Human Impacts and Sustainability
1. Pollution
Learning outcomes
- I can identify major types of pollution.
- I can explain how pollution affects ecosystems.
- I can describe sources of air, water, and soil pollution.
- I can evaluate the impacts of pollution on living organisms.
- I can propose solutions to reduce pollution.
What Is Pollution?
Pollution is the introduction of harmful substances or forms of energy into the environment at levels that cause undesirable changes.
A substance that causes pollution is called a pollutant.
Pollutants can affect:
- Air.
- Water.
- Soil.
- Living organisms.
- Entire ecosystems.
Pollution can come from natural processes, but many major pollution problems are associated with human activities such as industry, transportation, agriculture, energy production, mining, and waste disposal.
Pollution does not always remain where it was produced. Pollutants can be transported through the atmosphere, rivers, groundwater, oceans, soil, and food webs.
Major Types of Pollution
Pollution can be classified in several ways.
Major types include:
- Air pollution.
- Water pollution.
- Soil pollution.
- Plastic pollution.
- Nutrient pollution.
- Chemical pollution.
- Noise pollution.
- Light pollution.
- Thermal pollution.
These categories can overlap.
For example, chemicals released onto land can contaminate soil, enter groundwater, and eventually reach rivers.
Air Pollution
Air pollution occurs when harmful substances enter the atmosphere at concentrations that can damage organisms, ecosystems, or human health.
Important air pollutants include:
- Particulate matter.
- Nitrogen oxides.
- Sulfur dioxide.
- Carbon monoxide.
- Ground-level ozone.
- Volatile organic compounds.
Air pollution is especially serious in densely populated areas where large numbers of people may be exposed.
Sources of Air Pollution
Major human sources include:
- Vehicle exhaust.
- Fossil-fuel power stations.
- Factories.
- Construction.
- Burning waste.
- Agricultural activities.
- Household heating and cooking with polluting fuels.
- Wildfires influenced by human activity.
Natural sources can include:
- Volcanoes.
- Dust storms.
- Naturally occurring wildfires.
The type and severity of pollution depend on both the source and environmental conditions.
Particulate Matter
Particulate matter consists of tiny solid particles or liquid droplets suspended in air.
Sources include:
- Vehicle exhaust.
- Combustion.
- Wildfires.
- Construction.
- Industrial processes.
- Dust.
Very small particles can remain suspended for long periods and can be inhaled deeply into the respiratory system.
Particulates can also settle onto plants, soil, and water.
Smog
Smog is polluted air containing a mixture of pollutants.
Modern urban smog often develops when pollutants such as nitrogen oxides and volatile organic compounds react in sunlight.
This can produce ground-level ozone.
Ground-level ozone can:
- Damage plant tissues.
- Reduce photosynthesis.
- Irritate respiratory systems.
- Reduce crop productivity.
It is important to distinguish this harmful ground-level ozone from the ozone layer higher in the atmosphere, which helps absorb ultraviolet radiation.
Acid Deposition
Burning fossil fuels can release sulfur dioxide and nitrogen oxides.
These gases can undergo chemical reactions in the atmosphere and contribute to acidic substances that return to Earth's surface.
This is called acid deposition.
It may occur through:
- Rain.
- Snow.
- Fog.
- Dry particles.
Acidification can affect lakes, soils, plants, and aquatic organisms.
How Air Pollution Affects Plants
Air pollutants can damage leaves and interfere with photosynthesis.
Possible effects include:
- Reduced growth.
- Leaf damage.
- Reduced photosynthesis.
- Greater vulnerability to disease.
- Lower reproductive success.
Pollution can therefore affect entire food webs when primary producers are damaged.
Water Pollution
Water pollution occurs when harmful substances or conditions reduce water quality.
It can affect:
- Rivers.
- Lakes.
- Wetlands.
- Groundwater.
- Estuaries.
- Oceans.
Aquatic ecosystems are especially vulnerable because pollutants can spread through water and enter organisms directly.
Sources of Water Pollution
Common sources include:
- Sewage.
- Industrial discharge.
- Agricultural runoff.
- Fertilizers.
- Pesticides.
- Oil spills.
- Mining waste.
- Plastic waste.
- Household chemicals.
Pollution may enter water from a clearly identifiable source or from many scattered sources across a large area.
Point-Source Pollution
Point-source pollution comes from a specific, identifiable location.
