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