Slash-and-burn

From Wikipedia, the free encyclopedia

Satellite photograph illustrating slash-and-burn forest clearing along the Xingu River in the state of Mato Grosso, Brazil.

 

Slash-and-burn agriculture, also called fire-fallow cultivation, is a farming method that involves the cutting and burning of plants in a forest or woodland to create a field called a swidden. The method begins by cutting down the trees and woody plants in an area. The downed vegetation, or "slash", is then left to dry, usually right before the rainiest part of the year. Then, the biomass is burned, resulting in a nutrient-rich layer of ash which makes the soil fertile, as well as temporarily eliminating weed and pest species. After about three to five years, the plot's productivity decreases due to depletion of nutrients along with weed and pest invasion, causing the farmers to abandon the field and move over to a new area. The time it takes for a swidden to recover depends on the location and can be as little as five years to more than twenty years, after which the plot can be slashed and burned again, repeating the cycle. In India, the practice is known as jhum or jhoom.

Slash-and-burn can be part of shifting cultivation, an agricultural system in which farmers routinely move from one cultivable area to another. It may also be part of transhumance, the moving of livestock between seasons. A rough estimate is that 200 million to 500 million people worldwide use slash-and-burn. In 2004, it was estimated that in Brazil alone, 500,000 small farmers each cleared an average of one hectare (2.47105 acres) of forest per year. The technique is not scalable or sustainable for large human populations. Methods such as Inga alley cropping and slash-and-char have been proposed as alternatives which would cause less environmental degradation.

A similar term is assarting, which is the clearing of forests, usually (but not always) for the purpose of agriculture. Assarting does not include burning.

History

Historically, slash-and-burn cultivation has been practiced throughout much of the world, in grasslands as well as woodlands. 

During the Neolithic Revolution, which included agricultural advancements, groups of hunter-gatherers domesticated various plants and animals, permitting them to settle down and practice agriculture, which provides more nutrition per hectare than hunting and gathering. This happened in the river valleys of Egypt and Mesopotamia. Due to this decrease in food from hunting, as human populations increased, agriculture became more important. Some groups could easily plant their crops in open fields along river valleys, but others had forests blocking their farming land.

In this context, humans used slash-and-burn agriculture to clear more land to make it suitable for plants and animals. Thus, since Neolithic times, slash-and-burn techniques have been widely used for converting forests into crop fields and pasture. Fire was used before the Neolithic as well, and by hunter-gatherers up to present times. Clearings created by the fire were made for many reasons, such as to draw game animals and to promote certain kinds of edible plants such as berries. 

Slash-and-burn fields are typically used and owned by a family until the soil is exhausted. At this point the ownership rights are abandoned, the family clears a new field, and trees and shrubs are permitted to grow on the former field. After a few decades, another family or clan may then use the land and claim usufructuary rights. In such a system there is typically no market in farmland, so land is not bought or sold on the open market and land rights are traditional. In slash-and-burn agriculture, forests are typically cut months before a dry season. The "slash" is permitted to dry and then burned in the following dry season. The resulting ash fertilizes the soil and the burned field is then planted at the beginning of the next rainy season with crops such as upland rice, maize, cassava, or other staples. Most of this work is typically done by hand, using such basic tools such as machetes, axes, hoes, and makeshift shovels. Old American civilizations, like the Inca, Maya and Aztecs, also used this agricultural technique. Sometimes, the flames spread and caused forest fires which would lead to loss of life (both wild animals and human beings).

Large families or clans wandering in the lush woodlands long continued to be the most common form of society through human prehistory. Axes to fell trees and sickles for harvesting grain were the only tools people might bring with them. All other tools were made from materials they found at the site, such as fire stakes of birch, long rods (Vanko), and harrows made of spruce tops. The extended family conquered the lush virgin forest, burned and cultivated their carefully selected swidden plots, sowed one or more crops, and then proceeded on to forests that had been noted in their wanderings. In the temperate zone, the forest regenerated in the course of a lifetime. So swidden was repeated several times in the same area over the years. But in the tropics the forest floor gradually depleted. It was not only in the moors, as in Northern Europe, but also in the steppe, Savannah, prairie, pampas and barren desert in tropical areas where shifting cultivation is the oldest type of farming. Cultivation is similar to slash-and-burn. (Clark 1952 91–107).

Historical references

Painting by Eero Järnefelt of forest-burning

 

Southern European Mediterranean climates have favored evergreen and deciduous forests. With slash-and-burn agriculture, this type of forest was less able to regenerate than those north of the Alps. Although in northern Europe one crop was usually harvested before grass was allowed to grow, in southern Europe it was more common to exhaust the soil by farming it for several years. 

Classical authors mentioned large forests, with Homer writing about "wooded Samothrace," Zakynthos, Sicily, and other woodlands. These authors indicated that the Mediterranean area once had more forest; much had already been lost, and the remainder was primarily in the mountains.

Although parts of Europe aside from the north remained wooded, by the Roman Iron and early Viking Ages, forests were drastically reduced and settlements regularly moved. The reasons for this pattern of mobility, the transition to stable settlements from the late Viking period on, or the transition from shifting cultivation to stationary farming are unknown. From this period, plows are found in graves. Early agricultural peoples preferred good forests on hillsides with good drainage, and traces of cattle enclosures are evident there. 

In Italy, shifting cultivation was a thing of the past by the birth of Christ. Tacitus describes it as a strange cultivation method, practiced by the Germans. In 98 AD, he wrote about the Germans that their fields were proportional to the participating cultivators but their crops were shared according to status. Distribution was simple, because of wide availability; they changed fields annually, with much to spare because they were producing grain rather than other crops. A W Liljenstrand wrote 1857 in his doctoral dissertation, "About Changing of Soil" (p. 5 ff.), that Tacitus discusses shifting cultivation: "arva per annos mutant". This is the practice of shifting cultivation.

During the Migration Period in Europe, after the Roman Empire and before the Viking Age, the peoples of Central Europe moved to new forests after exhausting old parcels. Forests were quickly exhausted; the practice had ended in the Mediterranean, where forests were less resilient than the sturdier coniferous forests of Central Europe. Deforestation had been partially caused by burning to create pasture. Reduced timber delivery led to higher prices and more stone construction in the Roman Empire (Stewart 1956, p. 123). Although forests gradually decreased in northern Europe, they have survived in the Nordic countries.

Tribes in pre-Roman Italy (including the Etruscans, Umbrians, Ligurians, Sabines, Latins, Campanians, Apulians, Saliscans, and Sabellians) apparently lived in temporary locations. They cultivated small patches of land, kept sheep and cattle, traded with foreign merchants, and occasionally fought. These Italic groups developed identities as settlers and warriors around 900 BC. They built forts in the mountains which are studied today, as are the ruins of a large Samnite temple and theater at Pietrabbondante. 

Many Italic peoples saw benefits in allying with Rome. When the Romans built the Via Amerina in 241 BC, the Falisci settled in cities on the plains and aided the Romans in road construction; the Roman Senate gradually acquired representatives from Faliscan and Etruscan families, and the Italic tribes became settled farmers.

