Chlorobenzenes biodegradation

PROBABLE FATE photolysis, expected to oecur slowly oxidation no data available on aqueous oxidation, oxidized by hydroxyl radicals in atmosphere hydrolysis not important process first-order hydrolytic half-life >879 yrs volatilization volatilizes at a relatively rapid rate, half-life is about 10 hr volatilization from soil surfaces is expected to be a signifieant transport mechanism sorption sorbed by organic materials adsorption to sediment expected to be a major environmental fate process based on research in the Great Lakes area biological processes bioaccumulates more than chlorobenzene, biodegradation is not as significant as volatilization slightly persistent in water, half-life 2-20 days approximately 98.5% of 1,3-dichlorobenzene ends up in air 1% ends up in water the rest is divided equally between terrestrial soils and aquatic sediments. 

Toxicity to fish is included in the data Hsted in Table 4. Marine life, particularly fish, may suffer damage from spills in lakes and streams. The chlorobenzenes, because they are denser than water, tend to sink to the bottom and may persist in the area for a long time. However, some data indicate that dissolved 1,2,4-trichlorobenzene can be biodegraded by microorganisms from wastewater treatment plants and also has a tendency to slowly dissipate from water by volatilization (34). 

Pettigrew CA, BE Haigler JC Spain (1991) Simultaneous biodegradation of chlorobenzene and toluene by a Pseudomonas strain. Appl Environ Microbiol 57 157-162. 

FIGURE 9.20 Outline of the biodegradation of 4-chlorophenol, 4-chloroaniline, 4-chlorobenzoate, and chlorobenzene. 

Biological. In activated sludge, 31.5% of the applied chlorobenzene mineralized to carbon dioxide after 5 d (Freitag et al., 1985). A mixed culture of soil bacteria or a Pseudomonas sp. transformed chlorobenzene to chlorophenol (Ballschiter and Scholz, 1980). Pure microbial cultures isolated from soil hydroxylated chlorobenzene to 2- and 4-chlorophenol (Smith and Rosazza, 1974). Chlorobenzene was statically incubated in the dark at 25 °C with yeast extract and settled domestic wastewater inoculum. At a concentration of 5 mg/L, biodegradation yields at the end of 1 and 2 wk were 89 and 100%, respectively. At a concentration of 10 mg/L, significant... 

Chlorobenzene is used as a solvent and as an intermediate in industry. A portion of that is lost to the environment in water and air discharges. Chlorobenzene adsorbs moderately to soil and is biodegraded comparatively rapidly. With a moderate index of bioaccumulation, chlorobenzene was found in almost every individual tested for it in the United States. The EPA has identified 1,177 NPL sites. Chlorobenzene has been found at 97 of the sites evaluated for the presence of this chemical. As more sites are evaluated by the EPA, the number may change. The frequency of these sites within the United States can be seen in Figure 5-1. 

Biodegradation of chlorobenzene is rapid, leaving no detectable residues after 1 or 2 weeks. Adaptation is also rapid (Tabak et al. 1981). 

Studies on the migration and in situ biodegradation of chlorobenzene in hazardous waste sites are being conducted in the laboratory of Perry McCarty and others. 

McNabb JF, Smith BH, Wilson JT. 1981. Biodegradation of toluene and chlorobenzene in soil and groundwater [Abstract], Proceedings of the 81 st Annual Meeting of the American Society of Microbiology, March 1-6, 213. 

In the ambient atmosphere, chlorobenzene will exist as a vapor, and will be degraded by reaction with photochemically produced hydroxyl radicals, with an estimated half-life of 21 days. Photolysis half-lives of 4-18 h were measured in aqueous media. Chlorobenzene is expected to volatilize from soil, and is predicted to have high mobility based on the Kqc values. Biodegradation results are variable based on soil type and bacteria type. In river water, the biodegradation half-life was reported to be 150 days, and 75 days in the sediment. Volatilization is expected to occur from water surfaces. Hydrolysis is not predicted to occur. 

Reduced microbial activity and lower metabolic diversity are likely reasons for the reduced biodegradation of herbicides in subsoils and groundwater aquifers. Although the total microbial population in most aquifers range between 104 and 107 cells/g aquifer material (22). the proportion of these populations that can degrade xenobiotics appears to be low. In a pristine aquifer from Lulu, Oklahoma, degrader populations measured by 14C-MPN were less than 5 cells/g for chlorobenzene, napthalene, and toluene (4Q). 

PROBABLE FATE photolysis-, probably occurs slowly, in an isooctane solvent, it hardly adsorbs any radiation above 300 nm, direct photolysis in the environment should not be significant oxidation resistant to autooxidation by peroxy radical in water oxidation by hydroxyl radicals occurs in atmosphere photooxidation half-life in air 6.4 days-63.7 days hydrolysis not important, first-order hydrolysis half-life >879 years volatilization generally rapid volatilization occurs, half-life <9 hr, volatilization from soil surfaces may be an important transport mechanism sorption significant amount of adsorption by organic materials expected in environment biological processes bioaccumulated more than chlorobenzene, volatilization is more important than biodegradation will wash out in rain water... 

Dechlorination of chlorobenzenes has been shown to occur under anaerobic conditions. Sewage sludge completely transformed 190 pM hexachlorobenzene to DCB [102]. The metabolic pathway for biodegradation of o-DCB [42], m-DCB [93], and p-DCB [99] proposes that they all form a common intermediate dichlorocatediol, and then the benzene ring is broken as indicated in Figure 3. 

The industrial importance of monochlorobenzene is in sharp decline, since, from the mid 1970 s, it has largely been replaced as a starting material for the production of phenol, and consumption of DDT has fallen dramatically because of its poor biodegradability and the ban on its use in many countries (e.g. in the USA in 1973). Chlorobenzene has also lost its importance for aniline production in recent years. 

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