or less, in various substrates within the aquatic ecosystem. Because of 

 their very low concentration, such chemical contaminants may not be 

 detected until they appear in undesirable levels within some trophic level. 

 Serious ecological damage or effects on human health have sometimes 

 occurred before we have taken action to prevent further contamination. An 

 example is the environmental mercury problem, which first received world- 

 wide attention when human beings were poisoned by eating contaminated fish 

 and shellfish during the 1950's in Minamata, Japan. 



EFFECTS ON FISHERY RESOURCES 



Synthetic organic chemical residues that accumulate in aquatic 

 organisms can have far-reaching effects on an entire fishery resource. In 

 particular, the problem is exemplified by the impact of polychlorinated 

 biphenyls (PCB) on fishery resources of the Great Lakes. 



Occurrence and Accumulation 



Polychlorinated biphenyls are a widely used class of chlorinated 

 hydrocarbons found in a variety of manufactured products and in many 

 industrial processes. Environmental monitoring has shown that PCB are 

 distributed throughout the Great Lakes ecosystem, but the highest 

 concentrations are generally found near industrial and urban area. Some 

 specific industries are known to discharge PCB in their effluents, but 

 non-specific sources such as municipal wastewater effluents are more 

 difficult to control. Atmospheric contributions in the form of rain, snow, 

 and particulate fall-out also may be significant. 



Concentrations of PCB in the Great Lake waters are generally only a few 

 parts per trillion (nanograms per liter), but because of biological concen- 

 tration residues in some fish exceed 20 parts per million (milligrams per 

 kilogram). Laboratory studies indicate that fish can accumulate PCB by 

 more than 40,000 times the exposure concentration (Stalling and Mayer, 

 1972). The residues are most concentrated in the lipids of body tissue. 

 Careful monitoring studies have shown that residue concentrations vary with 

 different species in proportion to their fat content. The highest concen- 

 trations are found in mature salmon and trout just before or during their 

 spawning migration (Veith, 1975). 



It has been suggested but not proven that PCB and other chemical 

 residues accumulated in the eggs are responsible for high mortalities of 

 some fish during the early stages of development. Mortality of young 

 salmon has been high where the eggs contained PCB, DDT, and some other 

 chemical residues (Johnson and Pecor, 1969; Halter and Johnson, 1974). 

 More recently PCB are suggested as the cause for losses of northern pike 

 ( Esox lucius ) embryos in Michigan hatcheries (Waybrant, 1975). In Sweden 

 Jensen, Johansson, and Olson (1970) suggested a correlation between PCB 

 residues and mortality of salmon eggs and fry. 



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