On Monday NAAA submitted a letter to the EPA’s Office of
Pesticide Programs requesting the agency reevaluate how they conduct modeling
to calculate drift estimates for aerial applications of pesticides when they
conduct risk assessments as part of the pesticide registration and
re-registration process.
All current risk assessments are conducted by the EPA using
the Tier 1 model in AgDRIFT. This model uses many inaccurate assumptions about
how modern aerial applications are conducted that results in significant
overestimates of drift. These include variables such as the application uses a
radial powered aircraft, a smaller than commonly used droplet size, a swath
displacement shorter than industry standards, a slight inversion during the
application, wind speed measured at a height appropriate for ground
applications instead of aerial applications, an application to bare ground
instead of a standing crop, and the assumption that a second application would
occur with a wind speed and direction identical to the first application.
NAAA has established a good working relationship with EPA
and has commented on numerous risk assessments and proposed interim decisions. It
has also met with key professional staff of EPA-OPP over the past number of
years on this very topic which EPA been open to hearing. Many of NAAA’s comments have focused on the
inaccuracies of the Tier 1 AgDRIFT model which results in an over estimation of
drift from aerial applications. These over estimations can then result in risk
assessments that find potential hazardous risks to the environment, and human
health which in turn can lead to stricter label requirements in order to
mitigate the risks. NAAA feels the Tier 3 AgDRIFT model with more realistic
assumptions should be used to estimate more realistic estimates of drift and
thus more realistic risk assessments.
NAAA suggested the EPA use the more detailed Tier 3 model in
AgDRIFT because it allows for many of the variables from the Tier 1 model to be
changed to improve the model’s accuracy at estimating drift from aerial
applications. NAAA recommended specific assumptions and settings to be used in
the Tier 3 model. To start, NAAA suggested a turbine powered aircraft be used
instead of one with a radial engine. NAAA suggested the wind speed be increased
from 10 to 15 mph to reflect real world spraying conditions and the fact that many
labels currently allow spraying in wind speeds up 15 mph.
NAAA suggested boom length be set at 75% of the wingspan and
boom drop set at 1.3 feet lower than the current Tier 1 level to reflect the boom
positioning commonly seen on agricultural aircraft today. Instead of a fine
droplet size, NAAA suggested using a medium droplet size which is easily
created by many of the commonly used nozzles on agricultural aircraft today. A
swath displacement of half a swath displacement was suggested instead of only a
1/3 of a swath displacement on the downwind field edge. Settings for the
atmospheric stability component of the model were recommended to accurately
model applications not occurring during an inversion, as all labels already
prohibit applications when an inversion is present. NAAA recommended a more
appropriate height for measuring wind speed and direction such as at the
location of where a a smoker or Aircraft
Integrated Meteorological Measurement System (AIMMS) would measure the conditions
and to run the Tier 3 model assuming the presence of a crop instead of bare
ground. Bare ground aerial applications are not nearly as common as aerial
applications to a standing crop and the bare ground setting in AgDRIFT results
in a much higher drift estimate.
Finally, NAAA urged EPA to use a component of the AgDRIFT model to reflect the unlikelihood that if more than one application of a single pesticide is made, both applications will take place under identical weather conditions with wind blowing in the exact same direction at the same speed. The full letter to EPA can be read here. The next step in the process to improve risk assessments for aerial applications will likely be for NAAA to meet with EPA staff involved in the using the AgDRIFT model to further discuss the request to more accurately model drift from aerial applications.