Free Unit Notes

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I. Sources of Pollution (Topic 8.1)

A. Point and nonpoint sources

1. Pollution is the addition of a substance or form of energy that harms organisms or the environment.

2. A point source releases pollution from one identifiable location, such as a factory pipe or sewage outfall.

3. Nonpoint source pollution comes from scattered sources, such as fertilizer washed from fields or oil washed from roads. It is harder to trace and control.

4. A watershed is the land area draining into a common water body. Controlling runoff often requires changes throughout the watershed.

II. Human Impacts on Ecosystems (Topic 8.2)

A. Tolerance and habitat damage

1. A range of tolerance includes the conditions an organism can survive. Within its optimum range, it maintains homeostasis, or relatively stable internal conditions.

2. Near tolerance limits, organisms experience stress, slower growth, or reduced reproduction. Beyond those limits, they may die.

3. Turbidity is water cloudiness caused by suspended material. Sediment reduces light for photosynthesis and makes hunting harder for visual predators.

4. Settling sediment can bury eggs and bottom habitats. Vegetated stream buffers and erosion control reduce sediment runoff.

5. Warm water can cause corals to lose their symbiotic algae, producing coral bleaching. Prolonged bleaching can kill corals; sediment and destructive fishing also damage reefs.

B. Oil, metals, and litter

1. Oil hydrocarbons can poison organisms. Oil coating feathers or fur reduces waterproofing and insulation; components reaching sediments can harm bottom-dwelling organisms.

2. Spills can close beaches and fisheries, reducing tourism and fishing income. Booms, skimmers, absorbents, and microbial breakdown help cleanup, but do not remove all oil.

3. Dispersants break oil into droplets rather than eliminate it. They can increase exposure within the water column.

4. Mining, industry, and fossil-fuel combustion release metals that can contaminate surface water and groundwater. Certain microbes convert mercury into highly toxic methylmercury.

5. Litter can entangle animals or block their digestive tracts. Plastics fragment into microplastics, pieces smaller than 5 mm, rather than quickly decomposing.

6. Ocean currents concentrate floating debris in garbage patches. These contain scattered debris and small particles, rather than solid islands.

C. Oxygen depletion

1. Dissolved oxygen (DO) is oxygen gas in water that aquatic organisms use for respiration. It is commonly measured in mg/L.

2. Biochemical oxygen demand (BOD) measures oxygen used by microbes decomposing organic matter under specified conditions. More organic waste generally increases BOD and lowers DO.

3. An oxygen sag curve plots DO against distance downstream from a pollution source. Oxygen falls as microbes decompose waste and may recover as waste declines and oxygen is replenished.

4. Low oxygen can kill sensitive organisms or force them to leave. Continued waste inputs can prevent recovery.

III. Endocrine Disruptors (Topic 8.3)

A. Hormone signaling and effects

1. Hormones are chemical messages that regulate growth, development, and reproduction. An endocrine disruptor interferes with these signals.

2. Disruptors may mimic hormones, block their receptors, or change hormone production and breakdown. Examples include BPA, some pesticides, PCBs, and some phthalates.

3. Exposure can cause developmental abnormalities, reduced fertility, and changes in reproductive traits or sex ratios in wildlife. Effects depend on dose, timing, and species.

4. Reducing chemical releases and properly collecting unwanted medicines can reduce exposure. Standard sewage treatment does not remove every hormone-like chemical.

IV. Human Impacts on Wetlands and Mangroves (Topic 8.4)

A. Ecosystem services

1. Wetlands have soil covered or saturated by water for part or all of the year. They trap sediment, take up nutrients, and support microbes that transform some pollutants.

2. Wetlands improve water quality, store floodwater and carbon, and provide wildlife habitat. Their filtering capacity is limited.

3. Mangroves are salt-tolerant trees and shrubs along tropical and subtropical coasts. Their roots shelter young fish, trap sediment, and reduce wave damage and erosion.

B. Threats and protection

1. Draining or filling wetlands for farms and development removes habitat and flood storage. Dams and dredging alter water flow and sediment supply.

2. Agricultural runoff, industrial waste, and overfishing damage wetlands or the food webs they support.

3. Protection and restoration include limiting development, reducing polluted runoff, restoring natural water flow, and planting appropriate native vegetation.

V. Eutrophication (Topic 8.5)

A. Nutrient enrichment and oxygen loss

1. Eutrophication is nutrient enrichment of water. Cultural eutrophication occurs when human activities accelerate this process through fertilizer runoff, manure, sewage, or phosphate detergents.

