Occupational Exposure to Inhalable Manganese at German Workplaces

How to Reduce the Exposure of Welders to an Acceptable Level: Results of the InterWeld Study

OBJECTIVES

Workplace measurements in the past have shown that the applicable occupational exposure limits (OELs) are regularly exceeded in practice when high-emission welding processes are applied. The InterWeld pilot study was planned as part of an intervention study to show under which conditions compliance with the OEL is achievable in gas metal arc welding (GMAW) with solid wire. The investigation focussed on local exhaust ventilation, i.e. captor hoods and welding torches with integrated fume extraction.

METHODS

Forty tests with hand-guided GMAW were configured by experts with regard to all technical parameters and carried out by a professional welder. Effects of protective measures and process parameters on the exposure to respirable welding fumes and airborne manganese (Mn), chromium, nickel, and hexavalent chromium were investigated. Personal sampling was carried out in the welder's breathing zone outside the face shield at high flow rates (10 l min-1) in order to achieve sufficient filter loading. Particle masses and welding fume concentrations were determined by weighing the sampling filters. Metal concentrations were analysed by inductive coupled plasma mass spectrometry. In order to evaluate the effects on exposure, the measurements were performed under similar conditions. The data were analysed descriptively and with mixed linear models. For measurements below the limit of detection, the exposure level was estimated using multiple imputation.

RESULTS

Two to five times higher exposures to respirable welding fumes and airborne metals were observed during welding of 10 mm sheets than during welding of 2- or 3-mm sheets. Welding fume and Mn exposure were reduced by 70 and 90% when on-torch extraction or a captor hood was applied. Other airborne metals were reduced to a similar extent. Modifications on welding parameters led to a reduction of exposure against respirable particles by 51 up to 54%.

CONCLUSIONS

Although proper extraction at the point of origin and lower-emitting process variants ensure a drastic reduction in exposure, compliance with current OELs is not guaranteed. In order to ensure adequate health protection, especially at workplaces where thick sheets with long relative arc times are processed, there is a need for technical development.

The Functions of ZIP8, ZIP14, and ZnT10 in the Regulation of Systemic Manganese Homeostasis

As an essential nutrient, manganese is required for the regulation of numerous cellular processes, including cell growth, neuronal health, immune cell function, and antioxidant defense. However, excess manganese in the body is toxic and produces symptoms of neurological and behavioral defects, clinically known as manganism. Therefore, manganese balance needs to be tightly controlled. In the past eight years, mutations of genes encoding metal transporters ZIP8 (SLC39A8), ZIP14 (SLC39A14), and ZnT10 (SLC30A10) have been identified to cause dysregulated manganese homeostasis in humans, highlighting the critical roles of these genes in manganese metabolism. This review focuses on the most recent advances in the understanding of physiological functions of these three identified manganese transporters and summarizes the molecular mechanisms underlying how the loss of functions in these genes leads to impaired manganese homeostasis and human diseases.

The effects of manganese overexposure on brain health

Manganese (Mn) is the twelfth most abundant element on the earth and an essential metal to human health. Mn is present at low concentrations in a variety of dietary sources, which provides adequate Mn content to sustain support various physiological processes in the human body. However, with the rise of Mn utility in a variety of industries, there is an increased risk of overexposure to this transition metal, which can have neurotoxic consequences. This risk includes occupational exposure of Mn to workers as well as overall increased Mn pollution affecting the general public. Here, we review exposure due to air pollution and inhalation in industrial settings; we also delve into the toxic effects of manganese on the brain such as oxidative stress, inflammatory response and transporter dysregulation. Additionally, we summarize current understandings underlying the mechanisms of Mn toxicity.

Occupational Co-exposures to Multiple Chemical Agents from Workplace Measurements by the US Occupational Safety and Health Administration

OBJECTIVES

The occupational environment represents an important source of exposures to multiplehazards for workers' health. Although it is recognized that mixtures of agents may have differenteffects on health compared to their individual effects, studies generally focus on the assessment ofindividual exposures. Our objective was to identify occupational co-exposures occurring in the United States using the multi-industry occupational exposure databank of the Occupational Safety and Health Administration (OSHA).

METHODS

Using OSHA's Integrated Management Information System (IMIS), measurement data from workplace inspections occurring from 1979 to 2015 were examined. We defined a workplace situation (WS) by grouping measurements that occurred within a company, within the same occupation (i.e. job title) within 1 year. All agents present in each WS were listed and the resulting databank was analyzed with the Spectrosome approach, a methodology inspired by network science, to determine global patterns of co-exposures. The presence of an agent in a WS was defined either as detected, or measured above 20% of a relevant occupational exposure limit (OEL).

