pHstatvs. single extraction tests to evaluate heavy metals and arsenic leachability in environmental samples

Here we compared the pHstat test, which examines the leachability of major elements (Ca, Mg, Al, Fe, and Mn), dissolved organic carbon, and trace elements (Cd, Zn, Cu, Pb, and As) in a wide pH range, with single extraction tests based on the use of mild extractants (calcium chloride, acetic acid or EDTA). For this purpose, we examined samples from a variety of environmental conditions (sludges, mineral soils, organic soils, and soils with particulate and/or soluble contamination). Extraction yields obtained with CaCl2 (0.01 mol L−1) and CH3COOH (0.43 mol L−1) correlated well with those from the pHstat at the same pH (r = 0.98 and 0.95, respectively), while the use of EDTA (0.05 mol L−1) led to systematically higher extraction yields than those quantified with the pHstat at the same pH. However, the pHstat test had three distinct advantages: (1) it revealed the relationship between the solubility of the main soil phases and pH; (2) it showed the variation in pollutant leachability due to changes in pH; and (3) it better predicted the maximum contaminant availability. Thus we propose that the pHstat is the best laboratory tests to evaluate the contaminant leachability over a wide range of sample types (soil, sludge, and sediment).