|
Occupational exposure limits are the maximum allowable concentrations of hazardous elements in the air. They are defined by scientific laboratories in order to control the level of pollution in different areas. Among the main atmosphere pollutants are large-scale industry, domestic boilers and transport. The portion of each of these pollutants is different from place to place, but industrial companies are considered to be the worst pollutants. The major sources of artificial aerosol pollution of the atmosphere are thermal power plants that burn a large amount of coal with high ash content, concentrating mills, metallurgical, cement, magnesite and soot plants. |
Pesticides as a polluting factor
The discovery of pesticides - chemical defenders of plants and animals from various pests and diseases is one of the most important achievements of the modern science. Today every 1 hectare of land is treated with 300 kilograms of chemical agents. However, the prolonged use of pesticides in agriculture led to the reduction of their efficiency due to the development of resistance types of pests and the spread of "new" hazardous organisms whose natural enemies and competitors were destroyed by pesticides. At the same time the effect of using pesticides is shown on the world scale. 250 species of the known insects have developed resistance to pesticides. This is aggravated by cross-resistance which is basically resistance not only to one specific substance but also to other substances of other classes. The phenomenon of resistance is connected with genetic, physiological and biochemical rearrangement of organisms. Excessive use of pesticides (herbicides, insecticides, defoliants) negatively affects the quality of the soil. In this connection the influence of pesticides on soil, as well as the possibility to render them harmless by chemical and biological means are being intensively studied. It is important to create and use only the substances with short lives measured by weeks or months. In this respect certain success has already been achieved and compounds have been introduced with higher destruction speeds, but the problem in general still stays unsolved.
