Chapter 22 Waste Flashcards
factors are thought to raise the risk of cancer: Indeed
in 2010
the President’s Cancer Panel concluded that the prevalence of
environmentally induced cancer has been “grossly underesti-
mated.” In our society today
the greatest number of cancer
cases is thought to result from carcinogens contained in ciga-
rette smoke. Polycyclic aromatic hydrocarbons (PAHs; p. 27)
make up some of the carcinogens found in cigarette smoke.
PAHs also occur in charred meats and are released from the
combustion of coal
oil
Carcinogens can be difficult to identify because there
may be a long lag time between exposure to the agent and
the detectable onset of cancer-up to 15-30 years in the
case of cigarette smoke. Moreover
as with all risks
a portion of people exposed to a carcinogen will eventually
get cancer. Cancer is a leading cause of death that kills mil-
lions and leaves few families untouched. Two of every five
Americans are diagnosed with cancer at some time in their
lives
and one of every five dies from it. Thus
carcinogens has played a large role in shaping the way that
toxicologists pursue their work.
Mutagens are substances that cause genetic mutations
in the DNA of organisms (p. 49). Although most mutations
have little or no effect
some can lead to severe problems
including cancer and other disorders. If mutations occur in
an individual’s sperm or egg cells
then the individual’s off-
spring suffer the effects.
Chemicals that cause harm to the unborn are called
teratogens. Teratogens that affect development of human
embryos in the womb can cause birth defects. One exam-
ple of a teratogen is the drug thalidomide
developed in the
1950s to aid sleeping and to prevent nausea during pregnancy.
Tragically
the drug caused severe birth defects in thousands
of babies whose mothers were prescribed thalidomide. Even
a single dose during pregnancy could result in limb deformi-
ties and organ defects. Thalidomide was banned in the 1960s
once scientists recognized its connection with birth defects.
Ironically
today the drug shows promise in treating a wide
range of diseases
including Alzheimer’s disease
Other chemical toxicants known as neurotoxins assault
the nervous system. Neurotoxins include venoms produced
by animals such as snakes and stinging insects
heavy met-
als such as lead and mercury
pesticides
weapons developed for use in war. A famous case of neu-
rotoxin poisoning occurred in Japan
where a chemical fac-
tory dumped mercury waste into Minamata Bay between the
1930s and 1960s. Thousands of people there ate fish contami-
nated with the mercury and soon began suffering from slurred
speech
loss of muscle control
some cases death.
The human immune system protects our bodies from dis-
ease. Some toxicants weaken the immune system
reducing
allergens
overactivate the immune system
immune response when one is not necessary. One hypothesis
for the increase in asthma in recent years is that allergenic
synthetic chemicals are more prevalent in our environment.
364 CHAPTER 14 Environmental Health and Toxicology
Alergens are not nine ly conut not toxican
once
focuse tay afect some people by nor others and becaus
one sure phonse does not necessarily corelate with the deares
of exposure.
pasuray inhibitors are toxisabs that interup vial bia.
aerial processes in chemicals by bloking one or more
step in important bia hemoral pins in so Rat poison
on
example
cause internal hemothysing in rodents by interter.
provins. Some herbicides
sis. Cyanide i kill plans by
blocking steps in photosynthesis. Ce enide ils by intermon:
ing inmical pathways that produce energy in mitochondia
thereby depriving cells of life-sustaining energy.
Most recently
scientists have recognized endocrine
disruptors
toxicants that interfere with the endocrine system.
The endocrine system consists of chemical messengers (hor.
mones) that travel through the bloodstream at extremely low
concentrations and have many vital functions. They stimulate
growth
development
brain function
appetite
of our physiology and behavior. Some hormone-disrupting
toxicants affect an animal’s endocrine system by blocking the
action of hormones or accelerating their breakdown. Others
are so similar to certain hormones in their molecular structure
and chemistry that they “mimic” the hormone by interacting
with receptor molecules just as the actual hormone would
(FIGURE 14.10).
BPA is one of many chemicals that appear to mimic
the female sex hormone estrogen and bind to estrogen
receptors. Many plastic products also contain another class
of hormone-disrupting chemical
called phthalates. Used to
soften plastics and enhance fragrances
phthalates are used
widely in children’s toys (FIGURE 14.11a)
perfumes and
cosmetics (FIGURE 14.11b)
and other items. Health research
on phthalates has linked them to birth defects
breast cancer
reduced sperm counts
and other reproductive effects. The
European Union and nine other nations have banned phthal-
ates
California and Washington enacted bans for children’s
toys
and the United States in 2008 banned six types of
phthalates in toys. Still
across North America many routes of
exposure remain. Like BPA
phthalates show how a substance
can be a carcinogen
a mutagen
all at the same time.
Organisms have natural defenses
against toxic substances
Although synthetic toxicants are new
organisms have long
been exposed to natural toxicants. Mercury
arsenic
and other harmful substances are found naturally in the
environment. Some organisms produce biological toxins to
avoid predators or capture prey. Examples include venom in
poisonous snakes and spiders
toxins in sea urchins
natural insecticide pyrethrin found in chrysanthemums. Over
time
organisms able to tolerate these harmful substances
have gained an evolutionary advantage.
Skin
scales
against toxic substances because they resist uptake from the surrounding environment.
