Nitrification potential in field-collected soils contaminated with Pb or Cu

Abstract

The influence of soil properties on nitrification potential was studied using a simple 4 h incubation test applied to 56 field-collected soils contaminated mainly with Pb or Cu. The soils were analyzed for total and dissolved metal and the soil solution was speciated for free Pb 2+ or Cu 2+ ions. The rates of nitrite production (NH + 4 oxidation to NO − 2) after the addition of a 1.0 mM NH + 4 substrate and 2.0 mM NaClO 3 varied between 25 and 4200 μmol NO − 2 kg −1 of soil d −1. The rates of nitrate production (NH + 4 oxidation to NO − 2 minus NO − 2 oxidation to NO − 3) for the same experimental conditions without chlorate varied between 2 and 2420 μmol NO − 2 kg −1 of soil d −1. The results show that the nitrification potential relationships with soil properties varied between sites. Soil pH and organic matter are the most influential parameters, but solution free metal activity and total metal content are also significant. It is not clear if soil pH and organic matter directly affect the nitrification potential or if they indirectly modify the chemical properties affecting metal speciation. However, given the high sensitivity of this microbial process towards many environmental soil parameters, the nitrification potential does not appear to be a straight-forward specific bioindicator for the evaluation of soil metal contamination.