TERT-independent telomere elongation and shelterin dysregulation after pulmonary exposure to stainless-steel welding fume in-vivo.

Telomeres are inert DNA sequences (TTAGGG) at the end of chromosomes that protect genetic information and maintain DNA integrity. Emerging evidence has demonstrated that telomere alteration can be closely related to occupational exposure and the development of various disease conditions, including cancer. However, the functions and underlying molecular mechanisms of telomere alteration and shelterin dysregulation after welding fume exposures have not been broadly defined. In this study, we analyzed telomere length and shelterin complex proteins in peripheral blood mononuclear cells (PBMCs) and in lung tissue recovered from male Sprague-Dawley rats following exposure by intratracheal instillation (ITI) to 2 mg/rat of manual metal arc-stainless steel (MMA-SS) welding fume particulate or saline (vehicle control). PBMCs and lung tissue were harvested at 30 d after instillation. Our study identified telomere elongation and shelterin dysregulation in PBMCs and lung tissue after welding fume exposure. Mechanistically, telomere elongation was independent of telomerase reverse transcriptase (TERT) activation. Collectively, our findings demonstrated that welding fume-induced telomere elongation was (a) TERT-independent and (b) associated with shelterin complex dysregulation. It is possible that an alteration of telomere length and its regulatory proteins may be utilized as predictive biomarkers for various disease conditions after welding fume exposure. This needs further investigation.

In vivo and in vitro toxicity of a stainless-steel aerosol generated during thermal spray coating.

Thermal spray coating is an industrial process in which molten metal is sprayed at high velocity onto a surface as a protective coating. An automated electric arc wire thermal spray coating aerosol generator and inhalation exposure system was developed to simulate an occupational exposure and, using this system, male Sprague-Dawley rats were exposed to stainless steel PMET720 aerosols at 25 mg/m3 × 4 h/day × 9 day. Lung injury, inflammation, and cytokine alteration were determined. Resolution was assessed by evaluating these parameters at 1, 7, 14 and 28 d after exposure. The aerosols generated were also collected and characterized. Macrophages were exposed in vitro over a wide dose range (0-200 µg/ml) to determine cytotoxicity and to screen for known mechanisms of toxicity. Welding fumes were used as comparative particulate controls. In vivo lung damage, inflammation and alteration in cytokines were observed 1 day post exposure and this response resolved by day 7. Alveolar macrophages retained the particulates even after 28 day post-exposure. In line with the pulmonary toxicity findings, in vitro cytotoxicity and membrane damage in macrophages were observed only at the higher doses. Electron paramagnetic resonance showed in an acellular environment the particulate generated free radicals and a dose-dependent increase in intracellular oxidative stress and NF-kB/AP-1 activity was observed. PMET720 particles were internalized via clathrin and caveolar mediated endocytosis as well as actin-dependent pinocytosis/phagocytosis. The results suggest that compared to stainless steel welding fumes, the PMET 720 aerosols were not as overtly toxic, and the animals recovered from the acute pulmonary injury by 7 days.

Lung toxicity profile of inhaled copper-nickel welding fume in A/J mice.

Objective: Stainless steel welding creates fumes rich in carcinogenic metals such as chromium (Cr). Welding consumables devoid of Cr are being produced in an attempt to limit worker exposures to toxic and carcinogenic metals. The study objective was to characterize a copper-nickel (Cu-Ni) fume generated using gas metal arc welding (GMAW) and determine the pulmonary deposition and toxicity of the fume in mice exposed by inhalation. Materials and Methods: Male A/J mice (6-8 weeks of age) were exposed to air or Cu-Ni welding fumes for 2 (low deposition) or 4 (high deposition) hours/day for 10 days. Mice were sacrificed, and bronchoalveolar lavage (BAL), macrophage function, and histopathological analyses were performed at different timepoints post-exposure to evaluate resolution. Results and Discussion: Characterization of the fume indicated that most of the particles were between 0.1 and 1 µm in diameter, with a mass median aerodynamic diameter of 0.43 µm. Metal content of the fume was Cu (∼76%) and Ni (∼12%). Post-exposure, BAL macrophages had a reduced ability to phagocytose E. coli, and lung cytotoxicity was evident and significant (>12%-19% fold change). Loss of body weight was also significant at the early timepoints. Lung inflammation, the predominant finding identified by histopathology, was observed as a subacute response early that progressively resolved by 28 days with only macrophage aggregates remaining late (84 days). Conclusions: Overall, there was high acute lung toxicity with a resolution of the response in mice which suggests that the Cu-Ni fume may not be ideal for reducing toxic and inflammatory lung effects.

