Maximum Contaminant Level
MCL
The highest concentration of a specific contaminant that the EPA legally allows in public drinking water. Set per chemical based on health risk and treatment feasibility.
Related terms
Legal Limit The maximum amount of a pollutant or contaminant that government regulators (like the EPA) allow in air, drinking water, or soil before the area or supply is considered out of compliance with the law. Parts Per Million A ratio expressing concentration as one unit of solute per million units of solution. For dilute aqueous samples, 1 ppm ≈ 1 mg/L. Environmental Protection Agency The U.S. federal agency responsible for setting and enforcing pollution standards for air, water, and soil, and for regulating hazardous chemicals.
Related contaminants
Perfluorooctanoic acid (PFOA) An 8-carbon long-chain PFCA — IARC Group 1 carcinogen (2023); 2024 NPDWR individual MCL of 4 ppt with MCLG of zero. Legacy Teflon manufacturing chemistry, phased out by major U.S. producers post-2002. Hexafluoropropylene oxide dimer acid (HFPO-DA) A perfluoroether carboxylic acid (GenX) developed by DuPont/Chemours as a PFOA replacement for fluoropolymer manufacturing. Federally regulated under EPA's 2024 PFAS NPDWR at MCL 10 ppt; widely detected in U.S. drinking water.