Effect of nitrate addition on reductive transformation of pentachlorophenol in paddy soil in relation to iron(III) reduction.

Reductive dechlorination is a crucial pathway for anaerobic biodegradation of highly chlorinated organic contaminants. Under an anoxic environment, reductive dechlorination of organic contaminants can be affected by many redox processes such as nitrate reduction and iron reduction. In the present study, batch incubation experiments were conducted to investigate the effect of nitrate addition on reductive dechlorination of PCP in paddy soil with consideration of iron transformation. Study results demonstrate that low concentrations (0, 0.5 and 1 mM) of nitrate addition can enhance the reductive dechlorination of PCP and Fe(III) reduction, while high concentrations (5, 10, 20 and 30 mM) of nitrate addition caused the contrary. Significant positive correlations between PCP degradation rates and the formation rates of dissolved Fe(II) (pearson correlation coefficients r = 0.965) and HCl-extractable Fe(II) (r = 0.921) suggested that Fe(III) reduction may enhance PCP dechlorination. Furthermore, consistent variation trends of PCP degradation and the abundances of the genus Comamonas, capable of Fe(III) reduction coupled to reductive dechlorination, and of the genus Dehalobacter indicated the occurrence of microbial community variation induced by nitrate addition as a response to PCP dechlorination.