Pre-industrial mercury exposure in early modern Europe: integrating hair Hg, stable isotopes, and burial geochemistry from a 17th-century plague mass grave

Human mercury (Hg) exposure in pre-industrial Europe remains poorly quantified, despite widespread therapeutic and artisanal use during the early modern period (ca. 1500–1800). We combined hair total Hg (THg), bulk stable isotopes (δ13C, δ15N, δ18O), and burial-sediment geochemistry to reconstruct Hg exposure in a 17th-century mass grave in Nuremberg, Germany (1632–1634). X-ray fluorescence identified three sediment facies, including a metal-enriched backfill; elemental Hg0 droplets, probably from medical pills, were observed in the fill, raising post-burial contamination concerns. Hair from a low-Hg facies distinct from these deposits, was decontaminated (validated by a paired washed/dry-brushed comparison); reported THg values are upper bounds on ante-mortem exposure. Hair THg ranged 0.51–3.38 µg g–1 (median 1.63; n = 15), 80% exceeding 1.0 µg g–1. δ13C and δ15N values are consistent with homogeneous terrestrial C3-based diets. Systematic 15N enrichment may partly reflect ante-mortem catabolism associated with famine and illness, although a contribution from animal-protein intake cannot be excluded. In a multivariable model, THg covaried weakly with δ13C but not with δ15N or δ18O; this exploratory trend, sensitive to a single influential individual, is compatible with mixed exposure routes and a limited dietary contribution. Narrow clustering of δ18O shows no clear geographic heterogeneity, consistent with Hg burden being driven primarily by local factors (e.g. therapeutic or occupational exposure) rather than by access to isotopically distinct water sources. These rare pre-industrial hair-Hg benchmarks suggest exposure higher than in most modern populations. Given the small sample size (n = 15) and possible selection effects, these findings should be interpreted as exploratory.