The effect of Cu, Zn and Pb contamination on microbial activity in soils of Malta

Abstract

Soil microbial activities are significantly influenced by external variables including pollutants like heavy metals, that can turn from beneficial microelements to toxic and persistent polluters when excessive quantities are available. This in turn can have negative or adverse effects on the activity of soil microorganisms. The aim of this work was to study the effect of increasing concentrations of Cu, Zn, and Pb on microbial activity, and growth in calcareous soils. Soil samples were treated with increasing concentrations of Cu, Zn and Pb and subjected to short term and long-term incubations. Following the short- and long-term incubations the soil’s urease, arginase, and dehydrogenase activities together with the respiration rate were determined. Following the long-term incubation microbial growth was also investigated. From the overall findings, Cu exerted the most negative effects on both enzymatic activity and respiration rates, with continuously persisting effects on activity and respiration occurring the longer it remained in the soil matrix. To an extent Zn also exerted some negative effects on the soil, however these effects were more dependent on the type of enzyme being observed as well as the level of concentration incorporated. Indeed, enzymatic activity and microbial respiration were unresponsive to Pb, following prolonged exposure to this metal contaminant. However, under the short-term incubation, Pb did exert a negative effect on urease activity and to a lesser extent arginase, when higher concentrations were applied. In, terms of microbial plate growth, all treatments displayed no negative correlations and/or limitations of growth, regardless of concentration or the nature of the metal. In fact, in the case of Zn contamination an increase in microbial growth was noted with an increase in concentration. These findings might imply that microorganisms do in fact, have the ability to adapt to the altered soil conditions or indeed in some instances flourish.