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Total Organic Iodine Quantification and Occurrence in Drinking Water, and Toxicity Assessment of Iodinated Disinfection By-Products

The focus of this work has been placed is on iodinated DBPs (I-DBPs), measured using total organic iodine (TOI), a surrogate measure of iodinated organics. This is due to the growing toxicity literature that places I-DBPs among the most toxic of all DBPs. To measure TOI in water, a new method was developed. This method combines adsorption, combustion, and trapping of combustion products, with an offline inductively coupled plasma/mass spectrometer (ICP-MS) for iodide detection. Three factors were varied across two levels each in order to optimize the method. The chosen method used a sample pH of less than 1 prior to adsorption, a solution of 2% tetramethyl ammonium hydroxide (TMAH) in the trap solution, and a TMAH wash solution for the ICP-MS. The method was then used to quantify TOI in raw and treated waters in three water treatment plants in the Northeast US over a period of fifteen months across different treatment plants and in different locations within the same systems. The results showed that there was substantial inter-monthly variability in TOI where values cluster high or low for months at a time. There was no change in TOI concentration upon treatment, suggesting that the TOI components may have shifted between the raw and treated waters. The results of a multivariate regression showed that dissolved organic carbon, specific UV254 absorbance, combined residual chlorine, and pH were all correlated with TOI concentration. These parameters were then used to fit a predictive model for TOI formation in water. Expanding on the current literature on the toxicological profile of I-DBPs, the impact of six I-DBPs on healthy human colon epithelial cells, CCD 841 CoN, was tested. The rank order for cytotoxicity of the I-DBPs was found to be iodoacetic acid >iodoacetamide >bromoiodoacetamide >chloroiodoacetamide> bromoiodoacetic acid ≈ diiodoacetic acid. Iodoacetamide was 3.5 times more cytotoxic than bromoiodoacetamide, which in turn was 2.7 times more cytotoxic than chloroiodoacetamide. For both dihaloacids, the cytotoxicity was less than 1% of that of the monohaloacid. Apart from iodoacetic acid, the nitrogenous I-DBPs evaluated in this study proved to be more cytotoxic than the carbonaceous I-DBPs.