SPECIATION IN METAL-CONTAMINATED SOILS AS REVEALED BY AN ION-EXCHANGERESIN MEMBRANE FRACTIONATION PROCEDURE

Ion exchangers have proven to be a useful tool in the study of metal s peciation in aquatic environments, but have seen little application in the study of metal behavior in soil environments. The labile metal sp ecies in polluted soils were evaluated by equilibrating soil suspensio ns with ion exchange resin membranes of different types at pH values r anging from 3 to 9. The total soluble metal content of cadmium (Cd), c hromium (Cr), nickel (Ni), and lead (Pb) contaminated Western Canadian soils was subdivided into (i) low-pH labile, (ii) weak-acid labile, ( iii) weak-base labile, (iv) high-pH labile, and (v) non-adsorbable for ms using cation and anion exchange membranes. Soil suspension is mixed overnight with different types of resin membranes and the cations tra nsferred from the soil are subsequently eluted from the membranes usin g 1N HCl. The HCl extract is then analyzed for Cd, Cr, Ni, and Pb. The aqueous phase remaining in contact with the soil residue is considere d the amount of released non-labile, non-adsorbable species. The low-p H labile fraction constituted the largest proportion of the added meta l in poorly buffered (sandy) soils. Weak-acid and base labile fraction s were typically highest in highly buffered soils. Clearly, metal cont aminated soils most likely to cause environmental damage are sandy tex tured soils subject to acidification, although the production of chela ting substances by roots and microorganisms may also mobilize consider able quantities of metal in soils of high clay content.