Wastewater toxicity screening of non-ionic surfactants by Toxalert ® and Microtox ® bioluminescence inhibition assays

Abstract

The toxic response of commonly used non-ionic surfactants with different bioluminescence inhibition assays (ToxAlert ®100 and Microtox ®) were established. The 50% effective concentration (EC50) values were determined for every standard substance using each assay, together with toxicity units (TU). A sigmoidal curve was fitted and the (EC50) was calculated. Chemical analysis and bioassays were used in conjunction to provide a determination of aquatic toxicity in wastewaters. This methodology was applied to real samples of influent and effluent wastewater treatment works in Spain and Portugal and also for untreated textile wastewater effluents. The protocol used in this paper involved different steps. First, the aquatic toxicity evaluation for every effluent was carried out using ToxAlert ®100. For every one, a sigmoidal curve was fitted, the (EC50) and the toxicity impact index (TII 50) were calculated. Second, the identification and quantification of polar organic cytotoxic substances and their contribution to the total toxicity was obtained, using sequential solid-phase extraction (SSPE) followed by liquid chromatography-mass spectrometry (LC-MS). The use of toxicity results (in terms of bioluminescence inhibition) like a screening parameter, is proposed. This procedure excludes the chromatographic analysis if the sample has less than the 20% inhibition. Overall, this procedure presented here helps to reduce the large number of samples and sub-samples that need to be processed in wastewater monitoring.