Chapter 9: Atmospheric Pollution
In this chapter, we’ll review two units (Unit 7 and Unit 8) covered on the AP Environmental Science Exam, which AP calls Atmospheric Pollution and Aquatic and Terrestrial Pollution. Obviously, these two topics are interrelated. According to the College Board, about 7–10% of the test is based directly on each of these topics, so that’s a total of about 14–20% of test material devoted to the ideas covered in this chapter. If you are unfamiliar with a topic presented here, consult your textbook for more in-depth information.
We’ll begin the chapter with a discussion of what it means for something to be toxic and a review of how toxicity impacts health, along with some related concepts, including common pathogens.
We’ll move on to discuss toxins in air pollution and then review the major aspects of thermal pollution, water pollution, and the problems that arise as a result of solid waste, finally mentioning hazardous waste and noise pollution. As we go through each type of pollution, we’ll also discuss the impact of pollution on the environment and human health, as well as some economic impacts. Let’s begin!
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TOXICITY AND HEALTH
One way to think about health is that each organism has a range of tolerance for almost any substance. For each substance it might come into contact with, an organism has an optimum range, inside of which it can maintain homeostasis. Outside of this range, the organism may experience physiological stress, limited growth, reduced reproduction, and in extreme cases, death.
A toxin is any substance that, when inhaled, ingested, or absorbed at sufficient dosages, damages a living organism, and the toxicity of a toxin is the degree to which it is biologically harmful. Almost any substance that is inhaled, ingested, or absorbed by a living organism can be harmful when it is present in large enough quantities—even water!
Substances are usually tested for toxicity using a dose-response analysis. In a dose-response analysis, organisms are exposed to a toxin at different concentrations, and the dosage that causes the death of the organism is recorded. The information from a set of organisms is graphed, and the resulting curve is referred to as a dose-response curve. The dosage of toxin it takes to kill 50 percent of the test animals is termed LD50, and this value can be determined from the graph. A high LD50 indicates that a substance has a low toxicity; a low one indicates high toxicity. A poison is any substance that has an LD50 of 50 mg or less per kg of body weight \n
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The government regulates certain types of toxins in air, water, and food. The Food and Drug Administration (FDA) is the body that regulates food and related products; it was empowered to do so by the Federal Food, Drug, and Cosmetic Act of 1938. One important part of this act is the Delaney Clause (part of the Food Additives Amendment of 1958), which specifically bans any food additives found to cause cancer in humans or in animal testing.
When the Delaney Clause was included, no one thought it would have a very broad application, but as scientists have identified more and more cancer-causing substances, its relevance has grown. The Delaney Clause is on the list of legislations required for the exam, so make sure to memorize it!
Two more terms you should know for the test are acute effect and chronic effect.
An acute effect is an effect caused by a short exposure to a high level of toxin; a snakebite, for example, causes an acute effect.
A chronic effect is what results from long-term exposure to low levels of toxin; an example of this would be long-term exposure to lead paint in a house. An infection is the result of a pathogen invading the body, and disease occurs when the infection causes a change in the state of health. For example, HIV, the virus that causes the disease AIDS, infects the body and typically has a long residence time. When it causes a change in a person’s state of health, it has morphed into a disease called AIDS. \n
Pathogens can attack directly or via a carrier organism (called a vector).
- One example of a pathogen that relies on a vector is the bacteria that causes Rocky Mountain spotted fever. It lives in the bodies of ticks, and when ticks bite humans, the ticks inject the bacteria, which causes the disease.
Pathogens, being single-celled organisms, are usually able to adapt quickly to take advantage of new opportunities to infect and spread through human populations. Poverty-stricken, low-income areas often lack sanitary waste disposal and have contaminated drinking water supplies, leading to havens and opportunities for the spread of infectious diseases. However, specific pathogens can occur in many environments, regardless of how sanitary conditions may appear to be. The AP exam may test your knowledge of specific pathogens and infectious diseases: here are the ones it specifically tests.
Plague is a disease carried by organisms infected with the plague bacteria. It is transferred to humans via the bite of an infected organism (vector) or through contact with contaminated fluids or tissues. It has distinct forms (bubonic, septicemic, and pneumonic), but all are characterized by fever, chills, headaches, and nausea.