Review of the physicochemical properties and associated health effects of aerosols generated during thermal spray coating processes.

Thermal spray coating is a process that applies a molten metal product under pressure onto a surface. Although thermal spray processes have been used for decades, exposure to aerosols formed during thermal spray coating is an emerging risk. Reports indicate that high concentrations of aerosols composed of toxic metals (e.g. chromium) are generated in the workplace. A knowledge gap exists related to the physicochemical properties of thermal spray coating aerosols as well as any potential associated health effects. The objective of this manuscript was to review thermal spray coating and previous studies that have examined the aerosols produced from this process. A thermal spray coating generator and exposure system is also described that has recently been developed to further evaluate the physical and chemical properties of aerosols formed during thermal spray coating as well as to assess the possible health effects of this process in an effort to mitigate potential occupational health hazards related to the industry.

A possible relationship between telomere length and markers of neurodegeneration in rat brain after welding fume inhalation exposure.

Inhalation of welding fume (WF) can result in the deposition of toxic metals, such as manganese (Mn), in the brain and may cause neurological changes in exposed workers. Alterations in telomere length are indicative of cellular aging and, possibly, neurodegeneration. Here, we investigated the effect of WF inhalation on telomere length and markers of neurodegeneration in whole brain tissue in rats. Male Fischer-344 (F-344) rats were exposed by inhalation to stainless steel WF (20 mg/m3 x 3 h/d x 4 d/wk x 5 wk) or filtered air (control). Telomere length, DNA-methylation, gene expression of Trf1, Trf2, ATM, and APP, protein expression of p-Tau, α-synuclein, and presenilin 1 and 2 were assessed in whole brain tissue at 12 wk after WF exposure ended. Results suggest that WF inhalation increased telomere length without affecting telomerase in whole brain. Moreover, we observed that components of the shelterin complex, Trf1 and Trf2, play an important role in telomere end protection, and their regulation may be responsible for the increase in telomere length. In addition, expression of different neurodegeneration markers, such as p-Tau, presenilin 1-2 and α-synuclein proteins, were increased in brain tissue from the WF-exposed rats as compared to control. These findings suggest a possible correlation between epigenetic modifications, telomere length alteration, and neurodegeneration because of the presence of factors in serum after WF exposure that may cause extra-pulmonary effects as well as the translocation of potentially neurotoxic metals associated with WF to the central nervous system (CNS). Further studies are needed to investigate the brain region specificity and temporal response of these effects.

Inhalation of welding fumes reduced sperm counts and high fat diet reduced testosterone levels; differential effects in Sprague Dawley and Brown Norway rats.

BACKGROUND: Previous studies have shown that inhalation of welding fumes may induce pulmonary and systemic inflammation and organ accumulation of metal, to which spermatogenesis and endocrine function may be sensitive. Also obesity may induce low-grade systemic inflammation. This study aimed to investigate the effects on sperm production of inhaled metal nanoparticles from stainless steel welding, and the potential exacerbation by intake of a high fat diet. Both the inbred Brown Norway and the outbred Sprague Dawley rat strains were included to study the influence of strain on the detection of toxicity. Rats were fed regular or high fat (HF) diet for 24 weeks and were exposed to 20 mg/m3 of gas metal arc-stainless steel (GMA-SS) welding fumes or filtered air for 3 h/day, 4 days/week for 5 weeks, during weeks 7-12. Outcomes were assessed upon termination of exposure (week 12) and after recovery (week 24). RESULTS: At week 12, the GMA-SS exposure induced pulmonary inflammation in both strains, without consistent changes in markers of systemic inflammation (CRP, MCP-1, IL-6 and TNFα). GMA-SS exposure lowered daily sperm production compared to air controls in Sprague Dawley rats, but only in GMA-SS Brown Norway rats also fed the HF diet. Overall, HF diet rats had lower serum testosterone levels compared to rats on regular diet. Metal content in the testes was assessed in a limited number of samples in Brown Norway rats, but no increase was obsedrved. At week 24, bronchoalveolar lavage cell counts had returned to background levels for GMA-SS exposed Sprague Dawley rats but remained elevated in Brown Norway rats. GMA-SS did not affect daily sperm production statistically significantly at this time point, but testicular weights were lowered in GMA-SS Sprague Dawley rats. Serum testosterone remained lowered in Sprague Dawley rats fed the HF diet. CONCLUSION: Exposure to GMA-SS welding fumes lowered sperm production in two strains of rats, whereas high fat diet lowered serum testosterone. The effect on sperm counts was likely not mediated by inflammation or lowered testosterone levels. The studied reproductive outcomes seemed more prone to disruption in the Sprague Dawley compared to the Brown Norway strain.

