Optimized methods for adsorbable organic halides (AOX) and halogen‑specific speciation for tracking disinfection...

Disinfection by-products (DBPs) formed during drinking water treatment pose a significant public health risk due to their ubiquity and documented toxicity, including carcinogenic, genotoxic, and developmental effects. While European regulations currently limit monitoring to trihalomethanes (THMs) and haloacetic acids (HAAs), they overlook highly toxic brominated and iodinated DBPs, which exhibit greater toxicity than their chlorinated counterparts. To address this gap, adsorbable organic halides (AOX) have emerged as a promising bulk parameter, integrating both the total concentration and potential toxicity of halogenated DBPs. Halogen-specific AOX speciation (AOCl, AOBr, AOI) and the distinction between purgeable (POX) and non-purgeable organic halides (NPOX) further refine risk assessments, as these fractions differ in toxicity and exposure pathways. This study optimizes and validates analytical methods for AOX, NPOX, and halogen-specific AOX, focusing on critical parameters-including adsorption efficiency, volatilization, matrix interferences, and ion chromatography conditions-to enhance method robustness. The optimized protocol achieved limits of quantification (LOQs) of 25 µg Cl·L⁻¹ for AOX/NPOX and 0.9 and 2.8 µg Cl·L⁻¹ for AOBr/AOI, respectively. The optimized method was successfully applied to drinking water samples collected from four distribution networks across three regions in France, with multiple sampling points along each network. AOX concentrations ranged from < 25 to 200 µg Cl·L⁻¹. NPOX represented 50-90% of AOX. AOCl dominated at one site (> 90%), whereas others exhibited substantial AOBr (8-77%) and minor AOI (2-10%, rarely detected). Regulated THMs and HAAs accounted for only 0-54% of total AOX (≤ 20% at two sites), indicating that most organohalogens remain unidentified. These findings highlight the prevalence of unmonitored organohalogens and underscore the need for broader DBP surveillance to improve water safety assessments.