Toxicity assessment of wastewaters, river waters, and sediments in Austria using cost-effective microbiotests

The toxicity and chemical quality of surface water and sediment in the River Traun in Austria were studied because of recurrent fish mortality in some alpine rivers over the last few years. The analyses were carried out on samples collected during winter and summer upstream and downstream of two municipal wastewater treatment plants (WWTPs) and on effluents taken at the points of discharge of these two plants. Toxicity tests were performed on 20 samples of surface water, effluent, and sediment pore water. The test battery was composed of microbiotests with protozoans (Protoxkit F), microalgae (Algaltoxkit F), crustaceans (Daphtoxkit F magna and Thamnotoxkit F), and a higher plant (seed germination and root elongation assay on cress). Direct contact tests were performed on whole sediment with crustaceans (Ostracodtoxkit F). The physical-chemical characteristics of the surface water, effluent, and sediment pore water samples analyzed were conductivity, total hardness, pH, O(2), BOD(5), TOC, DOC, AOX, NH(4), NH(3), NO(2), PO(4)--P, Cd, Pb, Cu, and Zn. The toxicity data were expressed as percentage mortality or percentage inhibition, depending on the effect criterion of the respective assay. None of the water samples collected upstream and downstream of the WWTPs showed any significant (short-term) toxicity in either winter or in summer, but the effluents of the first municipal wastewater treatment plant were toxic to some of the test biota. All the sediment pore water samples induced serious inhibition of root growth of cress, and several pore waters were toxic to other test biota as well, particularly at the outlets of the WWTPs. The toxic character of some sediments was confirmed by direct contact tests with the ostracod crustacean. The chemical analyses did not reveal particularly high concentrations of any chemical that is very toxic. As a result no direct causal relationship could be established between the detected toxic effects and the chemical composition of the surface waters or sediment pore waters. The outcome of this preliminary study again highlights the need to complement chemical analyses with toxicity tests to determine the toxic hazard to aquatic environments that may be threatened by contamination. Furthermore, the investigations also confirmed the need to apply a battery of tests for an ecologically meaningful evaluation of the hazards of waters, sediments, and wastewaters. Finally, the results of the 360 bioassays performed show that culture-independent microbiotests are practical and reliable tools for low-cost toxicity monitoring of aquatic environments.