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 presence of heavy metal contamination in water is more threatening to human health, as well as animals and marine life, owing to their carcinogenic nature. These include arsenic (As), mercury (Hg), lead (Pb), cadmium (Cd), chromium (Cr), zinc (Zn), antimony (Sb), and nickel (Ni). The exposure to heavy metals by human beings is lethal and toxic (Mohankumar et al. 2016; Talabi and Kayode 2019; Ahamad et al. 2020; Pooja et al. 2020). To address the carcinogenic nature of the elements, various foundations like the WHO, Bureau of Indian Standard (BIS), United States Environmental Protection Agency (US‐EPA), European Commission Environment (ECE), Australian Drinking Water Guidelines (ADWG), and Norma Official Mexicana (NOM)‐127‐SSA1‐1994 prescribe the limit (Fernandez‐Luqueno et al. 2013) of contaminants in water as described in Table 4.1.
4.3.3.1 Arsenic
Arsenic (As), the twentieth‐most abundant element in the Earth’s crust, is a well‐known deadly poison from time immemorial (Mandal and Suzuki 2002). The compounds of arsenic in water are found in both organic and inorganic moieties. The organic moieties of arsenic existing in compound form are monomethylarsonicacid (MMA[V]), dimethylarsinic acid (DMA[V]), monomethylarsonous acid (MMA[III]), dimethylarsinous acid (DMA[III]), thiomethylarsonic acid (Thio MMA), thiodimethylarsinic acid (Thio DMA), arsenobetaine, and arsenocholine (Gomez‐Caminero et al. 2001). Apart from this, the inorganic compounds of As are about 100 times more toxic than the organic ones and are more prevalent in water (Jain and Ali 2000). The major inorganic compounds of arsenic as pentavalent arsenate ions [As(V)] like H3AsO4, H2AsO4−, HAsO42−, and AsO43− are found in surface water and trivalent arsenite ions [As(III)] like H3AsO3, H2AsO3−, and HAsO32− are found in groundwater (Jain and Ali 2000). As(V) is found as an oxidizing agent in surface water. Arsenic exists as H3AsO4 at pH > 2 and in the form like H2AsO4− and HAsO42− at pH 2–11. However, As(III) is found under reducing conditions at low pH. Considering this, As(III) is more toxic than As(V). Although As(III) is more lethal, the metabolism of As(V) plays an important role in its toxicity in the human body. Arsenate has the same structure as the phosphate ion and it can replace the phosphate ion from enzymatic reactions, which occur in the human body (Fan et al. 2018). The mechanism of As(V) in human body is completed in the following steps (Thomas et al. 2001; Hughes 2002; Fan et al. 2018):
Table 4.1 Acceptable limits of heavy metals in ppb in drinking water reported by different foundations.
| Heavy metal | WHO | ECE | USEPA | ADWG | NOM‐127 | BIS |
|---|---|---|---|---|---|---|
| Arsenic | 10 | 10 | 10 | 10 | 25 | 10 |
| Mercury | 6 | 1 | 2 | 1 | 1 | – |
| Cadmium | 3 | 5 | 5 | 2 | 5 | 3 |
| Chromium | 50 | 100 | 50 | 50 | 50 | 50 |
| Antimony | 20 | 5 | 6 | 3 | – | – |
| Lead | 10 |
10
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