Pups on mercury: Tracking early life exposure on South American fur seals (Arctocephalus australis) and South American sea lions (Otaria byronia) in the Southeastern Pacific

Abstract

Mercury exists in three forms: elemental, inorganic, and organic, with methylmercury (MeHg) being the most concerning due to its ability to cross cellular barriers and bioaccumulate, particularly in marine mammals, where over 90 % of total mercury is in the MeHg form. Despite its importance, there is limited data on mercury bioaccumulation in marine mammals and maternal transfer mechanisms in the Southern Hemisphere. Pinnipeds, as ocean sentinels, are valuable for monitoring contaminants due to their ecological and biological traits. This study investigates mercury burdens and maternal transfer of mercury in South American sea lions (SASL) and South American fur seals (SAFS). Samples of clots and vibrissae from SASL pups and clots and milk from SAFS pups and females were analyzed. Total mercury (THg) levels in SASL ranged from 8.36 to 305.43 μg/Kg w.w. in clots and from 3071.8 to 28,034.5 μg/Kg d.w. in vibrissae. In SAFS, THg levels in clots ranged from 0.40 to 358.77 μg/Kg w.w. and in milk from 3.4 to 14.1 μg/Kg w.w. Significant differences were observed between newborn pups of both species, with a positive correlation between THg levels in clots from SAFS pups and females and between clots and vibrissae in SASL pups, indicating maternal transfer during gestation. Additionally, THg levels in SAFS pups decreased over time, suggesting biodilution. These species allow us to have a long term monitoring in both colonies and two different areas in Chile and are relevant findings to food security and the treatment of heavy metal contamination.