and oil-fired electric generating units (EGUs or power plants). According to EPA, the proposed rule reflects the maximum achievable control technology and would impose new limits on emissions of heavy metals, including mercury, arsenic, chromium, and nickel. At the same time, EPA is proposing to amend the new source performance standards for fossil-fuel-fired EGUs to revise the particulate matter, sulfur dioxide (SO2) and nitrogen oxides (NOx) standards.

Compliance with the metals emissions standards would be verified via testing of input fuels. The proposed standards would also impose new work practice standards, instead of numerical emissions limits, to reduce emissions of organic air toxics which the EPA claims result from inefficient combustion.