organisms. Most pollution is in the form of chemical additions to air, water or soil; however, in modern times starting in the mid-twentieth century noise and light have been considered as pollution sources. Most pollution is man-made, with natural fluctuations in atmospheric composition, surface water bodies and soil considered temporal gyrations in the Earth's natural history. The chief driver of pollution is the massive growth in human population, which induces the proximate causes of intensive agriculture and extraordinary industrial output. The United Nations and the Blacksmith Institute are two prominent organisations that tabulate locales of the greatest pollution intensity; while their listings do not correspond precisely, the overlap countries that both entities agree are the worst polluted are: China, India, and Russia. Beyond the human health effects of pollution, habitat destruction is a widespread consequence, especially with regard to water pollution.Pollution is environmental contamination that results in harm or death to living
See main article: Pollution: a brief history
Earliest evidence of man-made pollution derives from ice core records, from which aspects of the prehistoric atmosphere can be deduced. Analyses of this data indicate noteworthy mass burning by early man in the early to middle Holocene period, giving rise to significant air pollutants. The records from that era reflect deposition of air pollutants from vegetation burning on lake and ice surfaces. Studies on cave dwelling Homo sapiens in Europe document the presence of indoor air pollution from soot residues on the cave ceilings at an even earlier time from the pre-Holocene.
The Holocene also witnessed the first clearly defined water pollution in the form of excessive sediment transport, which clogged certain ancient ports of Europe and Asia Minor, notably the Danube Delta of the Black Sea; such river siltation was generated from soil erosion caused by the first farmers who were clearing forests at a rapid pace for crops and grazing. Evidence of some of the earliest industrially generated air pollution is found in the ice core records of Greenland's glaciers, in which traces of metals refining can be recovered dating to the classical Greek and Roman eras, as well as the Han Dynasty of China.
Some of the first recorded history of pollution relates to 13th century England, when coal burning began to replace wood use, after significant deforestation had by this time occurred in much of Europe. In 1272 and 1306 AD there were significant bans placed on burning coal in London, due to significant public outcry from the air pollution. By-products of the Industrial Revolution in much of Europe were substantial air and water pollution, a milestone of which was the Great Stink of 1858 arising from untreated sewage discharged to the River Thames in London.
Major sources of air pollution are transportation, agriculture, industrial, construction and solid waste landfills. Transportation sources, mainly due to combustion of petroleum fuels, are some of the most difficult to mitigate since the emissions are generated in the heart of populated areas. Agricultural sources include significant methane generation from livestock; particulate dust from land cultivation and pesticide aerosol sprays. The principal industrial sources of air pollution are fossil fuel burning power plants; heavy manufacturing; petroleum and metals refining. Construction work generates particulate and fossil fuel combustion products as well as a variety of paint and solvent off-gasses. Landfill decaying organic matter produces methane gas, and landfill working face operations produce significant dust; in addition, landfill burning in lesser developed countries is a source of significant carbon monoxide and other air pollutants.
Chief producers of water pollution are agricultural, transportation and industrial uses as well as human sewage sources. Agricultural runoff includes a host of phosphate and nitrogen fertilizers; however, the most toxic elements of agricultural runoff are often from pesticide usage. The most significant physical water pollutant from agricultural use is excess sediment in runoff from crop cultivation as well as clearcut forests. Transportation impacts derive chiefly from runoff of roadways and parking lots, where petroleum hydrocarbons, lead and sediment are common constituents of such runoff. Leaking underground fuel storage tanks may be attributed to both transportation and industrial functions. Other Industrial sources include solvents, heavy metals, acids and a host of organic chemicals. Principal industries contributing to water pollution are metals refining, food processing, pulp and paper industries and chemical factories. Worldwide untreated sewage is an important source of water pollution in the form of suspended solids, decrease of dissolved oxygen and pathogenic microbes; over three billion people are currently subjected to unsafe drinking water, chiefly due to such microbial contamination. Leaching of chemicals from poorly designed landfills is a further component of water pollution, which affects both surface as well as groundwater. Thermal pollution may be a considered a manifestation of water pollution, and it is mainly associated with the waste heat discharge from large power generation and manufacturing plants.
Noise pollution sources are chiefly transportation related, since motor vehicles, trains and aircraft produce approximately 90 percent of all unwanted acoustical energy, with industrial plants and amplified sound contributing most of the balance. Light pollution, or over-illumination, is a more subtle form of environmental contamination, but excessive lighting causes not only annoyance, but also health effect impacts; additionally large scale atmospheric lighting can interfere with astronomical observations.
See main article: Air pollution
Air pollutants are dispersed in the atmosphere through convective and turbulent movement. In addition, some pollutants undergo chemical reaction with others, particularly in the presence of sunlight, where photochemical oxidants are formed by combination of certain hydrocarbon molecules with oxides of nitrogen.
