Formulation, pesticide organophosphorus compounds

The major classes of pesticides in use in the Region are organochlo-rine and organophosphorus compounds, Ccirbamates, pyrethroids and bacterial larvicides. Organophosphorus compounds are the most common, followed by pyrethroids. Insecticides are available in a variety of formulations, including emulsifiable concentrates (EC), wet-table powders (WP), dustable powders (DP), suspension concentrates (SC), oil-in-water emulsions (EW) and capsule suspensions (CS). 

Diazinon, an organophosphoras compound with an anticholinesterase mode of action, was released for experimental evaluation in the early 1950s. Diazinon is now used extensively hy commercial and home applicators in a variety of formulations to control flies, cockroaches, lice on sheep, insect pests of ornamental plants and food crops (especially com, rice, onions, and sweet potatoes), forage crops such as alfalfa, and nematodes and soil insects in turf, lawns, and croplands. Diazinon is the most widely used organophosphorus pesticide in Pakistan to control cabbage root fly and carrot fly. In 1992, more than 612,000 kg of diazinon were used in California on alfalfa, nuts, stone fmits, vegetables, and other crops. 

Bioemulsifiers are potentially useful in agriculture, especially in various formulations of herbicides and pesticides. The active compounds in these formulations are hydrophobic, and emulsifiers are required for dispersing them in the aqueous solutions. One example is the use of bioemulsifiers—probably glycolipo-peptides—produced by strains of Bacillus for emulsifying immiscible organophosphorus pesticides (Patel and Gopinathan 1986). 

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. 

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. 

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