Researchers produce first ever global map of mercury bioaccumulation

In 2017, the Minamata Convention on Mercury that had been signed some years earlier came into force, having been ratified by 148 states. With its stated ‘objective’ being ‘to protect the [sic] human health and the environment from anthropogenic emissions and releases of mercury and mercury compounds’, new methods of monitoring and reporting were needed that could be up to the mammoth task of tackling global mercury pollution – indeed, in Article 21, the Convention explicitly calls for decisions to be made about ‘the timing and format of the reporting to be followed by the Parties’.¹ Now, almost 7 years after its ratification, the Minamata Convention finally has its first fully global map of mercury contamination in fish and wildlife.²

Using over 550,000 data points from the Global Biotic Mercury Synthesis (GBMS) database, the researchers provide a comprehensive overview of Hg concentrations in various species, including fish, sea turtles, birds, and marine mammals. They highlight significant regional data gaps and emphasize the importance of standardized, evidence-based approaches for monitoring Hg levels to assess the progress of global efforts in reducing Hg pollution's impact on human health and the environment.  

The researchers propose a framework for a global Hg biomonitoring network with a three-step approach to integrate existing efforts and fill regional data gaps, especially in under-monitored areas like Africa, Australia, the Indo-Pacific, and certain oceanic regions. Firstly, continental and oceanic scale monitoring would integrate existing biomonitoring efforts across continents and ocean basins to ensure a broad geographic coverage of mercury data, with the aim to compile and standardize data from different regions to create a comprehensive global overview. Secondly, regional monitoring would focus on identifying and filling data gaps in underrepresented regions, such as Africa, Australia, the Indo-Pacific, and certain oceanic regions, to ensure that all significant areas are covered, particularly those with high ecological sensitivity or significant mercury sources. Finally, according to the researchers, there’s local monitoring which will oversee specific ecologically-sensitive sites or hotspots identified through regional and continental data, closely tracking mercury levels in these areas to understand local variations and impacts, ensuring that mitigation measures are effective at the ground level. By understanding and quantifying ecosystem sensitivity to Hg, the authors aim to establish efficient biomonitoring programs that can provide reliable measures of Hg exposure and its effects on biota.  

In fact, another recent study demonstrates that researchers are already beginning to further contribute to this global picture. A fascinating example of regional monitoring, a team of researchers monitored the mercury levels in bottlenose dolphins across the Southeast Atlantic and Gulf of Mexico, using them as ‘sentinel species’ indicative of the wider presence of mercury in the region because they are end-of-chain predators.³ Mercury concentrations were measured in dolphin skin samples from various locations, revealing significant spatial variation. Dolphins in St. Joseph Bay, the Florida Everglades, and Choctawhatchee Bay exhibited the highest mercury levels, while those in Charleston and Skidaway River Estuary showed the lowest, highlighting the varying impact of local biogeochemical processes and anthropogenic activities on mercury accumulation. Notably, the elevated mercury levels in specific areas like St. Joseph Bay are attributed to historical industrial activities, while natural processes in mangrove forests contribute to high levels in the Florida Coastal Everglades. 

So, a big step forward for mercury monitoring, and the movement to limit harmful mercury pollution. With this framework in place, more comprehensive and accurate reporting for signatories to the Minamata Convention becomes possible – and with the UK falling behind its peers when it comes to mercury regulations, this might just provide the wake-up call needed.  

¹ Minamata Convention on Mercury: Text and Annexes – 2023 Edition. United Nations Environment Programme. 2023. 

² Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework. Evers et al. Ecotoxicology. 2024. 

³ Spatial Variation in Mercury Accumulation in Bottlenose Dolphins (Tursiops spp.) in Southeastern U.S.A. Griffin et al. Toxics. 2024.