AP Environmental Science Unit 8: Aquatic and Terrestrial Pollution Study Guide

Introduction to Human Environmental Impact and Range of Tolerance

• General Human Impact: Human activities often result in negative consequences for the environment due to the use of various chemicals, the release of trash, and the emission of air pollution from multiple sources.
• Range of Tolerance: Every organism and environment has a range of conditions it can withstand.
  • Optimal Zone: The range where an organism is most comfortable and functions at its best (e.g., a polar bear in its natural cool climate).
  • Zone of Physiological Stress: Ranges where conditions are sub-optimal. Organisms may experience changes in growth, reduced reproduction, or general discomfort.
  • Zone of Intolerance: Ranges that are completely not tolerated by the species. Exposure to these conditions typically results in death.
• Examples of Tolerance Deviations:
  • Temperature: Polar bears experiencing temperatures much hotter or much colder than their natural range.
  • pH Levels: Acid rain can change the pH of soil and water bodies. Amphibians are particularly sensitive, possessing a very narrow range of tolerance for pH, leading to physiological stress or death when levels shift.

Specific Environmental Pollutants and Their Effects

• Coral Reefs:
  • Climate change causes increasing ocean temperatures worldwide.
  • Coral Bleaching: A process where coral turns white and dies due to the stress of rising temperatures.
• Oil Spills:
  • Notable Incidents: The Deepwater Horizon spill ($2011$) and the Exxon Valdez accident (the $1980s$).
  • Physical Properties: Oil is hydrophobic and floats on top of the water, which allows it to spread rapidly.
  • Environmental Damage:
    • Coats bird feathers, destroying their natural insulation and buoyancy.
    • Oil can sink, covering the benthic area (sea floor) and killing bottom-dwelling species.
    • Chemicals in oil are toxic, making fish in the area unsafe for human consumption.
• Plastics:
  • Degradation: Plastics do not decompose; they photo-degrade into smaller and smaller pieces.
  • Marine Impact: Small animals often mistake small plastic pieces for food and ingest them. As plastics break down, they release toxins into the water.
• Endocrine Disruptors:
  • These chemicals interfere with the body's hormones by competing with them, altering them, or preventing them from reaching cell receptors.
  • Consequences: Can result in birth defects, developmental issues, reproductive effects, and compromised immune systems.

Identifying Sources of Pollution

• Point Source Pollution: Pollution emitted directly from a specific, identifiable source.
  • Examples include a smokestack or an outflow pipe at an industrial facility.
  • Rule of thumb: You can literally point at exactly where the pollution is originating.
• Non-Point Source Pollution: Pollution that is diffuse and spread out over a wide area.
  • Often influenced by runoff (water collecting materials as it moves across the land).
  • Example: Fertilizers applied to a farm field that are washed into a river by rain.

Nutrient Excess and Eutrophication

• Nutrient Excess: Caused by nitrogen and phosphorus-based chemicals, typically from inorganic fertilizers.
• The Process of Eutrophication:
  1. Runoff carries excess nutrients into a waterway.
  2. Algae populations increase dramatically (algal blooms).
  3. Thick algae layers block sunlight from reaching deeper water.
  4. Submerged plants are unable to photosynthesize and die.
  5. Algae have short lifespans and die off in large quantities.
  6. Decomposers (bacteria) break down the dead algae and plants.
  7. Oxygen Depletion: The decomposition reaction consumes high amounts of dissolved oxygen ($DO$).
  8. The water becomes hypoxic (lacking oxygen), leading to massive fish and plant die-offs.
• Dead Zones: Hypoxic areas resulting from severe eutrophication.
  • Gulf of Mexico: A famous dead zone forms here most summers due to nutrients from the Mississippi River watershed.
  • Summer Stratification: In the summer, the Gulf of Mexico water separates into hot and cold layers. This prevents oxygen-rich surface water from mixing with deeper, hypoxic water, leaving the bottom layer completely dead.

Water Quality Measurement: Oxygen Sag Curve and BOD

• Biological Oxygen Demand (BOD): The amount of oxygen used up per quantity of water by the organisms living there.
  • Low BOD: Indicates the water is clean and full of oxygen.
  • High BOD: Indicates the water is polluted and organisms are consuming oxygen rapidly.
• The Oxygen Sag Curve: A graph charting the relationship between $DO$ and $BOD$ relative to a pollution point source.
  • At the Point Source: $BOD$ spikes and $DO$ begins to drop.
  • The "Sag": As the distance downstream increases, the high biological demand "chews up" the available oxygen, creating a dip (sag) in the $DO$ levels.
  • Recovery: Further downstream, as the pollution is processed or diluted, $BOD$ declines and $DO$ eventually recovers, allowing fish to return.

