Acid drainage: the global environmental crisis you’ve never heard of

Dr Stephen Tuffnell, Associate Professor of Modern History, at the University of Oxford, describes the environmental damage caused by acid mine drainage in an article for the Conversation.

Red river waterfall, “Rio Tinto”. alredosaz / shutterstock

Romania’s prime minister, Mihai Tudose, recently raised the prospect of reopening the country’s huge Roșia Montană goldfield. The area had been mined from Roman times until the last state-run operation closed in 2006. An application by a previous government to make the area a UNESCO world heritage site has now been withdrawn, paving the way for new development.

Roșia Montană is nestled in the Carpathian mountains and, with 314 tonnes of gold, has Europe’s largest known deposits. A short-term mining bonanza promises employment for thousands of labourers and hundreds of millions of Romanian Leu in investment in the EU’s fastest-growing economy. But is the boom really worth it? After all, gold mining has historically resulted in long-term, chronic environmental problems. Roșia Montană is big, but the threats posed by acid mine drainage are bigger.

The problem is, if completed, the so-called Roșia Montană project would use “cyanide amalgamation” to extract the gold from its ore body. This is the same cyanide used to poison people, fish and elephants. It has a toxic past in Roșia Montană, too: back in the 1970s, a copper mine in the area needed somewhere to store its cyanide-contaminated waste and the nearby village of Geamana was evacuated and flooded. It has been submerged under toxic waters ever since.

Geamana is one of Romania’s greatest ecological disasters, surpassed only in 2000 when a gold mine in Baia Mare in the north of the country spilled an estimated 100 tonnes of cyanide into a river. The latter incident was described as Europe’s worst environmental disaster since Chernobyl. No wonder that when the government first mooted the resumption of mining in 2013, it led to weeks of protests – protests which now threaten to erupt again.

Gold’s dirty secret
Cyanidation was the breakthrough gold mining technology of the 1890s, when it enabled Anglo mining conglomerates to make colossal profits from low grade ores. Simply put: cyanidation involves mixing finely crushed ores (referred to as “sands” or, when water-based, “slimes”) in a weak cyanide solution (usually calcium cyanide). This solution is then mixed in large tanks and the gold separated from its ore body.

The process increases yields of gold but produces immense quantities of highly-toxic waste that releases acid and metals into the environment. Around 90% of all gold extracted worldwide uses this method.

The waste from cyanidation is a fine rock solution that is left in open air ponds while the concentration of acid is reduced to legal limits. The risk here is from dam failure or breakages in the lining of waste ponds, which can lead to catastrophic spills or leakage through the porous land surface into the water table.

In nearly all metal mines, and some coal mines, acid drainage occurs because of the oxidation of iron ore found alongside precious mineral deposits. Uncovered by the mining process, the iron reacts with the air and releases sulphuric acid into the water. This process can last centuries. Spills from cyanidation waste are more short-lived, but more highly toxic than acid mine drainage occurring through iron oxidation.

The ratio of waste to metal recovered in gold mining is vastly disproportionate: the Fimiston Super Pit, near the West Australian town of Kalgoorlie, and until recently the largest open cut mine in the world, has returned approximately 1,640 tonnes of gold since operations began there in 1989. But that’s only a small portion of the 15m tonnes of rock extracted per year. A typical gold wedding ring will generate about 30 tonnes of waste.

The river runs yellow
Cyanidation poses catastrophic ecological risks because cyanide leaks so easily into groundwater. Historical parallels suggest the Romanian proposal will most likely leave a toxic legacy.

In 2015, as the US Environmental Protection Agency attempted to drain polluted water from the Gold King Mine, Colorado, which was closed in 1920, more than 3m gallons were accidentally spilled into the Animas River. The polluted plume turned the entire river a deep mustard yellow. Water acidity levels increased 100-fold, and in some places a thousand times over levels considered safe for wildlife.

The spill only posed no threat to fish in the Animas because ongoing pollution had already killed them. But the plume drained into the San Juan, a larger and cleaner river that flows into the spectacular Glen Canyon and, eventually, the Grand Canyon. There, the pollution threatened rare birds and endangered fish like the Colorado pikeminnow and razorback sucker.

The Animas River as normal, on the day of the Gold King Mine spill. Barbara K Powers / shutterstock

The Animas River a day later. Barbara K Powers / shutterstock

EPA chief Scott Pruitt returned to the site at the beginning of August this year vowing to complete the clean-up after the agency had “walked away” from the problem. At a water treatment plant installed on the site, 500 gallons of mercury and arsenic-laced water a minute flow from the Gold King Mine. The clean-up could take a decade and has already cost the EPA US$29m. The EPA has estimated that the cost of cleaning up just 156 mines in the US could be between US$7billion and US$24 billion. Clean-up on most sites will take decades – those with acid drainage will require water treatment in perpetuity.

A global crisis
Acid drainage is a little-known global crisis. The UN has even labelled it the second biggest problem facing the world after global warming. In the US, an estimated 22,000km of streams and 180,000 acres of freshwater reservoirs are affected by acid mine drainage. Rivers and lakes in Arizona, Patagonia, Guangdong (China), Ontario, Papua New Guinea, and at Rio Tinto in Spain, to name just a few, have all been polluted by acid mine drainage. In South Africa, the problem is chronic.

These threats are prescient. Brazil recently announced a huge reserve in the Amazon rainforest has been earmarked for mining, including gold. In New Zealand, local activists fear the Karangahake Gorge is now under threat after a large, high-quality gold seam was found in the region. Around the Yellowstone National Park, mining companies are positively salivating at the possibility that Obama-era restrictions will be lifted, granting access to 3,000 tonnes of proven in-ground gold reserves. In Peru, marines have been dispatched to wage war against illegal mining on the River Santiago in the northern Amazon, which has done enormous damage to the region’s bio-diversity and placed the livelihoods of 70,000 indigenous Awajúns and Wampís at risk.

