Pesticide Drift: Seeking Reliable Environmental Indicators of Exposure Assessment

Abstract

Pesticide drift, the physical movement of the pesticide droplets or particles through the air at the time of pesticide application or soon thereafter from the target site to any non-target site, is a constant concern in pesticide use because it inevitably occurs even in the most careful applications, and thus, can increase the possibility of detrimental effects of pesticide use on the environment. Numerous factors can affect the occurrence and the extent of pesticide drift, but the main ones are the application method and the spraying equipment used, the canopy type and height, the weather conditions, the physicochemical properties of the spray liquid, and the decisions made by the applicator. Several pesticide risk indicators have been developed so far to predict the potential environmental impact of agrochemicals (including pesticide drift), many of which have the advantage of requiring a small amount of inputs, being rather fast to calculate and easy to interpret, allowing comparisons both in space and time, and representing an integration of different processes in rather complex systems. However, the information to be included in such indicators varies widely among the different indicators utilized, with the selection process often reflecting to a great extent the specific background of the developers. Thus, different indicators may provide different results, depending on the compartments and effects taken into account, often resulting in difficult judgements about which results are most accurate. Assessing the contribution of each single pesticide to potential environmental problems, in addition to eco-toxicological aspects of the products, requires consideration of the method and the timing of application, without ignoring other aspects of pesticide use. Yet, a major problem in such assessments is the lack of reliable quantitative exposure information, a fact which is also related to the paucity of appropriate pesticide usage data, including the behavioural variable of the pesticide applicator. Nevertheless, it appears that indicators for assessing pesticide impact on the environment will presumably proliferate as long as more complete datasets and indicator prototypes are produced and as long as the pioneering efforts are continuously criticized and improved. It should be kept in mind, however, that the potential negative consequences of pesticide use are largely displaced both spatially and temporally, and also that the effects on humans or other organisms may show up far from the site of application or often are not manifested for many years. Taking into account all the above, environmental indicators for the assessment of exposure by pesticide drift, albeit useful instruments for a relative risk rating among pesticides, can be questioned from both a technical and a practical point of view.