AP Environmental Science, AP exams, 7–10%

Unit 8: Aquatic and Terrestrial Pollution

Unit 8 covers pollution of water and land: point and nonpoint sources, eutrophication, thermal pollution, persistent organic pollutants, solid waste, and sewage treatment. It also introduces the toxicology vocabulary the exam uses, including dose-response curves and the median lethal dose. Bioaccumulation and biomagnification are among the most reliably tested ideas.

Position: 8 of 9 units
Published weighting: 7–10% in the official framework
Topics covered: 6 topics in this guide

What is covered

Topics inside this unit.

These topics describe the scope students most often review for this part of AP Environmental Science. Treat them as a study checklist rather than an exhaustive list of what a single exam form can sample.

Sources of pollution: Point and nonpoint sources, and the range of human activities that introduce contaminants.
Eutrophication and thermal pollution: Nutrient loading, algal blooms, oxygen depletion, and the effect of warm discharge on dissolved oxygen.
Persistent organic pollutants: Why some compounds resist breakdown, and how persistence and fat solubility drive their spread.
Bioaccumulation and biomagnification: Accumulation within one organism versus concentration increases up trophic levels, with worked examples.
Solid waste and sewage treatment: Landfill design, incineration, waste reduction strategies, and the stages of wastewater treatment.
Dose-response and human health: Reading a dose-response curve, interpreting the median lethal dose, and linking pathogens to disease.

Study tips

How to practice Aquatic and Terrestrial Pollution.

Section-specific guidance that follows from how this material is usually tested.

Work at least one numeric biomagnification problem; the concept is easy but the calculation trips people up.
Sequence the stages of wastewater treatment in order and note what each removes.
Learn eutrophication as a causal chain ending in low dissolved oxygen so you can write it under time pressure.

Where this fits

Unit 8: Aquatic and Terrestrial Pollution is 8 of 9 units in the AP Environmental Science guide, and it carries a published weighting of 7–10% in the official framework. Use the full guide to balance it against everything else you have to review.

Back to the AP Environmental Science guide Official exam information

Sample Aquatic and Terrestrial Pollution questions

Practice questions, not yet expert-reviewed

Original practice questions written to the published framework for this section. No expert has reviewed them, and they are not taken from any official exam. Try each one before you open the answer.

Question 1Foundational
What is the term for water pollution that enters a body of water from diffuse, hard-to-trace origins such as runoff from farm fields, lawns, and streets?
1. APoint source pollution
2. BThermal pollution
3. CNonpoint source pollution
4. DPrimary pollution
Show answer
Answer: C. Nonpoint source pollution
Nonpoint source pollution has no single identifiable discharge location, so it cannot be fixed by regulating one outfall pipe and instead requires changes in land management across a watershed. Point source pollution is the tempting distractor, but that comes from a discrete, traceable location such as a factory pipe or a sewage outfall. Nonpoint sources are the larger share of the nutrient load in most agricultural watersheds.
Key insight: If you cannot point at one pipe, you cannot permit it either, which is why nonpoint pollution is so hard to regulate.
Question 2Foundational
During eutrophication, what happens to the dissolved oxygen in a lake after a large algal bloom dies and decomposes?
1. AIt rises sharply
2. BIt falls sharply
3. CIt stays exactly the same
4. DIt rises and then remains high
Show answer
Answer: B. It falls sharply
Decomposer bacteria consume oxygen as they break down the enormous mass of dead algae, so dissolved oxygen crashes and fish and other aerobic organisms suffocate. The tempting answer is that oxygen rises, which is true only while the algae are alive and photosynthesizing during daylight. The decomposition stage, not the bloom itself, is what creates hypoxic dead zones.
Key insight: Nutrient loading kills a lake at the decomposition step, when bacteria outcompete everything else for oxygen.
Question 3Intermediate
A fat-soluble pesticide measures 0.02 parts per million in lake water, 0.5 parts per million in zooplankton, and 25 parts per million in the fish that eat them. What process explains the rising concentration at each higher trophic level?
1. ABioaccumulation
2. BEutrophication
3. CLeaching
4. DBiomagnification
Show answer
Answer: D. Biomagnification
Biomagnification is the increase in the concentration of a persistent contaminant as it moves up a food chain, because each consumer takes in the accumulated burden of everything it eats. Bioaccumulation is the tempting distractor, but that term describes the buildup of a contaminant within one organism over its lifetime rather than the increase across trophic levels. Only compounds that resist breakdown and dissolve in fat behave this way.
Key insight: Bioaccumulation happens inside one organism; biomagnification happens up the food chain.
Question 4Intermediate
What does the primary treatment stage of a wastewater treatment plant remove?
1. ASolids that settle or float, removed by physical screening and settling
2. BDissolved organic matter, removed by bacteria in aerated tanks
3. CNitrogen and phosphorus, removed by chemical treatment
4. DPathogens, removed by chlorination or ultraviolet light
Show answer
Answer: A. Solids that settle or float, removed by physical screening and settling
Primary treatment is entirely physical: screens catch large debris and settling tanks let heavy solids sink while grease is skimmed from the surface. Secondary treatment is the tempting distractor, because that is the biological stage where microorganisms digest the dissolved organic matter. Nutrient removal and disinfection belong to tertiary treatment and the final disinfection step.
Key insight: Wastewater treatment runs physical, then biological, then chemical, so name the mechanism to identify the stage.
Question 5Advanced
In toxicology, what does the LD50 of a substance represent?
1. AThe dose at which 50 percent of a test population shows any symptom
2. BThe dose that is lethal to 50 percent of a test population
3. CThe concentration that kills an exposed population within 50 hours
4. DThe dose considered safe for 50 percent of the population
Show answer
Answer: B. The dose that is lethal to 50 percent of a test population
LD50 is the median lethal dose read off a dose-response curve, and a smaller LD50 means a more toxic substance because less of it is needed to kill half the test organisms. The tempting distractor describes ED50, the effective dose that produces a measured nonlethal response in half the population. Both values come from the same curve, so read the axis labels before interpreting either one.
Key insight: A low LD50 means high toxicity, because toxicity is measured by how little it takes.

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Unit 8: Aquatic and Terrestrial Pollution