Hartnell's time machine: 170-year-old nails reveal severe zinc deficiency played a greater role than lead in the demise of the Franklin Expedition

The Franklin Expedition (1845-1848) left in search of the Northwest Passage and ended tragically with the loss of all crew members. Mystery surrounds their ultimate fate, with particular speculation around the role of lead poisoning. Our unique study turns nails from crew member John Hartnell into a time machine to determine what happened to the Franklin Expedition crew members. Using micro-X-ray fluorescence mapping, stable isotopic measurements, and laser ablation inductively coupled plasma mass spectrometry, we navigate through the nails and temporally characterize lead, copper and zinc content in our subject during the early expedition. By circumventing external contamination on exposed nail surfaces, we challenge the theory that crew members were exposed to high levels of lead on the expedition. Our analyses suggest that lead exposure actually decreased over the course of the expedition and Hartnell's levels were within a healthy, normal range. Our study also finds, however, that Hartnell was severely zinc-deficient, possibly leading to immuno-suppression and ultimately, tuberculosis and death. The significant weight loss from his illness resulted in a flush of previously stored lead from his bones into his blood (and nail), but only in the last few weeks of life. These findings provide new insight on the fate of the other crew members, including the role that diet and zinc deficiency played in the lives of stranded crew members before their demise.