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The toxicological hazards associated with disinfecting drinking water with either chlorine dioxide or chlorine are reviewed and compared. Adverse health effects shown in animal experiments as well as human poisoning incidents are reported. Toxicological effects, which are associated with the disinfectants themselves and the products formed when the disinfectants react with organic material present in water, are considered.

In separate subchronic toxicity studies, male and female Sprague–Dawley rats received various dosages of chlorine, monochloramine, or chlorine dioxide in their drinking water for 90 consecutive days. None of the disinfectants caused premature death at any of the concentrations used. The highest dose of chlorine tested (250 mg/L) was concluded to be a no observable adverse effect level. At 200 mg/L (the lowest observable adverse effect level), monochloramine produced decreased body and organ weights in both sexes and a small decrease in red blood cell count and serum calcium in males. Chlorine dioxide produced dosage‐related decreases in body and organ weight at concentrations as low as 25 mg/L, but its most significant toxic effect was the induction, at all concentrations, of nasal lesions.

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