Challenging Habitat Blog

I am fascinated by the eery beauty of the shore’s reflections in the mirror of the water.

Horizontal symmetry.

Rocks and branches disappear into the image.

And I see different things every time.

Living by the banks of the Tamar estuary is a privilege I am immensely grateful for.

During lockdown, while working part-time from home, it allows me to nip out and spend an hour or two on the water around high tide.

It’s beautiful and calming.

It eases the eye fatigue that relentless online work inflicts on me.

Quietly paddling along, an egret gracefully crossed the river in front of me, brilliant white in the bright sun.

Every cityscape is enhanced when viewed through the rigging of a tall ship. OK, perhaps that’s only so these days when we’re aboard voluntarily!

Plenty of people turned out to see Pelican of London arrive in the historic docks outside Merseyside Maritime Museum.

And I am happy to join the ship today and lead the science education programme for the next few weeks.

Meanwhile, the new contingent of young people are undergoing Covid-19 security before stepping on board while we wait in the sunshine getting to know each other.

Follow our journey of discovery, thrills and learning around the northern part of Britain on this blog and @plymenv @darwin200

Back on Dartmoor!

The expanse of valleys and tors, a distant glimmer of the sea.

What a treat!

An ancient stand of oak amidst boulders, moss and lichen.

The call of a cockoo.

Swathes, no, ‘fields’ of cotton grass like I’ve never seen before.

A sheep-free zone and freedom for my dog.

Crossing a water course, getting soaked knee-deep.

A good workout climbing out of the valley.

Buffeted by a sharp wind on top of tors. Time to put on a woolly hat!


Evocative names on the map: Devil’s Tor, Foxholes, Tinner’s Hut, Beardown Tor, Crow Tor…

Torrents cascading over large rocks in a beechwood valley.

Uplifting. Restorative. Magic.

A tranquil morning paddle is a perfect start to my day.

All is quiet, a heron changes perch from Cornwall to the Devon bank of the Tamar.

Fish disturb the surface and their ripples on the water mingle with mine, creating new patterns.

Time for coffee! and I paddle on.

Would you encourage your children onto a playground you know is heavily contaminated with arsenic?

Most probably not!

But the public is encouraged to use the heavily arsenic contaminated grounds of Devon Great Consols mine near Plymouth (UK) for recreation: walking, riding, biking, picnicking, exploring…

You think that’s crazy? You may be in a minority!

In 2007, the Tamar Valley AONB were successful in attracting £7 million investment from the Heritage Lottery Fund, Europe, County Councils and others for the Mining Heritage Project. Works commenced with consultancy surveys and finished with the opening of 25 km of trails that allow the public to access some of the most contaminated land in the country.

Some of this money was spent on remediation and mitigation: shafts were fenced off and signs were installed (not barriers) that intended to prevent access into some of the most polluted parts of the site.

Today, a lovely video praises this site for its family-friendly atmosphere and shows people jogging and biking on highly polluted ground – oblivious of the dangers they are in.

What’s more: the land owner permits a mountain bike club to use one of the most contaminated mining waste heaps for downhill practice and competitions.

Time to get real:

Arsenic is a deadly poison: the dose necessary to kill a person is somewhere between 100 mg and 300 mg, or one tenth to roughly one third of one gram of inorganic arsenic.

Chronic poisoning, the type people around the world are exposed to as a result of contaminated water supplies and occupational exposure, leads to serious consequences, including cancers of many organs, skin diseases, abdominal pain and diarrhoea, confusion and memory loss, neonatal morbidity and mortality, lung diseases and disruption of endocrine and haematological systems (Ratnaike, 2003).

Is anybody doing something about this?

I’ve tried for over a decade for this contamination to be taken seriously with respect to environmental health. Now, we’ve published work relating to human health.

