The history of coal

The use of coal as a fuel is often associated with the industrial revolution of 18th Century Britain, but coal was an important source of energy even in Roman times.

A century before the industrial revolution, many cities in England were dependent on coal for heating and for artisanal manufacturing. Air pollution was already a huge problem in the capital. In 1656, the English poet Sir William Davenport published a tract that complained about the ‘canopy of smoke’ that covered the city of London.  He even wrote a song that included the lines [1]

The problem of air pollution in the capital was not really tackled until the mid-20th Century after the ‘Great Smog’ of 1952 killed several thousand people. So for at least 300 years, the air pollution caused by the burning of coal in the city was atrocious.

Coal is still a major source of primary energy—it was only knocked into 2nd place by oil in the mid-20th Century. Although its use as a fuel is declining in north America and Europe, it is increasing in Asia, and the production of coal is not expected to peak until after 2020.  In 2017, about 30 % of global primary energy production was still being supplied by coal.

All mining operations are inherently dangerous. The list of catastrophic coal mine disasters that have occurred over the last 200 years is long and horrendous–but coal mining today is a lot safer. Even so, coal mining leads US industries in fatal injuries : the 2007 fatality rate in coal mining was almost 25 per 100,000 workers—more than 6 times greater than all private industry. In the USA, employees in coal mining are more likely to be killed or to incur a non-fatal injury or illness, and their injuries are more likely to be severe, than workers in private industry as a whole [2].

The miners and the mines

Progressive massive fibrosis (PMF) is an advanced, debilitating, and lethal form of coal workers’ pneumoconiosis. It is known as black lung disease, which gives you an idea of what it does to a miner’s lungs.  Breathing in coal mine dust is the sole cause of PMF in working coal miners. There is no cure.

One would think that, at least in the US with all the awareness of environmental issues and  worker’s safety, that an occupational hazard of this type would have been eradicated by now.  In fact, the disease was almost eliminated 20 years ago with a reported prevalence of just 0.33% among active underground workers with at least 25 years of mining tenure.  Since that time, the incidence of the disease has risen substantially. For example, the Coal Workers Health Surveillance Program (CWHSP) reported in 2012 that the incidence of the disease in Kentucky, Virginia, and West Virginia had increased by a factor of ten[3].

In China in 2013, the government’s National Health and Family Planning Commission reported that there were 750,000 people suffering from black lung disease [4].

It’s not just the miners who suffer.  China, for example, has the largest number of premature deaths attributable to outdoor air pollution related to particulate matter—more than 1 million; followed by India with 620,000. In both cases, particulate emissions from coal combustion are reportedly a key underlying factor [5].

The mining of coal has a massive and often irreversible impact on the environment. A form of surface mining called mountaintop removal, or MTR, involves stripping all trees from a mountaintop and blasting away the top of the mountain with explosives.  The resulting thousands of tons of debris is generally dumped into adjacent valleys, burying watercourses, totally disrupting watersheds, and often permanently changing the biodiversity of the area. In the US, in Appalachia alone, coalfields cover 48,000 km2 of mountaintops and valleys, displacing forests and polluting or burying more than 5% of the region’s streams [6].

Drainage from coal mines is acidic, laced with heavy metals, and an environmental nightmare.  In the US, it has been described as one of the worst environmental problems facing the mining industry [7].  Acid mine drainage (AMD) is the acidic water produced when rock containing sulfide minerals, particularly iron pyrites, comes into contact with water and oxygen.  The chemistry is complex but the result is that downstream watercourses are turned red, orange and yellow by the accumulating concentrations of ferrous compounds. The acidity of the water also dissolves other minerals from the rock: zinc, copper, arsenic, cadmium and lead. Left untreated the problem can last for centuries: some Roman mines in Britain still generate acidic drainage [8].

Coming clean

Before it is transported to power stations, coal is generally cleaned up to remove soil and other rock fragments. The preparation includes crushing the coal and removing extraneous non-coal materials. If the coal is high in sulfur or other impurities, it is washed with a water or chemical bath to remove inorganic sulfur in the coal.

The process requires the application of complex chemicals and large quantities of water, and produces a thick slurry waste that may contain arsenic and mercury—which are both common in mined rock. This liquid waste is generally stored in huge surface impoundments, sometimes called tailing ponds, to prevent the pollution of local rivers and streams. While generally safe, they occasionally will fail. Catastrophically.

In Inez, Kentucky, three coal mines owned by Martin County Coal Corporation fed coal into a preparation plant on conveyor belts through underground mine workings. Waste coal slurry from the plant was pumped into a 29 ha tailings pond called the Big Branch impoundment.  The dam held back over 2 billion gallons of slurry.

