The Big Picture

Pollutants are emitted from a great variety of natural sources, from volcanoes that alter entire landscapes with deposits of ash and expose plants and animals to toxic vapors, to photosynthesis itself which produces oxygen, a pollutant to anaerobic microbes. Species evolved tolerances in response to pollutants. In recent decades (especially during the second half of the twentieth century) hundreds of thousands of new, synthetic pollutants have been introduced into the environment. Some of these pollutants are highly toxic and persist in the environment and in biological tissue. As a result species populations that are live in areas receiving pollutants in high concentrations or species that have low tolerances for pollutants may experience detrimental effects at the organism and population scale. The effects of pollutants on human health are well founded. Considerable research (at great expense) has been conducted to determine how pollutants affect humans and how exposure to pollutants can be minimized. Risk assessment is necessary to objectively ascertain the risks to human and environmental health posed by specific pollutants. Certain risks to human health are well documented and well known (such as cancer risks due to smoking tobacco), other risks are poorly understood and subject to misinformation or misinterpretation (such as cancer risks associated with asbestos).

Frequently Asked Questions

• Pollution is the state of being impure, defiled, dirty, or unclean.
• Contamination is pollution that makes something unfit for a particular use by the introduction of undesirable materials.
• Toxic refers to pollution by poisonous substances.
• Carcinogenic refers to pollutants that have been determined to cause cancer.

• Reactions to pollutants are highly variable.
• Individuals vary in their response; differences may be due to such factors as body size, age, general health, immune response, previous exposures, sensitivity, or other known or unknown causes.
• Pollutants have a threshold; below this threshold, exposure causes no effects; above the threshold, effects may be manifest.
• Some responses to exposure are reversible; other responses are permanent.
• Pollutants may be changed by ecological processes and biological processes thus their effects may be altered by these processes.
• The effects of multiple exposures to one or several pollutants may have a synergetic effect, where the combined effect of multiple exposures is greater than any single exposure.

• Pollutant pathways are innumerable; some of these pathways are discussed in more detail in the chapters on water and air pollution (Chapters 20, 22, and 23), nuclear energy (Chapter 18), and agriculture (Chapter 11).
• Generally, however, pollutant sources are categorized as point sources or area sources (non-point sources).
• Point sources usually emit pollutants in high concentrations; point sources include wastewater discharge pipes, smokestacks, and accidental spills. Most point sources are more easily monitored, regulated, and remediated than area sources.
• Area sources are more diffuse than point sources. Concentrations from area sources are usually less concentrated than point sources, but they are also more difficult to detect, monitor, and control. Agricultural and urban runoff, and automobile exhaust are common examples of area sources.

• In the United States, the EPA has standard methods (published guidelines) that are used to collect and analyze samples of air, water, soil, and biological tissue for pollutants. Primarily for legal purposes, the EPA standard methods must be followed by agencies or private concerns that are collecting, handling, or analyzing samples for pollution analysis. Analytical laboratories conducting pollutant analysis must be EPA-approved.
• The EPA publishes a list of pollutants along with the threshold concentrations for human health and the environment. Most threshold levels have been determined in laboratory settings using non-human test subjects and clinical studies; as indicated earlier, the actual effects for individuals are highly variable.
• The units used to measure and report pollutant concentrations depend upon the questions being asked. For example, if you want to know the total amount of cadmium (a potentially toxic heavy metal) discharged in a watershed, the appropriate units may be tons discharged per year. If you are interested in the threshold concentration for human health, the appropriate units for cadmium would be ug/L.
• Commonly reported units include:
• metric tons/year for watershed or air shed discharges or emissions
• m3 per day or year or gallons per day or year for wastewater discharges
• ppb for extremely toxic substances; or ppm for high toxic substances; or percent for less toxic substances
• mg/L or mg/L are standard units for water pollutants
• microorganisms or colonies per mL for waterborne pathogens

