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This article in JEQ

  1. Vol. 31 No. 6, p. 1885-1892
     
    Received: July 24, 2001


    * Corresponding author(s): yonachen@agri.huji.ac.il
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doi:10.2134/jeq2002.1885

Cadmium Binding by Fractions of Dissolved Organic Matter and Humic Substances from Municipal Solid Waste Compost

  1. Arno Kaschla,
  2. Volker Römhelda and
  3. Yona Chen *b
  1. a Institute of Plant Nutrition (330), University of Hohenheim, 70593 Stuttgart, Germany
    b Dep. of Soil and Water Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, P.O.B. 12, Rehovot 76100, Israel

Abstract

The agricultural practice of amending soils with composted municipal solid waste (MSW) adds significant amounts of organic matter and trace metals, including Cd. Under these conditions, soluble organic complexes of Cd formed in the compost may be more significant than previously thought, due to Cd bioavailability and mobility in the soil environment. To study the relative importance of different types of organic ligands in MSW compost for the binding of Cd, six fractions of the dissolved organic matter (DOM) in addition to humic acid (HA) and fulvic acid (FA) were extracted and their complexation of Cd quantified at pH 7 using an ion-selective electrode (ISE). The highest complexing capacities (CC) for Cd were found for the most humified ligands: HA (2386 μmol Cd g−1 C of ligand), predialyzed FA (2468 μmol Cd g−1 C), and HoA, a fulvic-type, easily soluble fraction (1042 μmol Cd g−1 C). The differences in CC for Cd of the various organic ligands were not directly related to total acid-titratable or carboxylic groups, indicating the importance of sterical issues and other functional groups. The strength of association between Cd and the organic ligands was characterized by calculating stability constants for binding at the strongest sites (pKint) and modeling the distribution of binding site strengths. The pKint values of the DOM fractions ranged between 6.93 (HiN: polysaccharides) and 8.11 (HiB: proteins and aminosugars), compared with 10.05 for HA and 7.98 for FA. Hence, the highly complex and only partially soluble organic molecules from compost such as HA and FA demonstrated the highest capacity to sequester Cd. However, strong Cd binding of organic ligands containing N-functional groups (HiB) in addition to a high CC of soluble, humified ligands like HoA indicated the relevance of these fractions for the organic complexation of Cd in solution.

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Copyright © 2002. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyPublished in J. Environ. Qual.31:1885–1892.