Comparison of different biological methods for the assessment of ecotoxicological risks

To test the effects of heavy metals in river water, we compared the sensitivity of seven different biological test methods, using bacteria (Vibrio fischeri), human FL cells, protozoans (Paramecium spp.), nematodes (Rhabditis oxycerca), aquatic plants (Lemna minor), and fishes (Leuciscus idus melanotus). As test substance we used a representative mixture of 3.0 microg/l As, 2.5 microg/l Pb, 0.8 microg/l Cd, 1.7 microg/l Cr, 3.9 microg/l Cu, 6.7 microg/l Ni, 0.4 microg/l Hg, and 23.0 microg/l Zn, imitating the detectable heavy metal contamination of the Odra estuary (NE Germany/NW Poland). This mixture was defined as normal concentration (NC). Most sensitive was the test with L. minor (exposure time 10 d). The plants already showed phytotoxic effects at the heavy metal concentration found in the Odra estuary. Test systems with human cells, protozoans, and nematodes (exposure time 1-7 d) reacted at concentrations 85-100 times above the NC. Fish toxicity (exposure time 2 d) occurred from 130-fold concentration upwards. In contrast, the standard test carried out with luminescent bacteria (exposure time 30 min) was affected only at > 1000-fold concentrations. This test is therefore not suitable as an early warning system to detect ecological risks. Even the NC of heavy metals measured in the Odra estuary inhibits cells and the growth of aquatic plants. Of the single heavy metals tested, copper produced the strongest effects. Therefore, the reduction of heavy metal emissions, especially of copper-which can amplify the toxicity of other heavy metals-should be a task of highest priority.