Interactions between pesticides; a review of reported effects and their implications for wildlife risk assessment.

: Reviews of pesticide usage survey data and vertebrate wildlife and honeybee poisoning incident schemes in the UK show that there is considerable potential for wildlife to be exposed to combinations of agricultural pesticides. According to the published literature the toxicity of many pesticide combinations is at least additive. In some cases pesticide mixtures, particularly those involving insecticides, have been shown to be synergistic, with reported increases in toxicity of up to 100-fold. However, these effects are species, time and dose dependent and are therefore difficult to predict routinely. It is suggested that risk assessments should routinely take additive toxicity into account and those based on synergism should be targeted at those mixtures for which a further defined increase in toxicity would result in a high-risk classification. In order to support this risk assessment approach there is a need to develop and validate a standard in vivo test in order to confirm the interaction in those cases where additive or synergistic toxicity results in a high-risk classification.