CHEMICAL-REACTIVITY OF TRACE-METALS IN 2 POLLUTED SOILS AS AFFECTED BY A REDUCING COMPOUND

Two soil samples polluted by sewage sludge or atmospheric deposition w ere mixed with hydroxylamine hydrochloride as reducing agent, in order to simulate anoxic conditions able to occur in natural medium, thus e valuating the reactivity of trace metals. Metal extractability in redu cing conditions was studied as a function of time and pH. Although the effect of the reducing reagent is more pronounced in acidic medium, o ne must keep in mind the extracting effect of proton. The calculated d ifference between reducing medium and acidity effects shows that, for instance, zinc is not mobile, due to reducing conditions. The monitori ng of trace metals during hydroxylamine extraction does not reveal ref ixation phenomena. However, in a second part of the study, readsorptio n phenomena able to occur during leaching were investigated using a se cond chemical reagent (Baryum perchlorate). It was shown that refixati on of Copper and Lead effectively occurs. Such processes constitute a serious limitation in the interpretation of speciation found using seq uential extraction procedures with hydroxylamine.