Influence of redox conditions on the microbial degradation of polychlorinated biphenyls in different niches of rice paddy fields

The biotransformation of PCBs in three niches with contrasting redox conditions (water-soil interface, rhizosphere and non-rhizosphere subsoil) was studied using rhizoboxes subjected to the sequential flooding and draining conditions associated with rice cultivation in paddy fields. Rice cultivation favored PCB dechlorination and further transformation of the degradation products. Microbial dechlorination activity not only began earlier but was also 50% greater in the rhizosphere in comparison with bulk soil. Distinct profiles of both phospholipid fatty acids (PLFAs) and PCB congeners arose in each niche. Signature PLFAs attributed to Gram-positive (G+) bacteria were significantly correlated with the dissipation of PCB congeners in paddy field soils, especially in the rhizosphere.