Fractionation of copper and cadmium and their binding with soil organic matter in a contaminated soil amended with organic materials

State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, 430070 People’s Republic of China
Journal of Soils and Sediments (Impact Factor: 1.97). 10(6):973-982. DOI: 10.1007/s11368-010-0199-1

ABSTRACT PurposeThe contamination of agricultural soils by heavy metals is a worldwide problem. Organic amendments can be used for the immobilization
and binding of heavy metal ions in soils by complexation, adsorption, and precipitation. A field trial was carried out to
evaluate the influence of some low-cost organic materials such as rice straw (RS), green manure (GM), and pig manure (PM)
on the distribution of Cu and Cd and the retention of these metals by organic matter fractions in heavy metal-polluted soils.

Materials and methodsThe experiment was conducted in Miaoyunao Village, Daye County, Hubei province, China. PM, GM (peanut plants), and RS were
obtained from a farm close to the village. Sixteen treatments with three replicates were designed. Soil chemical properties
such as soil pH, electrical conductivity (EC), organic matter (OM), and available P were measured by standard methods. Soluble/exchangeable,
organic-bound, inorganic precipitates and residual Cu and Cd in the soil were sequentially extracted and analyzed. The amounts
of Cu and Cd bound with soil particulate organic matter (POM) fractions and humic substances were also determined.

Results and discussionThe addition of organic amendments declined significantly the concentrations of soluble/exchangeable Cu and Cd, but increased
the amounts of these metals in organic-bound and inorganic precipitate forms in the soil. RS was more effective than GM and
PM in diminishing the solubility of Cu and Cd. The largest retention for Cu and Cd by humic substances and POM was noticed
in RS treatments, whereas the lowest was found in PM treatments. Humic substances showed higher potential in the fixation
of Cu and Cd than POM fractions. The conversion of soluble/exchangeable Cu and Cd to other insoluble forms after the application
of organic amendments may be ascribed to the increases of soil OM, pH, EC, and available P contents. The highest binding of
Cu and Cd with POM fractions and humic substances after the incorporation of RS mainly resulted from the greatest increase
of soil OM contents.

ConclusionsRS, GM, and PM can be employed as good and cheap substances for the immobilization of Cu and Cd in heavy metal-polluted soils.
RS was the best amendment in decreasing the solubility of Cu and Cd, and also in enhancing the retention of these metals by
humic substances and POM fractions in the soil. Futures studies should focus on the influence of these organic amendments
or their mixtures on the phytotoxicity of Cu and Cd for different plants in heavy metal-contaminated soils.

KeywordsFractionation-Heavy metal-Humic substances-Organic amendments-POM

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