Polychlorinated organic compounds (PCOCs), which are still produced and used heavily, are typical contaminants in soils and sediments. They bring serious harm to the environment due to their high toxicity and persistence. Thus, it is of critical significance to probe into the mechanism of PCOCs degradation and to seek the effective degradation methods. PCOCs could be dechlorinated in anaerobic conditions, thus decreasing their persistence and toxicity. The resultant lower chlorinated products from dechlorination can be sequentially degraded until completely mineralized in aerobic conditions.
Starting with the process of PCOCs degradation, this article mainly reviews the mechanism of dechlorination of several typical PCOCs, i.e., chlorinated hydrocarbon, chlorinated benzene, organic chlorinated pesticide, PCBs and PCDD/PCDF, including their processes of dechlorination and the relation between dechlorination and molecular structure. Some important influencing factors are also discussed. This article elucidates in detail that dechlorination is the key step during the degradation of PCOCs. The participation of microorganisms is particularly essential. The environmental condition, primarily including the physical and chemical characteristics of soils or sediments, brings great influence on the degradation of PCOCs. The occurrence of the dechlorination must involve the electron donors offered by the reducers, such as metals and organic carbon. Other electron acceptors also have certain effects. Finally, the application of isotopic tracing techniques to the study on the degradation mechanism of PCOCs, as well as the need of developing economical organic carbon compounds and highly effective microorganisms for the degradation of PCOCs is recommended.