Conclusion
The inhibition of soil microbial activity (measured as DHA activity) with the Cd concentration can be predicted by a simple kinetic model of enzyme inhibition in most cases, and it can be said that microbial activity is more sensitive than microbial biomass to soil Cd contamination. The ED values predicted by the two models used in our study can contribute to establish threshold values of heavy metal, in particular conditions, to avoid soil contamination or to establish the remediation strategies of soil contaminated and, thus, preserve environmental health. As was observed in our
study, the effect of Cd on microbial activity was different depending on the different soil characteristics and soil management, and such effects varied with the time of exposure to Cd. In this way, ED values enabled a direct comparison of the relative fragility of different environments to the same pollutant. In the other side, for the same environment, it is necessary to follow the
changes in the ED values with the time of exposure to the contaminant until a stable value is reached. Moreover, the effects of Cd on both soil microbial activity and crops must be taken into consideration to establish the risk of transference of this contaminant to the food chain.