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Chapter 14
Testing Your Comprehension
1. Environmental health hazards can be physical, chemical, biological, or cultural.
2. Infectious disease is the worst of the biological health hazards, and causes more human
deaths than any other environmental health hazard.. It is a problem that can grow over time,
is communicable, and can only be understood in the context of complex interrelationships
among technology, land use, and ecology.
3. Exposure to lead, asbestos, radon, and PBDEs occurs primarily indoors. Lead exposure can
occur though contamination of water flowing through older pipes with lead solder, or by
ingestion of paint containing lead. Both of these uses have been largely discontinued, and in
older homes, can be abated. Asbestos was a commonly used insulating material, and can be
inhaled if the material is disturbed. This use has also been largely discontinued, and old
asbestos insulation can be removed by a qualified contractor. Radon is a naturally occurring
radioactive gas that, in certain geological areas, can seep into the basements of homes and
accumulate there. When inhaled it increases the risk of lung cancer. If the basement is both
sealed and well ventilated, radon levels can be kept very low. PBDEs (polybrominated
diphenyl ethers) are used as flame retardants in many consumer products. They are
environmentally persistent, are bioaccumulated, and appear to be endocrine disruptors. Little
has been done to address this situation in the United States.
4. Concern over pesticides in the United States has been growing since Silent Spring was
published in 1962. Carson argued that DDT was harmful to the health of people, wildlife, and
ecosystems. DDT use was subsequently banned in the United States, although it is still
produced domestically, sold abroad, and used there.
5. Toxicants include: carcinogens, which cause cancer; mutagens, which alter DNA; teratogens,
which affect embryonic development; allergens, which overactivate the immune system;
neurotoxins, which affect the nervous system; and endocrine disruptors, which interfere with
the hormone system.
6. Toxicants may move with water in the environment, or be carried in the atmosphere. They
tend to be found near sites of their production or release, where they are soluble, and
wherever the rate of transport to a location is greater than the rate of transport away (e.g.,
sedimentation). The lifespan of toxins is inversely proportional to their rates of degradation in
the environment, and can range from hours to millennia. Bioaccumulation and
biomagnification occur for compounds that are fat-soluble and are stored in an organism’s
fatty tissues. The concentration in those tissues will come to exceed that in the food supply. If
the bioaccumulating organism is itself eaten, organisms at the next trophic level will
accumulate even higher doses of the toxicant, in the process called biomagnification.
7. Epidemiological studies involve large-scale comparisons of groups of people, usually
contrasting a group known to have been exposed to some toxicant and a group that has not
been exposed. The groups’ members are followed for a long period of time (years to
decades), and rates of health problems and death are monitored. The data are then statistically
analyzed to determine whether there is a correlation between the exposure to the toxicant and
some health effect.
8. Animal testing enables scientific advances that would not be possible otherwise, given ethical
prohibitions against testing on human subjects. A dose-response curve is a graphical
representation of the relationship between the dose of a toxicant administered to a subject,
and the subject’s response of to the toxicant. An LD50 is a dose that is lethal to 50% of the
sample population, while an ED50 is a dose that has an effect (i.e., a non-lethal one) on 50%
of the sample population. Toxicants with high LD50 and ED50 values are considered safer
because larger doses are required to have an effect. Conversely, toxicants with low LD50 and
ED50 values are considered dangerous because even small doses have a substantial effect.
9. Individuals’ sensitivities to toxicants vary for genetic reasons or due to prior health
conditions and stresses. Measuring chronic exposure is more difficult due to the need for
long-term exposure data. Most laboratory dose-response studies are of the effects of acute
exposure, not chronic exposure, and are of the effects of a single toxicant at a time. They do
not consider the potential interactions of the effects to multiple toxicants simultaneously,
although these effects are often synergistic (greater than or different from the sum of the
individual effects).
10. Assessing risks involves studying the dose-response of the substance/activity and its effects,
and measuring the population’s likely exposure to the substance or rate of engagement in the
activity.
Interpreting Graphs and Data
1. The greatest risk from UV exposure (40%) would be when no sunscreen is applied. The
greatest risk due to the chemicals in the sunscreen (30%) occurs at the highest dosage of
applied sunscreen. The greatest risk from UV exposure is greater than the greatest risk due to
the chemicals in the applied sunscreen.
2. The minimum risk from UV exposure (2%) would be when the highest dosage of sunscreen
is applied. The minimum risk due to the chemicals in the sunscreen (0%) occurs when none
of the sunscreen is applied. The minimum risk from UV exposure is greater than the
minimum risk due to the chemicals in the applied sunscreen.
3. The greatest total risk (40%) occurs when no sunscreen is applied. This risk is entirely due to
the effects of the UV radiation. The minimum total risk (approximately 20%) occurs at a low
dose of applied sunscreen. This dosage is sufficient to substantially lower the risk from UV
exposure, but not so high as to have greatly increased the risk due to the chemicals in the
sunscreen. One would want to know whether the risk factors vary depending on the active
ingredient or by SPF, etc. Answers will vary, but one example would be studies that link
moderate consumption of red wine to decreased incidence of heart disease although high
levels of consumption can cause liver problems, etc.
Calculating Ecological Footprints
You
Your class
Annual pesticide use
(pounds of active ingredient)
4.21
Answers will vary
Your state
United States
World (total)
World (per capita)
Answers will vary
1,200,000,000
5,050,000,000
0.82
1. Pesticide use ratio U.S./world: 4.21pounds per capita / 0.82 pounds per capita = 5.13.
Ecological footprint ratio U.S/world: 25.4 acres per capita / 6.9 acres per capita = 3.68
In terms of both pesticide usage and total ecological footprint, the United States consumes
several times its per capita share. Pesticide usage is an advanced technology that has been
adopted in the United States at rates greatly exceeding the world average.
2. Answers will vary, but take into consideration that the aggregate use data do not tell you
which pesticides are being used, where they are being used, what their fate in the
environment is (are they persistent? are they bio-accumulated? are they mobile?), what the
likelihood of exposure is, nor what the toxicity is to humans. All of these are important
factors in making a realistic assessment of the risk posed by those few pounds of pesticides
used per person per year.