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Environmental Impacts of Mining and Smelting
In Zamfara, Nigeria a worker mines for gold. In 2010 hundreds of children in this area died from severe lead poisoning associated with gold ore processing. (Photo courtesy of TerraGraphics Environmental Engineering.)
The mining sector is responsible for some of the largest releases of heavy metals into the environment of any industry. It also releases other air pollutants including sulfur dioxide and nitrogen oxides in addition to leaving behind tons of waste tailings, slag, and acid drainage. Occupational and environmental exposure to heavy metals, silica, and asbestos can occur during mining and milling operations. The smelting process (extracting the metal from the ore) is associated with the highest exposures and environmental releases.
The hazards to human health caused by exposure to heavy metals – including lead, cadmium and mercury – have been thoroughly documented. These metals are associated with a range of neurological deficits in both children and adults in addition to a range of other systemic effects. Exposure to airborne silica and asbestos can cause lung cancer, pneumoconiosis and numerous other health effects.
Lead and Mercury Emissions from Mining
- Global releases of lead from smelting and refining nonferrous metals (e.g. gold, lead,
zinc, copper) total over 28,000 metric tons/year.1
- Global releases of mercury from smelting and refining nonferrous metals total 710 metric tons/year – the second largest source after power plants. 2
- Estimates of releases of mercury into the environment from artisanal/ small scale gold mining range from 400 to 1,102 metric tons/year.2 3
- Airborne emissions from metal mining and smelting in Australia, Canada, and the U.S.
– countries with some of the world’s best environmental controls – total 980 metric tons of lead and 9 metric tons of mercury annually (2008/2009). These lead emissions amount to more than 80% of lead production in these countries.4 5
While pollution controls can minimize exposures to workers and surrounding communities, these safeguards are often absent in mining and smelting operations in developing countries. Even relatively efficient mining operations result in enormous waste, emissions to air and water, and a legacy of environmental contamination in nearby communities. Around the world, unsafe mining and smelting practices have been responsible for a continuing series of environmental and human health disasters, which cause great human tragedy and undermine social stability, economic development and sustainability goals.
For example, in 2010, more than 400 children died in Zamfara, Nigeria from acute lead poisoning caused by unsafe mining and processing lead-containing gold ore. People grinding the ore, often in and around their homes, contaminated at least 180 villages over a wide area.
Even large-scale gold mining has significant mercury releases associated with ore processing. It is now known that significant mercury emissions result from cyanide leaching and even from mine tailings where no mercury has been added.6
Manual mills are used to grind ore from which gold is then recovered by mercury amalgamation in Mozambique. This is a very inefficient process that recovers less than 30% of the gold. (Photo courtesy of Rodolfo Neiva de Sousa.)
More commonly, small-scale gold mining utilizes significant quantities of mercury to extract gold from the ore. Exposure to mercury in these operations not only endangers miners and their families, but is also detrimental to the environment when deposited into the water supply. Artisanal gold mining employs an estimated 10-15 million miners in more than 55 countries.7 Estimates are that these small operations produce about 20% of the world's gold supply.
Many studies have documented significant mercury exposures in these gold mining communities. In the Madre de Dios region of Peru, gold shops serving small artisanal miners were found to have mercury levels that were more than 20 times the World Health Organization (WHO) occupational health standard for mercury.8 This region of Peru alone has over 20,000 informal gold mining operations.
Children Are Most Susceptible
Children suffer a disproportionate share of the disease burden imposed by mining pollution. The International Labour Organization (ILO) estimates that 250 million children are involved in child labor and that over 70 percent of them face hazardous conditions. Children in Asia, South America, and Africa participate in the mining of gold, tin, and precious metals. According to the United Nations Environment Program (UNEP), small-scale gold processing operations in developing countries employ one million children. Children, who are more susceptible to the impacts of heavy metals, tend to have higher exposures and generally account for the majority of deaths and disease associated with mass poisoning incidents from these operations. Studies have documented that children involved in mining have higher exposures to mercury, lead, and other metals and suffer severe lead and mercury intoxication.9
Grinding and crushing operations in gold processing result in unsafe exposures to lead, arsenic, and silica dust.
Assessing Hazards from Artisanal Mining in Nigeria
In 2012, OK International conducted an investigation of artisanal small-scale mines (ASM) throughout Nigeria to assess health hazards in an effort to prevent tragedies like the one in Zamfara. We visited gold mines, ore processing sites and lead mines where we collected soil and water samples and completed a hazard evaluation for each site. We also worked with the Nigerian Ministry of Mines and Steel Development (MMSD) in coordination with other government agencies to conduct a three-day training session to increase the capacity within government agencies to evaluate hazards in ASM.
