In trying to set or guide policies, the U.S. Environmental Protection Agency (EPA), Occupational Health and Safety Administration (OSHA) and National Institute for Occupational Safety and Health (NIOSH) take into account scientific findings based on research which are usually published in peer reviewed journals. However, for the average person, epidemiology and statistics are vague or sometimes even unknown concepts. Thus, we depend on researchers and academicians to establish the relationship between exposure and disease.
During the Independent Lubricant Manufacturers Association (ILMA) Management Forum in April, John Howell, president of GHS Resources Inc., led the discussion on the health effects of metalworking fluids (MWF) on workers. Howell reviewed several studies by Picciotto and associates, using a relatively new sophisticated statistical method called g-estimation.
Picciotto et al’s GM-UAW cohort study on 38,666 workers from three plants hired between 1938-1982 who worked for three years or more compared observed survival times and the hypothetical scenario if the workers had not been exposed to MWFs.1 They concluded that banning straight MWFs could have saved a total of 8,648 person-years of life among those who died, specifically 4,334 person-years of life among those who died from ischemic heart disease (IHD). The authors stated that the results of the study “provide evidence supporting hypothesis of a detrimental relationship between straight metalworking fluids and mortality, particularly from ischemic heart disease.”
Another study by Picciotto et al was on hypothetical exposure limits and the possibility of saving lives if exposure limits were reduced.2 Howell pointed out several significant points that the authors reported. If straight MWFs had been banned, exposed workers who died of cardiovascular disease would have lived 1.58 years longer, while deaths from cerebrovascular disease would have occurred on average 3.19 years later and workers who died from heart attacks (acute myocardial infarction) or IHD would have lived 3.13 years longer. Howell said that the study’s conclusion that “reducing the occupational exposure limit for straight MWFs to 0.01 mg/m3 would have saved 2,000 life-years in this cohort who died of cardiovascular disease” is something that the industry should be aware of.
The “healthy worker survivor effect” by Garcia E, Picciotto S, Costelo S et al is another large study. Workers in this group of 31,845 workers were followed from 1985 to 1994 and were checked for the development of cancer by looking at the Michigan Cancer registry. As always, confounding factors need to be considered to prevent researchers from coming up with the wrong conclusions, so they used g-estimation to avoid bias and to adjust for the relationship between employment, exposure (and non exposure by termination of employment) and disease (cancer). Howell pointed out several key findings based on the authors’ analysis: 1) the hazards ratio (HR) for leaving work as a predictor for all cancers was elevated only for lung and colorectal cancers for men, but not for prostate cancer or all cancers combined. Second, leaving work associated with cancer as a disease outcome is more clearly seen if they leave work by age 50. Lastly, higher exposure to all three types of MWFs (straight or neat, soluble and synthetic) were associated with increased rates of leaving work except for straight MWF among women. The reason for this was not elucidated in the study. Another cancer study that was brought up by Howell was Shrestha et al’s research on renal cell carcinoma (RCC) in the GM-UAW cohort comprised of 33,421 workers followed through 1985 to 2009 in the Michigan Cancer Registry and analyzed using Cox Proportional Hazards Regression. Incidence of RCC was analysed in relation to exposure to three types of MWFs, straight, soluble and synthetic and also all three MWF as a single variable, with a 15-year lag. They found 135 incident cases in all and they found evidence of a dose-dependent relationship between MWFs exposure and development of RCC with the trend for white males steeper than for African Americans with the exposure to synthetic MWF yielding the strongest dose-response relationship.
These exposures occurred decades ago when exposures were significantly higher and MWFs were formulated with less refined base oils. But even though today’s MWFs are formulated based on up-to-date knowledge of base oils and component health effects, the industry should consider and take into account these studies when looking to make decisions, regulatory and business-wise, as workers’ exposure to MWFs has an impact on their health. While issues of workplace exposure caused disease and mortality from today’s MWFs, although likely much reduced, the research articles as described bring into focus these questions even today: How long will they live? How long should they have lived? Can they live a little bit longer? Can their deaths be prevented? Can cancer be avoided? How much is an extra year of life worth: to the worker and his family and how much is it worth to the employer and to the industry?
1. Picciotto S, Ljungman P, Eisen E, et al. Straight Metalworking Fluids and All-Cause and Cardiovascular Mortality Analyzed by Using G-Estimation of an Accelerated Failure Time Model With Quantitative Exposure: Methods and Interpretations. Amer J Epidemiology 2016; 183(7): 680-688.
2. Picciotto S, Peters A and Eisen E. Hypothetical Exposure Limits for Oil-Based Metalworking Fluids and Cardiovascular Mortality in a Cohort of Autoworkers: Structural Accelerated Failure Time Models in a Public Health Framework. Amer J Epidemiology 2015; 181(8): 563-570.
3. Garcia E, Picciotto S, Costello S et al. Assessment of the Healthy Worker Survivor Effect in Cancer Studies of the United Autoworkers-General Motors Cohort. Occup Environ Med 2017; 74: 294-300.
4. Shrestha D, Liu S, Hammond SK et al. Risk of Renal Cell Carcinoma Following Exposure to Metalworking Fluids Among Autoworkers. Occup Environ Med 2016; 73(10): 256-662.