Chemical Fractionation of Cadmium, Copper, Nickel, and Zinc in Contaminated Soils

Abstract

Heavy metals are potentially toxic to human life and the environment. Metal toxicity depends on chemical associations in soils. For this reason, determining the chemical form of a metal in soils is important to evaluate its mobility and bioavailability. Sequential extraction was used to fractionate four heavy metals (Cd, Cu, Ni, and Zn) from nine contaminated soils into six operationally defined groups: water soluble, exchangeable, carbonate, Fe‐Mn oxide, organic, and residual. The residual fraction was the most abundant pool for all four metals examined. A significant amount (2.4–44%) of Zn was present in the potentially available fraction: nonresidual fraction. A major portion (40–74%) of Cu was associated with the organic, Fe‐Mn oxide, and carbonate fractions in most of the soils. Contamination of Cd and Ni in these soils was not as severe as Zn and Cu. Assuming that mobility and bioavailability of these metals are related to their solubility and geochemical forms, and that they decrease in the order of extraction sequence, the apparent mobility and potential bioavailability for these four metals in the soils were: Zn > Cu > Cd > Ni. Metal distributions in different chemical fractions in these soils depended on respective total metal concentrations, except for Zn.

Using soil heavy metal enrichment and mobility factors to determine potential uptake by vegetables

“…Pb bioavailability in SAL decreased slightly with increase in SAR (Table 3). Fractionation studies indicate that Pb will preferentially sorb into S 2 , S 3 , S 5 (Ma and Rao 1997) and S 4 fractions (Ščančar et al 2001) depending on prevailing soil chemical environment. Binding of Pb in these fractions may reduce Pb concentration in the S 1 fraction, resulting in decreased Pb bioavailability.…”

The effect of ageing on the bioaccessibility and fractionation of cadmium in some typical soils of China

“…In an artificially polluted Mollisol, the exchangeable (48%), EDTA-extractable (26%), and residual fractions (21%) were reported to be the dominant Cd forms (Ma and Uren, 1998). An order of residual N exchangeable N carbonate N Fe/Mn oxide N organic N water-soluble fraction of Cd was observed in contaminated soils from various US locations (Ma and Rao, 1997). Generally, the reported great variations in soil Cd fractionation within each study or among different studies may be attributed not only to the difference in the origin (native or polluted) of Cd, pollution source, and soil properties (soil pH, organic matter, clay mineralogy), but also to the difference in sequential extraction procedure that they have adopted.…”

“…There are a number of previous reports in the literature characterizing Cd fractionation in unpolluted and polluted soils using various sequential extraction procedures (Mann and Ritchie, 1994;Ma and Rao, 1997;Ma and Uren, 1998;Ahnstrom and Parker, 1999;Petit and Rucandio, 1999;Száková et al, 1999;Naidu, 2000, 2003). It was reported that concentrated acid-extractable Cd was the only fraction of indigenous Cd detected in the yellow earth and lateritic podzolic soil collected from Western Australia, using graphite furnace atomic absorption spectrophotometer (GFAAS).…”

Distribution and contamination pattern of heavy metals from surface sediments in the southern part of Caspian Sea, Iran

“…[34] Assuming that bioavailability is related to solubility, then metal bioavailability decreases in the order of exchangeable forms > acid reduction forms > organic forms > residual forms. [23,24,35] The residual phase represents metals largely embedded in the crystal lattice of the sediment fraction and should not be available for remobilization except under very harsh conditions. [23] Figure 2 compares non-resistant with resistant fractions in the surface sediments of the southern part of the Caspian Sea.…”