Classical writers described peoples who practiced shifting cultivation, which characterized the Migration Period in Europe. The exploitation of forests demanded displacement as areas were deforested. Julius Caesar wrote about the Suebi in Commentarii de Bello Gallico 4.1, "They have no private and secluded fields ("privati ac separati agri apud eos nihil est") ... They cannot stay more than one year in a place for cultivation’s sake" ("neque longius anno remanere uno in loco colendi causa licet"). The Suebi lived between the Rhine and the Elbe. About the Germani, Caesar wrote: "No one has a particular field or area for himself, for the magistrates and chiefs give year by year to the people and the clans, who have gathered together, as much land and in such places as seem good to them and then make them move on after a year" ("Neque quisquam agri modum certum aut fines habet proprios, sed magistratus ac principes in annos singulos gentibus cognationibusque hominum, qui tum una coierunt, a quantum et quo loco visum est agri attribuunt atque anno post alio transire cogunt" [Book 6.22]). 

Strabo (63 BC—c. 20 AD) also writes about the Suebi in his Geography (VII, 1, 3): "Common to all the people in this area is that they can easily change residence because of their sordid way of life; they do not cultivate fields or collect property, but live in temporary huts. They get their nourishment from their livestock for the most part, and like nomads, pack all their goods in wagons and go on to wherever they want". Horace writes in 17 BC (Carmen Saeculare, 3, 24, 9ff.) about the people of Macedonia: "The proud Getae also live happily, growing free food and cereal for themselves on land they do not want to cultivate for more than a year" ("Vivunt et rigidi Getae, / immetata quibus iugera liberas / fruges et Cererem ferunt, / nec cultura placet longior annua"). 

Locations of Norwegian tribes described by Jordanes in his Getica

 

Jordanes, of Gothic descent, became a monk in Italy. In his mid-sixth-century AD Getica (De origine actibusque Getarum; The Origin and Deeds of the Goths) he described the large island of Scandza, on which the Goths originated. According to Jordanes, of the tribes living there, some are Adogit from within 40 days of the midnight sun. After the Adogit were the Screrefennae and Suehans, who also lived in the north. The Screrefennae did not raise crops, instead hunting and collecting bird eggs. The Suehans, a semi-nomadic tribe with good horses (comparable to the Thuringii), hunted furs to sell; grain could not be grown so far north. In about 550 AD, Procopius also described a primitive hunting people he called "Skrithifinoi": "Both men and women engaged incessantly just in hunting the rich forests and mountains, which gave them an endless supply of game and wild animals."

Slash-and-burn in Småland, Sweden (1904)

 

The use of fire in northeastern Sweden changed as agriculture evolved. Although the Sami people did not burn land (since burning killed the lichen required by their reindeer), later farmers frequently used slash-and-burn techniques. The 19th-century Swedish timber industry moved north, clearing the land of trees but leaving waste behind as a fire risk; during the 1870s, fires were frequent. There was a fire in Norrland in 1851, followed by fires in 1868 and 1878; two towns were lost in 1888.

Forest Finns

Huuhta cultivation spread: within the circle in 1500 AD, within the line in 1600, and to the dashed line in 1700.

 

One culture which flourished in pre-agricultural Europe survives: the Forest Finns in Scandinavia. Martin Tvengsberg, a descendant of the Forest Finns, studied them in his capacity as curator of the Hedmark Museum in Norway. The Savo-Karelians had a sophisticated system for cultivating spruce forests. A runic poem about Finland's spruce forests reads, "Gåivu on mehdien valgoinen valhe" ("The birch is the forest’s white lie"). The best spruce forests reportedly contain birch trees, which grow only after a forest has burned once or twice.

Modern Western world

Slash-and-burn may be defined as the large-scale deforestation of forests for agricultural use. Ashes from the trees help farmers by providing nutrients for the soil.

In industrialized regions, including Europe and North America, the practice was abandoned with the introduction of market agriculture and land ownership. Slash-and-burn agriculture was initially practiced by European pioneers in North America such as Daniel Boone and his family, who cleared land in the Appalachian Mountains during the late 18th and early 19th centuries. However, land cleared by slash-and-burn farmers was eventually taken over by systems of land tenure focusing on long-term improvement and discouraging practices associated with slash-and-burn agriculture.

Northern European heritage

In the Telkkämäki Heritage Farm in Finland, some areas are still burned annually.

 

Telkkämäki Nature Reserve in Kaavi, Finland, is an open-air museum which still practices slash-and-burn agriculture. Farm visitors can see how people farmed when slash-and-burn agriculture became the norm in the Northern Savonian region of eastern Finland beginning in the 15th century. Areas of the reserve are burnt each year.

South Asia

Tribal groups in the northeastern Indian states of Tripura, Arunachal Pradesh, Meghalaya, Mizoram and Nagaland and the Bangladeshi districts of Rangamati, Khagrachari, Bandarban and Sylhet refer to slash-and-burn agriculture as jhum or jhoom cultivation. The system involves clearing land, by fire or clear-felling, for economically-important crops such as upland rice, vegetables or fruits. After a few cycles, the land's fertility declines and a new area is chosen. Jhum cultivation is most often practiced on the slopes of thickly-forested hills. Cultivators cut the treetops to allow sunlight to reach the land, burning the trees and grasses for fresh soil. Although it is believed that this helps fertilize the land, it can leave it vulnerable to erosion. Holes are made for the seeds of crops such as sticky rice, maize, eggplant and cucumber are planted. After considering jhum's effects, the government of Mizoram has introduced a policy to end the method in the state. Slash-and-burn is typically a type of subsistence agriculture, not focused on a need to sell crops globally; planting decisions are governed by the needs of the family (or clan) for the coming year.

Ecological implications

Although a solution for overpopulated tropical countries where subsistence agriculture may be the traditional method of sustaining many families, the consequences of slash-and-burn techniques for ecosystems are almost always destructive. This happens particularly as population densities increase, and as a result farming becomes more intensively practiced. This is because as demand for more land increases, the fallow period by necessity declines. The principal vulnerability is the nutrient-poor soil, pervasive in most tropical forests. When biomass is extracted even for one harvest of wood or charcoal, the residual soil value is heavily diminished for further growth of any type of vegetation.

Sometimes there are several cycles of slash-and-burn within a few years' time span. For example, in eastern Madagascar, the following scenario occurs commonly. The first wave might be cutting of all trees for wood use. A few years later, saplings are harvested to make charcoal, and within the next year the plot is burned to create a quick flush of nutrients for grass to feed the family zebu cattle. If adjacent plots are treated in a similar fashion, large-scale erosion will usually ensue, since there are no roots or temporary water storage in nearby canopies to arrest the surface runoff. Thus, any small remaining amounts of nutrients are washed away. The area is an example of desertification, and no further growth of any type may arise for generations.

The ecological ramifications of the above scenario are further magnified, because tropical forests are habitats for extremely biologically diverse ecosystems, typically containing large numbers of endemic and endangered species. Therefore, the role of slash-and-burn is significant in the current Holocene extinction.

Slash-and-char is an alternative that alleviates some of the negative ecological implications of traditional slash-and-burn techniques. However, the endgame - unsustainability - is the same as for slash-and-burn.

Emissions taxes could help reduce the magnitude on which slash-and-burn agriculture is practised.

