Highlights of Heavy Metals: Molecular Toxicity Mechanisms, Exposure Dynamics, and Environmental Presence

1,2Esther Ugo Alum

1Department of Biochemistry, Faculty of Science, Ebonyi State University, P.M.B. 053 Abakaliki, Ebonyi State, Nigeria.

2Department of Publication and Extension Kampala International University Uganda

*Corresponding author: Esther Ugo Alum;

Email:; +2348034789993


Elements denser than water are known as heavy metals, and they are a major global danger to the environment and human health. The ubiquity of each metal in diverse environmental matrices is highlighted by its existence in both natural and industrial sources. Human exposure pathways include everything from food consumption to work environments, and they all contribute to a variety of health effects and organ system damage. Notably, long-term exposure to these metals is associated with increased cancer incidence rates, which can impact the neurological systems, lungs, kidneys, skin, liver, and other organs. The molecular details of the toxicity and carcinogenicity of individual metals reveal a variety of processes, such as DNA damage, oxidative stress induction, disruption of cellular respiration, disruption of signal transduction pathways, and changes in gene expression. Priority heavy metals (cadmium, chromium, arsenic, lead, and mercury) have distinct toxicological profiles, but this review emphasizes the urgent need for comprehensive strategies to reduce environmental contamination and human exposure. It does this by highlighting the complex interactions between environmental events, anthropological sources, and the molecular basis of heavy metal-induced carcinogenicity and toxicity.

Keywords: Environmental Contamination, Heavy Metals, Environmental Health Impacts, Molecular Mechanisms, Metal Toxicity


Heavy metals are metallic elements denser than water. Metalloids that are hazardous at low exposure levels, such as arsenic, are also classified as heavy metals if toxicity and heaviness are associated [1]. These metals’ poisoning of the environment has become an increasingly serious worldwide ecological and public health issue in recent years. Furthermore, human exposure has significantly increased as a result of the exponential growth in the number of industrial, agricultural, household, and technical applications of these compounds [2]. Known sources of heavy metals in the environment include geogenic, industrial, agricultural, pharmaceutical, domestic effluent, and atmospheric [3]. Major sources of pollution to the environment are metal-based industrial operations and point sources such as foundries, smelters, and mines [2, 3]. The main ways that humans contaminate and come into contact with naturally existing elements like heavy metals are through mining, industrial production, and agricultural use. Air deposition, soil erosion, leaching, sediment re-suspension, metal evaporation, and metal corrosion are additional sources [3, 4]. It has also been noted that weathering and volcanic eruptions are examples of natural events that greatly contribute to heavy metal contamination [5]. Paper processing factories, plastics, textiles, microelectronics, wood preservation, metal processing in refineries, coal burning in power plants, petroleum combustion, nuclear power plants, and high tension lines are examples of industrial sources [5]. According to reports, metals including zinc (Zn), cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), manganese (Mn), magnesium (Mg), molybdenum (Mo), nickel (Ni), selenium (Se), and zinc (Mg) are necessary nutrients needed for a variety of physiological and biochemical processes [6]. Numerous deficiency illnesses or syndromes are brought on by an inadequate intake of certain micronutrients [6]. Physical factors that affect heavy metals include temperature, phase association, adsorption, sequestration, complexation kinetics, lipid solubility, and chemical variables. Heavy metals are present in trace levels in a variety of environmental matrices [7, 8]. Additionally, biological elements such trophic relationships, species traits, and physiological and biochemical adaptability are crucial [9]. In both plants and animals, the important heavy metals perform physiological and metabolic roles. They are crucial components of a number of essential enzymes and are involved in a number of different oxidation-reduction processes [6]. Ferroxidases, catalase, and peroxidase are among the enzymes linked to oxidative stress for which copper is an essential co-factor. For the creation of hemoglobin, the metabolism of carbohydrates, the manufacture of catecholamines, and the cross-linking of collagen, it is integrated into metalloenzymes. Cuproenzymes make use of the reduced and oxidized forms of copper [10]. But because superoxide and hydroxyl radicals can be produced during the switches among Cu(II) and Cu(I), this feature of copper also gives it the potential to be poisonous [11]. Additionally, Wilson disease in humans has been related to cellular damage caused by high copper exposure [10, 11]. Like copper, a number of other elements are necessary for biologic functioning; however, an excess of these elements results in damage to cells and tissues, which can lead to a variety of negative effects and human diseases. For some, like copper and chromium, there is a very narrow range of concentrations between beneficial and toxic effects [11, 12]. Other elements, like aluminum (Al), antinomy (Sb), arsenic (As), barium (Ba), beryllium (Be), bismuth (Bi), cadmium (Cd), gallium (Ga), germanium (Ge), gold (Au), indium (In), lead (Pb), lithium (Li), nickel (Ni), platinum (Pt), silver (Ag), strontium (Sr), tellurium (Te), thallium (Tl), tin (Sn), titanium (Ti), vanadium (V), and uranium (U) have no known biological functions and are regarded as non-essential metals [12]. The effects of heavy metals on cellular organelles and components in biological systems have been documented. These consist of the endoplasmic reticulum, mitochondria, lysosome, cell membrane, nuclei, and specific enzymes that are involved in damage repair, metabolism, and detoxification [13]. Metal ions can cause damage and conformational changes to DNA and nuclear proteins, which can lead to apoptosis, cancer, or abnormalities in the cell cycle. Some laboratory research has shown in multiple studies that the generation of reactive oxygen species (ROS) and oxidative stress are important factors in the toxicity and carcinogenicity of metals including arsenic [14], cadmium [15], chromium [16], lead [17], and mercury [18]. These five elements are considered priority metals of major public health relevance due to their high degree of toxicity. Even at lower exposure levels, these are all recognized to be systemic toxicants that can cause damage to various organs. There are numerous mechanistic components to heavy metal-induced toxicity and carcinogenicity, some of which are not fully understood or clarified. Nonetheless, it is well recognized that every metal has distinct characteristics and physicochemical qualities that give rise to particular toxicological modes of action. The environmental occurrence, production and usage, human exposure potential, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity of arsenic, cadmium, chromium, lead, and mercury are all reviewed in this article using relevant published articles from various scholarly databases.


This paper explores the environmental impact of heavy metals such as cadmium, chromium, lead, mercury, and arsenic their toxicity and carcinogenicity. These metals are found in various sources, including food, work, and pollution. Long-term exposure can cause organ damage and cancer. The toxicity mechanisms include oxidative stress, signal transduction disruption, DNA damage, and gene expression changes. The paper calls for interdisciplinary research to understand these metals’ interactions and develop effective policies to minimize environmental contamination and mitigate health risks.


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CITE AS: Esther Ugo Alum (2023). Highlights of Heavy Metals: Molecular Toxicity Mechanisms, Exposure Dynamics, and Environmental Presence. IAA Journal of Applied Sciences 10(3):8-19.