|IDENTIFICATION AND USE: Chlorine dioxide is a yellowish-brown gas with unpleasant odor similar to chlorine and nitric acid. Its uses include bleaching cellulose, paper-pulp, flour, leather, fats and oils, textiles, and beeswax. It is also used for purification of water, taste and odor control of water, cleaning and detanning leather, in the manufacture of chloride salts, and as an oxidizing agent, bactericide, antiseptic and deodorizer. Chlorine dioxide was found to be highly effective against various microorganisms tested at very low concentrations in a minimum contact time of 30 to 60 seconds. HUMAN STUDIES: Potential symptoms of overexposure are irritation of eyes, nose, and throat, as well as coughing, wheezing, bronchitis, and pulmonary edema. Workers industrially exposed to low concentrations of the gas in air have been noted occasionally to suffer from irritation of the eyes and to see haloes about lights, but these effects have been minor compared to respiratory irritation. Bronchoscopy and biopsy revealed slight chronic bronchitis in 7 of 12 workers. Only two workers who had been exposed just prior to examination showed physical signs of respiratory effects. Workers acutely exposed to chlorine dioxide developed both reactive airways dysfunction syndrome (RADS), a form of occupational asthma, and an upper airways reactive disorder that was called reactive upper airways disfunction syndrome (RUDS). A positive association was found between exposure of the mother to chlorine dioxide-treated water during pregnancy and prematurity of the newborn. Children born of mothers who drank disinfected water treated with either chlorine dioxide or hypochlorite were noted to have an increased incidence of small cranial circumference, small body length, and neonatal jaundice. Chlorine dioxide was found to be weakly genotoxic in human leukocytes. ANIMAL STUDIES: Chlorine dioxide is very toxic by inhalation in rats. Clinical signs of toxicity included respiratory distress. Macroscopically, pulmonary edema and emphysema were seen in all groups of chlorine dioxide-exposed animals, with the incidence increasing in a dose-related manner. Chlorine dioxide is toxic when administered in solution by the oral route to rats. Two males and two females receiving 80 mg chlorine dioxide/kg body weight died, and a further two males at 40 mg/kg body weight also died within 48 hr of administration. There were no deaths at 20 mg/kg body weight. A developmental study in rats did not demonstrate any impairment of reproductive function, and there were no signs of developmental effects among rats receiving up to 10 mg aqueous chlorine dioxide/kg body weight per day. A negative result was obtained for micronucleus formation, and there were no increases in the number of structural or numerical chromosome aberrations in mice treated with chlorine dioxide. However, chlorine dioxide increased water genotoxicity in assays with E. coli and with S. cerevisiae. In Chinese hamster ovary cells at 2.5-15 ug/mL, there was a marked dose-related, statistically significant increase in the number of metaphases with chromosome aberrations. In the presence of metabolic activation, cell toxicity and an absence of mitotic cells were observed at 75 ug/mL. An increase in the number of metaphases with chromosome aberrations was noted at 50 ug/mL. ECOTOXICITY STUDIES: Developmental abnormalities in the sea urchin were evident at exposure to the chlorine dioxide concentration 250 mg/L. Compared with the control, pre-hatch malformations were 6% higher; retarded development, 2%; post-hatch malformations, 20%; skeletal malformations, 21%; and gut malformations, 11%. Survival of larval kelp bass was not significantly affected by chlorine dioxide. In Fathead minnows (Pimephales promelas) chlorine dioxide exposure produced dose-dependent gill pathology including epithelial lifting, hypertrophy, hyperplasia, lamellar fusion, and necrosis. Complete recovery, even in fish with severe hypertrophy and lamellar fusion, was achieved within 4 days. Chlorine dioxide concentrations ranging from 0.1 to 0.5 mg/L induced micronuclei in Vicia faba at acid pH, while 1-2 mg/L chlorine dioxide gave positive responses at neutral pH. Chlorine dioxide produced positive responses in the Tradescantia micronucleus test.