A Comprehensive Review of the Literature on Exposure to Metalworking Fluids

Abstract

An extensive literature review was conducted of studies with exposure measurements to metalworking fluids (MWFs). A database of 155 arithmetic means based on 9379 aerosol measurements from published studies was compiled. Weighted arithmetic means (WAMs) and their variance calculated across studies were summarized based on decade (prior to 1970s through 2000s), industry (auto, auto parts, small job shops, and others), operation (grinding and machining), and fluid type (straight, soluble, synthetic, and semisynthetic). Total mass and total extractable mass measurements that were simultaneously collected were compared. Average concentrations by size fractions and mass median aerodynamic diameters (MMADs) were also analyzed. Analysis of the WAMs indicated a reduction in exposure levels over time regardless of industry or type of operation or fluid, with mean levels prior to the 1970s of 5.4 mg/m³, which dropped to 2.5 mg/m³ in the 1970s, to 1.2 mg/m³ in the 1980s, and to 0.5 mg/m³ in the 1990s. No further reduction was seen in the 2000s. A comparison by industry, operation, and fluid type found no consistent patterns in the measurement results. The percent extractable mass in the total aerosol samples varied by fluid type, with an average 84% in straight fluids, 58% in synthetic fluids, 56% in soluble fluids, and 42% in the semisynthetic fluids. Exposure means from the thoracic fraction (0.3–0.5 mg/m³) were slightly less than those for total aerosol for both the 1990s and 2000s, the only decades for which thoracic data were available. Respirable means did not change from the 1980s to the 2000s (generally about 0.2–0.3 mg/m³). The MMADs of the MWF aerosols averaged 4–6 μm. These measurement data indicate a clear reduction of exposure levels over time. They will be used for the retrospective assessment of exposure levels to MWFs in a population-based, case-control study of bladder cancer.

Keywords:

• grinding operation
• machining operation
• metalworking fluids (MWFs)
• weighted arithmetic means (WAMs)

ACKNOWLEDGMENT

This research was supported by intramural funds from the National Cancer Institute, National Institutes of Health, Department of Health and Human Services.

Notes

^A Includes mixed operations (n = 132).

^B Includes mixed fluid types (n = 653).

^A WAM_g : mass by the gravimetric method.

^B WAM_e : mass by solvent extraction and either gravimetric or infrared analysis.

^C (WAM_g/WAM_e)× 100.

^D 100-extractable mass (%).

^A The number of measurements within subcategories is not equal to the corresponding broader category because the numbers of NI are not identified separately.

^B Total measurements include measurements with no information (NI). For example, the total number of measurements for the auto part industry (all operations and all fluids) during < 1970s is 63, which includes 17 on grinding operations and 46 on machining operations. The 46 measurements from machining include 9 measurements on straight fluids and 37 on measurements with no information (NI) on fluid type.

^A Includes milling, drilling, hobbing, tapping, broaching, turning.

^A Includes milling, drilling, hobbing, tapping, broaching, turning.