Significance of the long range transport of pesticides in the atmosphere -(Technical report)

Since the 1960s there has been a growing body of data regarding the presenc e of pesticides in the atmosphere. The monitoring results obtained show tha t traces of pesticides may undergo long range transport and be deposited co nsiderable distances away from the treatment areas, including remote areas such as the Arctic and Antarctic regions. Pesticides have been found in air , rain, cloud water, fog and snow. The appearance and subsequent behaviour of pesticides in the atmosphere are complex processes and the concentration s found depend on several variables such as their volatility, photostabilit y, method of application and extent of use. Whilst volatility of pesticides can be linked to their Henry's Law constant this is very much a simplifica tion since it is also influenced by the surfaces treated, e.g. soil or leav es, and by the extent to which aerosols are formed during the application. The disappearance of pesticides from the atmosphere is due to hydrolysis, i ndirect photolysis via OH. radicals and to deposition in rain. Pesticides w hich are resistant to hydrolysis and photolysis can be transported over gre at distances, for example, organochlorine insecticides have been detected i n the Arctic regions. In general, concentrations in rainwater are, when det ected, in the low or sub mu g/L range and highest concentrations are found during the time of application. The use of fugacity models has been shown t o be a useful approach to predict concentrations in air. Under most conditi ons the presence of pesticides in air, or rainwater, has no significant eff ects on nontarget systems, including direct and indirect effects. Exception s to this are damage by auxintype herbicides to sensitive plants which has resulted on restrictions in their use in certain areas and transient chloro tic spotting thought to be caused by drift of aerosols from application of low rate sulfonyl urea herbicides. For animal species one possible exceptio n has been postulated. This is for persistent organochlorine pesticides in Arctic regions where, due to the very oligotrophic nature of the Arctic oce an, they are more liable to bioaccumulate and be transported in the food we b giving enhanced levels in mothers' milk.