The Fate of Inhaled Nanoparticles: Detection and Measurement by Enhanced Dark-field Microscopy.

Assessing the potential health risks for newly developed nanoparticles poses a significant challenge. Nanometer-sized particles are not generally detectable with the light microscope. Electron microscopy typically requires high-level doses, above the physiologic range, for particle examination in tissues. Enhanced dark-field microscopy (EDM) is an adaption of the light microscope that images scattered light. Nanoparticles scatter light with high efficiency while normal tissues do not. EDM has the potential to identify the critical target sites for nanoparticle deposition and injury in the lungs and other organs. This study describes the methods for EDM imaging of nanoparticles and applications. Examples of EDM application include measurement of deposition and clearance patterns. Imaging of a wide variety of nanoparticles demonstrated frequent situations where nanoparticles detected by EDM were not visible by light microscopy. EDM examination of colloidal gold nanospheres (10-100 nm diameter) demonstrated a detection size limit of approximately 15 nm in tissue sections. EDM determined nanoparticle volume density was directly proportional to total lung burden of exposed animals. The results confirm that EDM can determine nanoparticle distribution, clearance, transport to lymph nodes, and accumulation in extrapulmonary organs. Thus, EDM substantially improves the qualitative and quantitative microscopic evaluation of inhaled nanoparticles.

Altered ion transport in normal human bronchial epithelial cells following exposure to chemically distinct metal welding fume particles.

Welding fume inhalation causes pulmonary toxicity, including susceptibility to infection. We hypothesized that airway epithelial ion transport is a target of fume toxicity, and investigated the effects of fume particulates from manual metal arc-stainless steel (MMA-SS) and gas metal arc-mild steel (GMA-MS) on ion transport in normal human bronchial epithelium (NHBE) cultured in air-interface. MMA-SS particles, more soluble than GMA-MS particles, contain Cr, Ni, Fe and Mn; GMA-MS particles contain Fe and Mn. MMA-SS or GMA-MS particles (0.0167-166.7µg/cm2) were applied apically to NHBEs. After 18h transepithelial potential difference (Vt), resistance (Rt), and short circuit current (Isc) were measured. Particle effects on Na+ and Cl¯ channels and the Na+,K+,2Cl¯-cotransporter were evaluated using amiloride (apical), 5-nitro-2-[(3-phenylpropyl)amino]benzoic acid (NPPB, apical), and bumetanide (basolateral), respectively. MMA-SS (0.0167-16.7µg/cm2) increased basal Vt. Only 16.7µg/cm2 GMA-MS increased basal Vt significantly. MMA-SS or GMA-MS exposure potentiated Isc responses (decreases) to amiloride and bumetanide, while not affecting those to NPPB, GMA-MS to a lesser degree than MMA-SS. Variable effects on Rt were observed in response to amiloride, and bumetanide. Generally, MMA-SS was more potent in altering responses to amiloride and bumetanide than GMA-MS. Hyperpolarization occurred in the absence of LDH release, but decreases in Vt, Rt, and Isc at higher fume particulate doses accompanied LDH release, to a greater extent for MMA-SS. Thus, Na+ transport and Na+,K+,2Cl¯-cotransport are affected by fume exposure; MMA-MS is more potent than GMA-MS. Enhanced Na+ absorption and decreased airway surface liquid could compromise defenses against infection.

Inhalation of gas metal arc-stainless steel welding fume promotes lung tumorigenesis in A/J mice.

Epidemiologic studies suggest an increased risk of lung cancer with exposure to welding fumes, but controlled animal studies are needed to support this association. Oropharyngeal aspiration of collected "aged" gas metal arc-stainless steel (GMA-SS) welding fume has been shown by our laboratory to promote lung tumor formation in vivo using a two-stage initiation-promotion model. Our objective in this study was to determine whether inhalation of freshly generated GMA-SS welding fume also acts as a lung tumor promoter in lung tumor-susceptible mice. Male A/J mice received intraperitoneal (IP) injections of corn oil or the chemical initiator 3-methylcholanthrene (MCA; 10 µg/g) and 1 week later were exposed by whole-body inhalation to air or GMA-SS welding aerosols for 4 h/d × 4 d/w × 9 w at a target concentration of 40 mg/m3. Lung nodules were enumerated at 30 weeks post-initiation. GMA-SS fume significantly promoted lung tumor multiplicity in A/J mice initiated with MCA (16.11 ± 1.18) compared to MCA/air-exposed mice (7.93 ± 0.82). Histopathological analysis found that the increased number of lung nodules in the MCA/GMA-SS group were hyperplasias and adenomas, which was consistent with developing lung tumorigenesis. Metal deposition analysis in the lung revealed a lower deposited dose, approximately fivefold compared to our previous aspiration study, still elicited a significant lung tumorigenic response. In conclusion, this study demonstrates that inhaling GMA-SS welding fume promotes lung tumorigenesis in vivo which is consistent with the epidemiologic studies that show welders may be at an increased risk for lung cancer.

Pulmonary toxicity following acute coexposures to diesel particulate matter and α-quartz crystalline silica in the Sprague-Dawley rat.

The effects of acute pulmonary coexposures to silica and diesel particulate matter (DPM), which may occur in various mining operations, were investigated in vivo. Rats were exposed by intratracheal instillation (IT) to silica (50 or 233 µg), DPM (7.89 or 50 µg) or silica and DPM combined in phosphate-buffered saline (PBS) or to PBS alone (control). At one day, one week, one month, two months and three months postexposure bronchoalveolar lavage and histopathology were performed to assess lung injury, inflammation and immune response. While higher doses of silica caused inflammation and injury at all time points, DPM exposure alone did not. DPM (50 µg) combined with silica (233 µg) increased inflammation at one week and one-month postexposure and caused an increase in the incidence of fibrosis at one month compared with exposure to silica alone. To assess susceptibility to lung infection following coexposure, rats were exposed by IT to 233 µg silica, 50 µg DPM, a combination of the two or PBS control one week before intratracheal inoculation with 5 × 105 Listeria monocytogenes. At 1, 3, 5, 7 and 14 days following infection, pulmonary immune response and bacterial clearance from the lung were evaluated. Coexposure to DPM and silica did not alter bacterial clearance from the lung compared to control. Although DPM and silica coexposure did not alter pulmonary susceptibility to infection in this model, the study showed that noninflammatory doses of DPM had the capacity to increase silica-induced lung injury, inflammation and onset/incidence of fibrosis.

Exposure to welding fumes and lower airway infection with Streptococcus pneumoniae.

