**3. Effect on living organism**

#### **3.1 Effect on aquatic environment**

Water from estuaries and freshwater is not polluted till now to some extent, but that water is also at threat of being polluted in the long term due to metal deposition because of human past activities [66]. The water in the river and lakes can be highly polluted depending on the volume of flow and proximity to the point sources. Due to the human civilization, the element content in water is raised. Such elements are cadmium, lead, mercury, zinc, and chromium. Unlike organic chemicals, there are some metals that cannot be converted into compounds with lesser toxicity, and one of its characteristics is the loss of biodegradability. Once the heavy metals enter the water system it gets redistributed throughout the column and gets accumulated in the sediments [67]. The sediments constitute a partial contribution to polluting the natural phenomena due to their activity and metal remobilization processes. Metal residues that are present in the contaminated surroundings have the flexibility to get bioaccumulated into the aquatic environment [68]. Growth in fish larvae and juveniles is rapid. But when these heavy metals enter they might inhibit the growth rate. The fish grows in length and bulk when given the right conditions, such as a specific temperature and an acceptable amount of food. Fish growth, on the other hand, may be impeded in water contaminated with toxicants, such as heavy metals. One of the most noticeable signs of metal toxicity in fish larvae is growth inhibition. As a result, the length and bulk of fish are indications of environmental conditions [69]. Heavy metals are introduced in liquid form and surface water constituents (carbonate, sulfate, organic substances humic, fulvic, and amino acids) cause the formation of non-soluble salts or complexes. Aquatic species are not expected to be harmed by these salts and compounds. Some of them sink and collect in the sediments at the bottom. A decrease in pH of water either due to acid rain or any other acidic incidents, due to the heavy metal's deposition into the water column, causes aquatic biota to become poisonous. Low levels of heavy metals can also make chronic stress, through fish might not get dead but can cause them to lose weight and become

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

smaller, reducing their capacity to compete for food and habitat [70]. Pollution poses a hazard to both freshwater and marine habitats. Heavy metal poisoning of water is a significant environmental hazard that has detrimental consequences for organisms who are exposed to it be that plant-animal or humans. Fish from freshwater are majorly exposed to various heavy metals, which are added into the water bodies through the different-different sources. Contamination of these heavy metals into aquaculture has intensified global issues because it shows a risk to fish and has harmful impacts on fish buyers [71]. There are three different modes through which heavy metals enter the fish. These methods are either through the gills of fish, by the body of the fish, or by the digestive tract of the fish. Heavy metals immediately enter the fish body through the gills, while the body surface takes time for uptaking of these heavy metals through this mode [72]. Mostly the metals get accumulated in the liver, kidney, and gills. In fishes, the muscles have most of the metals present there as compared to the other body parts of the fish. Too much accumulation of these heavy metals inside the fish organ can cause lesions and operative disturbances [73]. These heavy metals also interfered with the embryo's shape and the metabolic processes of the fishes. Structural and functional defects throughout the development of the embryo resulted in fewer larvae hatching. Several freshly born larvae die shortly after hatching owing to lead and copper absorption [74, 75]. Heavy metals get into the fish through three routes: the first is via the fish gills, the second is through the digestive tract of the fish and the last one is through the body of the fish. The gills of fish are the area that is known for the primary metal intake from the contaminated water. On the fish gills, zinc accumulates. It suggests a depressing influence on tissue respiration, which leads to hypoxia and mortality. Zinc pollution also causes alterations in the structure of the lungs and heart [76]. Humans and fish are both affected by mercury. Brain damage, with postnatal and fetal problems, leads to abortions, congenital deformity, and development differences in young fry due to Monomethyl. Minamata illness and Hg poisoning (via methyl Hg) both showed considerable neurotoxicity [77]. Nickel is necessary for tiny amounts for the formation of RBC, but when its concentration gets increased, at that time, it becomes harmful or poisonous. Cd has been linked to an increase in blood pressure and cardiac illness in fish. Blood vessels damage, hemorrhages, and depletion of blood cell count of a fish are induced by Hg, from previous research. Anemia, eosinophilia, lymphocytosis, bronchial, and renal injuries can affect chromium levels in the blood [18]. Malformations in fish are caused by cadmium, nickel, mercury, chromium, lead, and arsenic. The accumulation of these heavy metals in excessive amounts causes a variety of physiological effects. Fin loss, gill underdevelopment, liver dysfunction, and fin function in fingerlings were all prevalent findings in the studies [78]. The harmful effects of heavy metals have the greatest impact on the death rate, reproduction, individual development rates, and physiological capacity of fish. There have been effects on physical functioning and chemical parameters in the tissues and blood of fish living in water that is polluted via metals. It has been reported that fish exposed to metals developed immune system defects, making them more susceptible to infectious infections and increasing their chances of dying (**Figure 3**) [79].

