Household cooking with seaweed salts and chloraminated tap water produce harmful iodinated disinfection by-products

Abstract

• Dominate iodine species of seaweed salts are iodide and organic iodine rather than iodate. • Cooking with seaweed salt and chloraminated water produced I-DBPs with hundreds of μg/L level. • Effects of temperature, time, chloramine dose, and salt dose on I-DBP formation were examined. • Cooking with seaweed salts enhanced the toxicity of tap water by 4.6 ∼ 8.7 times on the basis of EC 50 . • The potential risks of I-DBPs generated from cooking with seaweed salts should be spotlighted. Among the harmful halogenated disinfection by-products (DBPs) produced from water disinfection, iodinated DBPs (I-DBPs) are of the highest toxicity. Here we reported for the first time that daily household cooking using seaweed salts and tap water with chloramine residual could produce high concentrations of I-DBPs. At a typical household cooking setting (1-hr heating at 80 °C), the reactions of chloramines (1.0 mg/L as Cl 2 ) with 10 g/L seaweed salt in ultrapure water generated 96.8 ± 3.2 μg/L of iodo-containing trihalomethanes (I-THMs) and 385.3 ± 10.9 μg/L of total organic iodine (TOI). The yields are 1 ∼ 3 orders of magnitude greater than their typical occurrence levels in drinking water. At the unintended scenario, chloramines reacted with iodine and trace dissolved organic matter, both of which derived from seaweed salts containing iodide and organic iodine species. When chloraminated tap water was used at the identical conditions, aliphatic I-DBPs (i.e. I-THMs and iodo-containing haloacetic acids) significantly increased up to 163.5 ± 3.9 μg/L as a result of more natural organic matter, which could serve as DBP precursors, present in the tap water. Speciation and concentrations of different I-DBPs generated relied heavily on temperature, heating duration, chloramine concentration, and salt dose. Following a simulated household cooking in the presence of seaweed salts, the toxicity of tap water to luminescent bacteria ( Vibrio qinghaiensis sp.-Q67) increased by 4.6 ∼ 8.7 times on the basis of EC 50 . These findings spotlight the potential risks of I-DBPs generated from daily household cooking with seaweed salts, because salt consumption contributes to more than half of daily iodine intake.