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AP Environmental Science · Unit 8 of 9
Aquatic & Terrestrial Pollution
7–10% of the exam4 lessons · 50 min21 terms
What this unit covers
The topics below follow the published Env. Science course framework for Unit 8. This unit is worth 7–10% of the exam, so budget your time against that rather than against how long the unit takes to teach.
Point sourcesEutrophicationSolid wasteBioaccumulation
Lessons in this unit
- Sources of Pollution & Water Quality12 min · 3 objectivesDistinguish point-source from nonpoint-source pollution · Identify major categories of water pollutants and the stages of sewage treatment · Calculate the concentration of a pollutant discharged into a waterway
- Eutrophication & Dissolved Oxygen13 min · 3 objectivesTrace the steps of cultural eutrophication from nutrient input to a dead zone · Relate biochemical oxygen demand (BOD) to dissolved oxygen and aquatic life · Explain how hypoxic dead zones form and give a real-world example
- Solid & Hazardous Waste12 min · 3 objectivesDescribe how municipal solid waste is disposed of in landfills and incinerators · Explain the management of hazardous waste and the role of key U.S. laws · Calculate waste generation and the effect of recycling on landfill volume
- Bioaccumulation, Biomagnification & Human Health13 min · 3 objectivesDistinguish bioaccumulation from biomagnification · Interpret a dose-response relationship and the meaning of LD50 · Calculate how a persistent toxin concentrates up a food chain
Formulas in Unit 8
Pollutant concentration
concentration = mass of pollutant / volume of water
Keep units consistent. 1 g/L = 1,000 mg/L; concentrations in water are often reported in mg/L, which for dilute solutions is approximately equal to ppm.
The eutrophication cascade
excess N & P → algal bloom → algae die → decomposers ↑ → BOD ↑ → dissolved O₂ ↓ → fish die (dead zone)
The key insight: the harm is not the algae directly but the oxygen depletion caused by decomposers breaking down the dead algae. High BOD = low dissolved oxygen.
Waste generation and diversion
total waste = population × per-capita waste rate ; landfilled = total × (1 − recycling rate)
Multiply population by the per-person waste rate for the total, then subtract the recycled fraction to find what still reaches the landfill.
Biomagnification up the food chain
concentration at a level ≈ base concentration × (magnification factor)^(number of levels up)
If a toxin roughly multiplies by 10 at each trophic level, a predator three levels above the base carries about 10³ = 1,000 times the base concentration. LD50: lower value = more toxic.
Every term in Unit 8
All 21 terms we publish for Aquatic & Terrestrial Pollution, with definitions. Reading them through is the fastest way to find the ones you cannot define — then drill those in cram mode until you can produce them without the prompt.
- Eutrophication
- Nutrient enrichment causes an algal bloom; when the algae die, decomposers consume dissolved oxygen and fish suffocate, creating a hypoxic dead zone.
- Bioaccumulation vs biomagnification
- Bioaccumulation is buildup within one organism over its lifetime; biomagnification is increasing concentration up trophic levels, so top predators are worst affected.
- Point vs nonpoint source pollution
- Point sources are identifiable single locations like a discharge pipe; nonpoint sources are diffuse, like agricultural runoff — much harder to regulate.
- Biochemical oxygen demand
- Oxygen consumed by decomposers breaking down organic waste. High BOD means low dissolved oxygen available for aquatic life.
- Dissolved oxygen and temperature
- Cold water holds more dissolved oxygen than warm, so thermal pollution reduces oxygen availability just as fish metabolism rises.
- Thermal pollution
- Heated water discharged from power plants lowers dissolved oxygen and stresses organisms adapted to cooler conditions.
- Persistent organic pollutants
- DDT, PCBs and dioxins resist breakdown, are fat-soluble and biomagnify. DDT thinned raptor eggshells, nearly eliminating bald eagles.
- Heavy metal pollution
- Mercury, lead, arsenic and cadmium are neurotoxic and do not degrade. Mercury from coal burning methylates in water and biomagnifies in fish.
