Water-insoluble pesticides

Repeated applications of pesticides to crops and soil will result in a buildup in their concentration in the soil over a period of time, especially if they have a low solubility in rain water, more so if they are stable and of low volatility. If the pesticides have an appreciable solubility in rainwater, the build-up in their concentration in soil with repeated applications will be lower than is the case of relatively water insoluble pesticides. This is important from the point of view of transfer of insecticides from the soil to crops, grown on the land, or to watercourses, streams, rivers and perhaps eventually the oceans. 

Bratz, M. Jaeger, K. Solvent-free suspensions of water-insoluble pesticides with low melting point. Eur. Pat. Appl. EP 1319336, 2003 Chem. Abstr. 2003,139, 32098. 

Aldrin org chem CijHgCI Trade name for a water-insoluble, white, crystalline compound, consisting mainly of chlorinated dimethanonaphthalene used as a pesticide. al-dron ... 

The study was conducted to evaluate in situ sedimentation as an abatement procedure. DDT was chosen as the test pesticide since it is a persistent, water-insoluble compound that has created difficult disposal problems and since a contaminated site exists in Alabama where DDT residues estimated to exceed 500 tons have been found in the bottom sediment of a 3-mile stream segment. 

The yellow carotene binding protein of M. sexta hemolymph is a more complicated case. Carotenes are extrerraTTy water-insoluble materials. They share this property with several other natural products including sterols, fats and hydrocarbons, all of > hich are important to insects. This property is also shared by many xenobiotics, including pesticides. Transport of hydrophobic materials within the aqueous compartments of living organisms, e.g. blood or hemolymph, is accomplished by lipoproteins. Extensive... 

Solvents are important ingredients of emulsifiable concentrates and of solution formulations. When the formulation is to be used on crops, it is critical that the solvent be nonphytotoxic. The solvent must have a high level of solvent power if an EC is being formulated. Because most toxicants are insoluble in water, the solvent must also be water insoluble. Otherwise, when the EC is added to water in the spray tank, the solvent will mix with the water and leave the toxicant behind as a crystalline precipitate. The carrying power of the solvent, i.e., the amount of pesticide it will hold in solution, is important in the storage stability of formulations. If near its saturation point at ordinary temperatures, it may exceed this at low temperature with the result that solvent and pesticide may separate, causing crystal formation and phase separation (Terriere, 1982). 

A ow). The aqueous solutions may be preferred for the more water-soluble pesticides, whereas the organic solvents may provide better results for highly water-insoluble chemicals. The water used for preparing aqueous solutions should be either distilled or deionized if possible. Several commercially available surfactants have been nsed to prepare hand-rinse solutions ( Snr-Ten , Aerosol OT-75 , Emcol 4500 and Nekal WT-27 ) at concentrations of abont 0.01 %. 

Su oemulsions are defined as a mixture of a dispersed solid phase and an emulsified oil phase in water as the continuous or bulk phase. The solid phase is a solid, water insoluble active ingredient, the oil phase a liquid pesticide in pure form or dissolved in a water insoluble solvent. The oil phase can sometimes also be an oil or adjuvant. Suspoemulsions are a relatively new formulation type as becomes evident by the fact that a FAO specification was established only as late as 1997. At the same time specific evaluation methods were officially published (CIPAC MT 180) [2]. 

Currently, the use of water insoluble solvents such as ethyl acetate that do not require partition is preferred. Unfortunately, using ethyl acetate, lower recoveries are observed for the most polar pesticides. If the raw extract is saturated with sodium sulphate, satisfying recoveries are observed for methamidophos, acephate and omethoate (Holland and Malcolm, 1992). 

Fulvic acids, being more soluble than humic acids, may have a special function with regard to the fate of organic compounds applied to soil as pesticides. Ogner and Schnitzer (1970a) suggested that fulvic acids act as carriers of alkanes and other normally water-insoluble organic substances in aquatic environments, and it is possible that these constituents also function... 

Natural organic polyelectrolytes are some of the most active components of natural soil-water systems entering into physical and chemical reactions with practically all other components of the systems. Most pesticides are strongly sorbed by insoluble natural organic polyelectrolytes, such as humic acid. The soluble humic salts, however, may solubilize insoluble pesticides. Pesticides also enter into chemical reactions with natural organic poly electrolytes. The mechanisms of most of these interactions have not yet been elucidated. Elucidation will require isolation of well-defined, chemically and physically homogeneous natural polyelectrolyte fractions. 

Percutaneous absorption studies using in vitro techniques appear to be of value in the assessment of pesticide absorption as well as with other types of compounds. As with any procedure, precautions may need to be taken in certain steps to ensure the accuracy of the data. For water-insoluble compounds, the llpophilicity of the... 

SSF technology can be applied to a wide range of pesticide materials, including herbicides, fungicides, and insecticides. Surfactant chemistry can be used to optimize the formulation efficacy in the development of an herbicide SSF. Combination packs diat include both water-soluble and water-insoluble actives can also be developed. Formulation adjuvants such as oils or electrolytes can be incorporated into an SSF formulation to increase its biological activity. 

Uses Dispersant, compatiblllty/anticaking agent for pesticide wettable powds. Properties White odorless powd. pract. insoluble in water insoluble in polar and aromatic solvents bulk dens. 0.5 g/cc flash pt. > 100 pH (5% aq.) 7-8 = 60% act. 

Pentachlorophenol is readily soluble in most organic solvents, oils, and highly aromatic and olefinic petroleum hydrocarbons — a property that makes it compatible for inclusion in many pesticide formulations (Table 23.1 Figure 23.1). Purified PCP, however, is practically insoluble in water therefore, the readily water-soluble sodium pentachlorophen-ate salt is substituted in many industrial applications (Table 23.1) (Bevenue and Beckman 1967 USPHS 1994). 

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