Co-Occurrence of Bromine and Iodine Species in US Drinking Water Sources That Can Impact Disinfection Byproduct Formation

Bromine and iodine species are precursors for forming disinfection byproducts in finished drinking waters. Our study incorporates spatial and temporal data to quantify concentrations of inorganic (bromide (Br^-), iodide (I^-), and iodate (IO₃^-)), organic, and total bromine (Br_T) and iodine (I_T) species from 286 drinking water sources and 7 wastewater effluents across the United States. Br^- ranged from <5-7800 μg/L (median of 62 μg/L in surface water (SW) and 95 μg/L in groundwater (GW)). I^- was detected in 41% of SW (1-72 μg/L, median = <1 μg/L) and 62% of GW (<1-250 μg/L, median = 3 μg/L) samples. The median Br^-/I^- ratio in SW and GW was 22 μg/μg and 16 μg/μg, respectively, in paired samples with detect Br^- and I^-. Br_T existed primarily as Br^-, while I_T was present as I^-, IO₃^-, and/or total organic iodine (TOI). Inorganic iodine species (I^- and IO₃^-) were predominant in GW samples, accounting for 60-100% of I_T; however, they contributed to only 20-50% of I_T in SW samples. The unknown fraction of I_T was attributed to TOI. In lakes, seasonal cycling of I-species was observed and was presumably due to algal productivity. Finally, Spearman Rank Correlation tests revealed a strong correlation between Br^- and I_T in SW (R_Br^-,IT = 0.83) following the log₁₀ (Br^-, μg/L) = 0.65 × log₁₀ (I_T, μg/L) - 0.17 relationship. Br^- and I^- in treated wastewater effluents (median Br^- = 234 μg/L, median I^- = 5 μg/L) were higher than drinking water sources.