Black Carbon Facilitated Dechlorination of DDT and its Metabolites by Sulfide

Abstract

1,1-trichloro-2,2-di(4-chlorophenyl)ethane (DDT) and its metabolites 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (DDD) and 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (DDE), are often detected in soils and sediments containing high concentrations of black carbon. Sulfide (∼5 mM) from biological sulfate reduction often coexists with black carbon and serves as both a strong reductant and a nucleophile for the abiotic transformation of contaminants. In this study, we found that the abiotic transformation of DDT, DDD, and DDE (collectively referred to as DDX) require both sulfide and black carbon. 89.3 ± 1.8% of DDT, 63.2 ± 1.9% of DDD, and 50.9 ± 1.6% of DDE were degraded by sulfide (5 mM) in the presence of graphite powder (21 g/L) after 28 days at pH 7. Chloride was a product of DDX degradation. To better understand the reaction pathways, electrochemical cells and batch reactor experiments with sulfide-pretreated graphite powder were used to differentiate the involvement of black carbon materials in DDX transformation by sulfide. Our results suggest that DDT and DDD are transformed by surface intermediates formed from the reaction between sulfide and black carbon, while DDE degradation involves reductive dechlorination. This research lays the groundwork for developing an alternative in situ remediation technique for rapidly decontaminating soils and sediments to lower toxic products under environmentally relevant conditions.

Application of biochar-based materials in environmental remediation: from multi-level structures to specific devices

“…The reduction of nitroaromatics sorbed on biochar was deemed to directly react with sorbed sulfides (Xu et al 2015). However, the reduction dichlorination of DDT and DDD was attributed to the surface intermediates formed by sulfide and biochar; while, DDE degradation was promoted by the quinone functional groups and graphitic regions in biochar which facilitate electrons transfer from sulfide to DDE (Ding and Xu 2016). Recently, a research of biochar-catalytic abiotic transformation of azo dyes by sulfide in anaerobic environment provided a better understanding of the mediation mechanisms, which the surface functional groups (especially the quinones) transformed sulfide into polysulfides which enhanced the reaction rates of azo dyes degradation by accelerating the electrons transfer (Zhao et al 2019).…”

Abiotic reductive removal of organic contaminants catalyzed by carbon materials: A short review

“…These studies have received increasing attention for two reasons. First, carbon materials constitute 5-30% of total organic carbon in soils and sediments (Ding & Xu, 2016), and reductive transformations catalyzed by these materials significantly contributed to the chemical transformation of organic contaminants in the environment. Therefore, investigations on carbon-catalyzed reduction can advance the understanding on natural transformation of pollutants.…”

Mechanisms for sulfide‐induced nitrobenzene reduction mediated by a variety of different carbonaceous materials: Graphitized carbon‐facilitated electron transfer versus quinone‐facilitated formation of reactive sulfur species

“…Among the CM-mediated redox reactions, sulfideinduced reduction of nitroaromatic compounds (NACs) has received considerable attention (Ding & Xu, 2016;Kemper et al, 2008;Oh & Chiu, 2009;Oh et al, 2013;Xu et al, 2010Xu et al, , 2013Xu et al, , 2015Yu et al, 2011). Nitroaromatic compounds are produced in large quantities and are widely used as pesticides, explosives, organic solvents, and intermediates in organic synthesis.…”

“…Once adsorbed on CMs, HOC molecules may be subject to a variety of complex reactions (including abiotic hydrolysis and redox transformation and biodegradation), in which CMs act as effective reactors and/or mediators (Ding & Xu., 2016; Fu, Guo, Chen, Gu, & Zhu, 2014; Kemper, Ammar, & Mitch, 2008; Oh & Chiu, 2009; Oh, Son, & Chiu, 2013; Saquing, Yu, & Chiu, 2016; Tang, Zhu,Li, Kong, & Chen, 2011; Xu, Dana, & Mitch, 2010; Xu, Pignatello, & Mitch, 2013, 2015; Yu et al., 2011). The graphitized carbons of CMs have high electron conductivity and thus are proposed to facilitate the redox reaction of adsorbed HOCs by enhancing electron transfer (Fu et al., 2014; Oh & Chiu, 2009; Oh et al., 2013; Tang et al., 2011; Xu et al., 2013).…”

“…Notably, the strong electron‐withdrawing nitro group(s) makes NACs ideal π‐electron acceptors that interact strongly with polarized π‐electron−rich graphitized carbons via the π−π electron donor acceptor mechanism, leading to extraordinarily strong adsorption affinity to CMs (Björk et al., 2010; Pan & Xing, 2008; Zhu & Pignatello, 2005). Both the above‐mentioned mechanisms—enhanced electron transfer by graphitized carbons and facilitated electron shuttling by surface quinone moieties—have been explored to explain the accelerated reduction of NACs mediated by CMs such as BC, AC, and CNMs (Ding & Xu., 2016; Fu et al., 2014; Kemper et al., 2008; Oh & Chiu, 2009; Oh et al., 2013; Saquing et al., 2016; Tang et al., 2011; Xu et al., 2010, 2013, 2015; Yu et al., 2011). Recently, an additional mechanism was proposed that the reduction of NACs was driven by CM‐catalyzed formation of reactive sulfur species (polysulfides) (Wei, Yin, & Zhu, 2018; Zhao et al., 2019).…”