Mercury Speciation in Whole Blood and Dried Blood Spots from Capillary and Venous Sources

There is interest in measuring total mercury (THg) and methylmercury (MeHg) in dried blood spots (DBS) though more research is required to evaluate mercury (Hg) speciation in DBS and to validate the agreement between blood sources (venous vs capillary) and matrices (whole blood vs DBS). Therefore, the present study aimed to develop, evaluate, and validate a DBS-based method to assess MeHg and inorganic mercury (InHg) exposure in human population studies. First, we used volume-controlled (40 μL) paired DBS-whole blood samples to develop an analytical method that involved the extraction and quantification of MeHg and InHg with gas chromatography-cold vapor atomic fluorescence spectrometry (GC-CVAFS). Next, we carried out a validation study using paired DBS-whole blood samples from venous and capillary sources from 49 volunteers with Hg exposures similar to background populations (i.e., MeHg in venous whole blood ranged from 0.2 to 3 μg/L with a median value of 0.8). The limits of detection were higher for InHg (1.9 and 1.1 μg/L in DBS and whole blood, respectively) than MeHg (0.3 and 0.2 μg/L in DBS and whole blood, respectively). The MeHg concentrations among blood sources and matrices were highly correlated (r ranged from 0.85 to 0.95), with no constant bias (intercept ranged from -0.05 to 0.13 μg/L) and small proportional bias (slopes ranged from 0.92 to 1.08). Bland-Altman plots indicated little bias between MeHg measurements with 82-98% of the cases meeting the analytical acceptance criterion of 35% maximum allowed difference. Our results indicate that measures of MeHg in capillary DBS reflect concentrations in the gold standard (i.e., venous whole blood) and that DBS is a suitable tool for assessing MeHg exposure in human population studies, but that more work is required to assess InHg exposures.