Manganese exposures during shielded metal arc welding (SMAW) in an enclosed space

Levels and control of welding fume exposure to total particulate, hexavalent chromium, and manganese in contracted activities in an oil refinery setting (2008-2018)

In response to increasing focus on occupational exposures to welding fume, a 10-year series of personal exposure measurements was analyzed for the two main welding processes (Shielded Metal Arc Welding or Stick and Tungsten Inert Gas welding or TIG) used in an oil refinery setting. Exposures from ancillary gouging and grinding were also analyzed. The operations were conducted under a permit-to-work system, which stipulated control measures in the form of ventilation and respiratory protective equipment (RPE) depending on the work environment, base metal, and welding process. The analysis focused on three health hazards of interest: total particulate (TP); hexavalent chromium (Cr (VI)); and manganese (Mn). The study's aims were the analysis of exposure levels related to operational conditions to verify the adequacy of required control measures and the generation of quantitative information for the development of predictive exposure models. Arithmetic mean exposures were 2.01 mg/m3 for TP (n = 94), 13.86 µg/m3 for Cr (VI) (n = 160), and 0.024 mg/m3 for Mn (n = 95). Requirements and practices for ventilation and use of RPE appeared adequate for maintaining exposure levels below maximum use concentrations. Predictive models for mean exposure levels were developed using multiple linear regression. Different patterns emerged for TP, Cr (VI), and Mn exposure determinants. Enclosed or confined work environments were associated with elevated exposure levels, regardless of the provision of local exhaust or general dilution ventilation. Carbon arc, used with gouging and grinding, contributed significantly to TP exposure (p = 0.006). The relative TP source strengths of the two main welding processes were comparable to the literature data. For Cr (VI), stick welding was associated with approximately 50-fold (p < 0.001) higher exposure potential than TIG welding. For Mn, this difference was approximately 2.5-fold. Differences were observed across the three analytes in exposure reduction efficiency of local exhaust ventilation (LEV) compared to natural ventilation, possibly due to ineffective use in confined spaces. These findings contribute to the overall understanding of TP, Cr (VI), and Mn exposures from welding and required controls in an oil refinery setting.

Occupational Exposure to Manganese Among Welders: Association Between Airborne Manganese Concentration and Blood Manganese Levels

Background: Manganese (Mn) is an essential element for the human body, but it can cause adverse effects on the Central Nervous System at high doses. Exposure to manganese fumes during welding can harm welders' health. Objectives: The current study aimed to measure manganese produced by shielded metal arc welding (SMAW) in the breathing zone air and blood of welders and investigate the relationship between manganese concentrations in air and blood. Methods: In this descriptive-analytical cross-sectional study, 35 welders were enrolled as the exposed group and 40 office workers as the control group. Manganese concentration in air was measured according to NIOSH method 7301. Air and blood sample analyses were carried out by ICP-OES. Statistical analysis was performed with MINITAB 17. Data were analyzed using Pearson correlation coefficient, one-sample t-test, paired t-test, and logistic regression. The significance level was set at P < 0.05. Result: The mean concentration of welding respirable particles and manganese fumes were 9.56 ± 1.67 and 0.45 ± 0.08 mg/m3, three and 22 times the exposure limit recommended by ACGIH, respectively. Average manganese was significantly higher in the welders’ blood (0.16 ± 0.02 µg/mL) than in the controls’ blood (0.04 ± 0.002 µg/mL). There were strong and significant correlations between the welding respirable particles and manganese concentration in welders’ breathing zone and blood manganese levels. Also, with each year of work experience, the manganese concentration in the welders’ blood increased by 1.5%. Conclusions: Welders are at risk of contamination with manganese. Manganese exposure reduction through more efficient ventilation systems, reducing welder’s exposure time, staff training, and appropriate respiratory protection equipment should be applied to reduce manganese exposure among welders and prevent health complications.

Welding Fume Exposure and Health Risk Assessment in a Cohort of Apprentice Welders

Welding fumes vary in composition depending on the materials and processes used, and while health outcomes in full-time welders have been widely studied, limited research on apprentices exists. Besides, few data are available for metals such as vanadium and antimony. This study aimed to look at individual metals present in welding fumes in the learning environment of apprentice welders. Forty-three welders and 41 controls were chosen from trade programmes at the Northern Alberta Institute of Technology. Ambient and personal air samples were collected at days 0, 1, 7, and 50 of their training and analysed for mass and metal concentrations using Inductively Coupled Plasma Mass Spectrometry. Results showed increases in particle and metal concentrations as apprentices progressed throughout their education and that concentrations at day 50 were similar to levels found in the literature for professional welders. Variable concentrations indicate that some individuals may not properly use the local exhaust ventilation system. Other possible explanation for variations are the position of the sampler on the shoulder, the time spent welding and in each welding position, and the skills of the welders. Strong relationships were observed between particle and metal concentrations, suggesting that these relationships could be used to estimate metal exposure in welders from particle exposure. Welding processes were the most important determinant of exposure in apprentice welders, with Metal Core Arc Welding producing the largest particle concentrations followed by oxyacetylene cutting, and Gas Metal Arc Welding. Health risk assessment showed that welder apprentices are at risk for overexposure to manganese, which suggests that professional welders should be monitored for manganese as they are exposed more than apprentices. Training in proper positioning of local exhaust ventilation system and proper use of respirators are recommended in training facilities.

Occupational survey of airborne metal exposures to welders, metalworkers, and bystanders in small fabrication shops

The objective of this study was to characterize worker exposure to airborne metal and particulate matter in shops where multiple types of metalworking tasks were performed. The sampling strategy included full-shift and task-based personal samples on workers who performed flux-cored arc welding, personal samples on workers performing non-welding metalworking tasks, and area samples near welders, representing bystanders to welding. Size-fractionated particulate matter adjacent to welding activities was measured using real-time monitoring devices. Samples were analyzed for 21 individual metals, of which 8 were frequently detected. Exceedance fractions were calculated based on the distribution of results for each frequently detected metal. Exceedance fractions were <5% for all metals, except manganese (6% of the REL, 55% of the inhalable TLV-TWA and 91% of the respirable TLV-TWA) and iron oxide (10% of the REL and TLV-TWA) for Shop 1 bystander samples, manganese (68% for the inhalable TLV-TWA and 98% of the respirable TLV-TWA) for welder samples, and manganese (35% for the inhalable TLV-TWA and 80% of the respirable TLV-TWA) and iron oxide (12% for the PEL and 23% for the REL and TLV-TWA) for metalworker samples. Particulate matter concentrations measured at distances of 0.9-1.5 m and 2.1-2.7 m from the welder were within the same order of magnitude. The results of this study allow for comparison to health-based exposure limits for select individual components of welding fume with a low to medium degree of censorship.