2. Added nitrogen or phosphorus can trigger an algal bloom, or rapid algae growth. Phosphorus often limits freshwater production; nitrogen often limits coastal production.

3. Blooms block light, causing submerged plants to die. When algae and plants die, aerobic decomposers consume oxygen as they break down the material.

4. Increased decomposition raises BOD and lowers DO. Fish may die or leave when oxygen use exceeds replacement.

5. Hypoxia means low DO; anoxia means no DO. A dead zone has too little oxygen to support many typical aquatic animals, although some organisms survive.

6. Some blooms produce toxins, but not all do. Oxygen depletion can occur without toxin production.

B. Water conditions and prevention

1. Oligotrophic waters contain few nutrients and generally have low algae growth, clear water, and oxygen-rich deeper layers.

2. Eutrophic waters contain abundant nutrients and greater producer growth. Deeper water is more likely to lose oxygen during decomposition, especially when mixing is limited.

3. Reduce nutrient inputs through careful fertilizer application, manure management, vegetated buffers, wetland protection, and nutrient removal from wastewater.

4. Aeration can temporarily increase oxygen, but it does not stop continued nutrient loading.

VI. Thermal Pollution (Topic 8.6)

A. Causes, effects, and controls

1. Thermal pollution occurs when human-caused temperature changes harm aquatic life. Sources include heated cooling-water discharge, loss of streamside shade, and runoff from hot pavement.

2. At the same pressure and salinity, warmer water holds less oxygen at saturation. Warming also often increases organism and microbial respiration within their tolerance ranges.

3. Lower oxygen availability and higher oxygen demand can stress or kill organisms. A sudden temperature change can cause thermal shock.

4. Cooling towers, cooling ponds, and recirculating systems reduce heated discharges. Streamside trees reduce solar heating; cooling systems may consume water through evaporation.

VII. Persistent Organic Pollutants (POPs) (Topic 8.7)

A. Persistence and movement

1. Persistent organic pollutants (POPs) are carbon-based pollutants that resist environmental breakdown. Examples include the insecticide DDT and industrial chemicals called PCBs.

2. Many POPs dissolve in fat and remain in fatty tissues instead of being quickly removed. They can harm development, immunity, and reproduction.

3. Wind and water carry POPs far from their sources. Contaminated soils, sediments, and old equipment can continue releasing them after new use stops.

4. Restricting production, safely disposing of old materials, and controlling contaminated sites reduce further exposure. Persistence means slow breakdown, not impossibility of breakdown.

VIII. Bioaccumulation and Biomagnification (Topic 8.8)

A. Buildup in organisms and food webs

1. Bioaccumulation is buildup within an organism when uptake exceeds breakdown or removal. Exposure can occur through food, water, or other routes.

2. Biomagnification is increasing pollutant concentration at successively higher trophic levels. Predators retain pollutants from the many contaminated prey they eat.

3. Persistent, readily retained pollutants are most likely to magnify. Top predators can have high concentrations even when environmental concentrations are low.

4. DDT and its breakdown products can thin birds’ eggshells and reduce reproductive success. PCBs can impair development and reproduction.

5. Methylmercury can damage the nervous system, especially the developing brain. Contaminated fish expose humans; other retained pollutants can harm reproductive and circulatory systems.

6. Mercury is an element, so it is not a POP. Methylmercury biomagnifies and binds strongly to tissue proteins; not every accumulating pollutant is stored mainly in fat.

B. Concentrations and evidence

1. For tissue, 1 mg/kg = 1 ppm and 1 µg/kg = 1 ppb. For dilute water, 1 mg/L is approximately 1 ppm.

2. A concentration ratio equals predator concentration ÷ prey concentration. Convert to matching units first; 2.0 mg/kg ÷ 0.20 mg/kg = 10.

3. To test biomagnification, compare the same pollutant in comparable tissues across trophic levels. Use multiple samples and consider age, size, and location.

IX. Solid Waste Disposal (Topic 8.9)

A. Waste types and landfill design

1. Solid waste is discarded material from homes, businesses, industry, and agriculture. Municipal solid waste includes everyday community trash.

2. E-waste consists of discarded electronics. It contains valuable materials but may also contain hazardous metals such as lead and mercury.

3. Hazardous waste is harmful because it is toxic, corrosive, reactive, or easily ignited. It requires suitable handling rather than ordinary disposal.

