Photo by Tómas Munita
Mercury and Why It’s Dangerous
Mercury is a naturally occurring element found in air, water, and soil. The only metal that remains liquid at room temperature, mercury is difficult to contain and, once released, can travel long distances through water, air and the food chain. When not handled properly, it can have extremely damaging – even fatal – effects on humans, animals, and the environment. Exposure to mercury affects the brain, nervous system, kidneys, and lungs and can include symptoms such as lower IQ, sensory impairment, susceptibility to disease, disturbed sensation, and a lack of coordination. Exposure is particularly dangerous for children in utero and in early development. According to the WHO, mercury is one of the top ten most dangerous chemicals to public health.1
The toxicological effects of mercury are not only dangerous to humans. Experts have found evidence that mercury contamination affects populations of wildlife impacting reproduction, growth, neurodevelopment, and learning ability. Mercury exposure can lead to behavioral changes that debilitate an animal’s capacity to mate, hunt, and avoid predation, compromising the survival of affected populations and overall biodiversity.2
Mercury and Artisanal and Small-Scale Gold Mining
Artisanal and small-scale gold mining (ASGM) is the largest human-caused source of mercury in the environment, emitting as much as 1,000 tons of mercury, roughly 40% of the global total.3 Miners typically use mercury to separate the gold, forming a mercury-gold amalgam. There are two ways of using mercury in gold mining: concentrate amalgamation, in which miners apply lesser quantities of mercury after concentrating the ore; and whole-ore amalgamation, in which miners apply greater quantities of mercury without prior concentration. While relatively uncommon in the Amazon, whole-ore amalgamation is considered by the Minamata Convention on Mercury as a worst practice, to be eliminated.4
When miners mix the gold-bearing ore with mercury to extract gold, mercury enters the local environment, where it can precipitate into ecosystems, poisoning rivers, fish and crops. Once in waterways, bacteria absorb mercury and transform it into methylmercury, an organic compound more toxic than inorganic mercury, which bioaccumulates up the food chain. Furthermore, when miners and owners of gold shops burn the mercury-gold amalgam to purify the gold, their families and communities may directly inhale dangerous amounts of mercury vapor. Some miners and mineral processors may also use sodium cyanide to obtain residual gold from mercury-contaminated tailings (mining waste). When disposed of improperly, this process releases mercury-cyanide complexes into waterways, which are highly bioavailable and represent a significant threat to downstream aquatic life.
Mercury in the Amazon
Mercury contamination and exposure endangers the health of the people, plants and animals of the Amazon. Elevated mercury levels in humans are widespread in the Amazon region, particularly in indigenous communities, which report on average 7.5 times higher than background levels in the general population.5 People are exposed in a variety of ways, but fish consumption is a dominant pathway. In Madre de Dios in the Peruvian Amazon, authorities declared a state of emergency in eleven districts in 2016 due to mercury poisoning in local populations.6 Fish-consuming animals like river dolphins and jaguars are also at risk. One study in the Amazon and Orinoco Rivers found that 26% of river dolphins exceeded safe limits for humans set by the WHO.7
ASGM is widespread in the Amazon and accounts for a significant source of mercury pollution. While there is a lot of uncertainty when it comes to estimating mercury pollution, one study estimated that ASGM accounts for 71% of total emission in the Amazon.8 Estimates of mercury emissions in the Peruvian Amazon have been particularly alarming, with 185 tons released in riverways per year.9
It is important to note that ASGM is not the only factor to consider when assessing mercury contamination. Many areas in the Amazon have soils naturally enriched with mercury and processes such as geologic weathering, erosion from deforestation, biomass burning, plant transpiration and decomposition, and hydrological patterns all play an important role in the release and transport of mercury. For these reasons, non-ASGM sources of deforestation and soil disturbance must also be carefully considered to properly understand the sources and exposure routes of mercury.10
The Minamata Convention on Mercury
Currently governments and non-governmental organizations are making efforts to reduce and eradicate the use of mercury. On January 19, 2013, 140 countries ratified the Minamata Convention on Mercury, an international treaty designed to protect human health and the environment from anthropogenic mercury releases through the phase out and phase down of mercury-use in products, processes and economic sectors. As of 2021, 133 countries are party to the Convention, including all Amazon countries apart from Venezuela. Under the Convention, countries with significant ASGM are obligated to create a National Action Plan (NAP) to reduce, and where feasible, eliminate the use of mercury. NAPs typically include training in mercury-free or mercury-reducing mining techniques, steps to facilitate formalization, strategies to regulate the mercury trade, education in affected communities, public health strategies, and market-based incentive mechanisms.11
While some progress has been made, mercury is still being released into the atmosphere at alarming rates. Educational groups, human rights organizations, governments, and other NGO’s must take immediate action in regulating the release of mercury by promoting safer mercury-free gold mining practices, and by educating populations on how to protect themselves and their ecosystem from the extreme consequences of mercury poisoning.
