Hexachlorocyclohexanes HCHs

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). 

There are several isomers of 1,2,3,4,5,6-hexachlorocyclohexane (HCH). The Y isomer is insecticidally active, whereas most of the others are relatively inactive. These compounds have been shown to activate inflammatory functions of neutrophils (35,36). Using Indo-1, we have characterized intracellular Ca mobilization in response to these compounds. Figure 9 shows the responses of cells labeled with Indo-1 to stimulation by y, < " P , and 6-HCH at a concentration of 260 pH. 

The organochlorine insecticides (henceforward OCs) can be divided into three main gronps, each of which will be discnssed separately in the sections that follow. These are (1) DDT and related componnds, (2) the cyclodiene insecticides, and (3) isomers of hexachlorocyclohexane (HCH Brooks 1974 Fignre 5.1). 

Hexachlorocyclohexanes (HCHs) have not caused the problems of bioconcentration or bioaccumulation associated with DDT or the cyclodienes, and they have not been implicated in large-scale environmental problems. They will only be discussed briefly here, drawing attention to certain differences from the foregoing groups. 

Particularly the chlorinated compounds have enjoyed range of applications vinyl chloride (chloro-ethene) as monomer for the production of PVC, tetra- and trichloroethenes as solvents for degreasing, and the insecticides l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and isomers of hexachlorocyclohexane (HCH) (benzene hexachloride). The biodegradation of fluorinated aliphatic compounds is generally different from the outlines that have emerged from investigations on their chlorinated, brominated, and even iodinated analogues. They are therefore treated separately in Part 4 of this chapter. 

In another AT study, Terrado et al. [15] characterised pollution patterns in different parts of the Ebro catchment. In the upper part of the Ebro, pollution was found to be mainly in the form of heavy metals (Zn, Cu, Cr, Pb, Cd and Hg), polycyclic aromatic hydrocarbons (PAHs), hexachlorocyclohexanes (HCHs) and trichlorobenzenes (TCBs). Etrophic conditions were also found. Pollution was found to source mainly from industry and urbanisation. The central Ebro was characterised by nutrient pollution such as the accumulation of Ca, Na, Mg and K, which highlighted the importance of salinisation effects from intensive irrigation and soils with high salt content. In the lower Ebro, organic [DDTs, hexachlorobenzene (HCB) and hexachlorobutadiene (HCBu)] and heavy metal (Hg, Cd, Zn and As) contamination was found to derive mainly from industrial and agricultural activities. 

Fig. 5 Main contamination sources identified by PCA for sediments, fish, and suface water in the Ebro River basin, and explained variances for each principal component. Variable identification. Organic compounds in sediments 1, summatory of hexachlorocyclohexanes (HCHs) 2, summa-tory of DDTs (DDTs) 3, hexachlorobenzene (HCB) 4, hexachlorobutadiene (HCBu) 5, summatory of trichlorobenzenes (TCBs) 6, naphthalene 7, fluoranthene 8, benzo(a)pyrene 9, benzo(b) fluoranthene 10, benzo(g,h,i)perylene 11, benzo(k)fluoranthene 12, indene(l,2,3-cd)pyrene. Organic compounds in fish 1, hexachlorobenzene (HCB) 2, summatory of hexachlorocyclohexanes (HCHs) 3, o,p-DDD 4, o,p-DDE 5, o,p-DDT 6, p,p-DDD 7, />,/>DDE 8, />,/>DDT 9, summatory of DDTs (DDTs) 10, summatory of trichlorobenzenes (TCBs) 11, hexachlorobutadiene (HCBu) 12, fish length. Physico-chemical parameters in water 1, alkalinity 2, chlorides 3, cyanides 4, total coliforms 5, conductivity at 20°C 6, biological oxygen demand 7, chemical oxygen demand 8, fluorides 9, suspended matter 10, total ammonium 11, nitrates 12, dissolved oxygen 13, phosphates 14, sulfates 15, water temperature 16, air temperature...