Health effects of particulates

From Wikipedia, the free encyclopedia

Air pollution measurement station in Emden, Germany

Size, shape and solubility matter

The size of the particle is a main determinant of where in the respiratory tract the particle will come to rest when inhaled. Larger particles are generally filtered in the nose and throat via cilia and mucus, but particulate matter smaller than about 10 micrometers, can settle in the bronchi and lungs and cause health problems. The 10-micrometer size does not represent a strict boundary between respirable and non-respirable particles, but has been agreed upon for monitoring of airborne particulate matter by most regulatory agencies. Because of their small size, particles on the order of 10 micrometers or less (coarse particulate matter, PM₁₀) can penetrate the deepest part of the lungs such as the bronchioles or alveoli; when asthmatics are exposed to these conditions it can trigger bronchoconstriction.

Similarly, so called fine particulate matter (PM_2.5), tend to penetrate into the gas exchange regions of the lung (alveolus), and very small particles (ultrafine particulate matter, PM_0.1) may pass through the lungs to affect other organs. Penetration of particles is not wholly dependent on their size; shape and chemical composition also play a part. To avoid this complication, simple nomenclature is used to indicate the different degrees of relative penetration of a PM particle into the cardiovascular system. Inhalable particles penetrate no further than the bronchi as they are filtered out by the cilia. Thoracic particles can penetrate right into terminal bronchioles whereas PM_0.1, which can penetrate to alveoli, the gas exchange area, and hence the circulatory system are termed respirable particles. In analogy, the inhalable dust fraction is the fraction of dust entering nose and mouth which may be deposited anywhere in the respiratory tract. The thoracic fraction is the fraction that enters the thorax and is deposited within the lung's airways. The respirable fraction is what is deposited in the gas exchange regions (alveoli).

The smallest particles, less than 100 nanometers (nanoparticles), may be even more damaging to the cardiovascular system. Nanoparticles can pass through cell membranes and migrate into other organs, including the brain. Particles emitted from modern diesel engines (commonly referred to as Diesel Particulate Matter, or DPM) are typically in the size range of 100 nanometers (0.1 micrometer). These soot particles also carry carcinogens like benzopyrenes adsorbed on their surface. Particulate mass is not a proper measure of the health hazard, because one particle of 10 µm diameter has approximately the same mass as 1 million particles of 100 nm diameter, but is much less hazardous, as it is unlikely to enter the alveoli. Legislative limits for engine emissions based on mass are therefore not protective. Proposals for new regulations exist in some countries, with suggestions to limit the particle surface area or the particle count (numerical quantity) instead.

The site and extent of absorption of inhaled gases and vapors are determined by their solubility in water. Absorption is also dependent upon air flow rates and the partial pressure of the gases in the inspired air. The fate of a specific contaminant is dependent upon the form in which it exists (aerosol or particulate). Inhalation also depends upon the breathing rate of the subject.

Another complexity not entirely documented is how the shape of PM can affect health, except for the needle-like shape of asbestos which can lodge itself in the lungs. Geometrically angular shapes have more surface area than rounder shapes, which in turn affects the binding capacity of the particle to other, possibly more dangerous substances.

Health problems

Air quality information on PM10 displayed in Katowice, Poland

 

The effects of inhaling particulate matter that has been widely studied in humans and animals include asthma, lung cancer, respiratory diseases, cardiovascular disease, premature delivery, birth defects, low birth weight, and premature death. 

Inhalation of PM_2.5 – PM₁₀ is associated with elevated risk of adverse pregnancy outcomes, such as low birth weight. Maternal PM_2.5 exposure during pregnancy is also associated with high blood pressure in children. Exposure to PM_2.5 has been associated with greater reductions in birth weight than exposure to PM₁₀. PM exposure can cause inflammation, oxidative stress, endocrine disruption, and impaired oxygen transport access to the placenta, all of which are mechanisms for heightening the risk of low birth weight. Overall epidemiologic and toxicological evidence suggests that a causal relationship exists between long-term exposures to PM_2.5 and developmental outcomes (i.e. low birth weight). However, studies investigating the significance of trimester-specific exposure have proven to be inconclusive, and results of international studies have been inconsistent in drawing associations of prenatal particulate matter exposure and low birth weight.  As perinatal outcomes have been associated with lifelong health and exposure to particulate matter is widespread, this issue is of critical public health importance and additional research will be essential to inform public policy on the matter. 

Increased levels of fine particles in the air as a result of anthropogenic particulate air pollution "is consistently and independently related to the most serious effects, including lung cancer and other cardiopulmonary mortality." A large number of deaths and other health problems associated with particulate pollution was first demonstrated in the early 1970s and has been reproduced many times since. PM pollution is estimated to cause 22,000–52,000 deaths per year in the United States (from 2000) contributed to ~370,000 premature deaths in Europe during 2005. and 3.22 million deaths globally in 2010 per the global burden of disease collaboration.

A 2002 study indicated that PM_2.5 leads to high plaque deposits in arteries, causing vascular inflammation and atherosclerosis – a hardening of the arteries that reduces elasticity, which can lead to heart attacks and other cardiovascular problems. A 2014 meta analysis reported that long term exposure to particulate matter is linked to coronary events. The study included 11 cohorts participating in the European Study of Cohorts for Air Pollution Effects (ESCAPE) with 100,166 participants, followed for an average of 11.5 years. An increase in estimated annual exposure to PM 2.5 of just 5 µg/m³ was linked with a 13% increased risk of heart attacks. In 2017 a study revealed that PM not only affects human cells and tissues, but also impacts bacteria which cause disease in humans. This study concluded that biofilm formation, antibiotic tolerance, and colonisation of both Staphylococcus aureus and Streptococcus pneumoniae was altered by Black Carbon exposure.

The World Health Organization (WHO) estimated in 2005 that "... fine particulate air pollution (PM(2.5)), causes about 3% of mortality from cardiopulmonary disease, about 5% of mortality from cancer of the trachea, bronchus, and lung, and about 1% of mortality from acute respiratory infections in children under 5 years, worldwide.". A 2011 study concluded that traffic exhaust is the single most serious preventable cause of heart attack in the general public, the cause of 7.4% of all attacks.

The largest US study on acute health effects of coarse particle pollution between 2.5 and 10 micrometers in diameter. was published 2008 and found an association with hospital admissions for cardiovascular diseases but no evidence of an association with the number of hospital admissions for respiratory diseases. After taking into account fine particle levels (PM_2.5 and less), the association with coarse particles remained but was no longer statistically significant, which means the effect is due to the subsection of fine particles.

Particulate matter studies in Bangkok Thailand from 2008 indicated a 1.9% increased risk of dying from cardiovascular disease, and 1.0% risk of all disease for every 10 micrograms per cubic meter. Levels averaged 65 in 1996, 68 in 2002, and 52 in 2004. Decreasing levels may be attributed to conversions of diesel to natural gas combustion as well as improved regulations.

The Mongolian government agency recorded a 45% increase in the rate of respiratory illness in the past five years (reported in September 2014). Bronchial asthma, chronic obstructive pulmonary disease and interstitial pneumonia were the most common ailments treated by area hospitals. Levels of premature death, chronic bronchitis, and cardiovascular disease are increasing at a rapid rate.

A study In 2000 conducted in the U.S. explored how fine particulate matter may be more harmful than coarse particulate matter. The study was based on six different cities. They found that deaths and hospital visits that were caused by particulate matter in the air were primarily due fine particulate matter.

Effects on vegetation

Particulate matter can clog stomatal openings of plants and interfere with photosynthesis functions. In this manner, high particulate matter concentrations in the atmosphere can lead to growth stunting or mortality in some plant species.

