Pyrethroid in water

Most pyrethroids undergo acid- and base-catalyzed hydrolysis to form the corresponding acid and alcohol (Fig. la), typically with U-shaped pH-rate profiles [8, 40]. The hydrolysis of pyrethroids in water basically obeys first-order kinetics with a half-life simply calculated from hydrolysis rate constant (A obs) as 0.693/kobs. Pyrethroids are generally stable under the acidic and neutral conditions at pH 4—7,... 

Liu W, Gan JJ (2004) Determination of enantiomers of synthetic pyrethroids in water by solid phase microextraction - enantioselective gas chromatography. J Agric Food Chem 52 736-741... 

Hladik ML, Kuivila KM (2009) Assessing the occurrence and distribution of pyrethroids in water and suspended sediments. J Agric Food Chem 57 9079-9085... 

Pyrethroid Esters of Benzene Acetate. These insecticides have more extensive stmctural optimization in both acid and alcohol moieties. Fenvalerate [51630-58-17, a-cyano-(3-phenoxyphenyl)methyl (+)-(2R,5)"Ct"isoprop5i-4-chlorophenylacetate (24) d 1.17, vp 1.4 p.Pa at 25°C), a mixture of four isomers, is soluble in water to 0.3 mg/L The rat oral LD q is 450 mg/kg. Esfenvalerate [66230-04-4] is the (+)-2-(i, 5)-isomer (mp 59°C). The rat LD qS are 75, 458 (oral), and the rabbit dermal LD q is 2000 mg/kg. These pyrethroids are widely used general-purpose insecticides for field, vegetable, and fmit crops. 

Because of the high toxicity of pyrethroids to aquatic invertebrates, these organisms are likely to be adversely affected by contamination of surface waters. Such contamination might be expected to have effects at the population level and above, at least in the short term. In one study of a farm pond, cypermethrin was applied aerially, adjacent to the water body (Kedwards et al. 1999a). Changes were observed in the composition of the macroinvertebrate community of the pond that were related to levels of the pyrethroid in the hydrosoil. Diptera were most affected, showing a decline in abundance with increasing cypermethrin concentration. Chironimid larvae first declined and later recovered. 

Pistocchi A, Vizcaino P, Hauck M (2009) A GIS model-based screening of potential contamination of soil and water by pyrethroids in Europe. J Environ Manage 90(11) 3410-3421... 

Feo ML, Eljarrat E, Ginebreda A et al (2010) Presence of pyrethroid pesticides in water and sediments of Ebro River Delta. J Hydrol doi 10.1016/j.jhydrol.2010.08.012... 

Synthetic pyrethroids now account for at least 30% of the world insecticide market and are rapidly replacing other agricultural chemicals for control of insect pests. Fenvalerate is one of the more widely used synthetic pyrethroid insecticides. It is derived from a combination of a-cyano-3-phenoxybenzyl alcohol and a-isopropyl phenylacetate ester. Technical fenvalerate is a mixture of four optical isomers, each occurring in equal amounts but with different efficacies against insect pests. Fenvalerate does not usually persist in the environment for >10 weeks, and it does not accumulate readily in the biosphere. Time for 50% loss (Tb 1/2) in fenvalerate-exposed amphibians, birds, and mammals was 6 to 14 h for reptiles, terrestrial insects, aquatic snails, and fish it was >14 h to <2 days and for various species of crop plants, it was 2 to 28 days. Fenvalerate degradation in water is due primarily to photoactivity, and in soils to microbial activity. Half-time persistence in nonbiological materials is variable, but may range up to 6 days in freshwater, 34 days in seawater, 6 weeks in estuarine sediments, and 9 weeks in soils. 

The second difference between the laboratory tests and exposure under realistic environmental conditions is that in the laboratory exposure concentrations are maintained, or the ecotoxicological endpoints are adjusted to account for any decline. Under natural conditions a combination of the pyrethroids tendency to partition rapidly and extensively to organic matter, coupled with their susceptibility to degradation in aquatic systems where algae and macrophytes are present [13,14], means their overall dissipation rate from the water phase is generally relatively rapid. Water column dissipation half-lives tend to be around 1 day (see Sect. 5). This behavior means that it is unlikely that aquatic organisms will be exposed to pyrethroids in the water phase for prolonged periods in natural water bodies. 

In summary, the bioavailability and observed toxicity of synthetic pyrethroids in sediment-water systems is influenced by a number of physicochemical factors, including the quantity and type of organic and inorganic matter in sediment and in water, as well as by temperature. The use of equilibrium partitioning calculations can be a useful tool for estimating the dissolved and potentially bioavailable fraction of pyrethroids. 

The movement of synthetic pyrethroids in soil and sediment is basically controlled by diffusion, convection, and dispersion. When entering a water-sediment system... 

Lauridsen RB, Kronvang B, Friberg N (2006) Occurrence of sediment-bound pyrethroids in Danish streams and their impact on ecosystem function. Water Air Soil Pollut Focus 6 423-432... 

This assumption is reasonable because the toxicity of pyrethroids to benthic organisms is predictable from the equilibrium partitioning-derived pore water concentration (8), and the pyrethroids in this study have values comparable to those of cypermethrin (10). 

The persistent pyrethroids such as permethrin, cypermethrin, cyfluthrin, and fenvalerate are effective mothproofing agents when applied as spot treatments from ready to use (RTU) formulations. Sodium fluosilicate [16893-85-9] is an effective mothproofing agent used at 0.5 to 0.7% in water solution with 0.3% potassium aluminate and 0.03% oxalic acid, and applied to fabrics by spraying or dipping. It is not removed by dry cleaning. 

The accountibility of (14C)-fenitrothion was considerably reduced by 21 days. In Year 1 estimates of total fenitrothion in water were obtained by use of extractable radioactivity which was low by Day 5 resulting in low estimates of the total fenitrothion in water. Another source of error could be greater deposition of fenitrothion on sediments on the sides of the ponds which is not taken into account by sampling the pond bottom. This has been observed with pyrethroid insecticides in similar outdoor ponds... 

Serodio, P. and J.M.F. Nogueira. 2005. Development of a stir-bar-sorptive extraction-liquid desorption-large-volume injection capillary gas chromatographic-mass spectrometric method for pyrethroid pesticides in water samples. Anal. Bioanal. Chem. 382 1141-1151. 

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). 

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