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field studies
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
2 (reliable with restrictions)

Data source

Reference Type:
Chemical Fractionation of Cadmium, Copper, Nickel, and Zinc in Contaminated Soils
Ma LQ. and Rao GN.
Bibliographic source:
J. Environ. Qual. 26:259-264 (1997)

Materials and methods

Test guideline
no guideline followed
Principles of method if other than guideline:
GLP compliance:
not specified
Type of measurement:
All extractions were conducted in triplicate in acid-washed (5% HN03) polycarbonate labware. All chemicals used in this study were of analytical grade or better. Double deionized water, from a Barnstead NANOpure water system was used. Total metal concentrations of the supernatants from each step were analyzed by atomic absorption spectrophotometer (Perkin-Elmer 2380) equipped with a graphite furnace atomizer. Flame atomic absorption was used to analyze metal concentrations >I mg L-’ and graphite furnace atomizer was used to measure metal concentrations <1 mg L-’. Multilevel standards (Fisher Scientific) for all metals were prepared for each extraction step in the same matrix as the extracting reagents to minimize matrix effects. Blanks were used for background correction and other sources of error. At least one duplicate and one spike sample were run for every 10 samples to verify precision of the method. The spike recovery and precision were found to be within 100 f 10%.
Nine contaminated soils collected from various U.S. locations were used in this study. These soils reflect various sources of metal contamination, which can be classified into two broad categories: agricultural activities, such as the application of pesticide PbHAs04; and industrial activities, such as mining and smelting. The procedure of Tessier et al. (1979), selected for this study, is designed to separate heavy metals into six operationally defined fractions: water soluble, exchangeable, carbonate bound, Fe-Mn oxides bound, organic bound, and residual fractions.

Test material

Constituent 1
Reference substance name:
EC Number:
EC Name:
Cas Number:
Details on test material:
no further details

Results and discussion

Any other information on results incl. tables

Zinc was mostly concentrated in the residual fraction, although it was also present in other fractions. The percentage of total Zn in the residual fraction ranged from 55.8% (EF1) to 97.6% (PT). The greater percentage of Zn in the residual fraction probably reflects the greater tendency for Zn to become unavailable once it was in soils. Similar Zn results were reported for a soil from tailing dumps (Jordao and Nickless, 1989) and in near-shore sediments (Gupta and Chen, 1975). The amount of Zn present in the nonresidual fractions ranged from 2.4% (PT) to 44.2% (EFl) (Table 2). Among the nonresidual fractions, the Fe-Mn oxide fraction contained the greatest amount of Zn in all soils except BL and DA soils, in which the exchangeable and the carbonate fractions, respectively, had the greatest amount of Zn. This may be partially due to the high stability constants of Zn oxides. Several other workers have also found Zn to be associated with Fe-Mn oxides (Kuo et al., 1983; Ramos et al., 1994). Xian (1989) found that the sum of the exchangeable and the carbonate-bound forms were strongly correlated with Zn uptake by cabbage plants (Brussicu oleruceu). The sum of Zn in the exchangeable and carbonate fractions in our study ranged from 0.73% (PT) to 25% (DA), which indicates that the Zn in some of these soils may be highly available for plants. The concentrations of the water soluble and organic fractions in these soils was relatively low. Soils used in this study were contaminated from four different sources. The order of Zn association with various chemical fractions was the same for the three soils collected from former smelter sites (EF1, EF2, and PT), whereas the trend varied for the rest of the soils contaminated from other three sources (Table 2). In general, the association of Zn in these soils was in the decreasing order of residual > Fe-Mn oxides > carbonates > organic > exchangeable > water soluble. Soils EFl and EF2 were more contaminated than the other soils. Although a large percentage of the total Zn was in the residual fraction in these soils, the amount of Zn present in the nonresidual fractions was also appreciable from the standpoint of potential Zn mobility and bioavailability . The potential mobility and bioavailability of Zn in these soils would be in the order: EFl > DA > BP > BU > EF2 > BL > TW > RR > PT. An attempt was made to correlate the effect of total Zn content in soils on the distribution of Zn in the various chemical fractions and found that the distribution was independent of the total amount of Zn present in the soils.

Applicant's summary and conclusion

A sequential extraction procedure was used to fractionate Zn, Cu, Cd, and Ni present in nine contaminated soils. Different geochemical fractions are operationally defined by an extraction sequence that generally follows the order of decreasing solubility. The residual fraction was the most abundant pool for all the metals in the soils studied. However, in most of the soils, a significant percentage of total metals was associated with the nonresidual fractions. Therefore, they should be evaluated when studying the pollution levels of heavy metals in soils. A significant amount of Zn was associated with the nonresidual fractions in soils studied, indicating that this metal was potentially more bioavailable than other metals examined. Copper was found primarily in the residual or the organic fractions in most of the soils. Little Cd and Ni were found in these soils. Overall, the order of contamination was Zn > Cu > Cd > Ni. Among the nine soils tested, EF1, EF2, and DA soils were the most contaminated soils with the four heavy metals studied. The distribution of Zn in various chemical fractions was independent of the total Zn concentration in soils, whereas the distribution of Cu, Cd, and Ni in different fractions depended on respective total metal concentrations in the soils.