Crude influent sewages were collected from 30 English wastewater treatment works representing rural, urban and industrial catchments as part of a screening study to assess the significance of the concentrations of substances from the Water Framework Directive priority pollutants list in crude sewage. Composite samples were analysed for a range of determinands including metals and organic compounds. Of the determinands quantified, the pesticides were almost exclusively below the limit of detection. Most trace metals (with the exception of mercury) were detectable in all wastewaters, reflecting their ubiquitous nature. Organic determinands detected in the influent at μg/L levels included surfactants (linear alkylbenzene sulphonates and nonylphenol ethoxylates), phthalates (diethylhexyl phthalate), polynuclear hydrocarbons and solvents. Trace concentrations of trichlorobenzene, tributyltin and polychlorinated biphenyl 153 were detected in a limited number of works. Little correlation was observed between runoff or trade effluent inputs entering the works and determinand concentration (chromium being the only exception).

Tightening quality standards for European waters have seen a move towards enhanced wastewater treatment technologies such as granulated organic carbon treatment and ozonation.Although these technologies are likely to be successful in degrading certain micro-organic contaminants these may also destroy compounds which would otherwise complex and render metals significantly less toxic. This study examined the impact of enhanced tertiary treatment on the capacity of organic compounds within sewage effluents to complex copper and zinc. The data show that granulated organic carbon treatment removes a dissolved organic carbon (DOC) fraction that is unimportant to complexation such that no detrimental impact on complexation or metal bioavailability is likely to occur from this treatment type. High concentrations of ozone (>1mg O 3 /mg DOC) are, however, likely to impact the complexation capacity for copper although this is unlikely to be important at the concentrations of copper typically found in effluent discharges or in rivers. Ozone treatment did not affect zinc complexation capacity. The complexation profiles of the sewage effluents show these to contain a category of non-humic ligand that appears unaffected by tertiary treatment and which displays a high affinity for zinc, suggesting these may substantially reduce the bioavailability of zinc in effluent discharges. The implication is that traditional metal bioavailability assessment approaches such as the Biotic Ligand Model may overestimate zinc bioavailability in sewage effluents and effluent impacted waters.

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