US EPA Weakens Mercury Rules, Reversing 90 Percent Emission Reduction Standard

The United States Environmental Protection Agency on February 20, 2026 finalised a rollback of mercury emission standards for coal-fired power plants, reverting to 2012 limits and weakening controls on arsenic, cadmium, chromium, lead and nickel while dropping requirements for continuous smokestack monitoring. The original Mercury and Air Toxic Standards rule had reduced mercury emissions from coal power plants by an estimated 90 per cent.

Research by Indiana University biogeochemist Gabriel Filippelli found that before the original MATS rule, mercury from a large coal plant on the edge of Indianapolis was falling as rain across the city and accumulating in the White River. Surveys found a clear mercury plume in surface soils extending from near the plant up to 31 miles downwind. Mercury levels in White River sediments rose substantially as the river flowed through the city, placing rural fishermen far from Indianapolis at significant risk through bioaccumulation in fish such as smallmouth bass, walleye and largemouth bass. Mercury is neurotoxic and causes irreversible harm to brain development in young children.

Mercury emitted from coal-plant smokestacks rapidly reacts with atmospheric constituents and water vapour, washing out over surrounding areas within roughly 15 kilometres of the smokestack. The metal is transformed in waterways by bacteria into methylmercury, which bioaccumulates up the food chain, concentrating in top predators to levels dangerous for developing foetuses and children. Lost productivity from mercury harm was estimated at approximately $9 billion per year in 2005 dollars. The original MATS rule's costs to the electricity sector were estimated at about $9.6 billion annually in 2012 dollars — roughly equal to productivity-loss estimates alone.

The Trump administration's rollback is expected to face legal challenge. The administration simultaneously weakened limits on arsenic, cadmium, chromium, lead and nickel emissions from coal plants, and dropped requirements for continuous emissions monitoring from smokestacks — a change critics say will reduce accountability for compliance. The rollback is intended to boost coal power production. Many plants had previously complied with MATS by converting from coal to natural gas rather than installing mercury-capturing filters, reducing mercury risk but maintaining fossil fuel combustion and associated emissions.

Key figure — MATS rule reduced mercury emissions from coal power plants by an estimated 90%