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Pollution is when harmful substances are added to the environment and then change it in a bad way. There are five kinds of pollution of the environment: water pollution, air pollution, noise pollution, soil pollution and thermal pollution.
As pollution grows, ways to combat it have grown. Solar energy and wind energy give people clean ways to power their homes. When people use these alternative forms of energy, they put less carbon dioxide into the environment. 
Water pollution is the presence of harmful materials in water, such as sewage, dissolved metal, waste from farms, factories and crude oil spilled from oil tankers. The three main substances that pollute water are nitrates from fertilizers, sewage and detergents.
Activities such as bathing and washing clothes near lakes, ponds or rivers add nutrients like nitrate and phosphate into the water bodies.This leads to excessive growth of algae on the surface of water. It blocks the penetration of sunlight and air, thus reducing oxygen.
Water pollution has been a problem from the time human population increased, and live in cities. Cities have been prone to cholera and typhoid fever and other infectious diseases since Roman times. Existing water systems put in place in the 19th century are overwhelmed by the rapid growth of population in cities.
Air can be polluted by many things. Examples include poisonous gases, sulphur dioxide, nitrogen dioxide, carbon monoxide and very small particulates. Smoke and harmful gases released by fires, industries, and thermal power plants cause air pollution. Using coal and wood as fuels for fire causes a lot of air pollution. Petroleum produces less pollution per ton, but it causes a lot of pollution since a lot of it is burned globally. Air pollution may cause health problems such as asthma or other breathing problems.
Noise pollution/Sound pollution
Noise pollution also known as sound pollution is harmful to the brain and hearing of all animals and humans. This includes the sound of vehicles, loud speakers, airplanes, jets, train horns etc. Noise pollution can cause ear problems or even permanent deafness, especially to older people. The schools which are beside the roads suffer from noise pollution. Students cannot concentrate in their studies. People in hospitals near main roads also suffer.
Thermal pollution is the harmful release of heated liquid into a body of water or heat released into the air as a waste product of a industry.
A common cause of thermal pollution is using water as a coolant by power stations and industrial manufacturers. This puts back warm water, and so raises the temperature and decreases how much oxygen is in the water. The heat released into the air will make the air warmer which increase global warming.