Day 3 of ICMGP 2022: New Voices, Gold Mining and Metrological Innovations

Even in 2013, when it was formally ratified, the United Nations’ Minamata Convention on Mercury had a desperate sense of urgency, of having already run out of time. As one of the most harmful anthropogenic pollutants, the coordinated reduction of both exposure and emission leapt immediately to the top of the list of priorities in the management of public health worldwide. More recently, however, this urgency has become part of another global race against time, as concerns began to be raised over mercury’s role in the climate crisis. As a contribution to these discussions, this year’s International Conference on Mercury as a Global Pollutant (ICMGP), which kicked off today, will centre innovations aimed at reducing mercury emissions to achieve a greener world.  

It’s worth emphasising the global scope of these ambitions. For a while now, most international conferences have focussed on research coming out of institutions in the Global North, limiting the breadth of discussion. As such, ICMGP 2022 decided to bring together researchers from the Southern Hemisphere to discuss the innovative work that’s been going on down under for many years. One of those innovators is Miao Shi, Ph.D., of Tianjin University, who delivered a presentation on tracing the sources of mercury in deep-sea sediments. Even though it is well-understood that the ocean plays a critical role in mercury cycling, due to the in-situ formation and bioaccumulation of neurotoxic methylmercury, the sources and transformations of this marine mercury remain unclear – and particularly under-researched in the Southern Hemisphere. With her team of researchers, Ms. Shi tracked stable isotopes of mercury within two deep-sea sediment cores from the North Ross Sea, with the hope of revealing the impact of glacial-interglacial change. It concluded that the sources of marine mercury change significantly over time. 

For one of the sediment cores, atmospheric deposition via long-range transport was the dominant source before the Last Glacial Maximum, as evidenced by slightly positive mass independent fractionation and negative mass dependent fractionation, both of which are similar to those of modern open-ocean sediments. By contrast, the other core gives readings closer to the isotopic signatures of Antarctic snow, leading the researchers to suggest that the core was dominated by mercury input from glacial materials transported from the Antarctic icesheet. However, after the Last Glacial Maximum, readings in both cores drift consistently towards zero, and mercury concentration begins to increase, perhaps as a result of an up-tick in volcanic mercury emissions as well as terrigenous input from Antarctica’s retreating glaciers. 

Let’s leave the big picture for a moment, though, and zoom in on a single industry. Artisanal and small-scale gold mining in the Peruvian Amazon - a biodiversity hotspot - is expanding, leading to large releases of mercury into the atmosphere. From the University of California, Berkeley, Jacqueline Gerson, Ph.D., outlined her findings on the atmospheric transport and fate of mercury within such terrestrial ecosystems to determine whether mercury from artisanal and small-scale gold mining activity was entering local soils and food-webs. It was disturbing, Gerson notes, to have discovered that resident mercury concentrations in the Peruvian Amazon were 2-12 times higher than those in remote forests – sometimes, these concentrations were in exceedance of the thresholds known to impact reproductive success. While the fate of mercury within these forests is concerning, these results do suggest that forests are crucially important for sequestering the element. Therefore, Gerson underlines, if these forests are burned or cleared, mercury could enter nearby aquatic ecosystems, and the extent of lake area in heavily-mined watersheds has increased by 670% over the past 34 years in direct association with artisanal and small-scale activity. In another horrific twist, the proportion of mercury as methylmercury was 5-7 times greater in these lakes than in rivers, ensuring that the level of risk to organisms is compounded by this change. All of Ms. Gerson’s results raise important questions about the impact of mercury pollution on aquatic and terrestrial ecosystems – and, crucially, for indigenous communities and wildlife that depend on them. 

Like many of this week’s presentations, Mrs. Gerson provides the audience with fascinating results that spur further discussion, but it’s important to discuss exactly how we arrive at the measurement standards by which data is produced. For example, calibration for atmospheric mercury species at ambient concentration levels, along with sampling, is one of the major problems in atmospheric mercury speciation. Partly, it’s because these species of mercury tend to have a high adsorption rate and are highly reactive, all of which greatly complicate the reliability of calibration methods. As an attempt to solve this frustrating problem, Jan Gačnik of the Jožef Stefan Institute gave an intriguing presentation detailing an approach to calibration based on non-thermal-plasma oxidation of Hg0 to HgII. This calibration procedure, Mr. Gačnik outlines, began with the production of Hg0 by quantitative reduction of HgII in an aqueous solution with SnCl2 and aeration. Then, Hg0 was oxidized into different species within a stream of He and traces of reaction gas by non-thermal plasma. By changing the reaction gas, three different species of mercury could be produced: HgO, HgCl2 and HgBr2. Since validation of calibration at ambient concentration levels is not possible by conventional methods, like isotope dilution inductively-coupled plasma mass spectrometry, a highly sensitive radiotracer was used. Ultimately, traceability to the System of Units was achieved through traceability to SRM NIST 3133. Combined with validated sampling procedures, the developed calibration could provide comparable mercury measurements. Indeed, it might just be the foundation for the future of atmospheric mercury speciation. 

It’s been another whirlwind of a day, then, with more than twenty unique and challenging presentations from some of the world’s leading researchers, regulators and inventors working in the field of mercury pollution. Perhaps the best part, though, is that we have another four days ahead of us. It has to be said, and said again, that if you’re involved in environmental mercury, there’s really nowhere else that you should be than at ICMGP 2022. 

For more information, visit the International Conference on Mercury as Global Pollutant.