Long-term effects of decabromodiphenyl ether on denitrification in eutrophic lake sediments: Different sensitivity of six-type denitrifying bacteria.

Abstract

The widespread use of polybrominated diphenyl ethers inevitably results in their increased release into natural waters and subsequent deposition in sediments. However, their long-term effects on the bacteria participating in each step of denitrification in eutrophic lake sediments are still unknown. Here, we conducted a one-year microcosm experiment to determine the long-term effects of decabromodiphenyl ether (BDE-209), at low (2\xa0mg\xa0kg-1 dry weight) and high (20\xa0mg\xa0kg-1 dry weight) contamination levels, on six-type denitrifying bacteria and their activities in sediments collected from Taihu Lake, a typical eutrophic lake in China. At the end of the experiment, sediment denitrifying reductase activities were inhibited by BDE-209 at both levels, with the greatest inhibition seen for nitric oxide reductase activity. The higher nitrate concentration in the contaminated sediments was attributed to the inhibition of nitrate reductase activities. The abundances of six-type denitrifying genes (narG, napA, nirK, nirS, norB, and nosZ) significantly decreased under high BDE-209 treatment, and narG and napA genes were more sensitive to the toxicity of BDE-209. The results from pyrosequencing showed that BDE-209, at either treatment concentration, decreased the six-type denitrifying bacterial diversities and altered their community composition. This shift of six-type denitrifying bacterial communities might also be driven by the debrominated products concentrations of BDE-209 and variations in sediment inorganic nitrogen concentrations. In particular, some genera from phylum Proteobacteria such as Pseudomonas, Cupriavidus, and Azoarcus were decreased significantly because of BDE-209 and its debrominated products.