Toenail Metal Concentration as a Biomarker of Occupational Welding Fume Exposure

Abstract

In populations exposed to heavy metals, there are few biomarkers that capture intermediate exposure windows. We sought to determine the correlation between toenail metal concentrations and prior 12 month work activity in welders with variable, metal-rich, welding fume exposures. Forty-eight participants, recruited through a local union, provided 69 sets of toenail clippings. Union-supplied and worker verified personal work histories were used to quantify hours welded and respirator use. Toenail samples were digested and analyzed for lead (Pb), manganese (Mn), cadmium (Cd), nickel (Ni) and arsenic (As) using ICP-MS. Spearman correlation coefficients were used to examine the correlation between toenail metal concentrations. Using mixed models to account for multiple participation times, we divided hours welded into three-month intervals and examined how weld hours correlated with log-transformed toenail Pb, Mn, Cd, Ni and As concentrations. Highest concentrations were found for Ni, followed by Mn, Pb and As, and Cd. All of the metals were significantly correlated with one another (rho range=0.28-0.51), with the exception of Ni and As (rho=0.20, p=0.17). Using mixed models adjusted for age, respirator use, smoking status and BMI, we found that Mn was associated with weld hours 7-9 months prior to clipping (p = 0.003), Pb was associated with weld hours 10-12 months prior to clipping (p=0.03) and over the entire year (p=0.04). Cd was associated with weld hours 10-12 months prior to clipping (p=0.05), and also with the previous year's total hours welded (p=0.02). The association between Ni and weld hours 7-9 months prior to clipping approached significance (p=0.06). Toenail metal concentrations were not associated with the long-term exposure metric, years as a welder. Results suggest Mn, Pb, and Cd may have particular windows of relevant exposure that reflect work activity. In a population with variable exposure, toenails may serve as useful COMPETING INTERESTSThe authors declare they have no competing financial interests. HHS Public Access

Toenail Metal Concentration as Biomarker of Heavy Metal Exposure among Welders

“…It is highlighted that comparison of several biomarker such as blood, urine and nail may not help to determine the accuracy of individual marker since none of them can serve as a gold-standard marker [2]. Thus, the choice of appropriate biomarker is the reflection between exposure, biomarker and the exposure time period that the biomarker reflects [3]. Blood and urine may reflect exposure over a short and a recent period of time (hours to days), while nails and hair integrate exposure over a longer period of time and represent exposures over several months or longer [4].…”

“…In recent years, several researches had explored the possibility of toenail as biomarker of welding fumes exposure [3], [5]. Compare to hair, the toenail had the advantages of being sheltered from environmental contaminants and are less likely to have contaminants through hair shampooing, dyeing and bleaching [2].…”

“…Toenail clippings collected from all ten toes are likely to reflect exposure integrated over the previous 6 to 12 months, due to a growth rate of approximately 1.6 mm/month and maximum average toenail length of 20 mm [3]. Given that nails are non-invasively and painlessly collected, and easy to store and transport, nail metal concentration should be intensively studied as a potential biomarker of internal dose for welding fume exposures [3].…”

“…Given that nails are non-invasively and painlessly collected, and easy to store and transport, nail metal concentration should be intensively studied as a potential biomarker of internal dose for welding fume exposures [3].…”

“…Research on concentration of heavy metal in welder's toenail had been largely focused on manganese elements [3], [5]- [7]. Thus, this study focused on the concentration of overall 13 constituents of heavy metal detected in toenail and the airborne exposure in the welder's breathing zone.…”