Effect of Heavy Metals on the Enzymatic Activity of Haplic Chernozem under Model Experimental Conditions

The biological activity of soils is an essential parameter of their ecological status. The anthropogenic Heavy Metals (HMs) disturb the normal functioning of soil biota and, hence, the entire soil system. The aim of this work was to estimate the toxicity of loosely bound HM compounds in Haplic Chernozem using parameters of cellulose-degrading and urease activities. Contamination of Haplic Chernozem with Zn, Cd, Cu and Pb enlarged the group of mobile (loosely bound to soil) metal compounds, which includes exchangeable, complexed and specifically sorbed compounds of HMs. The increase of mobile HM forms content in soil inhibited the cellulose-degrading and urease activities after 30 days of the input of metal into the soil. A decrease in the toxic effect of metals on the studied parameters mainly occurred in the next 30 days. It was found that all HM forms similarly affected biological activity parameters. During two months from the moment of soil contamination with HMs, their toxic effect on cellulose-degrading and urease activities decreased. According to the degree of inhibition of biological activity in Haplic Chernozem, the studied metals formed the following series: Cd >Pb > Zn > Cu.