Hexachlorocyclohexanes degradation

Miyauchi K, H-S Lee, M Fukuda, M Takagi, Y Nagata (2002) Cloning and characterization of linR, involved in regulation of the downstream pathway for y-hexachlorocyclohexane degradation in Sphingomonas paucimobilis UT26. Appl Environ Microbiol 68 1803-1807. 

Miyazaki R, Y Sato, M Ito, Y Ohtsubo, Y Nagata, M Tsuda (2006) Complete nucleotide sequence of an exogenously isolated plasmid, pLBl, involved in y-hexachlorocyclohexane degradation. Appl Environ Microbiol 12 6923-6933. 

Nagata Y, A Futamura, K Miyauchi, M Takagi (1999) Two different types of dehalogenases LinA and linB, involved in y-hexachlorocyclohexane degradation in Sphingomonas paucimobilis are localized in the periplasmic space without molecular processing. J Bacterial 181 5409-5413. 

Thomas J-C, F Berger, M Jacquier, D Bernillon, F Baud-Grasset, N Truffaut, P Normand, TM Vogel, P Simonet (1996) Isolation and characterization of a novel y-hexachlorocyclohexane-degrading bacterium. J Bacteriol 178 6049-6055. 

Nagata, Y., K. Miyauchi, J. Damborsky, K. Manova, A. Ansorgova, and M. Takagi. 1997. Purification and characterization of a haloalkane dehalogenase of a new substrate class from a y-hexachlorocyclohexane-degrading bacterium, Sphin-gomonas paucimobilis UT26. Appl. Environ. Microbiol. 63 3703-3710. 

The a-isomer of hexachlorocyclohexane exists in two enantiomeric forms, and both are degraded by Sphingomonas paucimobilis strain B90A by dehydrochlorination to 1,3,4, 6-tetrachlorocyclohexa-l,4-diene that is spontaneously degraded to 1,2,4-trichlorophenol. 

Endo R, M Kamakura, K Miyauchi, M Fukuda, Y Ohtsubo, M Tsuda, Y Nagata (2005) Identification and characterization of genes involved in the downstream degradation pathway of y-hexachlorocyclohexane in Sphingomonas paucimobilis UT26. J Bacterial 187 847-853. 

Although quite extensive use of has been made in studies on the degradation of alkyl sulfonates (Hales et al. 1986), C1 has achieved only limited application on account of technical difficulties resulting from the low specific activities and the synthetic inaccessibility of appropriately labeled substrates. One of the few examples of its application to the degradation of xenobiotics is provided by a study of the anaerobic dechlorination of hexachlorocyclohexane isomers (Jagnow et al. 1977), the results of which are discussed in Chapter 7, Part 3. 

Jagnow G, K Haider, P-C Ellwardt (1977) Anaerobic dechlorination and degradation of hexachlorocyclohexane by anaerobic and facultatively anaerobic bacteria. Arch Microbiol 115 285-292. 

Nagata Y, Z Prokop, Y Sato, P Jerabek, A Kumar, Y Ohtsubo, M Tsuda, J Damborsky (2005) Degradation of b-hexachlorocyclohexane by haloalkane dehalogenase LinB from Sphingomonas paucimobilis UT 26. Appl Environ Microbiol 71 2183-2185. 

Xun et al. 1999 Ohtsubo et al. 1999). The degradation of 2-chlorohydroquinone, which is produced during the degradation of y-hexachlorocyclohexane, is carried out analogously by dioxygenation followed by hydrolysis of the acyl chloride to 3-hydroxymuconate, which is mediated by an unusual extradiol fission enzyme encoded by linE (Miyauchi et al. 1999 Endo et al. 2005). 

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. 

Heritage, A.D. and MacRae, I.C. Identification of intermediates formed during the degradation of hexachlorocyclohexanes by Clostridium sphenoides, Appl Environ. Microbiol, 33(6) 1295-1297, 1977. 

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. 

