Industrial activities, from energy production to mining are major sources of soil pollution. Intentional and accidental pollutant releases from industrial processes can pollute soils in close proximity or nearby industrial operations. Although most countries have legislation about environmentally sound management of emissions and wastes, and international standards for best practices for safe disposal, industrial accidents as well as historical sources continue to cause soil pollution, especially in low to middle-income countries. In the next few posts, I will unpack the industrial sources of soil pollution, focusing on a select few industries, and the socioeconomic complexities involved with how they contribute to pollution.
Mining can be a major source of trace metals during extraction and processing. Many rocks are naturally rich in deposits of trace elements including lead, chromium, arsenic, zinc, cadmium, copper, mercury and nickel (Martinez et al., 2018). These metals could be mobilized during ore extraction or natural weathering. A particular gold extraction method known as amalgamation, also abbreviated as ASGM (Mercury-dependent artisanal and small-scale gold mining), is popularly used among small-scale or artisanal miners, as it is inexpensive. However, this process is the largest source of mercury pollution on Earth, which is of concern as mercury is a highly toxic metal even at low concentrations.
Figure 1. The process of using liquid mercury in small-scale or artisanal gold mining, from crushing the rock to isolating mercury from the mercury-gold amalgam. Source: Esdaile & Chalker (2018).
How does mercury pollution affect soils? Elemental mercury is used to extract gold from the ore as an amalgam. The amalgam is isolated by hand and heated to distill mercury to leave the gold. Some of the vaporized mercury can settle in soil, where it is initially adsorbed. Non-adsorbed mercury might take several pathways such as volatilize or be taken up by organisms. They could even be transformed by anaerobic organisms to methylmercury. If the mercury becomes bioavailable, it can be transported into the food chain and water systems, disproportionately burdening children, and miners themselves. Mercury poisoning is especially harmful to fish which is a staple in many local communities diets and can lead to dire human health effects such as neurological damage.
Figure 2. ASGM can lead to the release of mercury in the atmosphere where it may end up in soils and water. Mining tailings also deposit mercury on land, and soil microbes could convert mercury into methylmercury (MeHg), which can be taken up by living organisms, including fish and people. Source: Phys.Org
Rising gold prices have driven the widespread use of ASGM. Approximately 1000 tonnes of mercury are released from ASGM. Gold mining and utilizing such methods to cut costs is a critical means of livelihood for approximately 10-19 million miners across Asia, Africa, and South America, including 5 million women and children. Esdaile & Chalker (2018) in their paper argue that this is an issue of chemistry, outlining suggestions for the chemistry community to develop mercury-free technologies and soil remediation to address this issue.
However, soil pollution resulting from ASGM is also implicated with social injustice and the broader political economy. Global gold demand directly impacts the speed and scale of mining operations, including using ASGM which is an inexpensive method, so as to cut costs. Large-scale mining is already becoming more difficult due to increasing resource scarcity. In addition to green chemistry, we must also be looking at reducing overall gold demand by designing circular economies. Gold is used in a variety of goods from electric cars to our smartphones. Luckily, gold is recyclable and we can reduce our excessive (or luxury) consumption of these goods.
Addressing labor issues, from child labor to worker's rights in global mining processes is also important. Many artisanal miners involved are part of an informal or illegal economy. Esdaile & Chalker (2018) outline that these gold miners should be integrated into a formalized economy where nonmercury alternatives can be introduced. However, I wondered why these miners turned to illegal activities to earn a living and found that many mining companies hold a monopoly over gold mines, thus communities turn to artisanal mining to extract and finish the gold product, giving them more financial benefits and independence.
Across regions in the Amazon rainforest, from Peru to Brazil, the occurrence of gold mining is rising and driving deforestation. At the same time, environmental regulations are limited due to corruption and power asymmetries between locals and authorities. Encouraging sustainable livelihoods, worker's rights and safety such as a fair living wage needs to be part of the solution when engaging policymakers and mining companies, aligned with the principles of environmental justice.
References
Esdaile, L. J., & Chalker, J. M. (2018). The Mercury Problem in Artisanal and Small-Scale Gold Mining. Chemistry – A European Journal, 24(27), 6905–6916. https://doi.org/10.1002/chem.201704840
Gerson, J., Wadle, A., & Parham, J. (2020, May 28). Small-scale mining for gold has produced long-lasting toxic pollution, from 1860s California to modern Peru. Phys Org. Retrieved February 13, 2022, from https://phys.org/news/2020-05-small-scale-gold-long-lasting-toxic-pollution.html
Gyamfi, O., Sørensen, P. B., Darko, G., Ansah, E., Vorkamp, K., & Bak, J. L. (2021). Contamination, exposure and risk assessment of mercury in the soils of an artisanal gold mining community in Ghana. Chemosphere, 267, 128910. https://doi.org/10.1016/j.chemosphere.2020.128910
Harper, B. J. (2020, September 23). How much gold is there left to mine in the world? BBC News. https://www.bbc.com/news/business-54230737
Kalamandeen, M., & Galbraith, D. (2020, June 30). Gold mining leaves deforested Amazon land barren for years, find scientists. The Conversation. https://theconversation.com/gold-mining-leaves-deforested-amazon-land-barren-for-years-find-scientists-141639
Mercury Poisoning in Artisanal Gold Mining. (2020, July 1). The Borgen Project. Retrieved February 13, 2022, from https://borgenproject.org/mercury-poisoning-artisanal-gold-mining/
Martinez, J. G., Torres, M. A., dos Santos, G., & Moens, T. (2018). Influence of heavy metals on nematode community structure in deteriorated soil by gold mining activities in Sibutad, southern Philippines. Ecological Indicators, 91, 712–721. https://doi.org/10.1016/j.ecolind.2018.04.021