Quick answer: Pollution is the release of harmful substances into the air, water and soil. It is damaging ecosystems and human health: the Lancet Commission on Pollution and Health linked it to about 9 million deaths in 2019, one in every six worldwide. Fossil fuels, plastics, agriculture and poor waste management are the main causes, and cleaner energy and better waste systems are the main solutions.
Pollution comes in many forms, some visible and some invisible. Some of it harms people within hours, while some builds up in our bodies and in ecosystems over decades. The air we breathe, the water we drink and the soil our food grows in are all affected, and no country is fully immune. The burden, though, falls hardest on the people with the fewest resources to protect themselves.
Pollution at a glance
| Fact | Data | Source |
|---|---|---|
| People living where WHO air quality guidelines are not met | About 99% | WHO |
| Deaths linked to pollution (2019) | About 9 million, 1 in 6 deaths | Lancet Commission on Pollution and Health |
| Deaths from unsafe water, sanitation and hygiene | About 1.4 million a year | WHO |
| Monitored water bodies with good quality (2023) | 56% | UN SDG indicator 6.3.2 |
| Plastic accumulated in oceans and rivers (by 2019) | About 140 million tonnes | OECD |
| Plastic waste that is recycled | About 9% | OECD |
| Cities meeting the WHO PM2.5 guideline (2025) | 14% | IQAir |
| Most polluted countries (2025) | Pakistan, Bangladesh, Tajikistan, Chad, DR Congo (India 6th) | IQAir |
The 5 major types of pollution
1. Air pollution
About 99% of the world’s population lives in places where WHO air quality guidelines are not met.
Air pollution comes mainly from burning fossil fuels (coal, oil and gas) in power plants, vehicles and factories, and from burning wood, crop waste or coal for cooking and heating at home. The result is a mix of harmful substances: fine particles (PM2.5), nitrogen dioxide, sulfur dioxide, carbon monoxide and ground-level ozone.
PM2.5 particles are roughly 30 times smaller than the width of a human hair, so they can pass deep into the lungs and enter the bloodstream. IQAir found that 75 countries reduced PM2.5 in 2025 while 54 saw increases, and that only 14% of cities met the WHO guideline, down from 17% in 2024. Pakistan, Bangladesh, Tajikistan, Chad and the Democratic Republic of the Congo were the most polluted countries, with India ranking sixth.
Air pollution also harms nature. Acid rain, formed when sulfur dioxide and nitrogen oxides mix with water vapor, damaged forests and lakes across parts of Europe and North America in the 20th century. Ground-level ozone stresses plants, reduces crop yields and also acts as a greenhouse gas.
2. Water pollution
In 2023, 56% of the world’s monitored water bodies had good ambient water quality (UN SDG indicator 6.3.2). The rest fell short of quality targets.
Factories can release heavy metals such as mercury, lead and arsenic into rivers. Farm runoff carries fertilizers and pesticides into streams and groundwater, and the extra nutrients can trigger algal blooms that use up the oxygen in the water, creating “dead zones” where most marine life cannot survive. Untreated sewage adds disease-causing germs.
Microplastics, tiny fragments of broken-down plastic, have been found in tap and bottled water and in deep-sea sediments. Researchers have also detected them in human blood, lung tissue, placentas and breast milk, and the long-term health effects are still being studied.
The WHO estimates that unsafe water, sanitation and hygiene cause about 1.4 million deaths a year, more than a million of them from diarrhoeal disease. Children are hit hardest, because repeated illness from contaminated water stunts growth and keeps families trapped in cycles of poverty.
3. Soil and land pollution
Healthy soil stores carbon, filters water and grows our food. Pesticide overuse, industrial dumping, mining waste and landfill leachate can contaminate it. Heavy metals such as lead and cadmium can build up in crops and, through food, in people.
Waste is a big driver. According to the World Bank, high-income countries produce about 34% of the world’s waste while making up only about 16% of the population, and global waste generation is projected to reach 3.4 billion tonnes a year by 2050. At the same time, the UN projects the world population will reach about 9.7 billion by 2050, which will increase the pressure on farmland.
