Foliar sorption

While the occurrence of most processes affecting organophosphorus insecticide concentrations in surface runoff are well documented, many are relatively poorly understood on a mechanistic level. Key processes requiring further study include sorption to plant and soil surfaces, and transfer from soil water into overland flow. Sorption to foliar surfaces determines the amount of applied insecticide available for washoff onto the soil surface or into surface runoff The kinetics of desorption from plant cuticular materials and the effect of adjuvants on foliar sorption processes need additional research. 

Foliar Uptake Adsorption and Absorption The leaf surface provides an extensive surface area that can interact with chemicals either in the vapor phase or through wet or dry deposition. The cuticle limits water loss and protects against infection by plant pathogens. Detailed descriptions of the plant cuticle are available " and a brief synopsis has been provided in the discussion of the sorption of chemicals by foliage (see Sorption, Chapter 3). While the hydrophobic cuticle... 

Formulation and initial placement influence the susceptibility of organophosphorus insecticides to transport in surface runoff, as well as their degradation by abiotic and microbial processes. Formulation affects the kinetics of insecticide release into soil water and overland flow, as well as sorption to soil solids and plant surfaces. Spray adjuvants affect initial placement by influencing the amount of insecticide depositing on foliar and soil surfaces. Initial placement determines the relative importance of such processes as volatilization, photolysis, biodegradation, and leaching out of the zone of interaction with overland flow. 

Sorption to soil solids and plant cuticular material represents an important process influencing the chemodynamic behavior of insecticides, including their transport in surface runoff Sorption phenomena affect the volatilization, hydrolysis, photolysis and microbial transformation of organophosphorus insecticides. Furthermore, species sorbed to soil particles are transported by erosion processes rather than as solutes in the water phase. Sorption to foliar surfaces reduces the amount of pesticide mobilized by washoff. 

There now exists an extensive literature on the uptake and translocation of herbicides in plants. In this brief review, it is intended to elucidate the general principles that govern the transport of pesticides in plants. The transport behavior of the different classes of herbicides will be considered, together with ways of using physicochemical properties to predict the likely behavior of new chemicals. It should be noted that the processes of sorption in soil, of cuticular penetration in the case of foliar-applied compounds, and of metabolism in the plant all influence the availability of herbicides for uptake and redistribution in plants, and these factors are the subjects of separate chapters in this book. Interpretation of the literature on systemic transport usually needs substantial consideration of these additional factors. 

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