When herbicides and other agrochemicals are present in sources of drinking water, these chemicals can be transformed during water treatment processes, particularly via reactions with chemical disinfectants. For example, electron-rich moieties of agrochemicals can become chlorinated during water treatment with free chlorine. Such electron-rich sites can also undergo bromination when bromide-containing waters are treated with free chlorine. These halogenation reactions can also occur when agrochemical formulations are diluted prior to application with water containing a chlorine residual. The purpose of this study is to explore how solution chemistry (e.g., pH, [Cl–], [Br–], and chlorine dose) during water chlorination influences the competition between rates of chlorination and bromination at nucleophilic sites of selected agrochemicals and other model organic compounds. Particular attention is paid to the influence of commonly-overlooked aqueous halogenating agents (e.g., Cl2, Cl2O, BrCl, BrOCl, and Br2O) on chlorine/bromine branching ratios. Understanding how solution conditions influence selectivity toward chlorination versus bromination is important because brominated disinfection byproducts are often more toxic relative to their chlorinated counterparts. The applicability of our findings to other food-energy-water systems that are routinely disinfected with free chlorine (e.g., cooling water at power plants, agricultural produce, and wastewater) will also be discussed.

Halogenation of agrochemicals and related compounds in waters disinfected with free chlorine: Competition between rates of chlorination and bromination

255th National Meeting (2018)

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