Production and Dechlorination of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in Historically-Contaminated Estuarine Sediments

Polychlorinated dibenzo- p -dioxins (PCDD) are ubiquitous and considered to be unreactive to biotic and abiotic transformation processes. Here we demonstrate that sediment-associated 2,3,7,8-substituted dioxin residues in general, and 2,3,7,8-TCDD in particular, are in a state of flux, as they are produced from peri -dechlorination of octaCDD, and further laterally dechlorinated to 2-MCDD. This reaction can be stimulated in the presence of organic acids, 2-monobromodibenzo- p -dioxin (2-MBDD) and hydrogen, which result in the production of HpCDD, 2,3,7,8-TCDD, and 2-MCDD, respectively. The results indicate that dechlorination of 2,3,7,8-TCDD is not likely a rate-limiting step in the hydrogen-stimulated reaction, which presents a potential strategy to decontaminate dioxin-contaminated environments.