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

^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

View larger version (22K): [in a new window]   Fig. 1. Data obtained with the ion-selective electrode for titrations of humic acid (HA), fulvic acid (FA), fulvic acid after dialysis with a molecular weight cutoff of 1000 Da (FA > 1000), FA, and dissolved organic matter (DOM) fractions (HoA, HoN, HiA, HiN, and HiB) from municipal solid waste (MSW) compost with Cd(ClO4)2 at pH 7. The x axis intercept of the regression line with a unity slope is defined as the complexing capacity (CC) for Cd of the respective ligand. Data shown were obtained from triplicated separate titrations for each ligand. CdF, free (ionic) cadmium.

View larger version (19K): [in a new window]   Fig. 2. Complexing capacities (CC) at pH 7 for Cd of humic acid (HA) and fulvic acid after dialysis with a molecular weight cutoff of 1000 Da (FA > 1000) from municipal solid waste (MSW) compost as determined by two different methods: Cd ion-selective electrode (ISE) and equilibrium dialysis (EQ; data from Kaschl, 2001).

View larger version (26K): [in a new window]   Fig. 3. Complexing capacities for Cd of dissolved organic matter (DOM) fractions (HoA, HoN, HiA, HiN, and HiB) and fulvic acid (FA) from municipal solid waste (MSW) compost as determined with the Cd ion-selective electrode at pH 7.

View larger version (24K): [in a new window]   Fig. 4. Incremental stability constants (pKi) for Cd binding by humic acid (HA), fulvic acid after dialysis with a molecular weight cutoff of 1000 Da (FA > 1000), FA, and dissolved organic matter (DOM) fractions (HoA, HoN, HiA, HiN, and HiB) from municipal solid waste (MSW) compost at pH 7. The pKi data were obtained by calculating the slope of adjacent points in the Scatchard plot representation (/CdF vs. , where CdF is free [ionic] cadmium) of the titration data. The scale of ' varies in accordance with the total complexing capacity (CC) of each ligand (the maximum value of ' corresponds to 100% CC). Three titrations were performed for each ligand except for HiA (1). The data shown were obtained from triplicated separate titrations for each ligand.

View larger version (28K): [in a new window]   Fig. 5. Distribution of binding site strengths for Cd at pH 7 determined using the normal distribution approach. The upper diagram displays data for humic acid (HA) and fulvic acid after dialysis with a molecular weight cutoff of 1000 Da (FA > 1000) and the lower, for dissolved organic matter (DOM) fractions (HoA, HoN, HiA, HiN, and HiB) from municipal solid waste (MSW) compost. The term µ is the average, is the standard deviation, and s is skewness.