There are a variety of chemical contaminants found in a variety of sources. These could be of natural origin or resulting from human activity (anthropogenic). The primary source of anthropogenic compounds is the chemical industry (industrial solvents, paints, adhesives, oil and petrochemical industries, household products, pesticides and fertilizers, fabric materials & furnishings, etc.). Regarding chemicals of natural origin, a good example are heavy metals that are present in the environment (mercury, lead, etc.) apart from being the result of human activity.