Chlorine dioxide and sodium chlorite both are strong oxidizers. The primary toxic effect associated with compounds at high doses is methemoglobinemia, the oxidation of hemoglobin in red blood cells. Other effects have been reported, but these generally are associated with high doses or the evidence for the association is conflicting. In an experimental study of humans ingesting chlorine dioxide and chlorite in drinking water, no adverse effects were observed at doses as high as 24 mg/L and 5 mg/L, respectively (Lubbers et al. 1982). In addition, two epidemiological studies of populations exposed to water disinfected with chlorine dioxide did not demonstrate any hematological or teratogenic effects.

There is no currently available RfD for either chlorine dioxide or sodium chlorite. The Final Draft for the Drinking Water Criteria Document on Chlorine Dioxide, Chlorite, and Chlorate (USEPA 1994), is currently under review by a USEPA work group. The draft includes proposed RfDs for chlorine dioxide, 0.01 mg/kg/day, and chlorite, 0.003 mg/kg/day, which is equivalent to a dose of 0.004 mg/kg/day for sodium chlorite on a mass basis. The proposed RfD for chlorine dioxide was used in this assessment. However, for sodium chlorite a thorough subchronic study by Harrington et al. (I 995) was recently published and led to the derivation of an RfD of 0. I mg/kg/day.

Non-carcinogenic risk is assessed by USEPA based on the ratio of the daily dose of the compound to the RfD. We have estimated daily doses of chlorine dioxide and sodium chlorite to be 0. 00 12 and 0. I mg/kg/day, respectively, from the manufacturer's recommended use of ProFresh. We have included incidental ingestion while rinsing with ProFresh.

The daily doses for both compounds, chlorine dioxide and sodium chlorite, are at or below the RfD. Given the conservative nature of the risk assessment approach, the lack of effects reported in exposed humans, and the reduction of these compounds in the mouth during rinsing and swallowing the manufacturers recommended use of the product ProFresh by adults, including incidental ingestion, does not represent a risk to human health.