Cytotoxicity of settling particulate matter and sediments of the Neckar River (Germany) during a winter flood

To investigate the cytotoxic and genotoxic potentials of settling particula te matter (SPM) carried by the Neckar River, a well-studied model for a loc k-regulated river in central Europe, during a hood, acute cytotoxicity war investigated using the fibroblast-like fish cell line RTG-2 with the neutra l red retention, the succinic acid dehydrogenase (MTT), and the lactatedehy drogenase (LDH) release assays as well as microscopic inspection as endpoin ts. Genotoxicity of water, pore water, sediments, and SPM were assessed usi ng the Ames test. Different extraction methods (Soxhlet extraction with sol vents of variable polarity as well as a fluid/fluid extraction according to pH) in addition to a supplementation of biotests with S9 fractions from th e liver of beta-naphthoflavone/phenobarbital-induced rats allowed a further characterization of the biological damage. Both sediments and SPM extracts caused cytotoxic effects in RTG-2 cells. Cytotoxicity was found to increas e significantly with polarity of extracting solvents (NR50 = effective conc entration for 50% cell death in the neutral red test: 80 [65], 100 [70], 18 0 [220], and 225 [270] mg/ml for ethanol, acetone, dichloromethane, and n-h exane extracts, respectively, if measured with [without] S9 supplementation ). Following extraction according to pH, cytotoxicity could be attributed m ainly to neutral substances (NR50: 80 and 218 mg dry SPM/ml test medium for the neutral and the acid fractions, respectively), whereas the slightly ac id and basic fractions already showed little or no cytotoxicity. Samples ta ken during the period of Hood rise showed the highest cytotoxic activities. Cytotoxicity was significantly enhanced by the addition of S9 preparations . In contrast, no genotoxic activity was found in native surface waters, po re waters, and SPM.