Speciation of cadmium, copper, lead, and zinc in contaminated soils

To investigate the activity of free cadmium (Cd2+), copper (Cu2+), lead (Pb 2+), and zinc (Zn2+) ions and analyze their dependence on pH and other soil properties, ten contaminated soils were sampled and analyzed for total con tents of Cd, Cu, Pb, and Zn (CPT Cu-T, Pb-T, and Zn-T, respectively), 0.43 MHNO3- extractable Cd, Cu, Pb, and Zn (Cd-N, Cu-N, Pb-N, and Zn-N, respecti vely), pH, dissolved organic matter (DOC), cation exchange capacity (CEC), ammonium oxalate extractable aluminum (Al) and iron (Fe), and dissolved cal cium [Ca2+]. The activity of free Pb2+, Cd2+, Cu2+, and Zn2+ ions in soil s olutions was determined using Donnan equilibrium/graphite furnace atomic ab sorption (DE/GFAA). The solubility of Cd in soils varied from 0.16 to 0.94 mu g L-1, Cu from 3.43 to 7.42 mu g L-1, Pb from 1.23 to 5.8 mu g L-1, and Zn from 24.5 to 34.3 mu g L-1. In saturation soil extracts, the activity of free Cd2+ ions constituted 42 to 82% of the disserved fraction, for Cu2+ t he range was 0.1 to 7.8%, for Pb2+ 0.1 to 5.1% and for Zn(2+)2 to 72%. The principal species of Cd, Cu, Pb, and Zn in the soil solution is free metal ions and hydrolyzed ions. Soil pH displayed a pronounced effect on the acti vity of free Cd2+, Cu2+, Pb2+, and Zn2+ ions.