Unit 8: Pollution, Ecosystems, and Human Health

Sources of Pollutants (8.1)

• Point Source Pollution:     * Definition: A pollutant that enters the environment from a single, easily identified and confined place where you can directly “point” to the origin.     * Examples:         * A waste discharge pipe from a factory or sewage treatment plant.         * Smokestacks from coal-fired power plants releasing $CO_2$, $NO_x$, $SO_2$, and particulate matter ($PM$).         * Animal waste runoff from a Concentrated Animal Feeding Operation (CAFO) containing ammonia ($N$) and fecal coliform bacteria.         * The BP Oil Spill, which released hydrocarbons and benzene from a specific blowout point.
• Nonpoint Source Pollution:     * Definition: Pollutants entering the environment from many diffused places at once, making it difficult to “point” to one individual source of origin.     * Examples:         * Urban runoff: Motor oil, nitrate fertilizer, road salt, and sediment washed from many city streets and lawns.         * Pesticides: Sprayed on agricultural fields and carried by wind or washed off large agricultural regions into bodies of water.         * Watersheds: Estuaries and bays are often polluted by many nonpoint sources from the large areas of land that drain into them.
• Pollutants vs. Pollution for FRQs:     * Pollutants: Specific chemicals or groups of chemicals from specific sources with specific environmental and human health effects (e.g., Mercury, Lead, $SO_2$). Using specific pollutant names is much more likely to earn credit on an AP Environmental Science (APES) Free Response Question (FRQ).     * Pollution: A vague, nondescript term for any substance harmful to the environment. This term is generally unacceptable on an APES FRQ unless referring to specific categories like Thermal pollution, Noise pollution, or Sediment pollution.

Human Impacts on Ecosystems (8.2)

• Range of Tolerance:     * Organisms have a range of tolerance for abiotic conditions in their habitat, including $pH$, temperature, salinity, sunlight, and nutrient levels (ammonia, phosphate).     * Range also applies to human-released pollutants. Outside the optimum range, organisms experience physiological stress, including:         * Limited growth.         * Reduced reproductive function.         * Difficulty respiring (breathing) or asphyxiation (suffocation).         * Hormonal disruption.         * Death (at high concentrations).
• Environmental Effects of Acid Rain:     * As $pH$ decreases (becomes more acidic), population declines occur outside the optimal range.     * Causes of death at low $pH$: Aluminum toxicity and disrupted blood osmolarity (the balancing of $Na^+$ and $Cl^-$ is disrupted).     * Indicator Species: Used to determine ecosystem health. For example, high populations of whitemoss/filamentous algae indicate a $pH < 6.0$, while high crustacean populations indicate a $pH > 6.0$.
• Coral Reef Degradation:     * Mutualism: Corals exist in a mutualistic relationship with photosynthetic algae called zooxanthellae. Algae provide sugar; coral provide $CO_2$ and detritus (nutrient-containing organic matter).     * Coral Bleaching: Algae have narrow temperature tolerances. When ocean temperatures rise due to greenhouse gas emissions, algae leave the reef. Coral loses color and becomes stressed and vulnerable to disease/starvation.     * Other Threats:         * Sediment pollution: Increases turbidity, reducing sunlight for photosynthesis.         * Toxicants: Sunscreen chemicals, roadway oil, and pesticides.         * Nutrient Pollution ($P$ and $N$): Ammonia from animal waste and nitrates/phosphates from fertilizers.         * Overfishing and bottom trawling: Destroys physical reef structures and stirs up sediment.
• Oil Spill Impacts:     * Direct Toxicity: Hydrocarbons in petroleum are toxic and can be ingested or absorbed through gills/skin.     * Physical Effects: Oil coats bird feathers and marine mammal fur. It can sink to the bottom, killing bottom-dwellers through suffocation or toxicity.     * Economic Consequences: Decreased tourism and fishing industry revenue.     * Estuaries: Oil can settle in the roots of mangroves or salt marshes, killing grasses and leading to coastline erosion.
• Oil Spill Cleanup Methods:     * Containment: Booms on the surface to contain the spread.     * Extraction: Ships with vacuum tubes or skimmers handle surface oil.     * Physical: Removing oil from rocks/sand with towels, soaps, and shovels.     * Chemical Dispersants: Sprayed to break up oil and sink it, though this can smother bottom-dwellers.     * Burning: Burning off the surface oil slicks.

