To define a pollutant precisely is difficult; just as a weed is a ‘plant in the wrong place’, so a pollutant may be described as ‘a substance present at the wrong concentration’. For example: oil is a natural product and the yearly hydrocarbon input by organisms to the environment (Smith (1954) estimated global marine input to be c. 5 tons km−2y−1) vastly exceeds the petroleum spillage resulting from man’s activities (0.15 tons km−2y−1; a probably high estimate by Wilson, 1974). Yet the latter is rightly regarded as pollution because it causes local hydrocarbon concentrations far in excess of the natural levels which organisms are adapted to.
KeywordsMytilus Edulis Fouling Organism Thermal Pollution Sheep Shead Minnow Cooling Water Flow Rate
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