Prediction of an occupational exposure limit for a mixture on the basis of its components: application to metalworking fluids.

Using a previously developed mouse bioassay, a semisynthetic metalworking fluid (MWF "B") and its major components were evaluated. In mice MWF "B" and its components produced both sensory (S) and pulmonary (P) irritation. Using respiratory frequency (f) depression, concentration-response relationships were developed for each component as well as for MWF "B." From such relationships the concentration capable of evoking a 50% decrease in mean f was determined for each component and designated as RD50S if the decrease in f was due to sensory irritation, or RD50P if the decrease in f was due to pulmonary irritation. Based on RD50P values, the results indicated that the alkanolamides, potassium soap, sodium sulfonate, and triazine components were similar in irritation potency both to one another and to MWF "B." Through an examination of potency and fractional composition it was concluded that these five components largely contributed to the irritancy of MWF "B." From the RD50P values, occupational exposure limits that would protect workers from respiratory irritation were proposed for MWF "B" and each of its components. Using the approach of the American Conference of Governmental Industrial Hygienists for mixtures, an occupational exposure limit was calculated for MWF "B" employing the component data. The two limits for MWF "B" were similar to one another, suggesting that exposure limits for MWFs may be obtained through the evaluation of the fluids themselves or through evaluation of the components.