They may also be transmitted to other places which means that their harm is not restricted to their sources, but may extend to other places. Pollution of the environment includes the change in its characteristics due to both quantitative and qualitative changes affecting that environment. Polluted air , for example, differs in its properties from pure air. These changes may be due to human interference. Pollution can be defined as the presence of any substance or energy in the wrong place, the wrong time or the wrong quantity.
Water is considered as pollutant if it is added to the soil in amounts that displace the soil air.
Salts, accumulated in the cultivable soil due to an inefficient drainage system, are also considered as pollutants. Petroleum, may become a pollutant if it percolates to seawater. Sound, when it increases in intensity above a certain level is considered as pollutant. These may be annoying and lead to deafness.