The numbers in brackets correspond with the list of references at the end of the article. For example, toxic arsenic present in fungicides, herbicides and insecticides can attack –SH groups in enzymes to inhibit their catalytic activities as shown in Figure 3. Heavy metals generated free radicals inside the cell selectively activates these transcription factors and thus, may suggest that cell proliferation or cell death may be related to the exposure to carcinogenic metals. By making research easy to access, and puts the academic needs of the researchers before the business interests of publishers. More so under physiological conditions at approximately pH of 7, V(IV) can generate OH• from the decomposition of H2O2 according to the Fenton reaction. Heavy metals have industrial, domestic, agricultural, medical and technological applications, and as a result they are now widespread in our environment. 2000 Owerri, Imo State, Nigeria. More so, repeated long-term contact with some heavy metals or their compounds may even damage nucleic acids, cause mutation, mimic hormones thereby disrupting the endocrine and reproductive system and eventually lead to cancer [7]. HHS Clear exposure-response relationships and high risks have been observed. Alterations of histones, DNA methylation, and miRNA are the key epigenetic changes induced by arsenic which have shown to possess potentials to cause malignant growth [37]. Even rice is known to contain high levels of arsenic. Olawoyin R(1), Oyewole SA, Grayson RL. Mechanisms of heavy metal intoxication in humans. Most of the other heavy metals are generally toxic to the body at very low level. Cadmium compounds are currently mainly used in re-chargeable nickel-cadmium batteries. Also, occupational exposure to mercury as observed by researchers has been associated with measurable declines in performance on neurobehavioral tests of motor speed, visual scanning, visuomotor coordination, verbal and visual memory. © 2019 The Author(s). Nickel has been shown to be implicated in regulating the expression of specific long non-coding RNAs, certain mRNAs and microRNAs. When heavy metals are ingested through food or water into the body, they are acidified by the acid medium of the stomach. Cadmium has been implicated in promoting apoptosis, oxidative stress, DNA methylation and DNA damage. Cadmium is also classified as group 1 carcinogens for humans by the International Agency for Research on Cancer. The main sources of lead exposure include drinking water, food, cigarette, industrial processes and domestic sources. MMT has been claimed to be an occupational manganese hazard and linked with the development of Parkinson’s disease-like syndrome of tremour, gait disorder, postural instability, and cognitive disorder [95]. Arsenic compounds have been shown in an in vitro cell line study to promote genotoxicity in humans and mice leucocytes [39]. It is well documented that metal-induced generation of oxygen reactive species can attack polyunsaturated fatty acid such as phospholipids. Many of the heavy metals are known carcinogens. However, there are no studies so far that have been able to show any associations between amalgam fillings and ill health. Heavy metals may also inhibit protein folding. It is used in the production of batteries, nickel-plated jewelry, machine parts, nickel plating on metallic objects, manufacture of steel, cigarette smoking, wire, electrical parts, etc. Saccharomyces cerevisiae (budding yeast) cells was shown to accumulate aggregated proteins after it was exposed to equi-toxic concentrations of cadmium, arsenite and chromium (Cr(VI)) and the effect of protein aggregation was influenced by heavy metals in this order: arsenic > cadmium > chromium [80]. In the hippocampus, NMDAR is a neural receptor which consists of two or more subunits; an obligatory NR1 subunit and one or more subunits from the NR2 particularly NR2A, NR2B and NR3 families. Exposure to higher amounts of chromium compounds in humans can lead to the inhibition of erythrocyte glutathione reductase, which in turn lowers the capacity to reduce methemoglobin to hemoglobin. Acute arsenic poisoning can lead to the destruction of blood vessels, gastrointestinal tissue and can affect the heart and brain. Iron is known to generate free radicals which are suggested to be responsible for asbestos related cancer. Epub 2013 Jun 19. Heavy metals affect the reticulo endothelial system and haematopoisis, changing osmotic resistance of erythrocytes. Chronic levels of mercury exposure can lead to erethism, a disease condition characterized by excitability, tremor of the hands, memory loss, timidity, and insomnia. Several heavy metals are found naturally in the earth crust and are exploited for various industrial and economic purposes. 