**Abstract**

Heavy metals (HMs) are natural environmental constituents, but their geochemical processes and biochemical equilibrium have been altered by indiscriminate use for human purposes. Due to their toxicity, persistence in the environment and bioaccumulative nature; HMs are well-known environmental contaminants. As result, there is excess release into natural resources such as soil and marine habitats of heavy metals such as cadmium, chromium, arsenic, mercury, lead, nickel, copper, zinc, etc. Their natural sources include the weathering of metal-bearing rocks and volcanic eruptions, while mining and other industrial and agricultural practices include anthropogenic sources. Prolonged exposure and increased accumulation of such heavy metals may have detrimental effects on human life and aquatic biota in terms of health. Finally, the environmental issue of public health concern is the pollution of marine and terrestrial environments with toxic heavy metals. Therefore, because of the rising degree of waste disposal from factories day by day, it is a great concern. Pollution of HMs is therefore a problem and the danger of this environment needs to be recognized.

**Keywords:** Bioaccumulation, Contamination, Heavy metal, Health hazard, Soil, Toxicity, Water

## **1. Introduction**

Heavy metals (HMs) are an environmental threat and are of grave concern worldwide [1]. Rapid industrialization and urbanization have caused heavy metals to contaminate the atmosphere and it is a problem for human health [2–4]. HMs poses a major environmental threat to living organisms and habitats due to their non-biodegradability, bioaccumulation, environmental stability, persistence and biotoxicity characteristics [5–7]. In order to prevent microbial activities, they can directly influence the physical and chemical properties of sediment, soils and water [8]. They can also disrupt the natural ecosystem and impact the human body acutely and permanently through the food chain [9–11]. The non-degradable HMs can also accumulate in the surface sediment for a

**Figure 1.** *Sources, metals and the environmental degradation.*

long time via the food chain's amplification effect, causing various diseases and complications in the human body [1, 12, 13].

Natural activities (e.g. geological weathering, atmospheric precipitation, wave erosion, wind and bioturbation) and anthropogenic activities (e.g. rapid industrialization, urbanization, agricultural runoff and transport) play a key role in the spread of HMs to the marine habitats of aquatic ecosystems such as rivers and estuaries [2, 4, 14]. In addition, human activities that can produce industrial pollution, the deposition of urban waste and the offensive use of chemical fertilizers and pesticides result in the accumulation and sinking of HMs in aquatic habitat surface sediments [15–17]. The HMs released into the water column have a negative effect on water quality [11, 18] and on surface sediments that alter environmental parameters such as pH, temperature, bioturbation etc. [19, 20]. Sediment quality can therefore play a critical role in identifying the effects of natural and anthropogenic activities [21–23]; sediment quality can also provide information on the anthropogenic impact on the ecosystem and guide environmental policy and management [24].

Farm waste, agricultural runoff, pesticides, solid waste, waste management, effluents from fish processing plants, jute processing, cement manufacturing, oil refining, fertilizer manufacturing, building materials, soup and detergent factories and brickyard waste are the major sources of pollution (**Figure 1**). Due to the potential risk of HMs in water, soil and sediment through the disposal of the effluents mentioned, this riverine water, sediment and environment may be important.

## **2. Heavy metals**

#### **2.1 Definition**

Any metal or metalloid of environmental significance is a heavy metal [25]; the term originated in reference to the adverse effects, all denser than iron, cadmium, mercury and lead (**Figure 2**). It has since been extended to some other similarly toxic metal or metalloid, irrespective of density, such as arsenic, chromium, cobalt, nickel, copper, zinc, arsenic, selenium, silver, cadmium, antimony, mercury, thallium and lead are commonly found to be heavy metals [26, 27].

In a general, collective term that refers to a group of metals and metalloids with an atomic density greater than 4 g/cm3 or 5 times or more than water, the term heavy metal is often referred to as trace elements as they exist in minute concentrations in biological systems [28].

Heavy metals are classified as "metals that occur naturally and have an atomic number greater than 20" [29, 30]. They are a significant class of contaminants that

#### *Environmental Pollution with Heavy Metals: A Public Health Concern DOI: http://dx.doi.org/10.5772/intechopen.96805*


#### **Figure 2.**

*Position of heavy metals in periodic table.*

affect the environment. A serious problem with cultural, ecological and economic consequences is heavy metal contamination in the environment. Because of the toxicity, persistence, and bioaccumulative nature of these materials, research on heavy metals in the atmosphere is an important part of environmental research.

### **2.2 Sources of heavy metals**

Heavy metals may come from natural and anthropogenic processes and end up in various environmental compartments (soil, water, air and their interface). **Figure 3** gives information on natural and anthropogenic sources of heavy metals.

#### *2.2.1 Natural sources*

Various natural sources of HMs have been recorded in several studies. Natural emissions of HMs occur under numerous and certain environmental conditions. Volcanic eruptions, sea-salt sprays, forest fires, rock weathering, biogenic sources and particles of wind-borne soil are included in these pollutants. The release of metals from their endemic spheres to different environmental compartments will lead to natural weathering processes. In the form of hydroxides, oxides, sulfides, sulfates, phosphates, silicates and organic compounds, heavy metals can be found.

Lead (Pb), nickel (Ni), chromium (Cr), cadmium (Cd), arsenic (As), mercury (Hg), selenium (Se), zinc (Zn) and copper (Cu) are the most popular heavy metals. While the above-mentioned heavy metals can be present in traces, humans and other mammals still cause significant health problems.

## *2.2.2 Anthropogenic sources*

Industries, irrigation, drainage, mining and metallurgical processes, as well as runoff, also contribute to the release of pollutants into various compartments of the ecosystem. For certain metals, anthropogenic heavy metal processes have been noted to go beyond natural fluxes. In wind-blown dust, metals naturally released are mainly from industrial areas. Car exhaust that releases lead; smelting that releases arsenic, copper and zinc; insecticides that release arsenic and the burning

*Sources of heavy metals in the environment.*

of fossil fuels that release nickel, vanadium, mercury, selenium and tin are some essential anthropogenic causes that contribute significantly to heavy metal pollution in the environment. Because of the everyday manufacture of products to meet the demands of the large population, human activities have been found to contribute more to environmental pollution.
