Chloride Enhances DNA Reactivity with Chlorine under Conditions Relevant to Water Treatment

Abstract

Free available chlorine (FAC) is widely used to inactivate viruses by oxidizing viral components, including genomes. It is commonly assumed that hypochlorous acid (HOCl) is the chlorinating agent responsible for virus inactivation; however, recent studies have underscored that minor constituents of FAC existing in equilibrium with HOCl, such as molecular chlorine (Cl 2 ), can influence FAC reactivity toward select organic compounds. This study measures the FAC reaction kinetics with dsDNA and ssDNA extracted from representative bacteriophages (T3 and ϕX174) in samples augmented with chloride. Herein, chloride enhances FAC reactivity toward dsDNA and, to a lesser extent, toward ssDNA, especially at pH < 7.5. The enhanced reactivity can be attributed to the formation of Cl 2 . Second-order rate constants were determined for reactions of ssDNA and dsDNA with HOCl and Cl 2 . DNA chlorination kinetics followed the reactivity-selectivity principle, where the more-reactive nucleophilic species (ssDNA, ∼100× more reactive than dsDNA) reacted less selectively with electrophilic FAC species. The addition of chloride was also shown to enhance the inactivation of bacteriophage T3 (dsDNA genome) by FAC but did not enhance the inactivation of bacteriophage ϕX174 (ssDNA genome). Overall, the results suggest that Cl 2 is an important chlorinating agent of nucleic acids and viruses.

Linear Mixed Model of Virus Disinfection by Free Chlorine to Harmonize Data Collected across Broad Environmental Conditions

“…The AIC best-subset model suggests that experimental conditions related to pH, chloride concentration, the interaction between pH and chloride, ΔpH 2 , and the interaction between temperature and pH contribute to chlorine inactivation of viruses, matching results of previous studies. ,,,,, Multiple terms related to [H+] were tested, and pH was selected as opposed to α HOCl (calculated using [H+] concentration). pH and α HOCl are highly colinear (Pearson correlation = 0.951), and the selection of pH over α HOCl could be due to the role OCl – plays in virus inactivation or the role that pH-sensitive functional groups in the virion play in chlorine disinfection (e.g., amino acid side chains).…”

Systematic analysis of the scientific-technological production on the use of the UV, H2O2, and/or Cl2 systems in the elimination of bacteria and associated antibiotic resistance genes

“…This reaction produces singlet oxygen (O 2 ∙ − ) and can increase the effectiveness of the disinfection and oxidation process (Al-Nu’airat et al 2021 ; Chen et al 2023 ; Kribeche et al 2022 ; Krystynik 2022 ; Lu et al 2022 ; Mora et al 2022 ; Salmerón et al 2021 ). On the other hand, at high Cl 2 concentrations, hydroxyl radicals can react with Cl 2 to produce hypochlorite (OCl − ) and hypochlorous acid (HClO), active chlorine species (ACS) that have a lower reduction potential than Cl 2 , but still contribute to the treatment or disinfection of water (Angyal et al 2023 ; Delgado-Vargas et al 2022 ; Martínez-Pachón et al 2021 ; Szczuka et al 2022 ).…”

Linear Mixed Model of Virus Disinfection by Chlorine to Harmonize Data Collected Across Broad Environmental Conditions

“…We then considered for inclusion additional features including buffer, purification level, α HOCl , year of publication, and high chloride. Finally, given previous research showing that the interaction between chloride and pH could be significant to virus inactivation, 39 we tested the interaction of high chloride and pH terms. We conducted residuals analysis and tested additional features and interactions suggested by patterns in the residuals, including ΔpH 2 and the interaction between temperature and Baltimore class (Figure S4).…”