Experimental study of heavy metals distribution, attenuation and mobility in two Oklahoma soils amended with sewage sludge

Scope and method. This study was conducted to provide information on leaching and attenuation of heavy metals on two different soil types applied with sewage sludge (Biosolids). The research was based on soil column leaching procedure to evaluate the leaching capacity of clay and sandy soils. The objectives of the study were (1) to study the pollution potential of leachate from land application of sewage sludge in relation to the attenuation mechanisms in soils of different characteristics and (2) to recommend future research aimed at providing a base for development of pollution control procedures and guidelines regarding land disposal of sewage sludge. Two soil types (Norge clay and Dougherty sandy soils), three soil horizons, three treatments and three replications were used for the design of this experiment. The study showed the soil properties most useful in predicting mobility of trace metals in soils are texture, content of iron oxides, content of lime, soil pH, and organic matter. The most mobile heavy metals were zinc and nickel and the least mobile was chromium.; Findings and conclusions. There is no general agreement concerning the maximum allowable concentrations of various metals in sewage sludge. Faced with the difficult question of determining what levels of metals are harmful, one approach is to sidestep the issue by minimizing any accumulation. This could be achieved by an attempt to match the metal inputs from sludge to soil with the small annual losses of metals due to crop removal, soil erosion, and leaching, so that metal concentrations do not exceed background levels. This study was conducted to provide information on soil heavy metals mobility and retention as a result of land application of sewage sludge. Land application of sewage sludge containing heavy metals currently presents the potential for pollution. Although, the application of sewage sludge on agricultural land is beneficial to crops as a source of nutrients such as nitrogen and phosphorus, there is considerable concern for the amounts of heavy metals added as constituents of sludge. The concentrations of heavy metals in soils such as chromium, nickel, and zinc applied with sewage sludge are much higher than those in agricultural soils. Specific objectives of this research were to (a) examine the effects of land application of sewage sludge on soil types and heavy metal mobility and leaching, (b) evaluate the retention, release and distribution of heavy metals in soils amended with sewage sludge, and (c) recommend remediation mechanisms for soils with high contents of heavy metals. Two chemically and physically different soil types were selected and sampled by master diagnostic horizons. The research was based on laboratory based soil column leaching procedure to evaluate the leaching capacity of the two soil types.