Assessment of river health by combined microscale toxicity testing and chemical analysis

A battery of commercially available toxicity bioassays was applied to assess the quality status of two polluted coastal rivers in Israel: the Yarkon, polluted with treated domestic wastewater, and the Kishon, that at the time of sampling served as a conduit of industrial wastewaters. Samples from the latter displayed much higher toxicity; in both cases, sediment toxicity was considerably higher than that of the water. Highest sensitivities were exhibited by assays based on the micro-crustaceans Daphnia pulex and Thamnocephalus platyurus. A new index (total relative toxicity) is presented for river health assessment, which integrates and normalizes the toxicity of all identified pollutants. Calculated total relative toxicity values were in excellent agreement with the biological toxicity tests. We highlight the significance of toxicity bioassays as an essential component of any river monitoring program, both for the assessment of river health and for following the progress of remediation schemes. For this purpose, it is proposed that a river-specific panel of toxicity bioassays is selected, representing different trophic levels and taxonomic complexity.