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Purpose The presented study investigated on contamination of suspended particulate matter (SPM) in rivers that was sampled long-term and with higher frequency during a flood event at the river Rhine. It was conducted to determine in vitro biological effects as well as to identify and quantify compound classes and effective contaminants. Research was part of investigation on hazards of contaminants bound to SPM to inundated sites and retention areas that are inundated during flood events. Material and methods SPM was sampled in 2006 and more frequently in a flood event (August, 2007) at the river Rhine barrage of Iffezheim, Germany. SPM was GC-MS analyzed for hexachlorobenzene (HCB), several polychlorinated biphenyls (PCBs) as well as for polycyclic aromatic hydrocarbons (PAHs). Flood samples were fractionated applying a recently developed automated fractionation method to receive further insight into contaminant loads in flood SPM. Impacts on biological scale were assessed using in vitro biotests for xenometabolic 7-ethoxyresorufino-deethylase (EROD) assay as well as for mutagenic activity (Ames fluctuation assay). EROD induction was calculated as biological equivalent concentrations (bioTEQs) and mutagenic potentials were shown as NOECs and maximum induction factors. Results and discussion Chemical analysis gave low concentrations of PCBs (2006 and2007) and HCB (2006). HCB concentrations increased during the flood in 2007 (maximum, 110 µg/kg SPM). Concentrations of PCBs were only initially elevated in the flood (maximum, 67 µg/kg SPM). EROD induction bio-TEQs ranged from 1,160 to 6,640 pg/g SPM in 2006 and showed maximum bio-TEQ at the peak discharge in 2007. There was no mutagenic activity with SPM of both years. Fractionation indicated highest EROD induction in PAH fractions with prioritized (EPA-) PAHs contributing to less than 1% to the fractions total bio-TEQ but also fractions containing more polar-topolar substances were shown to contribute minor. FurtherResponsible editor: