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Vol. 24 No. 4 - October 2018

Mining and Human Health Hazards

By: Babita Kumari and O. P. Dwevedi*

Mine dusts in ambient air are generally above allowable limits. Prolong exposure to these dusts by miners could lead to respiratory diseases (asthma, silicosis and tuberculosis) and skin disorders. The concentrations of these dusts present great risks to the health of miners and inhabitants around the mine. It is necessary to have control measures such as wet drilling, sprinkling of water on mine roads and planting of vegetation around mine to trap mine dusts. Although many countries require reclamation plans for coal mining sites, undoing all the environmental damages to water supplies, destroyed habitats, and poor air quality is a long and problematic task. Bad mining practices can ignite coal fires, which can burn for decades, release fly ash and smoke laden with greenhouse gasses and toxic chemicals. Furthermore, mining releases coal mine methane, a greenhouse gas 20 times more powerful than carbon dioxide.

Coal dust inhalation causes black lung disease among miners and those who live nearby, and kills thousands every year.

Major types of mining practices

There are two widely used ways of mining: strip mining and underground mining.

Strip mining

Strip mining (also known as open cast, mountaintop or surface mining) involves scraping away earth and rocks to get to coal buried near the surface. In many cases, mountains are literally blasted apart to reach thin coal seams within, leaving permanent scars on the landscape as a result.

Strip mining accounts for about 40 percent of the world’s coal mines but in some countries, such as Australia, it accounts for about 80 percent of mines. Even though it is highly destructive, industry often prefers strip mining as it requires less labour and yields more coal than underground mining.

There is an increased risk of chemical contamination of ground water when minerals in upturned earth seep into the water table, and watersheds are destroyed when disfigured land loses the water it once held. Strip mining causes dust and noise pollution when top soil is disrupted with heavy machinery and coal dust is created in mines.

The result of all this is barren land that stays contaminated long after a coal mine shuts down.

Underground mining

The majority of the world’s coal is obtained through underground mines. While underground mining, which allows coal companies to extract deeper deposits of coal, is viewed as less destructive than strip mining.

The principal airborne hazards in the mining industry include several types of particulates, naturally occurring gases, engine exhaust and some chemical vapours; the principal physical hazards are noise, segmental vibration, heat, changes in barometric pressure and ionizing radiation. These occur in varying combinations depending on the mine or quarry, its depth, the composition of the ore and surrounding rock, and the method(s) of mining. Among some groups of miners who live together in isolated locations, there is also risk of transmitting some infectious diseases such as tuberculosis, hepatitis (B and E), and the human-immunodeficiency virus (HIV).

Common health threats posed by coal mining

  • Pneumoconiosis, aka black lung disease or CWP, is caused when miners breathe in coal dust and carbon, which harden the lungs. Estimates show that 1,200 people in the US still die from black lung disease annually. The situation in developing countries is even worse.

  • Cardiopulmonary disease, chronic obstructive pulmonary disease, hypertension, lung disease, and kidney disease have been found in higher-than-normal rates among residents who live near coal mines.

Airborne Particulate Hazards

Free crystalline silica is the most abundant compound in the earth’s crust and, consequently, is the most common airborne dust that miners and quarry-workers face. Free silica is silicon dioxide that is not chemically bonded with any other compound as a silicate. The most common form of silica is quartz. Respirable particles are formed whenever silica-bearing rock is drilled, blasted, crushed or otherwise pulverized into fine particles. Exposure can occur in any mining operation, surface or underground, where silica is found in the overburden of a surface mine or the ceiling, floor or ore deposit of an underground mine. Silica can be dispersed by the wind, by vehicular traffic or by earth-moving machinery.

With sufficient exposure, silica can cause silicosis, a typical pneumoconiosis that develops insidiously after years of exposure. Exceptionally high exposure can cause acute or accelerated silicosis within months with significant impairment or death occurring within a few years. Exposure to silica is also associated with an increased risk of tuberculosis, lung cancer and of some autoimmune diseases, including scleroderma, systemic lupus erythematosus and rheumatoid arthritis. Freshly fractured silica dust appears to be more reactive and more hazardous than old or stale dust. This may be a consequence of a relatively higher surface charge on freshly formed particles.

The most common processes that produce respirable silica dust in mining and quarrying are drilling, blasting and cutting silica-containing rock.

Silica exposure also occurs at stone quarries where stones are cut to specified dimensions. Often attached to or nearby a stone quarry is a mill where pieces are sculpted into a more finished product. Unless there is very good local exhaust ventilation, exposure to silica can be high because vibrating and rotating hand tools are used to shape the stone into the desired form.

