Total organic halogen (TOX) in treated wastewaters: an optimized method and comparison with target analysis

Abstract

Wastewater effluents are complex mixtures that may potentially contain thousands of compounds that are not well removed from conventional wastewater treatment. There are more than 350 000 chemicals registered for production or use that can potentially end up in the environment. Quantification of micropollutants by target analysis has been extensively applied; however, these methods are often limited by the availability of analytical standards and resources. The total organic halogen (TOX) method is a comprehensive evaluation of the total halogen content in water including emerging halogenated contaminants and disinfection by-products. In this study, an analytical method was developed to simultaneously quantify TOX as total organic fluorine (TOF), total organic chlorine (TOCl), total organic bromine (TOBr), and total organic iodine (TOI). Halophenol recovery experiments were performed in secondary wastewater effluents for TOF, TOCl, TOBr, and TOI with recoveries between 61 and 105%. Also, nine halogenated contaminants were spiked into ultrapure water with recoveries between 19 and 107%. The TOX method was used to evaluate four secondary wastewater effluents prior to disinfection across 2 cities in Alberta, Canada. It was observed that TOF, TOCl, and TOBr ranged from 4.9–10.5 μg L⁻¹, 67.5–80.0 μg L⁻¹, and 5.0–9.0 μg L⁻¹, respectively whereas TOI was only detected in two samples at 1.8 and 6.1 μg L⁻¹. A sample was analyzed for 196 micropollutants (99 were halogenated) to characterize and identify TOX in wastewater for the first time. Target analysis with liquid chromatography tandem mass spectrometry only identified 1.5% of TOX which underlines the severe limitations of target analysis in wastewater samples. These results highlight the importance of the TOX method as an indicator of halogenated emerging contaminants in wastewater.