Identification of polar toxicants in industrial wastewaters using toxicity-based fractionation with liquid chromatography/mass spectrometry.

Abstract

An efficient and novel method for the identification of toxic compounds in industrial wastewater was developed. In the first step, the samples collected were tested for toxicity using the recently developed ToxAlert 10 system based upon luminescence inhibition of freeze-dried Vibrio fischeri. In the second step, sequential solid-phase extraction (SSPE) and liquid chromatography/mass spectrometry (LC/MS) for compound identification were employed to isolate and identify compounds in the waters. Average recoveries ranging from 72 to 95% were obtained using the SSPE methodology for ubiquitous analytes such as poly(ethylene glycol)s, nonylphenol and alcohol polyethoxylates, phenols, linear alkylbenzenesulfonates, and benzene- and naphthalenesulfonates. In the third step, all the extracts obtained after SSPE followed by LC/MS identification were tested again with the ToxAlert system. The procedure was applied to influent and effluent samples of a sewage treatment plant (STP) and to a raw tannery effluent that constitutes the main type of influent in the receiving waters of the STP. This method has shown that, despite the complexity of the untreated tannery wastewaters with an average total organic carbon (TOC) value of 1960 mg of C/L, the biological treatment of the STP eliminates compounds that inhibit luminiscence of V. fischeri. In the final step, the chemical toxicity of the tentatively identified chemicals was tested to identify the toxicants in the waters. Comparison of the toxicities of the sample, the extracts, and individual components has shown that diverse classes of pollutants were responsible for toxicity, as all fractions of toxic samples gave significant bioluminescence inhibition values. Toxicity of the two intermediate-polarity SSPE fractions was attributed to alcohol ethoxylates, nonylphenol ethoxylates, bis(2-ethylhexyl)phthalate, and linear alkylbenzenesulfonates. In the most nonpolar and most polar fractions, identification of the compounds responsible for toxicity was unclear. By the toxicity-based fractionation, followed by LC/MS methodology, it was feasible to identify between 1.4 and 7.5% of the TOC, thus expanding the number of toxicants identified in these complex wastewaters as compared to those identified by conventional gas chromatography/mass spectrometric (GC/MS) methods. When artificial water samples were reconstituted using similar concentrations of the chemicals detected in the wastewaters, nonsynergetic toxicity effects were observed for all analytes with the exception of 2,6-naphthalenedisulfonate (2,6-NPS), which promoted the bioluminescence inhibition. The toxicity-directed identification was successful for the STP's samples and showed 1400 times higher toxicity for the raw tannery wastewaters as compared to the mixed industrial and domestic wastewaters by applying the Weibull model.