Influence of welding fume metal composition on lung toxicity and tumor formation in experimental animal models

Millions of workers in the US and worldwide are exposed to complex, metal-rich welding fumes. Although welding is a crucial industrial process, the generated fumes are known to cause acute and chronic health effects when inhaled. The International Agency for Research on Cancer (IARC) classified welding fumes as carcinogenic to humans (Group 1) in 2017, based on sufficient epidemiological evidence and limited evidence in animals, an upgrade from the former Group 2B (possibly carcinogenic to humans) classification. There is human evidence that both iron-abundant mild steel as well as chromium- and nickel-containing stainless steel welding fumes contribute to an increased risk of lung cancer. Recent animal studies show that welding fumes may act as lung tumor promoters, regardless of the presence or absence of potentially carcinogenic metals, such as chromium and nickel. The goal of this manuscript was to examine the pulmonary responses associated with welding fumes by reviewing a series of recent experimental animal studies that assessed the influence of welding fume metal composition (e.g., stainless steel versus mild steel welding fume) on markers of lung toxicity and tumor development. Additional in vivo laboratory studies are needed to further explore the association between welding and lung cancer and to help advance our understanding of a potential mechanistic link.

Thalamic GABA levels and occupational manganese neurotoxicity: Association with exposure levels and brain MRI

Excessive occupational exposure to Manganese (Mn) has been associated with clinical symptoms resembling idiopathic Parkinson's disease (IPD), impairing cognitive and motor functions. Several studies point towards an involvement of the brain neurotransmitter system in Mn intoxication, which is hypothesized to be disturbed prior to onset of symptoms. Edited Magnetic Resonance Spectroscopy (MRS) offers the unique possibility to measure γ-amminobutyric acid (GABA) and other neurometabolites in vivo non-invasively in workers exposed to Mn. In addition, the property of Mn as Magnetic Resonance Imaging (MRI) contrast agent may be used to study Mn deposition in the human brain. In this study, using MRI, MRS, personal air sampling at the working place, work history questionnaires, and neurological assessment (UPDRS-III), the effects of chronic Mn exposure on the thalamic GABAergic system was studied in a group of welders (N=39) with exposure to Mn fumes in a typical occupational setting. Two subgroups of welders with different exposure levels (Low: N=26; mean air Mn=0.13±0.1mg/m³; High: N=13; mean air Mn=0.23±0.18mg/m³), as well as unexposed control workers (N=22, mean air Mn=0.002±0.001mg/m³) were recruited. The group of welders with higher exposure showed a significant increase of thalamic GABA levels by 45% (p<0.01, F(1,33)=9.55), as well as significantly worse performance in general motor function (p<0.01, F(1,33)=11.35). However, welders with lower exposure did not differ from the controls in GABA levels or motor performance. Further, in welders the thalamic GABA levels were best predicted by past-12-months exposure levels and were influenced by the Mn deposition in the substantia nigra and globus pallidus. Importantly, both thalamic GABA levels and motor function displayed a non-linear pattern of response to Mn exposure, suggesting a threshold effect.

Association of exposure to manganese and iron with relaxation rates R1 and R2*- magnetic resonance imaging results from the WELDOX II study

OBJECTIVE

Magnetic resonance imaging is a non-invasive method that allows the indirect quantification of manganese (Mn) and iron (Fe) accumulation in the brain due to their paramagnetic features. The WELDOX II study aimed to explore the influence of airborne and systemic exposure to Mn and Fe on the brain deposition using the relaxation rates R1 and R2* as biomarkers of metal accumulation in regions of interest in 161 men, including active and former welders.

MATERIAL AND METHODS

We obtained data on the relaxation rates R1 and R2* in regions that included structures within the globus pallidus (GP), substantia nigra (SN), and white matter of the frontal lobe (FL) of both hemispheres, as well as Mn in whole blood (MnB), and serum ferritin (SF). The study subjects, all male, included 48 active and 20 former welders, 41 patients with Parkinson's disease (PD), 13 patients with hemochromatosis (HC), and 39 controls. Respirable Mn and Fe were measured during a working shift for welders. Mixed regression models were applied to estimate the effects of MnB and SF on R1 and R2*. Furthermore, we estimated the influence of airborne Mn and Fe on the relaxation rates in active welders.

RESULTS

MnB and SF were significant predictors of R1 but not of R2* in the GP, and were marginally associated with R1 in the SN (SF) and FL (MnB). Being a welder or suffering from PD or HC elicited no additional group effect on R1 or R2* beyond the effects of MnB and SF. In active welders, shift concentrations of respirable Mn>100μg/m³ were associated with stronger R1 signals in the GP. In addition to the effects of MnB and SF, the welding technique had no further influence on R1.

CONCLUSIONS

MnB and SF were significant predictors of R1 but not of R2*, indicative of metal accumulation, especially in the GP. Also, high airborne Mn concentration was associated with higher R1 signals in this brain region. The negative results obtained for being a welder or for the techniques with higher exposure to ultrafine particles when the blood-borne concentration was included into the models indicate that airborne exposure to Mn may act mainly through MnB.

Automated entry technologies for confined space work activities: A survey

Work in confined spaces poses a significant risk to workers and rescuers involved in the emergency response when an accident occurs. Despite several standards and regulations define the safety requirements for such activities, injuries, and fatalities still occur. Furthermore, the on-site inspections after accidents often reveal that both employers and employees fail to implement safe entry procedures. Removing the risk is possible by avoiding the worker entry, but many activities require the presence of the operator inside the confined space to perform manual tasks. The following study investigates the available technologies for hazardous confined space work activities, e.g., cleaning, inspecting, and maintenance tasks. The aim is to provide a systematic review of the automated solutions for high-risk activities in confined spaces, considering the non-man entry as the most effective confined space safety strategy. Second, this survey aims to provide suggestions for future research addressing the design of new technologies. The survey consists of about 60 papers concerning innovative technologies for confined space work activities. The document review shows that several solutions have been developed and automation can replace the workers for a limited number of hazardous tasks. Several activities still require the manual intervention due to the complex characteristics of confined spaces, e.g., to remove the remains of the automatic cleaning process from the bottom of a tank. The results show that available technologies require more flexibility to adapt to such occupational environments and further research is needed.

Effects of pulmonary exposure to chemically-distinct welding fumes on neuroendocrine markers of toxicity

Exposure to welding fumes may result in disorders of the pulmonary, cardiovascular, and reproductive systems. Welders are also at a greater risk of developing symptoms similar to those seen in individuals with idiopathic Parkinson's disease. In welders, there are studies that suggest that alterations in circulating prolactin concentrations may be indicative of injury to the dopamine (DA) neurons in the substantia nigra. The goal of these studies was to use an established model of welding particulate exposure to mimic the effects of welding fume inhalation on reproductive functions. Since previous investigators suggested that changes in circulating prolactin may be an early marker of DA neuron injury, movement disorders, and reproductive dysfunction, prolactin, hypothalamic tyrosine hydroxylase (TH) levels (a marker of DA synthesis), and other measures of hypothalamic-pituitary-gonadal (HPG) function were measured after repetitive instillation of welding fume particulates generated by flux core arc-hard surfacing (FCA-HS), manual metal arc-hard surfacing (MMA-HS) or gas metal arc-mild steel (GMA-MS) welding, or manganese chloride (MnCl₂). Exposure to welding fume particulate resulted in the accumulation of various metals in the pituitary and testes of rats, along with changes in hypothalamic TH and serum prolactin levels. Exposure to particulates with high concentrations of soluble manganese (Mn) appeared to exert the greatest influence on TH activity levels and serum prolactin concentrations. Thus, circulating prolactin levels may serve as a biomarker for welding fume/Mn-induced neurotoxicity. Other reproductive measures were collected, and these data were consistent with epidemiological findings that prolactin and testosterone may serve as biomarkers of welding particulate induced DA neuron and reproductive dysfunction.

Exploring Manganese Fractionation Using a Sequential Extraction Method to Evaluate Welders' Gas Metal Arc Welding Exposures during Heavy Equipment Manufacturing

The National Institute for Occupational Safety and Health (NIOSH) has conducted an occupational exposure assessment study of manganese (Mn) in welding fume at three factories where heavy equipment was manufactured. The objective of this study was to evaluate exposures to different Mn fractions using a sequential extraction procedure. One hundred nine worker-days were monitored for either total or respirable Mn during gas metal arc welding. The samples were analyzed using an experimental method to separate different Mn fractions based on selective chemical solubility. The full-shift total particle size Mn time-weighted average (TWA) breathing zone concentrations ranged 0.38-26 for soluble Mn in a mild ammonium acetate solution; 3.2-170 for Mn0,2+ in acetic acid; 3.1-290 for Mn3+,4+ in hydroxylamine-hydrochloride; and non-detectable (ND)-130 µg m-3 for insoluble Mn fractions in hydrochloric and nitric acid. The summation of all the total particulate Mn TWA fractions yielded results that ranged from 6.9 to 610 µg m-3. The range of respirable size Mn TWA concentrations were 0.33-21 for soluble Mn; 15-140 for Mn0,2+; 14-170 for Mn3+,4+; 5.3-230 for insoluble Mn; and 36-530 µg m-3 for Mn (sum of fractions). Total particulate TWA GM concentrations of the Mn (sum) were 53 (GSD = 2.5), 150 (GSD = 1.7), and 120 (GSD = 1.8) µg m-3 for the three separate factories. Although all of the workers' exposures were measured below the OSHA regulatory permissible exposure limit and NIOSH recommended exposure limit for Mn, 70 welders' exposures exceeded the ACGIH Threshold Limit Values® for total Mn (100 µg m-3) and 29 exceeded the recently adopted respirable Mn TLV (20 µg m-3). This study shows that a welding fume exposure control and management program is warranted for Mn, which includes improved exhaust ventilation and may necessitate the use of respiratory protection, especially for welding parts that impede air circulation.

Longitudinal T1 relaxation rate (R1) captures changes in short-term Mn exposure in welders

OBJECTIVES

We demonstrated recently that the T1 relaxation rate (R1) captured short-term Mn exposure in welders with chronic, relatively low exposure levels in a cross-sectional study. In the current study, we used a longitudinal design to examine whether R1 values reflect the short-term dynamics of Mn exposure.

METHODS

Twenty-nine welders were evaluated at baseline and 12 months. Occupational questionnaires estimated short-term welding exposure using welding hours in the 90days prior to each study visit (HrsW₉₀). In addition, blood Mn levels, the pallidal index (PI; globus pallidus T1-weighted intensity (T1WI)/frontal white matter T1WI), and R1 values in brain regions of interest (ROIs) were determined as Mn biomarkers at each visit. Associations between changes in estimated welding exposure and changes in purported Mn biomarkers were assessed by Spearman's correlations with adjustment for age and baseline R1, HrsW₉₀, and blood Mn values.

RESULTS

Changes in welding hours (HrsW₉₀: the short-term welding exposure estimate), was associated significantly with changes in R1 values in the putamen (r=0.541, p=0.005), caudate (R=0.453, p=0.023), globus pallidus (R=0.430, p=0.032), amygdala (R=0.461, p=0.020), and hippocampus (R=0.447, p=0.025), but not with changes in blood Mn levels or the PI.

DISCUSSION

Changes in R1 values correlated with changes in the short-term welding exposure estimate, but not with more traditional measures of Mn exposure (blood Mn levels or PI). These results suggest that R1 may serve as a useful marker to capture the short-term dynamics in Mn brain accumulation related to welding exposure.

Setting evidence-based occupational exposure limits for manganese

In 2004, a review by the Institute of Environment and Health (IEH) made recommendations on occupational exposure limits (OELs) for manganese and its inorganic compounds for inhalable and respirable fractions respectively. These OELs were based on a detailed comprehensive evaluation of all the scientific data available at that time. Since then, more published studies have become available and a number of occupational standard-setting committees (EU SCOEL, US ACGIH-TLV, and German MAK) have proposed OEL's for manganese and its inorganic compounds that are somewhat lower that those proposed in the 2004 review. Based on current understanding, the key toxicological and human health issues that are likely to influence a health-based recommendation relate to: neurotoxicology; reproductive and developmental toxicology; and mutagenicity/carcinogenicity. Of these, it is generally considered that neurotoxicity presents the most sensitive endpoint. As such, many of the studies that have been reported since the IEH review have sought to use those neurofunctional tests that appear to be particularly sensitive at identifying the subtle neurological changes thought to associate with manganese toxicity. These recent studies have, however, continued to be limited to a significant extent by reliance on cross-sectional designs and also by use of unreliable exposure estimation methods. Consequently the strength of the potential association between manganese exposure and these subtle subclinical cognitive or neuromotor changes is still poorly characterised and the relevance of these minor differences in terms of either their clinical or quality of life consequences remains unknown. Based upon the overall evidence, it is concluded that the 8-h time weighted averages (TWA) for respirable (0.05mg/m³ as Mn) and inhalable (0.2mg/m³ as Mn) fractions as recommended by the SCOEL in 2011 are the most methodologically-sound, as they are based on the best available studies, most suited to the development of health-based OELs for both respirable and inhalable fractions. The dose-response characterisation informed by the examined studies used can be considered to establish a true human NOAEL for all the neurofunctional endpoints examined within the selected studies.

