Reducing Mercury Pollution: Is the ASGM sector ready for mercury free mining?


21 July 2023

By Nobuhle Chikuni

Studies have shown that in Zimbabwe, most artisanal and small-scale gold mining (ASGM) is dependent on mercury, and the sector is allegedly the largest source of mercury pollution. Artisanal and small-scale mining dates to several years ago, and the use of mercury in ASM activities has been a significant concern. There are considerable mercury emissions, largely from the open burning of amalgam during gold processing. Mercury volatilized and emitted into the air at the national level were estimated in the range of 7,729 to 83,765 kg (average: 24,285 kg) for the base year 2018 [1]

Mercury has been used in Zimbabwe’s ASM sector primarily for gold extraction. The process involves amalgamation, where mercury is mixed with gold-bearing ore to form a mercury-gold amalgam. The amalgam is then heated to evaporate the mercury, leaving behind the gold. This method is often used because it is relatively simple and inexpensive compared to other gold extraction techniques.

The use of mercury in ASM has raised environmental and health concerns due to mercury’s toxic nature. Mercury is a potent neurotoxin that can have severe health effects, especially when exposure occurs through inhalation or ingestion. It can contaminate water bodies, soil, and the food chain, leading to long-term ecological damage.

To address these concerns, efforts have been made to promote the use of alternative gold extraction methods that do not involve mercury. These include the use of gravity concentration techniques such as panning and sluicing, which rely on the density difference between gold and other materials.

The Zimbabwean government has recognized the need to reduce mercury use in ASM and has taken steps to regulate and control its use. In 2019, the government implemented the Minamata Initial Assessment (MIA) project, which aimed to assess the mercury situation in the country and develop a national action plan to address mercury-related issues.

The MIA project highlighted the need for capacity building, awareness-raising, and technical assistance for miners to adopt mercury-free alternatives. It also emphasized the importance of formalizing the ASM sector and promoting safer mining practices.

Regulations and efforts to reduce mercury pollution have been implemented globally to mitigate its impacts. The Minamata Convention on Mercury, adopted in 2013, is an international treaty that aims to protect human health and the environment from the adverse effects of mercury. It establishes measures to control mercury emissions, reduce mercury use in various industries, and promote safe handling and disposal of mercury-containing products.

Furthermore, Zimbabwe is a signatory to the Minamata Convention on Mercury, an international treaty aimed at protecting human health and the environment from anthropogenic mercury emissions. The country has made commitments to reduce and, where feasible, eliminate mercury use in ASGM and promote sound environmental practices.

While efforts are being made to reduce mercury use in Zimbabwe’s ASM sector, it remains a complex challenge due to various factors, including limited access to appropriate technology, a lack of awareness, and economic constraints. Continued support, collaboration, and investment in sustainable mining practices are crucial to achieving a significant reduction in mercury use and promoting responsible ASM in Zimbabwe.

The communities near these mines are also affected due to mercury contamination of water and soil and subsequent accumulation in food staples, such as fish—a major source of dietary protein in many ASGM regions.

  1. Environmental Impact:

Water Contamination: Mercury can contaminate water bodies through various sources, including industrial discharges and atmospheric deposition. It can accumulate in aquatic ecosystems and transform into methylmercury, a highly toxic form that bioaccumulates in the food chain.

Soil Contamination: Mercury can also contaminate soil through industrial activities, mining, and waste disposal. It can persist in soil for long periods and pose risks to plants, animals, and humans.

Air Pollution: Mercury emissions from industrial processes, coal-fired power plants, and waste incineration contribute to air pollution. Once released into the atmosphere, mercury can be transported over long distances and deposited in ecosystems far away from the original source.

  1. Human Health Impact:

Neurological Effects: Exposure to high levels of mercury, especially methylmercury, through contaminated fish consumption can cause severe neurological damage, including cognitive impairment, developmental delays in children, and motor dysfunction.

Developmental Effects: Pregnant women exposed to mercury can pass it on to their developing fetus, leading to developmental delays, neurological disorders, and a reduced IQ.

Cardiovascular Effects: Chronic exposure to mercury has been linked to cardiovascular problems, including an increased risk of heart attacks, high blood pressure, and compromised heart function.

Renal Effects: Mercury toxicity can impair kidney function and damage the kidneys, leading to chronic kidney disease.

Other Health Effects: Mercury exposure has also been associated with immune system dysfunction, respiratory problems, gastrointestinal disturbances, and reproductive issues.

  1. Wildlife Impact:

Mercury toxicity affects a wide range of wildlife species, including birds, mammals, and fish. Birds and mammals can be exposed to mercury primarily through the consumption of contaminated prey, while fish and other aquatic organisms accumulate mercury directly from water and sediment.

Mercury contamination in wildlife can lead to impaired reproduction, developmental abnormalities, reduced survival rates, and population declines.

In a field visit to a demonstration site in Kadoma in early July 2023, miners indicated that a lack of information was one of the barriers to adopting mercury-free methods. Strides have been made to raise awareness about the challenges associated with the use of mercury in the ASM sector. Some mining sites around Zimbabwe have been funded by the UNDP-GEF to implement mercury-free gold processing methods. Among those miners, some have used table shakers, gold catchers, and retorts, and some have substituted mercury with Borax. While the efforts by the different players are commendable, more still needs to be done to ensure that the whole ASGM sector moves towards mercury-free processing methods. It is important to make sure all stakeholders work together toward the vision of a mercury-free ASGM sector.

In the coming months, ZELA will be sharing more on why miners should opt for mercury-free methods.

[1] NAP 2018

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