Environmental Science - 12e - Chapter 14.pdf - po ang - Januszek66

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Environmental Hazards

and Human Health

The Global HIV/AIDS Epidemic

CORE CASE STUDY

The global spread of acquired immune deficiency syndrome

(AIDS), caused by infection with the human immunodeficiency

virus (HIV), is a serious and rapidly growing health threat. The

virus itself is not deadly, but it cripples the immune system and

leaves the body susceptible to infections such as tuberculosis (TB)

and rare forms of cancer such as Kaposi’s sarcoma (Figure 14-1).

The virus is transmitted from one person to another through

unsafe sex, sharing of needles by drug users, infected mothers

who pass the virus on to their offspring before or during birth,

and exposure to infected blood.

Since the HIV virus was identified in 1981, this viral infection

has spread exponentially around the globe. According to the

World Health Organization (WHO), in 2006 about 37 million

people worldwide (1.1 million in the United States) were infected

with HIV. Almost two-thirds of them were in African countries lo-

cated south of the Sahara Desert (sub-Saharan Africa). The

Caribbean is the second most affected region.

In 2006 alone, about 4.3 million people (42,500 in the

United States) became infected with HIV—an average of 11,800

new cases per day—half of them between the ages of 15 and

24. Within 7–10 years, at least half of all HIV-infected people will

develop AIDS. This long incubation period means that infected

people often spread the virus for several years without knowing

they are infected.

There is no vaccine to prevent HIV and no cure for AIDS. If

you get AIDS, you will almost certainly die from it. Drugs help

some infected people live longer, but 90% of those suffering

from AIDS cannot afford to use these drugs.

Between 1981 and 2006, more than 37 million people

(531,000 in the United States) died of AIDS-related diseases.

Each year, AIDS claims about 3 million more lives (16,000 in the

United States).

AIDS has reduced the life expectancy of the 750 million peo-

ple living in sub-Saharan Africa from 62 to 47 years—40 years in

the seven countries most severely affected by AIDS. The prema-

ture deaths of teachers, health-care workers, soldiers, and other

young productive adults in such countries leads to diminished

education and health care, decreased food production and eco-

nomic development, and disintegrating families.

This means that countries like Botswana and Zimbabwe

will each lose half of their adult population within a decade.

Such death rates drastically alter a country’s age structure (Fig-

ure 14-2). AIDS has also left more than 15 million children or-

phaned—roughly equal to the number of children under age 5

in the United States. Many of them are forced into child labor or

Figure 14-1 Lesions that are a

sign of Kaposi’s sarcoma, a rare

form of cancer common among

AIDS patients.

100+

95–99

90–94

85–89

80–84

75–79

70–74

65–69

60–64

55–59

50–54

45–49

40–44

35–39

30–34

25–29

20–24

15–19

10–14

5–9

0–4

Males

Females

120

100 80 60

20 40

80 100

120

Population (thousands)

With AIDS

Without AIDS

Figure 14-2 Global outlook: Worldwide, AIDS is the leading cause

of death for people of ages 15–49. This loss of productive working

adults can affect the age structure of a population. In Botswana, more

than 24% of this age group is infected with HIV. This figure shows the

projected age structure of Botswana’s population in 2020 with and with-

out AIDS. Question: How might this affect Botswana’s economic devel-

opment? (Data from the U.S. Census Bureau)

the sex trade. Between 2006 and 2030, the WHO projects 117

million more deaths from AIDS and a death toll reaching as high

as 5 million a year—an average of about 13,700 largely prevent-

able deaths per hour.

In this chapter, we will look at connections between environ-

mental hazards and human health and at what we can do to

reduce the deadly global pandemic of AIDS and other environ-

mental health threats.

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Key Questions and Concepts

14-1 What major health hazards do we face?

CONCEPT 14-1 People face health hazards from biological,

chemical, physical, and cultural factors and from the choices they

make in their lifestyles.

14-4 How can we evaluate chemical hazards?

CONCEPT 14-4A Any synthetic or natural chemical can be

harmful if ingested in a large enough quantity.

CONCEPT 14-4B Many health scientists call for much greater

emphasis on pollution prevention to reduce our exposure to

potentially harmful chemicals.

14-2 What types of biological hazards do we face?

CONCEPT 14-2 In terms of death rates, the most serious

infectious diseases are flu, AIDS, diarrhea, and malaria, with most

of these deaths occurring in developing countries.

14-5 How do we perceive risks and how can we

avoid the worst of them?

