Anne Kahru, Lee Põllumaa, Rain Reiman and Annely Rätsep

The chemical composition and toxicity of five phenolic wastewater samples collected from the Kohtla-Järve (Estonia) oil-shale industry region were analysed. The total phenolic contents (HPLC data) of these samples ranged from 0.7mg/l to 195mg/l. A total of 11 phenolic compounds were found in the wastewater samples, the most abundant being phenol (up to 84mg/l) and p-cresol (up to 74mg/l). Artificial phenolic mixtures were also composed, to mimic the content of phenolic compounds in the wastewater samples. The theoretical toxicities of these artificial mixtures were calculated by using the toxicities of the individual phenolic constituents to photobacteria (the BioToxTM test) and were assumed to have an additive mode of action. From the BioTox data, the additive toxic effects of phenolic compounds in the artificial mixtures were confirmed to be highly probable. The toxicities of the wastewater samples and their artificial phenolic analogues (mixtures) were studied by using a battery of Toxkit microbiotests (Daphtoxkit FTM magna, Thamnotoxkit FTM, Protoxkit FTM and Rotoxkit FTM) and three photobacterial tests (MicrotoxTM, BioToxTM and Vibrio fischeri 1500). The wastewaters were classified as toxic (two samples), very toxic (two samples) and extremely toxic (one sample). Comparison of the test battery responses showed that the industrial wastewaters were 2–28-fold more toxic than the respective artificial phenolic mixtures. The photobacterial tests proved to be the most appropriate for screening purposes. This was the first attempt to use a test battery approach in the toxicity testing of Estonian wastewaters. The study showed that the toxicity of oil-shale industry wastewaters could not be predicted solely on the basis of their phenolic composition, since only 7–50% of their toxicity was shown to be due to phenolic compounds. It is true, to a certain extent, that the majority of environmental samples are usually very complex and contain various types of pollutants. As even a full chemical analysis (which is very expensive) can easily miss the constituent(s) with the greatest toxic effect(s), the use of toxicity tests in parallel to chemical analysis should be encouraged.
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