ORGANIC-MATTER - COPPER-COMPLEXES IN SOILS TREATED WITH SEWAGE-SLUDGE

The ligands complexing copper in various organic matter fractions isol ated from a soil treated with copper-contaminated sewage sludge have b een characterized using electron paramagnetic resonance (EPR) spectros copy. A soil of the Countesswells series was treated with sewage sludg e at the rate of 100 t dry matter/ha. Copper in the form of copper car bonate was then applied to give copper loadings of 140 mg/kg and 280 m g/kg in the top 25 cm of the profile, values at the EEC directive limi ting values and at twice these values, respectively. After 3 years, th e soil was sampled to a depth of 10 cm for analysis. Soil solution obt ained by centrifugation of fresh soil contained organically-complexed copper. The EPR spectroscopic parameters (A11 and g11) for Cu have val ues consistent with the presence of oxygen coordination at the equator ial position. Organic matter was isolated from soil by successive extr actions with 0.1 M sodium pyrophosphate (pH 7) and 0.1 M sodium hydrox ide and fractionated by selective adsorption and precipitation procedu res. Copper was present in several different complexes. Hyperfine stru cture from N-14 was observed in pyrophosphate extract unprecipitated b y 80% ethanol, the fulvic acid and humic acid fractions, indicating th at copper was in coordination with at least two nitrogen atoms in thes e fractions. The precipitable pyrophosphate-extracted substances only contained oxygen ligands. Soil solutions from three other soil series from sites which had received contaminated sludge treatments 20 years previously were also examined. Their spectra at 100 K were dominated b y manganese(II) signals but a copper signal could be resolved which wa s indistinguishable from that from the Countesswells series soil.