4. Plastic pollution
Plastic is cheap and durable, and that durability is the problem: it breaks into smaller pieces rather than disappearing. The OECD estimates that about 140 million tonnes of plastic had accumulated in oceans and rivers by 2019, and that this stock could more than triple by 2060. Only about 9% of plastic waste is recycled, and about 22% is mismanaged, meaning it is dumped, burned in the open or leaks into the environment.
Marine animals ingest plastic or become entangled in it, and microplastics now travel through food chains. On land, plastic clogs drains, which worsens flooding, and burning plastic waste releases toxic fumes, including dioxins.
5. Noise and light pollution
These two are often forgotten, but they have real ecological effects. Noise from traffic, shipping and industry can disrupt how animals communicate, mate and navigate. Whales and dolphins, which rely on sound, are especially affected by underwater noise from ships and sonar. Artificial light at night disrupts the rhythms of nocturnal animals, confuses migrating birds and can lead sea turtle hatchlings inland instead of toward the sea.
How pollution damages ecosystems
Ecosystems are webs, and pollution weakens the connections between species. Coral reefs show this clearly. Rising ocean temperatures, driven by greenhouse gas emissions, combine with runoff and pollution to bleach and kill reefs. The Great Barrier Reef has suffered eight documented mass bleaching events since 1998, six of them since 2016 (AIMS, data through 2025). When a reef declines, fish populations decline with it, and so does the food security of the coastal communities that depend on them.
Wetlands, which filter water, are degraded by farm runoff and industrial discharge. Forests suffer from acid rain and ozone, and deforestation and fires in the Amazon release stored carbon and destroy biodiversity. A 2022 study in Environmental Science & Technology concluded that humanity has moved beyond the safe limit, or planetary boundary, for “novel entities” such as synthetic chemicals and plastics. Pollution is also one of the five main direct drivers of biodiversity loss identified by IPBES.
The human cost
The Lancet Commission on Pollution and Health linked pollution to about 9 million deaths in 2019, one in every six deaths worldwide. That is more than the deaths from AIDS, tuberculosis and malaria combined. Its authors also found that more than 90% of pollution-related deaths occur in low- and middle-income countries.
Beyond deaths, long-term exposure is linked to asthma, heart disease, stroke, lung cancer, chronic lung disease and kidney damage. Children are especially vulnerable: lead exposure can cause lasting damage to brain development, and air pollution in early life can affect lung growth. The University of Chicago’s Air Quality Life Index estimates that meeting the WHO PM2.5 guideline would add almost two years to average global life expectancy.
Pollution is therefore a question of fairness as well as health. The people who have contributed the least to pollution often live closest to dumps, factories and busy roads, and have the fewest resources to cope.
Pollution and climate change
Pollution and climate change are linked. The fossil fuels that produce air pollution also produce the carbon dioxide that drives global warming. WMO confirmed 2024 as the warmest year on record, at about 1.55°C above pre-industrial levels, and the IPCC reports that carbon dioxide levels are now higher than at any point in at least 2 million years.
Warming and pollution feed each other. Hotter, drier conditions make wildfires more likely, and wildfire smoke is a major source of air pollution. Methane from landfills, farming and fossil fuel operations is a powerful greenhouse gas, responsible for around 30% of warming since pre-industrial times. In 2025, disasters triggered 29.9 million internal displacements worldwide, down 35% from the exceptional level of 2024 but still above the decade average (IDMC, 2026). Tackling pollution and climate change together is more effective than treating them separately.
What are the real solutions?
The tools already exist. What is needed is scale and speed.
- Switch to renewable energy. Solar and wind produce electricity with no direct emissions, cutting the biggest source of air pollution and greenhouse gases.
- Fix the plastic system. Reduce single-use plastics, design products to be reused and recycled, and invest in waste collection where it is weakest.
