DETERMINATION OF CHEMICAL AVAILABILITY OF CADMIUM AND ZINC IN SOILS USING INERT SOIL-MOISTURE SAMPLERS

A rapid method for extracting soil solutions using porous plastic soil -moisture samplers was combined with a cation resin equilibration base d speciation technique to look at the chemical availability of metals in soil. Industrially polluted, metal sulphate amended and sewage slud ge treated soils were used in our study. Cadmium sulphate amended and industrially contaminated soils all had >65% of the total soil solutio n Cd present as free Cd2+. However, increasing total soil Cd concentra tions by adding CdSO4 resulted in smaller total soil solution Cd. Cons equently, the free Cd2+ concentrations in soil solutions extracted fro m these soils were smaller than in the same soil contaminated by sewag e sludge addition. Amendment with ZnSO4 gave much greater concentratio ns of free Zn2+ in soil solutions compared with the same soil after lo ng-term Zn contamination via sewage sludge additions. Our results demo nstrate the difficulty in comparing total soil solution and free metal ion concentrations for soils from different areas with different phys iochemical properties and sources of contamination. However, when comp aring the same Woburn soil, Cd was much less available as Cd2+ in soil solution from the CdSO4 amended soils compared with soil contaminated by about 36 years of sewage sludge additions. In contrast, much more Zn was available in soil solution as free Zn2+ in the ZnSO4 amended so ils compared with the sewage sludge treated soils. (C) 1998 Elsevier S cience Ltd. All rights reserved.