The appearance of new components in the natural environment, caused by human activity or some grandiose natural phenomena (for example, volcanic activity), is characterized by the term pollution. So, pollution is the presence of harmful substances in the environment that interfere with the functioning of ecological systems or their individual elements and reduce the quality of the environment in terms of human habitation or economic activity. This term describes all substances, phenomena, processes that appear in the environment in the given place, but not at that time and not in the amount that is natural for nature, and can bring its systems out of equilibrium.
Note that the environmental effects of polluting agents can manifest themselves in different ways; it can affect either individual organisms or individual populations, biocenoses, ecosystems, and even the biosphere as a whole.
Under the influence of polluting agents, there may be a violation of certain physiological functions of organisms, a change in their behavior, a decrease in growth and development, and a decrease in resistance to the effects of adverse environmental factors.
At the population level, environmental pollution can cause a change in their abundance and biomass, fertility, mortality, structural changes, annual migration cycles, and a number of other functional properties.
Environmental pollution affects the structure and functions of communities. The same pollutants affect different components of communities in different ways. At the same time, quantitative ratios in the biocenosis change, up to the complete disappearance of some forms and the appearance of others. The spatial structure of communities changes, detrital decomposition chains begin to prevail in the community. In this case, ecosystems degrade, deteriorate them as elements of the human environment, decrease the positive role in the formation of the biosphere, and depreciate economically.