Examples include:
- A discharge pipe.
- A leaking storage tank.
- A sewage outlet.
- An industrial facility.
Because the source can be identified, it may be easier to monitor and regulate.
Non-Point-Source Pollution
Non-point-source pollution comes from many scattered sources.
Agricultural runoff is a common example.
Rainwater may carry:
- Fertilizers.
- Pesticides.
- Soil.
- Animal waste.
from large areas of farmland into waterways.
This type of pollution can be more difficult to control because there is no single source.
Sewage Pollution
Untreated or poorly treated sewage can introduce:
- Organic matter.
- Nutrients.
- Disease-causing microorganisms.
- Chemicals.
into aquatic ecosystems.
Microorganisms decompose organic material.
This process requires oxygen.
Large quantities of organic waste can therefore decrease the concentration of dissolved oxygen in water.
Fish and other organisms may die if oxygen becomes too low.
Nutrient Pollution
Plants require nutrients such as nitrogen and phosphorus.
However, excessive nutrients entering water can cause serious environmental problems.
Common sources include:
- Fertilizers.
- Sewage.
- Animal waste.
Excessive nutrient enrichment can lead to eutrophication.
Eutrophication
Eutrophication can occur through a sequence of events:
Excess nutrients enter water
→ algae and aquatic plants grow rapidly
→ an algal bloom develops
→ algae and plants die
→ decomposers break down the dead material
→ decomposition consumes dissolved oxygen
→ oxygen levels decrease
→ aquatic animals may die.
Severe oxygen depletion can create areas where relatively few oxygen-dependent organisms survive.
Worked Example: Fertilizer Runoff
Imagine fertilizer is applied to farmland.
Heavy rain occurs.
Some fertilizer is washed from the soil into a nearby lake.
The sequence could be:
Fertilizer
→ increased nitrate and phosphate concentrations
→ increased algal growth
→ large algal bloom
→ algae die
→ bacterial decomposition increases
→ dissolved oxygen decreases
→ fish and aquatic invertebrates die.
This demonstrates how pollution can affect an ecosystem indirectly through a chain of biological processes.
Oil Pollution
Oil can enter marine and freshwater environments through:
- Spills.
- Shipping.
- Industrial accidents.
- Leaks.
- Runoff.
Oil can:
- Coat feathers.
- Coat fur.
- Damage tissues.
- Contaminate food.
- Damage coastal habitats.
Animals that depend on feathers or fur for insulation can be particularly vulnerable.
Plastic Pollution
Plastic is useful because it is durable.
Unfortunately, this durability also means that many plastics persist in the environment for long periods.
Plastic waste can enter:
- Rivers.
- Lakes.
- Oceans.
- Beaches.
- Soil.
Animals may become entangled in plastic or mistake it for food.
Microplastics
Large plastic objects can gradually break into tiny pieces.
Microplastics are small plastic particles, generally smaller than 5 mm.
They can originate from:
- Breakdown of larger plastics.
- Synthetic textiles.
- Industrial products.
- Tire wear.
- Other plastic materials.
Microplastics have been detected in aquatic and terrestrial environments and can be consumed by organisms.
Scientists continue to investigate their ecological and health effects.
Soil Pollution
Soil pollution occurs when harmful substances accumulate in soil.
Sources can include:
- Pesticides.
- Industrial chemicals.
- Mining waste.
- Oil.
- Heavy metals.
- Improper waste disposal.
- Contaminated water.
Soil pollution can affect plants, microorganisms, animals, and groundwater.
Pesticides
Pesticides are chemicals or biological agents used to control organisms considered pests.
They include:
- Insecticides.
- Herbicides.
- Fungicides.
Pesticides can protect crops and reduce losses.
However, inappropriate or excessive use can affect non-target organisms.
For example, an insecticide intended to kill crop pests may also affect beneficial insects.
Effective environmental management therefore considers both the benefits and potential ecological costs of pesticide use.
Heavy Metals
Some metals become toxic at sufficiently high concentrations.
Examples of pollutants of concern include:
- Mercury.
- Lead.
- Cadmium.
These substances can enter ecosystems through activities such as mining, industry, waste disposal, and combustion.
Some can persist in ecosystems and accumulate in organisms.
Bioaccumulation
Bioaccumulation occurs when a substance gradually builds up within an organism.
