Anthropogenic pollutants rarely occur in the environment as single constituents, thus combination effects rather than separate effects of pollutants are expected to occur in the environment. PAH contamination of soil is often associated with the presence of high levels of potentially toxic metals which may impact on PAH biodegradation. In this study, the impact of zinc and copper mixtures (0, 50,100, 500 and 1000 mg kg(-1)) on the development of phenanthrene catabolism and impact on bacterial numbers in soil were investigated over 168 day incubation. The presence of low concentrations of Zn and Cu (50 and 100 mg kg(-1)) had no significant effect (p > 0.05) on the development of phenanthrene catabolism, but phenanthrene biodegradation was significantly reduced at higher concentrations of Zn + Cu mixture (p <0.05). Bacterial cell numbers decreased significantly in the higher concentrations of the mixtures relative to the control. Thus, in soils impacted with organic and metallic contaminants, biodegradation may be inhibited. (C) 2013 Elsevier Ltd. All rights reserved.