This text considers the risks to human health and other biota in the environment arising from pesticide use. The basis of pesticide use lies in selectivity of compounds: the ability at the dose applied to control target weeds, pests and diseases without causing unacceptable effects to human health or other nontarget species. The text considers the mechanisms of selectivity that explain why many pesticides are specific in their action – some to an almost extraordinary degree. Considerations of dose form an integral part of the evaluation, and risks to human health and the environment are compared with those arising from other hazards.

The stimulus to produce this text originated in the late 1990s when, in the same week, the author experienced great frustration in questioning speakers with ingrained, almost blinkered opinions: the first from a major pesticide company keen to emphasise the very low risks to health from pesticide residues, but who would not acknowledge the problems arising from the use of his company's products in their concentrated form in developing countries; and secondly from an organic cooperative who claimed that major medical problems were likely to arise from pesticide residues in food, but would not recognise the much greater problem that might arise from naturally occurring carcinogens, particularly mycotoxins. Such polarised attitudes to pesticides are common. Indeed, the non-target effects of pesticides have been much debated since the publication of Silent Spring by Rachel Carson in 1961.