Long-Term Continuous Exposure to Sulfur Dioxide in Cynomolgus Monkeys

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Abstract
Cynomolgus monkeys were exposed to sulfur dioxide while a control group was exposed to filtered air. The exposure was for 24 hours a day, seven days a week, for 78 weeks. Frequent measurements were made to evaluate mechanical properties of the lung, distribution of pulmonary ventilation, diffusing capacity of the lung, and arterial blood oxygen tension. Hematological and clinical biochemical determinations were conducted. Microscopic evaluation of organs and tissues was conducted at termination of the exposure of the animals. No deleterious effect could be attributed to SO2 exposure at concentrations of 0.14 to 1.28 ppm. Following 30 weeks of exposure to 4.69 ppm, an overexposure occurred in this group. This was followed by deterioration in pulmonary function which persisted during the following 48 weeks of observation, and alterations in pulmonary tissues were observed upon microscopic examination.