Bioaccumulation and Biomagnification

• Mercury Pollution: Burning coal releases mercury into the atmosphere. It eventually settles into waterways and converts into a toxic form called methylmercury.
• Bioaccumulation: The process where a compound (like methylmercury) builds up in the tissues (usually fats) of a single organism over its lifetime due to repeated exposure.
• Biomagnification: The process where the concentration of a toxin increases as it moves up the food chain.
  • Example Chain: methylmercury enters krill $\rightarrow$ eaten by small fish $\rightarrow$ eaten by medium fish $\rightarrow$ eaten by big fish.
  • Top-level predators end up with the highest, most dangerous levels of toxic substances.

Thermal Pollution

• Definition: Environmental damage caused by the release of heated water into a natural body of water.
• Source: Coal-fired and nuclear power plants boil water to spin turbines for electricity. If the water is not sufficiently cooled before being released back into the environment, it causes thermal shock.
• Effects:
  • Fish may avoid the heated location.
  • Gas Solubility: Warmer water cannot hold as much dissolved oxygen as cooler water.
  • Organisms experience physiological stress due to temperature shifts and oxygen deprivation.

Terrestrial Pollution and Solid Waste Management

• Sanitary Landfills: Engineering pits designed to hold trash safely.
  • Liners: Plastic or other barriers that prevent fluids from leaking into the soil.
  • Leachate Collection System: Collects the fluids (leachate) that accumulate from rainwater and decomposition within the landfill.
  • Methane Collection: Decomposition produces methane, which is flammable and explosive. It must be collected and can be burned to produce electricity.
  • Capping: Once a landfill is full, it is capped with a liner and soil (often planted with grass) to revert it to green space.
• Incineration: Burning trash at very high temperatures. It effectively reduces the volume of the waste but releases significant air pollution.
• Recycling: The process of reusing materials like some plastics. While beneficial, it is energy-intensive and expensive, and not every community has the infrastructure to support it.

Sewage Treatment Processes

• Primary Treatment (Physical): The removal of large objects (leaves, trash, sticks) from water using grates and screens.
• Secondary Treatment (Biological): Bacteria are used to break down organic waste, such as human feces, food waste, and detergents. Aeration tanks are often used to provide oxygen to the bacteria so they work faster.
• Tertiary Treatment (Chemical): The removal of remaining nutrients from the water.
• Disinfection: Prior to release, water is treated to kill remaining pathogens using:
  • Chlorine chemicals.
  • Ozone gas bubbled through the water.
  • UV light (Ultraviolet radiation).

Human Health and Toxicology

• Disease Range Expansion: As climate change warms the planet, the range of vectors (organisms that transmit diseases) like mosquitoes is expanding north and south. Diseases such as West Nile Virus, Zika, and Malaria are spreading to new areas.
• Poverty and Pathogens: Pathogenic spread is highest in areas with a lack of sanitation, dirty water, and no access to water treatment. This is a significant issue in developing countries.
• Lethal Dose 50 (LD50): The dose of a chemical required to kill $50 \%$ of a test population.
  • LD50 Calculation: On a dose-response curve, find $50 \%$ on the y-axis (mortality percentage), move horizontally to the curve, and then move vertically down to the x-axis to find the dosage.
  • Example: A dosage of $100\,mg/kg$ that kills $50 \%$ of the population is identified as the $LD50$.

Significant Environmental Laws

• Clean Water Act: Makes it unlawful to discharge pollutants from a point source into navigable waters.
• Safe Drinking Water Act: Protects underground sources of drinking water, such as aquifers, from contamination.
• Resource Conservation and Recovery Act (RCRA): Governs the monitoring of hazardous waste from "cradle to the grave" (from the moment it is created to the moment it is destroyed).
• Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA/Superfund): Makes companies financially responsible for cleaning up hazardous waste sites they created.
• Delaney Clause: A part of the Food, Drug, and Cosmetic Act that bans food additives known to cause cancer in humans or animals.