Determinants of exposure to metalworking fluid aerosols: a literature review and analysis of reported measurements.

An extensive literature review of published metalworking fluid (MWF) aerosol measurement data was conducted to identify the major determinants that may affect exposure to aerosol fractions (total or inhalable, thoracic and respirable) and mass median diameters (MMDs). The identification of determinants was conducted through published studies and analysis of published measurement levels. For the latter, weighted arithmetic means (WAMs) by number of measurements were calculated and compared using analysis of variance and t-tests. The literature review found that the major factors affecting aerosol exposure levels were, primarily, decade, type of industry, operation and fluid and engineering control measures. Our analysis of total aerosol levels found a significant decline in measured levels from an average of 5.36 mg m(-3) prior to the 1970s and 2.52 mg m(-3) in the 1970s to 1.21 mg m(-3) in the 1980s, 0.50 mg m(-3) in the 1990s and 0.55 mg m(-3) in the 2000s. Significant declines from the 1990s to the 2000s also were found in thoracic fraction levels (0.48 versus 0.40 mg m(-3)), but not for the respirable fraction. The WAMs for the auto (1.47 mg m(-3)) and auto parts manufacturing industry (1.83 mg m(-3)) were significantly higher than that for small-job machine shops (0.68 mg m(-3)). In addition, a significant difference in the thoracic WAM was found between the automotive industry (0.46 mg m(-3)) and small-job machine shops (0.32 mg m(-3)). Operation type, in particular, grinding, was a significant factor affecting the total aerosol fraction [grinding operations (1.75 mg m(-3)) versus other machining (0.95 mg m(-3))], but the levels associated with these operations were not statistically different for either the thoracic or the respirable fractions. Across all decades, the total aerosol fraction for straight oils (1.49 mg m(-3)) was higher than for other fluid types (soluble = 1.08 mg m(-3), synthetic = 0.52 mg m(-3) and semisynthetic = 0.50 mg m(-3)). Fluid type was also found to be partly associated with differences in the respirable fraction level. We found that the total aerosols were measured by a variety of sampling media, devices and analytical methods. This diversity of approaches makes interpretation of the study results difficult. In conclusion, both the literature review and the measurement data analyzed found that decade and type of industry, operation and fluid were important determinants of total aerosol exposure. Industry type and fluid type were associated with differences in exposure to the thoracic and respirable fraction levels, respectively.