Global mercury contamination is an urgent matter for the international community. In 2003, the Global Mercury Assessment report noted significant adverse global impacts from mercury and its compounds and urged further international action. Due to its long-range atmospheric transport, its persistence in the environment and its significant negative impacts on human health, mercury accumulation and exposure have become global concerns, leading to adoption of the Minamata Convention on Mercury in 2015. Having entered into force in August 2017, the Minamata Convention aims to protect human health and the environment from anthropogenic emissions and releases of mercury. It restricts anthropogenic releases of mercury throughout its lifecycle, from mining, trade, usage, emissions and releases to storage and disposal. The Convention also highlights social issues related to mercury, such as vulnerable populations facing risks from mercury—particularly children and women of child-bearing age and the informal sector working in the field of artisanal and small-scale gold mining (ASGM). The international community has been working hard to comply with the measures established in the Convention. One of the remaining issues is how to certify long-term management of mercury waste as environmentally sound. There is estimated to be a large amount of surplus mercury in stocks around the world, and mercury waste generated unintentionally will continue to be emitted every year. Thus, proper management of mercury waste is the next big challenge for the Convention. Some countries, such as Japan and the EU have already legislated final disposal of mercury, but permanent mercury stabilization technologies are still new and need further development for certification of safe long-term storage in the environment. Enhancement of mercury waste management capacities in developing countries is also crucial. In this Special Issue of Global Environmental Research, the latest research is reported by scientists and experts in the areas of mercury management, including the Secretariat of the Minamata Convention as well as government bodies and research institutes. What is unique about this Special Issue is that the ten manuscripts it presents cover a wide range of scientific and social aspects of mercury waste management, including analyses of mercury final disposal measures, long-term behavior of mercury in landfills, cognitive aversion to mercury, management of mercury-containing products, development of mercury thresholds, development of the Convention in the context of the Sustainable Development Goals (SDGs), implementation of the Convention and future challenges. I appreciate these experts for their efforts to provide valuable knowledge and expertise on this important matter, and hope that this information will facilitate global efforts to establish environmentally sound long-term management schemes for mercury waste.

July 2020

Guest Editor

Reiko SODENO (Shibaura Institute of Technology, Japan)

A column leaching test was conducted for 258 days to demonstrate Hg emissions in an engineered landfill where stabilized and solidified mercury by using sulfur and a binder such as cement was disposed of under monofill conditions with a granite soil layer. Thermodynamical analysis considering leachate quality showed that the mercury in the leachate could be chlorides, indicating that the mercury in metacinnabar in stabilized/solidified products (below, s/s products) dissolved in percolation water. However, the gaseous and liquid emissions of soluble mercury were extremely low because of adsorption in the granite soil. Nearly all mercury released from the stabilized/solidified product into the soil stayed within 1.5 cm of the product. Mercury contents were greater in deeper soil than in upper soil layers. It seems that migration of Hg out of the columns was delayed due to absorption of mercury in the soil and moisture. Sulfur polymer effectively immobilized mercury than low-alkali cement. However, both s/s products could achieve effective containment of mercury-containing waste under monofill conditions with a mercury-adsorbing soil layer. It is important not only to achieve stabilization/solidification of mercury but also to install a mercury-adsorption layer surrounding the treated waste to minimize mercury emissions from landfills.

This study investigates the environmental safety of landfill sites in which mercury metal waste is disposed. Serial batch tests were conducted to evaluate the long-term leaching and volatilization rates of mercury waste stabilized in its sulfide form, and solidified using either a sulfur polymer or two different types of low-alkaline cement. Using measured mercury leaching and volatilization rates, numerical simulations were conducted to investigate the long-term behavior of mercury after its disposal in landfill sites. For leaching behavior, the concentration profiles of dissolved mercury accumulating in a drainage pipe at the bottom of a landfill site were calculated, while volatilization behavior was assessed by analyzing the gaseous mercury emissions from the final cover surface. The effects of covering the disposed mercury waste with either soil sorption layers or cut-off layers were evaluated through analysis of the calculated concentration profiles.

Waste landfills are a potential mercury (Hg) sink due to disposal of wastes containing mercury. In addition, anaerobic environments created under the surface in landfills facilitate Hg methylation, which produces methyl Hg (MeHg), the most potent mercury neurotoxin. Although Hg methylation in the environment is primarily mediated by microorganisms, little is known about the occurrence of Hg-methylating microorganisms in landfills. Therefore, this study aimed to assess the potential of biological Hg methylation in waste landfills by applying a DNA-based monitoring tool. First, useful polymerase chain reaction (PCR) primers targeting hgcAB genes that are involved in Hg methylation were selected from previously-developed ones, and PCR detection conditions were optimized. Then, the occurrence of hgcAB genes was investigated in core samples collected from landfills in Japan. Among a total of 20 samples from five landfill sites, hgcAB genes were detected in five samples. In addition, the abundance of hgcAB genes was estimated in three of the five positive samples by most probable number-PCR. The results indicated not ubiquitous but only sporadic occurrence of biological Hg methylation potential in landfill sites even under anaerobic conditions favorable for Hg-methylating microorganisms.

Entry into force of the Minamata Convention on Mercury has changed the supply-demand balance, leading to an oversupply of mercury worldwide. We assessed sulfurization and solidification technologies for wastes consisting of elemental mercury for disposal in specially engineered landfills. For chemical stabilization of elemental mercury, gas phase sulfurization, wet sulfurization in water phase and dry mechanochemical sulfurization were evaluated. Solidification for sulfurized mercury was examined using cement/mortar/concrete, dicyclopentadiene-modified sulfur and epoxy resin as solidification materials. In this research, crucial environmental requirements (limits of leaching and emission) for sulfurized and solidified products were defined and evaluated using three Japanese leaching tests (JLT-13, JLT-46 and a tank leaching test) and a headspace test. Overall, each sulfurization and solidification technology fulfilled the crucial environmental requirements for sulfurized and solidified products and compressive strength of the solidified products.

Mercury (Hg) released from landfill Hg waste poses serious health and environmental risks. The Minamata Convention on Mercury (2017) emphasizes preventative management: landfills are to be stabilized and Hg waste controlled. When developing stabilization/solidification technologies to ensure the safety of landfilled Hg waste, leaching and headspace tests are currently used to assess dissolution and diffusion. However, it remains unclear whether Hg wastes remain stable in real landfill environments because there are few findings from long-term landfill experiments on Hg wastes. We used lysimeters and followed previous long-term semi-aerobic/anaerobic simulated-landfill experiments on dry-cell batteries to investigate Hg dissolution and diffusion of sulfurized/solidified Hg wastes in simulated landfill environments. Total Hg (T Hg) release from the lysimeters, containing sulfurized/solidified Hg waste, to the atmosphere was extremely small. Examination of Hg behavior in different landfill types, however, found semi-aerobic types to be associated with lower Hg dissolution and diffusion risks than anaerobic types. Regarding Hg behavior of sulfurized/solidified Hg wastes, Hg sulfide (HgS) waste solidified by cement was found to be more stable than non-solidified HgS waste and dry-cell batteries. Methyl Hg (M-Hg) monitoring in leachates found M-Hg concentration in leachates to fall below 0.5 µg/L under almost all landfilling conditions, with time change trends moving in tandem with changes in leachate T-Hg. Volatilization and leaching tests involving sulfurized/ solidified Hg wastes were performed while simulating landfill changes to judge important factors in landfilling conditions regarding Hg dissolution and diffusion through comparison with lysimeter experiment results. Laboratory tests showed temperature and pH (alkaline) to affect the stability of sulfurized/solidified Hg wastes and elucidated effects assumed to enhance Hg dissolution and diffusion in the lysimeter experiments.

The Minamata Convention on Mercury, which entered into force on Aug. 2017, requires mercury to be recovered from society and its final disposal to be accomplished in environmentally safe ways. Because it is very difficult to obtain public acceptance of mercury landfill disposal, this study focuses on emotional perceptions of mercury. The author quantitatively evaluated aversions to mercury and other harmful matters such as radioactive waste or those perceived as hazardous using a pairwise comparison method with Thurstone’s law of comparative judgement (sample size = 1030). The strongest aversion was found for radioactive waste, followed by mercury. Although gender and age usually affect risk perception to any hazard, this study found that gender and age had no significant impact on mercury aversion at the 5 percent significance level. When the participants had strong concerns about well-known hazards (radioactive waste, dioxins, infectious medical waste and cadmium), they had a stronger aversion to mercury than those who were concerned more with other matters like genetically modified foods or ultraviolet light. On the other hand, the participants who had moderate or weak concerns about well-known hazards had even greater mercury aversion than the group with strong concerns. No clear difference in mercury aversion was found regardless of different strengths of concerns regarding waste recycling. Cognitive aversion to mercury is associated with hazard perceptions and not affected by concerns regarding waste recycling.

