Speciation and fractionation of heavy metals in soil
experimentally contaminated with Pb, Cd, Cu and Zn together and effects on soil
negative surface charge
Affiliations: Institute of Soil Science, Chinese Academy of
Sciences, Nanjing 210008, China, E-mail: [email protected]
Abstract: Speciation of heavy metals in soil subsamples experimentally loaded
with Pb, Cd, Cu and Zn in orthogonal design was investigated by sequential
extraction, and operationally defined as water-soluble and exchangeable(SE),
weakly specific adsorbed(WSA), Fe and Mn oxides-bound(OX) and
organic-bound(ORG).The results show that speciation of heavy metals in the soil
subsamples depended on their kinds. About 90% of Cd and 75% of Zn existed in
soil subsamples in the SE fraction. Lead and Cu existed in soil subsamples as
SE, WSA and OX fractions simultaneously,although SE was still the major
fraction. Organic-bound heavy metals were not clearly apparent in all the soil
subsamples. Theconcentration of some heavy metal speciation in soil subsamples
showed good correlation with ionic impulsion of soil, especially for the SE
fraction. Continuous saturation of soil subsamples with0.20 mol/L NH_4Cl, which
is the first step for determination of the negative surface charge of soil by
the ion retention method, resulted in desorption of certain heavy metals from
the soil. It was found that the percentage desorption of heavy metals from soil
sub samples depended greatly on pH, the composition and originalheavy metal
content of the soil subsamples. However, most of theheavy metals in the soil
subsamples were still retained aftermultiple saturation. Compared with the
parent soil, the negative surface charge of soil subsamples loaded with heavy
metals did notshow differ significantly from that of the parent one
bystatistical analysis. Heavy metals existed in the soil subsamplesmainly as
exchangeable and precipitated simultaneously.
Keywords: soil, heavy metals, speciation, soil surface charge