Bioaerosol

From Wikipedia, the free encyclopedia

 

Bioaerosols (short for biological aerosols) are a subcategory of particles released from terrestrial and marine ecosystems into the atmosphere. They consist of both living and non-living components including organisms, dispersal methods of organisms, and excretions.

Common bioaerosol isolated from indoor environments

Background

Charles Darwin was the first to observe the transport of dust particles but Louis Pasteur was the first to research microbes and their activity within the air. Prior to Pasteur’s work, laboratory cultures were used to grow and isolate different bioaerosols. Because not all microbes can be cultured, many were undetected before the development of DNA-based tools. Pasteur also developed experimental procedures for sampling bioaerosols and showed that more microbial activity occurred at lower altitudes and decreased at higher altitudes.

Types of bioaerosols

Bioaerosols include fungi, bacteria, viruses, and pollen. Their concentrations are greatest in the planetary boundary layer (PBL) and decrease with altitude. Survival rate of bioaerosols depends on a number of biotic and abiotic factors which include climatic conditions, ultraviolet (UV) light, temperature and humidity, as well as resources present within dust or clouds. Bioaerosols found over marine environments primarily consist of bacteria, while those found over terrestrial environments are rich in bacteria, fungi and pollen. The dominance of particular bacteria and their nutrient sources are subject to change according to time and location.

Bioaerosols can range in size from 10 nanometer virus particles to 100 micrometers pollen grains. Pollen grains are the largest bioaerosols and are less likely to remain suspended in the air over a long period of time due to their weight. Consequently, pollen particle concentration decreases more rapidly with height than smaller bioaerosols such as bacteria, fungi and possibly viruses, which may be able to survive in the upper troposphere. At present, there is little research on the specific altitude tolerance of different bioaerosols. However, scientists believe that atmospheric turbulence impacts where different bioaerosols may be found.

Fungus

Fungal cells usually die when they travel through the atmosphere due to the desiccating effects of higher altitudes. However, some particularly resilient fungal bioaerosols have been shown to survive in atmospheric transport despite exposure to severe UV light conditions. Although bioaerosol levels of fungal spores increase in higher humidity conditions, they can also can be active in low humidity conditions and in most temperature ranges. Certain fungal bioaerosols even increase at relatively low levels of humidity.

Bacteria

Unlike other bioaerosols, bacteria are able to complete full reproductive cycles within the days or weeks that they survive in the atmosphere, making them a major component of the air biota ecosystem. These reproductive cycles support a currently unproven theory that bacteria bioaerosols form communities in an atmospheric ecosystem. The survival of bacteria depends on water droplets from fog and clouds that provide bacteria with nutrients and protection from UV light. The four known bacterial groupings that are abundant in aeromicrobial environments around the world include Bacillaceae, Actinobacteria, Proteobacteria, and Bacteroidetes.

Virus

The air transports viruses and other pathogens. Since viruses are smaller than other bioaerosols, they have the potential to travel further distances. In one simulation, a virus and a fungal spore were simultaneously released from the top of a building; the spore traveled only 150 meters while the virus traveled almost 200,000 horizontal kilometers.

Pollen

Pollen are non-living bioaerosols. Despite being the heavier and larger than other bioaerosols, some studies show that pollen can be transported thousands of kilometers. They are a major source of wind-dispersed allergens, coming particularly from seasonal releases from grasses and trees. Tracking distance, transport, resources, and deposition of pollen to terrestrial and marine environments are useful for interpreting pollen records.

Collection

The main tools used to collect bioaerosols are collection plates, electrostatic collectors, mass spectrometers, and impactors, other methods are used but are more experimental in nature. Polycarbonate (PC) filters have had the most accurate bacterial sampling success when compared to other PC filter options.

Single-stage impactors

To collect bioaerosols falling within a specific size range, impactors can be stacked to capture the variation of particulate matter (PM). For example, a PM₁₀ filter lets smaller sizes pass through. This is similar to the size of a human hair. Particulates are deposited onto the slides, agar plates, or tape at the base of the impactor. The Hirst spore trap samples at 10 liters/minute (LPM) and has a wind vane to always sample in the direction of wind flow. Collected particles are impacted onto a vertical glass slide greased with petroleum. Variations such as the 7-day recording volumetric spore trap have been designed for continuous sampling using a slowly rotating drum that deposits impacted material onto a coated plastic tape. The airborne bacteria sampler can sample at rates up to 700 LPM, allowing for large samples to be collected in a short sampling time. Biological material is impacted and deposited onto an agar lined Petri dish, allowing cultures to develop.

Cascade impactors

Similar to single-stage impactors in collection methods, cascade impactors have multiple size cuts (PM₁₀, PM_2.5), allowing for bioaerosols to separate according to size. Separating biological material by aerodynamic diameter is useful due to size ranges being dominated by specific types of organisms (bacteria exist range from 1-20 micrometers and pollen from 10-100 micrometers). The Andersen line of cascade impactors are most widely used to test air particles.

Cyclones

A cyclone sampler consists of a circular chamber with the aerosol stream entering through one or more tangential nozzles. Like an impactor, a cyclone sampler depends upon the inertia of the particle to cause it to deposit on the sampler wall as the air stream curves around inside the chamber. Also like an impactor, the collection efficiency depends upon the flow rate. Cyclones are less prone to particle bounce than impactors and can collect larger quantities of material. They also may provide a more gentle collection than impactors, which can improve the recovery of viable microorganisms. However, cyclones tend to have collection efficiency curves that are less sharp than impactors, and it is simpler to design a compact cascade impactor compared to a cascade of cyclone samplers.

Impingers

Instead of collecting onto a greased substrate or agar plate, impingers have been developed to impact bioaerosols into liquids, such as deionized water or phosphate buffer solution. Collection efficiencies of impingers are shown by Ehrlich et al. (1966) to be generally higher than similar single stage impactor designs. Commercially available impingers include the AGI-30 (Ace Glass Inc.) and Biosampler (SKC, Inc).

Electrostatic precipitators

Electrostatic precipitators, ESPs, have recently gained renewed interest for bioaerosol sampling due to their highly efficient particle removal efficiencies and gentler sampling method as compared with impinging. ESPs charge and remove incoming aerosol particles from an air stream by employing a non-uniform electrostatic field between two electrodes, and a high field strength. This creates a region of high density ions, a corona discharge, which charges incoming aerosol droplets, and the electric field deposits the charges particles onto a collection surface. Since biological particles are typically analysed using liquid-based assays (PCR, immunoassays, viability assay) it is preferable to sample directly into a liquid volume for downstream analysis. For example, Pardon et al. show sampling of aerosols down to a microfluidic air-liquid interface, and Ladhani et al., show sampling of airborne Influenza down to a small liquid droplet. The use of low-volume liquids is ideal for minimising sample dilution, and has the potential to be couple to lab-on-chip technologies for rapid point-of-care analysis.

Filters

Filters are often used to collect bioaerosols because of their simplicity and low cost. Filter collection is especially useful for personal bioaerosol sampling since they are light and unobtrusive. Filters can be preceded by a size-selective inlet, such as a cyclone or impactor, to remove larger particles and provide size-classification of the bioaerosol particles. Aerosol filters are often described using the term "pore size" or "equivalent pore diameter". Note that the filter pore size does NOT indicate the minimum particle size that will be collected by the filter; in fact, aerosol filters generally will collect particles much smaller than the nominal pore size.