In October 2000, the dam failed, releasing about 300 million gallons of coal waste slurry into local streams, flooding stream banks to a depth of five feet. About 120 km of rivers and streams turned black, killing fish, and polluting the river water along the Tug Fork of the Big Sandy River, and some of its tributaries. Like all coal mine tailing ponds, the slurry contained detectable levels of arsenic, mercury, lead, copper and chromium.  Martin County Coal eventually paid out over $6 million in penalties and damages [9].

In 1972, the most destructive flood in West Virginia’s history occurred when a coal waste impounding structure collapsed on the Buffalo Creek tributary of Middle Fork. The failure released 132 million gallons of water. As a result of the flood, 125 people were killed, 1100 were injured and more than 4000 were left homeless [10].

While the regulations in the US and Canada are now much stricter, accidents still happen—if less frequently.  In December 2008, a failure of the northwest side of the dike used to contain coal ash occurred at a dewatering area of the Kingston Fossil Plant operated by the Tennessee Valley Authority in Harriman, Tennessee. Approximately 5 million cubic meters of coal ash was released into Swan Pond Embayment and three adjacent sloughs, eventually spilling into the main Emory River channel.  The spill spread out over a 300 acre area outside the plant. The contaminated area was finally designated a Superfund site by the US Environmental Protection Agency [11].

In January 2018, it was reported that Duke Energy, one of the largest electricity companies in the US will pay an $84,000 penalty and work to stop potentially toxic waste from three North Carolina coal-burning plants from leaking into groundwater and nearby rivers.  Two dozen leaky spots were detected at coal ash pits before 2015.  Duke Energy acknowledged that the leaks into the Catawba and Broad rivers were from unlined earthen holding basins at the power plants. Groundwater in the vicinity may have been polluted, and Duke Energy has been providing hundreds of homes using wells within a half-mile of its coal plants with bottled water as a precaution. In January 2018, it was reported that some families had been using bottled water for 1000 days.[12]

But these impoundment and tailings pond failures pale in comparison to the disaster at the Mount Polley mine in the remote Caribou region of British Columbia in western Canada.  When the  dam failed in August 2014, it released 3.9  billion gallons of thick toxic waste containing lead, copper, and mercury, into nearby Hazeltine Creek, Polley Lake, and  Quesnel Lake. The environmental impact was catastrophic.

The Mount Polley tailings pond failure

The Mount Polley mine was not a coal mine. Imperial Metals was mining for gold and silver. But the risk is exactly the same for the mining of coal: the toxic slurry waste resulting from the processing and washing of coal or rock cannot be released into the environment—it has to be held in impoundments and tailings ponds. Even though dam and dike failures are infrequent, they still happen[13].  It is worth noting that a report on the cause of the breach by an expert review panel found that the “dominant contribution to the failure resides in the design.”  The construction did not follow the proposed design.[14]

Apart from the slurry waste from the preparation process, solid wastes are generated in coal mines in substantial quantities. The piles of waste can be huge and, since they contain coal dust and fragments of  coal, are prone to combust spontaneously. In the UK they are called slag heaps and were a dominant feature of the mining towns in Wales and the North of England when coal was a major industry in the last century.

The Aberfan tragedy is still remembered.

The Welsh mining village of Aberfan lies at the bottom of a small valley.  The Merthyr Vale coal mine, the mainstay of the local economy, was higher up the hill—where the colossal slag heaps dominated the skyline.

Mining in Aberfan started in 1869. Initially the waste was dumped in tips on the slope adjacent to the colliery, But as the volume of waste material increased, new tips were created on the slopes higher up the hillside.  By 1966, seven tips had been constructed. Tip number 7, the one that failed, held about 230,000 m3 of mine waste and had reached a height of 40 meters.  The photo above shows the village just after the disaster.

Just after 9 a.m., on October 21, 1966, after several days of rain, about half of the slag heap slid away, and over 100,000 m3 of mud and coal mine waste descended on the village below.  The mud and rubble roared down the valley, crashed through a row of small houses, and crushed the Plantglas junior school– where about 120 young children had just come into their classrooms. The slag heap slide killed 144 people: 116 children aged 7 to 10; six adults in the school including 5 teachers, and 22 people who were in the houses that were destroyed [15]. It was an appalling tragedy.

Coal ad nauseum

In 2016, the world consumption of coal was about 5.3 billion tons. Coal is always burned: it has no other use except the production of intense heat. When coal is burned in a power plant to generate the steam that powers the turbines, the resulting mix of flue gases is a toxic cocktail of gas-phase chemical compounds and particulates.

The main constituent is carbon dioxide—a gas which has little direct impact on human health, although it is the chief culprit when it comes to climate change.

