Volatilization of Parathion and Chlorothalonil from a Potato Crop Simulated by the PEARL Model

The volatilization of pesticides from crop canopies in the
field should be modeled within the context of evaluating
environmental exposure. A model concept based on diffusion
through a laminar air-boundary layer was incorporated
into the PEARL model (pesticide emission assessment at
regional and local scales) and used to simulate volatilization
of the pesticides parathion and chlorothalonil from a
potato crop in a field experiment. Rate coefficients for the
competing processes of plant penetration, wash off, and
phototransformation in the canopy had to be derived from
a diversity of literature data. Cumulative volatilization of
the moderately volatile parathion (31% of the dosage in 7.6
days) could be simulated after calibrating two input data
derived for the related compound parathion-methyl. The less
volatile and more slowly transformed chlorothalonil
showed 5% volatilization in 7.6 days, which could be
explained by the simulation. Simulated behavior of the
pesticides in the crop canopy roughly corresponded to
published data.