Characterization of Tungsten Inert Gas (TIG) Welding Fume Generated by Apprentice Welders

Tungsten inert gas welding (TIG) represents one of the most widely used metal joining processes in industry. Its propensity to generate a greater portion of welding fume particles at the nanoscale poses a potential occupational health hazard for workers. However, current literature lacks comprehensive characterization of TIG welding fume particles. Even less is known about welding fumes generated by welding apprentices with little experience in welding. We characterized TIG welding fume generated by apprentice welders (N = 20) in a ventilated exposure cabin. Exposure assessment was conducted for each apprentice welder at the breathing zone (BZ) inside of the welding helmet and at a near-field (NF) location, 60cm away from the welding task. We characterized particulate matter (PM₄), particle number concentration and particle size, particle morphology, chemical composition, reactive oxygen species (ROS) production potential, and gaseous components. The mean particle number concentration at the BZ was 1.69E+06 particles cm⁻³, with a mean geometric mean diameter of 45nm. On average across all subjects, 92% of the particle counts at the BZ were below 100nm. We observed elevated concentrations of tungsten, which was most likely due to electrode consumption. Mean ROS production potential of TIG welding fumes at the BZ exceeded average concentrations previously found in traffic-polluted air. Furthermore, ROS production potential was significantly higher for apprentices that burned their metal during their welding task. We recommend that future exposure assessments take into consideration welding performance as a potential exposure modifier for apprentice welders or welders with minimal training.

Hair Manganese as an Exposure Biomarker among Welders

Quantifying exposure and dose to manganese (Mn) containing airborne particles in welding fume presents many challenges. Common biological markers such as Mn in blood or Mn in urine have not proven to be practical biomarkers even in studies where positive associations were observed. However, hair Mn (MnH) as a biomarker has the advantage over blood and urine that it is less influenced by short-term variability of Mn exposure levels because of its slow growth rate. The objective of this study was to determine whether hair can be used as a biomarker for welders exposed to manganese. Hair samples (1cm) were collected from 47 welding school students and individual air Mn (MnA) exposures were measured for each subject. MnA levels for all days were estimated with a linear mixed model using welding type as a predictor. A 30-day time-weighted average MnA (MnA30d) exposure level was calculated for each hair sample. The association between MnH and MnA30d levels was then assessed. A linear relationship was observed between log-transformed MnA30d and log-transformed MnH. Doubling MnA30d exposure levels yields a 20% (95% confidence interval: 11-29%) increase in MnH. The association was similar for hair washed following two different wash procedures designed to remove external contamination. Hair shows promise as a biomarker for inhaled Mn exposure given the presence of a significant linear association between MnH and MnA30d levels.

Cardiovascular effects in rats after intratracheal instillation of metal welding particles

Studies have indicated that pulmonary exposure to welding fumes can induce a series of adverse effects in the respiratory system, including infection, bronchitis, siderosis and decreased pulmonary function. Recent clinical and epidemiological studies have found that pulmonary exposure to welding fumes is also associated with a higher incidence of cardiovascular events. However, there is insufficient evidence to confirm a direct effect of welding fumes on the cardiovascular system. The present study investigated the effects of pulmonary exposure to welding fumes on the heart and the vascular system in rats. Two chemically distinct welding fumes generated from manual metal arc-hard surfacing (MMA-HS) and gas metal arc-mild steel (GMA-MS) welding were tested. Three groups of rats were instilled intratracheally with MMA-HS (2 mg/rat), GMA-MS (2 mg/rat) or saline as control once a week for seven weeks. On days 1 and 7 after the last treatment, basal cardiovascular function and the cardiovascular response to increasing doses of adrenoreceptor agonists were assessed. MMA-HS treatment reduced the basal levels of left ventricle end-systolic pressure and dP/dt(max) at 1 day post-treatment, and decreased dP/dt(min) in response to isoproterenol (ISO) at 7 days post-treatment. Unlike MMA-HS, GMA-MS only affected left ventricular end-diastolic pressure in response to ISO at 7 days post-treatment. Treatment with MMA-HS or GMA-MS did not alter heart rate and blood pressure. Our findings suggest that exposure to different welding fumes can induce different adverse effects on the cardiovascular system, and that cardiac contractility may be a sensitive indicator of cardiovascular dysfunction.

Manganese Fractionation Using a Sequential Extraction Method to Evaluate Welders' Shielded Metal Arc Welding Exposures During Construction Projects in Oil Refineries

The National Institute for Occupational Safety and Health has conducted an occupational exposure assessment study of manganese (Mn) in welding fume of construction workers rebuilding tanks, piping, and process equipment at two oil refineries. The objective of this study was to evaluate exposures to different Mn fractions using a sequential extraction procedure. Seventy-two worker-days were monitored for either total or respirable Mn during stick welding and associated activities both within and outside of confined spaces. The samples were analyzed using an experimental method to separate different Mn fractions by valence states based on selective chemical solubility. The full-shift total particulate Mn time-weighted average (TWA) breathing zone concentrations ranged from 0.013-29 for soluble Mn in a mild ammonium acetate solution; from 0.26-250 for Mn(0,2+) in acetic acid; from non-detectable (ND) - 350 for Mn(3+,4+) in hydroxylamine-hydrochloride; and from ND - 39 micrograms per cubic meter (μg/m(3)) for insoluble Mn fractions in hydrochloric and nitric acid. The summation of all Mn fractions in total particulate TWA ranged from 0.52-470 μg/m(3). The range of respirable particulate Mn TWA concentrations were from 0.20-28 for soluble Mn; from 1.4-270 for Mn(0,2+); from 0.49-150 for Mn(3+,4+); from ND - 100 for insoluble Mn; and from 2.0-490 μg/m(3) for Mn (sum of fractions). For all jobs combined, total particulate TWA GM concentrations of the Mn(sum) were 99 (GSD = 3.35) and 8.7 (GSD = 3.54) μg/m(3) for workers inside and outside of confined spaces; respirable Mn also showed much higher levels for welders within confined spaces. Regardless of particle size and confined space work status, Mn(0,2+) fraction was the most abundant followed by Mn(3+,4+) fraction, typically >50% and ∼30-40% of Mn(sum), respectively. Eighteen welders' exposures exceeded the ACGIH Threshold Limit Values for total Mn (100 μg/m(3)) and 25 exceeded the recently adopted respirable Mn TLV (20 μg/m(3)). This study shows that a welding fume exposure control and management program is warranted, especially for welding jobs in confined spaces.

