**11.2 Contaminants and pollutants in the sea**

The evidence is clear that it is not global warming, but some other underlying reason behind the declining marine life. A possible cause, and that explanation offered here, is the pollutants and toxins being discharged into the oceans.

We now look at the effect of the garbage, sewage, and industrial wastes being dumped into the oceans in much of the world. The dumping of such waste into oceans was legal until the early 1970's when it became regulated and restricted. However, dumping still occurs illegally everywhere. The peak of sewage dumping was 18 million tons in 1980, a number that has decreased to 12 million tons in the 1990s.

Rivers, canals, and harbors are dredged to remove silt and sand buildup or to establish new waterways. About 10% of all dredged material is polluted with heavy metals such as cadmium, mercury, and chromium, and pesticides which ultimately find their way into the sea.

Today it is acknowledged that accumulation of waste in the ocean is detrimental to marine health. Ocean dumping can destroy entire habitats and ecosystems when excess sediment builds up and toxins are released. Although ocean dumping in critical habitats and at critical times is regulated, toxins are still spread by ocean currents.

One of the best explanations for the declining marine life could be this increasing contamination of the oceans, caused by disposal of these wastes into the sea. It is known that the fishes are very sensitive to contamination in the water. Those in charge of aquariums, especially marine aquariums, are aware that fishes may be harmed or killed by even quantities of toxins. As any hobbyist with a fish tank may know, dropping a small contaminant such as a cigarette butt, could easily kill a tankful of fish. The exception to this could be fish which have coexisted with humans for a long time, (such as gold fish) and those that have learnt to survive well in contaminated waters (farmed fish).

Large numbers of fishes are known to wash up on shores, often for no apparent reason; a phenomena for which contamination is a likely explanation. A satisfactory explanation has not been found for why whales and other fish beaching, and ultimately killing themselves. This act of self-destruction is clearly highly destructive to the continuity of their genes, from an evolutionary point of view. One possible explanation for this counter-evolutionary behaviour of fishes beaching themselves could be to get away from chemically contaminated waters. The chemicals in the water may also confuse the fish into getting away from the water into the beach.
