Quantifying Depuration of Methylmercury from Fish Consumption by Travelers

During a two-week field sampling expedition in Gabon, two American scientists consumed fish daily from the Ogooué River watershed. We sampled their scalp and facial hair periodically to evaluate hair as a biomarker to track shifts in methylmercury (MeHg) exposure from diet. Each individual differed in the onset and extent of MeHg accumulation but showed similar depuration rates. Pretrip baseline Hg isotope values between participants were distinct from Gabonese fishes allowing us to detect shifts in MeHg sources in the hair of both individuals. δ²⁰²Hg values tracked the mass-dependent fractionation of MeHg depuration stemming from in vivo metabolism, leading to δ²⁰²Hg increases of 0.014 ± 0.001 per mille and total Hg losses of 8.3 ± 1.1 ng g^-1 daily. While limited in scope due to minimal participants, our findings reveal a complex interaction between prior MeHg burdens, contemporary MeHg intakes, and sources of consumed fishes (locally caught versus market-sourced) in determining the dynamics of MeHg concentrations and δ²⁰²Hg in human hair. We also suggest that the offset in δ²⁰²Hg values used in literature between fish and human hair (1.75 ± 0.25‰) may overlook a time domain that increases starting fish-hair δ²⁰²Hg offsets (0.94‰), through time.