Y-HCH

Lindane is one of eight different hexachlorocyclohexane (HCH), C H Cl, isomers and its Chemical Abstract n.2cniQ is la, 2a 3P, 4a, 5a 6P-hexachlorocyclohexane [58-89-9] (y-HCH or y-BHC, ben2ene hexachloride) (80). Commercial products containing lindane are marketed as either a mixture of isomers or as the pure y-BHC isomer. Not unexpectedly, lindane is a highly stable lipophilic compound and it has been used extensively worldwide as an insecticide. In contrast, hexachloropentadiene, C Cl, is an extremely reactive industrial intermediate used as a chemical intermediate in the synthesis of a broad range of cyclodiene-derived pesticides, which include endosulfan, endrin, heptachlor, and several different organohalogen flame retardants (81). 

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. 

Aldrin, chlordecone (Kepone), 2,4-D, DDT and metabolites, dieldrin, endosulfan, endrin, f]- and y-HCH (lindane), linuron, methoxychlor, mirex... 

In 1974, the Harmonized Monitoring Programme was set up by the Department of the Environment (DoE). The objective was to provide a network of sites at the lower end of catchments, where water quality data could be collected and analysed in a nationally consistent manner, allowing the loads of materials carried through river catchments into estuaries to be estimated and long-term trends in river quality to be assessed. The complete list of substances to be monitored is diverse and specifies about 115 substances. The pesticides aldrin, dieldrin, y-HCH, heptachlor, p,p -DDT and p,p -DDE are included. Figures 1 and 2 show the downward trend of y-HCH and dieldrin over the past 20 years at the Harmonized Monitoring Sites. This confirms that reductions in environmental concentrations have been achieved, particularly over the past 10 years. 

The concentrations of dieldrin show a marked decline throughout the 1980s following the ban on its use. The concentrations of y-HCH have also declined during the same period, but the reduction is not as significant. This is probably due to the fact that y-HCH still has a wide variety of uses in the UK in agriculture. 

Figure 1 y-HCH in rivers in Great Britain (% distribution of eoneentrations). (Data from Harmonized Monitoring Sites)... 

Figure 13.19 Chromatograms obtained by on-line SPE-GC-MS(SIM) of (a) 10 ml of tap water spiked with pesticides at levels of 0.1 ng 1 (b) 10 ml of a sample of unspiked tap water. Peak identification foi (a) is as follows 1, molinate 2, a-HCH 3, dimethoate 4, simazine 5, ati azine 6, y-HCH 7, S-HCH 8, heptachloi 9, ametiyn 10, prometiyn 11, fen-itrothion 12, aldrin 13, malatliion 14, endo-heptachlor 15, a-endosulfan 16, teti achlor-vinphos 17, dieldrin. Reprinted from Journal of Chromatography, A 818, E. Pocumll et al., On-line coupling of solid-phase exti action to gas cliromatography with mass specti ometiic detection to determine pesticides in water , pp. 85-93, copyright 1998, with permission from Elsevier Science.

The increase in Ca is initiated rapidly and begins to recover after 1 min. The order of potency correlates fairly well with the solubilities of these compounds in organic solvents (37) and their abilities to accumulate in phospholipid vesicles (38), i.e., 6>y>a>p, but not with their insecticidal activity (y 6>a p 39). At these concentrations, crystals of p-, a-, and y-HCH were evident in the cell suspensions when we made simultaneous measurements of the right-angle light scatter, indicating that the order of aqueous solubilities is 6>y>a>p. However, stimulation by 6-HCH at concentrations below its aqueous solubility limit shows a typical dose dependency of the response (Figure 10). 

Wada H, K Sendoo, Y Takai (1989) Rapid degradation of y-HCH in the upland soil after multiple application. Soil Sci Plant Nutr 35 71-77. 

Nagasawa S, R Kikuchi, Y Nagata, M Takagi, M Matsuo (1993a) Stereochemical analysis of y-HCH degradation by Pseudomonas paucimobilis UT26. Chemosphere 26 1187-1201. 

Nagasawa S, R. Kikuchi, Y. Nagata, M. Takagi, M. Matsuo. (1993b) Aerobic mineralization of y-HCH by Pseudomonas paucimobilis UT26. Chemosphere 26 1719-1728. 

Sendoo K, H Wada (1989) Isolation and identification of an aerobic y-HCH-decomposing bacterium from soil. Soil Sci Plant Nutr 35 79-87. 

Semeena VS, Lammel G (2003) Effects of various scenarios of entry of DDT and y-HCH on the global environmental fate as predicted by a multicompartment chemistry-transport model. Fresenius Environmental Bulletin 12 925-939... 

In the case of DDTs, the three compounds (DDT, DDE and DDD) are considered as the sum of both 2,4 and 4,4 isomers. Half of the samples were above the limits proposed by Canadian guidelines and for DDT more than 95% of the samples were above this limit. The highest concentration levels were ranging from 15.3 to 351 pg kg-1. Two compounds with very small percentage of appearance in the samples, y-HCH and dieldrin, have concentrations above the Canadian guidelines. 

In the EMEP region within the period from 1990 to 2001 emission reduction took place for all POPs under consideration. In particular, during the considered period emissions of B[a]P were reduced by 25% emissions of PCDD/Fs and PCBs—more than by half and emissions of y-HCH—almost twice. As an example, temporal trends of total European emissions of PCDD/Fs and y-HCH for the considered period are presented in Figure 2. For preparation of the data used in calculations available official information supplemented by expert estimates where necessary are used. As a whole a considerable reduction of POP emissions are also characteristic of the most part of Eastern European countries. 

Figure 2. Temporal emission trends of PCDD/Fs (a) and y-HCH (b) in Europe (Mantseva et al., 2004).

Such pollutants as PAHs and PCBs also tend to be accumulated in the terrestrial environment but HCB and y-HCH in the marine ones. Thus, this information gives us an idea of the POPs exposure pathways to human beings. 

Fate modeling of y-hexachlorocyclohexane (y-HCH) in Tianjin, China (TAO Shu, China)... 

HCH bisecticides applied to food and forest crops, banned for use in many countries. Technical HCH, a mixture of a-, P", 5-, -, and y-HCH, is no longer made. y-HCH (a.k.a. Lindane) is still manufactured and used in shampoos and creams against lice and scabies... 

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