pH_(stat) vs. single extraction tests to evaluate heavy metals and arsenic teachability in environmental samples

摘要

Here we compared the pH_(stat) test, which examines the teachability 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 pH_(stat) at the same pH (r=0.98 and 0.95, respectively), while the use of EDTA (0.05mol L~(-1)) led to systematically higher extraction yields than those quantified with the pH_(stat) at the same pH. However, the pH_(stat) 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 teachability due to changes in pH; and (3) it better predicted the maximum contaminant availability. Thus we propose that the pH_(stat) is the best laboratory tests to evaluate the contaminant leachability over a wide range of sample types (soil, sludge, and sediment).