Chlorinated hydrocarbon pesticides, detection

The non-polar chlorinated hydrocarbon pesticides are routinely quantified using gas chromatography (GC) and electron capture(EC) detection. Alternate detectors include electrolytic conductivity and microcoulometric systems. Organophosphate pesticides which are amenable to GC are responsive to either the flame photometric detector (FPD) or the alkali flame detector (AFD). Sulfur containing compounds respond in the electrolytic conductivity or flame photometric detectors. Nitrogen containing pesticides or metabolites are generally detected with alkali flame or electrolytic conductivity detectors. 

In place of heating, irradiation by UV light is necessary to complete the reaction of some chromogenic reagents. An example is the detection of chlorinated hydrocarbons (pesticides) by spraying with silver nitrate reagent and exposure to 254-nm light. 

Much of this chlorinated hydrocarbon is placed directly into wastewater via lavatory use and into the air we breathe at home and at work. Studies of the environmental aspects are negligible to date, and the conventional method used for analysis of chlorinated hydrocarbon pesticides in water does not normally detect dichlorobenzene. It has, however, been detected in the blood of workers exposed to it regularly and appears to accumulate in fatty tissues like other chlorinated hydrocarbons, (p. 354)... 

The performance of SCWO for waste treatment has been demonstrated (15,16). In these studies, a broad number of refractory materials such as chlorinated solvents, polychlorinated biphenyls (PCBs), and pesticides were studied as a function of process parameters (17). The success of these early studies led to pilot studies which showed that chlorinated hydrocarbons, including 1,1,1-trichloroethane /7/-T5-6y,(9-chlorotoluene [95-49-8] and hexachlorocyclohexane, could be destroyed to greater than 99.99997, 99.998, and 99.9993%, respectively. In addition, no traces of organic material could be detected in the gaseous phase, which consisted of carbon dioxide and unreacted oxygen. The pilot unit had a capacity of 3 L/min of Hquid effluent and was operated for a maximum of 24 h. 

Haberl [8] volatile chlorinated hydrocarbons, PCB and pesticides detected limits for each volatile compounds ... 

Analysis of PDP data from 1994 to 1999 showed that 73% of approximately 27,000 food samples that had no market claim (conventional or organic) showed detectable residues, while 23% of 127 fresh food samples designated as organic had detectable residue levels (Baker et al., 2002). Unavoidable contamination of some of the organic samples was due to the presence of persistent chlorinated hydrocarbon insecticides, which had been banned several years earlier, but 13% of the organic samples showed residues of pesticides other than the chlorinated hydrocarbon insecticides. 

Pesticides and Fungicides. Modern pure food regulations require that the food processor be responsible for their finished products. Since so many pesticides and fungicides are used in agriculture, their detection and quantitative analysis are difficult (5, 22). Organophosphorus and chlorinated hydrocarbons are the most common pesticides. When GLC is used for halogens, electron capture or microcoulometric detectors are used for phosphorus, a thermionic flame photometric detector is required. 

Pesticides can be analyzed on a C18 column, the chlorinated hydrocarbon type (chlordane) at 80% An/water UV, 220 nm, the carbamate type (sevin) at 40% An/water UV, 254 nm, and the organic phospahate (malathion) at 50% An/water with UV, 192 nm or with a CAD. The organic phosphate types are hard to detect at low concentration and various phosphate analysis techniques have been evaluated. LC/MS, where available, is the technique of choice for analyzing all of these pesticides, but especially the organic phosphates, in a general gradient HPLC scheme. 

Biosensors differ from bioassays mainly by the fact that in bioassays the transducer is not an integral part of the analytical system and biosensors can extract quantitative analytical information of single compounds in complex mixtures. One example is the determination of concentrations of dioxin-like compounds in the blood and environmental samples using the Calux assay, where within a complex matrix its levels are determined with great accuracy (see, e.g., Murk et al. 1997). Additionally, compounds that are difficult to detect (e.g., surfactants, chlorinated hydrocarbons, sulfophenyl carboxylates, dioxins, pesticide metabolites) can more easily be evaluated using biosensors. 