Variance components of short-term biomarkers of manganese exposure in an inception cohort of welding trainees

Various biomarkers of exposure have been explored as a way to quantitatively estimate an internal dose of manganese (Mn) exposure, but given the tight regulation of Mn in the body, inter-individual variability in baseline Mn levels, and variability in timing between exposure and uptake into various biological tissues, identification of a valuable and useful biomarker for Mn exposure has been elusive. Thus, a mixed model estimating variance components using restricted maximum likelihood was used to assess the within- and between-subject variance components in whole blood, plasma, and urine (MnB, MnP, and MnU, respectively) in a group of nine newly-exposed apprentice welders, on whom baseline and subsequent longitudinal samples were taken over a three month period. In MnB, the majority of variance was found to be between subjects (94%), while in MnP and MnU the majority of variance was found to be within subjects (79% and 99%, respectively), even when controlling for timing of sample. While blood seemed to exhibit a homeostatic control of Mn, plasma and urine, with the majority of the variance within subjects, did not. Results presented here demonstrate the importance of repeat measure or longitudinal study designs when assessing biomarkers of Mn, and the spurious associations that could result from cross-sectional analyses.

Significance and Usefulness of Biomarkers of Exposure to Manganese

Manganese (Mn) accomplishes functions essential to maintaining human health, but at the same time this trace element can be toxic at low levels of exposure and accurate estimation of internal exposure is needed. A biomarker of exposure to Mn is meaningful only if there is sufficient knowledge of the toxicokinetics determining its presence in a biological medium (e.g. whole blood, plasma, urine, hair, nail). Moreover, biological monitoring of exposure to Mn is useful only when the biomarker is sufficiently specific and sensitive to distinguish exposed from non-exposed subjects, when it is dose-related to the external exposure (current, recent, or time-integrated), and when it displays reasonable dose–effect/response relationships with the occurrence of adverse effects on the central nervous system, the critical target for Mn exposure. Human investigations in which biomarkers of Mn exposure meet all these criteria are hard to locate. Overall, the available studies report poor or no associations on an individual basis between external (Mn in air or drinking water) and internal (Mn in blood, urine, hair, or nail) Mn exposure indices. This may be to some extent explained by features inherent of the Mn metabolism (homeostatic control), the Mn biomarker's half-life with respect to the exposure window, and the variable nature of external exposure scenarios. Studies particularly dealing with Mn inhalation exposure, different or poorly described methodological approaches, or air sampling strategies may render direct comparison and interpretation of results a tedious task. Nevertheless, several studies report significant dose–effect associations between biomarkers of Mn exposure and subclinical deficits of psychomotor or neuropsychological test performances. Because directly associated with the site of toxic action and providing the magnetic resonance imaging is done no later than three months after Mn exposure ceased, the Mn T1 relaxation time is potentially the better biomarker of Mn exposure in a clinical context (e.g. after long-term parenteral nutrition, chronic liver failure, methcathinone drug abuse). Magnetic resonance imaging is, however, unpractical as a tool for biological monitoring of exposure to Mn in the occupational setting (inhalation) and in the general population (air, drinking water). In conclusion, it would be inappropriate to recommend, on the basis of the currently available evidence, a reliable well-validated biomarker of exposure to Mn, or to establish a health-based threshold value for subclinical neurotoxic effects.

Neurological outcomes associated with low-level manganese exposure in an inception cohort of asymptomatic welding trainees

OBJECTIVE

Long-term, high-level exposure to manganese (Mn) is associated with impaired central nervous system (CNS) function. We quantitatively explored relations between low-level Mn exposure and selected neurological outcomes in a longitudinal inception cohort of asymptomatic welder trainees.

METHODS

Welders with no previous occupational Mn exposure were observed approximately every three months over the course of the five-quarter traineeship. Fifty-six welders were assessed for motor function using the Unified Parkinson Disease Rating Scale motor subsection part 3 (UPDRS3) and Grooved Pegboard tests. A subset of 17 also had MRI scans to assess T1-weighted indices. Personal exposure to Mn in welding fume was quantitatively assessed during the study period using a mixed model to obtain estimates of subject-specific exposure level by welding type. These estimates were summed to estimate cumulative exposure at the time of each neurological outcome test.

RESULTS

When adjusting for possible learning effects, there were no associations between cumulative exposure and UPDRS3 score or Grooved Pegboard time. T1-weighted indices of the basal ganglia (caudate, anterior putamen, posterior putamen, and combined basal ganglia, but not the pallidal index) exhibited statistically significant increases in signal intensity in relation to increased cumulative Mn exposure.

CONCLUSIONS

This study demonstrates that T1-weighted changes can be detected in the brain even at very low levels of exposure among humans before any clinically evident deficits. This suggests that with continued follow-up we could identify a T1 threshold of toxicity at which clinical symptoms begin to manifest.

Blood manganese as an exposure biomarker: state of the evidence

Despite evidence of adverse health effects resulting from exposure to manganese (Mn), biomarkers of exposure are poorly understood. To enhance understanding, mean blood Mn (MnB) and mean air Mn (MnA) were extracted from 63 exposure groups in 24 published papers, and the relationship was modeled using segmented regression. On a log/log scale, a positive association between MnA and MnB was observed among studies reporting MnA concentrations above about 10 μg/m(3), although interpretation is limited by largely cross-sectional data, study design variability, and differences in exposure monitoring methods. Based on the results of the segmented regression, we hypothesize that below the concentration of about 10 μg/m(3), Mn in the body is dominated by dietary Mn, and additional inhaled Mn only causes negligible changes in Mn levels unless the inhaled amount is substantial. However, stronger study designs are required to account for temporal characteristics of the MnA to MnB relationships that reflect the underlying physiology and toxicokinetics of Mn uptake and distribution. Thus, we present an inception cohort study design we have conducted among apprentice welders, and the analytical strengths this study design offers. To determine if blood could be a useful biomarker for Mn to be utilized by industrial hygienists in general industry requires additional time-specific analyses, which our inception cohort study design will allow.

The need for a comprehensive approach to managing confined space entry: summary of the literature and recommendations for next steps

Despite all the regulatory and standard-setting efforts that have been made in North America, judging from the most recent statistics many fatal incidents related to work in confined spaces still occur. In Canada, fatal incidents in the province of Quebec reveal failures in and absence of the identification and preparation of work situations in confined spaces and in risk management. In this study, we performed a literature review consisting of 77 documents on existing hazards and risk assessment for confined spaces. Moreover, we formulated proposals regarding the design of specific and improved tools for assessing such risks. We found that atmospheric hazards monopolized attention in the literature on confined spaces, while risk estimation specific to confined space interventions received little practical coverage overall, apart from atmospheric hazards. The parameters used to establish classes or groupings of confined spaces in existing tools were imprecise. The development of a risk analysis process that is (i) more systematic and based on the concepts recognized in risk management standards, (ii) multidisciplinary, and (iii) adapted to the specific characteristics of confined spaces is therefore needed. Such a process will better support managers and occupational health and safety (OH&S) personnel in their efforts to prioritize and reduce risks. Suggestions on such a risk analysis tool and categorization of interventions in confined spaces are proposed in this article. Lastly, risk analysis tools adapted to confined space interventions are needed to ensure the inherently safe design of these spaces.

