Free-Radical Chemistry of Disinfection Byproducts. 3. Degradation Mechanisms of Chloronitromethane, Bromonitromethane, and Dichloronitromethane

Abstract

Halonitromethanes (HNMs) are byproducts formed through ozonation and chlorine/ chloramine disinfection processes in drinking waters that contain dissolved organic matter and bromide ions. These species occur at low concentration but have been determined to have high cytotoxicity and mutagenicity and therefore may represent a human health hazard. In this study, we have investigated the chemistry involved in the mineralization of HNMs to nonhazardous inorganic products through the application of advanced oxidation and reduction processes. We have combined measured absolute reaction rate constants for the reactions of chloronitromethane, bromonitromethane, and dichloronitromethane with the hydroxyl radical and the hydrated electron with a kinetic computer model in an attempt to elucidate the reaction pathways of these HNMs. The results are compared to measurements of stable products resulting from steady-state (60)Co gamma-irradiations of the same compounds. The model predicted the decomposition of the parent compounds and ingrowth of chloride and bromide ions with excellent accuracy, but the prediction of the total nitrate ion concentration was slightly in error, reflecting the complexity of nitrogen oxide species reactions in irradiated solution.

Temperature dependence of hydroxyl radical reactions with chloramine species in aqueous solution

“…By taking this small side reaction into account, a final value of k 2 = (5.99 ± 0.12) × 10 8 M −1 s −1 is obtained, in very good agreement with the 22 ± 1 °C reported value (Poskrebyshey et al, 2003) of (5.1 ± 0.6) × 10 8 M −1 s −1 . Unfortunately, there is a paucity of reported rate constants for •OH with single chlorine-containing chemicals in aqueous solution; however, our measured room-temperature rate constant for NH 2 Cl is also comparable to the reaction of the hydroxyl radical with chloroethane, determined as 5.5 × 10 8 M −1 s −1 (Milosavljevic et al, 2005), but significantly higher than measured for chloroacetamide ((8.1 ± 0.3) × 10 7 M −1 s −1 , Xu et al, 2014) or chloronitromethane ((1.9 ± 0.3) × 10 8 M −1 s −1 , Mincher et al, 2010; Mezyk et al, 2006).…”