BACKGROUND: Welders are at increased risk of pneumococcal pneumonia. The mechanism for this association is not known. The capacity of pneumococci to adhere to and infect lower airway cells is mediated by host-expressed platelet-activating factor receptor (PAFR). OBJECTIVE: We sought to assess the effect of mild steel welding fumes (MS-WF) on PAFR-dependent pneumococcal adhesion and infection to human airway cells in vitro and on pneumococcal airway infection in a mouse model. METHODS: The oxidative potential of MS-WF was assessed by their capacity to reduce antioxidants in vitro. Pneumococcal adhesion and infection of A549, BEAS-2B, and primary human bronchial airway cells were assessed by means of quantitative bacterial culture and expressed as colony-forming units (CFU). After intranasal instillation of MS-WF, mice were infected with Streptococcus pneumoniae, and bronchoalveolar lavage fluid (BALF) and lung CFU values were determined. PAFR protein levels were assessed by using immunofluorescence and immunohistochemistry, and PAFR mRNA expression was assessed by using quantitative PCR. PAFR was blocked by CV-3988, and oxidative stress was attenuated by N-acetylcysteine. RESULTS: MS-WF exhibited high oxidative potential. In A549 and BEAS-2B cells MS-WF increased pneumococcal adhesion and infection and PAFR protein expression. Both CV-3988 and N-acetylcysteine reduced MS-WF-stimulated pneumococcal adhesion and infection of airway cells. MS-WF increased mouse lung PAFR mRNA expression and increased BALF and lung pneumococcal CFU values. In MS-WF-exposed mice CV-3988 reduced BALF CFU values. CONCLUSIONS: Hypersusceptibility of welders to pneumococcal pneumonia is in part mediated by the capacity of welding fumes to increase PAFR-dependent pneumococcal adhesion and infection of lower airway cells.

Bridging the gap between exposure assessment and inhalation toxicology: Some insights from the carbon nanotube experience.

The early incorporation of exposure assessment can be invaluable to help design, prioritize, and interpret toxicological studies or outcomes. The sum total of the exposure assessment findings combined with preliminary toxicology results allows for exposure-informed toxicological study design and the findings can then be integrated, together with available epidemiologic data, to provide health effect relevance. With regard to engineered nanomaterial inhalation toxicology in particular, a single type of material (e.g. carbon nanotube, graphene) can have a vast array of physicochemical characteristics resulting in the potential for varying toxicities. To compound the matter, the methodologies necessary to establish a material adequate for in vivo exposure testing raises questions on the applicability of the outcomes. From insights gained from evaluating carbon nanotubes, we recommend the following integrated approach involving exposure-informed hazard assessment and hazard-informed exposure assessment especially for materials as diverse as engineered nanomaterials: 1) market-informed identification of potential hazards and potentially exposed populations, 2) initial toxicity screening to drive prioritized assessments of exposure, 3) development of exposure assessment-informed chronic and sub-chronic in vivo studies, and 4) conduct of exposure- and hazard-informed epidemiological studies.

Comparison of cell counting methods in rodent pulmonary toxicity studies: automated and manual protocols and considerations for experimental design.

Pulmonary toxicity studies often use bronchoalveolar lavage (BAL) to investigate potential adverse lung responses to a particulate exposure. The BAL cellular fraction is counted, using automated (i.e. Coulter Counter®), flow cytometry or manual (i.e. hemocytometer) methods, to determine inflammatory cell influx. The goal of the study was to compare the different counting methods to determine which is optimal for examining BAL cell influx after exposure by inhalation or intratracheal instillation (ITI) to different particles with varying inherent pulmonary toxicities in both rat and mouse models. General findings indicate that total BAL cell counts using the automated and manual methods tended to agree after inhalation or ITI exposure to particle samples that are relatively nontoxic or at later time points after exposure to a pneumotoxic particle when the response resolves. However, when the initial lung inflammation and cytotoxicity was high after exposure to a pneumotoxic particle, significant differences were observed when comparing cell counts from the automated, flow cytometry and manual methods. When using total BAL cell count for differential calculations from the automated method, depending on the cell diameter size range cutoff, the data suggest that the number of lung polymorphonuclear leukocytes (PMN) varies. Importantly, the automated counts, regardless of the size cutoff, still indicated a greater number of total lung PMN when compared with the manual method, which agreed more closely with flow cytometry. The results suggest that either the manual method or flow cytometry would be better suited for BAL studies where cytotoxicity is an unknown variable.

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.

Oxidative stress and reduced responsiveness of challenged circulating leukocytes following pulmonary instillation of metal-rich particulate matter in rats.

