Keywords: 
• heavy metal polluted urban soil /
• siduron /
• nitrogen mineralization /
• basal respiration /
• soil enzyme /
• dose-effect relationship

Abstract: Combined pollution of heavy metals and organics in urban soil is ubiquitous. Herbicide such as siduron is frequently used in lawn management and pollution of these pesticides in urban soil has become a new focus. In this research, different heavy metal polluted urban soils were selected to evaluate the ecological risk of siduron pollution based on laboratory simulation experiments. Effects of siduron on soil organic nitrogen mineralization, basal respiration and soil enzyme activities were studied. It was suggested that: (1) The soil organic nitrogen mineralization, basal respiration, arylsulfatase and alkaline phosphatase activities were sensitive to heavy metal and siduron pollution, while urease and invertase activities were insensitive. (2) In the range of siduron concentrations from 0 mg·kg^-1 to 1 000 mg·kg^-1, significant linear correlations were observed between siduron concentrations and the inhibition (activation) rates of alkaline phosphatase activity in slightly heavy metal polluted soil N. Significant linear relationships were also observed between siduron concentrations and the inhibition (activation) rates of arylsulfatase activities in soil D and G which were more seriously heavy metal polluted. (3) The EC₁₀s of the effect of siduron on the inhibition (activation) rates of arylsulfatase activities in soil D and G and on the inhibition (activation) rates of alkaline phosphatase activity in soil N were 568 mg·kg^-1, 1 306 mg·kg^-1 (inhibiting value) and 56 mg·kg^-1 (activation value), 99 mg·kg^-1, respectively. And EC₅₀s were 1 901 mg·kg^-1, 3 806 mg·kg^-1,2 321 mg·kg^-1, respectively. The above results can provide basic data and technical methods for the ecological risk assessment of compound pollution of heavy metals and pesticide in urban soil.