Organochlorine insecticides Organophosphorus pesticides

A snpercritical flnid extraction (SEE) method for the determination in strawberries of a number of commonly used organochlorine insecticides, organophosphorus pesticides, and dichloroaniUde fungicides (Pearce et al., 1997). 

The reagent sequence is specific for endosulfan and phosphamidon. Other insecticides, e.g. organochlorine insecticides, such as endrin, aldrin, dieldrin, DDT and BHC, organophosphorus insecticides, such as malathion, parathion, dimethoate, quinalphos, phorate and fenitrothion, or carbamate insecticides, such as baygon, car-baryl and carbofuran do not react. Neither is there interference from amino acids, peptides or proteins which might be extracted from the biological material together with the pesticides. 

Snyder et al. [20] have compared supercritical fluid extraction with classical sonication and Soxhlet extraction for the extraction of selected pesticides from soils. Samples extracted with supercritical carbon dioxide modified with 3% methanol at 350atm and 50°C gave a =85% recovery of organochlorine insecticides including Dichlorvos, Endrin, Endrin aldehyde, p,p -DDT mirex and decachlorobiphenyl (and organophosphorus insecticides). 

Further, by virtue of their larger livers, the R fish have a greater xenobiotic biotransformation potential. However, the in vivo studies show few consistent differences in metabolism between the two populations. Biotransformation may be a major contributory factor in mosquitofish resistance to other pesticides, for example, organophosphorus and botanical insecticides, since the level of resistance to these chemicals is very low (4 fold or less) 08,20,21). However, biotransformation does not appear to play a major role in organochlorine insecticide resistance. 

Organophosphorus pesticides (OPPs) have been used extensively as insecticides, fungicides, herbicides, and animal pesticides for more than four decades. They have been used instead of organochlorine pesticides because their relatively rapid decomposition makes them less persistent in the environment and because their accumulation in the biological food chain is limited. Basic to the proper assessment of the potential health hazards of OPPs is the knowledge of their fate in biological systems and in the environment (12,13). 

In Figure 3, Bowman and Beroza s extraction p-values obtained from different pairs of immiscible solvents are plotted (10). The degree of correspondence for the p-values of these compounds—organochlorine and organophosphorus insecticides and other pesticides— from one pair of solvents to another is clearly featured. The additional independent evidence for identity gained by obtaining a second p-value is very small. 

Another important factor is defining the pesticide distribution coefficients for oil and water, which affect both their ability to enter the body by penetrating skin and cell membranes and their eventual location in the system. A high distribution coefficient (characteristic of many organophosphorus and organochlorine insecticides) means these substances can easily penetrate the skin, travel via the blood-brain barrier to the central nervous system and enter intracellular formations (Kagan 1985, Kundiev 1975). 

The purpose of Experiments 3 and 4 is to present methods for the TLC determination of pesticides. Experiment 3 describes procedures for the separation and detection of organochlorine (OCl), organophosphorus or organophosphate (OP), and Ai-methylcarbamate insecticides and metabolites (Sherma and Bloomer, 1977 Sherma et al., 1977, 1978 Sherma, 1978). Experiment 4 describes the quantitative TLC determination of three classes of herbicides after isolation from water by conventional separatory funnel extraction or solid-phase extraction (SPE) (Sherma, 1986c Sherma and Boymel, 1983). 

Pesticides are also a major source of concern as water and soil pollutants. Because of their stability and persistence, the most hazardous pesticides are the organochlorine compounds such as DDT, aldrin, dieldrin, and chlordane. Persistent pesticides can accumulate in food chains for example, shrimp and fish can concentrate some pesticides as much as 1000- to 10,000-fold. This bioaccumulation has been well documented with the pesticide DDT, which is now banned in many parts of the world. In contrast to the persistent insecticides, the organophosphorus (OP) pesticides, such as malathion, and the carbamates, such as carbaryl, are short-lived and generally persist for only a few weeks to a few months. Thus these compounds do not usually present as serious a problem as the earlier insecticides. Herbicides, because of the large quantity used, are also of concern as potential toxic pollutants. Pesticides are discussed in more detail in Chapter 5. 

Environmental Defence recently released Toxic Nation A Report on Pollution in Canadians (Environmental Defence 2005). Samples were collected from 11 people for the presence of 88 chemicals, including heavy metals, PBDEs, PCBs, perfluorinated chemicals, organochlorine pesticides, organophosphorus-insecticide metabolites, and VOCs. The study objectives included determining whether pollutants were present at measurable concentrations in Canadians, identifying chemicals of concern, and creating public awareness of methods for avoiding exposure. 

Apart from gases and oil, the most likely pollutants that will need to be determined are pesticides, solvents, polyaromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs). The pesticides may be either insecticides or herbicides and are usually organochlorine, organophosphorus or organonitrogen compounds. 

Pesticide residues in foodstuffs in Pakistan Organochlorine, organophosphorus and pyrethroid insecticides in fruit and vegetables, Richardson, M. (ed.). Environmental Toxicology Assessment, Taylor and Francis, 1995,438 pp. 

SPE is also an efficient procedure for recovery of organochlorine (Sherma, 1988b) and organophosphorus (Sherma and Bretschneider, 1990) pesticides from water and can be combined with the TLC procedures described in Experiment 3 for quantification of these compounds in water. SPE and TLC have also been used to quantify the benzoylurea insecticide diflubenzuron in water (Sherma and Rolfe, 1993). 

Synthetic pyrethroids constitute a new generation of pesticides that have been developed as good substitutes for persistent organochlorine and toxic organophosphorus insecticides. 

The mechanism by which pesticides exert their toxic effects on mammals has been characterized for only a few groups of compounds [17,18]. For example, the mechanism for organophosphorus and carbamate insecticides involves inhibition of cholinesterase also, nitrophenols and higher chlorinated phenols are inhibitors for oxidative phosphorylation [10]. Fat-soluble substances (e.g., organochlorines such as DDT, HCH, and other persistent substances) accumulate in the body and, when stored in fatty tissues, cannot be... 

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