Research Article Received: 15 January 2012 Revised: 28 March 2012 Accepted: 31 March 2012 Published online in Wiley Online Library: (wileyonlinelibrary.com) DOI 10.1002/jctb.3835 Enhancement of microbial reductive dechlorination of polychlorinated biphenyls (PCBs) in a marine sediment by nanoscale zerovalent iron (NZVI) particles Giulio Zanaroli, a∗ Andrea Negroni, a Marta Vignola, a Andrea Nuzzo, a Hung-Yee Shu b and Fabio Fava a Abstract BACKGROUND: Microbial reductive dechlorination of polychlorinated biphenyls (PCBs) in contaminated sediments is characterized by long lag periods and low rates. Zerovalent iron is a source of cathodic hydrogen that has been proposed as an easily amendable agent to stimulate PCB microbial dechlorination. The objective of this study was to evaluate the effect of nanoscale zerovalent iron (NZVI) particles on the reductive dechlorination of Aroclor 1254 PCBs and on the indigenous microbial community in a marine sediment under in situ-like biogeochemical conditions. RESULTS: A 30-weeks lag phase followed by a modest dechlorination (5.0 ± 0.4 mol%) of hepta- through penta-chlorinated PCBs occurred in NZVI-free cultures during 36 weeks of incubation. NZVI (6.7 g kg −1 ) reduced the lag phase of PCB dechlorination by 10 weeks, leading to a four-fold increase of the dechlorination extent at the end of the incubation. NVZI exerted some toxic effect on sulphate reducing bacteria, which were transiently inhibited until its complete oxidation occurred, and favoured the enrichment of a phylotype closely related to the PCB dehalorespiring bacterium Dehalobium chlorocoercia DF-1, probably via the simultaneous partial inhibition of sulphate reducing bacteria and the release of molecular hydrogen. Finally, DGGE analysis showed that NZVI did not affect markedly the biodiversity of the indigenous microbial community. CONCLUSION: NZVI displayed a very high biostimulation effect on PCB microbial dechlorination and a very low impact on the sediment indigenous microbial community. Supplementation with NZVI particles might thus be a sustainable effective strategy to intensify PCB reductive dechlorination processes in marine sediments. c  2012 Society of Chemical Industry Keywords: nanoscale zerovalent iron (NZVI); polychlorinated biphenyls (PCBs); microbial reductive dechlorination; marine sediments; Dehalobium chlorocoercia DF-1 INTRODUCTION Polychlorinated biphenyls (PCBs) were widely used for several industrial purposes until their production was banned in the 1980s. PCBs are globally dispersed 1 especially persisting in several anaerobic freshwater and marine sediments, 2 because of their very high hydrophobicity, chemical stability and recalcitrance to biodegradation. Furthermore, their highly lipophylic nature causes their bioaccumulation and biomagnification through the food chain up to humans, where they have been reported to act as endocrine disrupters and possible carcinogens. 3–5 For these reasons, PCBs are still considered contaminants of great environmental concern and are included among the 21 worldwide priority persistent organic pollutants (POPs). 6 The most widely applied technology for treating PCB-impacted sediments is their removal by dredging and subsequent transfer to hazardous waste landfills. 7 In addition to being cost prohibitive, this approach impacts remarkably on the treated sites and does not destroy the pollutants, which are simply transferred from an open environment to a confined one. Under the anoxic conditions occurring in site sediments, PCBs can undergo reductive dechlorination. The process replaces chlo- rine atoms with hydrogen, thus converting highly chlorinated congeners into low chlorinated PCBs, that have lower bioaccu- mulation potential and toxicity as well as a higher susceptibility to mineralization by native aerobic bacteria. 8,9 The process gen- erally occurs after very long lag periods and slowly; however, if properly stimulated, it might mediate the natural decontamina- tion of the sediment in situ by avoiding or reducing the need for ∗ Correspondence to: Giulio Zanaroli, Department of Civil, Environmental and Materials Engineering (DICAM), Faculty of Engineering, University of Bologna, via Terracini 28, 40131 Bologna, Italy. E-mail: giulio.zanaroli@unibo.it a Department of Civil, Environmental and Materials Engineering (DICAM), Faculty of Engineering, University of Bologna, via Terracini 28, 40131 Bologna, Italy b Institute of Environmental Engineering, Hungkuang University, No. 34 Chung- Chie Rd., Shalu, Taichung County 433, Taiwan J Chem Technol Biotechnol (2012) www.soci.org c  2012 Society of Chemical Industry