Aspects of Heavy Metal and Organohalogen Pollution in Aquatic Ecosystems

The pollutants of major concern in aquatic ecosystems are those which are produced and reach the environment in large amounts, are toxic to aquatic organisms, or are concentrated within organisms to a level greater than that in the environment and which persist for long periods of time so that the environmental concentrations can gradually increase. Toxic heavy metals and organohalogen compounds are among the materials of concern. The toxicity of pollutants is generally determined by short-term, acute bioassay tests which are useful in determining a dangerous concentration, but not necessarily for the determination of a “safe” concentration in the environment. Sometimes acceptable concentrations can be evaluated in the natural environment by comparative studies of polluted and unpolluted ecosystems. Long-term laboratory tests to evaluate chronic toxicity are also desirable to evaluate sublethal effects such as changes in feeding behavior or decrease of breeding capability. Some chronic studies should involve a full generation or more of a given species so that all stages of the life cycle are exposed to the pollutant. The three contributions which follow set forth some of the complexities of aquatic ecosystems and discuss some of the problems involved in their study.