MONITORING AND PRIORITIZATION OF ORGANIC CONTAMINANTS IN SEWAGE SLUDGES USING SPECIFIC CHEMICAL-ANALYSIS AND PREDICTIVE, NON-ANALYTICAL METHODS

Municipal sludge application on agricultural land (land utilization) i s practised widely and accounts for between 30-40% of production in Ca nada and the UK. Land utilization is subject to public concerns over t he potential for deleterious effects of organic contaminants on agricu ltural productivity and uptake into the foodchain. Consequently, relia ble data on the concentrations of organic contaminants in sludge are r equired to assess risks associated with land use. A detailed monitorin g survey has been carried out by WTC to determine the concentrations o f a range of industrial organic contaminants in 11 Canadian sewage slu dges and one sludge compost. Volatile, base-neutral and acid extractab le contaminants seldom exceeded 5 mg kg(-1) dry wt., organochlorine pe sticides and polychlorinated biphenyls did not exceed 1 mg kg(-1) dry wt, and toxaphene and N-nitrosodimethylamine were not detected in the materials analyzed. Mean total PCDD and PCDF concentrations were less than or equal to 36 mu g kg-l dry wt. (median 6.7 mu g kg dry wt.) and mean toxic equivalents were less than or equal to 0.12 mu g kg(-1) dr y wt. (median 0.02 mu g kg(-1) dry wt.). It was concluded that in many Canadian sludges the aforementioned organic contaminants represent no significant risk to agriculture and the environment. However, other o rganic contaminants potentially present in sewage sludge may not be am enable to analysis by the target compound techniques widely used. Cons equently, WRc have applied a non-analytical approach to assess which c ontaminants may occur in sewage sludges and persist in treated soils. Predictions of physicochemical properties using quantitive structure a ctivity relationships (QSARs) have been used to aid the screening and prioritisation of a range of high production volume chemicals (HPVCs) that may enter sewage treatment works. Analytical surveys for organic residues are expensive and this type of approach may assist in identif ying further contaminants which should be analyzed in sewage sludges a nd treated soils.