Transport mechanisms

Ejection of bioaerosols into the atmosphere

Bioaerosols are typically introduced into the air via wind turbulence over a surface. Once airborne they typically remain in the PBL, but in some cases reach the upper troposphere and stratosphere. Once in the atmosphere, they can be transported locally or globally: common wind patterns/strengths are responsible for local dispersal, while tropical storms and dust plumes can move bioaerosols between continents. Over ocean surfaces, bioaerosols are generated via sea spray and bubbles.

Small scale transport via clouds

Knowledge of bioaerosols has shaped our understanding of microorganisms and the differentiation between microbes, including airborne pathogens. In the 1970s, a breakthrough occurred in atmospheric physics and microbiology when ice nucleating bacteria were identified.

The highest concentration of bioaerosols is near the Earth’s surface in the PBL. Here wind turbulence causes vertical mixing, bringing particles from the ground into the atmosphere. Bioaerosols introduced to the atmosphere can form clouds, which are then blown to other geographic locations and precipitate out as rain, hail, or snow. Increased levels of bioaerosols have been observed in rain forests during and after rain events. Bacteria and phytoplankton from marine environments have been linked to cloud formation. However, for this same reason, bioaerosols cannot be transported long distances in the PBL since the clouds will eventually precipitate them out. Furthermore, it would take additional turbulence or convection at the upper limits of the PBL to inject bioaerosols into the troposphere where they may transported larger distances as part of tropospheric flow. This limits the concentration of bioaerosols at these altitudes.

Cloud droplets, ice crystals, and precipitation use bioaerosols as a nucleus where water or crystals can form or hold onto their surface. These interactions show that air particles can change the hydrological cycle, weather conditions, and weathering around the world. Those changes can lead to effects such as desertification which is magnified by climate shifts. Bioaerosols also intermix when pristine air and smog meet, changing visibility and/or air quality.

Large scale transport via dust plumes

Satellite images show that storms over Australian, African, and Asian deserts create dust plumes which can carry dust to altitudes of over 5 kilometers above the Earth's surface. This mechanism transports the material thousands of kilometers away, even moving it between continents. Multiple studies have supported the theory that bioaerosols can be carried along with dust. One study concluded that a type of airborne bacteria present in a particular desert dust was found at a site 1,000 kilometers downwind.

Possible global scale highways for bioaerosols in dust include:

• Storms over Northern Africa picking up dust, which can then be blown across the Atlantic to the Americas, or north to Europe. For transatlantic transport, there is a seasonal shift in the destination of the dust: North America during the summer, and South America during the winter.
• Dust from the Gobi and Taklamakan deserts is transported to North America, mainly during the Northern Hemisphere spring.
• Dust from Australia is carried out into the Pacific Ocean, with the possibility of being deposited in New Zealand.

Community dispersal

Bioaerosol transport and distribution is not consistent around the globe. While bioaerosols may travel thousands of kilometers before deposition, their ultimate distance of travel and direction is dependent on meteorological, physical, and chemical factors. One study generated an airborne bacteria/fungi map of the United States from observational measurements, resulting community profiles of these bioaerosols were connected to soil pH, mean annual precipitation, net primary productivity, and mean annual temperature, among other factors.

Biogeochemical impacts

Bioaerosols impact a variety of biogeochemical systems on earth including, but not limited to atmospheric, terrestrial, and marine ecosystems. As long-standing as these relationships are, the topic of bioaerosols is not very well-known. Bioaerosols can affect organisms in a multitude of ways including influencing the health of living organisms through allergies, disorders, and disease. Additionally, the distribution of pollen and spore bioaerosols contribute to the genetic diversity of organisms across multiple habitats.

Cloud formation

A variety of bioaerosols may contribute to cloud condensation nuclei or cloud ice nuclei, possible bioaerosol components are living or dead cells, cell fragments, hyphae, pollen, or spores. Cloud formation and precipitation are key features of many hydrologic cycles to which ecosystems are tied. In addition, global cloud cover is a significant factor in the overall radiation budget and therefore, temperature of the Earth. Bioaerosols make up a small fraction of the total cloud condensation nuclei in the atmosphere (between 0.001% and 0.01%) so their global impact (i.e. radiation budget) is questionable. However, there are specific cases where bioaerosols may form a significant fraction of the clouds in an area. These include:

• Areas where there is cloud formation at temperatures over -15 °C since some bacteria have developed proteins which allow them to nucleate ice at higher temperatures.
• Areas over vegetated regions or under remote conditions where the air is less impacted by anthropogenic activity.
• Near surface air in remote marine regions like the Southern Ocean where sea spray may be more prevalent than dust transported from continents.

The collection of bioaerosol particles on a surface is called deposition. The removal of these particles from the atmosphere affects human health in regards to air quality and respiratory systems.

Alpine lakes in Spain

Alpine lakes located in the Central Pyrenees region of northeast Spain are unaffected by anthropogenic factors making these oligotrophic lakes ideal indicators for sediment input and environmental change. Dissolved organic matter and nutrients from dust transport can aid bacteria with growth and production in low nutrient waters. Within the collected samples of one study, a high diversity of airborne microorganisms were detected and had strong similarities to Mauritian soils despite Saharan dust storms occurring at the time of detection.

Affected ocean species

The types and sizes of bioaerosols vary in marine environments and occur largely because of wet-discharges caused by changes in osmotic pressure or surface tension. Some types of marine originated bioaerosols excrete dry-discharges of fungal spores that are transported by the wind.

One instance of impact on marine species was the 1983 die off of Caribbean sea fans and sea urchins that correlated with dust storms originating in Africa. This correlation was determined by the work of microbiologists and a Total Ozone Mapping Spectrometer, which identified bacteria, viral, and fungal bioaerosols in the dust clouds that were tracked over the Atlantic Ocean. Another instance in of this occurred in 1997 when El Niño possibly impacted seasonal tradewind patterns from Africa to Barbados, resulting in similar die offs. Modeling instances like these can contribute to more accurate predictions future events.

Spread of diseases

The aerosolization of bacteria in dust contributes heavily to the transport of bacterial pathogens. A well-known case of disease outbreak by bioaerosol was the meningococcal meningitis outbreak in sub-Saharan Africa, which was linked to dust storms during dry seasons. Other outbreaks have been reportedly linked to dust events including Mycoplasma pneumonia and tuberculosis. Another instance of bioaerosol-spread health issues was an increase in human respiratory problems for Caribbean-region residents that may have been caused by traces of heavy metals, microorganism bioaerosols, and pesticides transported via dust clouds passing over the Atlantic Ocean.

Common sources of bioaerosols include soil, water, and sewage. Bioaerosols can transmit microbial pathogens, endotoxins, and allergens and can excrete both endotoxins and exotoxins. Exotoxins can be particularly dangerous when transported through the air and distribute pathogens to which humans are sensitive. Cyanobacteria are particularly prolific in their pathogen distribution and are abundant in both terrestrial and aquatic environments.

Future research

The potential role of bioaerosols in climate change offers an abundance of research opportunities. Specific areas of study include monitoring bioaerosol impacts on different ecosystems and using meteorological data to forecast ecosystem changes. Determining global interactions is possible through methods like collecting air samples, DNA extraction from bioaerosols, and PCR amplification.

