Assessing the inhalation risk of semi-volatile pest control products requires knowledge of the rate of evaporation (flux) of the chemical, the extent of off-site movement of the chemical, and the inhalation toxicity of the chemical. Numerous direct micro-meteorological methods as well as an indirect method have been used to estimate the flux of chemicals, primarily soil fumigants, from fallow soil. Since most pest control products are applied directly to field crops and orchards, it is necessary to adapt the current methods to take into account the competing processes at the plant surface including plant uptake, sorption to plant leaves and stems, formulation type, and canopy architecture. Currently, there is no model that can take into account these factors and reliably predict evaporation from a crop canopy. Once the evaporation rate of the chemical from the plant canopy has been adequately characterized, either experimentally or using a model, it can be used as an input to an appropriate air dispersion model to predict off-site movement. Air dispersion models have been used extensively to predict off-site movement of soil applied fumigants, but their use in modeling off-site movement of semi-volatile chemicals from a plant canopy has been limited. Modeling off-site movement from a crop or orchard canopy needs to take into consideration parameters including the height of the canopy and the effect of the canopy on the roughness boundary layer. The air dispersion model also requires meteorological data from representative geographies where the crops of interest are grown. Valid exposure estimates must then be coupled with appropriate inhalation toxicity data which also presents unique challenges for compounds with low vapor pressure.

Volatility and air dispersion modeling considerations for assessing bystander exposure and risk from semivolatiles applied to crops and orchards

246th National Meeting (2013)

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