school energy&environment

Alterations

The different types of pollution lead to chemical or physical alterations of the water, with mechanisms which are very complex at times. Contaminants that are dispersed in the water have harmful effects on animal populations and plants, that can be classified into the following categories:

• deoxygenation or oxygen-depleting effects: these effects are caused by the organic substances that are present in industrial waste. When industrial waste is dispersed in the water, it is degraded by microorganisms, with an excessive consumption of the oxygen dissolved in the water. The reduced availability of oxygen in the water is the cause of death of animal and plant species that are unable to tolerate this lack of oxygen and, on the other hand, an invasion of those species that are not influenced by the lack of oxygen;
• eutrophication effects: eutrophication is a phenomenon provoked by compounds (mineral nitrogen and phosphorus) that favour an abnormal growth of populations of phytoplankton and algae, at the expense of the survival of other plant and animal species. Lakes and sea-coasts are particularly affected by this;
• physical effects: are caused by very high temperature waste waters;
• effects caused by radiations;
• pathogenic and toxic effects: are caused by waste waters with a high content of suspended toxic or pathogenic materials (heavy metals, mineral oils, hydrocarbons, ammonia, solvents, detergents, pesticides, etc.)