Properties of pesticides

The fate of a given compound in the soil depends upon its partition between the soil particles themselves and the water, air and organisms it contains. Certain physicochemical properties of pesticides can be used to predict which are most likely to be leached. The most diagnostic properties are the sorption and degradation characteristics. 

A possible source of groundwater contamination, which has up to now almost been neglected, is associated with the introduction of surfactants into soils as pesticide additives (Table 6.7.3). Non-ionic surfactants composed of alcohols and fatty acids are most widely recommended as adjuvants to facilitate and enhance the absorbing, emulsifying, dispersing, wetting and penetrating properties of pesticides. Other pesticide adjuvants are silicone-based surfactants,... 

The key properties of pesticides that control their accumulation in sediment and biota are hydrophobicity and persistence. Generally, pesticides were found to have the potential to accumulate in sediments and in biota if they had a water solubility of < 1 mg/L or an octanol-water partition coefficient of (fC0w) > 1000 and a soil half-life of > 30 d. Pesticides that are rarely detected in sediment or in biota have high water solubilities and short soil half-lives. A few pesticides that are moderate in hydrophobicity and persistence can also be detected in the environment to some extent. Most of the current-use pesticides have relatively high water solubilities and short soil half-lives, and are not likely to accumulate in biota. However, some currently used pesticides that are intermediate in hydrophobicity and persistence are likely to be detected (Table 4). It is also important to take into account where, and in what amounts, these pesticides are applied. 

Typically, only 0.01-10% of the mass of pesticide compounds applied to fields is detected in streams [91]. The remaining 90-99% of pesticides adsorb to soil, percolate into groundwater, or volatilize [79]. The major degradates of the most heavily used herbicides found in surface water have not been studied widely. Many chemical properties of pesticides affect the amounts transported to streams. In general, acetanilide herbicides are more soluble in water, and thus more mobile than are the triazines [92], The solubilities of sulfonated degradates of acetanilides (ethane sulfonic acid, or ESA), can be 10 times the solubility of the parent compound [93]. The greater mobilities of the degradates of the acetanilides (amide family) can explain these com-... 

The chemical and physical properties of pesticides affect their behavior in the environment. Solubility in water, soil half-life, and organic carbon partition coefficient (Koc) play a major role in determining a chemical s runoff potential. Because families of pesticides have similar chemical structures and physical properties, similar frequencies of detections would be expected when... 

Heller, S.R., Scott, K., Bigwood, D.W. (1989) The need for data evaluation of physical and chemical properties of pesticides The ARS pesticide properties database. J. Chem. Inf. Comput. Sci. 29, 159-162. 

Toxic Properties of Pesticides, Nicholas P. Cheremisinoff and John A. King... 

From these data on pesticide usage, the environmental effects associated with adoption of GM crops will be assessed both qualitatively and quantitatively. Qualitatively, the impact will be predicted based on, for example, properties of pesticides, quantities of applied pesticides, times of application, pest characteristics, and geographic conditions. Subsequently, the quantitative assessment will employ methods such as environmental indicators that allow for a comparison of the environmental impacts of different pesticide regimes. The enviroiunental impact may also cover other important parameters associated with altered agronomic practices under GM crop cultivation, such as tillage practices and farmland biodiversity. 

Mackay et al. (1997) provide detailed examples of fugacity calculations to illustrate how variations in the physical and chemical properties of pesticides affect their partitioning among environmental media. Figure 3 displays the results from some of these calculations for three of the pesticides listed in Table 1. Consistent with the expectations described above, these computations predict that following their release into the hydro-logic system, the relatively water-soluble herbicide atrazine will come to reside mostly in the aqueous phase, the more hydrophobic insecticide... 

Kiso, Y. et al.. Rejection properties of pesticides with a hollow fiber NF membrane (FlNF-1), Desalination, 143, 147, 2002. 

From this discussion on this common parameter we now turn to consider some other issues relating to predictive models. Predictive models are typically based on statistical data. They involve a given uncertainty. Their natural variability is also often quite large. In order to compare the uncertainty of the model with that of the natural process, the latter has to be known. All these recommendations may seem obvious, but often they are disregarded or misunderstood. The programs to predict simple environmental properties are quite robust, even though far from perfect. For instance, they have been evaluated in their capability to predict properties of pesticides [68],... 

The EC funded HAIR project (http //www.rivm.nl/stoffen-risico/NL/hair.htm) is devoted to integrating the different methods for the assessment of pesticides into a combined index. The intention is to go beyond the environmental and ecotoxicological properties of pesticides and to address the human toxicity aspects as well. The ultimate target is to produce an index useful to regulators changed with evaluating the EU policy on pesticides and to reduce the overall impact of the pesticides. This project also considers other chemicals besides pesticides. As in many other examples, the lessons learned from pesticides... 

Many researchers have investigated the role of soil (8., 9.), microbes (10,21), management practices (.12, 13), and environment (14) on the enhanced degradation of pesticides. The properties of the pesticides that influence enhanced degradation have not been studied in detail. Because pesticides are metabolized after application to the soil, some of them within a short time, the properties of pesticide metabolites may also influence the degradation process significantly. 

These experiments are conducted to study the irritation properties of pesticides on albino rats, rabbits, and guinea pigs. Emulsifiable concentrates and other liquid pesticides are applied to thoroughly sheared skin areas of test animals, and one or two drops are placed in their eyes. In the event that inflammation of the skin or eye membranes is detected, the test is repeated with actual emulsions or solvents of the chemicals in question. 

The cumulative properties of pesticides may be studied under different experimental conditions. A necessary minimum of data can be obtained through acute and subacute experiments involving enteral administration of substances. 

Decisions taken by regulators have important economical consequences for the industry that manufactures pesticides, the farmers, the workers and the consumers. Such consequences, justify the need for regulators to have well supported data related to the four steps of the risk assessment process. Risk assessment requires a robust analytical basis studies addressed either to hazard identification or exposure estimation. Both have to be conducted under good laboratory practice (GLP) certification [6]. This paper deals with the key points of hazard identification and exposure assessment, both aspects highly influenced by the solubility and physical-chemical properties of pesticides. 

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