Of great importance is the need for an understanding of the results of man’s invasion of the oceans. Can this invasion affect the composition of the marine communities by altering the death rates of one or more species ? Can certain areas become hostile to sea creatures ? What is the probability of the pollutants being returned to man in his food products recovered from the marine environment ?
Studies are going on towards understanding our surroundings. In part, these studies have been motivated by curiosity; in part, by the need to protect man’s institutions against the attacks of nature such as winds, rains and flood water. Now, the ability of mankind to alter the earth’s surface gives a new point to environmental study. The results of man-made changes in nature can be harmful and perhaps may result in the loss or the restricted use of valuable resources. The ability to foresee undesirable results along these lines may lead to necessary and protective policy about them.
About 5,000 tons of mercury per year are estimated to
enter the oceans as a result of the release of industrial wastes into
rivers and the atmosphere. Agriculture and industry between them alone consume
9,200 tons of mercury per year, one-half of the world’s production. The mercury
in the sea is taken in by fish directly or through small organisms feeding on
mercury which has settled on the sea-bed. The mercury concentration increases
at each stage and poisoning can occur when people and domestic animals eat such
fish. Fish from ten lakes in Ontario, Canada, were recently declared unsafe to
eat. Canada has banned the sale of fish caught, within her boundaries, in Lake
St. Clair, where the level of mercury concentration has become dangerously
high.
Substances until recently unknown in the marine environment are
now being found in the sea. Perhaps the most abundant of the artificial
pollutants is an organic chemical, DDE, a product of the pesticide DDT. Many
marine species have been found to contain residues of other chemicals such as
dieldrin, endrin, heptachlor epoxide and benzene hexachlorides. These substances
are chemically stable and have a high chlorine content. Their effect on marine
creatures, in some cases, has been disastrous. Population decreases have been
found for marine birds and fish as a result of the presence of these
substances in their bodies.
Radio –active materials released from
the recent nuclear device testings by the USA, UK, USSR, China and France may
be found in all oceans. These nuclear tests have introduced into the seas such
materials as radio-active strontium-90 and caesium-137. There has also been a
big increase in the amounts of carbon-14 and tritium in the surface layers of
the oceans and the atmosphere. The radio-active materials have often been found
in very high concentrations in marine organisms.
By - Brendan J. Carroll 
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