Aquatic & Terrestrial Pollution

Name: AP Environmental Science Unit 8: Aquatic & Terrestrial Pollution
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7–10% of the exam5 lessons · 67 min33 terms

Cram this unit Flip through the cards Sit a unit test Math practice

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

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.

Eutrophication chain

nutrients → algal bloom → light blocked → plants and algae die → decomposers consume O₂ → hypoxia and fish kill

The oxygen is consumed by decomposers, not by the algae. Omitting that step loses the causal point.

Every term in Unit 8

All 33 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: a persistent, fat-soluble toxin builds up WITHIN one organism over its lifetime. Biomagnification: concentrations increase at each successive TROPHIC LEVEL, so top predators carry the highest burden. DDT, PCBs, and methylmercury are the standard examples.
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.
Where a watershed's nitrogen and phosphorus come from: Fertilizer runoff from cropland and lawns, animal manure from feedlots, treated and untreated sewage, and detergents. Cropland is usually the largest nonpoint source, which is why it is also the hardest to regulate.
Dead zones and hypoxia: Nutrient loading fuels an algal bloom; the algae die, decomposers consume oxygen breaking them down, and dissolved oxygen falls below about 2 mg/L. Mobile animals flee, sessile ones die, and the zone reappears each summer as the nutrients keep arriving.
Why dissolved oxygen falls at night: In daylight algae photosynthesize and release oxygen; after dark they only respire, and so does everything else. In a eutrophic pond the daily minimum comes just before dawn, which is when fish kills happen.
Fecal coliform testing: Coliform bacteria are harmless themselves but live in the gut, so their presence indicates fecal contamination and therefore the possible presence of pathogens. Testing for the indicator is far cheaper than testing for every pathogen individually.
Turbidity and sediment pollution: Suspended sediment blocks light, so submerged plants and algae lose productivity; it clogs fish gills and smothers spawning gravel. It also carries adsorbed phosphorus and pesticides, so sediment control is nutrient control.
Septic systems: Household wastewater settles in a tank and the liquid infiltrates a drain field where soil organisms treat it. Failures happen when the field is saturated, undersized or too near the water table, and the result is nutrient and pathogen loading to groundwater.
What tertiary treatment removes: Nitrogen and phosphorus, plus disinfection. Primary is physical settling and secondary is biological removal of organic matter — neither removes much nutrient, which is why plants without tertiary treatment still contribute to eutrophication.
Mercury methylation: Anaerobic bacteria in sediment convert inorganic mercury into methylmercury, which is fat-soluble and therefore biomagnifies. Reservoir flooding creates exactly these conditions, which is why new reservoirs often carry fish consumption advisories.
Endocrine disruptors: Compounds that mimic or block hormones at very low doses — some pesticides, plasticizers and pharmaceutical residues. They defy the usual dose-response logic because effects can appear at low concentrations and depend on developmental timing.
Acute vs chronic toxicity: Acute effects follow a single large exposure and are what LD50 measures; chronic effects follow small repeated exposures over years and are what most environmental contamination actually causes. Acute testing routinely misses chronic hazards.
Bioremediation: Using microbes or plants to break down or take up contaminants in place — bacteria on an oil spill, plants drawing metals out of soil. Cheaper and less disruptive than excavation, but slow and only viable for certain contaminants.
The waste hierarchy: Source reduction first, then reuse, then recycling, then energy recovery, then landfill. The order reflects how much embodied energy and material each option preserves, and source reduction leads because it is the only step that avoids the waste entirely.

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.

168 practice questionsEvery one with a written explanation FRQ trainerWritten answers scored against the rubric Env. Science study guideAll units, weights and score data in one place All 9 Env. Science unitsThe full course

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 33 terms with definitions for this unit, all of them on this page.

How should I study Env. Science Unit 8?

Read the 5 lessons below first — about 65 minutes — then drill the 33 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.