Welding fume is an exposure that consists of a mixture of metal-rich particulate matter with gases (ozone, carbon monoxide) and/or vapors (VOCs). Data suggests that welders are immune compromised. Given the inability of pulmonary leukocytes to properly respond to a secondary infection in animal models, the question arose whether the dysfunction persisted systemically. Our aim was to evaluate the circulating leukocyte population in terms of cellular activation, presence of oxidative stress, and functionality after a secondary challenge, following welding fume exposure. Rats were intratracheally instilled (ITI) with PBS or 2 mg of welding fume collected from a stainless steel weld. Rats were sacrificed 4 and 24 h post-exposure and whole blood was collected. Whole blood was used for cellular differential counts, RNA isolation with subsequent microarray and Ingenuity Pathway Analysis, and secondary stimulation with LPS utilizing TruCulture technology. In addition, mononuclear cells were isolated 24 h post-exposure to measure oxidative stress by flow cytometry and confocal microscopy. Welding fume exposure had rapid effects on the circulating leukocyte population as identified by relative mRNA expression changes. Instillation of welding fume reduced inflammatory protein production of circulating leukocytes when challenged with the secondary stimulus LPS. The effects were not related to transcription, but were observed in conjunction with oxidative stress. These findings support previous studies of an inadequate pulmonary immune response following a metal-rich exposure and extend those findings showing leukocyte dysfunction occurs systemically.

Alterations in cardiomyocyte function after pulmonary treatment with stainless steel welding fume in rats.

Welding fume is composed of a complex of different metal particulates. Pulmonary exposure to different welding fumes may exert a negative impact on cardiac function, although the underlying mechanisms remain unclear. To explore the effect of welding fumes on cardiac function, Sprague-Dawley rats were exposed by intratracheal instillation to 2 mg/rat of manual metal arc hard surfacing welding fume (MMA-HS) once per week for 7 wk. Control rats received saline. Cardiomyocytes were isolated enzymatically at d 1 and 7 postexposure. Intracellular calcium ([Ca(2+)]i) transients (fluorescence ratio) were measured on the stage of an inverted phase-contrast microscope using a myocyte calcium imaging/cell length system. Phosphorylation levels of cardiac troponin I (cTnI) were determined by Western blot. The levels of nonspecific inflammatory marker C-reactive protein (CRP) and proinflammatory cytokine interleukin-6 (IL-6) in serum were measured by enzyme-linked immunosorbent assay (ELISA). Contraction of isolated cardiomyocytes was significantly reduced at d 1 and d 7 postexposure. Intracellular calcium levels were decreased in response to extracellular calcium stimulation at d 7 postexposure. Changes of intracellular calcium levels after isoprenaline hydrochloride (ISO) stimulation were not markedly different between groups at either time point. Phosphorylation levels of cTnI in the left ventricle were significantly lower at d 1 postexposure. The serum levels of CRP were not markedly different between groups at either time point. Serum levels of IL-6 were not detectable in both groups. Cardiomyocyte alterations observed after welding fume treatment were mainly due to alterations in intracellular calcium handling and phosphorylation levels of cTnI.

Neurotoxicity following acute inhalation of aerosols generated during resistance spot weld-bonding of carbon steel.

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). Some applications in manufacturing industry employ a variant welding technology known as "weld-bonding" that utilizes resistance spot welding, in combination with adhesives, for metal-to-metal welding. The presence of adhesives raises additional concerns about worker exposure to potentially toxic components like Methyl Methacrylate, Bisphenol A and volatile organic compounds (VOCs). Here, we investigated the potential neurotoxicological effects of exposure to welding aerosols generated during weld-bonding. Male Sprague-Dawley rats were exposed (25 mg/m³ targeted concentration; 4 h/day × 13 days) by whole-body inhalation to filtered air or aerosols generated by either weld-bonding with sparking (high metal, low VOCs; HM) or without sparking (low metal; high VOCs; LM). Fumes generated under these conditions exhibited complex aerosols that contained both metal oxide particulates and VOCs. LM aerosols contained a greater fraction of VOCs than HM, which comprised largely metal particulates of ultrafine morphology. Short-term exposure to LM aerosols caused distinct changes in the levels of the neurotransmitters, dopamine (DA) and serotonin (5-HT), in various brain areas examined. LM aerosols also specifically decreased the mRNA expression of the olfactory marker protein (Omp) and tyrosine hydroxylase (Th) in the olfactory bulb. Consistent with the decrease in Th, LM also reduced the expression of dopamine transporter (Slc6a3; Dat), as well as, dopamine D2 receptor (Drd2) in the olfactory bulb. In contrast, HM aerosols induced the expression of Th and dopamine D5 receptor (Drd5) mRNAs, elicited neuroinflammation and blood-brain barrier-related changes in the olfactory bulb, but did not alter the expression of Omp. Our findings divulge the differential effects of LM and HM aerosols in the brain and suggest that exposure to weld-bonding aerosols can potentially elicit neurotoxicity following a short-term exposure. However, further investigations are warranted to determine if the aerosols generated by weld-bonding can contribute to persistent long-term neurological deficits and/or neurodegeneration.

