Comprehensive mass flow analysis of Swedish sludge contaminants

A screening of metals, persistent organic pollutants, pharmaceuticals and personal care products (PPCPs), and other organic contaminants in sludge from seven Swedish sewage treatment plants (STPs) was performed in this study. This extensive screening provides information on mass flows of 282 compounds used in the Swedish society to sewage sludge. It reveals constant relative contaminant concentrations (ng mg kg−1 d.w.), except for some pesticides and perfluorinated compounds, indicating that these originate from broad usage and diffuse dispersion rather than (industrial) point sources. There was a five order of magnitude difference in the sum concentrations of the most and least abundant species (metals and polychlorinated dibenzo-p-dioxins and -furans, respectively). Lower total concentrations were found in sludge from STPs processing primarily food industry or household sewage. Proportions of the amounts used (in Sweden) found in sludge were lower for compounds that are present in consumer goods or are diffusely dispersed into the environment (0.01-1% recovered in sludge) than for compounds used as detergents or PPCPs (17–63%). In some cases, the recovery seemed to be affected by evaporation (e.g. octamethylcyclotetrasiloxane) or biotransformation (e.g. adipates) losses, while polychlorinated alkanes and brominated diphenyl ethers were recovered to disproportionately high degree (ca. 4%); likely due to incomplete statistics for imported goods.

► We have performed an extensive screening of sewage sludge contaminants.
► Overall levels and distribution patterns of the contaminants were quite similar between the sewage treatment plants (STPs).
► Levels of sludge contaminants seem to be independent on location, size and treatment technique of the plants.
► Types of human activities connected to STPs, generally, did not affect the levels of sludge contaminants.