Study deviated from guidelines. "Deviations: Exposure chamber concentrations for the 2 and 20 mg/L exposures were not measured due to analytical difficulties and chamber concentrations for the 10 mg/L exposure did not remain within 25% of the target concentration. The average chamber concentration for the 10 mg/L exposure was significantly below the target concentration. Due to marked clinical signs of distress among the 20 mg/L animals, exposure of this group was suspended after approximately 1 hr."