New evidence on the health hazards and control of metalworking fluids since completion of the OSHA advisory committee report

The influence of ventilation modes on oil mist particles diffusion in a machining workshop

Mechanical processing and operations are widely involved in modern industry. Large amount of oil mist is tended to be produced and will diffuse in the processing workshop when metalworking fluids are applied on the high temperature workpiece. The ventilation modes and air distributions can influence the air pollutants dilution in machining workshops. Therefore, this paper presents both experimental investigation and simulation study on the oil mist particles diffusion under different ventilation modes. The results identified PM2.5 as the primary component among different oil mist particles generated during a typical machining process. The distribution of oil mist particles in a full-scale machining workshop laboratory was investigated under two ventilation modes: high-sidewall nozzle air supply and low-sidewall air supply. Results revealed obvious influences of both air supply modes on the distribution of oil mist particles. Under the high-sidewall-nozzle air supply mode, the airflow and the oil mist distribution in the workshop was relatively uniform; while the low-sidewall-vent air supply mode led to an uneven distribution of oil mist particles, and the maximum oil mist concentration appeared at the height of 3 m. Under both modes, the attempts to increase the airflow rate are not always successful. Compared with low-sidewall-vent air supply mode, the high-sidewall-nozzle air supply mode presents better performance in achieving lower overall particle concentration level. Overall, the results of this study give useful reference to improve the air quality of industrial plant by properly designing the ventilation mode of machining workshop.

Optimization Study of Sampling Device for Semi-Volatile Oil Mist in the Industrial Workshop

A large number of metalworking fluids in industrial manufacturing processes generate high-concentrations of oil mist pollution, which is a typical semi-volatile aerosol and is generally composed of liquid particles and volatile gas components. Long-term exposure to oil mist pollution brings a series of occupational diseases to workers. For the semi-volatile aerosol, the traditional filter sampling method will lead to particle volatilization, which underestimates the concentration of particles and overestimates the concentration of gas. Therefore, this study combined the advantages of the electrostatic method and the Tenax tube adsorption method, to develop a more accurate measurement technology. First, a dichotomous sampler that could efficiently separate the gas and liquid phases of aerosols was optimized through a numerical model, which was validated by literature results. Next, a test table for oil mist sampling was built with a sampler which was fabricated by 3D printing, and the performance of the sampler was evaluated. The results show that the sampling technique can separate the gas and particulate phases of the oil mist efficiently and accurately. Compared with the traditional single sampling methods, the new sampler can better determine the true concentration of oil mist.

Metalworking fluids and cancer mortality in a US autoworker cohort (1941-2015)

Objectives This report describes the extended follow-up (1941-2015) of a cohort of 38 549 automobile manufacturing workers with potential exposure to metalworking fluids (MWF). The outcomes of interest were mortality from cancers of the esophagus, stomach, intestine, rectum, bladder, liver, pancreas, larynx, lung, skin, prostate, brain, and female breast, as well as leukemia. This report includes 5472 deaths from cancer, more than ten times the numbers of deaths in our last summary report published 20 years ago. Methods Standardized mortality ratios were computed for the entire study period. Adjusted hazard ratios (HR) were estimated in Cox proportional hazard models with categorical variables for cumulative exposure to each type of MWF. Results Exposure-response patterns are consistent with prior mortality reports from this cohort. We found increased risk of skin and female breast cancer with straight fluids. For the first time, we found elevated risk of stomach cancer mortality. Overall, many of the exposure-response results did not suggest an association with MWF. Conclusions Mortality is a poor proxy for cancer diagnosis for treatable cancers and not the optimal outcome measure in etiological studies. Although the HR presented here handle bias from the healthy worker hire effect and left truncation, they do not handle bias from healthy worker survivor effect, which likely results in underestimates of the health impacts of MWF. Although this updated summary provides some information on the risk of cancer from MWF, targeted future analyses will help clarify associations.

Risk Assessment for Metalworking Fluids and Respiratory Outcomes

Background

Metalworking fluids (MWFs) are mixtures with inhalation exposures as mists, dusts, and vapors, and dermal exposure in the dispersed and bulk liquid phase. A quantitative risk assessment was performed for exposure to MWF and respiratory disease.

