Environmental Pollution

Environmental pollution is the release of chemical waste that causes detrimental effects on the environment. Environmental pollution is often divided into pollution of water supplies, the atmosphere, and the soil. In his book Environmental Chemistry, Stanley Manahan lists several different types of pollutants, including toxic inorganic and organic compounds, high concentrations of normally innocuous compounds, and heat and noise. While much pollution is produced by the chemical industry, domestic sources include human waste and automobile exhaust.

While physical sources, such as noise and light, of pollution are important, people most often notice the damage of chemical pollution on animals and plant life. These chemicals can react with tissues in the body and change the structure and function of the organ, cause abnormal growth and development of the individual, or bind with the genetic material of cells and cause cancer. The study of the effects of poisons on the body is called toxicology . One of the central tenets of toxicology states that the dose of a chemical determines its overall effects and that most chemicals can be dangerous at high exposures.

Individuals and chemical and petroleum companies contribute to the pollution of the atmosphere by releasing inorganic and organic gases and particulates into the air. The atmosphere is a paper-thin layer of gas (representing 1 percent of the mass of Earth) that protects the planet from damaging cosmic and ultraviolet radiation , contains life-giving oxygen, and allows the efficient cooling of the planet.

Atmospheric Pollution

Some examples of atmospheric pollutants include nitrogen dioxide (NO₂), sulfur dioxide (SO₂), carbon monoxide (CO), and chlorofluorocarbons (CFCs) . The first two pollutants combine with water to form acids, which not only irritate the lungs but also contribute to the long-term destruction of the environment due to the generation of acid rain . Carbon monoxide, generated by the incomplete combustion of hydrocarbons, displaces and prevents oxygen from binding to hemoglobin and causes asphyxiation. Also, it binds with metallic pollutants and causes them to be more mobile in air and water. CFCs and other halogenated hydrocarbons react with light to form highly reactive species, called radicals, which destroy ozone in the upper atmosphere. These reactions greatly reduce the protective effects of ozone against ultraviolet radiation.

Water Pollution

Fresh, clean, and drinkable water is a necessary but limited resource on the planet. Industrial, agricultural, and domestic wastes can contribute to the pollution of this valuable resource, and water pollutants can damage human and animal health. Three important classes of water pollutants are heavy metals , inorganic pollutants, and organic pollutants. Heavy metals include transition metals such as cadmium, mercury, and lead, all of which can contribute to brain damage. Inorganic pollutants like hydrochloric acid, sodium chloride, and sodium carbonate change the acidity, salinity, or alkalinity of the water, making it undrinkable or unsuitable for the support of animal and plant life. These effects can result in dire consequences for higher mammals such as humans. A list of organic pollutants includes pesticides such as chlorpyrifos and paraquat, and their byproducts, such as dioxin. All of these substances are highly lethal to animals, and many can be readily absorbed through the skin.

Pesticides

The use of pesticides in agriculture contributes to environmental pollution. Pesticides are used to control the growth of insects, weeds, and fungi, which compete with humans in the consumption of crops. This use not only increases crop yields and decreases grocery prices, but also controls diseases such as malaria and encephalitis. However, the spraying of crops and the water runoff from irrigation transports these harmful chemicals to the habitats of nontarget animals. Chemicals can build up in the tissues of these animals, and when humans consume the animals the increased potency of the pesticides is manifested as health problems and in some cases death. Chemists have recently developed naturally occurring pesticides that are toxic only to their particular targets and are benign to birds and mammals. The most significant pesticide of the twentieth century was DDT, which was highly effective as an insecticide but did not break down in the environment and led to the death of birds, fish, and some humans.