Effects of acute inhalation of aerosols generated during resistance spot welding with mild-steel on pulmonary, vascular and immune responses in rats.

Spot welding is used in the automotive and aircraft industries, where high-speed, repetitive welding is needed to join thin sections of metal. Epoxy adhesives are applied as sealers to the metal seams. Pulmonary function abnormalities and airway irritation have been reported in spot welders, but no animal toxicology studies exist. Therefore, the goal of this study was to investigate vascular, immune and lung toxicity measures after exposure to these metal fumes in an animal model. Male Sprague-Dawley rats were exposed by inhalation to 25 mg/m³ to either mild-steel spot welding aerosols with sparking (high metal, HM) or without sparking (low metal, LM) for 4 h/d for 3, 8 and 13 d. Shams were exposed to filtered air. Bronchoalveolar lavage (BAL), lung gene expression and ex vivo BAL cell challenge were performed to assess lung toxicity. Lung resistance (R(L)) was evaluated before and after challenge with inhaled methacholine (MCh). Functional assessment of the vascular endothelium in isolated rat tail arteries and leukocyte differentiation in the spleen and lymph nodes via flow cytometry was also done. Immediately after exposure, baseline R(L) was significantly elevated in the LM spot welding aerosols, but returned to control level by 24 h postexposure. Airway reactivity to MCh was unaffected. Lung inflammation and cytotoxicity were mild and transient. Lung epithelial permeability was significantly increased after 3 and 8 d, but not after 13 d of exposure to the HM aerosol. HM aerosols also caused vascular endothelial dysfunction and increased CD4+, CD8+ and B cells in the spleen. Only LM aerosols caused increased IL-6 and MCP-1 levels compared with sham after ex vivo LPS stimulation in BAL macrophages. Acute inhalation of mild-steel spot welding fumes at occupationally relevant concentrations may act as an irritant as evidenced by the increased R(L) and result in endothelial dysfunction, but otherwise had minor effects on the lung.

Development and characterization of a resistance spot welding aerosol generator and inhalation exposure system.

Limited information exists regarding the health risks associated with inhaling aerosols that are generated during resistance spot welding of metals treated with adhesives. Toxicology studies evaluating spot welding aerosols are non-existent. A resistance spot welding aerosol generator and inhalation exposure system was developed. The system was designed by directing strips of sheet metal that were treated with an adhesive to two electrodes of a spot welder. Spot welds were made at a specified distance from each other by a computer-controlled welding gun in a fume collection chamber. Different target aerosol concentrations were maintained within the exposure chamber during a 4-h exposure period. In addition, the exposure system was run in two modes, spark and no spark, which resulted in different chemical profiles and particle size distributions. Complex aerosols were produced that contained both metal particulates and volatile organic compounds (VOCs). Size distribution of the particles was multi-modal. The majority of particles were chain-like agglomerates of ultrafine primary particles. The submicron mode of agglomerated particles accounted for the largest portion of particles in terms of particle number. Metal expulsion during spot welding caused the formation of larger, more spherical particles (spatter). These spatter particles appeared in the micron size mode and accounted for the greatest amount of particles in terms of mass. With this system, it is possible to examine potential mechanisms by which spot welding aerosols can affect health, as well as assess which component of the aerosol may be responsible for adverse health outcomes.