Pesticides, chlorinated structures

Residue analytical chemistry has extended its scope in recent decades from the simple analysis of chlorinated, lipophilic, nonpolar, persistent insecticides - analyzed in the first Si02 fraction after the all-destroying sulfuric acid cleanup by a gas chro-matography/electron capture detection (GC/ECD) method that was sometimes too sensitive to provide linearity beyond the required final concentration - to the monitoring of polar, even ionic, hydrophilic pesticides with structures giving the chemist no useful feature other than the molecule itself, hopefully to be ionized and fragmented for MS or MS" detection. 

Pesticides include the broad categories of insecticides, fungicides, rodenticides, and herbicides. Insecticides in common use fall into three categories. The chloroinsec-ticides have chlorine in their structure. They are less soluble than the other insecticide forms and much less biodegradable (i.e., more persistent). While they are less acutely toxic, several have been identified as potential carcinogens. Carbamatea are a relatively new form of pesticide. They are less persistent and less... 

C. Structure of Common Chlorinated Pesticides and Abundant Ions... 

Attempts have been made to apply the structure-activity concept (Hansch and Leo 1995) to environmental problems, and this has been successfully applied to the rates of hydrolysis of carbamate pesticides (Wolfe et al. 1978), and of esters of chlorinated carboxylic acids (Paris et al. 1984). This has been extended to correlating rates of biotransformation with the structure of the substrates and has been illustrated with a number of single-stage reactions. Clearly, this approach can be refined with the increased understanding of the structure and function of the relevant degradative enzymes. Some examples illustrate the application of this procedure ... 

GC is coupled with many detectors for the analysis of pesticides in wastewater. At the present time the most popular is GC-MS, which will be discussed in more detail later in this section. The flame ionization detector (FID) is another nonselective detector that identifies compounds containing carbon but does not give specific information on chemical structure (but is often used for quantification because of the linear response and sensitivity). Other detectors are specific and only detect certain species or groups of pesticides. They include electron capture,nitrogen-phosphorus, thermionic specific, and flame photometric detectors. The electron capture detector (ECD) is very sensitive to chlorinated organic pesticides, such as the organochlorine compounds (OCs, DDT, dieldrin, etc.). It has a long history of use in many environmental methods,... 

OC are man-made chemical substances that encompass a wide range of compounds with different structures and applications. They are known for their high chemical stability, which stems from their large proportion of halogen substituents, either chlorine, bromine or others. Some of them were synthesised for use as pesticides and others for industrial applications. 

Lindane is a chlorinated pesticide with the following structure ... 

First, mobile phase and column we saw that most of the small molecule separations could be made on a C18 column in An/buffer water, with the exception of charged molecules and carbohydrates, which are too water soluble. We saw a range of polarity from fat-soluble vitamins, steroids, triglycerides, chlorinated pesticides eluting in 60-80% An/water, to carbamate, phosphate pesticides, anticonvulsants, antidepressants at 40-50% An/water, to nucleosides, nucleotides, aspirin, and water-soluble vitamins at 5-10% An/water. If you know something about the compound s structure or its solubility, you have a good clue as to what mobile phase can be used for its separation. 

Because of their extensive use in industrial activities, phenolic compounds are abundant in many wastewaters. They are present in oil refining, petrochemical, plastic, pesticide, carbon liquefaction, and food processing industrial wastewaters. In addition, phenol-like structures are part of the macromolecular natural humic substances present in water humics are known precursors of trihalomethane compounds in drinking water chlorination [176,177], These compounds are refractory to conventional processes such as biological oxidation because of their toxicity for microorganisms [178]. 

Regardless of one s position in this debate, it is apparent that the use of compounds that show persistence in the environment must be carefully examined and monitored. Any compound that is persistent and hydrophobic (lipophilic or fat soluble) will be subject to the process of biomagnification and may present special problems. In addition to DDT and other chlorinated pesticides, another example is provided by the polychlorinated biphenyls (PCBs). These compounds have two benzene rings bonded together, with varying numbers of chlorines substituted on the rings. One example is provided by the following structure ... 

New data from our experiments on enzyme changes with other chemicals now show that in rats, not only carbon tetrachloride but also ethylene dichloride, benzene, and methanol bring about a reduction in serum B-esterase during 4 days after a single oral dose at the acute level. These findings seem to indicate that the serum esterase activity response is considerably independent of the chemical structure and the molecular configuration of the stressing chemical, except that the stimulation of esterase activity occurs later than with the chlorinated hydrocarbon pesticides. 

Chlorinated Aromatic Hydrocarbon Environmental Toxins. As a result of human endeavor, toxic compounds containing chlorinated benzene rings have been widely distributed in the environment. The pesticide DDT and the class of chemicals called dioxins provide examples of chlorinated aromatic hydrocarbons and structurally related compounds that are very hydrophobic and poorly biodegraded (Fig. 5.28). As a consequence of their persistence and lipophilicity, these chemicals are concentrated in the adipose tissue of fish, fish-eating birds, and carnivorous mammals, including humans. 

Figure 1 Chemical structures of (A) polychlorinated biphenyls (PCBs) (B) dichlorodiphenyltrichloroethane (DDT) and the metabolites dichlorophenyidichloroethane (DDD) and DDE (C) other chlorinated pesticides. C, carbon atoms H, hydrogen atom Cl, chlorine atom.

Heptachlor [76-44-8], another cyclodiene insecticide of chemical structure similar to chlordane is a chlorination product of chlordane. Technical grade heptachlor contains about 73% heptachlor, 22% fran -chlordane and 5% nonachlor. This pesticide was extensively used until 1970s for the control of soil insects, cotton insects, grasshoppers and termite control. The use of this pesticide for underground termite control was banned in the United States in 1988. Its application after that was restricted to controlling fire ant in power transformers. The U.S. EPA has classified heptachlor as a Group B2 probable human carcinogen. 

The chemical structures of some organo-chlorine pesticides and their toxicity data as... 

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