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The population of the earth is increasing very fast. Humans must make the earth support the increasing population.This has made it necessary for agriculture and industry to develop rapidly. Such a rapid development produces more and more waste which goes into the water the soil and the air.Some of it is made harmless. However where there is too much of it the poisonous waste may do great harm to the things around the people.
When farmers add fertilizer to the soil to make plants grow better or use poison to kill pests poison is sent into the air the water and the soil. When birds fish and people eat the grain drink the water or breath the air harm will be done to their health.
The air in big cities is often made very dirty by cars and factories. Millions of tons of waste and poisonous gases are sent into the air with the smoke. In some places little is done to make the smoke clean before it goes into the air.
Fortunately people are beginning to realize just how serious the whole situation is. In many countries laws have been made to stop factories from sending out poisonous gases.