In the natural state, it is almost always associated with other metals (zinc and lead). Its natural concentration in the seas is of the command of the microgram. The agents of contamination due to the human activity are primarily the mines and the refineries, the rejections industrial and the urban waste water, the phosphate-enriched fertilizers and the insecticides.

  The total cadmium discharge in water is 7.1 million kg. In the marine medium, cadmium quickly is transferred to the sediments then absorbed by the living organisms on the mud. For the marine biotope, it is even more toxic than mercury.