Biomonitoring of exposure to multiple metal components in urine, hair and nails of apprentice welders performing shielded metal arc welding (SMAW)

Follow-up Biomonitoring Study of Metal Exposure in Apprentice Welders in Montreal, Quebec, During Gas Metal Arc Welding (GMAW)

Welding activities are known to expose workers to metal fumes, but few studies have focused on assessing the internal exposure of apprentices in learning environments. This study aimed at determining internal doses of metals in apprentices performing gas metal arc welding (GMAW) during their training course. A total of 85 apprentice welders were assessed, and multi-elements were measured in urine, hair, fingernail, and toenail samples collected at the beginning of the program, and at the beginning and end of GMAW practical training. Concentrations of welding fumes and metals were also determined in personal respirable air samples. Serial measurements of metal concentrations in urine and hair, which reflect more recent exposure, showed an increase in arsenic (As), chromium (Cr), iron (Fe), and manganese (Mn) (and to a lesser extent nickel (Ni)) levels at the end of the GMAW process. Metal concentrations in fingernails and toenails showed a time-dependent increase in Fe, Mn, and Ni (and to a lesser extent cobalt (Co)) levels, reflecting cumulative exposure. Levels of Mn and Fe were high in personal air samples with respective median concentrations (95th percentiles) of 21 (300) and 230 (1900) µg/m3. Results show that even short-term exposure to welding fumes in a learning environment leads to a significant increase in absorbed metal doses, particularly for Fe and Mn. This follow-up study confirmed the interest and usefulness of measuring multi-elements in multiple matrices to assess internal exposure to welding fumes and its applicability to occupational or even population exposure to metals.

MicroRNA Expression in Asymptomatic Welders: Implications for Biomarker Discovery for Environmentally-Linked Neurodegenerative Disorders

Chronic occupational exposure to metals in welding fumes has been implicated in the etiology of neurodegenerative diseases (NDDs), including Parkinson's disease (PD) and Alzheimer's disease (AD). Changes in microRNA (miRNA) expression have been associated with various neurodegenerative conditions. Circulating miRNAs, in particular, have emerged as promising, minimally invasive biomarkers for diagnosing and monitoring disease progression. This study was designed to characterize the expression of miRNAs in neuronally-enriched serum extracellular vesicles (EVs) among welders and non-welders to explore their potential link to metal concentrations and welding exposure measures and their potential as early diagnostic biomarkers for neurodegeneration. Serum samples from 39 welders and 27 healthy individuals were collected, and EV-enclosed miRNAs were extracted and analyzed. Also, whole blood metal concentrations and welding exposure measurements were obtained. Fifty miRNAs were found to be dysregulated in welders vs. non-welders, of which three (miR-16-5p, miR-93-5p, miR-486-5p) showing reduced expression and two (miR-4281 and miR-4417) exhibiting positive correlations with blood metal concentrations as well as with long- and short-term welding exposure measures. The dysregulation of these miRNAs suggests that exposure to metals could disrupt important biological processes, possibly contributing to an elevated risk of NDDs. These findings highlight the need for further research to validate the causal relationship between exposure to metals in welding fumes, the dysregulation of circulating miRNAs, and their role in neurodegenerative disease development, with implications for miRNA-based biomarkers in early disease detection and prevention.

Factors influencing metal concentrations in hair and nails during longitudinal follow-up of apprentice welders

The aim of this study was to determine factors influencing observed increased metal biomarkers of exposure levels in a group of 116 Quebec apprentice welders during a longitudinal follow-up of exposure. Analysis of 14 metals was carried out in hair, fingernail, and toenail samples taken from participants over the course of their welding curriculum at 6 different times. Personal and socio-demographic characteristics, lifestyle habits, and other potential confounding factors were documented by questionnaire. Multivariate linear mixed-effect models were used to assess main predictors of metal concentrations in each biological matrix including increasing time of exposure throughout the curriculum (defined as the repeated measure "time" variable"). Significant associations between repeated measure "time" variable and metal levels in hair, fingernails, and toenails were found for chromium, iron, manganese and nickel. Significant associations with "time" were also noted for arsenic levels in hair and fingernails, and for barium, cobalt and vanadium levels in fingernails and toenails. The repeated measure "time" variable, hence increasing time of exposure throughout the curriculum, was the predominant predictor of elevated biological metal levels. Reduced spaces and simultaneous activities such as oxyfuel-cutting and welding in the same welding room were suspected to contribute to higher metal levels. Age, ethnicity, and annual household income exerted an effect on metal levels and considered as confounders in the models. Variations observed in metal levels between hair and nails of apprentice welders also emphasized the relevance and importance of performing multi-matrix and multi-element biomonitoring to assess temporal variations in biological metal concentrations during welding curriculum.