Can preserved museum specimens be to be used to reconstruct fish mercury burden and sources through time?

To evaluate the utility of preserved fishes for reconstructing historical and spatial patterns of mercury (Hg) exposure, we experimentally tested the stability of Hg concentrations and Hg stable isotope ratios under standard museum practices of specimen preservation. We found that loss of unidentified constituents during preservation changed Hg concentrations in fish muscle. Fish reared in the lab with minimal Hg exposure were susceptible to exogenous contamination with inorganic mercury (iHg) when preservative fluids were intentionally spiked or iHg leached passively from contaminated wild fishes in the same container. This contamination impacted Hg isotope values of total Hg, but the conservative nature of MeHg allows us to quantitatively correct for iHg contamination. Our findings validate the potential to use fishes from the world’s museums to generate spatiotemporal baselines for the Minamata Convention on Mercury, but we indicate precautionary strategies to maximize inference strength. Selecting the largest specimens of a target species helps dilute any iHg contamination. Specimens should be drawn from lots that were not comingled with fishes from other collections, to minimize risk of iHg transfer among fish with different contamination histories. Focusing on low-lipid species will enhance the comparability of Hg concentrations between historical and contemporary collections.