الفهرس 
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Abstract
Various chemicals, entering the aquatic ecosystem through man’s activities, either accidentaly or by design, may cause adverse effects on the aquatic biota, including deleterious changes which disrupt the metabolic activity at a biochemical level (Hirth, 1964; Hinton et al., 1973; Verma et al., 1979-a, b, c).
Trace metals (lead, copper, zinc) and synthetic orga- nics (PCBs, dioxin) have received considerable attention in recent years. Sublethal quantities of these anthrogenic substances are ultimately deposited in lakes and rivers (Kemp et al., 1978). This increase has-been found in remote locations as well as those close to identifiable sources (Evans and Rigler, 1980).
Some effects of metals may be recognized as changes in the shape, colour or even the taste of edible organisms and the classical example of this is that of oysters tunring green with accumulated copper (Boyce and Herdman, 1898). In the oyster Crassostrea Virginica this greening has been shown to occur at a soluble copper concentration.