- World Health Organization. (2017). Mercury and Health. https://www.who.int/news-room/fact-sheets/detail/mercury-and-health
- Dalberg. (2018). Healthy Rivers Healthy People Addressing the Mercury Crisis in the Amazon. World Wildlife Fund. https://www.wwf.org.uk/sites/default/files/2018-11/WWF%20-%20Healthy%20Rivers%20Healthy%20People.pdf
- UN Environment Programme. (2019). $180-million investment to tackle the hidden cost of gold. https://www.unep.org/news-and-stories/press-release/180-million-investment-tackle-hidden-cost-gold
- UN Environment Programme (2014). Minamata Convention on Mercury. https://www.mercuryconvention.org/en, accessed 30 August 2014
- Basu N, Horvat M, Evers DC, Zastenskaya I, Weihe P, Tempowski J. A State-of-the-Science Review of Mercury Biomarkers in Human Populations Worldwide between 2000 and 2018. Environ Health Perspect. 2018 Oct;126(10):106001. doi: 10.1289/EHP3904. PMID: 30407086; PMCID: PMC6371716
- Ashe, K. (2012). Elevated Mercury Concentrations in Humans of Madre de Dios, Peru. Public Library of Science, ONE Vol. 7, No. 3: e33305. https://doi.org/10.1371/journal.pone.0033305
- Mosquera-Guerra, F., Trujillo F., Parks, D., Oliveira-da-Costa, M., Usma, S., Willems, D., Maldonado, R., Amorocho, D., Berg, K., Armenteras-Pascual, D., Van Damme, P., Sainz, L., Franco, N., Mantilla-Meluk, H., Carvajal-Castro, J., Cambell, E., Cordova, L., Echeverria, A., Caballero, S. & Marmontel, M., Presence of mercury in river dolphins (Inia and Sotalia) in the Amazon and Orinoco basins: evidence of a growing threat for these species.
- Arctic Monitoring and Assessment Programme, United Nations Environment Programme. (2013). Technical background report for the global mercury assessment 2013.
- Global Environment Facility (GEF). (2018). Mercury-free mining: UNDP, GEF, and the Government of Peru work together to reduce the use of mercury in artisanal and small-scale gold mining. Lima, Peru, January 17.
- Hacon, S., Barrocas, P.R,G., de Vasconcellos, A.C.S., Barcellos, C., Wasserman, J.C., Campos, R.C., Ribeiro, C., & Azevedo-Carloni, F.B. (2008). An overview of mercury contamination research in the Amazon basin with an emphasis on Brazil. Cadernos de Saúde Pública, 24(7), 1479-1492. https://doi.org/10.1590/S0102- 311X2008000700003
- United Nations Environment Programme (2014).Minamata Convention on Mercury. https://www.unep.org/resources/report/minamata-convention-mercury. Accessed 31 August 2021
Learn More about Mercury in the Amazon
Luis E. Fernandez is a research ecologist at the Carnegie Institution's Department of Global Ecology, and is the director of the Carnegie Amazon Mercury Project (CAMEP), a multi-institution research initiative that examines the impacts of artisanal gold mining,...