**2.5 Urbanization**

With an increase in the population has created many issues and one of the issues is the pollution of water [38]. An increase in the population leads automatically leads to more generations of solid waste [51]. Both solid waste and liquid waste are deposited into the water without any treatment. Human excreta also contaminate the water. Thus, contaminated water leads to a generation of a large number of bacteria, which is a threat to human well-being [39]. Government is unable to supply vital requirements to the People because of the increase in the number of people. Facility for sanitization is more in urban areas as compared to rural areas. Plastic bag and waste are a major contribution to pollution. People throw the waste in plastic bags into water sources [24]. From the research, it was found that around three crore people of the population defecate in the open, while 77% population use flush and around 8% use the pit latrines. Urbanization can cause many infectious diseases. Overpopulation, unhealthy conditions, and dangerous drinkable water are these major health problems in urban areas. One-third of urban people are vulnerable to disease [37].

### **2.6 Agriculture source**

The population in rural areas is less but the use of fertilizers, pesticides, and eroded soil contaminates the water. When it rains the water from the surface runoff and that rainwater enters the nearby water resource and thus pollutes the existing water [52]. Agricultural runoff cases freshwater bodies' eutrophication. Half of the lakes in the US are eutrophic. Phosphate has one of the major contributions to eutrophication. And the high concentration of phosphates promotes cyanobacteria and algae growth, which leads to the excessive use of the biologically dissolved oxygen inside the water [53]. Fertilizers that are too enriched with nitrogen decrease the dissolved oxygen in rivers and coastal zones thus bringing hazardous effects to the biota. Since 2006, the nitrogen in fertilizers is being controlled in America and Northwest Europe [54]. Like pesticides, which are used as pest control, these pesticides leach into groundwater, thus polluting groundwater. The pesticides that are water-soluble leach more and the sandy soil favors the process of leaching [55].

### **2.7 Atmospheric source**

Small pollutants particles which are present in the air, get into the water stream through the rain, when it rains these particles come down and then with the flow of water enters into the sea, thus polluting the water there. These pollutants that

*Heavy Metal Contamination of Water and Their Toxic Effect on Living Organisms DOI: http://dx.doi.org/10.5772/intechopen.105075*

are present in the air usually get from the burning of fossil fuels e.g. is CO2, which combines with water and produces sulfuric acid. Sulfur dioxide, which is formed via volcanic eruption and from industries, also gets attached to a water molecule to form the sulfuric acid. When coal is combusted then also sulfuric dioxide is produced and it is also produced from petroleum products. Just like this nitrogen dioxide also combines with the water and forms the nitric acid. And with the help of rainwater, they enter the water resources (**Figure 2**) [52, 56–59].

### **2.8 Mining source**

Heavy metals are present on the earth and thus they can enter the water system through various pathways and one of them is through mining sources. When it rains or through flowing water, it leaches heavy metals out from their geological formation. These processes get disturbed when manmade economic activities such as mining are done. Through these processes, the area that is already mined out gets exposed to water and air and this leads to the acid mine drainage (AMD). The low pH conditions associated with AMD mobilize heavy metals, including radionuclides where these are present [60].

#### **2.9 Heavy metal intake through water**

Soil gets polluted with the presence of heavy metal on surface and underground water and the pollution rises when mined ores are discarded on the ground surface for manual dressing [61]. Due to the dumping over the surface, the metals get exposed to air and rain thereby generating huge AMD. If soil is polluted at that time, it gets into the plant tissue and gets accumulated there. And when those plants are grazed

**Figure 2.**

*Circulation of contaminants between environmental sources under the effect of atmospheric sources.*

by animals and water is used for the drink from polluted waters, through there these heavy metals enter the body. Also, marine lives, which reproduce in contaminated water, also have the presence of heavy metals inside their body tissues, if they are lactating then inside their milk. As an overview, all organisms within a given ecosystem are contaminated via these pollutants through their food chains [62]. When nutrition from these contaminated vegetables is taken, the presence of heavy metals in those vegetables can lead to different chronic diseases. Toxic effects due to these heavy metals usually depend on the amount of concentration and the oxidative state of the particular heavy metals [63]. Heavy metals have a very dangerous impact as they are non-biodegradable in nature, have long biological half-lives, and have the potential to accumulate inside the body. Also, there are some heavy metals that are extremely toxic only because of their solubility. Fewer concentrations of heavy metals inside the food chain also show severe effects as there is no particular procedure through which these heavy metals pollutants can be extracted from the body of an organism. Nowadays presence of these toxic heavy metals is everywhere because of their extreme use in industries. In case of the wastewater, it contains a huge concentration of heavy metals, which create various health-related problems [64, 65].
