Pollution Revision Notes

Untreated sewage adds organic matter and harmful microorganisms to water. Bacteria decompose this organic material, using oxygen in the process. This reduces oxygen levels available for aquatic animals, which need oxygen to survive.

• Sewage increases decomposable organic waste.
• Bacteria multiply to break down waste.
• Oxygen is consumed during decomposition, lowering water oxygen.

Fertilizers contain nitrates and phosphates that enter water bodies through runoff. These nutrients cause rapid algae growth called algal blooms. When algae die, bacteria decompose them, consuming oxygen and causing oxygen depletion (hypoxia).

• Nutrients promote excessive algae growth.
• Algal blooms block sunlight and reduce oxygen.
• Decomposition of algae uses oxygen, lowering levels.

Low oxygen levels in water harm or kill fish and other aquatic animals. This disrupts the balance of aquatic ecosystems and reduces biodiversity.

• Aquatic animals need dissolved oxygen to respire.
• Oxygen depletion causes stress or death.
• Ecosystem balance is disturbed by loss of species.

Non-biodegradable plastics do not break down naturally and accumulate in water bodies. Aquatic animals may ingest plastic particles or become entangled, causing injury or death. Plastics also damage habitats like coral reefs and wetlands, reducing biodiversity.

• Animals mistake plastics for food and ingest them.
• Entanglement causes injury or drowning.
• Plastic debris alters and damages habitats.

On land, plastics block air and water flow in soil, harming microorganisms essential for soil health. This reduces soil quality and affects plants and animals living in the soil.

• Plastics prevent air and water reaching soil organisms.
• Soil organisms decline, reducing soil fertility.
• Plant growth and land animal habitats are affected.

Plastics can release harmful chemicals that poison wildlife and plants. These toxins accumulate in food chains, reducing biodiversity and ecosystem health.

• Chemicals leach from plastics into environments.
• Toxins accumulate in organisms causing harm.
• Biodiversity declines due to poisoning and habitat damage.

Methane is mainly released from livestock digestion, rice paddies, and landfill decomposition. Carbon dioxide is primarily produced by burning fossil fuels and deforestation.

These gases enter the atmosphere through both natural processes and human activities, with human activities significantly increasing their levels.

• Methane sources: livestock digestion, flooded rice fields, landfills.
• Carbon dioxide sources: combustion of fossil fuels, deforestation.

Both methane and carbon dioxide are greenhouse gases that trap heat energy in Earth's atmosphere by absorbing infrared radiation.

Increased concentrations of these gases intensify the natural greenhouse effect, causing more heat to be retained and raising global temperatures.

• Greenhouse gases absorb heat, preventing it from escaping into space.
• Higher levels of methane and carbon dioxide increase atmospheric heat retention.

The enhanced greenhouse effect leads to global warming, which causes changes in weather patterns, melting ice caps, and rising sea levels.

These changes disrupt ecosystems, affect biodiversity, and pose risks to human societies through extreme weather events and habitat loss.

• Global temperature rise due to trapped heat.
• Altered weather patterns and increased frequency of extreme events.
• Rising sea levels from melting ice and thermal expansion.

Nitrates enter water bodies mainly through runoff from fertilizers and waste.

This nutrient enrichment stimulates rapid growth of producers such as algae, leading to algal blooms.

• Nitrates act as nutrients promoting producer growth.
• Sources include agricultural runoff and sewage discharge.

When producers die, decomposers break down the dead organic matter using aerobic respiration.

This process consumes oxygen dissolved in the water, reducing oxygen availability for other organisms.

• Decomposers use oxygen to break down dead producers.
• Oxygen levels in water decrease as decomposition proceeds.

Reduced oxygen levels cause stress and death to oxygen-dependent organisms like fish.

This can lead to loss of biodiversity and disruption of aquatic ecosystems.

• Low oxygen (hypoxia) harms fish and other aquatic animals.
• Severe oxygen depletion can cause mass die-offs.