Monitoring and prioritisation of organic contaminants in sewage sludges using specific chemical analysis and predictive, non-analytical methods

Municipal sludge application on agricultural land (land utilization) is practised widely and accounts for between 30–40% of production in Canada and the UK. Land utilization is subject to public concerns over the potential for deleterious effects of organic contaminants on agricultural productivity and uptake into the foodchain. Consequently, reliable data on the concentrations of organic contaminants in sludge are required to assess risks associated with land use. A detailed monitoring survey has been carried out by WTC to determine the concentrations of a range of industrial organic contaminants in 11 Canadian sewage sludges and one sludge compost. Volatile, base-neutral and acid extractable contaminants seldom exceeded 5 mg kg−1 dry wt., organochlorine pesticides 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 ≤ 36 μg kg−1 dry wt. (median 6.7 μg kg−1 dry wt.) and mean toxic equivalents were ≤ 0.12 μg kg−1 dry wt. (median 0.02 μg 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 organic contaminants potentially present in sewage sludge may not be amenable to analysis by the target compound techniques widely used. Consequently, WRc have applied a non-analytical approach to assess which contaminants may occur in sewage sludges and persist in treated soils. Predictions of physicochemical properties using quantitive structure activity 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 identifying further contaminants which should be analyzed in sewage sludges and treated soils.