Visualizing Environmental Science

88 CHAPTER 4 Risk Analysis and Environmental Health Hazards

is, they add the known effects of each compound in the

mixture. Such an approach sometimes overestimates or

underestimates the actual risk involved, but it is the best

method currently available. The alternative—waiting

for years or decades until numerous studies have been

designed, funded, and completed—is unreasonable.

Children and Chemical Exposure

Children weigh less than adults, tend to interact more

with their environments and are undergoing rapid in-

ternal changes as they grow. They are also less aware of

each with a toxicity level of 1, might have a combined toxic-

ity of 3. For example, exposure to either tobacco smoke or

inhaled asbestos can cause lung cancer. However smokers

who worked in the asbestos industry were found to have

much higher rates of lung cancer than expected from a

simple additive relationship. An antagonistic interaction in a

chemical mixture results in a smaller combined effect than

expected; for example, two chemicals, each with a toxicity

level of 1, might have a combined effect of 1.3.

If toxicological studies of chemical mixtures are lack-

ing, how is risk assessment for chemical mixtures assigned?

Toxicologists use additivity to assign risk to mixtures—that

EnviroDiscovery

Smoking: A Significant Risk

chronic respiratory diseases than other nonsmokers. Passive smoking

is particularly harmful to infants and young children, pregnant women,

the elderly, and people with chronic lung disease.

There is good news and bad news about smoking. The good

news is that fewer people in highly developed nations such

as the United States are smoking. Recent research indicates

that bans on smoking in public buildings and restaurants have

reduced heart disease–related emergency room visits by as

much as 17 percent.

The bad news is that more and more people are taking up

the habit in China, Brazil, Pakistan, and other developing nations.

Tobacco companies in the United States promote smoking

abroad, and a substantial portion of the U.S. tobacco crop is

exported. The World Health Organization (WHO) estimates

that, worldwide, 5 million people die each year of smoking-

related causes. In an attempt to establish a global ban

on tobacco advertising, WHO developed the Framework

Convention on Tobacco Control. The treaty went into effect

in 2005, but as of early 2012, the United States was not

among the 167 parties that had joined.

Tobacco use is the single largest cause of preventable death.

Smoking causes serious diseases such as lung cancer, emphysema,

and heart disease and is responsible for the premature deaths of

nearly half a million people in the United States each year. Cigarette

smoking annually causes about 120,000 of the 140,000 deaths

from lung cancer in the United States. Smoking also contributes

to heart attacks and strokes and to cancers of the bladder, mouth,

throat, pancreas, kidney, stomach, voice box, and esophagus.

Passive smoking, which is nonsmokers’ chronic breathing of

smoke from cigarette smokers, also increases the risk of cancer.

Passive smokers suffer more respiratory infections, allergies, and other

A sugarcane worker smokes during

a break in his long, hard day

Cigarette use continues to increase in many developing

countries, even as consumption of tobacco decreases in

the United States. Photographed in the Philippines.

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© Petrut Calinescu/Alamy