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Pesticides are toxic substances that are deliberately released into our environment to kill organisms which, from the point of view of man, are undesirable. The perfect pesticide would eliminate the target organism and be otherwise harmless. Unfortunately, as Dr Wurster and others have shown, some pesticides become environmental contaminants and have harmful effects that are often distant in time and space from the place where they were applied. These are calculated risks which have to be taken when the pesticide is used; the user believes that the advantages of application outweigh the disadvantages when, or perhaps more particularly if, he himself will not suffer from the side-effects of his actions. My present purpose is to deal with some of the other chemicals which man may introduce into his environment—usually accidentally, but sometimes deliberately, as in the cases of wastes discharged into the air or the sea as a method of disposal— which can also be the cause of environmental degradation.

World opinion has been awakening to a variety of man-made environmental problems during the past few years, and few of these have received more public debate than ‘the pesticide problem’. Strong emotions are evoked in people when they get the idea that they or other animals are being poisoned, regardless of whether the threat is real or imagined. ‘The pesticide problem5 is by no means a single problem, but instead consists of a host of individual and highly diverse problems depending on the pesticide and circumstances involved. In considering the effects of pesticides on nontarget organisms, I propose to organize my remarks into several categories, touching only on those aspects of pesticides that seem more important, and omitting much that in my view appears less critical.