Industrial Pollution and Love Canal

The infamous case of the pollution of Love Canal, on Lake Erie in New York, brought environmental pollution to the public attention in the 1970s, and the history of this incident has been thoroughly described at a University of Buffalo web site. From 1942 to 1953, several chemical companies dumped 20,000 metric tons of chemical waste at this site. In 1953 the land was sold to the local board of education, and the 99th Street School was constructed on the land. The school attracted families to the neighborhood, which grew to contain 800 single-family homes and 240 apartment units by 1978. Unfortunately, eighty different chemicals, including dioxins and polychlorinated biphenyls (PCBs), started to leach through the soil, and residents began complaining of odd smells in their houses and experiencing many unexplainable health problems. The school was closed in August 1978, and the federal government contributed $10 million for the relocation of 200 families nearest the site. In 1980 President Carter sent additional funds, for the relocation of 700 more families. Today federal laws stipulate that generators of hazardous waste are responsible for the proper storage and disposal chemicals from the "cradle to the grave."

New Pollutants: Toxic Mold

Recently many people have complained of illnesses associated with the presence of toxic mold in their homes and workplaces. These molds, which thrive in damp surroundings, are members of the fungi kingdom and produce chemicals called mycotoxins that can produce a variety of health problems. Additionally, molds produce strong allergic reactions in some individuals. According to the Centers for Disease Control and Prevention (CDC), little strong evidence exists that can tie all of the health problems seen in damp or flooded areas to molds, but the CDC also recommends that one should repair leaking plumbing and all other causes of damp environments as soon as they occur.

While some of the environmental pollution created in society is avoidable, industrial nations will always produce a low level of pollutants. Pesticides greatly increase overall food production; pharmaceuticals, which require organic chemicals for their manufacture, extend life; and plastics are used in all aspects of medical and domestic life. Society must find a balance between the desire to minimize the cost of manufactured items and the desire to require industries and individuals to reduce pollution.

ERIN BROCKOVICH: THE STORY BEHIND THE MOVIE

In December 1987, Pacific Gas and Electric (PG&E) reported to the Environmental Protection Agency that it had detected levels of chromium (VI) at its natural gas compression station near Hinkley, California, that were ten times higher than those allowed by government standards. These reports devalued land in the community and sparked the curiosity of Erin Brockovich, who was working in a law office as a secretary. Her passionate investigation into the actions of the large public utility led to the discovery of a thirty-year cover-up of the improper disposal of cooling water contaminated with the chromium (VI). Dr. Robert A. Goyer has stated that chromium (VI) irritates the skin of humans and causes cancer in laboratory animals. According to an article by attorney Carole Bos on the LawBuzz web site, Erin Brockovich's work forced PG&E to pay damages of $300 million to the residents of Hinkley.

see also Air Pollution; Water Pollution.

G. Brent Dawson

Bibliography

Freedman, Bill (1989). Environmental Ecology: The Impacts of Pollution and Other Stresses on Ecosystem Structure and Function. San Diego: Academic Press.

Gallo, Michael (2001). "History and Scope of Toxicology." In Casarett and Doull's Toxicology: The Basic Science of Poisons, 6th edition, ed. Curtis D. Klaasen. New York: McGraw-Hill.

Goyer, Robert A., and Clarkson, Thomas W. (1996). "Toxic Effects of Metals." In Caserett and Doull's Toxicology: The Basic Science of Poisons, 5th edition, ed. CurtisD. Klaasen. New York: McGraw-Hill.

Manahan, Stanley (1999). Environmental Chemistry, 6th edition. Boca Raton, FL: Lewis Publishers.

Internet Resources

Bos, Carole D. "Erin Brockovich, Famous Trials." Law Buzz. Available from <http://www.lawbuzz.com/famous_trials/erin_brockovich/erin_brockovich_ch1.htm>.

Ecumenical Task Force of the Niagara Frontier. "Background on the Love Canal." Available from <http://ublib.buffalo.edu/libraries/projects/lovecanal/background_lovecanal.html>.

