Estimation of aerial deposition and foliar uptake of xenobiotics: Assessment of current models

Abstract

The primary objective of this report was to review existing mathematical and/or computer simulation models that can be used to estimate xenobiotic deposition to and transport through (both cuticular and stomatal) vegetative surfaces. The secondary objective was to evaluate the potential for coupling the best of those models to the existing UTAB (Uptake, Translocation, Accumulation, and Biodegradation) model to be used for future xenobiotic exposure assessments. Here xenobiotic compounds are defined as airborne contantinants, both organic particulate and gaseous pollutants, that are introduced into the environment by man. In an attempt to simplify a portion of complexity of the question posed, a review of several potential classification systems for organic xenobiotics is also provided. Specifically this document provides a detailed review of the state-of-the-art models that addressed: I) aerial deposition of particles and gases to foliage; 2) foliar and cuticular transport, metabolism, and uptake of organic xenobiotics; and 3) stomatal transport of gaseous and volatile organic xenobiotic pollutants. Where detailed information was available, parameters for each model are provided on a chemical by chemical as well as species by species basis. Sufficient detail is provided on each model to assess the potential for adapting or coupling the model to the existing UTAB plant exposure model. Based solely on the literature evaluation, mathematical linking of these models is possible; however, the immediate utility of this "master" model would be questionable. The inability to adequately link these models at this time results from either a lack of empirical data for specific types of xenobiotics, and/or a lack of detailed understanding of controlling processes in the plant. Specific models are identified and recommendations for further research are provided for each area: I) wet and dry aerial deposition of xenobiotics; 2) foliar adsorption and cuticular transport of or garlic xenobiotics; and 3) stomatal transport of gaseous and volatile organic pollutants.