Due to their toxicity, long environmental half-lives, and capacity for bioaccumulation, heavy metals are well-known environmental contaminants. Their anthropogenic origins include mining and other industrial and agricultural processes, while their natural sources include the weathering of metal-bearing rocks and volcanic eruptions. The extraction of mineral resources through mining and industrial processing and the subsequent use of those resources for industrial, agricultural, and economic development has increased the mobilisation of these elements in the environment and disrupted their biogeochemical cycles. An environmental issue of concern to human health is the hazardous heavy metal contamination of terrestrial and aquatic ecosystems. Heavy metals are persistent contaminants that build up in the environment and poison food systems as a result. With a focus on fish, rice, and tobacco, the bioaccumulation of these elements and their effects on human health are examined. The publication will be a useful instructional tool for environmental sciences researchers as well as undergraduate and graduate students. The most dangerous heavy metals and metalloids with regard to the environment include Cr, Ni, Cu, Zn, Cd, Pb, Hg, and As. These elements' trophic transmission in terrestrial and aquatic food chains/webs has significant effects on animal and public health. It is crucial to measure and keep an eye on the levels of potentially harmful heavy metals and metalloids in the resident biota and other environmental segments.

The Importance of Metals in Life     

According to the chemical definition of a metal, it is an element that "conducts electricity, has a metallic sheen, is malleable and ductile, forms cations, and has basic oxides." In biological and environmental sciences, words like "metal," "metalloid," "semimetal," "essential metal," "beneficial metal," "toxic metal," "abundant metal," "available metal," "trace metal," and "micronutrient" are frequently used in reference to metals. In the heavily industrialised human society, metals are used in a wide variety of ways. Certain metals play crucially important physiological and biochemical roles in biological systems, and either their excess or deficiency can cause metabolic disturbances, which in turn can cause a number of disorders. Life depends on a few metals and metalloids.

Heavy Metals

A heavy metal is described as "a metal with a density greater than 5 g/cm3" by Csuros & Csuros. The term "heavy metals" is frequently used to refer to metals and semimetals that have been linked to contamination, potential toxicity, or ecotoxicity, according to Duffus. Heavy metals are described as "naturally occurring metals with an atomic number larger than 20 and an elemental density greater than 5 g cm 3" in a recently proposed expanded definition of the word.

Advantages and disadvantages of heavy metals

Heavy metals are categorised into essential and nonessential roles in biological systems. Heavy metals that are essential to life may be needed in the body in very small amounts. Heavy metals that are unnecessary for life have no recognised biological function in living things. Mn, Fe, Cu, and Zn are a few examples of important heavy metals, whereas Cd, Pb, and Hg are poisonous and are thought to be biologically unnecessary. Mn, Fe, Co, Ni, Cu, Zn, and Mo are trace elements or micronutrients for plants. They are necessary for growth, stress resistance, and the manufacture and operation of a variety of biomolecules, including secondary metabolites, chlorophyll, nucleic acids, carbohydrates, and chlorophyll. Diseases or abnormal situations are caused by either a lack of or an overabundance of a necessary heavy metal. For various categories of creatures, such as plants, animals, and microbes, the lists of essential heavy metals may vary. It implies that a heavy metal may be necessary for one group of organisms but not for another. The relationships between heavy metals and various organismal groupings are extremely complex.

Hazardous Metals in the Environment: Sources

Among the natural toxins that have been examined the foremost are overwhelming metals. Depending on the measurements and length of presentation, nearly each overwhelming metal or metalloid may be dangerous to biota. In spite of the fact that many substances are included within the category of heavy metals, as it were many are critical within the context of the environment. Cr, Ni, Cu, Zn, Cd, Pb, Hg, and as are on the list of the foremost harmful heavy metals and metalloids that are pertinent to the environment. The overwhelming metal contaminants Cr, Mn, Ni, Cu, Zn, Cd, and Pb are the foremost predominant within the environment. In 2009, China has recommended four metals, i.e., Cr, Cd, Pb, Hg, and the metalloid as, as the most noteworthy need poisons.

Environmental Heavy Metals' Sources

Heavy metals in the environment can come from both anthropogenic and natural, geogenic, and lithogenic sources. Weathering of metal-bearing rocks and volcanic eruptions are two examples of the natural or geological sources of heavy metals in the environment. The proportion of heavy metals in the environment that are attributed to humans has increased as a result of the global trends of industrialization and urbanisation on Earth. Mining, industrial, and agricultural operations are some of the anthropogenic sources of heavy metals in the environment. The mining and extraction of various elements from their respective ores releases these metals. Through dry and wet deposition, heavy metals that are discharged into the atmosphere during mining, smelting, and other industrial activities come back to the ground.

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