The transport of air pollutants is studied using mathematical models, that can generally be grouped as follows:
- Point source models, used chiefly for industrial sources;
- Line source models, applied mainly to roadway, train and aircraft sources;
- Area source models, used for such large, two dimensional sources as windblown dust or wildfires; and
- Photochemical models, invoked to study the combination of transport and chemical reactions that produce photochemical oxidants.
The earliest point source model was originated in the early twentieth century, invoking a Gaussian dispersion model for buoyant pollution plumes to predict movement of pollutants, with consideration given to wind velocity, source stack height, emission rate and atmospheric turbulence. This model has been calibrated extensively with experimental data for a variety of atmospheric conditions.
A roadway air dispersion model was developed starting in the late 1950s and early 1960s in response to requirements of the National Environmental Policy Act and the U.S. Department of Transportation to understand impacts of proposed new highways upon air quality, especially in urban areas. Several research groups were active in this model development, among which were: the Environmental Research and Technology (ERT) group in Massachusetts, the ESL Inc. group in California and the California Air Resources Board group in California. The ESL group received a contract from the United States Environmental Protection Agency to validate a line source model using sulfur hexafluoride as a tracer gas. Some of the earliest uses of the model were in court cases involving highway air pollution at the Arlington, Virginia portion of Interstate 66 and the New Jersey Turnpike widening project through East Brunswick, New Jersey. Area source models were developed in 1971 through 1974 by the same groups pioneering the line source models, Similarly photochemical models were developed primarily in the 1960s and 1970s, but their use was more specialized and for such regional needs as understanding smog formation in the Livermore and Los Angeles air basins of California.
Indoor air pollution is a specialized aspect of this subject, whereby air contaminants are effectively trapped in an enclosed space occupied by humans. The most significant pathways for this type of pollution are: (a) Radon accumulation in buildings; and (b) tobacco smoke produced within buildings what about off gassing of consumer and building products (carpets, furniture, sheetrock etc?). A final aspect of air pollution worth noting is the effect of certain acidic air pollutants such as sulfur dioxide upon sculpture and artworks made of limestone or similar materials.
Chemical water pollutants are either discharged into surface or groundwater (point sources) or originate as soil deposition, thence carried to water bodies by surface runoff. Common examples of such chemical water pollutants are mercury emanating from mining activity, certain nitrogen compounds used in agriculture, chlorinated organic molecules arising from sewage or water treatment plants  various acids which are the externalities of various manufacturing activities. Contaminants discharged into the atmosphere from industrial stacks and other sources can also contaminant water bodies which are distant from the original source.
Physical water pollutants are either (a) particles much larger than molecular scale or (b) physical factors such as temperature change, both of which while not inherently toxic, cause a variety of harmful effects. The most obvious of physical pollutants are (a) excessive sediment load, mostly arising from over-intense land use practices and (b) rubbish discarded from human manufacturing activity (e.g. plastic bags, bottles). While these materials are not so harmful to human health as chemicals or pathogens, they comprise the majority of visual impact of water pollution. In the case of thermal pollution, these point source discharges typically affect the metabolism of aquatic fauna in adverse ways.
Radioactive substances are really merely a special sub-class of chemical pollutants, and by mass represent the smallest of the contributors to water pollution; however, their potential for harm allows recognition as a separate class. In fact, most discharge of radioactivity is not from the negligible escape from nuclear power plants, but rather arises from agricultural practices such as tobacco farming, where radioactive contamination of phosphate fertilizer is a common method of introduction of radioactive materials into the environment.
Common pathogenic microbes introduced into natural water bodies are pathogens from untreated sewage or surface runoff from intensive livestock grazing. One of the most common disease agents is Giardia lamblia, a parasitic protozoan common in fecal material of many fauna including humans; this microbe is particularly insidious, due to its resistance to conventional sewage treatment. This and other protozoans and bacteria are important causes of illness and mortality in developing countries where population density, water scarcity and inadequate sewage treatment combine to occasion widespread parasitic and bacterial disease.
Thermal pollution is the act of altering the temperature of a natural water body, which may be a river, lake or ocean. This condition chiefly arises from the waste heat generated by an industrial process such as certain power generation plants. The concept is most frequently discussed in the context of elevating natural water temperature, but may also be caused by the release of cooler water from the base of reservoirs into warmer rivers. Elevated river temperatures can also arise from deforestation or urbanization that can reduce stream shading. Thermal pollution is one parameter of the broader subject of water pollution.There can be significant environmental consequences of thermal pollution with respect to surface receiving waters such as rivers and lakes; in particular, decrease in biodiversity and creation of an environment hospitable to alien aquatic species may occur. Regulation of thermal pollution has been more elusive than for other forms of water pollution, although straightforward mitigation measures are available, especially in the case of elevated temperature discharges.
Land pollution occurs by rupture of chemical containment devices, improper disposal of chemical wastes, from surface runoff transporting man-made pollutants such as heavy metals from roadways or pesticides from agricultural uses and deposition of air pollutants settling out onto land. In some cases the residence time for such pollutants is very long, especially when chemical molecules are not readily broken down in the environment and when these pollutants are not sufficiently soluble to enable further transport.