- Oil spills
- Coat feathers and fur destroying insulation, smother intertidal organisms, and are treated with booms, skimmers, dispersants and bioremediation.
- Sewage treatment stages
- Primary is physical settling; secondary uses bacteria to reduce BOD; tertiary removes nutrients and disinfects.
- Solid waste disposal
- Sanitary landfills use liners and leachate collection to protect groundwater; incineration reduces volume but releases pollutants and produces toxic ash.
- Leachate
- Liquid that percolates through waste picking up contaminants. Landfill liners and collection systems exist to keep it out of groundwater.
- Superfund (CERCLA)
- Funds cleanup of abandoned hazardous waste sites and holds polluters liable for the cost.
- Dose-response curve
- Relates dose to the proportion of a population responding. LD50 is the dose lethal to half the test population — lower LD50 means more toxic.
- Waterborne diseases
- Cholera, typhoid, dysentery and giardia spread through faecal contamination of drinking water, the leading cause being inadequate sanitation.
- Cultural eutrophication
- Human-accelerated nutrient enrichment from fertilizer, sewage and detergents, as distinct from the slow natural process.
- Indicator organisms for water quality
- Coliform bacteria indicate faecal contamination; mayfly and stonefly larvae indicate high dissolved oxygen and low pollution.
- Clean Water Act
- Regulates point-source discharge into surface waters through permits and sets water quality standards. Nonpoint sources remain largely unregulated.
- Safe Drinking Water Act
- Sets maximum contaminant levels for public drinking water supplies, a separate statute from the Clean Water Act.
- RCRA
- Regulates hazardous waste from generation through disposal — "cradle to grave" — as opposed to Superfund, which cleans up past contamination.
- Plastic pollution and microplastics
- Plastics fragment rather than degrade, accumulating in gyres and entering food webs where they are ingested and can carry adsorbed toxins.
What examiners penalize here
- Two reliable exam facts: nonpoint-source (especially agricultural runoff) is the leading cause of water pollution and the hardest to regulate, and sewage treatment runs primary (physical) → secondary (biological) → tertiary (chemical/nutrient removal). The Clean Water Act targets point sources.
- Free-response graders want the full causal chain: excess N and P → algal bloom → algae die → decomposers increase → BOD rises → dissolved oxygen falls → fish die. Skipping the decomposer/oxygen step is the most common way to lose points — that step is the heart of the answer.
- For waste calculations, compute the total first (population × per-capita rate), then apply the recycling rate to find what is diverted versus landfilled. Watch unit conversions (kg → metric tons is ÷1,000). Pair RCRA (cradle-to-grave management) with CERCLA/Superfund (cleanup of old sites).
- Two quantitative anchors here: biomagnification multiplies at each level (×10 per level → 10ⁿ over n levels), and LD50 dose = (mg/kg) × body mass in kg. Remember the counterintuitive LD50 rule — a *lower* LD50 is *more* toxic, because less of it is needed to kill.
Practice Env. Science
Our practice bank is drawn from across the whole course rather than filtered to one unit, which is closer to how the exam asks anyway — it will not tell you which unit a question is testing.
Questions about this unit
How much of the AP Environmental Science exam is Unit 8?
Unit 8, Aquatic & Terrestrial Pollution, is worth 7–10% of the Env. Science multiple-choice section according to the published course framework. Across all 9 units that makes it a middling share, roughly what an even split across units would give.
What topics are covered in Env. Science Unit 8?
Aquatic & Terrestrial Pollution covers Point sources, Eutrophication, Solid waste and Bioaccumulation. We publish 21 terms with definitions for this unit, all of them on this page.
How should I study Env. Science Unit 8?
Read the 4 lessons below first — about 50 minutes — then drill the 21 terms in cram mode until you can produce each definition from memory rather than just recognize it. Recognition is what makes a unit feel finished when it is not. Finish with practice questions and read the explanation for every one you get right by elimination as well as the ones you miss.
All 9 units of AP Environmental Science
Unit names, topics and exam weights follow the published College Board course framework for AP Environmental Science. AP® is a trademark registered by the College Board, which does not endorse this site.