Environmental pollution

Scottish-American naturalist and Sierra Club founder, John Muir (1838–1914), wrote, "When we try to pick out anything by itself, we find it hitched to everything else in the Universe." Our rapidly growing, ever more industrialized human population exists within a carefully balanced global system of physical processes that circulates chemical elements through the solid earth, hydrosphere, atmosphere, and biosphere . From agricultural land and water management, to extraction and combustion of fossil fuels , to industrial and municipal disposal of waste products, modern human activity has overprinted natural Earth cycles with synthetic ones. In many cases, these man-made alterations to the natural environment negatively impact the very Earth systems that sustain human life. Contamination of the hydrosphere and atmosphere, depletion of radiation-shielding stratospheric ozone , and anthropogenic global climate change are examples of changes induced by human environmental pollution.

Accessible, uncontaminated water is essential to all human activities, and water pollution is a persistent environmental issue. Contamination of surface, ground, ocean, and atmospheric water occurs when chemical, radioactive, and organic waste is washed, spilled, or dumped into water reservoirs at point and non-point sources. Point sources of water pollution introduce concentrated waste products into rivers , aquifers, and oceans at focused entry points. Point sources such as oil spills, chemical leaks, and sewage discharges can often be easily corrected; the inflow of hazardous waste can be stopped, and the contaminated water reservoir can sometimes be cleansed. However, the immediate damage to ecosystems and water quality by highly concentrated chemicals at the spill site or pipe outlet may be irreversible, and cleanup is usually costly and difficult. The 1989 Exxon Valdez oil spill in Prince William Sound, Alaska was a dramatic example of a point source of marine water pollution.

Damaging materials also flow into streams and aquifers from diffuse, non-point sources like agricultural lands, logging tracts, mines, residential leach fields, and urban pavement. While non-point pollution is usually less concentrated, it is also more difficult to control, contain, and regulate. Furthermore, the environmental effects of non-point pollutants like fertilizers, pesticides, animal manure, and mining leachates often manifest themselves as systemic changes to aquatic environments that, in turn, reduce water quality. For example, addition of organic materials, fertilizers, and detergents to streams and lakes enhances the natural process of eutrophication, in which aquatic vegetation chokes a stream or lake, and eventually kills the reservoir's aquatic fauna. Even very low concentrations of toxic heavy metals like those found in leachates from mine tailings, or lead plumbing, can result in toxic contamination of fish and mammals in an aquatic ecosystem. Untreated sewage and agricultural runoff may introduce viral and bacterial pathogens that cause an array of human illnesses from typhoid to dysentery.

Groundwater pollution occurs when contaminants enter an aquifer from a point or non-point source in a recharge zone, contaminated surface water infiltrates, or buried tanks and landfills leak into the groundwater. Groundwater flow paths are complex, and the ultimate site of contamination is often difficult to predict. In karst aquifers, groundwater flows fairly rapidly through interconnected limestone dissolution cavities with little filtration of dissolved materials. Pollutants may thus be flushed from the groundwater in months or weeks, but contaminants often take unexpected paths through limestone aquifers, and eventually discharge, undiluted, at unexpected locations. In homogenous, porous aquifers, like the sandstone Ogalla aquifer in the south central United States, pollutants flow slowly from their points of entry, and are naturally filtered over time. However, it is difficult to flush contamination from a sandstone aquifer, and recharge with fresh water is extremely slow. Groundwater contamination is of particular concern for sitting buried landfills, petroleum tanks, and particularly nuclear waste repositories. Groundwater contamination by harmful radioactive waste buried at nuclear weapons laboratories in Hanford, Washington, and Oak Ridge, Tennessee has cast doubt on nuclear waste disposal schemes.

