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SUSTAINING ENVIRONMENTAL QUALITY
Chapter 17
Environmental Hazards and Human Health
Chapter Outline
CORE CASE STUDY Mercury’s Toxic Effects
17-1 What Major Health Hazards Do We Face?
17-2 What Types of Biological Hazards Do We Face?
CASE STUDY The Growing Global Threat from Tuberculosis
SCIENCE FOCUS Genetic Resistance to Antibiotics Is Increasing
Individuals matter Hayat Sindi: Science Entrepreneur and National Geographic Emerging Explorer
CASE STUDY The Global HIV/AIDS Epidemic
CASE STUDY Malaria—The Spread of a Deadly Parasite
SCIENCE FOCUS Ecological Medicine: Tracking How Humans Can Get Infectious Diseases from Other
Animals
17-3 What Types of Chemical Hazards Do We Face?
CASE STUDY PCBs Are Everywhere—A Legacy from the Past
SCIENCE FOCUS The Controversy Over BPA
17-4 How Can We Evaluate Chemical Hazards?
CASE STUDY Protecting Children from Toxic Chemicals
CASE STUDY Pollution Prevention Pays
17-5 How Do We Perceive Risks and How Can We Avoid the Worst of Them?
CASE STUDY Death from Smoking
TYING IT ALL TOGETHER Mercury’s Toxic Effects and Sustainability
Key Concepts
17-1 We face health hazards from biological, chemical, physical, and cultural factors, and from the
lifestyle choices we make.
17-2 The most serious biological hazards we face are infectious diseases such as flu, AIDS, tuberculosis,
diarrheal diseases, and malaria.
17-3 There is growing concern about chemicals in the environment that can cause cancers and birth
defects, and disrupt the human immune, nervous, and endocrine systems.
17-4A Scientists use live laboratory animals, case reports of poisonings, and epidemiological studies to
estimate the toxicity of chemicals, but these methods have limitations.
17-4B Many health scientists call for much greater emphasis on pollution prevention to reduce our
exposure to potentially harmful chemicals.
17-5 We can reduce the major risks we face by becoming informed, thinking critically about risks, and
making careful choices.
Key Questions and Case Studies
CORE CASE STUDY: Mercury’s toxic effects. Mercury and its compounds are all toxic. Natural
sources account for about one-third of the mercury reaching the atmosphere each year. Mercury is an
element and cannot be broken down, therefore it is an indestructible pollutant that accumulates in the soil,
water, and tissues of living organisms. Humans are exposed to mercury by eating fish or shellfish
contaminated with methylmercury. We also inhale vaporized mercury or mercury salts.
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17-1 What Major Health Hazards Do We Face?
A. A risk is a measure of your likelihood of suffering harm from a hazard. Hazards may cause
injury, disease, economic loss, or environmental damage. Risk assessment is projected as a
probability: a mathematical statement about how likely it is that harm will result from a hazard. It
gives the estimate of an event’s actually happening. Risk management involves deciding whether
or how to reduce a particular risk to a certain level and at what cost.
B. There are five major types of hazards.
1. Biological hazards come from more than 1400 pathogens (bacteria, viruses, parasites,
protozoa, and fungi) that can infect humans.
2. Chemical hazards from harmful chemicals in air, water, soil and food.
3. Physical hazards such as fire, earthquake, volcanic eruption, flood, tornado, and hurricane.
4. Cultural hazards such as smoking, unsafe working conditions, poor diet, drugs, drinking,
driving, criminal assault, unsafe sex, and poverty.
5. Lifestyle hazards such as smoking, drinking, etc.
17-2 What Types of Biological Hazards Do We Face?
A. Diseases not caused by living organisms do not spread from one person to another, while those
caused by living organisms such as bacteria and viruses can spread from person to person.
1. Non-transmissible diseases tend to develop slowly, have multiple causes, are not caused by
living organisms, and do not spread from one person to another. Examples are cancer,
diabetes, asthma, malnutrition, and blood vessel disorders.
2. Transmissible disease is caused by a living organism and can spread from one to another.
Infectious agents/pathogens are spread in air, water, food, body fluids, by some insects, and by
vectors.
CASE STUDY: The growing threat from tuberculosis. Tuberculosis has been spreading rapidly
since 1990, striking about 9 million people per year. The reasons for the spread include inadequate
screening, the development of new strains of TB and population growth.
SCIENCE FOCUS: Genetic resistance to antibiotics is increasing. Rapidly producing infectious
bacteria are becoming genetically resistant to widely used antibiotics. The bacteria can transfer this
resistance to nonresistant bacteria. Resistance to antibiotics has increased because of antibiotics
being over-prescribed, added to household products (e.g., soaps) and used in livestock and dairy
animals to control disease and promote growth.