Here is what we found:

  • across the site, the enrichment with arsenic is 600 fold relative to the soil concentrations in the Tamar river catchment (based on median)
  • concentrations ranged from around 140 to 75000 microgram per gram (µg/g) of soil or dust (that’s 7.5% by weight)
  • health-based soil guidelines values developed by the Environment Agency of England and Wales are 179 µg/g for park-type soil and 640 µg/g for commercial land
  • ingestion simulation with gastro-intestinal fluids testing the biologically accessible concentration in soils showed that most samples exceeded the park-type soil level
  • of 98 measurements taken on publicly accessible trails and places on site, only one (1) showed arsenic concentrations suitable for parkland and only 13 were suitable for commercial activities
  • particles in all air samples taken along trails and mountain bike tracks exceeded the current European Directive annual average target value of 6 nanogram arsenic per meter cubed (ng/m3), in one case by more than 10 times
  • lung fluid simulation showed that target values for arsenic were exceeded in many samples, indicating that the biologically accessible concentrations were too high
  • the calculated Index Dose of Minimal Risk from ingestion and inhalation of arsenic is 0.302 microgram per kilogram of body weight per day (µg/kg bw /day) and it is estimated that children ingest around 100 mg soil
  • a child of 1-2 years old and weighing 9.8 kg visiting the sites for 6 hours may ingest 25 mg of soil containing on average 13000 µg/g arsenic would be exposed to more than 10 times (33 µg/kg bw /day) the Index Dose of Minimal Risk
  • the equivalent exposure is more than 7 times (2.3 µg/kg bw /day) the Index Dose of Minimal Risk

What does this mean?

  • arsenic concentrations at Devon Great Consols are sufficiently high to be a public health concern
  • frequent visits, or indeed working on site, could significantly increase one’s risk of chronic arsenic poisoning
  • activities that encourage airborne dust, such as mountain biking, riding and walking in dry conditions increase the risk of inhalation
  • deviating from permissive paths onto mine waste material that is not fenced off increases the risk to health
  • mitigation measures are urgently needed to protect the public and employees

What can be done?

In my own opinion, and not necessarily reflecting the opinions of my co-authors of the scientific paper, the site should be instantly closed the general public. However, more pragmatically, and as a minimum, leisure pursuits should be minimised to less contaminated trails, areas fenced off that are highly contaminated and comprehensive information signage installed. Furthermore, the contaminated car parking area and timber storage yard to the north of the site must be closed to protect workers and visitors. The public must be excluded from the area of highly contaminated remains of arsenic processing and refining installation (calciners and labyrinth). Mountain biking activities must be disallowed on mining waste.

More mid-term, and in the interest of re-opening the site, contaminated trails could be remediated by removing surface layers and replacing them with inert materials.

In addition, covering the mine waste to prevent water ingress, erosion and dispersal of contaminated material would be a long-term target to protect the site and surrounding farmland and dwellings. Large-scale engineering solutions are expensive, disruptive and not sympathetic to the mining heritage. Therefore, I would suggest a phyto-stabilisation approach through re-vegetation.

I can only hope that someone out there cares enough to make it happen!

If you want a little bit more of the back story – go to my post ‘Challenging Habitat‘ and follow the links in the introductory paragraph.


All detail stated here has been either linked to external sources or is referenced in the published scientific article:

Braungardt C, Chen X, Chester-Sterne D, Quinn JGA, Turner A (2020). Arsenic concentrations, distributions and bioaccessibilities at a UNESCO World Heritage Site (Devon Great Consols, Cornwall and West Devon Mining Landscape). Environmental Pollution 264.

This work is accessible free of charge until 5th July 2020 from the publisher at:

After that date, please contact me directly for an electronic copy at


View over Anna Maria waste heap from one of the trails at Devon Great Consols mine. Photo: C Braungardt, 2018.

Let me take you to an excursion to the origin of this blog: I started writing about my thoughts on mining and its legacy in the UK and beyond. I wrote about the soils contaminated by metal mining and how lichens and mosses start natural succession in the most challenging habitats. There were posts on the toxicity of legacy mine sites and their effect on the wider environment, especially rivers, as well as touched on social and health aspects of the industry.

Together with two colleagues1 and two MSc students2 at University of Plymouth, I have taken up this latter thread again with a scientific risk assessment for people who frequent legacy mine sites contaminated with arsenic and metals for recreation or work.

Specifically, our research focused on the mining complex of Devon Great Consols in the Tamar Valley Area of Oustanding Beauty (AONB), an area of 67 hectare that is part of the UNESCO World Heritage Site ‘Cornwall and West Devon Mining Landscape‘. The mining history of Devon Great Consols began in the 16th century and ended in 1985 and broke several records, including ‘largest sulfide lode in West England’, ‘largest copper producer’ in the 1850s and in the 1870s, ‘largest arsenic producer’ in the world.