Manganism in the 21st century: the Hanninen lecture

Since the original description of the health effects of inhaled occupational manganese (Mn) by Couper in 1837, an extensive literature details the clinical syndrome and pathophysiology of what was thought to be a rare condition. In the last decade, conventional wisdom regarding the clinicopathological effects of Mn has been challenged. Past exposures to Mn were an order of magnitude higher than modern exposures in developed countries; therefore, the clinical syndrome seen in the time of Couper is no longer typical of modern Mn exposed workers. Parkinsonism (rigidity, bradykinesia, rest tremor, and postural instability) is present in 15% of Mn-exposed workers in welding industries, and these parkinsonian signs are associated with reduced health status and quality of life. These parkinsonian signs also overlap considerably with the clinical findings seen in early stages of Parkinson's disease (PD); although, molecular imaging suggests that Mn-exposed workers have dopaminergic dysfunction in a pattern unique from PD. Furthermore, geographic information system studies demonstrate that regions of the US with high industrial Mn emissions have an increased incidence of PD and increased PD associated mortality. This review will contrast historical, descriptive human studies in Mn-exposed subjects with more recent data and will suggest a research agenda for the 21st century.

Levels and predictors of airborne and internal exposure to manganese and iron among welders

We investigated airborne and internal exposure to manganese (Mn) and iron (Fe) among welders. Personal sampling of welding fumes was carried out in 241 welders during a shift. Metals were determined by inductively coupled plasma mass spectrometry. Mn in blood (MnB) was analyzed by graphite furnace atom absorption spectrometry. Determinants of exposure levels were estimated with multiple regression models. Respirable Mn was measured with a median of 62 (inter-quartile range (IQR) 8.4-320) μg/m(3) and correlated with Fe (r=0.92, 95% CI 0.90-0.94). Inhalable Mn was measured with similar concentrations (IQR 10-340 μg/m(3)). About 70% of the variance of Mn and Fe could be explained, mainly by the welding process. Ventilation decreased exposure to Fe and Mn significantly. Median concentrations of MnB and serum ferritin (SF) were 10.30 μg/l (IQR 8.33-13.15 μg/l) and 131 μg/l (IQR 76-240 μg/l), respectively. Few welders were presented with low iron stores, and MnB and SF were not correlated (r=0.07, 95% CI -0.05 to 0.20). Regression models revealed a significant association of the parent metal with MnB and SF, but a low fraction of variance was explained by exposure-related factors. Mn is mainly respirable in welding fumes. Airborne Mn and Fe influenced MnB and SF, respectively, in welders. This indicates an effect on the biological regulation of both metals. Mn and Fe were strongly correlated, whereas MnB and SF were not, likely due to higher iron stores among welders.

Exposure to inhalable, respirable, and ultrafine particles in welding fume

This investigation aims to explore determinants of exposure to particle size-specific welding fume. Area sampling of ultrafine particles (UFP) was performed at 33 worksites in parallel with the collection of respirable particles. Personal sampling of respirable and inhalable particles was carried out in the breathing zone of 241 welders. Median mass concentrations were 2.48 mg m(-3) for inhalable and 1.29 mg m(-3) for respirable particles when excluding 26 users of powered air-purifying respirators (PAPRs). Mass concentrations were highest when flux-cored arc welding (FCAW) with gas was applied (median of inhalable particles: 11.6 mg m(-3)). Measurements of particles were frequently below the limit of detection (LOD), especially inside PAPRs or during tungsten inert gas welding (TIG). However, TIG generated a high number of small particles, including UFP. We imputed measurements <LOD from the regression equation with manganese to estimate determinants of the exposure to welding fume. Concentrations were mainly predicted by the welding process and were significantly higher when local exhaust ventilation (LEV) was inefficient or when welding was performed in confined spaces. Substitution of high-emission techniques like FCAW, efficient LEV, and using PAPRs where applicable can reduce exposure to welding fume. However, harmonizing the different exposure metrics for UFP (as particle counts) and for the respirable or inhalable fraction of the welding fume (expressed as their mass) remains challenging.

Estimation of particulate mass and manganese exposure levels among welders

BACKGROUND

Welders are frequently exposed to Manganese (Mn), which may increase the risk of neurological impairment. Historical exposure estimates for welding-exposed workers are needed for epidemiological studies evaluating the relationship between welding and neurological or other health outcomes. The objective of this study was to develop and validate a multivariate model to estimate quantitative levels of welding fume exposures based on welding particulate mass and Mn concentrations reported in the published literature.

METHODS

Articles that described welding particulate and Mn exposures during field welding activities were identified through a comprehensive literature search. Summary measures of exposure and related determinants such as year of sampling, welding process performed, type of ventilation used, degree of enclosure, base metal, and location of sampling filter were extracted from each article. The natural log of the reported arithmetic mean exposure level was used as the dependent variable in model building, while the independent variables included the exposure determinants. Cross-validation was performed to aid in model selection and to evaluate the generalizability of the models.

RESULTS

A total of 33 particulate and 27 Mn means were included in the regression analysis. The final model explained 76% of the variability in the mean exposures and included welding process and degree of enclosure as predictors. There was very little change in the explained variability and root mean squared error between the final model and its cross-validation model indicating the final model is robust given the available data.

CONCLUSIONS

This model may be improved with more detailed exposure determinants; however, the relatively large amount of variance explained by the final model along with the positive generalizability results of the cross-validation increases the confidence that the estimates derived from this model can be used for estimating welder exposures in absence of individual measurement data.

Pulmonary toxicity and extrapulmonary tissue distribution of metals after repeated exposure to different welding fumes

Welders are exposed to fumes with different metal profiles. The goals of this study were to compare lung responses in rats after treatment with chemically different welding fumes and to examine the extrapulmonary fate of metals after deposition in the lungs. Rats were treated by intratracheal instillation (0.5 mg/rat, once a week for 7 weeks) with gas metal arc-mild steel (GMAW-MS) or manual metal arc-hardsurfacing (MMAW-HS) welding fumes. Controls were treated with saline. At 1, 4, 35, and 105 days after the last treatment, lung injury and inflammation were measured, and elemental analysis of different organs was determined to assess metal clearance. The MMAW-HS fume was highly water-soluble and chemically more complex with higher levels of soluble Mn and Cr compared to the GMAW-MS fume. Treatments with the GMAW-MS fume had no effect on toxicity when compared with controls. The MMAW-HS fume induced significant lung damage early after treatment that remained elevated until 35 days. Metals associated with each fume sample was cleared at different rates from the lungs. Mn was cleared from the lungs at a faster rate and to a greater extent compared to the other metals over the 105-day recovery period. Mn and Cr in the MMAW-HS fume translocated from the respiratory tract and deposited in other organs. Importantly, increased deposition of Mn, but not other metals, was observed in discrete brain regions, including dopamine-rich areas (e.g., striatum and midbrain).