The inclusion of a third-order term did not yield a significantly better fit (p > 0.6). There are no indications that PAHs and nonpolar chlorinated hydrocarbons have a different Ks - Ko dependence. By contrast, the moderately polar pesticides such as hexachlorocyclohexanes (HCHs), dieldrin, chlorpyrifos, heptachlor, and trifluralin (open and closed diamonds in Figure 3.3) have Ks values that are 0.6 log units lower than PAHs and PCBs with similar Ko values (p < 0.001). 

Guo et al. reported that trace amoimts of aqueous organochlorine pesticides, such as hexachlorocyclohexane (HCH), could be totally degraded and mineralized into CO2 and HCl by near-UV irradiation of a suspension of Mg/Al LDH intercalated with paratungstate anions [108]. They demonstrated that photocatalytic degradation of the pesticide occurs in the interlayer galleries. It was also found that Zn/Al/W(Mn) mixed oxides, formed by calcination of POM-intercalated Zn/Al LDHs [109], exhibited higher photocatalytic activity in the degradation of HCH compared with the POM-LDH precursors. 

Chlorination of benzene gives an addition product that is a mixture of stereoisomers known collectively as hexachlorocyclohexane (HCH). At one time, this was incorrectly termed benzene hexachloride. The mixtnre has insecticidal activity, though activity was found to reside in only one isomer, the so-called gamma isomer, y-HCH. y-HCH, sometimes under its generic name lindane, has been a mainstay insecticide for many years, and is about the only example of the chlorinated hydrocarbons that has not been banned and is still available for general use. Although chlorinated hydrocarbons have proved very effective insecticides, they are not readily degraded in the environment, they accumulate and persist in animal tissues, and have proved toxic to many bird and animal species. 

In ring systems with more than two substituted carbons, more isomers are possible. An example well known to environmental scientists and engineers is 1,2,3,4,5,6-hexachlorocyclohexane (HCH). Three of the possible 8 isomers (the so-called a-, /3-, y-isomers) are particularly important from an environmental point of view ... 

All benchmark chemicals, anthracene (AN), chlorpyrifos (CP), 2,6-di-t-butylphenol (DBP), y-hexachlorocyclohexane (HCH), and trichloroethylene (TCE) absorb UV light between 200-300 nm, but only anthracene and chlorpyrifos absorb solar photons (> 295 nm) rapidly enough to undergo direct photoreactions at significant rates. Table 15.2 summarizes the UV spectral properties of AN, CP, DBP, and two other compounds, p-nitroanisole (I) (PNA) and dinitramide ion (II) (DN ion), both of which directly photolyze in sunlight. 

Hexachlorocyclohexanes (HCHs) were found in fish from Bangkok,... 

Sahsuvar, L., Helm, P.A., Jantunen, L.M., Bidleman, T.F. (2003) Henry s law constants for CX-, 3-, and y-hexachlorocyclohexanes (HCHs) as a function of temperature and revised estimates of gas exchange in Arctic regions. Atmos. Environ. 37, 983-992. Saito, S., Tanoue, A., Matsuo, M. (1992) Applicability of the i/o-characters to a quantitative description of bioconcentration of organic chemicals in fish. Chemosphere 24(1), 81-87. 

A group of highly chlorinated polycyclic insecticides, exemplified by heptachlor (143) and aldrin (144), is prepared from hexachlorocyclopentadiene and cyclopentadiene. The y-isomer (lindane, 145) of hexachlorocyclohexane (HCH) is the toxic component of HCH, first prepared by Michael Faraday. Toxaphene consists of a complex mixture of chlorinated camphenes, of which 146 represents a particularly toxic isomer. 

Hexachlorocyclohexane (HCH) is the name of a technical mixture of various isomers. Only a-, P- and y-HCH is of toxicological relevance... 

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