The bioassay based on the bioluminescence inhibition of Vibrio fischeri has been successfully applied to test municipal wastewater toxicity, in fact, the ISO 11348-3 standard was especially issued to prescribe the application of this test in wastewater toxicity assessment. However, this protocol cannot take into consideration virtual toxicity caused by turbidity or color of the sample tested. On the contrary, the kinetic version of the V. fischeri assay (ISO 21338:2010: Water quality-Kinetic determination of the inhibitory effects of sediment, other solids and colored samples on the light emission of Vibrio fischeri /kinetic luminescent bacteria test/) was developed to mitigate the drawbacks of the original protocol. Municipal wastewaters are often turbid/colored. Two versions of the V. fischeri bioluminescence inhibition assays were applied for municipal wastewater samples, before and after filtering. In most cases, the traditional version of the bioassay detected higher toxicity than the kinetic version, most possibly implying that reduced light emittance caused by solid particles and/or color also contributed to toxicity readings.

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Whole effluent toxicity is most often considered as a static parameter. However, toxicity might change as degradation processes, especially biodegradation goes by and intermediate products appear. These intermediates can even be more toxic than the original effluent was, posing higher risk to the ecosystem of the recipient water body. In our test series it was assessed how toxicity of a municipal wastewater sample changes during biodegradation taking into consideration different temperature regimes (10, 20 and 30 degrees C). Results proved our null hypothesis: after the high initial toxicity of the fresh effluent sample toxicity did show a further increase. Biodegradation resulted in toxicity reduction only after an approx. 2 week-period.

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