**1. Introduction**

Expeditious expansion and industrial development near the rivers have led to more stress on the river, and with increased stress, the water becomes polluted, and worsening environmental health is observed [1]. The water-soil interface and the water-atmosphere interface are the medium through which the heavy metals travel [2, 3]. Both anthropogenic activities and geochemical processes are responsible for heavy metal contamination in ecosystems [4]. Elements that have high density and are less noxious are known as heavy metals. Examples of heavy metals are lead, iron, mercury, cadmium, zinc, arsenic, copper, and chromium and the actual volume of these heavy metals is more than 6 g/m3 [5]. Heavy metals have the property of

environmental persistence and bioaccumulation, and these heavy metals enter the aquatic system through various routes. These heavy metals not only impair the quality of the aquatic ecosystem but also human health [6, 7]. These heavy metals can be found on the layer of earth in their regular form. These heavy metals are so dangerous that they cannot be degraded or decomposed and they have the arability to bioaccumulate [8]. These heavy metals once get into the ecosystem through the air, via drinkable water, or multiple chemicals and products that are manmade. The route of administration of these heavy metals is via inhalation, ingestion, and skin absorption. These heavy metals get into the biosphere via human activities, which include industrial production, mining, agriculture, and transportation [9]. Some methods are fossil fuel burning, smelting of different, waste from the municipality, fertilizers, pesticides, and sewage these all are considered to be the primary sources of metal pollution [10–13]. The toxicity of these heavy metals in the human body reduces energy levels; disrupts brain functioning; disturbs the functioning of various other organs such as the brain, lungs, liver, and kidney; and also hinders blood composition. If the contact with heavy metals continues, then it can hinder the physical, neurological, and muscular functioning. And due to these diseases like multiple sclerosis, Parkinson's disease and muscular dystrophy, and Alzheimer's disease. Chronic exposure to some of the heavy metals and their compounds may even cause cancer [14]. Pollution of these heavy metals into the river may cause distressing effects on the ecological balance of the aquatic environment, and with the extent of contamination, the diversity of aquatic organisms becomes limited [15]. The fish in the aquatic ecosystem can be used for examining the well-being of biota. Due to pollutants in the food chain of organisms, harmful effects can be seen and the aquaculture can become dead [16]. These heavy metals are neurotoxins for the fish living in the aquatic environment. When these heavy metals enter the fish body, they interact with them to generate biochemical reaction inside the fish, which makes it difficult for fish to communicate with their surroundings [17]. The presence of these heavy metals leads to diseases like Minamata, which is organic mercury poisoning. When these heavy metals get bioaccumulated, they become a threat to both the human population and animals who uses that water [18]. Modeling of risk assessment is divided into four stages, i.e.,


#### **Table 1.**

*Permissible limit of heavy metal ions in water [21].*

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

exposure assessment, toxicity (dose-response) assessment, hazard identification, and risk characterization. There are three pathways through which humans get exposed to traced metals, which include directly ingesting, inhaling through the mouth or nose, and via skin absorption when it gets exposed. From the water, the heavy metals usually enter through ingestion and dermal absorption. To assess exposure, the average daily dose is measured for pollutants through different identified paths. In a dose-response assessment for no carcinogens, reference doses (RfD) are calculated, and for carcinogens, slope factors (SF) are obtained by the United States Environment Protection Agency (USEPA) Integrated Risk Information System (IRIS) database. With the help of the facts which are discussed above, there was a study done with an aim to evaluate the water quality of the Subarnarekha River relating to metals, their temporal classification, source of identification, and assessment of human health risk when that water was ingested or the contaminate when absorbed through the skin. Through this, it is possible to know the contamination level and accordingly, the strategies were planned (**Table 1**) [19, 20].