Personal exposure to metal fume, NO2, and O3 among production welders and non-welders

The objective of this study was to characterize personal exposures to welding-related metals and gases for production welders and non-welders in a large manufacturing facility. Welding fume metals and irritant gases nitrogen dioxide (NO(2)) and ozone (O(3)) were sampled for thirty-eight workers. Personal exposure air samples for welding fume metals were collected on 37 mm open face cassettes and nitrogen dioxide and ozone exposure samples were collected with diffusive passive samplers. Samples were analyzed for metals using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and welding fume metal exposure concentrations were defined as the sum of welding-related metals mass per volume of air sampled. Welding fume metal exposures were highly variable among similar types of welding while NO(2) and O(3) exposure were less variable. Welding fume metal exposures were significantly higher 474 μg/m(3) for welders than non-welders 60 μg/m(3) (p=0.001). Welders were exposed to higher concentrations of NO(2) and O(3) than non-welders but the differences were not statistically significant. Welding fume metal exposure concentrations for welders performing gas metal arc welding (GMAW) and shielded metal arc welding (SMAW) were higher than welders performing gas tungsten arc welding (GTAW). Non-welders experienced exposures similar to GTAW welders despite a curtain wall barrier separating welding and non-welding work areas.

Mitochondrial dysfunction and loss of Parkinson's disease-linked proteins contribute to neurotoxicity of manganese-containing welding fumes

Welding generates complex metal aerosols, inhalation of which is linked to adverse health effects among welders. An important health concern of welding fume (WF) exposure is neurological dysfunction akin to Parkinson's disease (PD), thought to be mediated by manganese (Mn) in the fumes. Also, there is a proposition that welding might accelerate the onset of PD. Our recent findings link the presence of Mn in the WF with dopaminergic neurotoxicity seen in rats exposed to manual metal arc-hard surfacing (MMA-HS) or gas metal arc-mild steel (GMA-MS) fumes. To elucidate the molecular mechanisms further, we investigated the association of PD-linked (Park) genes and mitochondrial function in causing dopaminergic abnormality. Repeated instillations of the two fumes at doses that mimic ∼1 to 5 yr of worker exposure resulted in selective brain accumulation of Mn. This accumulation caused impairment of mitochondrial function and loss of tyrosine hydroxylase (TH) protein, indicative of dopaminergic injury. A fascinating finding was the altered expression of Parkin (Park2), Uchl1 (Park5), and Dj1 (Park7) proteins in dopaminergic brain areas. A similar regimen of manganese chloride (MnCl(2)) also caused extensive loss of striatal TH, mitochondrial electron transport components, and Park proteins. As mutations in PARK genes have been linked to early-onset PD in humans, and because welding is implicated as a risk factor for parkinsonism, PARK genes might play a critical role in WF-mediated dopaminergic dysfunction. Whether these molecular alterations culminate in neurobehavioral and neuropathological deficits reminiscent of PD remains to be ascertained.

Manganese, iron, and total particulate exposures to welders

Welders are exposed to a variety of metal fumes, including manganese, that may elevate the risk for neurological disease. This study examines several large data sets to characterize manganese, iron, and total particulate mass exposures resulting from welding operations. The data sets contained covariates for a variety of exposure modifiers, including the presence of ventilation, the degree of confinement, and the location of the personal sampler (i.e., behind or in front of the welding helmet). The analysis suggests that exposures to manganese are frequently at or above the current ACGIH(R) threshold limit value of 0.2 mg/m(3). In addition, there is evidence that local exhaust ventilation can control the exposures to manganese and total fume but that mechanical ventilation may not. The data suggest that higher exposures are associated with a greater degree of enclosure, particularly when local exhaust ventilation is absent. Samples taken behind the helmet were, in general, lower than those measured outside of it. There were strong correlations among manganese, iron, and total particulate mass exposures, suggesting simple equations to estimate one fume component from any of the others.

Two-zone model application to breathing zone and area welding fume concentration data

This study assessed a professional pipefitter/welder performing shielded metal arc welding on carbon steel under field conditions. The resulting breathing zone (near field) and area (far field) welding fume concentration data were applied to the two-zone model for the purpose of determining field-derived personal exposure emission (generation) rates during actual welding work. The study is unique in that one welder was evaluated under high production conditions for 2 days at two different welding locations: a boiler room and a breezeway. Samples were collected and analyzed for total particulate following NIOSH Method 0500 and for select metals following NIOSH Method 7300. Breezeway average personal breathing zone sample total particulate concentrations ranged from 2.89 mg/m(3) to 4.38 mg/m(3), Fe concentrations ranged from 0.53 to 0.63 mg/m(3), and Mn concentrations ranged from 0.10 to 0.12 mg/m(3). The boiler room average personal breathing zone sample total particulate concentrations ranged from 4.73 mg/m(3) to 5.90 mg/m(3), Fe concentrations ranged from 0.48 to 0.85 mg/m(3), and Mn concentrations ranged from 0.06 to 0.16 mg/m(3). Average arc times ranged from 20 to 25% of the total sampling time. Both tracer gas and anemometer techniques were used to estimate ventilation of the boiler room. The steady-state form of the two-zone model was applied to long-term and short-term sample total particulate, Fe, and Mn concentrations obtained during welding in the boiler room and breezeway. The average generation rate in the boiler room was 39.2 mg/min for TP, 6.4 mg/min for Fe, and 1.3 mg/min for Mn. The average generation rate in the breezeway was 40.0 mg/min for TP, 6.6 mg/min for Fe, and 1.2 mg/min for Mn. The field-based generation rates were considerably lower than laboratory-derived published emission rates of between 280 and 650 mg/min for TP. This study emphasizes the need for field-derived welding fume generation rates and showed the personal breathing zone and area sample concentrations can be described by the two-zone model in a way that may help the industrial hygienist estimate exposures. [Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Occupational and Environmental Hygiene for the following free supplemental resource: Tables detailing the personal breathing zone and average area sample results for breezeway welding and boiler room welding, two-zone modeling results, and boiler room welding personal breathing zone and area sample results with mixing fans on.].