• Naturally occurring metallic elements; mercury, lead, cadmium, nickel, platinum, bismuth, arsenic, selenium, vanadium, chromium, thallium, even gold and silver, can be toxic in high enough concentrations.
• Heavy metals do not degrade in the environment and are especially persistent in biological tissue.
• Heavy metals originate from natural sources (rock and soil) but are concentrated and mobilized by human activities. Obviously many metals are mined, the ores refined, and the metal products are used in industry and manufactured products. Metals may also be inadvertently concentrated and mobilized by land use activities that disrupt soils (forestry, agriculture, and construction). Metals may be contained in emissions from smokestacks and discharges from wastewater discharge pipes.
• The physiological effects of heavy metals are commonly manifest in tissue of the nervous system and other internal organs. The effects are especially pronounced in fetuses and children.
• Because heavy metals persist in biological tissue, they are readily transferred and biomagnified in food chains. As a result of the biomagnification of heavy metals and other toxins, animals in the highest trophic levels (highest on the food chain) receive and retain the highest concentration of toxins.
• The total amount of heavy metals in an organism is called the body burden (Figure 14.3).
• Lead, mercury, and selenium are three heavy metals whose health risks have been well publicized in recent decades. Lead contamination is problematic in old house paint and in lead water pipes, mercury contamination is present in many marine and freshwater fish (even fish that live far from sources of pollution), and selenium, which has caused physiological problems for wildlife species in California.

• Organic compounds are produced naturally (the biota is composed of organic molecules) or produced synthetically.
• More than 4 million organic compounds are listed by the American Chemical Society. Synthetic organic molecules are used in industrial processing and consumer products, pesticides, pharmaceuticals, and food additives.
• Some natural organic compounds are toxic; for example the alkaloids in poison ivy or nicotine in cigarettes.
• Some synthetic organic compounds are toxic, such as the chlorinated hydrocarbons (e.g., PCB, DDT, and 2,4,5T, chlordane, Agent Orange); the organophosphates (e.g., malathion and parathion); and the carbamates (e.g., carbaryl or Sevin Dust, methiocarb).
• DDT, PCB, and dioxin are three types of synthetic compounds that have received national and international attention.
• DDT, an insecticide, was one of the main topics discussed in Silent Spring by Rachel Carson; following the publication of this book, government, industry, and citizens began reevaluating chemical usage and their effects on human and environmental health.
• PCBs are widely used in electrical transformers. Inadvertent or illegal disposal of PCBs has contaminated fish in lakes and rivers, such as the Hudson River in New York.
• Dioxin is actually a suite of toxic chlorinated hydrocarbons that may be found in herbicides (Agent Orange) and pulp and paper mill wastewater. Times Beach, Missouri is an infamous site of dioxin contamination.

• Intensive or prolonged exposure to ultra high frequency radiation from radioisotopes can cause damage to cellular DNA. Certain types of birth defects and cancers have been attributed to exposure to radiation.
• Radioactive isotopes occur naturally in rock formations and in some locations may emit sufficient radiation to present a problem to human health.
• The greatest risk to most individuals is from unnatural sources; primarily, medical X-rays and radioactive wastes or emission from nuclear power plants.
• Radiation risks are discussed in more detail in Chapter 18.

• Thermal pollution is the abnormal heating or cooling of natural waters.
• Thermal pollution does not usually present a direct threat to human health, but aquatic ecosystems can be significantly altered by temperature changes.
• Dissolved oxygen concentrations are dependent upon water; increased water temperature decreases dissolved oxygen concentration temperature, although other factors are involved as well. Abnormally warmed waters cannot support fish and other aquatic fish that require cool waters with high dissolved oxygen concentrations (Figure 14.6).
• Spawning in many aquatic species is dependent upon water temperature; abnormal heat or cooling of waters disrupts spawning behavior and success.
• Abnormal heat is attributed to warm water discharges from power plants (Figure 14.7), runoff from roads and parking lots, and the removal of streamside vegetation that would otherwise provide shade.
• Abnormal cooling occurs when cool or cold water is drawn from the bottom of hydropower lakes and reservoirs then discharged downstream.

