HUMAN BIOLOGY

430 Chapter 22

FOCUS ON OUr eNvirONmeNt

Cancer risk from environmental Chemicals

22.3

this ames test uses Salmonella bacteria as the “guinea

pigs,” because chemicals that cause mutations in bacterial

dna may also have the same effect on human dna. after

extensive experimentation, ames arrived at some interesting

conclusions. First, he found that more than 80 percent

of known cancer-causing chemicals do cause mutations.

however, ames testing at many different laboratories has not

revealed a “cancer epidemic” caused by synthetic chemicals.

ames’s findings do not mean we should carelessly

expose ourselves to environmental chemicals. the national

academy of sciences has warned that the active ingredients

in 90 percent of all fungicides, 60 percent of all herbicides,

and 30 percent of all insecticides used in the United states

have the potential to cause cancer in humans. at the same

time, responsible scientists recognize that it is virtually

impossible to determine that a certain level of a specific

chemical caused a particular cancer or some other harmful

effect. Given these facts, it seems wise to be cautious

and limit our exposure to the potential carcinogens in an

increasingly chemical world.

according to the american Cancer society, factors in our

environment lead to about half of all cancers. this statistic

includes exposure to UV light and radiation, and it also

includes agricultural and industrial chemicals. how are

people exposed to these chemicals? and how dangerous

are they? Let’s begin with the first question.

Government statistics indicate that about 40 percent

of the food in american supermarkets contains detectable

residues of one or more of the active ingredients in

commonly used pesticides. the residues are especially

likely to be found in tomatoes, grapes, apples, lettuce,

oranges, potatoes, beef, and dairy products. imported

crops, such as fruits, vegetables, and coffee beans, can

also carry significant pesticide residues—sometimes

including pesticides, such as ddt, that are banned in the

United states. the pesticide category includes roughly

600 chemicals used as fungicides, insecticides, and

herbicides, which are used alone or in combination.

avoiding exposure to pesticides is difficult. although

residues of some pesticides can be removed from the

surfaces of fruits and vegetables by washing, it can be

difficult to avoid coming into contact with pesticides used

in community spraying programs to control mosquitoes and

other pests, or used to eradicate animal and plant pests on

golf courses and along roadsides. We have more control over

chemicals we use in gardens and on lawns (Figure 22.8).

agricultural chemicals are not the only potential threats

to human health. industrial chemicals also have been linked

to cancer. in one way or another, the industrial chemicals in

table 22.2 all can cause carcinogenic mutations in dna.

Biochemist Bruce ames developed a test that could be

used to assess the ability of chemicals to cause mutations.

Figure 22.8 Home garden chemicals are just one way people
can come into contact with potentially carcinogenic substances.
Most commercially produced oranges are sprayed with fungicides
that are potential human carcinogens (right). Agricultural workers
have the greatest risk of significant exposure.

Tony Freeman/PhotoEdit

© Richard Peterson/Shutterstock.com

Table 22.2 Some industrial Chemicals Linked to Cancer

Chemical/Substance Type of Cancer

Benzene Leukemias

Vinyl chloride Liver, various connective tissues

Various solvents Bladder, nasal epithelium

Ether Lung

Asbestos Lung, epithelial linings of body cavities

Arsenic Lung, skin

Radioisotopes Leukemias

Nickel Lung, nasal epithelium

Chromium Lung

Hydrocarbons in Skin, lung

soot, tar smoke

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