The mine generated great wealth for its owners and shareholders (Stewart, 2013), which at the time, were not bound to undertake remediation upon mine closure. Yet ores below ground and great heaps of waste materials at surface remain rich in arsenic, copper, zinc, iron, tin, tungsten and a range of other metals. Sporadically, the mine was worked for arsenic, tin and tungsten up to the 1930s and the waste heaps were reworked for copper and tin in the 1940s and 1970s. The site remains heavily contaminated, as documented by many scientific publications by the British Geologic Survey and others.

The relatively recent disturbance by mining activities, car rallies (!) and mountain biking combined with the toxic nature of the material means that vast areas remain bare of vegetation. This leaves the toxic waste vulnerable to erosion by wind, rain and frost.

A substantial proportion of the 67 hectare site is less contaminated than the waste heaps and much of that is under woodland management. However, some of the work areas are close to or directly on land covered in mine waste. Moreover, the area has been opened up to the public for walking, biking, horse riding, learning and picnicking on and along a network of 25 km of trails, put in place by the Mining Heritage Project of the Tamar Valley AONB. Arsenic is still abundant on site and it is highly toxic and carcinogenic, as I detailed in a previous blog post and is a major chronic health concern in many areas of the world (e.g. Ratnaike, 2003; World Health Organisation)

The question is obvious: how safe is it today to work here or visit this place for recreation?

Our research investigated the risk to health associated with spending time at Devon Great Consols. We re-assessed general levels of contamination, what happens to arsenic in the human body when the waste material is ingested or inhaled.

We found that parts of the site accessible to the public greatly exceed soil guideline values for arsenic and that exposure of visitors and employees is greater than the dose of minimal risk to health. This led us to urge mining areas to be more thoroughly mitigated before being repurposed and opened to the public.

Our work has been published in the peer-reviewed scientific journal “Environmental Pollution“, which I have summarised for non-scientists in a related post: Arsenic Health Risk at UK World Heritage Site.


1 Dr Andrew Turner, Associate Professor in Environmental Science and
Mr Jamie Quinn, cartographer at the University of Plymouth, UK
2 Ms Xiaqing Chen and Mr Daniel Chester-Sterne, both graduates of MSc Environmental Consultancy at the University of Plymouth, UK


MSc students at the base of Anna Maria waste tip at Devon Great Consols mine, 2018. Image by C Braungardt.


Braungardt C, Chen X, Chester-Sterne D, Quinn JGA, Turner A (2020). Arsenic concentrations, distributions and bioaccessibilities at a UNESCO World Heritage Site (Devon Great Consols, Cornwall and West Devon Mining Landscape). Environmental Pollution 264. Accessible for free of charge from the publisher until 5th July 2020 at:
After that date, please contact me directly for an electronic copy at

Ratnaike RN (2003) Acute and chronic arsenic toxicity. Postgraduate Medical Journal 79:391-396. [link]

Stewart RJ (2013) Devon Great Consols. A Mine of Mines. The Trevithick Society, Camborne. Obtainable from The Trevithick Society [link]

It is such a gift being able to enjoy a tranquil paddle in the early morning.

It is balance on the board and balance for the mind.

The sound of nature. Reflections of clouds on the water. A fish jumps, a low flying shag passes by.

For an hour the river seems to be mine as I drift in the mist, feeling grounded and calm. Content. Happy.

Social isolation at its best!

A tranquil paddle before breakfast rewards me with experiencing the moment, hearing the birdsong, seeing beauty, feeling the water beneath the board, balancing, an empty mind – clarity.

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.

Blanchdown Adit

Blanchdown adit, the main drainage of Devon Great Consols mine in the Tamar Valley, UK. Photo (c) C Braungardt 2016.

Geevor mine, West Cornwall

Minerals precipitating from mineral-rich seepage on the rocks at Geevor mine in Cornwall. Photo (c) C Braungardt 2011.

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.


Efflorescent salts on the surface of mine waste at Devon Great Consols mine (UK). Photo (c) C Braungardt, 2007.

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. [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.

Featured image: River in southern Sardinia polluted by the mining industry. Photo (c) C Braungardt 2007.

General Reading

Stewart RJ (2013) Devon Great Consols. A Mine of Mines. The Trevithick Society, Camborne. Obtainable from The Trevithick Society [link]

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