© 1986 Oxford University Press
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The Effect of an Unusual Workshift on Chemical Toxicity
I. Studies on the Exposure of Rats and Mice to Dichloromethane1
Department of Pharmacology and Toxicology, School of Pharmacy and Pharmacal Sciences Purdue University West Lafayette, Indiana 47907
The Effect of an Unusual Workshift on Chemical Toxicity. I. Studies on the Exposure of Rats and Mice to Dichloromethane. KIM, Y. C., AND CARLSON, G. P. (1986). Fundam. Appl. Toxicol. 6, 162–171. The 10- or 12-hr workday has become increasingly popular in industry. Current occupational exposure limits are designed to protect workers on the standard 8-hr/day workshift and are not intended for use for longer workshifts. Experiments were conducted to compare the effects of a 12-hr exposure schedule to those of an 8-hr schedule on the carboxyhemoglobin (COHb) formation resulting from dichioromethane (DCM) inhalation. Rats and mice were exposed to 200, 500, or 1000 ppm DCM for 8 hr/day for 5 days or 12 hr/day for 4 days. The effect of the unusual exposure schedule on COHb levels was not significant. The metabolic pathway for the formation of COHb appeared to be saturated even at the lowest concentration of DCM. To examine the possible increase in the retention of inhaled DCM in the longer exposure schedule, single exposures for 8 and 12 hr were compared. The peak blood DCM level was dependent upon the DCM exposure concentration, but the half-life was independent of the duration of exposure and the concentration of DCM. The half-life of COHb in blood was prolonged by increasing the DCM concentration, but was not affected by the exposure period. Pyrazole treatment decreased COHb level and increased blood DCM level in rats exposed to DCM. These results suggest that the exposure limit for a chemical with a short biological half-life and readily reversible toxic effect may not need to be adjusted for a longer workshift which is in agreement with some of the mathematical models based upon the pharmacokineties of a toxicant.