RESULTS

Among the 334 648 detected exposure measurements of 105 distinct agents collected from 14 513 US companies, we identified 125 551 WSs, with 31% involving co-exposure. Fifty-eight agents were detected with others in >50% of WSs, 29 with a proportion >80%. Two clusters were highlighted, one for solvents and one for metals. Toluene, xylene, acetone, hexone, 2-butanone, and N-butyl acetate formed the basis of the solvent cluster. The main agents of the metal cluster were zinc, iron, lead, copper, manganese, nickel, cadmium, and chromium. 68 556 WS were included in the analyses based on levels of exposure above 20% of their OEL, with 12.4% of co-exposure. In this analysis, while the metal cluster remained, only the combinations of toluene with xylene or 2-butanone were frequently observed among solvents. An online web application allows the examination of industry specific patterns.

CONCLUSIONS

We identified frequent co-exposure situations in the IMIS databank. Using the spectrome approach, we revealed global combination patterns and the agents most often implicated. Future work should endeavor to explore the toxicological effects of prevalent combinations of exposures on workers' health to prioritize research and prevention efforts.

Modelling of exposure to respirable and inhalable welding fumes at German workplaces

The International Agency for Research on Cancer classified welding fumes as carcinogenic to humans, and occupational exposure limits should be established to protect welders. The aim of this study is to estimate exposure levels to inhalable and respirable welding fumes by welding process to use them for exposure assessment in epidemiological studies and to derive occupational exposure limits. In total, 15,473 mass concentrations of inhalable and 9,161 concentrations of respirable welding fumes could be analyzed along with welding-related and sampling information, which were compiled in the German database MEGA between 1983 and 2016. In both particle-size fractions, model-based geometric means of the concentrations were estimated by welding process and material for frequently used welding processes adjusted for sampling time and median-centered for calendar years. The inhalable concentrations were approximately twice the respirable concentrations, with medians of 3 mg/m³ (inter-quartile range: 1.2-7.0 mg/m³) and 1.5 mg/m³ (inter-quartile range: < limit of detection -3.8 mg/m³), respectively. The adjusted geometric means of flux-cored arc welding, metal inert and active gas welding, shielded metal arc welding and torch cutting ranged from 0.9 to 2.2 mg/m³ for respirable welding fumes and from 2.3 to 4.7 mg/m³ for inhalable fumes. In both particle-size fractions, geometric means were between 0.1 and 0.9 mg/m³ when performing tungsten inert gas, autogeneous, resistance, laser, and plasma welding or spraying. Results derived from this large dataset are useful for a quantitative exposure assessment to estimate health risks of welders.

Occupational exposure to metals and other elements in the tractor production

Background

Exposure to metals via air sampling in workplace has been extensively studied; however, the magnitude of individual exposure in various occupational groups may vary dramatically. The aim of this cross-sectional study was to ascertain exposure to selected metals from metal fumes in a series of typical workplaces of contemporary tractor production.

Methods

Ninety-eight (median age 41 (interquartile range (IQR) 23) years, all men) workers from Minsk Tractor Plant were categorized into four groups, including assembly shop workers (group 1); thermal shop staff (group 2); steelmakers (group 3) and welders (group 4). Hair samples (0.25 g) of each worker were tested for Ca, Mg, P, Cu, Fe, Zn, Al, Mn, Cr, Ni, Pb and Cd using atomic emission spectrophotometry. We then tested between-group differences of log-transformed element concentrations using analysis of variance, followed by logistic regression to determine the odds ratio (OR) with its 95% confidence interval (CI) of high exposure for four selected groups.

Results

The median work duration in workers was 6 (IQR 15) years, more in group 1 (10 (IQR 23)). Eight out of 12 included elements yielded significant between-group differences, including Mg, P, Fe, Zn, Mn, Cr, Ni and Cd. Steelmakers had higher Mn hair concentrations (F-ratio 10.41, p<0.001); whereas Fe (F-ratio 12.48, p<0.001), P (F-ratio 12.68, p<0.001), Zn (F-ratio 6.07, p<0.001) and Cr (F-ratio 20.54, p<0.001) were higher in welders. OR of high exposure to Mg in group 3 was 10.00 (95% CI 1.14–87.52), whereas the OR of high exposure to P in group 4 was 18.64 (95% CI 2.22–156.85) compared to group 1.

Conclusions

In the modern full-cycle tractor production, welders may have higher exposure to Fe, P, Zn and Cr, as opposed to steelmakers with higher Mn hair concentrations.