The effect of an unusual workshift on chemical toxicity: II. Studies on the exposure of rats to aniline

Abstract

Increasing numbers of workers in industry are working a novel or unusual 12-hr workshift in which the exposure time is longer and the recovery period is shorter than for a standard 8-hr workshift. Experiments were conducted to examine the effects of altering the exposure schedule of rats from 8 hr/day for 5 days to 12 hr/day for 4 days on the toxicity resulting from the inhalation of aniline at 10, 30, 50, and 150 ppm. When compared to the first day, methemoglobin (MetHb) levels, measured prior to and following the exposure, increased with the days of exposure at 50 ppm aniline. At 150 ppm aniline, the MetHb level determined prior to exposure to aniline increased with the days of exposure whereas the postexposure MetHb levels appeared to plateau after the second exposure. The MetHb levels determined prior to exposure were significantly different between the two groups at 50 or 150 ppm aniline whereas the postexposure MetHb levels were not. A residual MetHb level higher than the nonexposed control was observed in the 12 hr/day exposure group after a 3-day recovery period. There was an aniline concentration-dependent decrease in the hematocrit level when determined 1 week after the exposure started. Following a single exposure for 8 or 12 hr to 100 ppm aniline there was no difference in the maximum MetHb level, the peak aniline level in blood and fat, or the rate of aniline elimination from fat and blood. Repeated exposures to 100 ppm for 3 days did not produce a significant difference in aniline level in blood or fat between the 8 and 12 hr/day exposure groups immediately following the last exposure. However, the aniline level in blood was significantly higher in the 12 hr/day exposure group when determined on the morning following the last exposure. These results suggest that the residual burden resulting from previous exposures should be considered when the exposure limits are modified for longer workshifts in man.