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Unit 8 · Aquatic & Terrestrial Pollution Unit Hub Flashcards Cheat Sheet Essentials Visual Review MC Practice FRQ Practice

AP Environmental Science Unit 8 Visual Review

A 15-slide visual walkthrough of every Topic 8.1-8.15 concept — pollution sources, endocrine disruptors, eutrophication, bioaccumulation, waste disposal, toxicology, and pathogens — built right into the page.

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TOPIC 8.1 Sources of Pollution pipe Point source single, identifiable Nonpoint source diffuse, many small inputs Point sources A single, identifiable location — a factory discharge pipe, a smokestack. Easier to regulate and monitor because you can point to exactly where the pollution enters. Nonpoint sources Diffuse and widespread — agricultural runoff, urban stormwater, atmospheric deposition. Much harder to regulate since there's no single pipe to inspect — this is now the LARGER source of US water pollution overall. Point-source pollution has fallen sharply since the Clean Water Act; nonpoint sources are the harder remaining problem. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.2 Human Impacts on Ecosystems Habitat loss Development, farming, and logging fragment or destroy habitat outright. Pollution Chemical, thermal, and noise pollution stress or kill sensitive species directly. Resource overuse Overfishing, overgrazing, and groundwater depletion exceed natural regeneration rates. The shared consequence: lost ecosystem services Every impact above degrades the services an ecosystem provides — recall Topic 2.2's four categories (provisioning, regulating, supporting, cultural). A degraded wetland (8.4) no longer filters water or buffers floods; a polluted river no longer supports fisheries — the rest of Unit 8 details these mechanisms. Unit 8 is largely about the specific mechanisms behind this one general idea: human activity degrades ecosystem function. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.3 Endocrine Disruptors cell receptor normal hormone cell receptor mimics/blocks it How they interfere These chemicals are shaped closely enough to natural hormones that they bind the same receptors — either MIMICKING a hormone's signal or BLOCKING the real one from binding. Effective at tiny concentrations Hormone systems normally respond to trace amounts, so endocrine disruptors cause real harm at concentrations far below what would register on a standard LD50 test (8.12). BPA and certain pesticides are classic endocrine disruptors linked to reproductive and developmental effects in wildlife. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.4 Human Impacts on Wetlands & Mangroves wetland / mangrove buffer draining / filling Why they're so valuable Wetlands filter pollutants, absorb floodwater, and serve as nurseries for fish and birds. Coastal mangroves add storm-surge protection and store large amounts of carbon in their soil. Why they keep disappearing Drained or filled for farmland and coastal development, since "unused" wetland looks less economically valuable than farmland or real estate — a classic case of unpriced services. Coastal areas with intact mangroves consistently suffer less storm damage than those where mangroves were cleared. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.5 Eutrophication dissolved oxygen time after nutrient input → algal bloom hypoxic "dead zone" The chain reaction Excess nitrogen/phosphorus (fertilizer runoff, sewage) fuels explosive algae growth. The algae die, and decomposer bacteria consume huge amounts of dissolved oxygen breaking them down. The result: a dead zone Oxygen falls so low (hypoxic) that fish and other aerobic organisms suffocate or flee. The Gulf of Mexico's dead zone, fed by Mississippi River farm runoff, is a real example. Eutrophication is the ecosystem-level outcome of the phosphorus and nitrogen cycle disruptions from Topics 1.5-1.6. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.6 Thermal Pollution power plant warm cooling water river / lake Where it comes from Power plants and factories pull in water to cool equipment, then discharge it back several degrees warmer than the surrounding water. This is thermal pollution, not chemical pollution. Why warmer water is dangerous Warm water holds LESS dissolved oxygen — stressing cold-water species like trout and salmon. It also speeds up fish metabolism, raising their oxygen demand right when supply drops. Thermal pollution creates a double squeeze: less oxygen available, at the exact moment organisms need more of it. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.7 Persistent Organic Pollutants (POPs) weeks typical pesticide ~10-15 yrs DDT (soil) decades+ PCBs Persistence = time to break down in the environment. POPs resist normal decomposition for years to decades. Why persistence matters Long persistence means more time to travel, build up, and enter food chains — setting up bioaccumulation and biomagnification (8.8). DDT was banned in the US in 1972, yet residues are still detectable in soil and wildlife today. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.8 Bioaccumulation & Biomagnification plankton — 0.05 ppm small fish — 0.5 ppm big fish — 5 ppm osprey — 50 ppm Bioaccumulation A toxin builds up WITHIN one organism over its lifetime because it's absorbed faster than it's excreted — especially fat-soluble toxins like DDT, stored in fatty tissue. Biomagnification Concentration multiplies UP the food chain — each predator eats many prey, inheriting all their accumulated toxin. DDT thinning osprey eggshells is the classic example. Top predators — ospreys, eagles, orcas, humans eating large fish — absorb the compounded toxin load of everything below them. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.9 Solid Waste Disposal Landfill lined to stop leachate Incineration Landfills Modern landfills use liners to prevent leachate (contaminated liquid) from reaching groundwater. Trash decomposing anaerobically also releases methane gas. Incineration Burning waste drastically reduces its volume and can generate electricity — but releases air pollutants (7.1) and leaves toxic ash that still needs landfill disposal. Every disposal method just moves waste to a different medium — land, air, or ash — none of it truly disappears. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.10 Waste Reduction Methods REDUCE (best) REUSE RECYCLE / COMPOST DISPOSE (last resort) Why the order matters Waste never produced (reduce) needs no further handling at all. Recycling still consumes energy to collect, sort, and reprocess — better than a landfill, but not free. Composting Diverts food and yard waste from landfills (where it would decompose anaerobically and release methane), instead breaking it down aerobically into usable soil nutrients — closing the loop back to Topic 1.4's carbon cycle. This hierarchy is Unit 8's central theme in miniature: prevention beats cleanup, every time. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.11 Sewage Treatment Primary settle out solids Secondary bacteria break down waste Tertiary removes N, P, pathogens Not every plant reaches tertiary — it's the most expensive, cleanest-output stage. Three stages Primary: physical settling removes large solids. Secondary: bacteria digest dissolved organic matter. Tertiary: chemical/ filtration steps remove nutrients & pathogens before release. Skipping tertiary treatment is exactly how excess nitrogen and phosphorus reach waterways and trigger eutrophication (8.5). The Review Hub · AP Environmental Science Unit 8 TOPIC 8.12 Lethal Dose 50% (LD50) LD50 (mg/kg, log) lower bar = more toxic Botulinum (extremely toxic) DDT table salt (low toxicity) The definition The dose (usually mg of substance per kg of body weight) that kills 50% of a test population. It's a standard way to compare the acute toxicity of different substances. Lower LD50 = more toxic It takes only a TINY dose of botulinum toxin to kill half a population, but a LARGE dose of table salt — so botulinum's LD50 is far lower, making it dramatically more acutely toxic. LD50 only measures acute, short-term death risk — it says nothing about chronic harm at low doses (see 8.13). The Review Hub · AP Environmental Science Unit 8 TOPIC 8.13 Dose Response Curve % population responding dose (increasing) → 50% LD50 dose threshold Reading the S-curve As dose rises, the percent of the population responding (getting sick, dying) increases — typically forming an S-shape. LD50 (8.12) is just one specific point ON this curve, at 50%. Thresholds matter Many curves show a threshold — a dose below which no measurable effect occurs at all. Some toxins (and radiation) are modeled as having NO safe threshold whatsoever. “The dose makes the poison” — this curve is the visual proof that toxicity is about quantity, not just presence. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.14 Pollution and Human Health Acute short exposure, immediate effect Chronic long-term, low-level exposure Acute hazards A single high-dose exposure with fast, obvious effects — carbon monoxide poisoning, a chemical spill. Easy to trace back to its cause because of the fast onset. Chronic hazards Repeated low-level exposure over years — smog (7.2), radon (7.5), or POPs (8.7). Harder to link to a specific cause since symptoms (cancer, organ damage) emerge over decades. Risk always combines three variables: how toxic a substance is, how much you're exposed to, and for how long. The Review Hub · AP Environmental Science Unit 8 TOPIC 8.15 Pathogens & Infectious Diseases poor sanitation contaminated water human illness Waterborne pathogens Bacteria, viruses, and parasites (cholera, E. coli, giardia) spread when sewage contaminates drinking water — exactly what sewage treatment (8.11) exists to prevent. A global health burden Waterborne disease remains a leading cause of death in regions lacking treated water and sanitation infrastructure — disproportionately affecting children in developing nations. This ties Unit 8 back to Unit 3's population dynamics — sanitation access is a major lever on death rates worldwide. The Review Hub · AP Environmental Science Unit 8
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How to use the visual review

Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I draw this from memory and explain it?"

Use the fullscreen button () on desktop for the best experience. Use arrow keys to navigate. Tap "Show all slides" to jump around.

This covers every one of Unit 8's 15 CED topics, from point/nonpoint sources through pathogens and infectious disease.