Residual Toxicity of Iodinated Disinfection Byproducts in Boiled Drinking Water

Disinfection byproducts (DBPs) represent a persistent challenge to supply safe drinking water. While boiling drinking water has been confirmed to reduce human exposure risks to DBPs, the remaining risk, particularly waters with iodide, has been underestimated. Herein, we examined how volatilization and thermally accelerated transformations could shift the profiles of the priority DBPs in boiled water. We comprehensively evaluated the toxicity of samples before and after boiling, the results of which suggested that 40-70% of cytotoxicity and 59-89% of genotoxicity remain after boiling. The non-targeted analysis revealed that the phenolic iodinated DBPs (I-DBPs) accumulated and contributed significantly to the remaining total organic iodine. Specifically, the concentrations of 3,5-diiodosalicylic acid and 2,4,6-triiodophenol increased by 124.8 and 139.0% during boiling, respectively, which may be attributed to thermally accelerated reactions from large-molecule-weight precursors and low volatilization of these I-DBPs. In addition, continuous boiling, the addition of vitamin C, and baking soda were investigated to be effective in mitigating toxicity and phenolic I-DBPs resistant to boiling, with the degradation rates of I-DBPs ranging from 1.1% to 33.8%. Overall, we highlighted the occurrence and transformation of thermally stable DBPs during boiling, providing important insights for mitigating the residual risks in boiled drinking water.