• Particulates are small aerosol particles of dust.
• Particulates originate from natural sources such as volcanoes, wildfires, and dust storms.
• Particulates may also originate from anthropogenic sources or causes such as combustion of fossil fuels and biomass, dust from agricultural fields, and land use changes that exacerbate wind erosion.
• Most particulates are nontoxic but can contaminate lungs and cause respiratory and cardiovascular problems.
• Some particulates contain toxic materials.
• Particulates can interfere with photosynthesis in plants and lung function in animals.
• Chapter 22 addresses particulate pollutants.

• Asbestos is a natural mineral that occurs in two or more different types.
• Chrysolite-type asbestos accounts for about 95% of the usage in the United States. Usage is for pipe insulation, brake lining, and fire-retardant applications. Under normal conditions, this type of asbestos has not been found to be especially hazardous to human health.
• Crocidolite-type asbestos is less widely used but is a significant health risk. Lung damage and certain cancers have been attributed to exposure.
• Because most exposure is to chrysolite asbestos instead of crocidolite asbestos the health risks of asbestos exposure may be overstated, even though considerable time, effort, and expense have been devoted to asbestos removal from schools and other public buildings.

• The human health risk associated with exposure to electromagnetic fields is difficult to measure and is controversial.
• Some epidemiological studies suggest there is a link between long-term exposure to electromagnetic fields and certain cancers, but the studies are not definitive.

• Noise is unwanted sound.
• Sound waves moving through the atmosphere, are measured in units of decibels (dB), a logarithmic scale (Table 14.1).
• Noise at relatively low decibel levels may constitute an annoyance, thus stress and stress-related health problems may arise.
• Noise at higher decibel levels can cause physiological damage to ear structures resulting is partial or total hearing loss.
• Prolonged exposure to high levels of noise or short-term exposure to very high levels can permanently damage hearing.

• The voluntary intake of tobacco products, alcohol, and the illegal use or misuse of drugs present a much greater health threat to more people than exposure to any other toxin.
• An estimated 30% of all cancers and 80% of all lung cancers in the U.S. are linked to smoking tobacco.
• Second-hand smoke is now recognized as a serious health threat to non-smokers.
• Many people in the U.S. have heeded the cautions against smoking and have quit or never started smoking. Others, have not paid attention to the warnings and are continuing to risk their current and future health status by taking up smoking and other uses of tobacco.
• About 70% of all people in the U.S. drink alcohol; in moderation for most, but abused by others. Alcohol abuse is physically debilitating and is responsible for a great deal of domestic and societal ills.
• Illegal drug use continues to plague society. The addictive qualities of some drugs and detrimental health and societal effects of drug use are well documented. Illegal drug use in the U.S. supports a massive black-market trade that extends from many segments of our society to far beyond our national borders.

• As discussed earlier, pollutant effects on individual humans are variable dependent upon the individuals' physical characteristics, intensity or duration of exposure, and pollutant type.
• Many toxins target specific organs or organ systems (Figure 14.8). Others have more widespread effects. A general decline in health associated with a specific toxin may precipitate illness or disease not directly attributable to the toxin.
• Most toxicological studies have focused on human health problems. Most of the state and federal pollutant water and air quality standards are based on pollutant threshold levels from these human health studies.
• The responses of wildlife to pollutant exposure may be similar to some human responses, but because wildlife interrelates with the environment differently than humans, it is erroneous to assume the pollutant threshold levels that are suitable for humans are applicable to wildlife (Table 14.2). For example, low-level concentrations of pollutants in streams may pose no risk to humans wading or swimming in streams, but to filter feeding freshwater mussels in the streambed, low-level concentrations may be lethal.