2016 Nov;151:671-688. doi: 10.1016/j.envres.2016.08.027. A number of prospective epidemiologic studies in children less than 5 years of age have shown that low-level of lead exposure (5–25 μg/dL in blood) resulted to the impairment of intellectual development which was manifested by the lost of intelligence quotient points [85]. Kidney Cadmium Concentrations in an Urban Sri Lankan Population: an Autopsy Study. Although there is no clear definition of what a heavy metal is, density is in most cases taken to be the defining factor. Heavy metals have been used by humans for thousands of years. In this review we summarized effects of various toxic metals on human health. Heavy metals exhibit toxic effects towards soil biota by affecting key microbial Heavy metals exhibit toxic effects towards soil biota by affecting key microbial processes and decrease the number and activity of soil microorganisms. Potential risk effect from elevated levels of soil heavy metals on human health in the Niger delta. Also, cancers of the liver, skin, prostate and Kupffer cell were associated with Arsenic poisoning. Risk assessment for the consumers. In vivo and in vitro experiments have shown chromate compounds to induce DNA damage in many different ways and can lead to the formation of DNA adducts, chromosomal aberrations, alterations in replication sister chromatid exchanges, and transcription of DNA [92]. Vegetables are considered to be an important component of human diet as they are rich sources of vitamins, minerals and fibers. Licensee IntechOpen. As such, copper is present in some nuts, avocado, wheat germ and bran etc. These toxic metals are accumulated in the dietary articles of human beings. It is because heavy metals ‘bio-accumulate’ in our body, which means that once heavy metal is absorbed, our body cannot get rid of it. As such, heavy metal toxicity can have several consequences in the human body. Inhibition of thiol transferases lead to increased oxidative stress and cell damage. Certain heavy metals such as copper, iron and cobalt can exist both as sulfide and oxide ores.  |  Metals are natural constituents that exist in the ecosystem. As the source of drinking water sample mentioned surface; ground and tap waters collected in some part of Lagos Metropolis. In drinking water, presence of heavy metals is threat to human health. Due to man’s anthropogenic and industrial activities, it can accumulate in the soil and up taken by plants. Pathway of heavy metals sources and exposure to humans. Heavy metal contamination has generated serious harm to the health of local farmers after passing through the food chain. They are substances with high electrical conductivity which voluntarily lose their electrons to form cations. OH• is capable of reacting with biological molecules such as proteins, lipids and DNA damaging them. Even low concentration of heavy metals may inhibit the physiological metabolism of plant. Among the 35 natural existing metals, 23 possess high specific density above 5 g/cm3 with atomic weight greater than 40.04 and are generally termed heavy metals [1, 2]. The main mechanism of heavy metal toxicity include the generation of free radicals to cause oxidative stress, damage of biological molecules such as enzymes, proteins, lipids, and nucleic acids, damage of DNA which is key to carcinogenesis as well as neurotoxicity. Lead poisoning is mostly related to the gastrointestinal tract and central nervous system in children and adults [83]. The general population is exposed to lead from air and food in roughly equal proportions. Reaction of arsenic with the thio group of enzymes. Heavy metals can damage and alter the functioning of organs such as the brain, kidney, lungs, liver, and blood. Further, food chain polluted with toxic metals and metalloids is an important route of hu- man exposure and may cause several dangerous effects on human. Most heavy metals are distributed in the body through blood to tissues [21]. It is now suggested that inhibition of either NMDARs or VGCCs by lead would result in a significant decrease of Ca2+ influx into the cell. Other forms of mercury contamination in humans may be through anthropogenic activities such as municipal wastewater discharges, agriculture, incineration, mining, and discharges of industrial wastewater [13]. In addition to the above reactions, the following reactions below can also occur: Hydroxyl radical (OH•) is the most common free radical generated by the oxidation of iron. Therefore, breathing high levels of chromium (VI) can cause irritation to the lining of the nose and nose ulcers.  |  Also, lead exposure can disrupt the intracellular second messenger systems and alter the functioning of the central nervous system. Cadmium is emitted through industrial processes and from cadmium smelters into sewage sludge, fertilizers, and groundwater which can remain in soils and sediments for several decades and taken up by plants. Inactivation of p53 allows uncontrolled cell division and thus p53 gene disruption has been associated with most human cancers. The regulatory limit for some selected heavy metals is shown in Table 1. Human Health Effects of Heavy Metals Introduction Heavy metals are individual metals and metal com-pounds that can impact human health. However, the proposed mechanism of mercury-induced cancer is through the generation of free radicals inducing oxidative stress thereby damaging biomolecules. There has been a debate on the safety of dental amalgams and claims have been made that mercury from amalgam may cause a variety of diseases. Also, chronic long-term exposure of some heavy metals may cause cancer [7]. Mainly produced from industrial activities most hazardous heavy metals are- 1. arsenic (As) 2. lead (Pb) 3. mercury (Hg) 4. cadmium (Cd) 3. The main threats to human health from heavy metals are associated with exposure to lead, cadmium, mercury and arsenic. In vitro studies have shown arsenic to alter the expression of p53 protein which also led to decreased expression of p21, one downstream target [38]. In particular, the public should be aware of glazed food containers, which may leach lead into food. Its amount in the soil is related to rock type and industrial activity. Potential risk effect from elevated levels of soil heavy metals on human health in the Niger delta. Though some heavy metals such as iron and manganese are essential for certain biochemical and physiological activities in the body, elevated level in the body can have delirious health effects. Drinking water may be contaminated with arsenic which is present in wood preservatives, herbicides, pesticides, fungicides and paints [10]. Environ Epidemiol. Mercury is an element that can easily combine with other elements to form inorganic and organic mercury. Thus, cadmium exposure can cause renal dysfunction and kidney disease. By Godwill Azeh Engwa, Paschaline Udoka Ferdinand, Friday Nweke Nwalo and Marian N. Unachukwu, Submitted: September 11th 2018Reviewed: November 13th 2018Published: June 19th 2019. Others can enter the body by inhalation while others such as lead can be absorbed through the skin. The Egyptians and Indians ate with gold and silver utensils and cutlery and used copper vessels to store and drink water. The general population does not face a significant health risk from methyl mercury, although certain groups with high fish consumption may attain blood levels associated with a low risk of neurological damage to adults. Heavy metal contamination in drinking water poses a threat to humans and is often the root cause of various severe health issues such as cancer and organ damage. Thus, there are substantial evidence of chromium to promote carcinogenicity of humans as increase stomach tumors have been observed in animals and humans who were exposed to chromium(VI) in drinking water. BDNF activity is also dependent on Ca2+ and thus has been implicated in the development of neurological diseases. These heavy metals can be taken up through several routes. The NMDAR is known to enhance learning and memory mediated by the hippocampus [47] as this has been confirmed in animal studies in which animals exposed to lead during its developmental process exhibit similar learning deficits comparable to those with the absence or impaired NMDARs [48, 49]. NLM During these mining activities, heavy metals are released from the ore and scattered in open in the environment; left in the soil, transported by air and water to other areas. Long-term exposure to cadmium leads to its deposition in bones and lungs. Reactions of Heavy metals with sulphydryl groups of proteins or enzymes (A) = Intramolecular bonding; (B) = Intermolecular bonding; P = Protein; E = Enzyme; M = Metal. These are all naturally occurring substances which are often present in … Chronic arsenicosis may results to irreversible changes in the vital organs and possibly lead to death. Heavy metal toxicity can either be acute or chronic effects. Heavy metals are thus commonly defined as those having a specific density of more than 5 g/cm3. The issue of heavy metals contamination and its effects on human health and the environment is one of the biggest health concerns in recent years. 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