Noxious substances are substances or their mixtures occurring in the environment which may detrimentally affect human beings, animals, plants or other organisms and entire ecosystems. The adverse impact may be induced by intake by organisms or by input into an ecosystem.
Pollutants differ with respect to their “poisonousness” or toxicity. They may have acute or long term (chronic) effects. Chronic effects to human beings and animals are that substances give rise to cancer (carcinogenicity) that they may alter the genetic make-up (mutagenicity), cause deformities or have detrimental effects on the functioning of the hormone balance (endocrine effect). Persistent substances or substances accumulating in organisms (bioaccumulation) equally range among the pollutants. In addition, substances which are harmful to the biocoenosis as they reduce species diversity, they reduce the number of organisms or they modify species composition are also defined as pollutants.