Challenging Habitat Blog

A shard of pottery in a field reminds me of something in the history of the valley I live in.

Market gardening in the Tamar Valley (Devon and Cornwall, UK) has a rich tradition of growing anything from snowdrops and daffodils to soft fruit and apples. The industrial revolution brought on the intensification of horticulture, with higher demands on the maintenance of soil fertility.

This is where ‘night soil’ came in handy: human excreta, collected by the night soil men from buckets, cesspools and privies in Plymouth and Devonport Dockyards. It used to be transported in barges upstream with the tide and spread around the fields (I just hope that the same barges were not used to transport the food downstream …)

What is the significance of this shard of pottery in this story?

Night soil also contained other wastes: discarded pots, plates and bottles thrown out and broken when no longer useful. If you are lucky enough to have a garden in the Tamar Valley, you are as likely to find a beautiful glass medicine bottle, a clay orange marmalade jar or any number bits of patterned dinner plates, as you are to pierce your fingers on sharp pieces of broken greenhouse glass.

I fancy this as a piece of traditional Cornish blue and white striped crockery from many decades ago…but that’s just a fancy guess.

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.

References

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: https://authors.elsevier.com/a/1b18AzLNSVgDK

After that date, please contact me directly for an electronic copy at cbraungardt@plymouth.ac.uk

Image

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.

Footnotes

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

Image

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

References

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: https://authors.elsevier.com/a/1b18AzLNSVgDK
After that date, please contact me directly for an electronic copy at cbraungardt@plymouth.ac.uk

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]

Sometime it’s worth keeping your eyes glued to the ground.

Atypia affinis is a hunting spider that waits for prey to walk across its tuba shaped net spilling out of its burrow.

Then it rushes out, stabs its prey with big fangs and drags it home…

If you look closely, this one ‘munches’ on some winged insect while watching me watching it…

Metal mine waste tailings dam in Nova Scotia, Canada

Metal mine waste tailings dam in Nova Scotia, Canada. Photo C Braungardt 2010

Following on from writing about mining waste as a challenging habitat for plants (see ‘First Arrivals‘), I want to provide you with the means to make sense of the contamination present in the historic metal mining landscape in Southwest England (and by analogy, in similar settings elsewhere). Nearly 700 sites in England are considered contaminated with metals (DEFRA, 2009) and in the northern England alone, 12000 km2 of river catchment soils and sediments are directly affected by historic metal mining, with similar areas in the Cornwall and mid-Wales (EA, 2008). Here, I will try to answer the questions why (is it there ?), how much (of it?) and by placing numerical information into everyday context. .  Read More

DSC_0472

Mine waste and woodland in Cornwall, UK. Photo C Braungardt 2009

What makes plants thrive? The obvious answer is light, water and ‘good soil’. Light is not likely to be a limiting factor on most mine sites, as there is little growing that could provide too much shade. However, water can be an issue and that brings us to the concept of ‘good soil’.

So what is a ‘good soil’? It contains a mixture of humus (more than 5 %) and mineral particles (ca. 45 %) of different sizes, so that it has a good water retention capacity without making it water-logged, it is rich in major nutrients (nitrate, phosphate, potassium) and contains micro-nutrients within a concentration range that is somewhere between deficient and toxic, i.e. just right. Its acidity is modest and into its texture, plants can anchor their roots. Soil also contains air (ca. 25 %) and water.

A key component of fertile soil is humus that gives surface soils their dark colour and also can be found in well-tended compost heaps. Humus is defined by Oxford Dictionaries as ‘The organic component of soil, formed by the decomposition of leaves and other plant material by soil micro-organisms’.

Humus provides minerals and nutrients that are readily available for plants and is important for retaining water and nutrients in soils.   Read More

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