THE FORM AND BIOAVAILABILITY OF NONIONIC ORGANIC-CHEMICALS IN SEWAGE SLUDGE-AMENDED AGRICULTURAL SOILS

The application of sewage sludges to agricultural land may increase th e concentrations of many toxic organic chemicals in soils which could have adverse effects on wildlife and human health if these compounds e nter foodchains. Chlorobenzenes (CBs), polycyclic aromatic hydrocarbon s (PAHs), polychlorinated biphenyls (PCBs) and polychlorinated dibenzo -p-dioxins and furans (PCDD/Fs) are amongst those compounds currently receiving most attention. The 'form' in which these, and other organic chemicals, are present in soils and their potential to be lost by var ious processes including leaching, volatilisation and (bio)degradation is shown to be dependent on the physicochemical characteristics of th e soil and sewage sludge, environmental conditions and the properties of the chemicals themselves. The distinction is made between those com pounds that are labile, reversibly sorbed and irreversibly sorbed by s ewage sludge-amended soils. The implications of the form in which the chemicals are present in soil for their 'availability' to transfer fro m the soil to bacteria, fungi, earthworms, grazing livestock and food crops followed by the potential for further transfers, metabolism or b ioaccumulation are discussed. The importance of the timing and method of sewage sludge application to soil on 'form' and 'availability' are also considered.