• The health effects of chemicals, be they toxic or nontoxic, depends upon dosage (amount of exposure).
• Chemicals have a range of health effects and the effects vary among individuals.
• The health effects of chemical dosage can be predicted and depicted graphically as dose-response curves (Figures 14.9, 14.10, and 14.11).
• The general dose-response curve indicates that large dosages of a chemical may be toxic, small dosages may have no effect, but intermediate dosages may have beneficial effects (e.g., trace elements needed in our diet).
• A toxic dose-response curve can be graphed for environmental pollutants (Figure 14.11). Because the health effects of exposure to toxic chemicals vary within a population, a standard means of expressing the toxicity of a chemical is necessary.
• Toxicity of a particular chemical is usually reported as LD-50 and/or ED-50.
• Test for chemical toxicity are conducted on non-human subjects, thus the effects of a particular dosage in humans may not be the same.
• LD-50 (lethal dose- 50%) is the dosage at which 50% of a test population dies.
• ED-50 (effective dose - 50%) is the dosage at which 50% of the test population shows an effect.
• For many chemicals, the threshold concentration at which exposure causes health problems is not known.
• Ideally, if there are no known health benefits to exposure at low concentrations and exposure at high concentrations is detrimental, the best option is to avoid exposure all together. This becomes problematic, for example, because industrial and domestic waste treatment technologies do not adequately remove all pollutants from discharged material. For many chemicals, using more sophisticated waste treatment technologies are not cost effective.

• Acute effects occur immediately or soon after exposure to pollutants. Often the exposure is well in excess of threshold levels. Some, but not all, acute effects are reversible.
• Chronic effects result from long-term exposure to low concentrations of pollutants. The source of chronic effects may be difficult to determine and the effects may not be manifest until later in an organism's life span. Many chronic effects are non-reversible.

• Organisms nearest the source of pollutant contamination have the most severe and acute effects. Organisms far from the source are exposed to pollutants in diluted concentrations and would be more likely to experience chronic effects.
• The tolerance of organisms varies along ecological gradients.
• Tolerance is an indication of the ability of an organism to resist or withstand exposure.
• Tolerance is dependent upon:
• behavior (i.e., learning to avoid exposure to pollutants),
• physiology (i.e., physiological adjustment to a pollutant that increases tolerance; this includes detoxification of pollutants via metabolic process),
• genetic adaptability (i.e., the survival of more resistant individuals in a population thus altering the gene pool; pesticide resistance in insects is an example).
• Aquatic invertebrate species are often used as an index of environmental quality in streams. The presence and abundances of invertebrate species changes along an ecological gradient from more severely polluted sites, to less severely polluted sites.

• Assessing risk is important if strategies are to be developed that will minimize human and environmental health problems that stem from exposure to toxins or other types of hazards.
• Risk assessment involves four steps:
• Identification of the hazard (i.e., determining the effects of a particular hazard),
• Dose-response assessment (i.e., determining the dosage at which health problems arise),
• Exposure assessment (i.e., determining the intensity, duration, or frequency of exposure),
• Risk characterization (i.e., determining the magnitude of the problem for human and environmental health).
• By evaluating these aspects of risk assessment, risk management decisions can be made that integrate technical, legal, political, social, and economic factors.

Ecology In Your Backyard

• What pollutants do you think present the greatest risk to your health or to ecosystems in your area? Remember, recognition of a potential threat is an important first step. Potential sources to consider include:
• Are you exposed to indoor air pollutants, especially tobacco smoke?
• Are you exposed to noise pollution at concerts?
• Are urban air advisories issued for your area? (Check the air quality index published in local newspapers to find out what pollutant groups present the greatest risk.)
• What residual pesticides might be found in the foods you eat?
• In rural areas, are you ever exposed to drifting pesticides from crop dusting?
• Have health advisories been issued against consuming fish from local lakes, rivers, and streams?
• Are there any toxic waste sites in your area? What is the status of discharge or cleanup?
• You might find answers to some of these questions by searching web sites maintained by government agencies and independent organizations that provide information about pollutants and pollutant risks for locations throughout the United States.
• Check out the "right to know" databases and others listed in the Ecolinks section to find out which pollutants are a health or environmental threat in your watershed, air shed, or locality.
• Please respond to these questions or send your thoughtful examples and comments to:

