Ferrous ions accelerate sulfide-induced abiotic dechlorination of DDT in waterlogged paddy soil and in soil solution

摘要

Purpose Abiotic dechlorination of organochlorine pollutants seems to occur more efficiently in nature than previously thought. Ferrous (Fe~(2+)) and sulfide (S~(2-)) ions have been shown to be effective dechlorinating reagents. However, little is known about the interactions between Fe~(2+) and S~(2-) during dechlorination of l,l,l-trichoro-2,2-bis(p-chlorophenyl)-ethane (DDT) in soil, in spite of the fact that these ions co-exist in waterlogged soils. Materials and methods An anaerobic soil incubation experiment was run for 192 h to investigate S~(2-) (1.0, 10 mM)-induced abiotic dechlorination of p,p'-DDT in waterlogged soil (soil/water= 1/20). In addition, the influence of Fe~(2+) (3.0 mM) on S~(2-) (0.5, 5.0 mM)-induced abiotic dechlorination of p,p'-DDT (2 μg m l~(-1)) was evaluated in soil solution and in distilled deionized water to identify the dechlorination mechanism under anaerobic incubation conditions for 6 h due to the complexity of soil, based on the determination of residual p,p -DDT in media by gas chromatograph (GC)-ECD and the identification of metabolites of p,p'-DDT by GC-MSD. Results and discussion S~(2-)-induced dechlorination of p,p'-DDT exhibited rapid and slow phases in three media (waterlogged soil, soil solution, and distilled deionized water). The addition of Fe~(2+) significantly accelerated S~(2-) induced dechlorination, reduced the remaining concentrations of p.p'-DDT at the turning point and the end point for the dechlorination reaction, and shortened the time to reach equilibrium in two aqueous media. In all, 93% and 48% of p,p'-DDTwas dechlorinated in soils supplied with 1.0 and 10 mM S~(2-) respectively. The underlying mechanism can be attributed to the coupling effect of Fe~(2+) and S~(2-) on dechlorination of DDT since the rates of dechlorination of p,p'-DDT treated by 0.5 and 5.0 mM S~(2-) over 6 h were significantly greater with Fe~(2+) addition than without Fe~(2+) addition in aqueous phase media. The metabolites of p,p'-DDT found in the three media were identified as p,p'-DDD, p,p'-DDE, and p,p'-DDMU, with or without the addition of Fe~(2+). Conclusions Combined Fe~(2+)/S~(2~)-induced dechlorination of DDT could be important for in situ remediation of DDT-contaminated soil/sediment given that Fe~(2+) and S~(2-)often co-exist in anaerobic conditions.