Sorption agricultural pesticides

An extensive pesticide properties database was compiled, which includes six physical properties, ie, solubiUty, half-life, soil sorption, vapor pressure, acid pR and base pR for about 240 compounds (4). Because not all of the properties have been measured for all pesticides, some values had to be estimated. By early 1995, the Agricultural Research Service (ARS) had developed a computerized pesticide property database containing 17 physical properties for 330 pesticide compounds. The primary user of these data has been the USDA s Natural Resources Conservation Service (formerly the Soil Conservation Service) for leaching models to advise farmers on any combination of soil and pesticide properties that could potentially lead to substantial groundwater contamination. 

Insecticide methomyl is a very toxic pesticide and is highly soluble in water (57.9 g/1). It has a low sorption affinity to soil and can cause groundwater and surface water contamination in agricultural areas. Solubilities of methomyl in different solvents are in methanol 1000 g/1, in aceton 730 g/1, in ethanol 420 g/1, in isopropanol 220 g/1, in toluene 30 g/1. 

As discussed earlier in Section 3.17, the excessive application of arsenic-bearing pesticides and phosphate fertilizers on agricultural lands, golf courses, and lawns may locally contaminate surface waters and ground-waters (Welch et al., 2000), (Lewis et al., 2002), 590. Phosphates desorb arsenic from mineral surfaces and readily interfere with the sorption and coprecipitation of arsenic onto iron (oxy)(hydr)oxides (Campos, 2002). Commercial phosphate fertilizers also frequently contain >13 mg kg-1 of arsenic impurities (Campos, 2002), which may further contribute to groundwater contamination. 

In agriculture, phenolic compounds are used as pesticides (Figure 1) and can also form from the degradation of chlorinated phenoxycarboxylic acids and organophosphorous insecticides". The herbicide DNOC sorption in a sandy aquifer (Denmark) has been reported ". 

Solubility in water is one of the key characteristics of pesticides that determines their distribution and the stability of the individual components in the environment and in plants. Retention (sorption) of particularly soluble polar pesticides to soil particles is relatively small, but they can penetrate into undergroimd water resources. Polar pesticides are not very stable in the environment and are biodegradable they can be easily hydrolysed and oxidised. Their limited stability is then the cause of a relatively rapid decrease of their residual amounts in contaminated agricultural products during thermal processing. On the other hand, the loss of polar... 

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