Because of the prowess of the analytical chemist, it is now possible to find residues of the chlorinated hydrocarbon insecticides in the environment at concentrations of a few parts per trillion. He is not so adept at finding nanogram quantities of some of the other classes of compounds for many pesticides, the metabolites are not identified, so he doesn t know what to look for. There is little question, however, that many of the compounds that now escape detection are present in the environment, and it is only a matter of time until the analytical chemist finds them. 

Ultraviolet Spectrophotometry Pesticides in food, drink, and biological fluids may be detected by ultraviolet spectrophotometry, usually after a simple extraction procedure. However, care must be taken to ensure that there are no ultravioletabsorbing co-extracted compounds which could interfere. The main drawback of the method is a lack of specificity, because the UV spectrum usually only indicates the group to which a particular pesticide belongs. In addition, those pesticides which lack a chromophore, e.g. chlorinated hydrocarbons, cannot be screened by this method. Nevertheless, UV data can be useftil when used in conjimction with data derived from chrom-atographic methods. Table 2 (p. 85) gives data for those pesticides which show significmt UV absorption. 

One of the first references to the discovery of pesticides other than chlorinated hydrocarbons in groundwater was by Richard etal. (1975). Inthelate 1970s, however, the number of detections increased rapidly, along with concern from public authorities about chemical contamination of ground-water. 

It is practically impossible to identify all chemicals in a sample and yet such procedures are needed to detect the presence of unanticipated chemicals and to signal new or potential problems. Extracts of water, sediment, and biota have been extensively fractionated and analyzed by multidetector gas chromatography [ 145]. Compounds detected in addition to the usual hydrocarbons, chlorinated hydrocarbons, and organochlorine pesticides included chlorinated isocyanates and aniUnes, cyclohexanol, cyclohexanone, aromatic ketones and acids, thiophenes, nonyl- and cumyl-phenols, carbazoles, quinolines, indoles and tolyltriazoles, and the pesticides permethrin, triclosan, and bromacil. 

Polychlorinated alkane determinations NCI has frequently been used to identify chlorinated hydrocarbons and other chlorinated compounds such as toxaphene, chlorinated paraffins, chlorinated styrenes, chlorinated diphenylethers, pentachlorophe-nol, chlorinated pesticides, and pesticide metabolites. Even if the molecular ion cannot be detected in all... 

Systematic investigation of pesticides in the Chesapeake Bay watershed began in the 1970 s in response to the observed decline in SAV and fish populations during that period. Investigations typically spanned a few years and tested for specific families of herbicides (e.g., dUoro-s-triazines and chloroacetanilides) and insecticides (e.g., organophosphates and chlorinated hydrocarbons) in various media. Detection limits and consistency in the methods of data collection improved with time. The data that are sununarized below consist of measurements of concentrations of atrazine in the iiqruts to surface waters at several locations throughout the Bay. We should stress that data are sparse spatial and temporal distributions have to be estimated and/or extrapolated from measurements in the top 0.5-1.0 m of the surface layer. 

Cell components or metabolites capable of recognizing individual and specific molecules can be used as the sensory elements in molecular sensors [11]. The sensors may be enzymes, sequences of nucleic acids (RNA or DNA), antibodies, polysaccharides, or other reporter molecules. Antibodies, specific for a microorganism used in the biotreatment, can be coupled to fluorochromes to increase sensitivity of detection. Such antibodies are useful in monitoring the fate of bacteria released into the environment for the treatment of a polluted site. Fluorescent or enzyme-linked immunoassays have been derived and can be used for a variety of contaminants, including pesticides and chlorinated polycyclic hydrocarbons. Enzymes specific for pollutants and attached to matrices detecting interactions between enzyme and pollutant are used in online biosensors of water and gas biotreatment [20,21]. 

---