| Many chlorinated organic compounds are persistent organic pollutants due to their resistance to biodegradation and chemical degradation. As a result, they are ubiquitous in the environment. Some recent studies indicated that some of them are endocrine disrupting chemicals, such as p,p'-DDT, lindane (y-HCH) and hexachlorobenzene (HCB). Therefore it is of great importance to investigate transformation of these compounds in the environment. In aquatic environment, chlorinated organic compounds may partition into aquatic sediments. Because the sediments are usually anoxic, research on the reductive dechlorination of chlorinated organic compounds in the anoxic sediment is important.In the current study, anoxic dechlorinations of p,p'-DDT, y-HCH, HCB in the Liao River sediment were studied under the following conditions: (a) without any additional short chain carbon substrates or vitamin 612; (b) with the addition of short chain carbon sources (including sodium lactate, sodium propionate or sodium acetate); (c) with the addition of vitamin Bn; (d) with the addition of both short chain carbon substrates and vitamin 812, (e) with the addition of sodium dodecyl sulfate (SDS), a kind of surfactant; (f) the coexistence of the three chlorinated compounds.As a result, the following main conclusions were obtained:(a) The anoxic dechlorination of p,p'-DDT or HCB in the Liao Rive sediment follow pseudo-first-order kinetics. The dechlorination rate constants, 0.0082 d"1 and 0.0056 d"1 for p,p'-DDT and HCB respectively, are small.(b) With the addition of short chain carbon sources, which acted as the electron donor and energy sources, the anoxic dechlorination rate constants of p,p'-DDT were improved more than 10 times. For sodium acetate, sodium propionate and sodium lactate, the corresponding dechlorination rates were increased to 0.0881 d'1, 0.1023d"1 and 0.0917 d"1 respectively. However such effects were not observed for HCB.(c) It was observed that vitamin 812 could accelerate the anoxic dechlorination of y-HCH under the condition of adding sodium lactate. However vitamin Bn played a minor role on the degradation of p,p'-DDT or HCB in the sediment of Liao River, whether adding additional carbon sources or not.(d) When adding sodium acetate, SDS restrains the dechlorination of p,p'-DDT by decreasing the activities of the bacteria which can co-metabolize p,p'-DDT. Nevertheless, with the absent of additional carbon sources, SDS can increase the dechlorination rate because of the solubilization effect.(e) It is found that the anoxic dechlorination of p,p'-DDT usually occurred during the stage of pH rising of the system. With the existence of additional carbon sources, sodium lactate, sodium propionate or sodium acetate, the faster pH rised, the faster p,p'-DDT dechlorinated, which indicate that the existence of short chain organic substrate supplies sufficient electron donors for the dechlorination process, and p,p'-DDT can obtain electrons more easily during the stage of pH rising.(f) The main product of p,p'-DDT anoxic dechlorination is p,p'-DDD, which can be transformed to other substance subsequently. Furthermore, p,p'-DDE was formed as a minor product at the beginning of the degradation of p.p'-DDT. However it was not found the increase of the concentration of p,p'-DDD. This may be because that p,p'-DDT or its degradation products can inhibit the transformation of p,p'-DDT to p,p'-DDE.(g) With the coexistence of the three chlorinated compounds, the additional carbon sources decreased the dechlorination rate of y-HCH. However at the same time they promoted the dechlorination of p,p'-DDT. Generally speaking, the anoxic dechlorination of one chlorinated compound was restrained by the existence or the anoxic dechlorination of the other two. Nevertheless, without the additional carbon .substrate, the inhibition effects resulting from the existence or degradation of p,p'-DDT and HCB on the anoxic dechlorination of y-HCH were not significant.By comparing the dechlorination...
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