Tuberculosis is a bacterial infection that typically attacks the lungs. It is spread by breathing in the bacteria from the bodily fluids of an infected person. Its symptoms include chronic cough with bloody mucus, fever, night sweats, and weight loss.
Cholera is a bacterial disease that is contracted from infected water. Its main symptom is large amounts of watery diarrhea, which can lead to severe dehydration. Poverty, poor sanitation, and lack of clean drinking water are risk factors for the disease.
Dysentery is a type of gastroenteritis (inflammation of the stomach and small intestine) that results in diarrhea with blood, plus often fever and abdominal pain. It has multiple possible causes, including bacteria, amoebas, chemicals, and parasitic worms. The main risk factor for dysentery is contamination of food and water, usually from untreated sewage in streams and rivers.
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Malaria is a parasitic disease caused by bites from infected mosquitoes. It is widespread in the tropical and subtropical regions of the globe, especially in sub-Saharan Africa. It causes fever, tiredness, vomiting, headaches, and, in severe cases, yellowed skin, seizures, coma, and even death. There have been strident efforts worldwide to eradicate this disease, but results have been much more successful in some places than in others.
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West Nile virus is transmitted to humans via bites from infected mosquitoes. It is closely related to the viruses microencephaly and other brain malformations when transferred to a fetus, and in adults it has been linked to Guillain–Barré syndrome, a rapid-onset muscle weakness.
Severe acute respiratory syndrome (SARS) is a viral respiratory disease caused by severe acute respiratory syndrome coronavirus (SARS-CoV-1). There was an outbreak of this disease in 2002–2004. The respiratory symptoms were a form of pneumonia. Another coronavirus, MERS-coronavirus (MERS-CoV) caused an outbreak of Middle East respiratory syndrome (MERS), another viral respiratory illness, in 2012–2013.
In 2019–2021, a much more severe outbreak of the related virus strain severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) caused the COVID-19 pandemic. These viruses tend to move from animals to humans and are transferred by inhaling or touching infected fluids.
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\n If a person will become ill after exposure to a toxin or pathogen this is called a risk. Many environmental, medical, and public health decisions are based on potential risk. Calculating risk is referred to as risk assessment, and risk management means using strategies to reduce the amount of risk.
The U.S. Department of Public Health and Public Services is an organization that makes use of risk assessment and management. For example, the department decides who can receive the flu shot each year. If the risk of getting the flu is high for a particular year, most of the population is encouraged to get the shot; however, if the risk seems small or the predicted flu strains are mild, only older people and the immunocompromised are advised to get the flu shot.
AIR POLLUTION
Substances that are considered contributors to air pollution have two sources: they can be natural releases from the environment or they can be created by humans. The effects of air pollution on humans can range in severity from lethal to simply aggravating. Some natural pollutants include pollen, dust particles, mold spores, forest fire smoke, and volcanic gases.
One of the more recently described air pollutants from nature is produced by dinoflagellates, which, you might recall from Chapter 4, are the organisms that cause red tide. The toxins that are produced by these algae are caught in sea spray, in which they can be aerosolized and inhaled by humans, causing respiratory distress.
Although you may think that human-caused pollution is a relatively new phenomenon, people have added pollutants to the air throughout the history of humankind. Early humans’ fire created pollutants, and the Romans’ lead smelting resulted in air pollution that drifted thousands of miles from the source—and has even been discovered trapped in the ice of Greenland!
It is true, however, that the large-scale production of pollutants began with the Industrial Revolution, and this is especially true of air pollution. The beginning of the Industrial Revolution marked the entrance of pollutants from fossil fuel into the atmosphere, for example, which has been environmentally disastrous.
Let’s go over some terms used to describe pollution before we get into more specific details.
Primary pollutants are those that are released directly into the lower atmosphere (remember the troposphere?) and are toxic; one example of a primary pollutant is carbon monoxide (CO).
Secondary pollutants are those that are formed by the combination of primary pollutants in the atmosphere; an example of a secondary pollutant is acid rain. Acid rain is produced from the combination of sulfur oxides (such as SO2 and SO3) and water vapor.