Volatilization, organophosphorus insecticides

Pyrethroids generally have low vapor pressures. Although empenthrin (20) volatilizes at room temperature without external energy and is 31 times more volatile than allethrin, its vapor pressure is only 1/88 that of dichlorvos, a volatile organophosphorus compound. As profluthrin (40) is 13 times more volatile than allethrin and volatilizes gradually for 6 months to 1 year at room temperature, it is suitable as an insecticide for the protection of clothes. The vapor pressure of profluthrin is 10 mPa/25°C, almost the same as that of glycerin. 

Controlled-release solid formulations of selected volatile organophosphorus pesticides (malathion, DDVP, sumithion, chlorpyriphos, and sulprofos) were studied by Szente [33]. These solid formulations exhibited negligible vapor pressure and preserved their entrapped pesticide content even at elevated temperature. Malathion and chlorpyriphos formulations showed increased physical stability, and resulted in an effective masking of the unpleasant smell while the complex formulations existed as dry solid. Sulfluramid is an expensive insecticide that is lost by volatilization, but complexation to j8-CyD reduced the loss [21]. 

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. 

Prior to application of spray formulations, spray adjuvants are typically added to the insecticide mixture to enhance the efficacy of the active ingredient. Spray adjuvants include surfactants, compounds that impart adhesion and viscoelasticity to spray droplets (e.g., latex), compounds that provide protection from ultraviolet light and reduce volatilization, and activators. The coapplication of these compounds affects organophosphorus insecticide dissipation and transfer to surface runoff Some adjuvants and formulation ingredients are toxicologically significant themselves (e.g., nonylphenol ethoxylates). 

The effect of formulation and spray adjuvants on insecticide efficacy has received considerable attention from the pesticide industry. However, few detailed mechanistic studies on the role these additives play in environmental fate processes have appeared in the open literature. Application of laboratory-derived process information to field scenarios is hindered by the fact that most laboratory investigations have used technically pure (unformulated) organophosphorus insecticides. Including the effects of formulation ingredients on such processes as volatilization and sorption to soil solids would allow laboratory studies to better predict the environmental behavior of these compounds. 

Volatilization also represents an important loss process for foliar applied organophosphorus insecticides. Although volatilization generally occurs... 

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. 

Cholinesterase and acetylcholinesterase reactivator used to treat poisoning by organophosphorus insecticides and nerve gases. Used in detn. of Cd, Co, Cu, Fe, Pb, Mn, Hg, Sn, Zn. Leaflets (Et20/pet. ether), needles (by subl.). Sol. H2O, Et20, spar. sol. C H. Mp 69°. pA 8.39. Steam-volatile, readily subl. 

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