Nonylphenol (NP) is known as an endocrine disruptor and has consequently drawn much environmental concern. We investigated the effects of various factors on the anaerobic degradation of NP and characterized the structures of microbial communities in mangrove sediments collected at five sites along the Tanshui River in northern Taiwan. NP anaerobic degradation rate constants (k(1)) and half-lives (t(1/2)) ranged from 0.008 to 0.0131/day and 53.3 to 86.6 days, respectively. The addition of NaCl (1%, 2%). zero-valent iron (10g/L), humic acid (0.5 g/L), cellulose (0.96 mg/L), brij 30 (55 mu M) and brij 35 (91 mu M) enhanced NP anaerobic degradation. However, the addition of NaCl (3%), acetate (20 mM), lactate (20 mM). pyruvate (20 mM), and humic acid (5 g/L) inhibited NP anaerobic degradation. Sulfate-reducing bacteria, methanogen, and eubacteria are involved in the degradation of NP, sulfate-reducing bacteria being a major component of the sediment. Our results also show that the addition of various substrates changed the microbial community in mangrove sediments. Also noted was the presence of 2-butyl-1-octanol, an intermediate product resulting from the anaerobic degradation of NP accumulated in the sediments. (C) 2008 Elsevier B.V. All rights reserved.