Lindane is the active y-isomer of hexachlorocyclohexane. It also exerts a neurotoxic action on insects (as well as humans). Irritation of skin or mucous membranes may occur after topical use. Lindane is active also against intrader-mal mites (Sarcoptes scabiei, causative agent of scabies), besides lice and fleas. It is more readily degraded than DDT. 

The six axial bonds are directed upward or downward from the plane of the ring, while the other six equatorial bonds are more within the plane. Conversion of one chair form into another converts all axial bonds into equatorial bonds and vice versa. In monosubstituted cyclohexanes, for electronic reasons, the more stable form is usually the one with the substituent in the equatorial position. If there is more than one substituent, the situation is more complicated since we have to consider more combinations of substituents which may interact. Often the more stable form is the one with more substituents in the equatorial positions. For example, in ct-1,2,3,4,5,6-hexachlorocyclohexane (see above) four chlorines are equatorial (aaeeee), and in the /Tisomer all substituents are equatorial. The structural arrangement of the /3-isomer also greatly inhibits degradation reactions [the steric arrangement of the chlorine atoms is unfavorable for dehydrochlorination (see Chapter 13) or reductive dechlorination see Bachmann et al. 1988]. 

The issue of bioavailability is further clouded by the physical characteristics of soil and the role of a possible mass transfer limitation. Soil constituents are not simply flat surfaces with free and equal access to all bacterial species. The formation of aggregates from sand-, silt-, and clay-sized particles results in stable structures which control microbial contact with the substrate (Figure 2.7). Discussion of sorption mechanisms and binding affinities must include the possible impact of intra-aggregate transport of the substrate. If the substrate is physically inaccessible to the microorganism then both desorption from soil constituents and diffusion to an accessible site are necessary. The impact of intra-aggregate diffusion on degradation kinetics has been modeled for y-hexachlorocyclohexane (Rijnaarts et al., 1990) and naphthalene (Mihelcic Luthy, 1991). 

In environmental science chirality has an important role as degradation of some achiral pollutants result in chiral toxic metabolites. Therefore, predicting the exact toxicities of the pollutant concentrations of both enantiomers is required and essential. For example, two enantiomers of a-hexachlorocyclo-hexane pesticide have different toxicities. Moreover, the rates of degradation of the enantiomers of a-hexachlorocyclohexane are also different [9,10]. 

Faller, J. Hiihnerfuss, H. Kdnig, W.A. Rrebber, R. Ludwig, P., Do marine bacteria degrade a-hexachlorocyclohexane stereoselectively Environ. Sci. Technol. 1991, 25, 676-678. 

Pfaffenberger, B. Hiihnerfuss, H. Kallenborn, R. Kohler-Giinther, A. Konig, W.A. Kriiner, G., Chromatographic separation of the enantiomers of marine pollutants. Part 6 Comparison of the enantioselective degradation of a-hexachlorocyclohexane in marine biota and water Chemosphere 1992, 25, 719-725. 

Law, S.A. Diamond, M.L. Helm, P.A. Jantunen, L.M. Alaee, M., Factors affecting the occurrence and enantiomeric degradation of hexachlorocyclohexane isomers in northern and temperate aquatic systems Environ. Toxicol Chem. 2001, 20, 2690-2698. 

Buser, H.-R. Miiller, M.D., Isomer and enantioselective degradation of hexachlorocyclohexane isomers in sewage sludge under anaerobic conditions Environ. Sci. Technol 1995,29,664-672. 

MoUer, K. Huhnerfuss, H. Rimkus, G., On the diversity of enzymatic degradation pathways of a-hexachlorocyclohexane as determined by chiral gas chromatography J. High Resol. Chro-matogr. 1993, 16, 672-673. 

Even a cursory examination of the literature shows that analysis of virtually every environmental sample reveals contamination from polycyclic aromatic hydrocarbons — resulting from incomplete combustion processes — and a range of the more recalcitrant organohalogen compounds such as DDT (together with its degradation product DDE), PCBs, hexachlorocyclohexanes, compounds related to aldrin, and mixtures present in commercial toxaphene preparations. Possibly the most disturbing fact, which has already been noted, is the occurrence of these compounds in samples from remote and largely isolated locations in the Arctic and Antarctic. 

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