Free Essay: Exposure Routes and Health Effects of Heavy Metals on Children

Abstract

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Heavy metals, such as mercury, lead, chromium, cadmium, barium, aluminum, and copper, have adverse health impacts on individuals when they get into the body. Their entry into the body occur through many ways. Inhalation of contaminated air is one of the ways in which heavy metals get into the body. Another way is through skin absorption of these metals. Additionally, heavy metals get into the human bodies through foods such as fish products. Heavy metals can also get into the body through drinking of contaminated water. Entry of heavy metals to the human body has been associated with increased risk for cardiovascular diseases, cancer, respiratory complications, gastrointestinal problems, impaired physical and mental growth, poor academic outcomes, and behavioral and emotional problems in children. Overall, exposure to heavy metals has detrimental impacts on children's developmental outcomes.

Keywords: Heavy metal, Health effect, children health

1. Introduction:

Heavy metals include metals like mercury, lead, chromium, cadmium, barium, aluminum, and copper. These metals get into the body of human beings through various ways. Some of these exposure routes include inhalation of contaminated air, skin, food, and drinking water. Once they get into the human bodies, they cause adverse health effects. Some of these effects include increased risk for cardiovascular diseases, cancer, respiratory complications, gastrointestinal problems, impaired physical and mental growth, and behavioral and emotional problems in children.

Mercury

Mercury is an element found in group 12, period 6. It has a relative atomic mass (RAM) of 200.592. At room temperature, mercury is a heavy liquid which appears silvery-white. This element has a density of 13.5336 g cm3. According to CDC (n.d.), mercury exists in three forms: elemental mercury, organic mercury compounds, and inorganic mercury compounds. These forms of mercury have different properties, usage, and toxicity. According to NIOSH (n.d.), exposure routes of mercury include eye contact, skin contact, ingestion, skin absorption, and inhalation. Some of the primary health effects of mercury exposure include eye irritation, loss of weight, anorexia, proteinuria, gastrointestinal problems, indecisiveness, irritability, insomnia, and respiratory problems. The main organs affected my mercury toxicity include kidneys, brain, respiratory system, eyes, and skins. The diagram below shows the structure of mercury:

Lead

Lead is an element located group 14, period 6. It has an RAM of 207.2. At room temperature, mercury is a solid which has a dull, bluish-grey metal appearance. It has a density of 11.3 g cm3. Lead occur in three oxidation states: lead (0), lead (II); and lead (IV). The most common form of lead that is found in the environment is lead (II). According to the World Health Organization (2018), the primary routes of exposure of lead include ingestion of lead-contaminated substances and inhalation of lead particles given out by burning lead-containing materials. The main effects of high levels of lead exposure in children include damage to the central nervous system and the brain which lead to coma, spasms, and sometimes death. Children who are lucky to survive lead toxicity have been reported to be mentally retarded and to manifest behavioural disorders (World Health Organization, 2018). The target organs of mercury toxicity include bones, kidney, liver, and central nervous system (World Health Organization, 2018). Lead is primarily stored in the bones and teeth and undergoes accumulation over time. The diagram below shows the structure of lead:

Chromium

Chromium is an element located group 6, period 4. It has an RAM of 51.996. At 20C, chromium is a solid with silvery blue tinge. Chromium has a density of 7.15 g cm3. Chromium exists in three stable oxidation states from Cr (0), Cr (III), and Cr (VI). Noteworthy, chromium (III) is an important dietary nutrient whose deficiency is associated with infertility, cardiovascular conditions, and diabetes. On the other hand, Cr (VI) causes cancer. According to CDC (2013), entry of chromium into the body occurs through skin absorption, ingestion, inhalation, and ingestion. Skin contact and inhalation is the primary means of occupational exposure of chromium. On the other hand, chromium exposure in the general population takes place through ingestion of water and food contaminated with chromium. The primary impacts of high levels of chromium exposure include respiratory problems such as irritation of air passages, obstruction of airways, and respiratory diseases such as rhinitis, bronchitis, and asthma. Other effects of chromium (III) and chromium (VI) poisoning include sinus, lung, and nasal cancer (CDC, 2013). The target organs of chromium poisoning include the kidney, liver, lungs, and intestinal tract. The diagram below shows the structure of chromium:

Cadmium

Cadmium is an element found in group 12, period 5. It has an RAM of 112.414. At 20C, it is a solid and has a silvery metal containing a bluish tinge on its surface. It has a density of 8.69 g cm3. This element has eight naturally occurring isotopes. In nature, cadmium does not occur in elemental form. That is, it always exist as a compound. Some of the common compounds of cadmium are carbon oxide, cadmium carbonate, and cadmium sulphide. Cadmium is a highly toxic metal and thus must be handled with great caution. The main routes of exposure into the human body include ingestion through some foods such as shellfish, inhalation through smoking of cigarettes, improper handling of the metal itself, and drinking of cadmium-contaminated water. Some of the primary effects of cadmium poisoning include headaches, drying of the throat, diarrhoea, nausea, and vomiting. It is also associate with hypertension, liver disease, and cancer. Some of the primary health consequences of cadmium poisoning include renal damage (Chunhabundit, 2016), osteoporosis in children (Schoeters et al., 2006); Sughis, Penders, Haufroid, Nemery, & Nawrot, 2011).

