Organic precursors and formation mechanisms of iodinated phenolic disinfection byproducts in drinking water during chloramination.

Iodinated phenolic disinfection byproducts (DBPs) with high toxicity in drinking water are widely concerned for public health. However, the organic precursors and formation mechanisms of iodinated phenolic DBPs during drinking water chloramination have not been clarified previously. In this study, natural organic matter (NOM) was fractionated based on their hydrophilicity/hydrophobicity and molecular weight (MW), and then the formation of four categories of iodinated phenolic DBPs, including iodinated phenols, iodinated nitrophenols, iodinated hydroxybenzaldehydes and iodinated hydroxybenzoic acids, from different NOM fractions was examined. The results demonstrate that the NOM fractions of hydrophobic acids and weakly hydrophobic acids, as well as MW>100 kDa and 10 kDa<MW<100 kDa were the key fractions contributing to the formation of iodinated phenolic DBPs during chloramination. The four key fractions were further characterized and the results demonstrate that the organic precursors in these fractions might mainly comprise fulvic acid, lignin and tannic acid, which had high unsaturation degree and common structures of benzene rings, carboxyl groups, hydroxyl groups, carbonyl groups and ether groups. Thus, fulvic acid, gallic acid, digallic acid and guaiacylglycerol-β-guaiacyl ether were selected as the model organic precursors to investigate the formation mechanisms of iodinated phenolic DBPs. The results show that fulvic acid possessed the highest formation of iodinated phenolic DBPs, while iodinated phenols and iodinated hydroxybenzaldehydes were the abundant iodinated phenolic DBPs generated from fulvic acid during chloramination. Fulvic acid underwent a series of hydrolysis, substitution, haloform and oxidation reactions to form iodinated phenolic DBPs. The monochloramine dose, bromide/iodide concentration, pH and temperature significantly affected the formation of iodinated phenolic DBPs from fulvic acid during chloramination.