Efficacy of cleaning method for removal of exogenous welding fume contamination from nail tissue prior to use as a biomarker for welding fume manganese exposure
Nail tissue has been proposed as a biomarker for body burden of occupational exposure to manganese from welding fumes. Though recent studies have shown correlation between manganese exposure and both nail tissue concentration as well as concentrations in dopaminergic regions of the brain, concerns of the validity of nail tissue as a biomarker have arisen due to the potential for exogenous contamination of Mn to undermine the quantization of endogenous Mn in nail. Previous studies have used a cleaning method of 1% Triton X-100 surfactant plus sonication in order to attempt to remove exogenous welding fume contamination. Determination of the potential level of exogenous Mn from welding fume on welder nail tissue was investigated. In addition, an intentional welding fume contamination methodology was developed in order to deposit welding fume Mn onto control nail samples in a within-subject design in order to test the efficacy of the prior nail tissue cleaning method. Paired sample fingernails from welders exposed to gas metal arc welding (GMAW) welding fume were digested and analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). Uncleaned welder fingernails had a mean of 8.78 µg/g Mn (LCL = 5.58, UCL = 11.99) while those cleaned via the prior cleaning method showed a mean of 3.22 µg/g Mn (LCL = 3.07, UCL = 3.37). Results of a Cochran method two-sample t-test between cleaned and uncleaned welder fingernails showed significance at p=0.0117 and a Wilcoxon t-distribution 2-sided test approached significance at p=0.0671, indicating that exogenous Mn contamination is likely a threat to validity of nail tissue as a biomarker of body burden. GMAW welding fume exposed uncleaned control subject nails (at twice the level of exogenous Mn seen in the welder fingernails) had a mean concentration of 11.35 µg/g Mn (LCL95 = 9.41, UCL95 = 13.30) while unexposed uncleaned control nails had a mean concentration of 0.42 µg/g Mn (LCL95 = 0.23, UCL95 = 0.60). Results of a Cochran method two-sample t-test between exposed and unexposed uncleaned control fingernails showed significance at p=0.0001 and a Wilcoxon t-distribution 2-sided test approached significance at p=0.0172, indicating that the method of GMAW welding fume contamination effectively contaminated the tissue with welding fume Mn. Exposed cleaned control fingernails had a mean of 0.63 µg/g Mn (LCL 95 = 0.48, UCL95 = 0.79), while those unexposed prior to cleaning showed a mean of 0.14 µg/g Mn (LCL95 = 0.12, UCL 95 = 0.17). Results of a Cochran method two-sample t-test between exposed and unexposed cleaned control nails showed significance at p=0.0002 and a Wilcoxon t-distribution 2-sided test approached significance at p=0.00027, indicating that while not all exogenous Mn contamination was eliminated by the cleaning method, , the residual contamination amounted to only 4.45% ± 1.23% (95.55% of the contamination was removed). The results indicate that nail tissue can be cleaned effectively of the majority of exogenous Mn exposure, pointing to the utility of nail tissue as a biomarker for welding fume Mn internal exposure and likely occupational and environmental exposures to additional metals as well.
Dydak, Purdue University.
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