Endocrine Disruptors and Heavy Metals (8.3)

• Endocrine Disruptors:     * Definition: Chemicals that interfere with the endocrine (hormonal) system by binding to cellular receptors, either blocking hormones or amplifying their effects.     * Sources: Human medications in sewage, herbicides, and industrial chemicals.     * Atrazine: A broad-spectrum herbicide that binds to receptors in male frogs that convert estrogen into testosterone. This leads to feminization (egg development in testes) and low sperm counts.     * DDT: Insecticide that persists in the environment.     * Phthalates: Used in plastics (e.g., #3 plastic) and cosmetics; enter water through trash dumping or factory waste.
• Mercury ($Hg$):     * Sources: Coal combustion, trash incineration, medical waste burning, and heating limestone for cement.     * Mechanism: Bacteria in water convert elemental mercury into highly toxic methylmercury.     * Health Effects: A neurotoxicant that damages the central nervous system; also acts as a teratogen (harmful to fetuses) and endocrine disruptor (interferes with the menstrual cycle, estrogen, and insulin).
• Arsenic ($As$) and Lead ($Pb$):     * Arsenic: Naturally occurs in rocks; dissolution is worsened by mining. Anthropogenic sources include pesticides, wood treatment, and coal ash. It is carcinogenic (lungs, bladder, kidney).     * Lead: Found in old paint and water pipes, and soil contaminated by leaded gas exhaust. It is a neurotoxicant (especially damaging to children's central nervous systems) and endocrine disruptor.
• Coal Ash: A source of mercury, lead, and arsenic. It is often stored in ponds lined with plastic, but these can leach into groundwater or overflow into surface waters and fields.

Watersheds and Nutrient Pollution (4.6 & 8.4)

• Characteristics of a Watershed:     * Defined as all land draining into a specific body of water (river, lake, etc.).     * Divided by ridges (higher elevation land).     * Drainage is influenced by vegetation (more vegetation equals more infiltration), slope (steeper slope equals faster runoff/erosion), and soil permeability.
• Chesapeake Bay Case Study:     * A $6$-state drainage region. It is a productive estuary with salt marshes.     * Ecosystem Services: Tourism revenue, water filtration by grass roots, habitat for fish/crabs, and storm protection.     * Human Impacts: Nutrient pollution ($N$ and $P$) from sewage plants, CAFOs, and lawn fertilizers. Sediment pollution from deforestation and urbanization increases turbidity.
• Wetlands and Mangroves:     * Wetlands: Areas where soil is submerged/saturated for part of the year but shallow enough for emergent plants (e.g., cattails, reeds).     * Mangroves: Provide timber, coastal protection, carbon storage ($3 imes$ to $5 imes$ higher than tropical forests), and water filtration (treating aquaculture effluent).     * Threats: Commercial development, dam construction (reduces water and nutrient flow), overfishing, and pollutants.

Eutrophication and Thermal Pollution (8.5 & 8.6)

• Eutrophication Process:     1. Input of limiting nutrients ($N$ and $P$).     2. Algal bloom covers the surface, blocking sunlight.     3. Sub-surface plants die.     4. Algae die; aerobic bacteria decompose them using up dissolved oxygen ($DO$).     5. Low $DO$ (hypoxia) kills fish and aquatic organisms.     6. Positive Feedback Loop: Dead organisms lead to more bacterial decomposition, which further decreases $DO$.
• Oligotrophic vs. Eutrophic:     * Oligotrophic: Low nutrient levels, stable algae, and high dissolved oxygen.     * Eutrophic: High nutrient levels, low dissolved oxygen. Bodies of water naturally transition over time through succession.
• Thermal Pollution:     * Oxygen Solubility: There is an inverse relationship between temperature and $DO$. As temperature increases, $DO$ decreases: $T ↑, DO ↓$.     * Thermal Shock: Heat increases the respiration rate of aquatic organisms while oxygen levels are decreasing, potentially leading to suffocation.     * Sources: Nuclear and coal power plants return warm water used for cooling steam; urban runoff from hot asphalt also contributes.     * Solution: Cooling towers or ponds hold water to cool it before it is released back into the environment.