Imagine a fish repeatedly absorbs a pollutant faster than it can remove it.
Over time:
Pollutant entering body > pollutant leaving body
The concentration in the tissues increases.
This is bioaccumulation.
Biomagnification
Biomagnification occurs when the concentration of certain persistent pollutants increases at higher trophic levels in a food chain.
Consider:
Water → plankton → small fish → large fish → fish-eating bird
A large predator consumes many contaminated prey.
Pollutants can therefore reach particularly high concentrations in organisms near the top of the food chain.
Bioaccumulation vs Biomagnification
These terms are related but different.
Bioaccumulation
→ pollutant builds up within one organism over time.
Biomagnification
→ pollutant concentration increases across trophic levels.
An organism near the top of a food web may experience both processes.
Noise Pollution
Pollution does not have to be a chemical substance.
Noise pollution is excessive or disruptive human-generated sound.
Sources include:
- Traffic.
- Aircraft.
- Ships.
- Construction.
- Industry.
Noise can interfere with animal communication.
Animals use sound to:
- Find mates.
- Warn of predators.
- Defend territories.
- Locate prey.
- Maintain contact with group members.
Human-generated noise can therefore alter behavior and reproductive success.
Light Pollution
Light pollution is excessive or inappropriate artificial light at night.
It can affect:
- Insects.
- Birds.
- Sea turtles.
- Bats.
- Other nocturnal animals.
Artificial light can interfere with:
- Navigation.
- Feeding.
- Migration.
- Reproduction.
- Daily activity cycles.
For example, newly hatched sea turtles normally orient toward natural light over the ocean. Artificial coastal lighting can interfere with this behavior.
Thermal Pollution
Thermal pollution occurs when human activities significantly alter the temperature of natural water.
Some industrial facilities use water for cooling and then release warmer water into rivers or lakes.
Higher water temperatures can:
- Reduce dissolved oxygen.
- Change metabolic rates.
- Affect reproduction.
- Alter species distributions.
Species adapted to cool water can be particularly sensitive.
Pollution and Food Webs
Pollution can affect much more than individual organisms.
Suppose a pollutant reduces an insect population.
This may affect:
- Birds that eat the insects.
- Plants pollinated by the insects.
- Predators that eat those birds.
- Competitors using the same resources.
Pollution can therefore cause effects that spread through a food web.
Pollution and Biodiversity
Pollution can reduce biodiversity when sensitive species decline or disappear.
A polluted environment may become dominated by a smaller number of pollution-tolerant species.
This can change:
- Species diversity.
- Population sizes.
- Food-web structure.
- Competition.
- Predator-prey relationships.
- Ecosystem processes.
Pollution Can Affect Reproduction
Pollutants do not have to immediately kill an organism to damage a population.
They may instead affect:
- Fertility.
- Egg production.
- Development.
- Hormone systems.
- Growth.
- Behavior.
If fewer offspring survive and reproduce, the population can gradually decline.
Pollution Can Travel
Pollutants frequently move beyond the place where they were released.
Air pollutants can travel with wind.
Water pollutants can move downstream.
Chemicals can enter groundwater.
Plastic can travel through rivers into oceans.
Pollutants can also move through food webs.
Pollution can therefore become a regional or international problem.
Reducing Pollution
Pollution can be addressed at several stages.
A useful hierarchy is:
Prevent pollution
→ reduce pollution
→ capture or treat pollutants
→ clean up existing contamination
Preventing pollution before it enters the environment is often more effective than attempting to remove it afterward.
Reducing Air Pollution
Possible approaches include:
- Improving energy efficiency.
- Using lower-emission energy sources.
- Improving public transportation.
- Reducing unnecessary vehicle use.
- Installing industrial pollution-control equipment.
- Improving fuel and vehicle standards.
- Avoiding open burning of waste.
The most appropriate solutions depend on the major pollution sources in a particular location.
Reducing Water Pollution
Strategies can include:
- Treating sewage.
- Treating industrial wastewater.
- Reducing fertilizer runoff.
- Managing animal waste.
- Protecting wetlands.
- Preventing oil spills.
- Reducing plastic waste.
Wetlands can sometimes help remove nutrients and sediments from water before they reach larger waterways.
Reducing Agricultural Pollution
Farmers can reduce pollution while continuing to produce food.
Possible strategies include:
- Applying fertilizers more precisely.
