Understanding Trends in Pesticide Volatilization from Agricultural Fields Using the Pesticide Loss via Volatilization Model.

The Pesticide Loss via Volatilization model was developed to predict and understand pesticide volatilization rates from a planted agricultural field. The model allows the user to adjust the properties of the pesticide, various soil and plant descriptors, and climatic conditions. A useful output from the model is the 24 h cumulative percentage volatilization (CPV24h) loss. The model was validated by comparing modeled CPV24h values to measured ones compiled from the literature. Sensitivity analysis showed that the plant intercept fraction (%I), leaf area index (LAI), and leaf height (hleaf) strongly affect volatilization rates of plant- and soil-sorbed pesticides whereas LAI, hleaf, and the percent of water on the plant surface strongly affect more water-soluble pesticides. The model showed that most pesticides volatilize more readily from plants than from soil and that volatilization rates vary significantly for certain pesticides (but not all) when applied to plants at different growth stages and for different species of plants. Results are displayed on chemical space diagrams to paint a clear picture of how CPV24h varies for chemicals with different properties under different conditions.

Testing flow-through air samplers for use in near-field vapour drift studies by measuring pyrimethanil in air after spraying.

Pesticide volatilisation and subsequent vapour drift reduce a pesticide's efficiency and contribute to environmental contamination. High-volume air samplers (HVSs) are often used to measure pesticide concentrations in air but these samplers are expensive to purchase and require network electricity, limiting the number and type of sites where they can be deployed. The flow-through sampler (FTS) presents an opportunity to overcome these limitations. The FTS is a wind-driven passive sampler that has been developed to quantify organic contaminants in remote ecosystems. FTSs differ from other passive samplers in that they turn into the wind and use the wind to draw air through the sampling media. The main objective of this work was to evaluate the FTS in a near-field pesticide vapour drift study by comparing the concentrations of pyrimethanil in air measured using one HVS and three FTSs placed in the same location. Pyrimethanil was sprayed onto a vineyard as part of normal pest management procedures. Air samples were collected every eight hours for 48 h. The volume of air sampled by the FTSs was calculated using the measured relationship between ambient wind speed and the wind speed inside the sampler as determined with a separate wind tunnel study. The FTSs sampled 1.7 to 40.6 m(3) of air during each 8 h sampling period, depending on wind speed, whereas the mean volume sampled by the HVS was 128.7 m(3). Mean pyrimethanil concentrations ranged from 0.4 to 3.2 µg m(-3) of air. Inter-sampler reproducibility, as represented by percent relative standard deviation, for the three FTSs was ∼20%. The largest difference in FTS-derived versus HVS-derived pyrimethanil concentrations occurred during the lowest wind-speed period. During this period, it is likely that the FTS predominately acted like a traditional diffusion-based passive sampler. As indicated by both types of sampler, pyrimethanil concentrations in air changed by a factor of ∼2 during the two days after spaying. This work shows that the FTS has good potential for use in near-field vapour drift studies and that FTS technology could make multi-sampler experimental designs more feasible.