Effect of metalworking fluid mist exposure on cross-shift decrement in peak expiratory flow

Exposure to metalworking fluids (MWF) mist and cross-shift decrements in peak expiratory flow (PEF) were evaluated and their relationship was analyzed using several statistical methods. The objective of this study was to assess workers, exposure to MWF mineral mist and to find the MWF mist level for predicting cross-shift decrements in PEF. A total of 158 workers handling water-soluble MWF had MWF mist exposures with an arithmetic mean (AM) of 0.4 mg/m(3) (range: LOD-13.5 mg/m(3)), and 9.2% of workers (219) showed a cross-shift decline greater than 10% in PEF. MWF mist exposure and cross-shift decrements in PEF that were matched (n=113) were linearly significantly associated (R(2)=0.036, p=0.045) although the correlation was quite weak (r=0.189). We found a slight increase in cross-shift decrements in PEF with increased exposure to MWF aerosol mass concentration. The MWF mist exposure level was categorized into two or three groups by the cutoffs of either the National Institute for Occupational Safety and Health's Recommended Exposure Level (NIOSH REL: 0.5 mg/m(3)) or the American Conference of Governmental Industrial Hygienists Notice of Intended Change (ACGIH NIC: 0.2 mg/m(3)). The cross-shift decrement in PEF observed from workers exposed to > or =0.2 mg/m(3) was slightly higher than that of the exposure level of < or =0.2 mg/m(3) at p=0.207 while significant differences among categorized exposure groups (2 categories, <0.5 and > or =0.5 mg/m(3), or 3 categories, <0.2, 0.2-0.5 and > or =0.5 mg/m(3)) were not detected. In order to find out whether there is a specific level that allows us to predict cross-shift decrements in PEF, several statistical models were constructed. Logistic regression showed that the MWF concentration, whether treated as a continuous variable or a categorical variable, was not significantly associated with cross-shift decrements dichotomized by a cutoff of either 10% or 15% in PEF. We couldn't find evidence of a significant PEF decrement increase with increasing exposure category. Thus, we concluded that PEF decrements measured in workers exposed to MWF mist concentrations greater than either 0.2 mg/m(3) or 0.5 mg/m(3) was not significantly different from those found in workers exposed to lower MWF mist concentrations. Further study is needed to establish the level of MWF mineral mist predicting non-malignant respiratory health effects.