- Avoiding unnecessary pesticide use.
- Planting vegetation beside waterways.
- Preventing soil erosion.
- Managing animal waste.
- Using integrated pest management.
A buffer strip of vegetation beside a river can trap some sediment and nutrients before runoff reaches the water.
Reducing Plastic Pollution
Strategies can include:
- Reducing unnecessary single-use plastics.
- Reusing products.
- Improving waste collection.
- Improving recycling where appropriate.
- Preventing litter.
- Capturing waste before it reaches waterways.
- Designing products that create less waste.
Cleanup is useful, but preventing plastic from entering ecosystems addresses the problem earlier.
Wastewater Treatment
Wastewater can be treated before it returns to the environment.
Treatment can remove:
- Solid waste.
- Organic matter.
- Nutrients.
- Disease-causing microorganisms.
- Some chemical contaminants.
Effective wastewater treatment greatly reduces the amount of pollution entering aquatic ecosystems.
Laws and Regulations
Governments can establish limits on:
- Industrial emissions.
- Wastewater discharge.
- Vehicle emissions.
- Pesticide use.
- Waste disposal.
- Pollutant concentrations.
Regulations are most effective when pollution is:
- Measured.
- Reported accurately.
- Monitored.
- Enforced.
Scientific evidence is therefore important for environmental regulation.
Monitoring Pollution
Scientists can monitor pollution by measuring substances or biological responses.
Examples include:
- Dissolved oxygen.
- pH.
- Nitrate concentration.
- Phosphate concentration.
- Particulate matter.
- Heavy-metal concentrations.
- Species diversity.
Living organisms can sometimes serve as bioindicators.
A bioindicator is an organism whose presence, absence, or condition provides information about environmental quality.
Worked Example: River Pollution
Imagine scientists investigate a river downstream from a wastewater discharge.
They measure:
| Measurement | Upstream | Downstream |
|---|---|---|
| Dissolved oxygen | 9 mg/L | 4 mg/L |
| Nitrate | 2 mg/L | 12 mg/L |
| Number of aquatic invertebrate species | 18 | 7 |
The downstream site has:
- Lower oxygen.
- Higher nitrate.
- Lower species richness.
These observations suggest that environmental conditions differ downstream.
However, scientists would need further evidence to determine the precise cause and establish whether the wastewater discharge is responsible.
Worked Example: Choosing a Solution
Suppose a lake experiences repeated algal blooms.
Testing shows that large amounts of fertilizer are entering from surrounding farmland.
A solution focused only on removing algae treats the symptom.
A stronger long-term strategy would also reduce the cause:
Excess fertilizer runoff
Possible actions might include:
- More precise fertilizer application.
- Vegetated buffer strips.
- Improved soil management.
- Wetland restoration.
Good pollution management aims to address the source of the problem.
Evaluating Pollution Solutions
A proposed solution should be evaluated using evidence.
Ask:
- Does it reduce pollution at the source?
- How effective is it?
- What does it cost?
- Can it be maintained?
- Does it create another environmental problem?
- How will success be measured?
- Who is responsible for implementing it?
For example, replacing one disposable material with another is not automatically environmentally beneficial. The complete environmental impact should be considered.
Individual and Collective Action
Individuals can help reduce pollution by:
- Reducing unnecessary waste.
- Disposing of chemicals correctly.
- Avoiding littering.
- Reducing unnecessary energy use.
- Reusing materials.
- Participating in local cleanups.
However, large pollution sources may require action from:
- Governments.
- Industries.
- Farmers.
- Cities.
- International organizations.
Effective pollution reduction often involves both individual and system-level changes.
A Cause-and-Effect Approach
When analyzing pollution, use this sequence:
Source → pollutant → pathway → organism/ecosystem → effect
For example:
Farm
→ fertilizer
→ runoff into lake
→ algae
→ algal bloom
→ decomposition
→ oxygen depletion
→ fish mortality
Or:
Factory
→ air pollutant
→ atmosphere
→ plant leaves
→ reduced photosynthesis
→ reduced plant growth.
This approach makes it easier to explain how pollution produces ecological effects.
Common Mistakes
Thinking Pollution Is Only Litter
Pollution includes chemicals, gases, nutrients, plastics, noise, light, heat, and other harmful environmental changes.
