In 2008, the Environment Agency wrote “Abandoned mines are one of the most significant pollution threats in Britain” (EA, 2008). This pollution threat to fresh, ground and coastal waters arises from thousands of discharges of mine waters in England, Wales and Scotland carrying metals, such as cadmium, copper, iron, lead and zinc, as well as less common elements, such as thallium, arsenic and antimony. Metal pollution is not the only negative impact of mining in rivers, often minerals generate acid when they oxidise and this can lower the pH of water to levels far below the range of natural water courses (pH 5-8), with pH<4 observed in many mine waters, a significant number below pH 2, and some even exhibiting negative pH. As a result, an estimated 2858 km of river length in the UK are adversely impacted by abandoned metal mines, 981 km of which are located in the South West (EA, 2008). For example, every year the former mining centre around Calstock and Gunnislake contributes around 220 tonnes of iron, 62 tonnes of manganese, 14 tonnes of copper, 12 tonnes of zinc, 5 tonnes of nickel and 4.5 tonnes of arsenic to the contaminant load of the river Tamar (Cornwall/Devon, UK) (Mighanetara 2009).
This is a global issue. Growing population and increasing living standards demand more resource extraction. The detrimental impacts of mining on rivers and coastal waters are reported in the news, by non-governmental organisations and official records around the world: follow some links from South Africa, the USA, Colombia, Australia, China and Spain.
Mine waters can be very visible. For example, where iron-rich acid mine drainage emanates from an adit (a drainage channel leading out of underground mine workings), the iron that oxidises and precipitates as ochre when the mine waters gets into contact with the air. There are numerous examples of this phenomenon and a particularly (eerily) beautiful example is the outflow of Blanchdown adit accumulating and dewatering over time in its precipiation dam in the Tamar Valley.
In other places, ground water becomes enriched with salts as ores dissolve in old mine workings or mine waste piles. This may leave colourful traces on rocks as secondary minerals precipitate when the waters reach the surface. Examples are the rocks on the beach at Geevor Tin mine (Cornwall, UK) and the efflorescent salts observed on mine waste at Devon Great Consols mine (Devon, UK). Such salts, the product of wetting and drying cycles, are highly soluble and are easily washed into surface waters with rainfall.
But often, the contamination of rivers with elements, such as arsenic, zinc or thallium is not visible. Only investigations by scientists using sophisticated analytical techniques reveal the extent to which the environment is contaminated and what effects pollution has on plants, animals and ecosystems, as well as the risks to human health. But this will be the subject of future posts.
EA (2008) Abandoned Mines and the Water Environment. Science Project: SC030136-41. Environment Agency, Coal Authority and Environmental Protection Agency Scotland. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/291482/LIT_8879_df7d5c.pdf [accessed 24/07/2016]
Mighanetara K, Braungardt CB, Rieuwerts JS, Azizi F (2009) Contaminant fluxes from point and diffuse sources from abandoned mines in the River Tamar catchment, UK. Journal of Geochemical Exploration 100, 116-124.
Banner image: River in southern Sardinia polluted by the mining industry. Photo (c) C Braungardt 2007.
Stewart RJ (2013) Devon Great Consols. A Mine of Mines. The Trevithick Society, Camborne. Obtainable from The Trevithick Society [link]