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
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
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