Multinationals hold out the promise of sustainable development through mining. But without careful forethought we’ll find ourselves dealing with chronic pollution for centuries.

Stephen Tuffnell, Associate Professor of Modern US History, University of Oxford

This article was originally published on The Conversation. Read the original article.

Documenting climate change along Nepal’s Gandaki River, from peaks to plains.

An Oxford University and ICIMOD (International Centre for Integrated Mountain Development) team embarks on an expedition to Nepal’s Gandaki Basin to explore ways in which climatic changes are contributing to vulnerability in the mountains, hills and floodplains of Nepal.

Photo by H2O filmmaker Ross Harrison, from film Facing the Mountain, produced in 2016.

A team from Oxford University recently travelled to Nepal to join the Himalayas to Ocean (H20) expedition. This initiative, a partnership between Oxford University’s Environmental Change Institute and the International Centre for Integrated Mountain Development (ICIMOD) , will see the project team follow the course of the Gandaki river, documenting the impacts of climate change along the way. The journey will start in the mountains of Mid-Western Nepal in Mustang, before heading downstream to the hills of Gulmi, and finally, the floodplains of Nawalparasi. The project will complement research on the ground by communicating change in novel, engaging ways, using creative audio-visual approaches that blend photography, video, and sound to capture stories from those at the frontline of climate change. It aims to raise awareness about the varied and complex ways in which climatic changes are already affecting communities and are contributing to their vulnerability.

The Hindu Kush-Himalayas serve as freshwater towers, feeding the ten largest river systems in Asia and the rich cultural and ecological systems riparian to them. It is estimated that the Himalayas support drinking water, irrigation, energy, industry and sanitation needs to 1.3 billion people living in the mountains and downstream1. In Nepal in particular, water is a plentiful resource, with major sources found in glaciers, rivers, rainfall, lakes and ponds. Agriculture is a major water intensive source of livelihood; 81% of the working population engage in agricultural occupations2.

In past decades, however, the Hindu Kush Himalayan system has come under increasing threat due to growing pressures posed by population increase, urbanisation and poor planning. Compounding these factors is anthropogenic climate change. The Hindu Kush Himalayas are estimated to be warming three times faster than the global average, contributing to glacial retreat3. By 2050, parts of the Himalayas could see a 4-5C warming. However, the impacts of climate change in the Himalayas extend far beyond the melting of iconic glaciers. A growing body of research, led by the International Centre for Integrated Mountain Development (ICIMOD) among others, has indeed shown shifts in the hydrological cycle, with monsoon rain becoming more erratic, and extreme rainfall events becoming less frequent but more intense in nature. Such changes in hydrological patterns are likely to contribute to an increase in natural disasters such as floods, landslides, droughts, springs drying up, fires and storms.

As a relatively small landlocked country with a complex topography, unstable terrain, and irregular climate, Nepal is already one of the world’s most disaster prone countries. The expected increase in natural catastrophes under climate change scenarios will incur a growing burden on communities across Nepal, in particular in rural and impoverished areas where people’s capacity to adapt will be severely limited. In August 2017, Nepal recorded its worst rainfall in 15 years, which led to catastrophic floods in the south part of the country, killing over 150 people and displacing over 21,000 families, leaving them without adequate water access and sanitation. Although the links with climate change are unclear at this stage, these floods events follow an increasing trend of record precipitation, record temperatures and increasing frequency of natural disasters.

In response to these challenges, individuals, communities and organisations are coming up with innovative ways to minimise exposure to those hazard, and cope, adapt or build resilience to them. A recent publication by ICIMOD finds that communities in the Gandaki Basin have been using traditional knowledge, practices, and technologies already for quite some time to cope with adverse climatic stresses4. These include, for instance, the use of different soil and water conservation methods such as drip irrigation and technologies to retain soil moisture, and changing cropping patterns and crop composition. However, being largely reactive, these ‘autonomous’ mechanisms are being challenged due to the scale and intensity of climatic changes. As such, planned adaptation has become an important climate and development strategy in Nepal and across South Asia. Some examples of planned adaptation measures include, climate-smart farming, improved irrigation, soil and nutrient management technologies, and improved access to climate resilient seeds and technologies. Planned adaptation also means strengthening community-based institutions including insurance systems, and improved climate information services. The H2O team will explore these issues further during their expedition.

The expedition team is composed of students and professionals working on issues of environmental change and water security from the School of Geography and the Environment (Alice Chautard, Yolanda Clatworthy, Justin Falcone); professional filmmaker Ross Harrison, who has already produced a short film on change and resilience in the Himalayas; sound engineer Nicholas O’Brien; and humanitarian story-teller Sushma Bhatta from Nepal.

You can find more about the expedition on the H2website, or by following the team on Twitter, and Facebook.


  1. Karki, M (2012) Sustainable mountain development 1999, 2012 and beyond: Rio +20 assessment report for the Hindu Kush Himalayas. Kathmandu: ICIMOD
  2. FAO (n.d.) Nepal at a glance. 
  3. Xu, J; Grumbine, R; Shrestha, A; Eriksson, M; Yang, X et al. (2009) The melting Himalayas: cascading effects of climate change on water, biodiversity, and livelihoods. Conservation Biology 23: 520–530,
  4. B.R., Pandit, A. (2016). Classication of adaptation measures in criteria for evaluation: Case studies in the Gandaki River Basin. HI-AWARE Working Paper 6. Kathmandu: HI-AWARE


A version of this post was originally published on the Himalayas to Ocean blog.