Predicting the toxicity of oil-shale industry wastewater by its phenolic composition

The chemical composition and toxicity of five phenolic wastewater samples c ollected from the Kohtla-Jarve (Estonia) oil-shale industry region were ana lysed. 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 was tewater 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 theoretica l toxicities of these artificial mixtures were calculated by using the toxi cities of the individual phenolic constituents to photobacteria (the BioTox (TM) test) and were assumed to have an additive mode of action. From the Bi oTox data, the additive toxic effects of phenolic compounds in the artifici al mixtures were confirmed to be highly probable. The toxicities' of the wa stewater samples and their artificial phenolic analogues (mixtures) were st udied by using a battery of Toxkit microbiotests (Daphtoxkit F(TM) magna, T hamnotoxkit F(TM), Protoxkit F(TM) and Rotoxkit F(TM)) and three photobacte rial tests (Microtox(TM), BioTox(TM) and Vibrio fischeri 1500). The wastewa ters were classified as toxic (two samples), very toxic (two samples) and e xtremely toxic (one sample). Comparison of the test battery responses showe d that the industrial wastewaters were 2-28-fold more toxic than the respec tive artificial phenolic mixtures. The photobacterial tests proved to be th e most appropriate for screening purposes. This was the first attempt to us e 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 o nly 7-50% of their toxicity was shown to be due to phenolic compounds. It i s true, to a certain extent, that the majority of environmental samples are usually very complex and contain various types of pollutants. As even a fu ll chemical analysis (which is very expensive) can easily miss the constitu ent(s) with the greatest toxic effect(s), the use of toxicity tests in para llel to chemical analysis should be encouraged.