Though contamination is often introduced into the atmosphere at point sources like smokestacks and exhaust pipes, air pollution is usually diffuse because atmospheric circulation is unconfined. Sulfur dioxide emitted by coal-burning electrical generators disperses widely into the atmosphere before chemically combining with water vapor to form sulfuric acid. The resulting corrosive acid rain falls on widespread areas far downwind of the original point source. Nitrogen oxides released from automobile engines are a main component of the brown smog that blankets many cities. Nitrogen oxide and sulfur dioxide combine with other atmospheric chemicals in strong sunlight to form ozone, the component of smog that affects respiration and irritates humans' eyes. Ironically, ozone is harmful to humans in the lower atmosphere, but ozone in the outer atmosphere shields us from harmful, carcinogenic ultra-violet radiation. Another class of man-made chemicals, called chlorofluorocarbons (CFCs), has chemically destroyed the shielding ozone in the stratosphere over Antarctica , creating the "Ozone Hole." CFCs are common industrial chemicals used in air conditioners, aerosol spray cans, refrigerators, and foam packaging.

The dramatic decrease in air and water quality during the twentieth century has spurred the scientific community to better understand the types of environmental pollution described above, and to devise solutions that reduce contamination. Many governments have enacted legislation that encourages these solutions. In the United States, the Environmental Protection Agency's Clean Water Act of 1972, and Clean Air Act of 1990 strictly regulate industrial, agricultural and municipal sources of air and water pollution. Improved understanding of such complex processes as groundwater and atmospheric flow has led to safer methods of waste disposal, from properly-sited, lined landfills, to air filters on smoke stacks, to carburetors on automobiles. Countries that have enacted these relatively inexpensive measures now enjoy much cleaner air and water than existed in the 1970s. In 1987, the international community signed the Montreal Protocol that eventually bans production of CFCs. However, a handful of the thorniest environmental problems facing the Earth's human population have consequences we have yet to understand, let alone reverse. Solutions to the most threatening and highly-politicized environmental issues, including global climate change, overpopulation, and loss of biological diversity may require significant international socioeconomic changes.

See also Atmospheric pollution; Global warming; Greenhouse gases and greenhouse effect; Ozone layer and hole dynamics; Ozone layer depletion

environmental toxicology Environmental toxicology is the qualitative and quantitative study of the adverse or toxic effects of contaminants and other anthropogenic materials on living organisms. Toxic effects may be either lethal, causing death, or sublethal. Sublethal effects include changes in the reproduction, development, growth, pathology, physiology, and behaviour of organisms. The toxicity of a contaminant depends on the physical and chemical properties of the contaminant, the physical, chemical, and biological properties of the ecosystem studied, and the sources and rate of input of the contaminant into the ecosystem.

Environmental toxicologists study the potential of a contaminant to have harmful effects on living organisms. For any particular contaminant, this potential depends on its concentration and the duration of exposure. Toxicity tests are used to evaluate the adverse effects of contaminants on living organisms using standardized, reproducible conditions that enable comparison to be made with other contaminants that have been tested. After any chemical spill, bioassays are performed using the chemical in questions and various species of animals to assess the effects of the spilled material on the organisms. Toxicity depends on both abiotic factors such as pH, temperature, and organic matter, and biotic factors such as the species, life stage, size, and health of the organism. Chemical mixtures may demonstrate a toxicity greater than expected (synergistic) or less than expected (antagonistic) according to the effects of exposure on each individual contaminant in the mixture.

Many toxicological studies were performed after the Exxon Valdez oil spill in 1989 to evaluate the effects of crude oil on the organisms living in Prince William Sound (Alaska). As in other environments, the interaction of chemical, physical, and biological components had to be considered there. Polluted environments may be aquatic (freshwater, estuarine, or marine) or terrestrial, and each environment has its own mechanisms for responding to pollution.

Toxicology also entails the study of the distribution, transformation, transport, and fate of contaminants in plants and animals. Studies conducted after spills determine the horizontal and vertical extent of the contaminant and whether the original material has been transformed into other chemicals (metabolites) that might be more lethal. Environmental toxicologists also study the transport of contaminants through water currents, air currents, movement through porous sediments into groundwater, and volatilization. Toxicologists determine the fate of these chemicals, which can include ingestion by animals and eventual movement up the food chain, chemical uptake through the roots of plants that are then eaten by various animals and man, or absorption or adsorption by sediments ingested by bottom-feeding animals.

J. H. Baker