The main anthropogenic sources are copper and nickel smelting, batteries and fuel combustion. It mostly enters the marine ecosystem through atmospheric loading and riverine discharges.
Cadmium is regarded as one of the most toxic metals. It causes sublethal and behavioral effects at lower concentrations than mercury and lead. It causes cancer in animals, and in vertebrates it causes kidney toxicity.  In humans it might also lead to skeletal deficiencies and lung damage. 
Like other heavy metals, cadlium does not have biomagnifying properties. Higher trophic levels accumulate low amounts of cadmium and are able to deal with them efficiently with metallothioneins. Mollusks contain large amounts of cadmium and seem to accumulate them.
- ↑ Kennish, M. J. (1996): Practical Handbook of Estuarine and Marine Pollution, CRC Press 524 pp
- Biology of marine birds. Schreiber, E.A. & Burger, J. (Eds). 2002. Boca Raton, Florida: CRC Press. 722 pp.
- New perspectives: Toxicology and the environment. Toxicology of marine mammals, eds.J. Vos, G. Bossart, M. Fournier, and T. O'Shea, New York: Taylor & Francis. 643p
- Clark, R,B., 1999. Marine pollution. Oxford University press, Fourth edition, pp 161