Contaminantdefinitions

Contaminant definitions refer to the criteria used to identify and categorize substances or materials that are considered contaminants in a given context. A contaminant is typically any substance present in an environmental medium, product, or process where it does not belong, or is present at a concentration that may pose a risk to health, safety, or quality. The term is distinguished from related concepts such as pollutants, impurities, and additives, with the precise meaning depending on the regulatory, industry, or scientific context.

In regulatory frameworks, contaminant definitions drive surveillance and control. Authorities establish maximum contaminant levels (MCLs) or similar limits for drinking water, air quality, food, soil, and consumer products. These thresholds are often health-based, technologically achievable, or precautionary, and they may differ by matrix, use, and population. Detection and reporting require validated analytical methods and specified decision limits. When a substance is present above the defined limit, it is typically treated as a contaminant within that framework and subjected to remediation, monitoring, or regulatory action.

Common examples include inorganic contaminants such as arsenic and lead in water, microbial pathogens, organic solvents, pesticides, and industrial byproducts. Emerging concerns also include PFAS, pharmaceuticals, and microplastics, for which definitions and thresholds continue to evolve with scientific understanding. Because definitions are jurisdiction- and context-specific, they can vary over time and across sectors, influencing risk assessment, compliance, and public health protections.