Hardcopy Links In The Library

• Briggs, S.A. and the Rachel Carson Council. 1992. Basic Guide to Pesticides: Their Characteristics and Hazards. Taylor and Francis, Washington.
• Colborn, T. D. Dumanoski, and J. P. Meyers. 1996. Our Stolen Future. Penguin Group, New York. 306 pp.
• Klassen, C.D, M.O. Amdur, and J.O Doull. 1986. Toxicology: The Basic Science of Poisons. Macmillan Publishing Company, New York.
• Hallenbeck, W.H. and K.M. Cunningham Burns. 1985. Pesticides and Human Health. Spring-Verlag, New York.
• Rodricks, J. V. 1992. Calculated Rick: The Toxicity and Human Health Risks of Chemicals in Our Environment. Cambridge University Press, New York. 256 pp.
• Worthington, C.R. 1991. The Pesticide Manual: A World Compendium, 9th ed. British Crop Protection Council.

Ecolinks On The Web

• http://www.epa.gov/internet/oppts/ EPA Office of Prevention, Pesticides and Toxic Substances

• http://www.epa.gov/epahome/r2k.htm EPA Right to Know website. Find out about toxic exposure risks to U.S. citizens.

• http://www.rtk.net/www/rtknet/webpage/databas3.html The Right To Know Net is a database maintained by non-governmental, nonprofit organizations that can provide you with information concerning exposure to pollutants.

• http://water.wr.usgs.gov/pnsp/ USGS - NAWQA Program, pesticide usage in the USA by county.

• http://fs1dgadrv.er.usgs.gov/publications/acfpest/acfpest.html Examine the chart comparing the risks of drinking water containing pesticides.

• http://sis.nlm.nih.gov/tehip1.htm National Library of Medicine, Toxicology and Environmental Health Program website.

• Note: If any of these links are not working, please see if alternative links are available at the Ecolink Update Site.

Ecotest Online

1. The level or concentration at which a pollutant causes health problems is called the pollutant ______.

a. dosage

b. threshold

c. risk point

d. toxicity point

2. Pollutant sources such as runoff from agricultural and urban areas, and automobile exhaust are examples of ______ sources.

a. mobile

b. point

c. detectable

d. area

3. A measure of the total amount of heavy metals in an organism is its _______.

a. toxic load

b. body burden

c. chelation total

d. accumulation index

4. ______ is the name of a group of chlorinated hydrocarbons found in herbicides (like Agent Orange) and in wasterwater from pulp and paper mills. The community of Times Beach, Missouri was severely contaminated by this synthetic toxin.

a. DDT

b. PCB

c. Dioxin

d. Mirex

5. Exposure to _____-type asbestos is especially hazardous to human health; other types of asbestos are less problematic.

a. nonfiberous

b. crocidolite

c. chrysolite

d. silicofibric

6. An estimated ___ % of all lung cancers in the United States can be attributed to smoking tobacco.

a. 80

b. 75

c. 50

d. 20

7. LD-50 is:

a. the point at which a pollutant is diluted to 50% of its initial concentration

b. the point at which a pollutant is detoxified by 50% of its initial concentration

c. the point at which 50% of a test population dies after exposure to a pollutant

d. the point at which 50% of sampled natural population test positive for a toxin

8. The high concentration of toxins in the tissue of animals that feed high on the food chain is a consequence of ________.

a. toxification

b. high ED-50

c. low tolerance

d. biomagnification

9. Long-term exposure to low level concentrations of pollutants typically causes _______ health effects.

a. carcinogenic

b. nonadaptive

c. chronic

d. low-dosage

10. Three of the four steps involved in risk assessment are listed below; which is not one of those steps?

a. identification of the hazard

b. dose-response assessment

c. exposure assessment

d. remediation

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