Bromine (Br) and iodine (I) species such as bromide (Br-), iodide (I-), iodate (IO3-) and organic halogens (Org-X) have been identified as primary pre-cursors for the formation of toxic disinfection by-products (DBPs) in finished drinking waters. Prior work has elucidated on the oxidation pathways that convert benign Br- or I- to DBPs, assessed toxicity of regulated and non-regulated DBPs and developed predictive models for DBP formation. However, beyond an early 1990 study on bromide occurrence, we have few datasets on bromide or iodide occurrence in drinking water sources. While significant effort has characterized organic precursors in drinking water treatment plants (DWTP) source waters, limited information is available on inorganic DBP precursors, specifically Br and I species. Our study incorporates spatial and temporal data from over 700 newly collected samples from ~200 water utilities in USA during an 18 month period (2018-2020) to evaluate (a) current levels of Br and I species in drinking water sources (Figure); (b) spatial correlations with geography to potentially identify sources of Br and I; (c) temporal variability of Br and I species owing to seasonality changes in flow conditions and water quality parameters; and (d) association of co-occuring Br and I species. The GIS based statistical analyses suggest that Br exists primarily as Br- where I was present as iodide (I-), iodate (IO3-) and organic I. The median Br- concentration was 62 μg/L and 97 μg/L in surface water and groundwater respectively. The median Br/I ratio was 20 μg/μg and 17 μg/μg, but, I was detected in only 50% of the samples. Interestingly, groundwaters had inorganic forms of I i.e. I- and IO3-, whereas, organic I was the dominant specie of I in surface waters. The occurrence of I- was not correlated with Br- concentrations, however, Br- was strongly correlated with total iodine (I) concentrations. Furthermore, we will discuss the co-occurrence, sources and consequences of speciation of Br and I in drinking water sources for future Br-/I-DBP studies at DWTPs and implications for DBP regulations based on this nationwide occurrence study.

Co-occurrence of bromine and iodine species in drinking water sources of the USA

ACS Spring Meeting 2021

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