The effects of pesticides on life in fresh waters.

Abstract

About sixty pesticides are estimated to be used in Britain in circumstances where some contamination of fresh waters could occur. Apart from major fish kills, most of the evidence of contamination must be obtained from chemical analyses of water or fish, although these are mainly restricted to a few organochlorine and organophosphorus compounds. The potential hazards to fish and invertebrates have been identified in laboratory experiments and toxicity tests, but routine population surveys of susceptible species in rivers and lakes are rarely made. The nature of possible environmental effects of various types of pesticides is described, and the information on toxic levels of some chemicals, obtained from laboratory tests, is compared with the limited data available on levels existing in the environment. The need for more extensive screening of pesticide chemicals, especially the more persistent types, is discussed. Both adult fish and fry of several species should be used in tests, as well as representative invertebrates, which are known to be more susceptible to some pesticides than are fish. Long-period tests are also required, as for some pesticides the lethal concentrations are much lower in extended tests than in the usual short-period tests. Where possible, the test species, whether fish or invertebrates, should be analysed for the chemical under test. Analytical techniques should be developed, for levels existing in the environment, of a wider range of compounds than is currently investigated.