污染

The economic system takes resources from the natural environment, and returns the wastes generated by production and consumption——a cycle which may be harmful if the concentration of wastes exceeds the capacity of the environment to assimilate them. The subsequent pollution of the air, seas, lakes, rivers and underground fresh water resources——as well as the land's surface——affects not only human beings, but all living organisms and buildings. The unprecedented growth of cities in the 20th century makes them major contributors to local, regional and global environmental problems. This article briefly introduces trans-border effects of pollution, the principal sources of pollution, the impacts of pollution and pollution management and policy implications.