Contaminants are unwanted chemicals in the environment or in living organisms, which may be harmful to plants, animals or humans.

Every year, many thousand chemicals are produced and used. They are beneficial in households (e.g. cleaning and disinfectant products), agriculture (eg. pesticides and fertilisers), or industry (e.g. flame retardants, paints and electrics).

Many of these chemicals can, however, move from their original application or production area (through air, water or with soil) and end up in places where they have not been intended for use. Some accumulate in the marine environment and can be found in sediment, plants and biota.