Chlorination of natural waters containing organic matter can produce chloroform, bromodichloromethane, dibromochloromethane, and bromoform (collectively, trihalomethanes, THMs). THMs are monitored and regulated in municipal drinking water systems due to their potential health risks, which include bladder cancer and birth defects.  Chlorination of saltwater swimming pools or ballast waters in seafaring ships also generate THMs. High bromide levels in these waters promote the formation of brominating agents (e.g., HOBr) during chlorination, which may increase production of brominated THMs. Chloride, despite its common classification as a “spectator ion”, can contribute to increased rates of both chlorination and bromination by enhancing the formation of reactive halogenating agents such as Cl<sub>2</sub> and BrCl. The significance of this effect is not well established under saline conditions.The purpose of this investigation is to examine the effects of chloride ion concentration on THM formation at ionic strength and bromide concentrations comparable to seawater. Reactions are were conducted at pH 7 with fixed concentrations of bromide and an organic precursor (Suwannee River NOM extract or resorcinol). Chloride levels were varied while maintaining a constant ionic strength. Reactors spiked with free chlorine (as NaOCl) were held at 20.0 °C in a water bath and were sacrificed at fixed intervals. Free halogen residuals were quenched by the addition of excess 1,3,5-trimethoxybenzene. The quenched, aqueous solutions were extracted into methyl tert-butyl ether prior to analysis by gas chromatography coupled to a micro-electron capture detector.  Typically, the most abundant THM formed was bromoform, followed by dibromochloromethane, chloroform and dichlorobromomethane. High ionic strength promoted volatilization of THMs from the aqueous phase, reinforcing the need to perform reactions in the absence of headspace. Choice of organic precursor strongly influenced overall THM yields but varying the chloride concentration (at fixed ionic strength) did not appreciably influence THM yields or speciation from NOM or resorcinol. This suggests that changes in halogenating agent speciation (resulting from changes in chloride ion concentration) do not substantially affect THM production in these systems.

Quantification of trihalomethanes produced during chlorination of synthetic saline waters

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.