SELECTED CHEMICAL AND PHYSICAL SOIL PROPERTIES OF THREE SACRIFICIAL SEWAGE-SLUDGE DISPOSAL SITES

Large volumes of heavy metal containing sewage sludge are disposed of on sacrificial lands. Soil from two sacrificial sites in the Gauteng province were collected for investigations into their accumulated heavy metal levels, as well as certain chemical and physical properties. The soils differed in their clay content with the one being a light coloured gravely sandy loam (granitic parent material Soil 1) and the other a red sandy clay loam (dolomitic parent material). The red sandy clay loam soil was collected from two sites, namely one that had received regular additions of lime (Soil 2) and one that had not (Soil 3). The soils were analysed for pH (H2O, KCl, and CaCl2), texture, and organic carbon content. Heavy metal fractions were determined through an EPA 3050 digestion ( ≈ total metal content), NH4-EDTA (potentially plant available metals), BaCl2 (exchangeable metals), and saturated paste (water-soluble metals) extracts. The results indicated that the unlimed soils (Soils 1 and 3) accumulated high levels of organic matter and were severely acidified (pH 4) whereas the regularly limed soil (Soil 2) had less organic matter and was not acidified (pH 6.5). An incubation with lime was done over six months with Soils 1 and 3 and both soils exhibited a very large pH buffering capacity. Heavy metal levels in all three soils were very high and exceeded present guideline levels. NH4-EDTA extractable Cd, Cu, Fe, Mn, and Pb increased after liming. The effect of liming on the organic matter mineralisation and subsequent higher NH4-EDTA extractability of certain metals is being investigated