Contamination refers to the presence of harmful substances—chemicals, pollutants, pathogens, or other hazardous materials—in soil, water, air, or other environments where they pose risks to human health or ecosystems. Environmental contamination can result from industrial activities, chemical spills, improper waste disposal, or natural sources. Contaminated sites (brownfields) require remediation before safe reuse. Water contamination threatens drinking water supplies. Soil contamination affects food safety and land development. Provincial environmental ministries regulate contamination, setting standards for acceptable levels and requiring cleanup. Municipalities deal with contamination through land use planning, building permits, and sometimes brownfield redevelopment incentives.