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

The influence of soil properties on nitrification potential was studied usi ng a simple 4 h incubation test applied to 56 field-collected soils contami nated mainly with Pb or Cu. The soils were analyzed for total and dissolved metal and the soil solution was speciated for free Pb2+ or Cu2+ ions. The rates of nitrite production (NH4+ oxidation to NO2-) after the addition of a 1.0 mM NH4+ substrate and 2.0 mM NaClO3 varied between 25 and 4200 mu mol NO2- kg(-1) of soil d(-1). The rates of nitrate production (NH4+ oxidation to NO2- minus NO2- oxidation to NO3-) for the same experimental conditions without chlorate varied between 2 and 2420 mu mol NO2- kg(-1) of soil d(-1 ). The results show that the nitrification potential relationships with soi l properties varied between sites. Soil pH and organic matter are the most influential parameters, but solution free metal activity and total metal co ntent are also significant. It is not clear if soil pH and organic matter d irectly affect the nitrification potential or if they indirectly modify the chemical properties affecting metal speciation. However, given the high se nsitivity of this microbial process towards many environmental soil paramet ers, the nitrification potential does not appear to be a straightforward sp ecific bioindicator for the evaluation of soil metal contamination. (C) 199 9 Elsevier Science B.V. All rights reserved.