pollution-and-climate BOD Tap / Space to flip
pollution-and-climate Biological Oxygen Demand. Amount of dissolved O₂ used by decomposers to break down organic matter. High BOD = polluted water.
Unit 8 · 7–10% of exam
Aquatic & Terrestrial Pollution
Point vs. non-point sources, BOD/DO, eutrophication, heavy metals, biomagnification, solid & hazardous waste. Eutrophication and biomagnification get extra depth on the priority page.
Must-know content
- Point source — single, identifiable location: pipe, factory smokestack, oil tanker leak. Easier to regulate.
- Non-point source — diffuse origin: agricultural runoff, urban stormwater, atmospheric deposition. Hardest to regulate; the largest share of US water pollution.
- Eutrophication chain: N/P enrichment → algal bloom → algae die → bacterial decomposers proliferate → BOD ↑, DO ↓ → hypoxia → fish kill → "dead zone" (e.g., Gulf of Mexico from Mississippi runoff).
- BOD (Biological Oxygen Demand): O₂ consumed by decomposers. High BOD = polluted water.
- DO (Dissolved Oxygen): O₂ available for aquatic life. Healthy water has DO > 6 mg/L. Inversely related to BOD; warmer water also holds less DO.
- Sewage treatment:
- Primary — physical screening, settling.
- Secondary — biological (aerobic bacteria) reduces BOD.
- Tertiary — chemical removal of N, P. Disinfection (Cl₂, UV, ozone).
- Heavy metals (Hg, Pb, As): bioaccumulate within organisms; biomagnify up food chains. Mercury from coal burning + gold mining; bacteria methylate it (CH₃Hg) → tuna and swordfish concentrate it; neurotoxic in humans.
- Bioaccumulation — buildup in ONE organism over time. Biomagnification — concentration increases UP food chain (DDT in plankton → small fish → osprey → eggshell thinning).
- Solid waste: US generates ~4.9 lb per person per day. ~50% landfill, ~25% recycle/compost, ~25% incinerate. Plastics are the largest growth.
- Sanitary landfill — clay/plastic liner stops leachate; methane vents (often captured for energy).
- Incineration — 90% volume reduction; produces ash, dioxins, heavy metals. Energy can be recovered (waste-to-energy).
- Hazardous-waste laws: RCRA (cradle-to-grave tracking) and CERCLA / Superfund (cleanup of abandoned sites).
- Pathogens & waterborne disease: cholera, typhoid, giardia. Major mortality cause in developing world.
- LD50 — dose lethal to 50% of test population. Lower LD50 = MORE toxic.
- POPs (Persistent Organic Pollutants): DDT, PCBs, dioxins. Long-lived, lipid-soluble, biomagnify, transported by wind across continents. Stockholm Convention restricts.
- Endocrine disruptors — chemicals that mimic hormones (e.g., BPA, atrazine). Affect reproduction and development.
Example questions
MCQ Mercury accumulating to higher concentrations as it moves from plankton to small fish to tuna is an example of: (A) Bioaccumulation (B) Biomagnification (C) Eutrophication (D) Photolysis
Answer: B. Biomagnification = increasing concentration ACROSS trophic levels. Bioaccumulation refers to the buildup within a single organism over its lifetime.
FRQ Explain how nitrogen runoff from a farm causes a dead zone.
Answer: Excess fertilizer nitrogen (and often phosphorus) washes off cropland into waterways during rain. The added nutrients act as fertilizer for aquatic algae, triggering an algal bloom at the surface. When the algae die, decomposer bacteria proliferate to break them down, consuming large amounts of dissolved oxygen (BOD spikes; DO drops). Aerobic organisms — fish, crabs, shrimp — die or flee, creating a hypoxic dead zone where little life can survive. The Gulf of Mexico hypoxic zone, fed by the Mississippi watershed, can exceed 20,000 km² in summer.
MCQ During which step of sewage treatment do aerobic bacteria reduce BOD? (A) Primary (B) Secondary (C) Tertiary (D) Disinfection
Answer: B. Secondary treatment is biological — aerobic bacteria in aeration tanks consume organic waste, dramatically lowering BOD before water moves to tertiary or disinfection.
Drill flashcards
pollution-and-climate Dissolved oxygen (DO) Tap / Space to flip
pollution-and-climate O₂ available in water for aquatic life. Inversely related to BOD; higher temperature lowers DO solubility.
pollution-and-climate Eutrophication Tap / Space to flip
pollution-and-climate Nutrient enrichment (N, P) → algal bloom → algae die → bacterial decomposition spikes → O₂ depleted → fish kill.
pollution-and-climate Bioaccumulation Tap / Space to flip
pollution-and-climate Buildup of toxin (e.g., DDT, mercury) within an individual organism over its lifetime.
pollution-and-climate Biomagnification Tap / Space to flip
pollution-and-climate Toxin concentration increases up the food chain because each predator eats many prey. Top predators most affected.
Unit 8 Point-source pollution Tap / Space to flip
Unit 8 Comes from a single, identifiable source — pipe, factory smokestack, tanker spill. Easier to regulate.
Unit 8 Non-point-source pollution Tap / Space to flip
Unit 8 Diffuse, multiple sources — agricultural runoff, urban stormwater. Hardest to regulate. Largest share of water pollution.
Unit 8 Dead zone (hypoxic zone) Tap / Space to flip
Unit 8 Region with O₂ too low to sustain life. Caused by eutrophication (e.g., Gulf of Mexico from Mississippi runoff).