**2. Pollutant removal**

## **2.1 Sources of water pollution**

Water, especially surface water, is exposed to the dangers of pollution, as the water source is considered polluted when it directly or indirectly changes its composition or condition as a result of human action, that is, if it becomes less suitable for some or all uses. These include sewage, household waste, hospital wastewater, and rainwater, where these pollutants are loaded with large quantities of various organic and inorganic materials and many types of microorganisms that cause many diseases, as well as urination, defecation, and throwing dead animals into the water, especially in rural areas, as well as picnic places represented by excreta. and food waste, where the type of sewage network systems plays a major role in the aggravation of these

*Algae Toxins and Their Treatment DOI: http://dx.doi.org/10.5772/intechopen.102909*

pollutants, as there are two types of sewage network systems in Baghdad, which are the separate system and the combined system. Also, the term (red tide) is considered to refer to types of Plankton (phytoplankton) that are spread in high density in any water body (may reach more than ten million cells per liter) and are known as harmful algae. Of the (4400 species) of Plankton plant there are only from (50–60 poisonous species). One of the most important spread of the phenomenon of red tide is a defect in environmental factors, including the difference in the ratio of phosphorous to nitrogen through sewage pollution. The higher the phosphorous rate in the water mass, the higher the rate of red tide or harmful algae appearing with the availability of other environmental conditions. The effects of the red tide are the destruction of fish from economic fish farms if this phenomenon spreads in the farm and costs thousands or even millions of dollars annually. The eyes, nose and mouth are irritated during the presence of algae toxins in the tourist beaches. The toxins increase the toxicity rate of marine food, which is transmitted to humans through marine meals (**Figure 1**).