CONCEPT 14-5 We can reduce the major risks we face by

becoming informed, thinking critically about risks, and making

careful choices.

14-3 What types of chemical hazards do we face?

CONCEPT 14-3 There is growing concern about chemicals that

can cause cancer and disrupt the human immune, nervous, and

endocrine systems.

Note: Supplements 7, 12, and 17 can be used with this chapter.

The dose makes the poison.

PARACELSUS, 1540

14-1 What Major Health Hazards Do We Face?

CONCEPT 14-1 People face health hazards from biological, chemical, physical, and cultural

factors and from the choices they make in their lifestyles.

Risks Are Usually Expressed

As Probabilities

A risk is the probability of suffering harm from a hazard

that can cause injury, disease, death, economic loss, or

environmental damage. It is usually expressed in terms

of probability —a mathematical statement about how

likely it is that harm will be suffered from a hazard. Sci-

entists often state probability in terms such as “The life-

time probability of developing lung cancer from smok-

ing one pack of cigarettes per day is 1 in 250.” This

means that 1 of every 250 people who smoke a pack of

cigarettes every day will likely develop lung cancer over

a typical lifetime (usually considered to be 70 years).

It is important to distinguish between possibility and

probability. When we say that it is possible that a smoker

can get lung cancer, we are saying that this event could

happen. Probability gives us an estimate of the likeli-

hood of such an event.

Risk assessment is the scientific process of using

statistical methods to estimate how much harm a par-

ticular hazard can cause to human health or to the en-

vironment. It is a way to estimate the probability of a

risk, compare it with the probability of other risks, and

establish priorities for avoiding or managing risks. Risk

management involves deciding whether or how to

reduce a particular risk to a certain level and at what

cost. Figure 14-3 summarizes how risks are assessed

and managed.

A major problem is that most people are not good

at understanding and comparing risks. Because of sen-

Risk Assessment

Hazard identification

What is the hazard?

Risk Management

Comparative risk analysis

How does it compare

with other risks?

Risk reduction

How much should

it be reduced?

Probability of risk

How likely is the

event?

Risk reduction strategy

How will the risk

be reduced?

Consequences of risk

What is the likely

damage?

Financial commitment

How much money

should be spent?

Figure 14-3 Risk assessment and risk management. Question:

When was the last time you applied this process in your own daily

living? Explain.

324

Links:

refers to the Core Case Study.

refers to the book’s sustainability theme.

indicates links to key concepts in earlier chapters.

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sational news coverage about the latest scare, many

people worry about the highly unlikely possibility of

minor risks and ignore the significant probability of

harm from major risks. In other words, many people

suffer from possibility anxiety over minor risks and proba-

bility neglect and denial over serious risks.

For example, some Americans worry about getting

avian flu, which by mid-2007 had killed no one in the

United States, but they do not get vaccinated for the

common flu, which contributes to the deaths of about

36,000 Americans each year. Thus, educating people

and members of the news media about the meaning of

risk assessments and the ability to make risk compar-

isons is an important priority.

ous are the risks we face, and do the benefits of certain

activities outweigh the risks? We examine many of

these risks in this chapter.

We can suffer harm from four major types of haz-

ards ( Concept 14-1 ):

• Biological hazards from more than 1,400 pathogens

(bacteria, viruses, parasites, protozoa, and fungi)

that can infect humans

• Chemical hazards from harmful chemicals in air, wa-

ter, soil, and food

• Physical hazards such as fire, earthquakes, volcanic

eruptions, floods, and storms

• Cultural hazards such as unsafe working conditions,

unsafe highways, criminal assault, and poverty

• Lifestyle choices such as smoking, poor food choices,

taking illicit drugs, drinking too much alcohol, and

having unsafe sex

We Face Many Types of Hazards

All of us take risks every day. Examples include driving

or riding in a car, eating foods with a high cholesterol

or fat content that contribute to heart attacks, drinking

alcohol, smoking or being in an enclosed space with a

smoker, lying out in the sun or going to a tanning par-

lor and increasing the risk of getting skin cancer and

wrinkled skin, practicing unsafe sex, and living in a

hurricane-prone area. The key questions are, How seri-

THINKING ABOUT

Hazards

Which three of the hazard types listed here are most likely to

harm you?

14-2 What Types of Biological Hazards Do We Face?

CONCEPT 14-2 In terms of death rates, the most serious infectious diseases are flu, AIDS,

diarrhea, and malaria, with most of these deaths occurring in developing countries.

