Dichloromethane (DCM) is a recalcitrant groundwater contaminant that shows nearly no reactivity with zero-valent iron (ZVI) nanoparticles. In this study, an effective dechlorination of DCM has been demonstrated using zero-valent copper (Cu-0) nanoparticles as a catalyst under sodium borohydride reduction conditions. The average diameter of Cu-0 nanoparticles was about 50 nm and the specific surface area was about 19 m(2) g(-1). Batch experiments revealed that 90% of DCM (26.4 mg L-1) was rapidly degraded within 1 h in the presence of Cu-0 nanoparticles (2.5 g L-1) and sodium borohydride (1 g L-1). The observed pseudo-first-order rate constant (k(obs)) was 2.19 h(-1), corresponding to a surface area normalized rate constant of 0.052 L m(-2) h(-1), which is 2-3 orders of magnitude higher than for other zero-valent metals. The DCM degradation rate is a function of the Cu-0 nanoparticle dose. Increasing the dose increased the observed reaction rate. Product analysis indicated that the degradation of DCM involved hydrodechlorination. Soluble copper ions generated by the dissolution of Cu-0 nanoparticles are lower than the World Health Organization drinking water standard, which suggests that the use of Cu-0 nanoparticles under reduction conditions may be potentially useful for the treatment of recalcitrant contaminants that are unable to be degraded by ZVI technology. (C) 2012 Elsevier B.V. All rights reserved.