Transport organophosphorus compounds

The organophosphorus compounds constitute one major group of insecticides, and a certain portion thereof may be transported to the aquatic environment resulting either from the actual use on paddy fields or from unavoidable transmittance to waterways. However, possibly because of its relatively shorter persistence, the translocation and transformation of organophosphorus compounds in the aquatic environment has not been extensively investigated as compared with more persistent organochlorine compounds. 

Dr. P. Jeffers at the State University of New York at Cortland is gathering information to determine the persistence of organophosphorus compounds in groundwater and the effects of various soils on the degradation and transport of these compounds. Both neutral and base hydrolysis processes will be evaluated. Transport studies in soil columns will be conducted to determine the mobility of diazinon in soils. 

Two examples of toxicity, where the target is known, are carbon monoxide, which interacts specifically with hemoglobin, and cyanide, which interacts specifically with the enzyme cytochrome a3 of the electron transport chain (see chap. 7). The toxic effects of these two compounds are a direct result of these interactions and, it is assumed, depend on the number of molecules of the toxic compound bound to the receptors. However, the final toxic effects involve cellular damage and death and also depend on other factors. Other examples where specific receptors are known to be involved in the mediation of toxic effects are microsomal enzyme inducers, organophosphorus compounds, and peroxisomal proliferators (see chaps. 5-7). 

Drewes, L. R., and A. K. Singh. 1987. Cerebral metabolism and blood brain transport toxicity of organophosphorus compounds. Govt. Rep. Announce. Index (U.S.) 88(22), Abstr. No. 856, p. 413 cited in Chem. Abstr. CA III(l) 2296k. 

Irrigation and precipitation events result in the entry of organophosphorus insecticides into the hydrologic cycle. Organophosphorus compounds deposited on foliar surfaces, dissolved in soil water and sorbed to particles are mobilized and transported with surface runoff The main mobilization processes are discussed below. 

The toxicant may react with an enzyme or a transport protein and inhibit its normal function. Enzymes may be inhibited by a compound that has a similar, but not identical structure as the true substrate instead of being processed, it blocks the enzyme. Typical toxicants of this kind are the carbamates and the organophosphorus insecticides that inhibit the enzyme acetyl cholinesterase. Some extremely efficient herbicides that inhibit enzymes important for amino acid synthesis in plants, e.g., glyphosate and glufosinate, are other good examples in this category. 

Organophosphorus insecticides are applied to plants and soils using a variety of methods and formulations. Because formulation and initial placement affect exposure of these compounds to transformation processes and their availability for transport in surface runoff, the influence of these factors must be understood. Formulation in particular may exert an important influence on organophosphorus insecticide loads in surface runoff. Organophosphorus insecticides are rarely applied alone, but are mixed with other substances to enhance their performance and safety. These formulation ingredients can make up to 99.5% of the applied pesticide product and include organic solvents, surfactants and polymers. 

A significant fraction of hydrophobic organophosphorus insecticides is transported sorbed to suspended particles. The movement of these compounds in the environment depends on the erosion and transport of the particles to which they are sorbed. Soil erosion is a selective process resulting in the enrichment of clay-sized particles and NOM, and therefore hydrophobic organophosphorus insecticides, in the eroded material. 

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