Some Diseases Can Spread

from One Person to Another

A nontransmissible disease is caused by something

other than living organisms and does not spread from

one person to another. Such diseases tend to develop

slowly and have multiple causes. Examples include

most cancers, most cardiovascular (heart and blood ves-

sel) disorders, asthma, emphysema, and malnutrition.

Other diseases can spread from one person to an-

other. Such diseases start when a pathogen such as a

bacterium, virus, or parasite invades the body and

multiplies in its cells and tissues. This can lead to an

infectious or transmissible disease —a disease that

is caused by a pathogen and can be spread among peo-

ple. If the body cannot mobilize its defenses fast

enough to keep the pathogen from interfering with

bodily functions, the disease can have worse effects

and be spread more easily.

Figure 14-4 (p. 326) shows major pathways for in-

fectious diseases in humans. Once people are infected,

such diseases can be spread through air, water, food, or

body fluids such as feces, urine, the blood of infected

people, or droplets sprayed by sneezing and coughing—

depending on the disease organism.

A large-scale outbreak of an infectious disease in an

area or country is called an epidemic, and a global epi-

demic is called a pandemic. AIDS ( Core Case

Study ) is a pandemic as is tuberculosis (Case

Study, p. 326). Figure 14-5 (p. 326) shows the annual

death toll from the world’s seven deadliest infectious

diseases ( Concept 14-2 ). The deaths each year from these

diseases are 58 times the 221,000 people killed by the

December 2004 tsunamis (see pp. S55–S56 in Supple-

ment 12).

Great news. Since 1900, and especially since 1950,

the incidences of infectious diseases and the death rates

from such diseases have been greatly reduced. This has

been achieved mostly by a combination of better health

care, the use of antibiotics to treat infectious diseases

caused by bacteria, and the development of vaccines to

prevent the spread of some infectious viral diseases.

Bad news. Many disease-carrying bacteria have de-

veloped genetic immunity to widely used antibiotics

325

CONCEPT 14-2

83376_15_ch14_p323-343.ctp 8/10/07 1:44 PM Page 326

Pets

Livestock

Wild animals

Insects

Food

Water

Air

Fetus and babies

Other humans

Humans

Figure 14-4 Science: pathways for infectious disease in humans. Question: Can you think of other pathways

not shown here?

Disease

(type of agent)

Deaths per year

■ CASE STUDY

The Growing Global Threat

from Tuberculosis

Since 1990, one of the world’s most underreported sto-

ries has been the rapid spread of tuberculosis (TB). Ac-

cording to the WHO, this highly infectious bacterial dis-

ease strikes 9 million people per year and kills 1.6 mil-

lion—about 84% of them in developing countries. The

WHO projects that between 2006 and 2020, 25 million

people will die of this disease unless current funding

and efforts to control TB are greatly strengthened and

expanded.

Many TB-infected people do not appear to be sick

and about half of them do not know they are infected.

Left untreated, each person with active TB typically in-

fects 10–15 other people.

Several factors account for the recent increase in TB

incidence. One is the lack of TB screening and control

programs, especially in developing countries, where

95% of the new cases occur. A second problem is that

most strains of the TB bacterium have developed ge-

netic resistance to most of the effective antibiotics.

Population growth, urbanization, and air travel have

greatly increased person-to-person contacts, and TB has

spread, especially in areas where large numbers of poor

people crowd together. In addition, AIDS ( Core

Case Study ) greatly weakens its victims’ im-

mune systems and allows TB bacteria to multiply in

AIDS victims.

Pneumonia and flu

(bacteria and viruses)

3.2 million

HIV/AIDS

(virus)

3.0 million

Diarrheal diseases

(bacteria and viruses)

2.1 million

Malaria

(protozoa)

2.0 million

Tuberculosis

(bacteria)

1.6 million

Hepatitis B

(virus)

1 million

Measles

(virus)

800,000

Figure 14-5 Global outlook: the WHO estimates that each year the

world’s seven deadliest infectious diseases kill 13.5 million people—

most of them poor people in developing countries ( Concept 14-2 ).

This amounts to about 37,000 mostly preventable deaths every day.

Question: How many people die prematurely on average from

these diseases each hour, 24 hours a day? (Data from the World

Health Organization)

(Science Focus, at right). Also, many disease-transmit-

ting species of insects such as mosquitoes have become

immune to widely used pesticides that once helped

control their populations.