Confusing Air Pollution with Climate Change
They are related in some ways, but they are not the same phenomenon. Some activities produce both greenhouse gases and conventional air pollutants.
Thinking All Algae Are Pollution
Algae are natural and important parts of aquatic ecosystems. Problems can occur when excessive nutrients cause unusually large blooms.
Confusing Bioaccumulation and Biomagnification
Bioaccumulation occurs within an organism.
Biomagnification occurs across trophic levels.
Thinking All Pesticide Use Is Automatically Harmful
Environmental effects depend on the chemical, concentration, application method, exposure, and affected organisms.
Assuming Pollution Only Affects Organisms That Die Immediately
Pollution can also reduce growth, reproduction, development, or behavior.
Assuming Cleanup Is Always the Best Solution
Preventing pollutants from entering the environment is often more effective than removing them later.
Check Your Understanding
1. Define pollution and pollutant.
2. Identify four major types of pollution.
3. Give three sources of air pollution.
4. Explain how air pollution can affect plants.
5. Give four possible sources of water pollution.
6. Distinguish between point-source and non-point-source pollution.
7. Explain the process of eutrophication.
8. Why can sewage reduce dissolved oxygen in water?
9. Describe two ways oil pollution can harm animals.
10. Explain two ways plastic pollution can affect organisms.
11. Distinguish between bioaccumulation and biomagnification.
12. Explain why predators near the top of a food chain can be particularly vulnerable to some persistent pollutants.
13. Describe one way noise pollution can affect animals.
14. Explain how light pollution can change animal behavior.
15. What is thermal pollution?
16. Explain how pollution affecting one species can influence an entire food web.
17. A lake beside farmland develops repeated algal blooms. Explain the likely chain of events and propose one method of reducing the problem.
18. Why is preventing pollution often preferable to cleaning it up afterward?
Key Terms
- Pollution – introduction of harmful substances or forms of energy into the environment.
- Pollutant – substance or form of energy that causes harmful environmental change.
- Air pollution – contamination of the atmosphere by harmful substances.
- Particulate matter – tiny solid particles or liquid droplets suspended in air.
- Smog – polluted air containing a mixture of pollutants.
- Acid deposition – acidic substances transferred from the atmosphere to Earth's surface.
- Water pollution – contamination or harmful alteration of water.
- Point-source pollution – pollution from a specific identifiable source.
- Non-point-source pollution – pollution originating from many scattered sources.
- Eutrophication – nutrient enrichment that can cause excessive biological growth and oxygen depletion.
- Microplastic – small plastic particle, generally less than 5 mm in size.
- Soil pollution – contamination of soil by harmful substances.
- Bioaccumulation – buildup of a substance within an organism over time.
- Biomagnification – increase in concentration of some pollutants at higher trophic levels.
- Noise pollution – harmful or disruptive human-generated sound.
- Light pollution – excessive or inappropriate artificial light.
- Thermal pollution – human-caused alteration of environmental temperature, particularly in water.
- Bioindicator – organism whose presence, absence, or condition provides information about environmental quality.
Key Takeaways
- Pollution can affect air, water, soil, organisms, and entire ecosystems.
- Major pollution sources include transportation, industry, agriculture, energy production, mining, sewage, and waste.
- Pollutants can move far beyond their original source.
- Air pollutants can damage respiratory systems, plants, and ecosystems.
- Water pollution can come from sewage, industry, agriculture, oil, chemicals, and plastics.
- Excess nutrients can cause eutrophication, leading to algal blooms and oxygen depletion.
- Soil pollution can affect plants, microorganisms, animals, groundwater, and food webs.
- Persistent pollutants can bioaccumulate within organisms and biomagnify through trophic levels.
- Plastic pollution can cause ingestion, entanglement, and long-term contamination.
- Noise and artificial light can disrupt animal communication, navigation, feeding, migration, and reproduction.
- Pollution can reduce biodiversity without immediately killing organisms by affecting growth, behavior, development, and reproduction.
- Effects on one species can spread through food webs.
- Pollution solutions can involve prevention, regulation, treatment, improved technology, better land management, and cleanup.
- Preventing pollution at its source is often more effective than trying to remove it after environmental contamination has occurred.
- Pollution problems can be analyzed using the sequence source → pollutant → pathway → organism or ecosystem → effect.
- Effective solutions should address the cause of pollution, not only its visible symptoms.