- Farm more sustainably. Using fertilizer and pesticides more precisely, protecting soil and managing manure and crop waste reduces water and soil pollution.
- Enforce industry rules. Emissions limits, treatment of wastewater before discharge and penalties for illegal dumping work when they are enforced.
- Electrify transport and invest in public transit. This cuts urban air pollution and noise together.
- Educate and inform. Clear public data on air and water quality helps communities and governments act.
Individual choices matter too: reducing waste, choosing reusable products, using public transport, eating less meat and supporting clean energy. But the scale of the problem also calls for systemic change by governments, companies and international institutions.
Proof that it works
- The Montreal Protocol (1987) phased out ozone-depleting chemicals, and the ozone layer is on track to recover over the coming decades.
- Leaded petrol has been phased out worldwide, removing a major source of lead exposure.
- London’s Clean Air Act (1956) helped end the deadly coal smogs of the mid-20th century.
Where strong policies have been enforced, air and water quality has often improved.
Frequently asked questions
What is the biggest cause of environmental pollution?
Burning fossil fuels (coal, oil and gas) is the largest single cause. It drives air pollution and greenhouse gas emissions, and contributes to acid rain and ocean acidification. Industry, agriculture and poor waste management are also major contributors.
How many people die from pollution each year?
The Lancet Commission on Pollution and Health linked pollution to about 9 million deaths in 2019, around one in six deaths worldwide. Air pollution accounts for most of them, and more than 90% occur in low- and middle-income countries.
How does pollution affect wildlife and ecosystems?
Pollution damages habitats, poisons food chains, acidifies water, contributes to coral bleaching and disrupts animal behavior. IPBES lists pollution as one of the five main direct drivers of biodiversity loss, alongside land and sea use change, overexploitation, climate change and invasive species.
Is pollution getting better or worse?
The picture is mixed. IQAir found that 75 countries reduced PM2.5 in 2025 while 54 saw increases. The OECD estimates the stock of plastic in oceans and rivers could more than triple by 2060, and a 2022 study concluded that chemical pollution has exceeded a planetary boundary.
What can individuals do to reduce pollution?
Use public transport, cycle or walk where possible, reduce single-use plastic, avoid food waste, use energy efficiently, support clean energy, and take part in local clean-ups. Voting for and asking for strong environmental policies matters too.
Which countries are the most polluted?
According to IQAir’s 2025 report, the most polluted countries by average PM2.5 were Pakistan, Bangladesh, Tajikistan, Chad and the Democratic Republic of the Congo. India ranked sixth. High-income countries also generate large amounts of waste and industrial pollution, and part of the impact is often felt elsewhere.
Sources
- WHO, Ambient (outdoor) air pollution fact sheet
- IQAir, World Air Quality Report 2025
- Fuller et al. (2022), Pollution and health: a progress update, The Lancet Planetary Health
- WHO, Burden of disease attributable to unsafe drinking-water, sanitation and hygiene, 2021 update (link: search the title on who.int)
- UN, SDG indicator 6.3.2: ambient water quality
- OECD, Plastic leakage and greenhouse gas emissions are increasing
- World Bank, What a Waste 2.0
- UN, World Population Prospects 2024
- AIMS, Coral bleaching events
- Persson et al. (2022), Outside the safe operating space of the planetary boundary for novel entities, Environmental Science & Technology
- IPBES, Global Assessment
- University of Chicago EPIC, Air Quality Life Index 2024
- WMO, 2024 warmest year on record; IPCC, AR6 Summary for Policymakers
- UNEP and Climate and Clean Air Coalition, Global Methane Assessment
- IDMC, Global Report on Internal Displacement 2026
- Studies on microplastics in humans: Leslie et al. (2022, blood), Jenner et al. (2022, lung tissue), Ragusa et al. (2021, placentas) (links: search the titles)
- UNEP, Ozone Secretariat (Montreal Protocol) and UNEP’s 2021 announcement of the end of leaded petrol (links: search on unep.org)
Related reading: What is pollution? | What is air pollution? | Ways to reduce global warming