Soil samples collected around gold ore processing at one site had lead concentrations as high as 1% in a location where miners also slept and ate. These concentrations pose a significant health risk to both the miners and surrounding communities. Not surprisingly, lead concentrations were also very high around artisanal lead mines where the ore had as much as 18% lead. We also found soil to be contaminated with mercury at gold processing sites where children were conducting amalgamation processes. In addition to the hazards of toxic metals in the ore, we noted very high silica dust exposures in ore processing.
Although some resources have been devoted to environmental remediation and medical treatment of poisoned children in Zamfara, little attention is being paid to the extent of the problem in other areas of Nigeria. There is no national or state level database of artisanal mines in Nigeria and information about the metal content in ore is lacking. Raising awareness among miners of the hazards and safer mining practices is desperately needed at ASM sites throughout Nigeria in order to prevent the occurrence of more lead and mercury contamination and silicosis. We are also recommending that the Nigerian authorities conduct a more thorough investigation of gold mines outside Zamfara to characterize locations with significant lead exposure.
Outsourcing Hazardous Processing – A Growing Problem
Over the past decade we have witnessed a growing shift to export the most polluting aspects of the mining industry to developing countries. For example, the U.S. exports millions of tons of lead ore to countries with more lenient environmental and occupational regulations and little enforcement. This trend has accelerated since the last primary smelter in the U.S. closed in 2013. In 2014, more than 70% of the lead ore mined in the U.S. was exported to China processing.
Sources: U.S. International Trade Commission; U.S. Geological Survey
The graph below shows that lead ore exports from the U.S. to China doubled between 2007 and 2014. China has reported more than 30 lead poisoning incidents around lead smelters and battery recycling plants since 2009.
Source: U.S. International trade Commission
Moreover, changes in the global economy threaten to increase the harm caused by unsafe mining and smelting practices. Growing demand for metals and increasing commodity prices are encouraging expansion of both formal and small-scale mining and recycling around the world.
In addition, initiatives aimed at reducing global carbon emissions can have the unintended consequence of increasing lead poisoning in developing countries. For example, the adoption of solar, wind power and electric vehicles is increasing demand for lead batteries. The development of new applications for larger lithium ion batteries is significantly increasing the demand for lithium, cobalt, manganese and other metals. This trend may continue if plans to accelerate the production of electric and hybrid vehicles are realized.
Global Campaign to End Hazardous Mining Activities
The response to the reported mass poisoning incidents surrounding mining and smelting operations is predictably similar from country to country: shock upon discovery of the problem, medical treatment of survivors (to the extent that resources are available), and a call for huge sums to remediate environmental contamination. In most cases no one is left to cover the costs of environmental cleanup or even to compensate workers harmed on the job. A new approach is needed to prevent these human health impacts and environmental contamination before the damage is done.
OK International is therefore calling for a global campaign to end dangerous mining, smelting and recycling practices that poison children, workers, and families in developing countries and leave adjacent communities devastated by widespread contamination. These efforts will instead encourage the adoption of improved practices in the most hazardous mining and smelting operations. This campaign would engage technical experts, create multi-stakeholder partnerships, develop and promote consensus standards, and link safety, health and environmental concerns with economic development. The campaign's goal is to change the norms of practice to prevent environmental contamination before medical treatment and costly cleanup operations are needed.
1 Soto-Jiménez MF, Flegal AR. “Childhood poisoning from a smelter in Torreon, Mexico.” Environmental Research 111 (2011): 590-596.
2 Pirrone N, et al. “Global Mercury Emissions to the atmosphere from anthropogenic and natural sources.” Atmospheric Chemistry and Physics 10 (2010): 5951-5964.
3 Telmer KH, Veiga MM. “World emissions of mercury from artisanal and small scale gold mining.” in Mercury Fate and Transport in the Global Atmosphere (2009): 131-172.
4 National Pollutant Release Inventory (Canada), National Pollutant Inventory (Australia), and Toxic Release Inventory (U.S.).
5 U.S. Geological Survey.
6 Eckley CS, Gustin M, Marsik F, Miller MB. “Measurement of surface mercury fluxes at active industrial gold mines in Nevada (USA).” Science of the Total Environment 409. 3 (2011): 514-22.
7 United Nations Environment Programme. “Draft business plan of the artisanal and small scale gold mining (ASGM) partnership area.” August 7, 2008.
8 Environmental Health News. “Townspeople, gold shopkeepers highly exposed to mercury in Peru.” April 11, 2011.
9 International Labour Organization. “Children in hazardous work.” 2011.