Enhancement of the DDT reductive dehalogenation by different cosubstrates: Role of sulfidogenic and biogeochemical processes in soil

Reductive dechlorination of DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane) in soil is an important pathway to favor its transformation to DDD (1,1-dichloro-2,2-bis(4-chlorophenyl) ethane) under anaerobic conditions. The reductive dechlorination has been reported to be coupled to the dissimilatory iron reduction and sulfate reduction processes. The aim of this study was to evaluate the reductive degradation of DDT using different types of cosubstrates (electron donors) to stimulate the sulfidogenic process in a pretreated zero-valent iron soil (ZVI-P soil). The addition of easily assimilable cosubstrates (glucose, ethanol, and lactic acid) at a concentration of 2.5 ± 0.1 mgC g?1 dry soil, as well as a complex cosubstrate (sugarcane bagasse, 2.5, 5, and 10%, w/w), enhanced the degradation of DDX (i.e., DDT and its degradation products). The highest degradation of DDT (96.1%), DDD (58.3%), DDE (43.9%), and DDNS (54.7%) was observed with the sugarcane bagasse (10% w/w) treatment. The biogeochemical transformation of gypsum and goethite into reactive iron sulfide species (mackinawite, Fe1+xS) suggested that the reductive dehalogenation of DDT to DDD was mediated abiotically for this sulfide species, while the degradation of DDD, DDNS, and DDE may have been linked to the bacterial consortia synergism favored during lignocellulose degradation. Members of the Firmicutes, Proteobacteria, and Actinobacteria were the dominant microorganisms in the soil amended with sugarcane bagasse. This indicated that DDX degradation in ZVI-P treated soil was related to abiotic and biotic processes.