326

CHAPTER 14

Environmental Hazards and Human Health

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SCIENCE FOCUS

Growing Germ Resistance to Antibiotics

e risk falling behind in our

efforts to prevent infectious

bacterial diseases because of the astounding

reproductive rate of bacteria, some of which

can produce well over 16 million offspring in

24 hours. Their high reproductive rate allows

these organisms to become genetically re-

sistant to an increasing number of antib iotics

through natural selection ( Con-

cept 4-1B , p. 64). Some can also

transfer such resistance to nonresistant bacte-

ria even more quickly by exchanging genetic

material.

Other factors play a key role in fostering

such genetic resistance. One is the spread of

bacteria around the globe by human travel

and international trade. Another is the over-

use of pesticides, which increases populations

of pesticide-resistant insects and other carriers

of bacterial diseases.

Yet another factor is overuse of antibiotics

by doctors. According to a 2000 study by

Richard Wenzel and Michael Edward, at least

half of all antibiotics used to treat humans are

prescribed unnecessarily. In many countries,

antibiotics are available without a prescrip-

tion, which also promotes unnecessary use.

Resistance to some antibiotics has also in-

creased because of their widespread use in

livestock and dairy animals to control disease

and to promote growth.

As a result of these factors acting together,

every major disease-causing bacterium now

has strains that resist at least one of the

roughly 160 antibiotics we use to treat bacte-

rial infections such as tuberculosis (Case

Study, p. 326). Each year, genetic resistance

to antibiotics plays a role in the deaths of

least 90,000 of the 2 million people who pick

up mostly preventable infections while they

are in U.S. hospitals.

Critical Thinking

What are three things you would do to slow

the rate at which disease-causing organisms

develop resistance to antibiotics?

Slowing the spread of the disease requires early

identification and treatment of people with active TB,

especially those with a chronic cough. Treatment with

a combination of four inexpensive drugs can cure 90%

of individuals with active TB. To be effective, the drugs

must be taken every day for 6–8 months. Because the

symptoms disappear after a few weeks, many patients

think they are cured and stop taking the drugs, allow-

ing the disease to recur in drug-resistant forms and to

spread to other people.

Antiviral drugs can slow the progress of AIDS, but

they are expensive. With such drugs, an American with

AIDS, on average, can expect to live about 24 years at a

cost of about $25,200 a year. Such drugs cost too much

for widespread use in developing countries.

According to the WHO, a global strategy to slow the

spread of AIDS should have five major priorities. First,

reduce the number of new infections below the num-

ber of deaths. Second, concentrate on the groups in a so-

ciety that are most likely to spread the disease, such as

sex workers, intravenous drug users, and soldiers.

Third, provide free HIV testing, and pressure people

from high-risk groups to get tested.

Fourth, implement a mass-advertising and educa-

tion program geared toward adults and schoolchildren

to help prevent the disease, emphasizing abstinence,

condom use, and circumcision (which can reduce the

transmission of HIV by up to 60%). Fifth, provide free

or low-cost drugs to slow the progress of the disease.

Sixth, increase funding for research on the development

of microbiocides such as a vaginal gel that could help

women protect themselves against HIV in countries and

situations where men are reluctant to use condoms. If

these things are done, the WHO estimates that the pro-

jected death toll from AIDS between 2006 and 2030

could be reduced from 117 million to about 89 million.

Some Viral Diseases Kill Large

Numbers of People

What are the world’s three most widespread and dan-

gerous viruses? The biggest killer is the influenza or flu

virus ( Concept 14-2 ), which is transmitted by the body

fluids or airborne emissions of an infected person. Easily

transmitted and especially potent flu viruses could

spread around the world in a pandemic that could kill

millions of people in only a few months (Science Focus,

p. 328). Influenza occurs year round in the tropics. By

expanding

tropical

climates,

global

warming

could

lengthen the flu season in other areas.

The second biggest killer is the human imm uno-

deficiency virus (HIV) ( Core Case Study and Con-

cept 14-2 ). On a global scale, HIV infects about

4.9 million people each year and the resulting compli-

cations from AIDS kill about 3 million people annually.

AIDS is a serious and growing threat but fortunately it

is not as easily spread as the common flu.

■ ✓

HOW WOULD YOU VOTE?

Should developed and developing nations mount an

urgent global campaign to reduce the spread of HIV

( Core Case Study ) and to help countries afflicted by the

disease? Cast your vote online at www.thomsonedu

.com/biology/miller .

Examine the HIV virus and how it replicates by

using a host cell at ThomsonNOW.

The third largest viral killer is the hepatitis B virus

(HBV), which damages the liver and kills about a million

327

CONCEPT 14-2

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