Reductive Dechlorination of 1,2,3,4-Tetrachlorodibenzo-p-dioxin and Its Products by Anaerobic Mixed Cultures from Saale River Sediment

The capability of anaerobic bacterial consortia from different environmental sources including soils, sewage sludges, and sediment of the river Saale (Germany) to dehalogenate chlorinated dioxins was compared using 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) as the model compound. The inocula were amended with mineral medium and organic acids and spiked with a high concentration (50 μM) of 1,2,3,4-TCDD to stimulate microbial dehalogenating activity. Reductive dechlorination was observed to 1,3-dichlorodibenzo-p-dioxin (1,3-DCDD) as the main product and to minor amounts of the 1,2,4- and 1,2,3-trichlorodibenzo-p-dioxins (TrCDD) using incubations with Saale River sediment. No reaction was observed in the controls and in incubations with soils or sewage sludges. The dechlorination of 1,2,4- and 1,2,3-TrCDD was analyzed in separate subcultures. Reductive dechlorination of 1,2,4-TrCDD was a relative fast process (about 6 μM converted within 58 days) and yielded only one product (1,3-DCDD). 1,2,3-TrCDD was slowly dechlorinated to equal amounts of 1,3- and 2,3-DCDD. These observations suggest that the main dechlorination route of 1,2,3,4-TCDD to 1,3-DCDD proceeds primarily via the removal of a lateral chlorine atom with 1,2,4-TrCDD as the intermediate.