Significance of the Long Range Transport of Pesticides in the Atmosphere

Since the 1960s there has been a growing body of data regarding the presence of pesticides in the atmosphere. The monitoring results obtained show that traces of pesticides may undergo long range transport and be deposited considerable 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 concentrations found depend on several variables such as their volatility, photostability, 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 simplification since it is also influenced by the surfaces treated, e.g. soil or leaves, and by the extent to which aerosols are formed during the application. The disappearance of pesticides from the atmosphere is due to hydrolysis, indirect photolysis via OH radicals and to deposition in rain. Pesticides which are resistant to hydrolysis and photolysis can be transported over great distances, for example, organochlorine insecticides have been detected in the Arctic regions. In general, concentrations in rainwater are, when detected, in the low or sub mg/L range and highest concentrations are found during the time of application. The use of fugacity models has been shown to be a useful approach to predict concentrations in air. Under most conditions the presence of pesticides in air, or rainwater, has no significant effects on nontarget systems, including direct and indirect effects. Exceptions to this are damage by auxintype herbicides to sensitive plants which has resulted on restrictions in their use in certain areas and transient chlorotic spotting thought to be caused by drift of aerosols from application of low rate sulfonyl urea herbicides. For animal species one possible exception has been postulated. This is for persistent organochlorine pesticides in Arctic regions where, due to the very oligotrophic nature of the Arctic ocean, they are more liable to bioaccumulate and be transported in the food web giving enhanced levels in mothers’ milk. THE IUPAC COMMISSION ON AGROCHEMICALS AND THE ENVIRONMENT MAKES THE FOLLOWING RECOMMENDATIONS Based on the conclusions from this review, several recommendations for further areas of research are suggested. Since the factors governing the fate and behaviour of pesticides in the atmosphere are the same for any organic contaminant, whether from natural or anthropogenic sources, research studies on pesticides in air should be considered in the same way as any organic contaminant in the atmosphere. 1 Investigations should be encouraged into obtaining a better understanding of cloud chemistry and its role in the long and intermediate transport of organic contaminants, including pesticides. 2 Investigations should be encouraged into the application of fugacity models in the prediction of atmospheric concentrations of organic contaminants, including pesticides, in defined areas due to long range transport. 3 In order to refine and validate current models specifically for pesticides additional investigations are required into: X the chemical reactivity of pesticides, particularly their photodegradation under environmental conditions. X the transfer of pesticides between environmental compartments to give the key factors leading to their occurrence in the atmosphere. X the parameters required to define the ‘unit world’, i.e. an identified and limited geographic area, for use in fugacity models. 1360 COMMISSION ON. AGROCHEMICALS AND THE ENVIRONMENT q 1999 IUPAC, Pure Appl. Chem. 71, 1359–1383 4 Since pesticides, as with all anthropogenic organic contaminants, will have an impact on sensitive ecosystems it is essential that steps are taken to ensure that they will not be distributed by long range transport in concentrations likely to pose a risk to non-target systems. It is recommended therefore that: X an assessment scheme is developed and validated to determine which pesticides show volatilisation behaviour and hydrolytic and photolytic stability which would indicate an extended residence time in the atmosphere. X for pesticides likely to have an extended residence time in the atmosphere assessments are carried out using fugacity models to predict their likely distribution in defined geographic areas.