Estimation of Soil Trace Metal Bioavailability using Unbuffered Salt Solutions: Degree of Saturation of Polluted Soil Extracts

Abstract

Soil trace metal extractability by 0.01 mol l−1 CaCl2, 0.1 mol l−1 NaNO3 and 1 mol l−1 NH4NO3 solutions is very low. The hypothesis, according to which the saturation of extracts limits the concentrations in solution, was tested by the study of polluted soils. Thus, according to our calculations, cadmium and copper did not precipitate as carbonates, hydroxides and phosphates. In contrast, zinc might precipitate as phosphate, lead as carbonate, hydroxide, sulfate and phosphates. The influence of such phenomena on the estimation of Pb bioavailability was tested by studying the lead uptake of radish plants cultivated in sandy soils artificially enriched with lead. It was then demonstrated that the saturation of the solutions did not in these conditions allow the evaluation of lead bioavailability using such chemical extractions.