Ecological effects of single and combined pollution of cadmium and phenanthrene on soil microorganisms

Soil microbial biomass carbon (Cmic), soil basic respiration and soil enzyme activities are the most important biological indicators of soil quality. The effects of single and combined pollution of cadmium (Cd 20mg/kg) and phenanthrene (Phe 50mg/kg) on these biological indicators were investigated in this study under the laboratory incubation conditions. The results showed that the level of Cmic and soil basic respiration were significantly reduced at different ratios in the whole experimental period (45d) when stress of single or combined pollution of Cd and Phe were imposed on. For the initial period of the stress, such inhibition was strong, and then gradually decreased or disappeared with the incubation time. The activities of urease, phosphatase, and dehydrogenase were also inhibited by the single Cd pollution or combined pollution of Cd and Phe during the whole experimental period. However, under the single Phe stress, the inhibition of soil enzyme activities could be observed at early stages of the incubation, and for the later stage of incubation, the soil enzyme activities were induced. Significant interactions between Cd and Phe in the condition of combined pollution were also found in this study. The toxicity effect of combined pollution of Cd and Phe was stronger than those caused by single Cd or Phe pollution, and mainly contributed by Phe.