Toxicity of Heavy Metals and Recent Advances in Their Removal: A Review

Abstract

Natural and anthropogenic sources of metals in the ecosystem are perpetually increasing; consequently, heavy metal (HM) accumulation has become a major environmental concern. Human exposure to HMs has increased dramatically due to the industrial activities of the 20th century. Mercury, arsenic lead, chrome, and cadmium have been the most prevalent HMs that have caused human toxicity. Poisonings can be acute or chronic following exposure via water, air, or food. The bioaccumulation of these HMs results in a variety of toxic effects on various tissues and organs. Comparing the mechanisms of action reveals that these metals induce toxicity via similar pathways, including the production of reactive oxygen species, the inactivation of enzymes, and oxidative stress. The conventional techniques employed for the elimination of HMs are deemed inadequate when the HM concentration is less than 100 mg/L. In addition, these methods exhibit certain limitations, including the production of secondary pollutants, a high demand for energy and chemicals, and reduced cost-effectiveness. As a result, the employment of microbial bioremediation for the purpose of HM detoxification has emerged as a viable solution, given that microorganisms, including fungi and bacteria, exhibit superior biosorption and bio-accumulation capabilities. This review deals with HM uptake and toxicity mechanisms associated with HMs, and will increase our knowledge on their toxic effects on the body organs, leading to better management of metal poisoning. This review aims to enhance comprehension and offer sources for the judicious selection of microbial remediation technology for the detoxification of HMs. Microbial-based solutions that are sustainable could potentially offer crucial and cost-effective methods for reducing the toxicity of HMs.

Evaluation of potentially toxic elements in soils developed on limestone and lead-zinc mine sites in parts of southeastern Nigeria

“…This could threaten consumers of agricultural produce in the area, as the metal may be bioaccumulated. In high concentrations, Pb could lead to the breakdown of the central nervous system and other vital human organs, such as the liver and kidney, with children having been reported to be at high risk [ 54 ]. In all the studied soils, Pb exceeded the world soil average value of 27 mg/kg [ 31 ] except in NNP.…”

Current Status of Biotechnological Approaches to Enhance the Phytoremediation of Heavy Metals in India—A Review

“…Along with this, another crucial factor is the individual age as well as the method of exposure to the poison. Children's growing neurological systems are susceptible to lead poisoning and other heavy metal toxicity [57]. Similarly, the effects of nickel (Ni) are detrimental to human health.…”

Heavy Metal Remediation by Dry Mycelium Membranes: Approaches to Sustainable Lead Remediation in Water

“…Furthermore, live mycelium, through biogeochemical processes, especially in the presence of compounds, such as chlorine and phosphorus, can biomineralize metallic lead into stable lead compounds, including oxalates, phosphates, and carbonates, at the hyphal surface. 25,26 These biomineralization pathways, along with crystal compositions and kinetics, are influenced by several environmental factors, including the concentration and oxidation state of the heavy metal, 27 composition of organic matter, 28 availability of other inorganic elements, 29 and the pH of the environment, 30,31 which assist the formation of stable compounds. For example, Aspergillus niger fungi, in a weakly acidic environment (pH ∼ 5.5), displayed an increased enzymatic phytase activity, leading to the hydrolysis of organic phosphorus into inorganic phosphates.…”

“…These biopolymers present a variety of surface functional groups, including hydroxyl, amide, and carbonyl groups, which actively participate in the sorption of heavy metal ions via processes, such as electrostatic interactions, surface chelation, and ion exchange. − Rudakiya et al showed that heavy metals, such as Cd 2+ , Cr 2+ , and mixed metals, were adsorbed by the biopolymers present on the hyphal cell wall of white rot (Phanerochaete chrysosporium) mushrooms, resulting in sorption efficiencies exceeding 90% across a wide range of pH values. Furthermore, live mycelium, through biogeochemical processes, especially in the presence of compounds, such as chlorine and phosphorus, can biomineralize metallic lead into stable lead compounds, including oxalates, phosphates, and carbonates, at the hyphal surface. , These biomineralization pathways, along with crystal compositions and kinetics, are influenced by several environmental factors, including the concentration and oxidation state of the heavy metal, composition of organic matter, availability of other inorganic elements, and the pH of the environment, , which assist the formation of stable compounds. For example, Aspergillus niger fungi, in a weakly acidic environment (pH ∼ 5.5), displayed an increased enzymatic phytase activity, leading to the hydrolysis of organic phosphorus into inorganic phosphates.…”