heavy metal pollution. In the fourth section, we have discussed the effect of heavy metal pollution on human body. The fifth and sixth sections throw light on recent strategies to control water pollution and remediation of heavy metals. We have discussed the future strategies adopted by different governments and suggest some measures to remove these exudates in the water. At last, this chapter ends with future expects and conclusions drawn.
4.2 Sources of Heavy Metal Contamination
Pollutants can enter the water bodies from various sources and then get transported along the streamline. Legal and illegal discharges from factories, spills and leakages in underground oil pipelines or during transportation, hydraulic fracturing operations, and sewer overflows pollute various water discharge bodies. Other potential sources include radiation leaks from nuclear power plants and drinking water disinfection processes.
This can be broadly categorized under pointed and non‐pointed sources. Pointed sources refer to pollutants that enter the waterway through traceable sources like industrial outlet pipes, domestic sewage outlets, etc. It should be noted that most of these pointed sources are due to human intervention and untreated waste discharge. Non‐pointed sources refer to diffused contamination of water bodies through activities like leaching, littering garbage, etc., which cannot be monitored and controlled owing to the difficulty of tracing them. The sources of heavy metal pollution in water can also be categorized as natural as well as anthropogenic. These are discussed in brief in Figure 4.1.
Figure 4.1 Sources of heavy metal pollution in ground water and their effects on human health.
4.2.1 Natural Sources
Natural sources like geothermal and volcanic activity and rock weathering are some natural sources known to play their part in contamination of water sources. Rainwater is also a common source of water contamination as it dissolves air pollutants and transports them in groundwater, as is the case in acid rain. Moreover, the rock oxidation, sea intrusion, decay of radioisotopes (uranium‐enriched bedrock), and surrounding vegetation add on to these contaminants in water sources. Rock oxidation and rock weathering are also some natural activities that are major causes of heavy metal pollution (Talabi and Kayode 2019).
4.2.2 Anthropogenic Sources
Anthropogenic sources (caused by human activity) are the main source of heavy metal pollution. Industries and chemical companies directly discharge contaminated water without any pretreatment in groundwater and surface water sources. On the other side, agricultural irrigation is a huge reason for the degradation of drinking water quality owing to excess use of various types of harmful pesticides, fertilizers, and insecticides for crop production (Talabi and Kayode 2019). Other reasons for water pollution are discharge of sewage waste (wastewater, waste dump, and solid waste), exoneration of the by‐products and wastes produced by mining activities, dissociation of radioactive elements, over pumping, etc. The discharges of waste chemicals (inorganic and organic) by laboratories, experimental wastes which are directly thrown in water, are some types of anthropogenic sources which deteriorate the water quality. These anthropogenic activities are more toxic and harmful for humans as well as animals.
4.2.3 Point Sources
Point sources are recognizable, quantifiable, and controllable sources. The drainage pipes of industries and factories that directly break out into the water, oil spilling by oil ship and tankers, and discharge of municipal and sewage waste are all major point sources of water pollution. The other point sources are domestic, hospital, industrial, and mining wastes. The domestic wastes that occur from residence, faculties, institutions, and laboratories are major threats to human health because these sources directly pollute the drinking water. While the industrials and landfills are vital sources, heavy metal pollution is a huge cause of contamination of groundwater as well as surface water (Talabi and Kayode 2019). Consequently, it has an adverse effect on human health, animals, and marine life owing to its carcinogenic nature. Most likely, the hospital waste discharged knowingly and unknowingly into water bodies diminishes the water quality day by day (Kümmerer 2001; Emmanuel et al. 2005; Emmanuel et al. 2009). Over the last decades, mining wastes have also drawn more attention for water pollution. The mining waste from minerals, coal mines, and heavy metal ores are major origins for heavy metal pollution (Pal et al. 2010; Lapworth et al. 2012).
4.2.4 Non‐Point Sources
Generally, the natural, agricultural and anthropogenic sources of water pollution are classified as non‐point sources, which are non‐recognizable and non‐controllable (Lapworth et al. 2012; Talabi and Kayode 2019). These sources are huge contributors to the contamination of water bodies as well as in diminishing the water resource quality. Naturally occurring volcanic activity, rain, rock dissociation, storms, and so on also produce heavy metal contamination in water. Soil erosion also contributes to water contamination. The chemical contamination includes heavy metals, organic impurities, and inorganic impurities (WHO 2011; Russoniello et al. 2013; Megremi et al. 2013; Werner et al. 2013). In the case of industrial waste, it directly involves contaminating the ground as well as surface water and is threatening to water bodies all over the world. Climate change and water scarcity are other causes of water pollution. Owing to water scarcity, the excessive use of groundwater is the other source of origin of heavy metal contamination. Nowadays, agricultural sources, for example pesticides, fertilizers, and insecticides, originate the pollution in surface and groundwater also (Velthof et al. 2009; Savci 2012; Cruz et al. 2013).
4.3 Types of Water Pollution
4.3.1 Surface Water Pollution
Surface water, such as rivers, streams, and lakes are directly consumed in rural areas. As we know, the surface water is a huge resource of drinking water for rural and urban areas. Mainly, anthropogenic sources lead to the pollution in surface water. However, industrial contaminants like heavy metals are directly released into surface water. The chemical companies which are situated in the bank of rivers, lakes and streams are a major cause of heavy metal and chemical pollution of surface water. The other reason for surface water pollution is discharge of municipal waste in water. Additionally, soil erosion is another cause of generating heavy metal contamination in surface water bodies.
4.3.2 Groundwater Pollution
Over the last decades, groundwater has become one of the important sources of water for human and animals provided by nature. Unfortunately, the groundwater gets contaminated both knowingly and unknowingly by human carelessness. The natural sources explained in Section 4.2.1 are major causes of groundwater contamination. These natural sources are playing a part in contaminating the groundwater by heavy metal. The excavation of rock, which is a rich source of heavy metal, creates the heavy metal pollution in groundwater because the heavy metals are easily soluble in water, and can also be suspended in water. Additionally, anthropogenic sources are a big contributor to the heavy metal pollution in groundwater.
4.3.3 Heavy Metal Pollution
The heavy metals, which are denser than water, are easily sustained in water and create heavy metal pollution in water. As documented in the literature, the