Methods

Risks associated with MWF were derived from published studies and NIOSH Health Hazard Evaluations, and lifetime risks were calculated. The outcomes analyzed included adult onset asthma, hypersensitivity pneumonitis, pulmonary function impairment, and reported symptoms. Incidence rates were compiled or estimated, and annual proportional loss of respiratory capacity was derived from cross-sectional assessments.

Results

A strong healthy worker survivor effect was present. New-onset asthma and hypersensitivity pneumonitis, at 0.1 mg/m³ MWF under continuous outbreak conditions, had a lifetime risk of 45%; if the associated microbiological conditions occur with only 5% prevalence, then the lifetime risk would be about 3%. At 0.1 mg/m³, the estimate of excess lifetime risk of attributable pulmonary impairment was 0.25%, which may have been underestimated by a factor of 5 or more by a strong healthy worker survivor effect. The symptom prevalence associated with respiratory impairment at 0.1 mg/m³ MWF was estimated to be 5% (published studies) and 21% (Health Hazard Evaluations).

Conclusion

Significant risks of impairment and chronic disease occurred at 0.1 mg/m³ for MWFs in use mostly before 2000. Evolving MWFs contain new ingredients with uncharacterized long-term hazards.

High-throughput toxicity study of lubricant emulsions and their common ingredients using zebrafish

Though lubricant emulsions have been widely used in many industrial processes, various human health hazards have been reported. Conducting a systematic toxicity study on emulsions is difficult since emulsions contain multiple chemical compounds, and hydrophobic compounds form complex emulsion particles via surfactants. For a quantitative toxicity study, we developed a high-throughput imaging system using zebrafish and conducted a large scale in vivo toxicity assay of lubricant emulsion and their common ingredients. By computing the locomotion activity of zebrafish from captured time-lapse images, we could quantify the degree of relative toxicity of 29 chemicals. The changes in the locomotion activity over time were observed to vary significantly depending on emulsions, indicating that the degree of toxicity of the commercial products was very diverse. We found that primary ethanolamines were more toxic than secondary or tertiary ethanolamines, and several factors, such as alkyl chain length, EO mole, test concentration, and emulsion particle size, affected toxicity.

Risk assessment for metalworking fluids and cancer outcomes

BACKGROUND

Metalworking fluids (MWF) are complex mixtures with dermal and inhalation exposure. Published reports reveal excess cancer risk.

METHODS

Using published findings exposure response was derived for each attributable cancer site. Aggregate excess lifetime risk was estimated by applying a lifetable calculation.

RESULTS

Cancer sites contributing the most attributable cases were larynx, esophagus, brain, female breast, and uterine cervix. With constant workplace MWF exposure of 0.1 mg/m³ over a 45 years working life, the risk of attributable cancer was 3.7% or, excluding the less certain female cancers, 3.1%.

CONCLUSION

Substantial cancer risks occurred at 0.1 mg/m³ MWF, one fourth of the current NIOSH recommended exposure limit for MWF total particulate. Because ingredients in current MWF remain from earlier formulations, it is likely that some MWF carcinogenicity persists today. Although important changes have occurred, newer agents are being continually introduced with little or no knowledge of chronic health risks.

Risk of renal cell carcinoma following exposure to metalworking fluids among autoworkers

OBJECTIVES

Metalworking fluids (MWF), used to cool and lubricate metal in occupational settings, are linked to several cancers but data on kidney cancer are limited. We examine how MWF influence the rate of renal cell carcinoma (RCC) in a large prospective study.

METHODS

A cohort of Michigan autoworkers consisting of 33 421 individuals was followed from 1985 to 2009. The cohort was linked to the Michigan Cancer Registry to identify new cases of RCC. We analysed RCC in relation to cumulative exposure to each specific type of MWF (straight, soluble and synthetic) and all 3 types pooled into a single MWF variable, with a 15-year lag. Cox proportional hazards regression with splines were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs), controlling for age, gender, race, calendar year, year hired, time since hire, plant and other MWF types.

RESULTS

There were 135 incident cases. A linear increase in the log-HR was observed for RCC with increasing cumulative exposure to each MWF type and total MWF exposure. At the mean of total MWF exposure (18.80 mg/m(3)-year), the estimated HR was 1.11 (95% CI 1.04 to 1.19).

