**1.1 Heavy metals**

In comparison to water, heavy metals are metallic elements with a higher density. Assuming that toxicity and heaviness are connected. Heavy metals also include metalloids such as arsenic, tin, lead, etc., which can cause harmful effects at low concentrations [6]. Environmental contamination of these metals is responsible for threatening the environment and global public health. Due to vast development in their use in numerous industrial, agricultural, domestic, and technological applications, human exposure has increased. Heavy metals in the environment could be found in geological, pharmaceutical, industrial, agricultural, atmospheric, and domestic effluent sources (**Table 1**). Smelters, foundries, mining, and other metal-based industrial operations are all major contributors to environmental contamination [7].

Heavy metals are naturally occurring elements found throughout the earth's crust; however, human activities such as mining and smelting, industrial application, and


#### **Table 1.** *Industrial uses of the heavy metals.*

### *Heavy Metal Contamination in the Coastal Environment and Trace Level Identification DOI: http://dx.doi.org/10.5772/intechopen.106653*

domestic and agricultural use of metals and metal-containing compounds end up causing the vast majority of environmental contamination and human exposure. Heavy metals are usually found in trace amounts in the earth's crust, ranging from a few parts per trillion (ppt) for noble metals to up to 5% for iron. They could be encountered in their elemental, metallic form. Weathering and erosion led them to leach into the soil, rivers, and groundwater. When the Earth's mantle was still liquid 4–5 billion years ago, heavy metals sank to the center and formed the iron- and nickel-rich core [8].

Due to their trace concentrations (ppt range to less than 10ppm) in a wide range of environmental matrices, heavy metals are classified as trace elements. Physical factors such as phase association, temperature, sequestration, and adsorption affect heavy metal bioavailability. Chemical parameters, such as lipid solubility, complexation kinetics, and octanol/water partition coefficients, have an impact on speciation at thermodynamic equilibrium. Biological factors include species characteristics, biochemical/physiological adaptability, and trophic interactions.

### **1.2 The significance of heavy metals to animal and plant life**

Metals are required for the proper performance of several biochemical and physiological processes in humans, animals, and plants. Microelements are trace elements having minor dietary requirements, such as chromium (Cr), iron (Fe), cobalt (Co), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), and selenium (Se). They are found in trace levels (ppt, ppb, or ppm) in a range of matrices and their bioavailability varies [9]. Trace elements are commonly added to animal feed as a nutritional supplement to enhance health and productivity. Heavy metals have been shown to impact a variety of cellular organelles and components, including the cell membrane, mitochondria, lysosome, endoplasmic reticulum, nuclei and enzymes involved in metabolism, detoxification, and damage repair. Excessive exposure to these elements at elevated concentrations has been associated with cellular or systemic problems and may be a source of pollution [10].

Chlorophyll production, protein modifications, DNA synthesis, photosynthesis, redox reactions in the chloroplast and mitochondria, nitrogen fixation, and sugar metabolism are all affected by heavy metals. More than 300 enzymes and 200 transcription factors required zinc as a cofactor for membrane integrity maintenance, auxin metabolism, and reproduction [11]. However, the remaining excess of heavy metals in the environment is responsible for harmful consequences.