See main article: Noise pollution
Noise pollution is unwanted or harmful sound that intrudes upon human or other faunal activity. Noise pollution is almost entirely human generated, whether by machine sources or amplified sound of human creation. Approximately ninety percent of all such intrusive sound arises from such transport devices as motor vehicles, aircraft and rail activities. Noise pollution gives rise to an assortment of adverse human health effects as well as disruption of faunal activity. Regulation of noise pollution began in a systematic way in the United States with enactment of the Noise Control Act of 1972. Within the next 22 years a number of other national governments had emulated the U.S. initiative.
Meteorlogical influences play an important role in sound propagation, particularly due to vertical stratification effects in temperature and wind velocity. These microclimate atmospheric layering effects induce refraction in the sound rays, such that sound intensities at the receptor may be greatly amplified or reduced, depending upon whether the sound rays are refracted upward or downward. For example a thermal profile in which warmer air is near the Earth's surface will create less dense air at the surface level and will cause sound to refract upwards, resulting in reduced sound intensity at a receptor.
Light pollution is the intrusion of unwanted or unneeded artificial light into a man-made or natural environment. A variety of somewhat separate phenomena comprise the overall issue of pollution due to excess artificial light: over-illumination, glare, light trespass and skyglow. Adverse impacts of light pollution include human annoyance, interference with ecosystems, human health effects, interference with astronomical observation and wasteful consumption of energy. Sources of interior light pollution consist chiefly of unnecessarily intense lighting; principal sources of outdoor light pollution include street lighting, poorly designed stadium and recreational lighting, gratuitous building uplighting and unnecessary use of office interior lighting intruding into the night sky.
Local governments have begun to regulate certain aspects of light pollution; in particular, numerous municipalities have established standards that control the amount of light traversing property boundaries. Regarding exterior lighting fixtures and skyglow issues, some governmental agencies and lighting manufacturers have established standards that limit the quantity of light that is wasted by emanating skyward and not illuminating the ground target.
Pollutants in the environment produce a broad array of health impacts on humans as well as other species. These adverse impacts may range from annoyance and metabolic disturbance to mortality. Air pollution causes deaths numbering in the millions of people per annum worldwide. Chief causes of mortality are respiratory and circulatory disease, including significant incidence of lung cancer. It is difficult to separate out the contributions of smoking and second hand smoke versus general ambient air quality, since all of these impacts are cumulative over the human lifespan. Heart disease is particularly strongly correlated with tobacco smoking and second hand derivatives. Respiratory diseases attributed to adverse air quality are chiefly lung cancer, emphysema and other obstructive lung disease.
The pathways of disease are not fully understood from a variety of carcinogenic air pollutants, since there are a vast array of airborne pesticides and other complex organic chemicals that produce mutagenic as well as carcinogenic effects. In addition, the variety of impacts from contaminants like heavy metals present in air pollution is not fully understood, due to the long time exposure required for many of the diseases to progress.
Furthermore, identifying the impacts of heavy metal and other pollutants is complex, since often there are dual pathways of pollutant exposure to the human body, most commonly being via water and via air pathways, as well as combined exposures to multiple contaminants.
sewage treatment systems, and, in the case of Asia, which have massive uncontrolled industrial sources of water pollution. With regard to inadequately treated sewage and livestock runoff sources, common pathogenic microbes are to Giardia lamblia and species of the genus Salmonella (which variously cause typhoid fever and food-borne illnesses); species in the genus Cryptosporidium, which are fecal-oral route parasites often transmitted as water pollutants and are associated with inadequate sanitation; parasitic worms that live inside faunal digestive systems for part of their life cycle (This widespread syndrome is spread partially as water pollutants, with an estimated three billion people currently affected). Hepatitis A is a viral disease, one of whose pathways of transmission is water-borne.Total deaths from water pollution worldwide conservatively number over fifty million people, with young children bearing a disproportionate amount of this mortality; the greatest incidence of these impacts are in Asia and Africa, regions which have the greatest lack of
Noise affects health through elevated sound levels, and may manifest as physiological as well as psychological impairments. Some of the chief health effects include hypertension, ischemic heart disease. Some studies have suggested changes in the immune system, and limited data attributing birth defects to noise exposure have come forward. Although some presbycusis, or loss of hearing, may occur naturally with age, in many developed nations the cumulative impact of noise is sufficient to impair the hearing of a large fraction of the population over the course of a lifetime. Also, noise exposure has been known to induce tinnitus, hypertension, vasoconstriction and other cardiovascular impacts. Beyond these effects, elevated noise levels can create stress, increase workplace accident rates. The most significant causes of exposure to sound levels causing adverse health effects are vehicle and aircraft noise, industrial noise and prolonged exposure to amplified music.
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