Respirable coal mine dust is a hazard in underground and surface coal mines and in coal-processing facilities. It is a mixed dust, consisting mostly of coal, but can also include silica, clay, limestone and other mineral dusts. The composition of coal mine dust varies with the coal seam, the composition of the surrounding strata and mining methods. Coal mine dust is generated by blasting, drilling, cutting and transporting coal.

More dust is generated with mechanized mining than with manual methods. The generation of coal mine dust can be reduced by changes in coal cutting techniques and its dispersion can be controlled with the use of adequate ventilation and water sprays.

Other mines where asbestos is found in the ore

Among miners throughout the world, exposure to asbestos has elevated the risk of lung cancer and of mesothelioma. It has also elevated the risk of asbestosis (another pneumoconiosis) and of airways disease.

Gases and Vapours

The most important naturally occurring gases are methane and hydrogen sulphide in coal mines and radon in uranium and other mines. Oxygen deficiency is possible in either. Methane is combustible. Most coal mine explosions result from ignitions of methane and are often followed by more violent explosions caused by coal dust. Throughout the history of coal mining, fires and explosions have been the principal cause of death of thousands of miners.

Radon is a naturally occurring radioactive gas that has been found in uranium mines, tin mines and some other mines. It has not been found in coal mines. The primary hazard associated with radon is its being a source of ionizing radiation.

Other gaseous hazards include respiratory irritants found in diesel engine exhaust and blasting by-products. Carbon monoxide is found not only in engine exhaust but also as a result of mine fires. During mine fires, CO can reach not only lethal concentrations but also can become an explosion hazard. Nitrogen oxides (NOx), primarily NO and NO 2, are formed by diesel engines and as a by-product of blasting.

Oxygen deficiency can occur in many ways. Oxygen can be displaced by some other gas, such as methane, or it may be consumed either by combustion or by microbes in an air space with no ventilation.

There is a variety of other airborne hazards to which miners are exposed. Exposure to mercury vapour is a hazard among gold miners and millers and among mercury miners. Exposure to arsenic, and risk of lung cancer, occurs among gold miners and lead miners. Exposure to nickel can lead to lung cancer and skin allergies among nickel miners.

Some plastics are finding use in mines also. These include urea-formaldehyde and polyurethane foams, both of which are plastics made in-place. They are used to plug up holes and improve ventilation and to provide a better anchor for roof supports. Formaldehyde and isocyanates, two starting materials for these two foams, are respiratory irritants and both can cause allergic sensitization. Formaldehyde is a human carcinogen (IARC Group 1).

Other hazards

Noise is ubiquitous in mining. It is generated by powerful machines, fans, blasting and transportation of the ore. The underground mine usually has limited space and thus creates a reverberant field.

Ionizing radiation is a hazard in the mining industry. Radon can be liberated from stone while it is loosened by blasting, but it may also enter a mine through underground streams. It is a gas and therefore it is airborne. Radon and its decay products emit ionizing radiation, some of which have enough energy to produce cancer cells in the lung. As a result, death rates from lung cancer among uranium miners are increased. For miners who smoke, the death rate is very much higher.

Heat is another hazard particularly in underground mines. The principal source of heat is from the rock itself. The temperature of the rock goes up about 1 °C for every 100 m in depth. Very deep mines (deeper than 1,000 m) can pose significant heat problems, with the temperature of mine rising to about 40 °C.

Many mines operate at high altitudes (e.g., greater than 4,600 m), and because of this, miners may experience altitude sickness. This can be aggravated if they travel back and forth between a mine at a high altitude and the site with more normal atmospheric pressure.

World Health Organization considers 55 µg/m3as acceptable value and above 90 µg/m3 as unacceptable value of dust in ambient air. Researches have shown that suspended particulate matter is the major causes of asthma, lung cancer, cardiovascular diseases and premature deaths in humans. The concentrations of SPM at drilling site were more than those prescribed by WHO.

The impact of these dusts on the health of miners depends on the exposure level, the duration of exposure, the frequency of exposure, the chemical and mineralogical composition of inhaled particle. Miners dressed in torn clothes without wearing any personnel protection equipment such as, hard hat, cover all, nose and ear muffs are more vulnerable.

In India, miners and people living in the coal fields, inhaling fine dust particles of up to 5µm in size often suffer from asthma and bronchitis, cancer, tuberculosis and skin diseases. There is a greater incidence of these occupational diseases among miners and people living in the coal fields in India compared to China, Japan and Western countries because the mines in India are emitting PM10 into the atmosphere in excess of allowable WHO limits.

 

*Rajiv Gandhi International Science and Technology Association, Saket, New Delhi, bbtmshr@yahoo.co.in


This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.


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