4. A sanitary landfill compacts and covers waste to reduce pests, odors, and windblown litter.
   a. A bottom liner slows leakage into soil and groundwater. Leachate is contaminated liquid that passes through waste; collection pipes send it for treatment.
   b. A cap limits rainfall entering a closed landfill. Stormwater systems direct runoff away from the waste.
   c. Gas wells collect methane, and monitoring wells help detect groundwater contamination. Liners can fail, so long-term monitoring is necessary.

B. Disposal effects and tradeoffs

1. Landfill decomposition depends on waste composition, moisture, temperature, and oxygen. Dry, compacted conditions can preserve biodegradable waste for years.

2. Anaerobic decomposition occurs without oxygen and produces methane and carbon dioxide. Methane is flammable and a powerful greenhouse gas.

3. Incineration burns waste, greatly reducing its volume and sometimes generating electricity. It releases carbon dioxide and requires controls for particles, metals, and other pollutants.

4. Incineration leaves ash that needs disposal; some ash is hazardous. Landfills require more land and continued leachate and gas management.

5. Illegally dumped tires hold standing water where mosquitoes breed. Unsafe e-waste processing releases toxic substances, and ocean dumping exposes wildlife to ingestion and entanglement.

X. Waste Reduction Methods (Topic 8.10)

A. Prevention, recovery, and tradeoffs

1. Source reduction prevents waste through less packaging, durable products, and reduced food waste. Reuse keeps items in service through repair, refill, or donation.

2. Recycling processes discarded materials into new products. It reduces demand for raw materials but still requires energy, water, transport, sorting, and money.

3. Contamination and mixed materials make recycling harder. Reducing and reusing generally avoid more processing than recycling.

4. Composting uses aerobic microbes to break down suitable organic waste. Compost improves soil organic matter, nutrient supply, and water retention.

5. Composting requires oxygen and suitable moisture. Poorly managed piles can smell, attract rodents, and develop anaerobic areas.

6. Using electronics longer and recycling them responsibly reduces e-waste and recovers metals while limiting hazardous releases.

B. Landfill mitigation and calculations

1. Captured landfill gas can fuel electricity generation. Burning methane lowers its climate impact compared with releasing it, but still produces emissions.

2. Waste-to-energy incineration reduces material requiring burial. Burning collected landfill gas does not remove the buried solid waste.

3. Closed landfills can become parks or habitat after suitable engineering. Caps, gas systems, monitoring, and restrictions on excavation remain necessary.

4. Percent reduction = [(original amount − new amount) ÷ original amount] × 100. Reducing disposal from 500 kg to 350 kg gives a 30% reduction.

5. Diversion rate = (amount diverted ÷ total waste generated) × 100. Diverting 200 kg of a 500 kg waste stream gives 40%; diversion does not necessarily reduce total waste generation.

XI. Sewage Treatment (Topic 8.11)

A. Treatment stages

1. Primary treatment physically separates waste. Screens remove large objects, grit chambers remove heavy particles, and settling tanks separate sinking solids and floating grease.

2. Sludge is the solid-rich residue removed during treatment. Primary treatment does not remove all dissolved pollutants or reliably disinfect water.

3. Secondary treatment uses microbes to break down biodegradable organic matter. Aeration supplies oxygen for microbial respiration, producing carbon dioxide, water, and microbial biomass.

4. Microbial clumps settle in another tank. Some return to the aeration tank; excess sludge is removed. These processes lower the treated water’s BOD.

5. Tertiary treatment adds steps targeting remaining pollutants, such as filtration or nitrogen and phosphorus removal. Denitrifying bacteria convert nitrate to nitrogen gas under low-oxygen conditions.

6. Disinfection uses chlorine, ozone, or UV light to reduce pathogens before discharge. Chlorine may require removal before release; UV works best in sufficiently clear water.

7. Effluent is the treated liquid leaving the system. Disinfection does not automatically remove nutrients, metals, or pharmaceuticals, and effluent is not automatically drinking water.

B. Residues, septic systems, and performance

1. Sludge digestion reduces organic matter and some pathogens. Anaerobic digestion produces usable methane; suitably treated biosolids may be applied to land if contaminant standards are met.

2. A septic system uses a settling tank and soil drain field. The tank needs periodic pumping; poor maintenance or unsuitable soil can contaminate groundwater.

3. Removal efficiency = [(incoming concentration − outgoing concentration) ÷ incoming concentration] × 100. Reducing BOD from 200 mg/L to 20 mg/L gives 90% BOD removal.

4. Removal efficiency for one pollutant does not describe every pollutant. If water flow changes, also compare pollutant loads: concentration × water volume per unit time.

XII. Lethal Dose 50% (LD50) (Topic 8.12)

A. Acute toxicity and dose

1. LD50 is the dose that kills 50% of a tested population under specified conditions. It is commonly expressed as mg of substance per kg of body mass.

