Mercury is the most common and most toxic in water bodies. It occurs in water as monomethyl mercury. Mercury posioning is responsible for minimata disease in Japan in epidemic form. The cause of death was the fish contaminated with mercury.
DDT leads to the phenomenon of biological magnification or food chain concentration, ie, the continuous increase in concentration of a toxicant at successive trophic levels in food chain.
Oil spills cause water pollution thus, affecting sea life.