Persistent Organic Pollutants and Biomagnification (8.7 & 8.8)

• Persistent Organic Pollutants (POPs):     * Definition: Synthetic, long-lasting, carbon-based molecules that do not easily break down.     * Traits: Fat-soluble, meaning they accumulate in fatty tissues rather than being excreted through urine/blood.     * Transport: They can travel long distances via wind and water.     * Examples: $DDT$ (insecticide), $PCBs$ (industrial additives), $PBDEs$ (flame retardants), Dioxins (byproducts of fertilizer production and combustion).
• Bioaccumulation vs. Biomagnification:     * Bioaccumulation: The absorption and concentration of a compound in a single organism over time.     * Biomagnification: The increase in concentration of fat-soluble substances per unit of body tissue at successively higher trophic levels.     * 10% Rule Impact: Because organisms consume more biomass at each successive level to get energy, they ingest higher total loads of toxins.
• Case Studies:     * DDT: Led to thin eggshells in predatory birds like eagles and osprey, causing population declines and prompting the Endangered Species Act of $1973$.     * Methylmercury: Reaches highest levels in top predators like tuna and sharks. It is a neurotoxicant in humans, especially affecting developing fetuses.

Solid Waste and Reduction (8.9 & 8.10)

• Municipal Solid Waste (MSW): Trash from cities. Typical composition: $\frac{1}{3}$ paper, $\frac{2}{3}$ organics (compostable).
• Sanitary Municipal Landfill Components:     * Clay/Plastic Liner: Prevents pollutants from leaking into soil/groundwater.     * Leachate Collection System: Pipes at the bottom to collect and treat contaminated water.     * Methane Recovery System: Pipes to collect methane ($CH_4$) for heat or electricity generation.     * Clay Cap: Covers the landfill when full to reduce smell and allow plant growth.
• Decomposition in Landfills: Very low due to lack of oxygen ($O_2$), moisture, and organic matter diversity.
• Environmental Issues: Groundwater contamination and greenhouse gas ($CO_2$ and $CH_4$) release.
• NIMBY (Not In My Back Yard): Opposition to landfills due to smell, sight, and safety concerns, often leading to landfills being placed near low-income/minority communities.
• The Three Rs:     1. Reduce: Most sustainable; decreases resource harvesting and energy use.     2. Reuse: Next most sustainable; extends product life without extra energy.     3. Recycle: Least sustainable of the three; energy-intensive to sort and process.         * Closed-loop: Glass turned back into glass.         * Open-loop: Plastic bottles turned into fabric.
• Composting: Decomposition of organic matter under aerobic conditions. Requires a Carbon-to-Nitrogen ratio of approximately $30:1$.
• Waste-to-Energy: Burning MSW or methane to turn a turbine: $\text{Heat} → ext{Water} → ext{Steam} → ext{Turbine} → ext{Generator}$.

Sewage Treatment (8.11)

• Primary Treatment: Physical removal of large debris (toilet paper, leaves, plastic) using screens and grates, and removing grit/sediment in chambers.
• Secondary Treatment: Biological process where bacteria break down organic matter into $CO_2$ and nutrients. The tank is aerated (bubbled with $O_2$) to support aerobic decomposition. Removes $70 imes 10^{-2}$ of Phosphorus and $50 imes 10^{-2}$ of Nitrogen.
• Tertiary Treatment: Chemical or ecological filters applied to remove remaining nitrates and phosphates to prevent eutrophication in discharge water. This step is expensive.
• Disinfection: Final step using Chlorine, Ozone, or UV light to kill remaining pathogens (e.g., E. coli).
• Effluent: The treated liquid waste discharged into surface waters.
• Sewage Sludge: Inorganic solid waste collected at the bottom of tanks; it can be landfilled, burned, or used as fertilizer pellets.