Developing more efficient modelling systems will reduce the spread of human disease and benefit economic and ecologic factors. An atmospheric modeling tool called the Atmospheric Dispersion Modelling System (ADMS 3) is currently in use for this purpose. The ADMS 3 uses computational fluid dynamics (CFD) to locate potential problem areas, minimizing the spread of harmful bioaerosol pathogens include tracking occurrences.

Agroecosystems have an array of potential future research avenues within bioaerosols. Identification of deteriorated soils may identify sources of plant or animal pathogens.

Environmental impact of the coal industry

From Wikipedia, the free encyclopedia

 

A coal surface mining site in Bihar, India

 

A mountaintop removal mining operation in the United States

 

The environmental impact of the coal industry includes issues such as land use, waste management, water and air pollution, caused by the coal mining, processing and the use of its products. In addition to atmospheric pollution, coal burning produces hundreds of millions of tons of solid waste products annually, including fly ash, bottom ash, and flue-gas desulfurization sludge, that contain mercury, uranium, thorium, arsenic, and other heavy metals. Coal is the largest contributor to the human-made increase of CO2 in the atmosphere. 

There are severe health effects caused by burning coal. According to a report by the World Health Organization in 2008, coal particulates pollution are estimated to shorten approximately 1,000,000 lives annually worldwide. A 2004 study commissioned by environmental groups, but contested by the US EPA, concluded that coal burning costs 24,000 lives a year in the United States. More recently, an academic study estimated that the premature deaths from coal related air pollution was about 52,000. When compared to electricity produced from natural gas via hydraulic fracturing, coal electricity is 10–100 times more toxic, largely due to the amount of particulate matter emitted during combustion. When coal is compared to solar photovoltaic generation, the latter could save 51,999 American lives per year if solar were to replace coal generation in the U.S. Due to the decline of jobs related to coal mining a study found that approximately one American suffers a premature death from coal pollution for every job remaining in coal mining.

In addition, the list of historical coal mining disasters is a long one, although work related coal deaths has declined substantially as safety measures have been enacted and underground mining has given up market share to surface mining. Underground mining hazards include suffocation, gas poisoning, roof collapse and gas explosions. Open cut hazards are principally mine wall failures and vehicle collisions. In the United States, an average of 26 coal miners per year died in the decade 2005–2014.

Land use management

Impact to land and surroundings

Strip mining severely alters the landscape, which reduces the value of the natural environment in the surrounding land. The land surface is dedicated to mining activities until it can be reshaped and reclaimed. If mining is allowed, resident human populations must be resettled off the mine site; economic activities, such as agriculture or hunting and gathering food and medicinal plants are interrupted. What becomes of the land surface after mining is determined by the manner in which the mining is conducted. Usually reclamation of disturbed lands to a land use condition is not equal to the original use. Existing land uses (such as livestock grazing, crop and timber production) are temporarily eliminated in mining areas. High-value, intensive-land-use areas like urban and transportation systems are not usually affected by mining operations. If mineral values are sufficient, these improvements may be removed to an adjacent area. 

Strip mining eliminates existing vegetation, destroys the genetic soil profile, displaces or destroys wildlife and habitat, alters current land uses, and to some extent permanently changes the general topography of the area mined. Adverse impacts on geological features of human interest may occur in a coal strip mine. Geomorphic and geophysical features and outstanding scenic resources may be sacrificed by indiscriminate mining. Paleontological, cultural, and other historic values may be endangered due to the disruptive activities of blasting, ripping, and excavating coal. Stripping of overburden eliminates and destroys archeological and historic features, unless they are removed beforehand.

The removal of vegetative cover and activities associated with the construction of haul roads, stockpiling of topsoil, displacement of overburden and hauling of soil and coal increase the quantity of dust around mining operations. Dust degrades air quality in the immediate area, has an adverse impact on vegetative life, and constitutes health and safety hazards for mine workers and nearby residents.

Surface mining disrupts virtually all aesthetic elements of the landscape. Alteration of land forms often imposes unfamiliar and discontinuous configurations. New linear patterns appear as material is extracted and waste piles are developed. Different colors and textures are exposed as vegetative cover is removed and overburden dumped to the side. Dust, vibration, and diesel exhaust odors are created (affecting sight, sound, and smell). Residents of local communities often find such impacts disturbing or unpleasant. In case of mountaintop removal, tops are removed from mountains or hills to expose thick coal seams underneath. The soil and rock removed is deposited in nearby valleys, hollows and depressions, resulting in blocked (and contaminated) waterways.

Removal of soil and rock overburden covering the coal resource may cause burial and loss of topsoil, exposes parent material, and creates large infertile wastelands. Soil disturbance and associated compaction result in conditions conducive to erosion. Soil removal from the area to be surface-mined alters or destroys many natural soil characteristics, and reduces its biodiversity and productivity for agriculture. Soil structure may be disturbed by pulverization or aggregate breakdown.

Mine collapses (or mine subsidences) have the potential to produce major effects above ground, which are especially devastating in developed areas. German underground coal-mining (especially in North Rhine-Westphalia) has damaged thousands of houses, and the coal-mining industries have set aside large sums in funding for future subsidence damages as part of their insurance and state-subsidy schemes. In a particularly spectacular case in the German Saar region (another historical coal-mining area), a suspected mine collapse in 2008 created an earthquake measuring 4.0 on the Richter magnitude scale, causing some damage to houses. Previously, smaller earthquakes had become increasingly common and coal mining was temporarily suspended in the area.

In response to negative land effects of coal mining and the abundance of abandoned mines in the US the federal government enacted the Surface Mining Control and Reclamation Act of 1977, which requires reclamation plans for future coal mining sites. These plans must be approved by federal or state authorities before mining begins.

Water management

Surface mining may impair groundwater in numerous ways: by drainage of usable water from shallow aquifers; lowering of water levels in adjacent areas and changes in flow direction within aquifers; contamination of usable aquifers below mining operations due to infiltration (percolation) of poor-quality mine water; and increased infiltration of precipitation on spoil piles. Where coal or carbonaceous shale is present, increased infiltration may result in: increased runoff of poor-quality water and erosion from spoil piles, recharge of poor-quality water to shallow groundwater aquifers and poor-quality water flow to nearby streams.

The contamination of both groundwater and nearby streams may be for long periods of time. Deterioration of stream quality results from acid mine drainage, toxic trace elements, high content of dissolved solids in mine drainage water, and increased sediment loads discharged to streams. When coal surfaces are exposed, pyrite comes in contact with water and air and forms sulfuric acid. As water drains from the mine, the acid moves into the waterways; as long as rain falls on the mine tailings the sulfuric-acid production continues, whether the mine is still operating or not. Also waste piles and coal storage piles can yield sediment to streams. Surface waters may be rendered unfit for agriculture, human consumption, bathing, or other household uses.

To anticipate these problems, water is monitored at coal mines. The five principal technologies used to control water flow at mine sites are: diversion systems, containment ponds, groundwater pumping systems, subsurface drainage systems, and subsurface barriers.