But the other constituent gases have a noxious impact.  The table below, adapted from a report published by Physicians for Social Responsibility, summarizes the health effects of the major power plant pollutants [16].

The PSR report lists coal’s contribution to major health impacts as follows [17]:

Asthma. Nitrogen oxides, ozone, and particulate matter are all implicated in the prevalence of the disease.  The most vulnerable are children and adults.

Chronic Obstructive Pulmonary Disease (COPD). Emphysema with chronic obstructive bronchitis permanently narrows airways. In the US, COPD is the 4th leading cause of death. Smokers are most vulnerable.  NOx and particulate matter are implicated.

Infant mortality. NOx and particulates are implicated in the deaths of infants less than 1 year old. Almost a quarter may have had respiratory causes.

Lung cancer. Leading cause of cancer mortality in US among both men and women. The disease is exacerbated by air pollution caused by particulate matter.

Acute myocardial infarction. Particulate matter is implicated in the disease

Coronary heart disease. CHD is a leading cause of death in the US and air pollution is known to negatively impact cardiovascular health.

Ischemic stroke. NOx, particulate matter and sulfur dioxide are all implicated in the prevalence of ischemic stroke.

What coal leaves behind

Apart from the air pollution, there’s the ash.  You can’t burn coal without producing ash.

Coal ash is the waste that is left behind after coal is combusted in a coal-fired power plant. It includes fly ash, captured from smoke stack effluents, and coarser ash from the furnaces. The ash typically contains a slew of heavy metals including arsenic, lead, mercury, cadmium, chromium and selenium. These metals are all extremely toxic.

Coal ash from power plants is generally dumped either into dry landfills or into wet surface impoundments. In the US, there are approximately 2000 coal ash dump sites across the country.

In 2007, roughly 140 million tons of coal ash were generated annually from power plants.  Coal ash is the second largest industrial waste stream in the US—second only to mine wastes.[18]

Wet ash ponds are just as liable to fail as the impoundments and tailings ponds at the coal mines themselves.  The most notorious incident occurredd in December 2008 when an earthen wall holding back a large coal ash disposal pond at the coal-powered power plant in Kingston, Tennessee, failed catastrophically.  The 40-acre pond spilled more than 1 billion gallons of coal ash slurry into the adjacent river valley, covering about 3000 acres of land with a thick, viscous, toxic sludge. The spill destroyed three homes, damaged several others, and contaminated the Emory and Clinch rivers.

When the EPA tested water samples after the spill, they found toxic heavy metals including arsenic—which they measured at 149 times the allowable standard for drinking water. The water also contained lead, thallium, barium, cadmium, chromium, mercury and nickel.[19]

Under a 2015 US EPA coal ash rule, all US electric generating utilities were required to analyze groundwater pollution at each of their operating coal ash dumps by the end of January 2018, and publish their results one month later. Initial results show that a majority of the coal ash pits are leaking polluted water into groundwater [20].

But there’s one other dangerous pollutant that is widespread in the environment, present in the human tissue of practically every man and woman on the planet, and whose toxic neurological effect is mainly due to the burning of coal.


Elemental mercury and mercury compounds occur naturally in geologic hydrocarbons including coal, natural gas, gas condensates and crude oil.  Coal contains trace amounts of mercury in the form of mercuric sulfate (HgS—known as cinnabar) that, when the coal is burned, is dissipated into the environment as mercury vapor [21].

Mercury is extremely toxic. It is considered by the World Health Organisation as one of the top ten chemicals or groups of chemicals of major public health concern.

Mercury moves around the world in three key ways. First, it is actively traded as a global commodity, often for uses like artisanal and small-scale gold mining in the developing world, where substantial mercury releases into the environment are routine. Second, airborne mercury, carried in the air pollution caused by the combustion of coal, is dissipated over very wide areas before being deposited on land and on water. Third, once mercury enters a river or ocean, natural bacteria can absorb it and convert it to a more toxic form: methylmercury.

Methylmercury accumulates in fish and shellfish. Large predatory fish are more likely to have high levels of mercury as a result of eating smaller fish that have acquired mercury through the ingestion of plankton. Large predatory fish at the top of the aquatic food chain may accumulate levels of methylmercury as high as 1 part per million.

In 2010, coal burning was responsible for the emission of some 475 tons of mercury worldwide, the majority of which was from power generation and industrial boiler use. This represents about 40% of the total global anthropogenic emissions of the metal [22].

In the US, power plants that burn coal account for about 42% of all manmade mercury emissions [23].

