Applicability of single and sequential extractions for assessing the potential mobility of heavy metals in contaminated soils

Heavy metal polluted sites are bearing an acute hazardous risk for the grou ndwater, but also a potential one. While the acute risk can be assessed dir ectly via seepage water measurements, determination of the potential risk i s much more complex. It results from the sum of all reactions that are capa ble to mobilize heavy metals under worst case environmental conditions. Usi ng a fourfold sequential extraction (SE4) such a worst case was simulated f or four soils highly contaminated with Pb, Zn, and Cu. The resulting potent ial mobilizable amounts phi(pm) have been compared with those derived from 6 single extractions. By means of variance analyses, it is shown that phi(p m) of lead can be represented by a single extraction with NH2OH. In contrar y, phi(pm) of zinc can be represented using the pH(stat) test or an extract ion with aqua regia, while phi(pm) of copper can be represented only by aqu a regia extraction. The water-soluble amounts deriving from the DEV-S4 test do not correlate with the potential mobilizable amounts of any metal. Ther efore, an assessment of contaminated sites should include an aqua regia ext raction additionally to the seepage water analysis.