River water pollution

Coal-fired boilers / power plants when using coal or lignite rich in limestone produces ash containing calcium oxide (CaO). CaO readily dissolves in water to form slaked lime / Ca(OH)₂ and carried by rainwater to rivers/irrigation water from the ash dump areas. Lime softening process precipitates Ca and Mg ions / removes temporary hardness in the water and also converts sodium bicarbonates in river water into sodium carbonate. Sodium carbonate (washing soda) further reacts with the remaining Ca and Mg in the water to remove / precipitate the total hardness. Also, water-soluble sodium salts present in the ash enhance the sodium content in water further. Thus river water is converted into soft water by eliminating Ca and Mg ions and enhancing Na ions by coal-fired boilers. Soft water application in irrigation (surface or ground water) converts the fertile soils into alkaline sodic soils. River water alkalinity and sodicity due to the accumulation of salts in the remaining water after meeting various transpiration and evaporation losses, become acute when many coal-fired boilers and power stations are installed in a river basin. River water sodicity affects downstream cultivated river basins located in China, India, Egypt, Pakistan, west Asia, Australia, western US, etc.

Waste management

Aerial photograph of Kingston Fossil Plant coal fly ash slurry spill site taken the day after the event (23 December 2008)

 

The burning of coal leaves substantial quantities of fly ash, which is usually stored in impoundment ponds. In the low-coal-content areas waste forms spoil tip. The U.S. EPA classified the 44 sites as potential hazards to communities (which means the waste sites could cause death and significant property damage if an event such as a storm, a terrorist attack or a structural failure caused a spill). The U.S. EPA estimated that about 300 dry landfills and wet storage ponds are used around the country to store ash from coal-fired power plants. The storage facilities hold the noncombustible ingredients of coal and the ash trapped by equipment designed to reduce air pollution.

Wildlife

Surface mining of coal causes direct and indirect damage to wildlife. The impact on wildlife stems primarily from disturbing, removing and redistributing the land surface. Some impacts are short-term and confined to the mine site however others have far-reaching, long-term effects.

The most direct effect on wildlife is destruction or displacement of species in areas of excavation and spoil piling. Pit and spoil areas are not capable of providing food and cover for most species of wildlife. Mobile wildlife species like game animals, birds, and predators leave these areas. More sedentary animals like invertebrates, reptiles, burrowing rodents, and small mammals may be destroyed. The community of microorganisms and nutrient-cycling processes are upset by movement, storage, and redistribution of soil.

Degradation of aquatic habitats is a major impact by surface mining and may be apparent many miles from a mining site. Sediment contamination of surface water is common with surface mining. Sediment yields may increase a thousand times their former level as a result of strip mining.

The effects of sediment on aquatic wildlife vary with the species and the amount of contamination. High sediment levels can kill fish directly, bury spawning beds, reduce light transmission, alter temperature gradients, fill in pools, spread streamflows over wider, shallower areas, and reduce the production of aquatic organisms used as food by other species. These changes destroy the habitat of valued species and may enhance habitat for less-desirable species. Existing conditions are already marginal for some freshwater fish in the United States, and the sedimentation of their habitat may result in their extinction. The heaviest sediment pollution of drainage normally comes within 5 to 25 years after mining. In some areas, unvegetated spoil piles continue to erode even 50 to 65 years after mining.

The presence of acid-forming materials exposed as a result of surface mining can affect wildlife by eliminating habitat and by causing direct destruction of some species. Lesser concentrations can suppress productivity, growth rate and reproduction of many aquatic species. Acids, dilute concentrations of heavy metals, and high alkalinity can cause severe damage to wildlife in some areas. The duration of acidic-waste pollution can be long; estimates of the time required to leach exposed acidic materials in the Eastern United States range from 800 to 3,000 years.

Air pollution

Air emissions

“	In northern China, air pollution from the burning of fossil fuels, principally coal, is causing people to die on average 5.5 years sooner than they otherwise might.	”
— Tim Flannery, Atmosphere of Hope, 2015.

Coal and coal waste products (including fly ash, bottom ash and boiler slag) release approximately 20 toxic-release chemicals, including arsenic, lead, mercury, nickel, vanadium, beryllium, cadmium, barium, chromium, copper, molybdenum, zinc, selenium and radium, which are dangerous if released into the environment. While these substances are trace impurities, enough coal is burned that significant amounts of these substances are released.

The Mpumalanga highveld in South Africa is the most polluted area in the world due to the mining industry and coal plant power stations and the lowveld near the famous Kruger Park is under threat of new mine projects as well.

During combustion, the reaction between coal and the air produces oxides of carbon, including carbon dioxide (CO₂, an important greenhouse gas), oxides of sulfur (mainly sulfur dioxide, SO₂), and various oxides of nitrogen (NO_x). Because of the hydrogenous and nitrogenous components of coal, hydrides and nitrides of carbon and sulfur are also produced during the combustion of coal in air. These include hydrogen cyanide (HCN), sulfur nitrate (SNO₃) and other toxic substances. 

SO₂ and nitrogen oxide react in the atmosphere to form fine particles and ground-level ozone and are transported long distances, making it difficult for other states to achieve healthy levels of pollution control. 

The wet cooling towers used in coal-fired power stations, etc. emit drift and fog which are also an environmental concern. The drift contains Respirable suspended particulate matter. In case of cooling towers with sea water makeup, sodium salts are deposited on nearby lands which would convert the land into alkali soil, reducing the fertility of vegetative lands and also cause corrosion of nearby structures. 

Fires sometimes occur in coal beds underground. When coal beds are exposed, the fire risk is increased. Weathered coal can also increase ground temperatures if it is left on the surface. Almost all fires in solid coal are ignited by surface fires caused by people or lightning. Spontaneous combustion is caused when coal oxidizes and airflow is insufficient to dissipate heat; this more commonly occurs in stockpiles and waste piles, rarely in bedded coal underground. Where coal fires occur, there is attendant air pollution from emission of smoke and noxious fumes into the atmosphere. Coal seam fires may burn underground for decades, threatening destruction of forests, homes, roadways and other valuable infrastructure. The best-known coal-seam fire may be the one which led to the permanent evacuation of Centralia, Pennsylvania, United States.

Approximately 75 Tg/S per year of Sulfur Dioxide (SO₂) is released from burning coal. After release, the Sulfur Dioxide is oxidized to gaseous H₂SO₂ which scatters solar radiation, hence their increase in the atmosphere exerts a cooling effect on climate that masks some of the warming caused by increased greenhouse gases. Release of SO₂ also contributes to the widespread acidification of ecosystems.

Mercury emissions

"Power plants... are responsible for half of... the mercury emissions in the United States."

In New York State winds deposit mercury from the coal-fired power plants of the Midwest, contaminating the waters of the Catskill Mountains. Mercury is concentrated up the food chain, as it is converted into methylmercury, a toxic compound which harms both wildlife and people who consume freshwater fish. The mercury is consumed by worms, which are eaten by fish, which are eaten by birds (including bald eagles). As of 2008, mercury levels in bald eagles in the Catskills had reached new heights. "People are exposed to methylmercury almost entirely by eating contaminated fish and wildlife that are at the top of aquatic food chains." Ocean fish account for the majority of human exposure to methylmercury; the full range of sources of methylmercury in ocean fish is not well understood.

In February 2012, the U.S. EPA issued Mercury and Air Toxics Standards (MATS), which require all coal plants to substantially reduce mercury emissions. "Today [2011], more than half of all coal-fired power plants already deploy pollution control technologies that will help them meet these achievable standards. Once final, these standards will level the playing field by ensuring the remaining plants – about 40 percent of all coal-fired power plants – take similar steps to decrease dangerous pollutants."

