Influence of halides on the formation of cytotoxicity and adsorbable organic halogen in peroxymonosulfate disinfection process

Abstract

Peroxymonosulfate (PMS) is a promising disinfectant; however, the formation of toxic byproducts during its application in water disinfection has raised concerns. This study investigates the influence of halides (Cl⁻, Br⁻, I⁻) on cytotoxicity and adsorbable organic halogen (AOX) formation during PMS disinfection, aiming to clarify the associated toxicity risks in PMS-based water treatment processes. Three secondary effluent (SE) samples and Suwannee River natural organic matter (SRNOM) solutions were used to evaluate cytotoxicity. Results showed that PMS disinfection significantly increased cytotoxicity across all SE samples, with higher halide concentrations and PMS dosages further exacerbating this effect. The order of cytotoxicity induced by different halides was I⁻ > Br⁻ > Cl⁻: at 200 μg/L I⁻, 2 mg/L Br⁻, and 200 mg/L Cl⁻, the cytotoxicity increments (in mg-phenol/L) ranged from 6.71 to 6.76 for SRNOM and 4.01–5.90 for SE with I⁻ and Br⁻, respectively, compared to 0.88–1.48 for Cl⁻. AOX formation was positively correlated with both PMS dosage and halide levels, with adsorbable organic iodine (AOI) and adsorbable organic bromine (AOBr) contributing more significantly than adsorbable organic chlorine (AOCl). Regression analysis confirmed a strong positive correlation between cytotoxicity and AOX concentrations (p < 0.05), particularly for AOI, indicating that highly toxic iodinated and brominated disinfection byproducts (DBPs) are key contributors to the observed increase in toxicity. This study highlights that halides, especially I⁻ and Br⁻, enhance toxicity risks during PMS disinfection by promoting the formation of toxic halogenated DBPs, thereby providing critical insights for evaluating the safety of PMS applications in water treatment.