Tillage effects on the accumulation of polychlorinated biphenyls in biosolid-amended soils

Soil tillage along with the application of organic waste probably affects the concentrations of organic carbon and the enrichment of introduced polychlorinated biphenyls (PCBs). In a three-year experiment the PCB status of soils from three different field sites (silty clay loam, silt loam, sandy loam) which were long-term differently tilled (NT = no-tillage, CT = conventional plough tillage) and amended with two different organic wastes such as sewage sludge and compost (biosolids) was examined. No significant alteration in soil-PCB quality and quantity with biosolid application could be proven within the course of the experiments. This indicates soil-air exchange of PCBs dominates their concentrations in soil. Organic carbon in soil was significantly tillage-dependent and determined the fate of PCBs resulting in a generally elevated PCB-level in the non tilled soils. Linear regression of PCB load and organic matter content of all investigated untreated soils was highly significant (R-2=0.73). Due to already elevated PCB levels in non tilled soils with a maximum of 65 mug kg(-1) in the superficial layer of the silt loam control plot, any additional potential input, i.e. through the amendment with organic wastes, should therefore be avoided.