### **3.2 Effects on aquatic plants**

For the growth of plants, few HMs like As, Cd, Hg, Pb, and Se are not important as they do not perform any known physiological function in them. Others, such as Co, Cu, Fe, Mn, Mo, Ni, and Zn, are key elements that are required for regular plant

**Figure 3.** *Harmful effects on the aquatic environment.*

development and metabolism, but their amounts can quickly exceed the appropriate levels, resulting in poisoning [80, 81]. Heavy metal concentrations in plants vary by plant species, and the efficiency with which various plants absorb metals is measured by plant absorption or metal transfer factors from soil to plant. An increased amount of Pb in agricultural soil decreases the productivity rate of the soil, and a less lead amount may hinder some important processes of plant, dark green leaves, withering of older leaves, stunted foliage, and brown short roots are poisonous indicators of photosynthesis, mitosis, and water absorption [82]. Heavy metals are poisonous and phytotoxic to plants, resulting in diseases such as chlorosis, poor plant development, and yield depression, as well as decreased nutrient absorption, plant metabolic problems, and a reduced capacity to fix molecular nitrogen in leguminous plants. Seed germination was gradually reduced in the presence of increasing levels of lead, it may be due to exposure to lead for a longer duration, some methods, such as leaching, chelation, metal binding, or microbe accumulation, have resulted in the neutralization of lead's harmful effects [83]. Heavy metals such as Cd, Pb, and Ni even their small concentration in plants can be hazardous to them. Poisoning due to this heavy metal will result in the complex interplay between the primary unpleasant ions and additional necessary or non-essential ions. Metals affect the activity of enzymes by swapping metal ions from metal enzymes, as well as preventing plant growth [84]. Some exceptional metals are vital for plants, as they reveal their roles in the catabolism of plants and biosynthesis, together as cofactors for enzymes and as metabolic yields. For example, Zn, Fe, Cu, Cr, and Co are the important nutrients but when their amounts are increased, they become toxic. Comparatively, Pb and Cd have *Heavy Metal Contamination of Water and Their Toxic Effect on Living Organisms DOI: http://dx.doi.org/10.5772/intechopen.105075*

no effect, which is favorable to the plant and is solely lethal [85]. The most abundant hazardous elements in the soil are lead. Pb poisoning in the soil is caused by municipal sewage sludge discharge, mining and smelting operations, Pb-containing paints, paper and pulp, gasoline, and explosives. They do not have any role in the shape of the plant or their growth and photosynthetic process of the plant. Pb poisoning also inhibits enzyme action, creates an imbalance of the water, alters membrane permeability, and disrupts mineral feeding [86].

#### **3.3 Effects on fish**

One of the main sources of contamination of the water is heavy metals, as it overwhelms the important species indirectly through biological chains or directly via chemical modifications in water. Three potential ways are there, through which heavy metals get into the fish body: though fish gills, through the body of the fish, and through the fish digestive tract. Gills are responsible for the immediate absorption of metals from the water, whereas the body surface is thought to have a smaller role in the intake of these elements in fish [87]. By altering the normal activities of numerous enzymes and metabolites, the accumulation of these heavy metals in the tissues causes significant biochemical, physiological, and histological changes in fish and other freshwater fauna. Fish are one of the most widely dispersed creatures in the aquatic ecosystem, and their susceptibility to metal poisoning may indicate the extent of metal pollution's biological impact [88]. Heavy metals, such as As, Cd, Cu, Cr, Fe, Pb, Mn, Hg, Ni, Zn, and tin (Sn), are major contaminants that cause serious toxicity in fish. Due to the heavy metals, the physiological and biochemical functions both in tissues and in blood Carpi can be altered. The compounds of As and inorganic As, Cd, Ni, silica in its crystal form, beryllium, and its compounds are considered to be chemical carcinogens, which results in the development of cancer inside the fishes. The drop in hematological parameters indicated that the exposed fishes had become anemic as a result of Cr exposure. This dangerous heavy metal was released into the aquatic ecosystem via trash, causing severe anemia and changes in hematological parameters in the *Labeo rohita* fish [89]. There are various studies on different fish such as *Noemacheilus barbatulus*, *Perca fluviatilis*, *Catostomus commersonii*, *Oreochromis mossambicus*, and *Oreochromis aureus*, and increased quantities of zinc, lead, cadmium, copper, mercury, and cadmium were found in the gonads of fish, according to the study. This causes contamination of eggs and sperm, as well as a reduction in fish fertility and embryonic development [90]. The number of hatched larvae was reduced due to anatomical and functional abnormalities during embryonic development. A percentage of freshly born larvae died shortly after hatching as a result of lead and copper absorption [75]. The sensitivity of heavy metals inhibits estrogenic and androgenic secretion and produces pathological differentiation in fish. The reproductive tissues of fish gonads are affected by effluents such as industrial and agricultural waste, pesticides, and heavy metals [91, 92]. Zinc gets accumulated over the gills of fish. It entails a depressing influence on tissue respiration, which leads to hypoxia and death. Zinc contamination also causes abnormalities in the structure of the ventilator and heart. Zinc is a toxicant that destroys gill tissue, disrupts acid–base and ion balance, and causes hypoxia in fish [93]. More importantly, heavy metal for neurotoxicity is Hg. While other factors play a role in neurotoxicity, mercury has a major impact on both fish and humans. Japan's rivers have been contaminated with mercury. Minamata illness and Hg poisoning (via methyl Hg) both showed considerable neurotoxicity [77]. Arsenic coagulates proteins, binds to coenzymes, and reduces the

production of adenosine triphosphate (ATP) during respiration. It can induce cancer in all of its oxidation states in combination, and high-level articulation can result in mortality. Carcinogenic metals such as cadmium, arsenic, nickel, and chromium [94] can damage DNA by deleting base pairs, mutating it, or attacking it with radical oxygen. Malformations in fish are caused by cadmium, nickel, mercury, chromium, lead, and arsenic. When the accumulation of these heavy metals gets excessive inside the water through this, many physical effects on fish can be seen. Fins get shortened; gills are underdeveloped; and liver and fin functions of fingerlings were commonly observed. The harmful effects of heavy metals have the greatest impact on the death rate, individual growth rates, reproduction, and physiological capacity of fish. The effects of metal pollution on physiological processes and biochemical parameters in the blood and tissue of fish have been studied. Fish that are exposed to heavy metals reveal faults in the immune system and thus are more exposed to diseases and chances of death increase [79].
