# Mercury and Air Toxics Standards > [!note] Stub — fill out The [[EPA]] rule (MATS), issued in 2012 under the [[Clean Air Act]], that set technology-based limits on Mercury (element) and other hazardous air pollutants from coal- and oil-fired power plants — one of the most cost-effective public-health rules in EPA history. Strengthened by the Biden EPA in 2024, then largely repealed by the Trump EPA: a final rule on February 19, 2026 (effective April 27, 2026) rolled back the tighter mercury and particulate limits and continuous-monitoring requirement, allowing plants to emit more than twice as much mercury, prompting state and environmental-group lawsuits. Expand with the rulemaking history, the cost-benefit fights, and the 2025 proclamation exempting coal units.