CONCLUSIONS

Our results provide evidence for a dose-dependent association between MWF exposure and RCC. The influence of components of oil-based and water-based MWF needs further examination.

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

Occupational exposure to aerosolized particles of oil-based metalworking fluid was recently linked to deaths from ischemic heart disease. The current recommended exposure limits might be insufficient. Studying cardiovascular mortality is challenging because symptoms can induce sicker workers to reduce their exposure, causing healthy-worker survivor bias. G-estimation of accelerated failure time models reduces this bias and permits comparison of multiple exposure interventions. Michigan autoworkers from the United AutoWorkers–General Motors cohort (n = 38,666) were followed from 1941 through 1994. Separate binary variables indicated whether annual exposure exceeded a series of potential limits. Separate g-estimation analyses for each limit yielded the total number of life-years that could have been saved among persons who died from specific cardiovascular causes by enforcing that exposure limit. Banning oil-based fluids would have saved an estimated 4,003 (95% confidence interval: 2,200, 5,807) life-years among those who died of ischemic heart disease. Estimates for cardiovascular disease overall, acute myocardial infarction, and cerebrovascular disease were 3,500 (95% confidence interval: 1,350, 5,651), 2,932 (95% confidence interval: 1,587, 4,277), and 917 (95% confidence interval: −80, 1,913) life-years, respectively. A limit of 0.01 mg/m³ would have had a similar impact on cerebrovascular disease but one only half as great on ischemic heart disease. Analyses suggest that limiting exposure to metalworking fluids could have saved many life-years lost to cardiovascular diseases in this cohort.

Hypersensitivity pneumonitis in workers exposed to metalworking fluids

Background

This study used data from a large UK outbreak investigation, to develop and validate a new case definition for hypersensitivity pneumonitis due to metalworking fluid exposure (MWF-HP).

Methods

The clinical data from all workers with suspected MWF-HP were reviewed by an experienced panel of clinicians. A new MWF-HP Score was then developed to match the “gold standard” clinical opinion as closely as possible, using standard diagnostic criteria that were relatively weighted by their positive predictive value.

Results

The new case definition was reproducible, and agreed with expert panel opinion in 30/37 cases. This level of agreement was greater than with any of the three previously utilized case definitions (agreement in 16–24 cases). Where it was possible to calculate, the MWF-HP Score also performed well when applied to 50 unrelated MWF-HP cases.

Conclusions

The MWF-HP Score offers a new case definition for use in future outbreaks. Am. J. Ind. Med. 57:872–880, 2014. © 2014 The Authors. American Journal of Industrial Medicine Published by Wiley Periodicals, Inc.

Trichloroethylene and cancer: systematic and quantitative review of epidemiologic evidence for identifying hazards

We conducted a meta-analysis focusing on studies with high potential for trichloroethylene (TCE) exposure to provide quantitative evaluations of the evidence for associations between TCE exposure and kidney, liver, and non-Hodgkin lymphoma (NHL) cancers. A systematic review documenting essential design features, exposure assessment approaches, statistical analyses, and potential sources of confounding and bias identified twenty-four cohort and case-control studies on TCE and the three cancers of interest with high potential for exposure, including five recently published case-control studies of kidney cancer or NHL. Fixed- and random-effects models were fitted to the data on overall exposure and on the highest exposure group. Sensitivity analyses examined the influence of individual studies and of alternative risk estimate selections. For overall TCE exposure and kidney cancer, the summary relative risk (RRm) estimate from the random effects model was 1.27 (95% CI: 1.13, 1.43), with a higher RRm for the highest exposure groups (1.58, 95% CI: 1.28, 1.96). The RRm estimates were not overly sensitive to alternative risk estimate selections or to removal of an individual study. There was no apparent heterogeneity or publication bias. For NHL, RRm estimates for overall exposure and for the highest exposure group, respectively, were 1.23 (95% CI: 1.07, 1.42) and 1.43 (95% CI: 1.13, 1.82) and, for liver cancer, 1.29 (95% CI: 1.07, 1.56) and 1.28 (95% CI: 0.93, 1.77). Our findings provide strong support for a causal association between TCE exposure and kidney cancer. The support is strong but less robust for NHL, where issues of study heterogeneity, potential publication bias, and weaker exposure-response results contribute uncertainty, and more limited for liver cancer, where only cohort studies with small numbers of cases were available.