What is Pollution?
The introduction of harmful substances or energy into the environment, causing negative effects on living organisms and ecosystems.
Pollution is one of the biggest threats to biodiversity on Earth. When harmful substances enter our air, water, or soil, they can disrupt ecosystems, kill organisms, and reduce the variety of species that can survive in an area.
Pollutants can be:
- Natural — volcanic ash, wildfire smoke (though these are usually temporary)
- Anthropogenic (human-made) — factory emissions, pesticides, sewage, plastic waste
The vast majority of pollution threatening biodiversity today is caused by human activity, making it a key topic in understanding how we impact the natural world.
MYP Conceptual Framework: Throughout this subtopic, we are exploring the key concept of Change and the related concept of Consequences. The global context is Globalisation and sustainability — how human activity at a local and global scale changes ecosystems, and what the consequences are for biodiversity. Keep these lenses in mind as you study each type of pollution.
Think of an ecosystem like a busy classroom. If someone slowly fills the room with smoke, some students leave, some get sick, and the whole class stops functioning properly. Pollution does exactly this to ecosystems — it gradually makes conditions unliveable for many species.
Types of Pollution
There are several major categories of pollution, each affecting biodiversity in different ways:
1. Air Pollution
Release of gases and particles into the atmosphere — e.g. carbon dioxide (CO₂), sulfur dioxide (SO₂), nitrogen oxides (NOₓ), and particulate matter from burning fossil fuels.
2. Water Pollution
Introduction of contaminants into rivers, lakes, oceans, or groundwater — e.g. sewage, agricultural runoff (fertilisers and pesticides), industrial chemicals, oil spills, and plastic waste.
3. Soil Pollution
Contamination of land with chemicals — e.g. heavy metals, pesticides, industrial waste, and excess fertilisers that change soil chemistry.
4. Noise Pollution
Excessive sound levels that interfere with animal communication, navigation, and behaviour. Ship engines and sonar disrupt whale and dolphin echolocation, causing strandings and separation of pods. Road noise reduces the ability of birds to communicate, lowering their reproductive success in urban areas. Nocturnal animals that rely on sound to hunt (such as owls and bats) are particularly vulnerable.
5. Light Pollution
Artificial lighting at night disrupts natural day/night cycles that many species depend on. Sea turtle hatchlings navigate to the ocean by moving towards the brightest horizon (naturally, the sea reflects starlight) — artificial lights on beaches cause them to move inland instead, where they die. Migrating birds use stars for navigation and are fatally attracted to bright city lights. Many insect species are drawn to artificial lights, disrupting their reproduction and depleting populations that other animals depend on for food.
6. Thermal Pollution
Waste heat released into water bodies (often from power plants using water for cooling) raises water temperature and reduces dissolved oxygen levels, since warmer water holds less dissolved oxygen. This can kill cold-water fish species and shift aquatic communities towards heat-tolerant, less diverse assemblages.
All types of pollution can reduce biodiversity, but they don't all work in the same way. Understanding the mechanism — how each type causes harm — is essential for MYP Science. The following sections explore air, water, and soil pollution in depth, as these have the greatest documented impacts on biodiversity at both local and global scales.
11 more sections in this topic
Pick this up in your Library: it holds the whole topic, notes, cheatsheet and questions.