Formulations, organophosphorus insecticides

The expected continued use of famphur in the environment and its vehicular transport along roads that border navigable waters suggest a need for aquatic toxicity data. Famphur data — like those on other organophosphorus insecticides — should reflect the influence of dose, exposure duration, formulation, and other biological and abiotic variables on growth, survival, and metabolism of representative species of aquatic organisms. 

Naled is a fast acting, nonsystemic contact and stomach organophosphorus insecticide used to control aphids, mites, mosquitoes, and flies on crops and in greenhouses, mushroom houses, animal and poultry houses, kennels, food processing plants, and aquaria. Naled is also used in outdoor mosquito control. Liquid formulations can be applied to greenhouse heating pipes to kill insects by vapor action. It has been used by veterinarians to kill parasitic worms (other than tapeworms) in dogs. Naled is available in dust, emulsion concentrate, liquid, and ultra-low volume (ULV) formulations. 

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. 

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. 

Several other aspects of organophosphorus insecticide sorption require further study. Although sorption-desorption hysteresis (20), aging and bound residue formation (30) have been noted, the molecular mechanisms responsible for these phenomena have not been elucidated. The kinetics of organophosphorus insecticide release from soil particles including the effects of biosurfactants (31) have not been extensively investigated, nor have the effects of formulation ingredients on sorption processes (32). 

Formulation strongly affects the amount of organophosphorus insecticide washed off from foliar surfaces. For example, azinphos-methyl and phosmet formulated as emulsifiable concentrates were highly susceptible to washoff, while wettable powder formulations were not (58). Thin-walled fenitrothion microcapsules were less prone to washoff than the emulsifiable concentrate (59). The composition of spray adjuvants also affected the degree of washoff (5<5). 

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). 

Carbamate anticholinesterases these are reversible in as much as their duration of action is short as compared to organophosphorus anticholinesterases, and are used extensively. An example is carbaryl (carbaril) and several analogues of carbaryl are used as insecticides. However, not all carbamates found in garden formulations are cholinesterase inhibitors the dithiocarbamates are fungicidal. 

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]. 

Since pyrethrins are highly photolytic, antioxidants are often added to preparations to stabilize formulations antioxidants adjoin include pyrocatechol, pyrogal-lol, hydroquinone, and l-benzene-azo-2-naphthol. Practically, all pyrethrins and many pyrethroids are commonly combined to additives (including synergists), some formulations include additional insecticides, insect repellents, or both, and many contain hydrocarbon solvents [3] to enhance their insecticidal activity. Pyrethrin and pyrethroid sprays may also be water based or be alcohol or petroleum based, which increases the overall toxicity. It is known that concomitant use of pyrethrins and pyrethroids with synergists such as piperonyl butoxide, A -octyl bicycloheptene dicarboximide, sulfoxide, sesamin, sesame oil, sesamolin, isosafrole, and organophosphorus compounds or carbamates may increase toxicity by mechanisms involving inhibition of microsomal oxidation [4]. 

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