Heart rate variability and DNA methylation levels are altered after short-term metal fume exposure among occupational welders: a repeated-measures panel study

Background: In occupational settings, boilermakers are exposed to high levels of metallic fine particulate matter (PM2.5) generated during the welding process. The effect of welding PM2.5 on heart rate variability (HRV) has been described, but the relationship between PM2.5, DNA methylation, and HRV is not known. Methods: In this repeated-measures panel study, we recorded resting HRV and measured DNA methylation levels in transposable elements Alu and long interspersed nuclear element-1 (LINE-1) in peripheral blood leukocytes under ambient conditions (pre-shift) and right after a welding task (post-shift) among 66 welders. We also monitored personal PM2.5 level in the ambient environment and during the welding procedure. Results: The concentration of welding PM2.5 was significantly higher than background levels in the union hall (0.43 mg/m(3) vs. 0.11 mg/m(3), p < 0.0001). The natural log of transformed power in the high frequency range (ln HF) had a significantly negative association with PM2.5 exposure (beta = -0.76, p = 0.035). pNN10 and pNN20 also had a negative association with PM2.5 exposure (beta = -0.16%, p = 0.006 and beta = -0.13%, p = 0.030, respectively). PM2.5 was positively associated with LINE-1 methylation [beta = 0.79%, 5-methylcytosince (% mC), p = 0.013]; adjusted for covariates. LINE-1 methylation did not show an independent association with HRV. Conclusions: Acute decline of HRV was observed following exposure to welding PM2.5 and evidence for an epigenetic response of transposable elements to short-term exposure to high-level metal-rich particulates was reported.