Biodegradability of chlorinated solvents and related chlorinated aliphatic compounds

Abstract

The biodegradability of chlorinated methanes, chlorinated ethanes, chlorinated ethenes, chlorofluorocarbons (CFCs), chlorinated acetic acids, chlorinated propanoids and chlorinated butadienes was evaluated based on literature data. Evidence for the biodegradation of compounds in all of the compound categories evaluated has been reported. A broad range of chlorinated aliphatic structures are susceptible to biodegradation under a variety of physiological and redox conditions. Microbial biodegradation of a wide variety of chlorinated aliphatic compounds was shown to occur under five physiological conditions. However, any given physiological condition could only act upon a subset of the chlorinated compounds. Firstly, chlorinated compounds are used as an electron donor and carbon source under aerobic conditions. Secondly, chlorinated compounds are cometabolized under aerobic conditions while the microorganisms are growing (or otherwise already have grown) on another primary substrate. Thirdly, chlorinated compounds are also degraded under anaerobic conditions in which they are utilized as an electron donor and carbon source. Fourthly, chlorinated compounds can serve as an electron acceptor to support respiration of anaerobic microorganisms utilizing simple electron donating substrates. Lastly chlorinated compounds are subject to anaerobic cometabolism becoming biotransformed while the microorganisms grow on other primary substrate or electron acceptor. The literature survey demonstrates that, in many cases, chlorinated compounds are completely mineralised to benign end products. Additionally, biodegradation can occur rapidly. Growth rates exceeding 1 d )1 were observed for many compounds. Most compound categories include chlorinated structures that are used to support microbial growth. Growth can be due to the use of the chlorinated compound as an electron donor or alternatively to the use of the chlorinated compound as an electron acceptor (halorespiration). Biodegradation linked to growth is important, since under such conditions, rates of degradation will increase as the microbial population (biocatalyst) increases. Combinations of redox conditions are favorable for the biodegradation of highly chlorinated structures that are recalcitrant to degradation under aerobic conditions. However, under anaerobic conditions, highly chlorinated structures are partially dehalogenated to lower chlorinated counterparts. The lower chlorinated compounds are subsequently more readily mineralized under aerobic conditions.Abbreviations: A

Characterization of a Dehalobacter Coculture That Dechlorinates 1,2-Dichloroethane to Ethene and Identification of the Putative Reductive Dehalogenase Gene

“…The estimated annual global production of 1,2-dichloroethane (1,2-DCA) is 1.6 ϫ 10 7 tons (17), the highest of all synthetic chlorinated compounds. It is also a common groundwater contaminant; in the United States, 1,2-DCA has been found in at least 287 of 932 National Priorities List sites identified by the U.S. Environmental Protection Agency (search of the National Priorities List database [http://www.epa.gov /superfund/sites/query/advquery.htm] on 31 July 2008).…”

Monooxygenases involved in the n-alkanes metabolism by Rhodococcus sp. BCP1: molecular characterization and expression of alkB gene

“…The redox reactions result in the flow of electrons from the substrate to a terminal electron acceptor (e.g. an oxidant such as O 2 ) and the release of energy that is used to support cell synthesis [8,9]. In the absence of O 2 , a large number of alternative terminal electron acceptors (NO 3 -, Fe 3+ , Fe(OH) 3 , SO 4 2-) can be utilized to support anoxic respiration.…”

Challenges of a feasible route towards sustainability in environmental protection

“…Regarding the extraordinary complex character of this matter it implies that a lot of long-term, very well coordinated multidisciplinary research activities need to be initiated. Use of electron and redox mediators Compounds like humic acids, activated-carbon, quinones, e.g., anthraquinone disulfonate (AQDS), anthraquinone-2-sulphonate (AQS) catalyze the anaerobic degradation reactions of numerous recalcitrant compounds; they facilitate electron transport in the degradation of, e.g., azo dyes [79][80][81][82][83][84][85][86][87], and reductive de-halogenation [88]. However, as with the issue of 'trace elements' in this particular field, a better understanding is required which will lead to a wider and more optimal application of AnWT.…”