Barium

Barium is an element found in group 2, period 6. It has an RAM of 137.327. At 20C, chromium is a solid with silvery appearance that is rapidly tarnished when exposed in air. Barium has a density of 3.62 g cm3. Barium does not exist in elemental form but in form of compounds. The major ores containing barium include barium carbonate and barium sulphate. Barium exposure occurs in many ways. Entry to the body can occur via inhalation of barium-contaminated air, through ingestion of contaminated food, and intake of water contaminated with the barium compounds. Additionally, barium can enter the body through dermal absorption (CDC, 2007). Barium poisoning has been linked to adverse health consequences such as impairment of heart rhythm, paralysis, gastrointestinal problems (e.g. diarrhoea, abdominal cramps, and vomiting), respiratory problems, elevated or reduced blood pressure, muscular problems, and cardiovascular diseases.

2 Exposure and Health effects of heavy metals on children's health

2.1- Mercury

Exposure routes

Health effect (mechaism )

Mechanism of Mercury Toxicity

The entry of mercury ions into the body produces toxic impacts through generalized corrosion, inhibition of enzymes, and precipitation of proteins. Mercury ions have been found to bind proteins with different groups including amine, amide, carboxyl, and phosphoryl groups. Proteins made up of these groups have been found to have a high susceptibility to mercury reaction. After binding with mercury, these proteins become inactive. Mercury toxicity is also affected by is oxidative state as well as its chemical form. For instance, mercury in elemental form is highly soluble in lipids hence readily cross plasma membranes. In its divalent oxidized state, they are more toxic than in monovalent state. Consequently, divalent mercury compounds are rapidly absorbed thus producing higher toxicity. Additionally, organic forms of mercury have higher absorption rates (90%) than inorganic forms (10%). Because of this, organic compounds of mercury have greater corrosive impacts on the gastrointestinal mucosa (Broussard, Hammett-Stabler, Winecker, & Ropero-Miller, 2002).

Mercury Exposure and Effects

Mercury exposure occurs in various ways. The chief source of mercury exposure to human natural degassing of the earth's crust (Clarkson, 1993; Gerstenberger, Pratt-Shelley, Beattie, & Dellinger, 1993; Dinis & Fiuza, 2011). Mercury pollution can also arise as a result of human activities. It is estimated that a thousand tonnes of mercury have been released to the environment due to human activities (Streets et al., 2017). Mercury vapor is found in the atmosphere, the primary passageway of global transport of the pollutant. In the atmosphere, mercury remains unaltered for about one year. After about a year, mercury undergoes conversion into a water-soluble form and is returned to the surface of the earth where it is converted to mercury vapor or mono-methyl mercury compounds by micro-organisms, mainly bacteria. Mono-methyl mercury enters the aquatic food chain through aquatic organisms (planktons then fish). When human beings eat fish contaminated with mercury, they are too exposed to mercury (Diez et al., 2009; Sagiv, Thurston, Bellinger, Amarasiriwardena, & Korrick, 2012). Therefore, exposure in human beings is primarily dietary (Habiba et al., 2017).

The impact of mercury exposure in children can be examined in two dimensions. First, fetal exposure of mercury through mothers' intake of contaminated shellfish and fish has been associated with adverse developmental outcomes such as impaired neurological development in children (Kampa & Castanas, 2008; Rice, Walker, Wu, Gillette, & Blough, 2014). Impaired nervous and cognitive development is linked to the neurotoxicity of mercury (Myers et al., 2009). Children exposed to mercury via their mothers have also been found to have low verbal Intelligence Quotient (IQ) scores and suboptimal scores in social development, fine motor skills, and prosocial behavior (Oken & Bellinger, 2008).

Exposure to mercury in children has also been found to lead to mental retardation (Ip, Wong, Ho, Lee, & Wong, 2004; Huang, Law, Li, Yu, & Li, 2014; Mohamed et al., 2015; Mahmud, Huq, & Yahya, 2016; Ye, Leung, & Wong, 2017). According to Liu, McDermott, Lawson, and Aelion (2010), mercury toxicity may also be manifested through growth disorders, epilepsy, excessive salivation, deformity of limbs, chorea and athetosis, dysarthria, damaged cerebellum, misalignment of the eyes, and primitive reflexes. Furthermore, according to the World Health Organization (2017), inhalation of mercury vapor has been found to lead to impairment of vital body organs such as the kidneys, the lungs, digestive and immune systems, and the nervous system. Mercury exposure has also been reported to cause eye and skin corrosion as well as to lead to neurocognitive disorders. Examples of neurocognitive disorders linked to mercury toxicity include impaired memory (Tang, Wang, & Jia, 2015; Aaseth, Ajsuvakova, Skalny, Skalnaya, & Tinkov, 2018; Kaur, Kaur, Singh, & Bhatti, 2018), insomnia (Zhou et al., 2014; Do et al., 2017; Sun, Hu, Yuan, Zhang, & Lu, 2017), and tremors (World Health Organization, 2017; Calabrese, Iavicoli, Calabrese, Cory-Slechta...