In this study, we investigated the influence of various types of carbonaceous materials (CMs) on the bioavailability of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) to polybrominated diphenyl ether (PBDE)degrading microorganisms in CM -amended sediments. The microbial debromination ratio of BDE-47 was reduced by 92.8%-98.2% in the 5.0% CM -amended sediment compared with in sediment without CM amendment after 100 d of anaerobic incubation. The concentrations of lower brominated products also decreased when the content of CMs increased from 0.2% to 5.0%. The inhibitory effects of CMs on BDE-47 debromination were CM content- and characteristic -specific. The reciprocals of BDE-47 debromination ratios and lower brominated product concentrations showed positive linear correlations with CM contents in sediments (p <0.01), and the slopes of linear regression fitting generally correlated with specific surface areas (SSAs) of CMs. Desorption of BDE-47 from CMs indicated the declined desorbing fraction of BDE-47 was responsible for the reduction in BDE-47 bioavailability to microorganisms, thus decreasing its debromination in sediments amended with CMs. This study revealed that CM amendment could reduce the PBDE bioavailability to PBDE-degrading microorganisms in sediments, and it is expected to help deepen our understanding of the environmental behaviors and risks of PBDEs. (C) 2016 Elsevier B.V. All rights reserved.