Endocrine Toxicity of Drinking Water Disinfectants. I. In Vivo Dehalogenation and Clearance of Iodinated Nutrients

Ingestion of aqueous chlorine-based disinfectants has been shown earlier to cause decreased serum thyroxine levels and increased 131-I thyroid uptake in nonhuman primates. Disinfectants also were shown to immobilize iodine on gastric mucosa and cause covalent binding of dietary iodide to gastrointestinal contents in laboratory rodents. It has been demonstrated that nutrients in the presence of chlorine oxides, under conditions simulating the alimentary tract, effectively organify I- in vitro. A logical consequence of these is that traces of iodinated organics are absorbed after ingestion of drinking water disinfectants. Since over 100 million consumers receive a daily dose of about 0.4 mM of free chlorine, the pharmacotoxicology of such modified nutrient molecules is of public health interest. Therefore, we examined the in vivo deiodination of randomly in vitro iodinated organic mixtures prepared from different nutrients. Using adult female rats, we determined the 24-hour thyroid uptake of 125-I liberated from nutrients administered by gavage, relative to simultaneously ip-injected I131-. Also, 24-hour fecal and urinary clearances of the iodinated organics as well as tissue distributions were determined. The results showed that although various iodinated nutrient classes widely differed in their in vivo fate, most were dehalogenated effectively. Thus, their iodine content was returned as inorganic I- for thyroid uptake. It was also shown that tissue (blood, liver, intestinal, adipose, and muscle) distribution of the two isotopes did not differ significantly, suggesting that at 24 hours, the originally organic iodine existed in the tissues as inorganic I-. It is likely that oral exposure to chlorine-based disinfectants did not disturb the bioavailability of I-, and any thyroid effects caused were due to mechanisms other than I- deficiency.