A headset-mounted mini sampler for measuring exposure to welding aerosol in the breathing zone

There is a need for a small personal aerosol sampler for measuring occupational exposure to airborne particles in the breathing zone. Existing aerosol samplers are too large to be mounted inside modern welder's protective equipment without disturbing the worker. A headset-mounted mini sampler has been developed to fill this gap with focus on manganese exposure. This mini sampler is easy to use and can be mounted inside modern, slimline welder's face shield. The mini sampler is based on a commercially available 13-mm filter holder that has been modified to incorporate an inlet nozzle made of aluminium. The nominal flow rate of the mini sampler is 0.75 l min(-1). The mini sampler is to be worn mounted on a headset, modified from professional microphone headsets. Several aspects related to using the mini sampler have been tested by personal and static sampling at five workplaces and in the laboratory. Four headset models were tested for their suitability as a sampler holder, of which three models were accepted by the welders. The sampling bias of the mini sampler versus the IOM sampler and the open-face 25-mm filter holder, respectively, depends on the size distribution of the sampled aerosol. At the lowest encountered mass concentration ratio of the open-face 25-mm filter holder to the IOM sampler (0.65), the sampling bias of the mini sampler versus the IOM sampler is approximately -26% and versus the open-face 25-mm filter holder is approximately +12%. For manganese, the negative root mean square (RMS) sampling bias of the mini sampler versus the IOM sampler is -0.046 and versus the open-face 25-mm filter holder is non-significant. Both these biases are statistically non-significant. The mini sampler can therefore be employed for determining welders' occupational exposure to manganese. The pressure drop across the filter can become excessive due to the small filtration area. Compared to the Casella Apex pump, the SKC AirChek2000 pump was generally found to be able to keep its flow rate constant within +/-5% at higher concentrations and for longer sampling times. Our results indicate that the inhalable fraction of the welding aerosol mass at the visited plants only consisted of 25-55% welding fume particles (agglomerates of coagulated particles generated by nucleation/condensation). The rest of the mass is made up of particles from spattering and grinding. More than 65% of manganese is generally found in the fume particles. The weighing precision of 13-mm filters is 2.2 microg. The RMS sample loss due to transport when loaded samples are shipped by mail in padded envelopes is 6 microg. Both figures are very low in comparison to the mass expected to be collected by personal sampling, generally exceeding 200 microg. The headset-mounted mini sampler is user-friendly, easy to adjust individually, does not disturb the welder during sampling and allows sampling inside personal protective equipment. The headset mounting arrangement improves personal sampling as it maintains the sampler close to the nose/mouth during the whole sampling period. This study shows that the developed headset-mounted mini sampler is suitable for assessing exposure to manganese in welding aerosol.

Manganese and welding fume exposure and control in construction

Overexposure to welding fume constituents, particularly manganese, is of concern in the construction industry due to the prevalence of welding and the scarcity of engineering controls. The control effectiveness of a commercially available portable local exhaust ventilation (LEV) unit was assessed. It consisted of a portable vacuum and a small bell-shaped hood connected by a flexible 2 inch (50.8 mm) diameter hose, in both experimental and field settings. The experimental testing was done in a semienclosed booth at a pipefitter training facility. Five paired trials of LEV control vs. no control, each approximately 1 hr in duration and conducted during two successive welds of 6 inch (152.4 mm) diameter carbon steel pipe were run in random order. Breathing zone samples were collected outside the welding hood during each trial. In the field scenario, full-shift breathing zone samples were collected from two pipefitters welding carbon steel pipe for a chiller installation on a commercial construction project. Eight days of full-shift sampling were conducted on both workers (n = 16), and the LEV was used by one of the two workers on an alternating basis for 7 of the days. All samples were collected with personal sample pumps calibrated at 2 L/min. Filter cassettes were analyzed for total particulate and manganese concentration by a certified laboratory. In the experimental setting, use of the portable LEV resulted in a 75% reduction in manganese exposure (mean 13 microg/m(3) vs. 51 microg/m(3); p < 0.05) and a 60% reduction in total particulate (mean 0.74 mg/m(3) vs. 1.83 mg/m(3); p < 0.05). In the field setting, LEV use resulted in a 53% reduction in manganese exposure (geometric mean 46 microg/m(3) vs. 97 microg/m(3); p < 0.05) but only a 10% reduction in total particulate (geometric mean 4.5 mg/m(3) vs. 5.0 mg/m(3); p > 0.05). These results demonstrate that LEV use can reduce manganese exposure associated with welding tasks in construction.

State-of-the-science review: Does manganese exposure during welding pose a neurological risk?

Recent studies report that exposure to manganese (Mn), an essential component of welding electrodes and some steels, results in neurotoxicity and/or Parkinson's disease (PD) in welders. This "state-of-the-science" review presents a critical analysis of the published studies that were conducted on a variety of Mn-exposed occupational cohorts during the last 100 yr, as well as the regulatory history of Mn and welding fumes. Welders often perform a variety of different tasks with varying degrees of duration and ventilation, and hence, to accurately assess Mn exposures that occurred in occupational settings, some specific information on the historical work patterns of welders is desirable. This review includes a discussion of the types of exposures that occur during the welding process--for which limited information relating airborne Mn levels with specific welding activities exists--and the human health studies evaluating neurological effects in welders and other Mn-exposed cohorts, including miners, millers, and battery workers. Findings and implications of studies specifically conducted to evaluate neurobehavioral effects and the prevalence of PD in welders are also discussed. Existing exposure data indicate that, in general, Mn exposures in welders are less than those associated with the reports of clinical neurotoxicity (e.g., "manganism") in miners and smelter workers. It was also found that although manganism was observed in highly exposed workers, the scant exposure-response data available for welders do not support a conclusion that welding is associated with clinical neurotoxicity. The available data might support the development of reasonable "worst-case" exposure estimates for most welding activities, and suggest that exposure simulation studies would significantly refine such estimates. Our review ends with a discussion of the data gaps and areas for future research.

Particulate and gaseous emissions when welding aluminum alloys

Fabrication and repair of aluminum components and structures commonly involves the use of electric arc welding. The interaction of the arc and the metal being welded generates ultraviolet radiation, metallic oxides, fumes, and gases. Aluminum is seldom used as the pure metal but is often alloyed with other metals to improve strength and other physical properties. Therefore, the exact composition of any emissions will depend on the welding process and the particular aluminum alloy being welded. To quantify such emissions, The Aluminum Association sponsored several studies to characterize arc welding emissions by the gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) processes for various combinations of base and filler alloys. In all cases, the tests were conducted under conditions that could be found in a production weld shop without forced ventilation. The concentrations of each analyte that a welder could be exposed to were greatly affected by the welding process, the composition of the base and filler alloys, the position of the welder, and the welding helmet. The results obtained can be used by employers to identify and control potential hazards associated with the welding of aluminum alloys and can provide the basis for hazard communication to employees involved in the welding of these alloys.