Parts Per Billion
ppb
A unit 1,000 times more sensitive than parts per million, used for very low concentrations of contaminants. One ppb equals one part pollutant per one billion parts of medium.
Related terms
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. 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. Maximum Contaminant Level 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.