Two groups of people are more sensitive to the effects of mercury.  Fetuses are most susceptible to the adverse developmental effects of the element. Methylmercury exposure in the womb can result from the mother’s consumption of fish and shellfish. It can adversely affect a baby’s growing brain and nervous system. The primary health effect of methylmercury is impaired neurological development.  Cognitive thinking, memory, attention, language, and fine  motor and visual spatial skills may be affected in children who were exposed to methylmercury as fetuses.[24]

The second group is people who re regularly exposed to high levels of mercury—such as populations that rely on subsistence fishing.  According to the World Health Organisation, among selected subsistence fishing populations, between 1.5 and 17 in 1000 children showed cognitive impairment and mild mental retardation caused by the consumption of fish containing mercury. These children were in populations in Brazil, Canada, China, Columbia and Greenland.[25]  The figure below shows how mercury moves through the environment and eventually into the human body [26].


In the US, a nationwide study of blood samples in 1999-2000 showed that 15.7% of women of childbearing age had blood mercury levels that would cause them to give birth to children with mercury levels exceeding the EPA’s maximum acceptable dose for mercury.  This dose was established to limit the number of children with mercury-related neurological and developmental impairments. Researchers have estimated that as many as 630,000 children are born in the US each year with blood mercury levels high enough to impair performance on neurodevelopmental tests and cause lifelong loss of intelligence [27].

Mercury vapor can be removed from coal fired power plants using a variety of pollution control technologies—but not completely. The mercury that is removed is then deposited in the solid waste products from the power plant. Impoundments, slag heaps, tailings ponds, and tips are never  permanent repositories of toxic pollutants.  Once coal is mined and  burned, one way or another, the mercury will find its way into the environment–and eventually into the food chain.


For a deeper dive:

[1] See the brilliant book by Geoffrey Parker: Global Crisis: War, climate change, & catastrophe in the seventeenth century. Yale University Press, New Haven, USA. 2013.

[2] See the US Bureau of Labor Statistics Fact sheet | coal mining| April 2010. Injuries, illnesses and fatalities in the coal mining industry, at

[3] See the article in the American Journal of Respiratory and Critical Care Medicine: Resurgence of debilitating and entirely preventable respiratory disease among working coal miners.  AJRCCM, Vol 190, No.6, September 15, 2014.

[4] See : Coal miners suffering from black lung disease fight for compensation.

[5] See the report :  Energy and Air Pollution. World Energy Outlook special report. International Energy Agency 2016. Page 35.

[6] See the article by the Union of Concerned Scientists: How coal works.  Accessed at :

[7] See : Technical Document : Acid mine drainage prediction.  US Environmental Protection Agency, Office of Solid Waste, Washington. DC. 1994.

[8] See: Acid mine drainage –a legacy of an industrial past. At

[9] See: The Inez coal tailings dam failure (Kentucky, USA).

[10] Coal waste impoundments: Risks, responses and alternatives. National Academy of Sciences, Washington DC.

[11] See : EPA response to Kingston TVA coal ash spill. At

[12] See: This is a first: Duke Energy agrees to pay $84K penalty for coal ash leaks.

[13] See : Ponds are the biggest environmental disaster youve never heard of, and Tailing pond spill: what happens to effluent over time

[14] See: Report on Mount Polley tailings storage facility breach. At : https://www.mountpolleyreviewpanel/default/files/report/ReportonMountPolleyTailingsStorageFacilityBreach.pdf. The breach was avoidable.  The report stated bluntly : “Had the downstream slope in recent years been flattened to 2.0 horizontal to 1.0 vertical, as proposed in the original design, failure would have been avoided.” (emphasis added).

[15] See: Remembering Aberfan. Institute of hazard, risk and resilience blog, Durham University UK.

[16] See: Coals assault on human health. A report from Physicians for Social Responsibility. 2009.

[17] See: Coals assault on human health, pages x, xi.  Op. cit.

[18] See: Coal ash: The toxic threat to our health and environment, Physicians for Social Responsablity and Earth Justice, 2010.

[19] Ibid.

[20] See: New industry data confirms toxics are polluting groundwater at coal ash sites.  At :

[21] See: Mercury in petroleum and natural gas: estimation of emissions from production, processing and combustion. EPA report EPA-600/R-01-066, September 2001

[22] See: Guidance on best available techniques and best environmental practices to control mercury emissions from . coal-fired power plants and coal-fired industrial boilers. UN Environment 2016.

[23] See the EPA website :

[24] See the World Health Organisation fact sheet: Mercury and health. Updated March 2017, at

[25] See the WHO Fact sheet: Mercury and health. Ibid.

[26] The chart is from Physicians for Social Responsibility report, Op.cit.

[27] The data are from the Physicians for Social Responsibility report, Op. cit.