Toxicity and Human Health (8.12 - 8.15)

• LD50 (Lethal Dose 50%):     * Definition: The dose or concentration of a chemical that is lethal to $50 imes 10^{-2}$ of the population studied.     * Measurements: expressed as $mass ext{(mg)}/body mass ext{(kg)}$ or $ppm$.
• Dose-Response Curve:     * Graphed with percent mortality on the y-axis and dosage on the x-axis.     * Threshold: The lowest dose where an effect starts to occur.     * ED50: The dose that causes a non-lethal effect (e.g., infertility) in $50 imes 10^{-2}$ of the population.     * Human safety levels are typically determined by taking the $LD_{50}$ and dividing by $1,000$.
• Specific Human Health Issues:     * Dysentery: Bacterial infection from feces-contaminated water; causing severe dehydration.     * Mesothelioma: Cancer caused primarily by exposure to asbestos (found in old insulation).     * Tropospheric Ozone: Irritates respiration muscles, causing shortness of breath and worsening asthma.
• Infectious Diseases and Pathogens:     * Pathogen: A living organism (virus, bacteria, fungus) that causes disease.     * Vector: An organism (rat, mosquito) that carries and transmits the pathogen.     * Climate Change: Shifting equatorial climate zones allow vectors (mosquitoes) to spread to previously colder temperate regions.     * Diseases:         * Plague: Bacteria transmitted by flea bites.         * Tuberculosis (TB): Bacterial infection of the lungs spread by respiratory droplets; kills approximately $2 imes 10^6$ people annually.         * Malaria: Parasitic protist transmitted by mosquitoes; common in sub-Saharan Africa.         * Cholera: Bacterial infection from contaminated water; causes severe vomiting and diarrhea.         * SARS/MERS: Coronaviruses causing respiratory failure/pneumonia.         * Zika/West Nile: Viral infections transmitted by mosquito bites.

Questions & Discussion

• FRQ 8.1: Describe the difference between a point and nonpoint source. Identify a point and nonpoint source of $NO_x$.
• FRQ 8.2 (ANWR Math): Given a demand of $20 imes 10^6$ barrels of oil per day and an estimated $10 imes 10^9$ barrels of oil in ANWR, calculate the number of supply days.     * Calculation: $\frac{10 imes 10^9}{20 imes 10^6} = 500 ext{ days}$.
• FRQ 8.3: Identify a toxic metal other than mercury and describe its environmental introduction.
• FRQ 4.6: Explain how deforestation leads to changes in water quality within a watershed.
• FRQ 8.4: Describe a human activity leading to increased phosphorus in estuaries and a step to reduce it.
• FRQ 8.5: Identify based on a map which state's fishing industry likely had lower profits in $2011$ due to dead zones.
• FRQ 8.6: Explain how nuclear power generation might decrease biodiversity in nearby aquatic ecosystems via thermal pollution.
• FRQ 8.7: Explain why PCBs have longer-lasting impacts than synthetic nitrates (Focus on persistence and fat-solubility).
• FRQ 8.8: Identify a testable hypothesis for studying "smedsium" biomagnification from bike tires.
• FRQ 8.9: Propose a government solution to reduce MSW volume in landfills by $15 imes 10^{-2}$ based on a composition graph (e.g., composting mandates).
• FRQ 8.10 (Device Math): Calculate the percent increase in mobile devices from $30 imes 10^6$ in $1998$ to $180 imes 10^6$ in $2007$. Also calculate total gold used in $2007$ if each device has $0.03 ext{ g}$.     * Percent Increase: \frac{180 - 30}{30}  100 = 500 imes 10^{-2}.     * Gold: $180 imes 10^6 imes 0.03 = 5.4 imes 10^6 ext{ grams}$.
• FRQ 8.11: Identify a step in primary treatment on a diagram and a pollutant it removes.
• FRQ 8.12 & 8.13: Use rat dose-response data to determine human safety levels and identify the threshold dose.
• FRQ 8.14: In a study on fecal coliform bacteria near Huangcang, identify the control site and a disease to test for (Dysentery or Cholera).
• FRQ 8.15: Based on a map, claim a region likely to have a high incidence of Cholera.