B. Viruses evolve quickly and are not affected by antibiotics. The influenza or flu virus is the
biggest killer. The second biggest killer is HIV, transmitted in a variety of ways.
C. Emergent diseases are newly discovered or have been absent from human populations for at least
20 years.
SCIENCE FOCUS: Ecological medicine: tracking how humans can get infectious diseases
from other animals. Infectious diseases that are transmitted from wild and domesticated animals to
humans include avian flu, SARS, West Nile virus, Hantavirus, and Lyme disease. The clearing and
fragmentation of forests has played a major role in exposing humans to new types of infectious
disease. Understanding the connections between human activities and ecosystem functioning is a key
to preventing or slowing the spread of infectious organisms from wild and domesticated animals to
humans.
CASE STUDY: The global HIV/AIDS epidemic. The global spread of AIDS is a major health
threat. It is transmitted sexually, by exposure to infected blood, and from mother to child. In 2008,
about 33 million people worldwide were living with HIV. Since 2006 the number infected has
begun to stabilize everywhere except sub-Saharan Africa.
CASE STUDY: Malaria - the spread of a deadly parasite. Malaria kills about 2,700 people per
day and has probably killed more people than all of the wars ever fought. Malaria is caused by a
parasite that is spread by the bites of certain mosquitoes. It is caused by four species of protozoan
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parasites in the genus Plasmodium and the parasite circulates from mosquito to human and back to
mosquito.
D. There are a number of ways to reduce the incidence of infectious diseases if the world is willing
to provide the necessary funds and assistance. Global death rate dropped by about 2/3rds
between 1970 and 2000. The number of children immunized between 1971 and 2006 went from
10% to 90% and saved an estimated 10 million lives a year. Only about 10% of global medical
research and development money is spent on preventing infectious diseases in developing
countries, even though more people worldwide suffer and die from these diseases than all other
diseases combined.
17-3 What Types of Chemical Hazards Do We Face?
A. A toxic chemical can cause temporary or permanent harm or death to humans or animals.
B. There are three major types of potentially toxic agents.
1. Mutagens are chemicals or ionizing radiation that cause or increase the frequency of random
mutations in the DNA molecules. It is generally accepted that there is no safe threshold for
exposure to harmful mutagens.
2. Teratogens are chemicals that cause harm or birth defects to a fetus or embryo. Alcohol and
thalidomide are examples of teratogens.
3. Carcinogens are chemicals or ionizing radiation that cause or promote cancer.
CASE STUDY: PCBs are everywhere - a legacy from the past. PCBs are a class of 200+
chlorine containing compounds that are very stable and non-flammable. Congress banned domestic
production in 1977 after they were shown to cause cancer. For decades they were released into air,
water and soil. As a result, they are now found almost everywhere.
C. Long-term exposure to some chemicals at low doses may disrupt the body’s immune, nervous,
and endocrine systems.
1. Some chemicals weaken the human immune system.
2. Some chemicals are neurotoxins, causing harm to the nervous system.
SCIENCE FOCUS: The controversy over BPA. BPA is an estrogen mimic that serves as a
hardening agent in certain plastics. A CDC study indicated that 93% of Americans over age 6 had
trace levels of BPA in their urine. BPA can leach from plastics into food. There are some conflicting
research findings.
D. Certain molecules can disrupt the endocrine system. These are called hormonally active agents
(HAAs).
1. Hormone blockers prevent natural hormones from attaching to their receptors.
17-4 How Can We Evaluate Chemical Hazards?
A. Factors determining the harm caused by exposure to a chemical include the amount of exposure
(dose), the frequency of exposure, the person who is exposed, the effectiveness of the body’s
detoxification systems, and the exposed person’s genetic makeup. Other factors can affect the
harm caused by a substance including solubility, persistence, bioaccumulation, biomagnification,
and chemical interactions.
1. Acute effects are immediate.
2. Chronic effects are permanent.
CASE STUDY: Protecting children from toxic chemicals. Children can be particularly sensitive
to toxic chemicals because they breathe more air and consume more water and food per unit body
weight, they put things in their mouths, and their immune systems are less well-developed.
B. Toxicity is usually measured using laboratory animals, but increasingly with computer
simulations or cell cultures.
C. There are two types of dose-response curve. With the non-threshold dose-response model, any
dosage causes harm that increases with the dosage. With the threshold dose-response model, a
certain level must be reached before harmful effects occur.
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D. Other ways to estimate the harmful effects of chemicals are case studies and epidemiological
studies.
E. It is difficult to assess the risk associated with trace amounts of chemicals found in our
environment.
