Comprehensive Biomarker Assessment Protocol

Biological samples including venous whole blood, spot urine, saliva, hair, fingernails and toenails were collected from each subject upon enrollment, as described in detail in previous studies (Smith et al., 2007 (link); Eastman et al., 2013 (link); Lucas et al., 2015 (link); Butler et al., 2019 (link)). Biological samples were processed and analyzed for metal concentrations using magnetic sector inductively coupled plasma mass spectroscopy (Thermo Element XR ICP-MS), as described elsewhere (Smith et al., 2007 (link); Eastman et al., 2013 (link); Lucas et al., 2015 (link); Butler et al., 2019 (link)). A complete overview of biomarkers can be found in Table 1, while Pearson’s correlations between biomarkers is reported in Supplementary Figure S1. Samples with values less than the LOD were substituted with LOD/square root of 2 (Ganser and Hewett, 2010 (link)).