Annual excess mortality and morbidity

In 2008 the World Health Organization (WHO) and other organizations calculated that coal particulates pollution cause approximately one million deaths annually across the world, which is approximately one third of all premature deaths related to all air pollution sources, for example in Istanbul by lung diseases and cancer.

Pollutants emitted by burning coal include fine particulates (PM2.5) and ground level ozone. Every year, the burning of coal without the use of available pollution control technology causes thousands of preventable deaths in the United States. A study commissioned by the Maryland nurses association in 2006 found that emissions from just six of Maryland's coal-burning plants caused 700 deaths per year nationwide, including 100 in Maryland. Since installation of pollution abatement equipment on one of these six, the Brandon Shores plant, now "produces 90 percent less nitrogen oxide, an ingredient of smog; 95 percent less sulfur, which causes acid rain; and vastly lower fractions of other pollutants."

Economic costs

A 2001 EU-funded study known as ExternE, or Externalities of Energy, over the decade from 1995 to 2005 found that the cost of producing electricity from coal would double over its present value, if external costs were taken into account. These external costs include damage to the environment and to human health from airborne particulate matter, nitrogen oxides, chromium VI and arsenic emissions produced by coal. It was estimated that external, downstream, fossil fuel costs amount up to 1–2% of the EU's entire Gross Domestic Product (GDP), with coal being the main fossil fuel accountable, and this was before the external cost of global warming from these sources was even included. The study found that environmental and health costs of coal alone were €0.06/kWh, or 6 cents/kWh, with the energy sources of the lowest external costs being nuclear power €0.0019/kWh, and wind power at €0.0009/kWh.

High rates of motherboard failures in China and India appear to be due to "sulfurous air pollution produced by coal that’s burned to generate electricity. It corrodes the copper circuitry," according to Intel researchers.

Greenhouse gas emissions

The combustion of coal is the largest contributor to the human-made increase of CO₂ in the atmosphere. Electric generation using coal burning produces approximately twice the greenhouse gasses per kilowatt compared to generation using natural gas.

Coal mining releases methane, a potent greenhouse gas. Methane is the naturally occurring product of the decay of organic matter as coal deposits are formed with increasing depths of burial, rising temperatures, and rising pressure over geological time. A portion of the methane produced is absorbed by the coal and later released from the coal seam (and surrounding disturbed strata) during the mining process. Methane accounts for 10.5 percent of greenhouse-gas emissions created through human activity. According to the Intergovernmental Panel on Climate Change, methane has a global warming potential 21 times greater than that of carbon dioxide over a 100-year timeline. The process of mining can release pockets of methane. These gases may pose a threat to coal miners, as well as a source of air pollution. This is due to the relaxation of pressure and fracturing of the strata during mining activity, which gives rise to safety concerns for the coal miners if not managed properly. The buildup of pressure in the strata can lead to explosions during (or after) the mining process if prevention methods, such as "methane draining", are not taken.

In 2008 James E. Hansen and Pushker Kharecha published a peer-reviewed scientific study analyzing the effect of a coal phase-out on atmospheric CO₂ levels. Their baseline mitigation scenario was a phaseout of global coal emissions by 2050. Under the Business as Usual scenario, atmospheric CO₂ peaks at 563 parts per million (ppm) in the year 2100. Under the four coal phase-out scenarios, atmospheric CO₂ peaks at 422–446 ppm between 2045 and 2060 and declines thereafter.

Radiation exposure

Coal also contains low levels of uranium, thorium, and other naturally occurring radioactive isotopes which, if released into the environment, may lead to radioactive contamination. Coal plants emit radiation in the form of radioactive fly ash, which is inhaled and ingested by neighbours, and incorporated into crops. A 1978 paper from Oak Ridge National Laboratory estimated that coal-fired power plants of that time may contribute a whole-body committed dose of 19 µSv/a to their immediate neighbours in a 500 m radius. The United Nations Scientific Committee on the Effects of Atomic Radiation's 1988 report estimated the committed dose 1 km away to be 20 µSv/a for older plants or 1 µSv/a for newer plants with improved fly ash capture, but was unable to confirm these numbers by test.

Excluding contained waste and unintentional releases from nuclear plants, coal-plants carry more radioactive wastes into the environment than nuclear plants per unit of produced energy. Plant-emitted radiation carried by coal-derived fly ash delivers 100 times more radiation to the surrounding environment than does the normal operation of a similarly productive nuclear plant. This comparison does not consider the rest of the fuel cycle, i.e., coal and uranium mining and refining and waste disposal. The operation of a 1000-MWe coal-fired power plant results in a nuclear radiation dose of 490 person-rem/year, compared to 136 person-rem/year, for an equivalent nuclear power plant including uranium mining, reactor operation and waste disposal.

Dangers to miners

Historically, coal mining has been a very dangerous activity, and the list of historical coal mining disasters is long. The principal hazards are mine wall failures and vehicle collisions; underground mining hazards include suffocation, gas poisoning, roof collapse and gas explosions. Chronic lung diseases, such as pneumoconiosis (black lung) were once common in miners, leading to reduced life expectancy. In some mining countries black lung is still common, with 4,000 new cases of black lung every year in the US (4 percent of workers annually) and 10,000 new cases every year in China (0.2 percent of workers). Rates may be higher than reported in some regions. 

In the United States, an average of 23 coal miners per year died in the decade 2007–2016. Recent U.S. coal-mining disasters include the Sago Mine disaster of January 2006. In 2007, a mine accident in Utah's Crandall Canyon Mine killed nine miners, with six entombed. The Upper Big Branch Mine disaster in West Virginia killed 29 miners in April 2010.

However, in lesser developed countries and some developing countries, many miners continue to die annually, either through direct accidents in coal mines or through adverse health consequences from working under poor conditions. China, in particular, has the highest number of coal mining related deaths in the world, with official statistics claiming that 6,027 deaths in 2004. To compare, 28 deaths were reported in the US in the same year. Coal production in China is twice that in the US, while the number of coal miners is around 50 times that of the US, making deaths in coal mines in China 4 times as common per worker (108 times as common per unit output) as in the US. 

The Farmington coal mine disaster kills 78. West Virginia, US, 1968.

 

Build-ups of a hazardous gas are known as damps:

• Black damp: a miture of carbon dioxide and nitrogen in a mine can cause suffocation. The anoxic condition results of depletion of oxygen in enclosed spaces, e.g. by corrosion.
• After damp: similar to black damp, after damp consists of carbon monoxide, carbon dioxide and nitrogen and forms after a mine explosion.
• Fire damp: consists of mostly methane, a highly flammable gas that explodes between 5% and 15% – at 25% it causes asphyxiation.
• Stink damp: so named for the rotten egg smell of the hydrogen sulphide gas, stink damp can explode and is also very toxic.
• White damp: air containing carbon monoxide which is toxic, even at low concentrations

Firedamp explosions can trigger the much more dangerous coal dust explosions, which can engulf an entire pit. Most of these risks can be greatly reduced in modern mines, and multiple fatality incidents are now rare in some parts of the developed world. Modern mining in the US results in approximately 30 deaths per year due to mine accidents.