Gold Mining and Mercury Emissions in Manica, Mozambique

Marcello  Veiga showing the retort to miners in Munhena.
Manica, Mozambique
Mercury, Elementel Mercury
Artisanal Mining, Mining
water, trophic accumulation, soil, direct contact, air
Potentially affected people:

The problem

This project seeks to contribute to the reduction of occupational health hazards of small-scale gold miners in the Manica District of Mozambique by promoting the use of mercury retorts, while at the same time leading to overall reduction of environmental degradation in the region.

Manica is a district of Mozambique in the Manica Province with a population of 155,731 people. Manica District borders with the Republic of Zimbabwe in the west, the District of Gondola in the east, the District of Barué to the north through the Pungué River, and the District of Sussundenga in the south, which is bounded by the Revué and Zonué Rivers.

In the Manica District of Mozambique, more than 10,000 people are directly and indirectly involved in artisanal (small-scale) gold mining activities (garimpagem) as their main source of income. Most of “garimpeiros” (artisanal miners) use mercury to extract gold form the mineral ore; the amalgation process recovers very little of that mercury, which pollutes the nearby environment. The majority of the mercury used pollutes local waterways and soil as well as threatens the livelihood of plant and animal species in the area. Mercury amalgamation results in the discharge of an estimated 1000 tons of mercury per annum, representing about 30 percent of the world’s anthropogenic mercury releases.

The process of amalgamation transforms elemental mercury into methylmercury—one of the most toxic organic compound and a powerful neurotoxin that works its way up the food chain through bioaccumulation. According to the Ban Mercury Group, as much as 95 percent of all mercury used in small-scale gold mining is released into the environment, constituting a dangers on all fronts—economic, environmental and human health. It is estimated that over 13 million people work as artisanal miners worldwide

Health Impact

What are the health effects of mercury exposure?

The nervous system is very sensitive to all forms of mercury. Methylmercury and metallic mercury vapors are more harmful than other forms, because more mercury in these forms reaches the brain. Exposure to high levels of metallic, inorganic, or organic mercury can permanently damage the brain, kidneys, and developing fetus. Effects on brain functioning may result in irritability, shyness, tremors, changes in vision or hearing, and memory problems.

Short-term exposure to high levels of metallic mercury vapors may cause effects including lung damage, nausea, vomiting, diarrhea, increases in blood pressure or heart rate, skin rashes, and eye irritation. (ATSDR - ToxFAQs™)

Current Activity

Blacksmith Institute is supporting the Ministry for the Coordination of Environmental Affairs (MICOA) in Mozambique to identify and train staff who will work with local miners. Once miners know how to use retort technology, their exposure to toxic mercury vapor is reduced, as is the release of mercury into the environment. The United Nations Industrial Development Organization has joined Blacksmith in this initiative in Manica Province. Blacksmith's Technical Advisor on Mercury related projects, Professor Marcello Veiga of the University of British Columbia, has been able to unite Blacksmith and UNIDO to contribute to the reduction of the occupational health hazards of small-scale gold miners in Manica Province. Professor Veiga, who serves as Chief Technical Advisor to UNIDO’s Global Mercury Project, traveled to Manica to provide technical assistance to officials from the government and academia by engaging in active demonstrations, discussion and analysis.  

Field visits were conducted to assess health and technological needs in Manica, with particular emphasis on the chosen pilot areas for community training. The program was carried out by a team of four international experts from the GEF/UNDP/UNIDO Global Mercury Projust, in collaboration with five locally-based practitioners who were selected and trained in Manica under the coordination of the Centre for Sustainable Development for Natural Resources Management (in Chimoio). Studies and breath test samples revealed that the average level of mercury in the miners in Munhena, the main training site, was 8.23 µg/m^3. Some burners had above 50 µg/m^3 (50 times higher than the WHO guideline for maximum public exposure to mercury vapour). Second, a training protocol was developed in the pilot project area to introduce miners and their families to mercury retort technologies and related ways of reducing mercury emissions. Tests performed with homemade retorts showed that mercury emissions can be reduced significantly and cheaply. Following the training sessions, preliminary use monitoring of these systems showed that the miners were using the retorts successfully. Adopting a community participatory approach, the implementing organizations devised follow-up plans including the establishment of a Community Amalgamation Centre and other opportunities for future collaboration.


The introduction of bowl- and pipe-shaped retorts was successful and well-received by the communities in Munhena, Manica District, Mozambique. Continued monitoring is necessary to ensure successful operation of the retorts left with the workers. The miners were also shown how to make their own retorts and further monitoring should ensure that they were able to do so successfully. Further fieldwork is also necessary to train more people in the community and develop their capacity to implement the solutions that were introduced in this pilot project.

Further fieldwork is necessary to train more community members and develop their capacity to implement the solutions that were introduced in this pilot project. Moreover, the impacts of methylmercury in the pilot study area were not assessed and should be investigated into in the future. Granted the rapid increase in artisanal gold mining activities in many African countries, the success of this project suggests that this model should be replicated on a larger scale in other communities as well.

In order to continue the effectiveness of the pilot project, an Amalgamation Centre in Munhena will be built with specifications including a cement tan to store amalgamation tailings, a small mill (as they use) made of gas tanks with a coarse chain inside or rubber balls to amalgamate their concentrates, avoiding manual amalgamation, a PVC filter that can be attached to a bicycle wheel to remove excess mercury from amalgams avoiding manual contact with mercury, etc.

We have also identified other exposure pathways for future observation. Mine tailings containing mercury are washed off into large rivers in the area therefore health conditions of fish must be analyzed. Moreover, during seasonal flood events, more mercury contaminated soil and dust enters into water bodies.

Since mining activities make up a major source of income in the area, technicians at the Provincial Direction of Mineral Resources who buy gold from artisanal miners are also exposed to high levels of mercury vapor. Studies show that these technicians are exposed to what could be 35 times higher of mercury levels compare to the WHO safety guidelines. One of the solutions for the employees is to receive the gold in the lab, i.e. under the fume hood, and dissolve residual mercury with nitric acid, instead of receiving the gold in the confined office space where contamination is more likely.

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