Identification of toxic compounds in wastewater treatment plants during a field experiment

Chemical analysis and toxicity bioassays were used in conjunction to determine the toxic compounds present in wastewater. This combined methodology was applied to wastewater samples collected at two wastewater treatment plants (WWTP) from the area of Barcelona (Spain), during a field experiment carried out from 1-4 April 2000. The efficiency of the WWTP was evaluated by collecting and analyzing samples at various stages of the water treatment process. The samples corresponded to the raw influent, from first settlement—before biological treatment—and from the effluent.Two bioluminescence inhibition assays: ToxAlert^®10 and ToxAlert^®100 from Merck both based on the bioluminescence inhibition of Vibrio fischeri (marine bacterial specie) were used. ToxAlert^®10 is a portable device with no temperature control and uses freeze-dried bacterial reagent and ToxAlert^®100 uses liquid-dried bacterial reagent and the incubation takes place at controlled temperature. Both tests showed similar results.Besides the toxicity studies, the wastewater samples were characterized by various analytical protocols involving the use of solid phase extraction (SPE) followed by liquid chromatography-mass spectrometry (LC-MS). Phenols, non-ionic surfactants, linear alkyl benzene sulphonates, benzene and naphthalene sulphonates and micro-pollutants with high endocrine-disrupting effects like estradiol and ethynyl estradiol were identified at the WWTP.The toxic responses obtained for the samples collected at WWTP were defined by the 50% effective concentration (EC₅₀), the Toxicity Units (TU) and the toxicity impact index (TII₅₀). The toxic effect at the different steps of the WWTP was attributed to the compounds identified and quantified by LC-MS like transformation products of nonylphenol polyethoxylate such as nonylphenol and nonylphenol carboxylate.