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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 be understood only 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 abroad.
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 life span 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 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 nonlethal 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 (10%) 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 15%) occurs at a moderate 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. Based on this
information alone, a rational decision would be to use moderate doses of sunscreen. One would want to
know, however, 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 and
other health impacts.
Calculating Ecological Footprints
Annual pesticide use
(pounds of active ingredient)
4.21
You
Answers will vary
Your class
Answers will vary
Your state
1,200,000,000
United States
5,050,000,000
World (total)
0.82
World (per capita)
1
Answers will vary.
2
Pesticide use ratio U.S./world: 4.21 pounds 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.
3
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 bioaccumulated? 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.