Hexachlorobenzene sources

Jones, K., Barber, ]., and Sweetman, A. 2005. Hexachlorobenzene-Sources, Environmental Fate and Risk Characterisation. European Ghlorinated Solvent Association (Euro Ghlor). 

Attention has been directed to the dechlorination of polychlorinated benzenes by strains that use them as an energy source by dehalorespiration. Investigations using Dahalococcoides sp. strain CBDBl have shown its ability to dechlorinate congeners with three or more chlorine substituents (Holscher et al. 2003). Although there are minor pathways, the major one for hexachlorobenzene was successive reductive dechlorination to pentachlorobenzene, 1,2,4,5-tetrachlorobenzene, 1,2,4-trichlorobenzene, and 1,4-dichlorobenzene (Jayachandran et al. 2003). The electron transport system has been examined by the use of specific inhibitors. lonophores had no effect on dechlorination, whereas the ATP-synthase inhibitor A,A -dicyclohexylcarbodiimide (DCCD) was strongly inhibitory (Jayachandran et al. 2004). 

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...

Source Hexachlorobenzene may enter the environment from incomplete combustion of chlorinated compounds including mirex, kepone, chlorobenzenes, pentachlorophenol, PVC, polychlorinated biphenyls, and chlorinated solvents (Ahling et al., 1978 Dellinger et al., 1991). In addition, hexachlorobenzene may enter the environment as a reaction by-product in the production of carbon tetrachloride, dichloroethylene, hexachlorobutadiene, trichloroethylene, tetrachloro-ethylene, pentachloronitrobenzene, and vinyl chloride monomer (quoted, Verschueren, 1983). 

Source Pentachlorobenzene may enter the environment from leaking dielectric fluids containing this compound. Pentachlorobenzene may be present as an undesirable by-product in the chemical manufacture of hexachlorobenzene, pentachloronitrobenzene, tetrachloroenzenes, tetrachloroeth-ylene, trichloroethylene, and 1,2-dichloroethane (U.S. EPA, 1980). 

Although hexachlorobenzene (HCB) was used as an active component of insecticides and fungicides in the UK until the 1970s, its major source to the environment now is now as a by-product of industrial processes such as aluminium smelting and production of perchloroethylene and vinyl chloride monomer.65 The MAFF survey mentioned earlier did not include HCB, but a later survey on milk samples from farms around potential point sources did analyse for HCB. No HCB was detected at or above the reporting limit of 1 fig/ kg in whole milk in samples from either around potential point sources or control farms.66... 

DDTs), hexachlorocyclohexane isomers (HCHs), chlordane compounds (CHLs) and hexachlorobenzene. Residues levels of industry-derived contaminants such as polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-/>-dioxins and dibenzofurans (PCDD/Fs) were also reviewed. Concentrations of these contaminants in different environmental compartments were expressed as unit equivalent to part-per-billion (ppb) level, unless otherwise specified. The cited values of concentrations from various literature sources were rounded to two significant digits for comparison. A number of factors can influence the concentrations in biological samples. Therefore, whenever possible, for biological samples the lipid normalized concentrations were cited for comparison. 

The sources of unintentionally produced POP chemicals, polychlorinated dibenzodioxins (PCDD), polychlorinated dibenzofurans (PCDF), and hexachlorobenzene (HCB), has been estimated through the National Implementation Plan (NIP) for Malaysia. However, an official report has not been made public. The draft final report on the assessment of unintentionally produced chemicals conducted by Universiti Sains Malaysia... 

Hexachlorobenzene could burn when exposed to extreme heat and toxic fumes may be produced. It should not be stored near sources of ignition. In cases of spills, hexachlorobenzene should be taken up with sand or other noncombustible material and then disposed off properly. For large-scale spills, it should be covered with sand/soil taking care to avoid dust formation. Protective clothing, gloves, and eyewear must be worn in handling spill situations. 

Competitive Substrate Utilization. Various experiments with phenanthrene mineralization demonstrated partial inhibition with nonionic surfactants at doses less than that resulting in micellization. Such data suggest an alternative explanation for inhibition, other than surfactant effects on cell membranes and proteins. Possibly PAH-degrading microorganisms, or their competitors, utilize the surfactant as preferential substrate or carbon source. Jalvert et al. (66) made a similar conclusion about the effect of C12E4 on reductive dechlorination of hexachlorobenzene. 

Reductive dehalogenation is a mechanism for the anaerobic biotransformation of chlorinated hydrocarbons such as hexachlorobenzene (HCB). In reductive dehalogenation, the halogenated compound serves as the electron acceptor rather than the donor that requires a separate carbon source. In a microbially catalyzed reaction, a halide ion is replaced by a hydrogen ion (Figure 13.7). The removal of halide ions results in compounds that are generally easier to degrade, and, in some instances, are completely mineralized. 

Pentachlorophenol-contaminated air, rain, snow, surface waters, drinking waters, ground-waters, and aquatic biota are common in the United States. Residues of PCP in food, water, and mammalian tissues may result from the direct use of PCP as a wood preservative and pesticide or as a result of use of other chemicals that form PCP as degradation products - i.e., hexachlorobenzene and lindane. To confound matters, PCP was judged to be the source of dioxin and dibenzofuran contamination in chickens in Canada. More than 50% of all chickens sampled contained hex-achlorinated dibenzo-p-dioxins (hexa CDDs) at concentrations of 27.0ng/kg fat and higher ... 

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