HCH isomers

Chemistry and Environmental Impact. Lindane is produced by the photocataly2ed addition of chlorine to ben2ene to give a mixture of isomers. The active y-HCH isomer can be preferentially extracted and purified. Composition of the technical-grade product is a (65—70%), B (7—10%), y (14—15%), 5 (7%), and S (1—2%). Lindane has been produced worldwide for its use as an insecticide and for other minor uses in veterinary, agricultural, and medical products. 

Figure 9. Increase of intracellular Ca stimulated by various HCH isomers. Cells were labeled with lndo-1 and suspended at 2 X 10 cells/mL buffer at 37°C. The HCH isomers were dissolved in DMSO and added to the cell suspensions such that the final HCH concentration was 260 pff and the final DMSO concentation was 0.25% (v/v). The various isomers are indicated in the plot. The control is DMSO alone. The data are plotted as the ratio of fluorescence at 400 nm (measured on channel A) to that at 490 nm (measured through a Corion 490-nm interference filter on channel B).

Of the other HCH isomers, the alpha and beta forms are less toxic than the gamma form. However, the beta form is more persistent than the gamma form, and unacceptably high residues have sometimes been reported in foods originating from countries where technical HCH is still used (Environmental Health Criteria 123). 

Elimination, dehydrogenation, and hydrogenolysis may take place during biotransformation of HCH isomers. 

Pesticides, and especially OCPs (DDT and its metabolytes, HCH isomers, aldrine, dieldrin, heptachlor, etc.), are seen everywhere in mammals. Table 4.7 gives data on the death of higher vertebrates from causes linked to agricultural production in the USSR. About 40% of the accidental deaths of animals, and about 80% of birds, are due to pesticides. It is difficult to evaluate how many mammals in the environment die from pesticide contamination, since sick and weakened individuals fall prey to predators [6]. 

Figure 2. Composition of PCB congeners, HCH isomers, CHL compounds, and DDT compounds in immature and mature Caspian seals and their diet fish (Hall et al., 2002).

A detection of p-isomer HCH in water in relatively larger quantities in comparison with other isomers shows a high degree of insecticide transformation in the soil (mainly by microorganisms), and hence loss or leaching of insecticide residues deposited some decades ago. It is known that p-isomer HCH is the most stable compound among others of HCH isomers, i.e., it is not or very weakly exposed to elimination reaction—dehydrochlorination (Cristol, 1947). High persistence of HCH p-isomer is... 

Gahulin, R. V., Gahuhna, R. A. (1996). Cartographic assessment of HCH isomers state in agrolandscape soils of the Mugano-Salyansk region (Azerbaijan). Agrochemistry, 8/9, 97-102. 

The recovery of chlorobenzenes (di- to hexachloro) and hexachlorocyclo-hexane (HCH) isomers from supercritical carbon dioxide by trapping in cold solvent was studied (Wenclawiak et al., 1994). 

Depending on the type of substituents, usually one of the forms is the most stable one. In the case of the HCH isomers, this is the chair form. If we have a closer look at the chair form, we see that six of the bonds linking substituents to the ring are directed differently from the other six ... 

Organochlorine pesticides are defined as fat soluble. Most have a log Pm. over 5 (aldrin, DDE, DDT, dieldrin, endrin, and heptachlor), and the HCH isomers have a log Pm. in the 3-4 range. The majority of the OPPs are also classified as fat soluble but present lower values of log Pow. Chlorfenvinphos, fenitrothion, and diazinon, with a log P[Pg.718]

Hubert et al. [101] state that accelerated solvent extraction compared to alternatives such as Soxhlet extraction, steam distillation, microwave extraction, ultrasonic extraction and, in some cases, supercritical fluid extraction is an exceptionally effective extraction technique. Hubert et al. [ 101 ] studied the effect of operating variables such as choice of solvent and temperature on the solvent extraction of a range of accelerated persistent organic pollutants in soil, including chlorobenzenes, HCH isomers, DDX, polychlorobiphenyl cogeners and polycyclic aromatic hydrocarbons. Temperatures ofbetween 20 and 180 °C were studied. The optimum extraction conditions use two extraction steps at 80 and 140 °C with static cycles (extraction time 35 minutes) using toluene as a solvent and at a pressure of 15 MPa. 

Zhang, Z.C., Dai, S.G., et al., 1998. Enantioselective breakdown of a-HCH and concentrations of a, p, y, 8-HCH isomers in Xingang Harbour marine water and Haihe River estuary water of Tianjin. China Environ. Sci. (Chinese) 18, 197-201. 

Note Values in parentheses indicate percentage compositions of HCH isomers and DDT compounds. 

Iwata, H., Tanabe, S., Tatsukawa, R., 1993b. A new view on the divergence of HCH isomer compositions in oceanic air. Mar. Pollut. Bull. 26, 302-305. 

As well, HCH isomers, including lindane, occur infrequently in human fats. Levels of up to 2.6 mg kg-1 were reported in 1972 by Siyali (1972). More recently, Quinsey et al. (1995) detected low median levels ( 0.1mg kg-1) of HCH isomers, with a measure of 4.4mg kg-1, in human milk fats for Victorian women. The presence of HCH isomers in all of the milk fats suggests a persistent background level of contamination in body fats consistent with POPs profiles for total HCH. 

Australian health authorities and researchers have conducted a number of studies into organochlorine insecticide residues and human milk that span three decades of organochlorine use, from 1969 to the early 1990s. Early Australian studies of human milk contamination (e.g. HCB, DDT and metabolites, HCH isomers and cyclodienes) cover the period from 1969 to 1972 and include Western Australia (Stacey Thomas, 1975), New South Wales (Siyali, 1973), Victoria (Monheit Luke, 1990) and Queensland (Miller Fox, 1973). Total DDT was shown to occur in the parts per billion range (pg kg-1) in whole milk and in the parts per million range (mg kg-1) in milk fats. 

Analytical results showed relatively uniform distribution of HCHs along with the latitudes, and the ratio (S/W) showed the highest degree of positive correlation with latitude. This phenomenon indicates that HCH isomers pose higher potency for atmospheric transport and global redistribution. Other compounds such as DDTs, CHLs and PCBs with lower correlations and gradients exhibited less efficiency for atmospheric transport. 

Figure 7. Conformations of the BHC (HCH) isomers and recent analogues of the aaaeee (lindane) structure, some of which have additional biodegradable groups (54)...

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