Mercury has been used in a wide range of products: batteries, lighting appliances, measuring devices and more. In compliance with the Minamata Convention on Mercury, efforts have been made for the production of mercury-free alternatives, but some mercury-containing products will continue to be used in the future. Appropriate management of used mercury-containing products will continue to be indispensable. Attention and inventiveness are demanded at each stage of the management flow process, which includes discharging, collecting, transporting, storing during transshipment, intermediate processing, final disposal and recycling. Therefore mercury-containing products discharged from households should be separated from and not be mixed with other wastes. In Japan, municipalities have their respective collection methods: receiving wastes at fixed collection bases, mobile collection bases, etc., sometimes combining several methods. Regarding wastes discharged from companies, criteria have been defined for each stage of the process from storage to disposal according to the categories specified by law, and the waste is disposed of in accordance with those criteria. As a future task, the collection rate of mercury-containing products in Japan must be raised. In many developing countries where the separation of waste has just begun, priority should be put on coping with hazardous substances, as well as separation and appropriate disposal of mercury-containing waste, a typical example, should be promoted.

Beneficial management of mercury can be achieved by applying certain logical, technically oriented principles. Swiss environmental provisions for soil, site remediation and waste have been developed using these strategic, long-term-oriented rules. Describing the historical development of state-of-the-art techniques might help others shorten their own pathway to development. This paper reviews development of these rules and gives practical guidance and a comparison of data in the specific matter of mercury. Special attention is paid to the design of a threshold system within the chain starting from observation, proceeding to remediation, followed by treatment and ending with final storage. Thresholds are shown not necessarily to be rigid borders, but beneficial frameworks, which can even be flexible to local circumstances if designed well. The overall target of the demonstrated strategy is to keep the anthroposphere safe from hazards and at the same time maintain the lithosphere in a way that does not add new risks of environmental damage. Finally, for a few holistic cases, keeping in mind the targets of the Minamata Convention, practically proven elements of a transparent and lucid management system for mercury are suggested. As in many processes, involving all stakeholders in a transparent and integrative way is crucial for success.

In response to global mercury pollution, the Minamata Convention on Mercury was adopted in 2013 and enacted in 2017. Parties have developed implementation mechanisms under the Convention. Compared to other multilateral environmental treaties, the Minamata Convention is unique in that its sole target is mercury, which it aims to manage throughout its lifecycle, including mining, trade, usage, emissions, releases, storage and disposal. The Convention also highlights social issues related to mercury, such as vulnerable populations facing risks from mercury, and the informal sector working in the field of artisanal and small-scale gold mining (ASGM). This paper seeks to identify how the Convention may be developed from the perspective of achieving the Sustainable Development Goals (SDGs), which also pursue comprehensive approaches to environmental, social and economic issues. The analysis provided shows that the Minamata Convention addresses all 17 goals of the SDGs, recognizing strong synergies with health (Goal 3), responsible consumption and production (Goal 12), and partnerships (Goal 17) in particular. For further development of the Convention, it is recommended that a gender perspective should be incorporated into the implementation of the Convention. In the context of trade-off relationships, the generation of mercury waste needs to be dealt with properly. By utilizing recovered mercury, mercury from primary mining can be phased-out in advance of the current schedule. ASGM and mercury waste management are still the biggest concerns for fulfillment of the Convention. Formulation of a global scheme of safe mercury waste management will be essential in the long term.

The Minamata Convention on Mercury was adopted at a diplomatic conference in October 2013, entering into force in August 2017. It had 113 parties at the time of the third meeting of the Conference of the Parties (COP) in November 2019. The first three COP meetings were held yearly, establishing rules and guidance needed for implementing the Convention. The objective of the Convention is to protect human health and the environment from anthropogenic emissions and releases of mercury. The largest source of anthropogenic mercury emissions to air is artisanal and small-scale gold mining (38%), 75% of which is from parties to the Convention. Their efforts to develop and implement national action plans are expected to curb this. Coal combustion and other point sources contribute to 47% of global emissions, 82% of which is from parties. The parties have legal obligations to take emission control measures as soon as practicable. Minamata Convention Initial Assessments being carried out in 111 countries provide critical information on parties’ needs that will support targeted assistance for the effective implementation of the Convention by developing countries. Work towards the effectiveness evaluation, which is to be done six years after entry into force, started at COP-1 in 2017, and this will be one of the main agenda items for COP-4 in 2021. The interface between science and policy is being strengthened through groups of experts nominated by parties and scientific meetings such as the International Conference on Mercury as a Global Pollutant. The views expressed herein are those of the author and do not necessarily reflect the views of the United Nations.