Hazards to wintering geese and other wildlife from the use of dieldrin, chlorfenvinphos and carbophenothion as wheat seed treatments.

Chemical treatments of cereal seeds are used in the United Kingdom to prevent damage by a number of pests including the wheat bulb fly, which is a serious pest of winter wheat. The persistent organochlorine dieldrin was introduced in the 1950s as a seed treatment but caused the death of large numbers of grain eating birds and gave rise to unacceptable environmental contamination. The withdrawal of dieldrin as a seed treatment was made possible by the introduction of two less persistent organophosphate insecticides, chlorfenvinphos and carbophenothion. Although the introduction of these chemicals has been beneficial in reducing environmental contamination, some side-effects on wildlife have still been discernible and carbophenothion has now been withdrawn from use in Scotland owing to the deaths of wintering geese from carbophenothion poisoning. Subsequent laboratory studies have demonstrated that Anser geese are particularly susceptible to carbophenothion poisoning, and the underlying biochemical mechanism has been investigated. The fundamental problem of species variation in toxicity among the organophosphorus and carbamate pesticides which this investigation illustrates presents difficulties for registration authorities when they are considered for clearance for agricultural use. The implications of the environmental problems encountered with dieldrin, chlorfenvinphos and carbophenothion for the pre-clearance testing of new chemicals are discussed and the critical surveillance of the early years of commercial use of a chemical is recommended to support pre-clearance studies aimed at assessing the potential hazard to the environment.