F. Only 10% of 100,000 registered chemicals have been screened for toxicity.
G. Pollution prevention is a strategy for implementing the precautionary principle.
CASE STUDY: Pollution prevention pays. Pollution Prevention Pays is a program run by 3M, a
leading manufacturing company. It redesigned its equipment and processes, used fewer hazardous
raw materials, identified its toxic chemical outputs, and began to recycle and sell many of those
outputs as raw materials to other companies. This program has been successful largely because
anyone at the 3M company can participate.
17-5 How Do We Perceive Risks and How Can We Avoid the Worst of Them?
A. There are scientific ways to evaluate and compare risk, to decide how much risk is acceptable,
and to find affordable ways to reduce risk. Risk assessment involves identifying hazards and
evaluating their associated risks.
1. The greatest risks are poverty and lifestyle choices.
CASE STUDY: Death from smoking. Cigarette smoking is the most preventable major cause of
premature death. Smoking kills about 442,000 Americans per year. Some nations are beginning to
enact smoking bans in certain areas, and in 2009 the FDA was given the power to classify and
regulate tobacco as a drug.
B. Estimation of risk for complex technology is difficult due to unpredictability of human behavior,
human error, and sabotage.
C. Most individuals are poor at evaluating the relative risks they face. Five factors can cloud this
judgment: fear, degree of control, whether a risk is catastrophic, optimism bias, and instant
gratification.
1. There are techniques to evaluate and reduce risk. These include comparing risks, determining
how much risk you are willing to accept, determining the actual risk involved, and
concentrating on making important lifestyle choices.
Teaching Tips:
Large Lecture Classes:
Start lecture with a recent event. The recent recall of plastic bottles due to Bisphenol A exposure is a good
example (http://www.fda.gov/oc/opacom/hottopics/bpa.html). Ask students how many of them have used
bottles with Bisphenol A and then ask them to gauge the risk that may have incurred from that use. Use
clickers if possible and leave open the option of “there is no way to evaluate the risk”. Start class with a
discussion of why it is so difficult to clearly identify the risk from exposure to chemicals.
Small Lecture Classes:
Begin class by breaking students into small groups. Give each group a card with the outlines of a human
health issue described on the card (see below for suggestions). Tell each group they have 10 minutes to
make a recommendation of what to do about the health problem. When you are done, compare the group
responses to governmental responses to the same problems. In all likelihood, the responses from class will
be more drastic than the actual governmental action and this is a good point to begin discussion of
environmental health issues. Two examples:
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A) A disease is found in a form of meat that appears to be passed through sick animals and which can
be passed on to humans. The disease can be identified in meat products once they are produced using
a molecular test. Contrast student responses to this example with responses to the Mad Cow Problems
in the U.S.
B) A chemical is found in plastic bottles that may disrupt the endocrine system. In tests of food and
liquids in these bottles, this chemical is present in detectable levels. Contrast student response to U.S.
(and Canadian) responses to recent information about Bisphenol A.
Key Terms
carcinogens
dose
dose response curve
emergent disease
infectious disease
mutagens
nontransmissible disease
pathogen
response
risk
risk analysis
risk assessment
risk management
teratogens
toxic chemical
toxicity
toxicology
transmissible disease
Term Paper Research Topics
1.
Environmental risks: brown lung disease and the textile industry; black lung disease and the coalmining industry; asbestos as a carcinogen; exposure to toxic chemicals; earthquakes and volcanoes.
2.
Lifestyle risks: health effects from secondary smoke; the rise in the lung cancer rate for women.
3.
Transmissible disease risks: history of infectious disease control; vaccines and immunology; how
smallpox was eradicated; waterborne diseases of the developing countries; the history of malaria;
schistosomiasis; cholera; tuberculosis; AIDS.
4.
When do smokers' rights infringe on nonsmokers' rights?
5.
Is there equity in exposure to hazardous chemicals? Use coal-fired power plants as an example.
6.
Should utility regulators assume a linear dose-response curve in evaluating levels of exposure of the
public to different hazardous chemicals?
7.
How does the global pharmaceutical industry invest their research dollars and how does this compare
to global health needs?
8.
What are the major bio-terror threats to the U.S.?
9.
What are primary threats to environmental health in the U.S. and how could they be addressed?
10. What is the human health risk of air pollution?
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Discussion Topics
1.
What is the value of organic food (in terms of contaminants)? Is there a risk with conventional food?
2.
What kinds of risks do you take every day?
3.
What kinds of risks from the natural environment occur in your area?
4.
What kinds of risks are you exposed to each day over which you have no control?
5.
Do you feel that societal risks should be distributed equally among all citizens?
6.
Should people who choose unhealthy lifestyles be covered by national health insurance?
7.
Does the government do enough to regulate industry and protect public health? Why or why not?
8.
How far should the precautionary principle go in terms of new chemical introductions?
9.
Do you buy organic food? Why or why not? How would you weigh cost versus health
considerations?
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