The goal of this project is harmonization of the use of agrochemical spray drift studies for risk assessment and development of mitigation measures. Four objectives are delineated.
Highly concentrated agrochemical residues generated during spray application can move (drift) from targeted sites to nontarget receptor sites. Nontarget receptors including water, plants, and animals can be exposed acutely and therefore face the greatest risk of adverse effects during and immediately after spray application. In addition to movement of agrochemical residues in turbulent air masses downwind of application, residues can also become concentrated in inversions or stable air masses and be transported long distances. Similarly, agrochemicals can volatilize from plant and soil surfaces in comparatively high concentrations for several days after application. These residues, known as secondary drift, also pose a hazard to nearby nontarget receptors.
The impact of spray drift must be estimated during risk assessment so that appropriate risk management can be applied to mitigate potential nontarget effects. Spray drift therefore must be characterized so that residues moving to nontarget receptors can be predicted. Spray drift can be characterized as a function of surface area deposition relative to downwind distance. The resulting function can be empirically obtained or estimated using both deterministic and stochastic models. While similar pesticides are registered throughout the world, dissimilar methods are employed to estimate both the magnitude of spray drift and its potential impact.
Especially lacking are common procedures for estimating the residues depositing in a body of water or on a nontarget organism. For example, different countries use different volumes of water as a nontarget receptor. Thus, residue concentrations in water resulting form spray drift can vary by several orders of magnitude, and such wide variation leads to wildly divergent perspectives on spray drift hazards.
Furthermore, every agrochemical product label includes warnings such as avoid spray drift, but little attention has been paid to mitigating such drift. In some cases, certain physical parameters (pressure and water volume) and nozzle technology are recommended. In other cases, no-spray buffers may be recommended between the sprayer and the nontarget receptor. However, critical analysis of all of the mitigation recommendations is lacking, nor is there a universal consensus for how to assess mitigation.
This project provide a much needed critical assessment of spray drift studies worldwide. It will examine models used for estimating downwind drift. The existing models and methods for drift estimation will be examined for their adequacy in estimating secondary drift and drift in inversions. The project will characterize mitigation recommendation worldwide and attempt to harmonize procedures for assessing mitigation.
Members of the task force will compile from around the world published and unpublished studies of agrochemical spray drift. A listing of all chemicals (both pesticide and tracers) that have been empirically studied will be made along with notes on the methodology employed to characterize drift. Each study will be examined for the function relating drift deposition to downwind distance. Recorded meteorological parameters and sprayer technology will be analysed for each study. Data gathering will be enhanced by consultation with the database developed in the U.S. by the group known as the Spray Drift Task Force. Both empirical and stochastic models designed to estimate drift will be reviewed. A compilation of models used by regulatory bodies will be made. The adequacy of these models for predicting drift will be assessed by comparing their output to the results of selected individual studies. How regulatory bodies worldwide use spray drift functions in risk assessment will be characterized. It is assumed that the nontarget receptor is water, and the various assumptions about the volume of this receptor will be characterized. Methods for examining and standardizing exposure estimates to nontarget receptors other than water will be suggested.
Mitigation measures recommended by regulatory bodies and extension trainers will be critically examined. The project will especially focus on buffer zone recommendations. Methods for designing appropriately sized buffer zones to protect nontarget receptors will be developed. Development of protective buffers will require gathering some data on toxicological endpoints, such as the NOAEL (No Observable Adverse Effects Level) for plant and aquatic organism toxicity, and the RfD (Reference Dose) or ADI (Acceptable Daily Intake) for humans.
A project plan will be drafted by the project leader and circulated via email to all task force members. Members will be requested to compile an annotated bibliography of all published and unpublished spray drift studies in their global region. All information will then be compiled by the project leader and circulated to members to capture any missing studies. Members will then gather and submit to the project leader via email procedures employed by their regions’ regulatory bodies for estimating drift and using it in risk assessments. Similarly, mitigation measures will be compiled from around the regions and submitted to the project leader. The project leader will develop a draft report of all the information. Team member will meet face-to-face to review, discuss, and critique all of the compiled information. At that point, selected team members will examine models for their adequacy in predicting spray drift. Team members will again meet face-to-face to review mitigation measures and make recommendations to harmonize best practices to reduce spray drift hazards.
Dec 2010 – project completed. A review titled ‘Agrochemical spray drift; assessment and mitigation’ is published in the Journal of Environmental Science and Health Part B (2010) 45 889-911. (doi:10.1080/03601234.2010.515161)