Experimental conditions in GMR chronic inhalation studies of diesel exhaust

A chronic inhalation exposure study was initiated to study the potential health effects of diesel exhaust on laboratory animals. Test atmospheres of clean air (control) or freshly diluted diesel exhaust at nominal particulate concentrations of 250, 750 and 1500 micrograms m-3 were supplied to four large volume inhalation chambers in which individually housed Fischer 344 albino rats (Rattus norvegicus) and Hartley guinea pigs (Cavia porcellus) were exposed for 20 h per day, 51/2 days per week. The diesel aerosol concentration, chamber temperature and relative humidity were continually monitored and controlled to maintain the exposure dose levels and an environment of 22 +/- 2 degrees C and 50 +/- 20% relative humidity. Animals were randomly sampled from the chambers for physiological, biochemical and pathological studies throughout the exposure period. The study was continued without interruption for 24 months with the mean diesel particle mass concentrations within 6% of the target values. The standard deviation of the mass concentration measurements was approximately 30% of the mean.