Toxicity of sediment-associated unresolved complex mixture and its impact on bioavailability of polycyclic aromatic hydrocarbons

► Sediment-associated unresolved complex mixtures (UCM) at environmentally relevant concentrations caused sub-lethal and lethal effects to benthic invertebrates. ► Toxicity of UCM was species-dependent. ► A low concentration of UCM increased the bioavailability of sediment-associated polycyclic aromatic hydrocarbons. ► High concentrations of UCM in sediment may have formed non-aqueous phase liquids and reduced PAH bioavailability.