AP® Environmental Science review sheet from Aim for Five (aimforfive.com/enviro/units/8/8-14)
Unit 8 · Topic 8.14
8.14 Pollution and Human Health
Linking a pollutant to a health problem is harder than it sounds, because people are exposed to many things at once and effects can take decades to show. Still, some links are firm: dysentery from contaminated water, mesothelioma from asbestos, and lung damage from ground-level ozone.
Key terms
- dysentery
- mesothelioma
- asbestos
- ground-level ozone
- acute vs. chronic exposure
Why cause and effect is hard to prove
- Multiple exposures: people breathe, eat and drink many substances every day, so it is hard to isolate the effect of one.
- Confounding variables: factors like smoking, diet, income, age and genetics also affect health and can hide or mimic a pollutant's effect.
- Long delays: some effects, such as cancers, appear years or decades after exposure, when it is hard to reconstruct what a person was exposed to.
- Ethics: you can't deliberately expose people to suspected toxins, so researchers rely on animal studies and on observational studies of groups exposed by accident or through their jobs.
- Individual differences: children, older adults, pregnant people and those with existing health conditions are often more sensitive.
Acute versus chronic exposure
Acute exposure is a single, short exposure, often at a high level, with effects that appear quickly, like carbon monoxide poisoning from a faulty heater. Chronic exposure is repeated or long-term exposure, often at lower levels, with effects that build up over time, like lung disease after years of breathing polluted air. A substance can be harmful in both ways at different doses.
Three well-established links
| Disease or effect | Cause | Key facts |
|---|---|---|
| Dysentery | Bacteria or amoebas in food or water contaminated with feces | Intestinal infection causing severe, often bloody diarrhea and dehydration; most common where sewage treatment and clean water are lacking |
| Mesothelioma | Breathing asbestos fibers | Cancer of the thin lining around the lungs and chest (or abdomen); often appears 20 to 50 years after exposure |
| Respiratory damage | Ground-level (tropospheric) ozone | Irritates and inflames airways, reduces lung function, triggers asthma attacks; worst on hot, sunny smog days |
Making the connection
These examples show different routes of exposure: dysentery comes through contaminated water, while mesothelioma and ozone damage come through the air you breathe. They also show different timescales: dysentery is acute and appears within days, while mesothelioma follows chronic or past exposure by decades. Because asbestos was widely used in buildings, ships and insulation until the 1970s, people still develop mesothelioma today from exposures long ago.
Other pollution and health links to recognize
- Lead (old paint, contaminated water pipes) → nervous system and brain damage, especially in children (topic 7.5).
- Methylmercury (in large predatory fish) → nervous system damage, especially in developing babies (topic 8.8).
- Fine particulate matter, PM₂.₅ → heart and lung disease (topic 7.4).
- Radon → lung cancer; carbon monoxide → oxygen deprivation (topic 7.5).
Worked examples
Try each one yourself first, then open the solution.
- Example 1Calculator allowed
Evaluating a health study
A study finds that children living within 500 m of a highway have 36 asthma emergency visits per 1,000 children per year, while children living farther away have 24 per 1,000. (a) Calculate the percent increase. (b) Identify one confounding variable and explain how it could affect the conclusion.
Show the solutionHide the solution
- Step 1: (a) Percent change = (36 − 24) ÷ 24 × 100 = 12 ÷ 24 × 100 = 50%.
- Step 2: (b) Household income is a possible confounding variable. Housing near highways is often cheaper, so families there may have lower incomes, which can mean older housing with more mold, more exposure to indoor smoke, or less access to regular medical care.
- Step 3: Any of those could raise asthma visits on their own, so the study can't conclude that highway pollution alone caused the difference unless it accounts for income.
Answer: (a) A 50% increase. (b) For example, income: lower-income families near highways may have other asthma risk factors, so traffic pollution may not be the only cause.
Common mistakes
- Saying a correlation proves a pollutant caused a disease. Name a confounding variable to show you understand why causation is hard to prove.
- Mixing up asbestos diseases. Mesothelioma is a cancer of the lining around the lungs, specifically linked to asbestos.
- Calling dysentery an airborne disease. It spreads through water and food contaminated with feces.
On the exam
- Expect to match a pollutant to its health effect (asbestos → mesothelioma; contaminated water → dysentery; ozone → respiratory problems).
- Study-design questions may ask you to identify a confounding variable or explain why animal or observational studies are used instead of experiments on people.
Connected topics
Videos
Check yourself
4 questions on 8.14 Pollution and Human Health. Pick an answer to see if you got it, and why.
Researchers notice that people living near a highway have higher rates of asthma. Which is the main reason it is difficult to prove that one specific pollutant from the traffic causes the asthma?
A village draws its drinking water from a stream that receives untreated sewage from a town upstream. Which health problem is most directly linked to this situation?
A retired shipyard worker is diagnosed with mesothelioma, a cancer of the lining around the lungs, about 35 years after working near pipe insulation. Which pollutant is the most likely cause, and what does the timing show?
Which situation is the best example of chronic exposure to a pollutant?
0 of 4 answered