Non-invasive assessment of mercury exposure in rodents and marsupials from a historically contaminated area of the Madeira River, Western Amazon

Abstract The Lower Madeira River (Western Amazon) is a hotspot for mercury (Hg) contamination due to both natural geochemical enrichment and long-term anthropogenic activities. Total mercury (THg) concentrations were significantly higher in marsupials (median = 0.136 mg kg −1 ) than in rodents (median = 0.032 mg kg −1 , p = 0.0006). Arboreal rodents showed lower Hg levels than omnivorous rodents. Terrestrial rodents showed higher Hg concentrations than arboreal rodents ( p < 0.00010). Age did not influence Hg levels in the studied orders. The marsupial species Marmosops sp. (3.379 mg kg −1 ) and Marmosa murina (2.571 mg kg −1 ) showed the highest Hg concentrations, while in the rodent Sphiggurus roosmalenorum (n = 4), the concentrations remained below the detection limit. Atmospheric deposition is likely a source of Hg for herbivores, in addition to insects to supplement the diet. For omnivores, the main source of Hg is insects, which transport the element from the aquatic environment to the terrestrial environment.