We correlated several soil properties of seven northeastern U.S. soils with metal-organic fractions obtained using the extractant N,N-dimethyl-formamide (DMF) to explain metal reactions in soils to which three sewage sludges had been added. The sludges—two anaerobically digested municipal (one pretreated with chlorine), and one aerobically digested municipal—were mixed with the soils at the rate of 300 metric tons (t)/ha (dry-weight basis) and incubated for 1 mo. The DMF extracts were fractionated on nonpolar, nonionic macroreticular and ion exchange resins into acidic, neutral, and basic hydrophilic solute fractions and acidic, neutral, and basic hydrophobic solute fractions and analyzed for Cu, Cd, Cr, Ni, Pb, and Zn.
Soil properties that seemed to be most closely associated (r > 0.73) with Cd, Cr, Ni, and Zn in the various fractions were pH and the amounts of illite, chlorite, and fine clay (< 0.2 μm). Thus, mineralogy seems to be related to organometallic components in soils. However, correlations were not significant for every fraction from every sludge used. One anaerobic sewage sludge incubated with the soils resulted in positive significant correlation between (1) soil pH and the amount of Zn associated with the hydrophobic base fraction (complex amines or porphyrins), and (2) total Ni and the amount of Ni associated with the hydrophilic base fraction (aminoacids). The other two sludges used showed no consistent significant correlation between soil properties and metal-organic fractions, indicating a need for classifying sewage sludge.
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