2. A lower LD50 means greater acute toxicity when species, exposure route, and test conditions are comparable. An LD50 of 5 mg/kg indicates greater acute toxicity than 500 mg/kg.

3. Dose per body mass = amount received ÷ body mass. A 0.20 kg animal receiving 4 mg has a dose of 20 mg/kg.

4. LD50 is not a safe exposure limit. Lower doses can cause nonlethal harm or kill some individuals; results do not directly establish safe human doses or long-term risk.

XIII. Dose Response Curve (Topic 8.13)

A. Interpreting the graph

1. A dose response curve shows how a measured effect changes with dose. Dose is on the horizontal axis; mortality or another measured response is on the vertical axis.

2. On a mortality graph, find 50% mortality, move across to the curve, and then read the dose below that point to identify LD50.

3. A curve farther left reaches the same response at a lower dose. A steeper slope means the response changes faster across that dose interval; slope alone does not determine LD50.

4. A threshold is a dose below which a particular effect is not detected under test conditions. Not every effect has a demonstrated safe threshold.

5. Acute exposure is short-term exposure. Chronic exposure is repeated or long-term exposure and can produce effects not captured by acute mortality tests.

6. Check the measured response: 50% affected does not necessarily mean 50% dead. Dose, exposure duration, and test conditions must be considered together.

XIV. Pollution and Human Health (Topic 8.14)

A. Exposure and health effects

1. A hazard can cause harm; risk is the chance of harm under particular exposure conditions. Dose, route, duration, age, and health influence risk.

2. Sewage can carry pathogens into drinking water. Dysentery is an intestinal infection causing severe diarrhea, sometimes with blood, after exposure to certain bacteria or parasites.

3. Inhaled asbestos fibers can cause mesothelioma, a cancer of organ linings, especially around the lungs. A long latency period may separate exposure from disease.

4. Tropospheric ozone irritates airways, reduces lung function, and worsens asthma. It forms when nitrogen oxides and volatile organic compounds react in sunlight.

B. Evaluating evidence

1. Multiple pollutant exposures and differences in smoking, occupation, age, and other factors make health causes difficult to isolate. Correlation alone does not prove causation.

2. Confounding variables can provide another explanation for an observed relationship. Suitable comparison groups, consistent measurements, and repeated studies strengthen conclusions.

3. In controlled organism studies, dose can be the independent variable and survival or growth the dependent variable. Use an unexposed control, replication, and consistent conditions.

XV. Pathogens and Infectious Diseases (Topic 8.15)

A. Transmission routes

1. A pathogen is a disease-causing agent, such as a bacterium, virus, or parasite. A host is infected; a reservoir maintains the pathogen; a vector transfers it between hosts.

2. Pathogens spread through contaminated water or food, respiratory particles, contact, or vectors. A place that appears clean can still contain pathogens.

3. Plague is a bacterial disease usually transmitted by infected fleas or contact with infected animal tissues. Pneumonic plague can also spread through respiratory droplets.

4. Tuberculosis is a bacterial infection that usually affects the lungs. It spreads through airborne particles from people with infectious lung disease.

5. Malaria is caused by Plasmodium parasites transmitted by infected female Anopheles mosquitoes. Its burden is especially high in sub-Saharan Africa.

6. West Nile virus cycles mainly between mosquitoes and birds; infected mosquitoes can transmit it to humans.

7. SARS is a coronavirus respiratory disease spread mainly through close contact and respiratory particles. It can cause pneumonia.

8. MERS is a coronavirus respiratory disease that can pass from dromedary camels to humans and spread between people through close contact.

9. Zika virus spreads mainly through infected Aedes mosquitoes and can also spread sexually. Infection during pregnancy can harm fetal development.

10. Cholera is a bacterial infection acquired through contaminated water or food. Severe watery diarrhea can cause rapid dehydration.

B. Environmental conditions and prevention

1. Inadequate sewage disposal and unsafe drinking water increase infection risk. Crowding and poor ventilation promote some respiratory infections; standing water supports mosquito breeding.

2. Changing temperature and rainfall can shift vector ranges and transmission seasons. Actual disease spread also depends on hosts, travel, sanitation, and vector control.

3. Safe water, sanitation, ventilation, mosquito nets, removal of standing water, and vaccination where available interrupt different transmission routes.

4. Pathogens evolve. Antibiotic use selects for resistant bacteria when susceptible bacteria die and resistant survivors reproduce. Antibiotics do not treat viruses.

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