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Cite this article as:

Palai, S., Dehuri, M., and  Patra, R (2021). Heavy Metals in the Food Chain: Health Consequences. Food and Scientific Reports. 2 (8) 33-36.

ABSTRACT

Heavy metals are naturally occurring elements in the earth`s outer coating that are used for a number of industrial and commercial purposes. Heavy metals like arsenic, lead, mercury, cadmium, chromium, copper, manganese, nickel, silver can be poisonous to humans in high doses, causing acute and chronic toxicities. Heavy metal toxicity is caused by biological pathways that produce free radicals, which enhance oxidative stress causing carcinogenesis. There is an increasing concentration of these heavy metals in the food chain due to various anthropogenic activities, consumption of heavy metal contaminated food and water as well as pollution. Therefore, the public must be aware of their harmful health influences as it can cause grievous impacts on health.

Keywords: heavy metals, free radicals, oxidative stress, carcinogenesis

Metals are elements that occur naturally in the biosphere. They lose electrons freely to form new cations being highly conductive. Metals can be found in the atmosphere, the crust, and the oceans, among other areas on the globe. It can also accumulate in living entities such as plants, animals, and bodies of water. Arsenic, lead, mercury, cadmium, chromium, copper, manganese, nickel, iron etc. are the examples.

Heavy metals are a type of metal that is known for not only having a high density, but also for having a harmful impact on the environment and living things. Natural processes like volcanic eruptions, spring water, and erosion, as well as anthropogenic activity like industrial operations, fossil fuel combustion, and agricultural actions, all contribute to heavy metal dispersion in the environment. These heavy metals accumulate in living creatures including human through various ways causing detrimental effects. These heavy metals are transported and compartmentalised into cells and tissues, where they bind to proteins and nucleic acids, causing damage and changing biological processes. Heavy metal poisoning is hence hazardous in nature (Engwa et al., 2019). Due to accumulation of heavy metals for longer period in the body, there will be various degenerative processes akin to Parkinson`s and Alzheimer`s disease. Chronic exposure with heavy metals/ complexes can lead to genetic mutations, hormonal alteration, endocrine and reproductive changes, damage nucleic acids leading to carcinogenesis eventually. The sources, signs and symptoms, and multiple detrimental effects of heavy metals will be discussed in this article.

Sources and health hazards of heavy metal exposure

Heavy metal is a natural part of our surroundings. They can be found in the biosphere hydrosphere, lithosphere and atmosphere. Heavy metals are released during mining activities through strewn ore that is left exposed to be transported by air and water to other sites. Heavy metal elements are also employed in several sectors. They are set out into the atmosphere during combustion or onto land/aquatic bodies as effluents of combustion process. Heavy metals are also found in industrial products like paints and cosmetics. Erosion, run-off, and acid rain, as well as bodies of water, can carry heavy metals to other sections of the soil (Pyatt et al., 2018). Heavy metal poisoning in the body produces a slew of health issues. Heavy metals can harm and cause pathological changes in organs like liver, kidney, brain and lungs. Heavy metal poisoning can have immediate or long-term consequences. Chronic heavy metal exposure can result in muscular, skeletal, and neurological issues. Degenerative physical and neurological processes may lead to multiple sclerosis, Parkinson`s disease, muscular dystrophy and Alzheimer`s disease. Free radicals produced by these heavy metals in the body causes oxidative stress, which destroys enzymes, nucleic acids, DNA, lipids, proteins resulting in carcinogenesis (Fig.-1). Continuing exposure to several heavy metals is also linked to the development of cancer.

Arsenic

Arsenic is the 20^th most common element found on the earth. Inorganic arsenite and arsenate compounds are hazardous to humans and other living creatures in the environment. Exposure to arsenic occurs from many sources, including industrial ones like smelting and mining. Drinking water polluted with arsenic is a potential source. It is also found in insecticides, paints, fungicides, herbicides and wood preservatives. Arsenic poisoning can be either acute or chronic. Acute arsenic poisoning can result in blood vessel and gastrointestinal tissue loss causing harm to the heart, brain and gut. Chronic arsenic toxicity is referred to as arsenicosis. Skin signs such as keratosis and pigmentation are common. Less severe stages of arsenic poisoning show nausea and vomition as well as a decrease in hormone production. Damage to blood vessels, erythrocytes and leukocytes cause abnormal heart rhythms. Prickling sensations occur in the hands and legs. Cancer can be caused by long-term exposure. Rashes on the skin, respiratory illnesses, neurological problems, peripheral neuropathy, hypertension, and diabetes are only a few of the symptoms. In this present scenario, environmental specialists are advising reduction in the existing acceptable limit of arsenic in drinking water or foods (Engwa et al., 2019).

 Lead

Lead is bright, bluish silvery metal found in a dry environment. Most prevalent sources of lead are food, cigarettes, drinking water and industrial operations. Industrial sources of lead include household paint and gasoline. Examples include lead bullets, pewter pitchers, plumbing pipes, paint, toys, and storage batteries. As a result of industrial processes and automotive emissions, lead is released into the environment. As a result, it is possible that it will leak into the ground and into the water. Humans are also exposed to lead through water or food since it can be absorbed by plants. Lead poisoning is the toxicity produced by lead exposure. In both children and adults, lead poisoning usually affects the intestine and brain. Headaches, nausea, vomiting, stomach discomfort, weariness, sleeplessness, hallucinations, and other symptoms can occur as a result of acute lead poisoning. Vertigo, renal failure, hypertension and arthritis are all common symptoms of chronic lead poisoning. Birth defects, autism, allergies, psychosis, mental retardation are other issues affecting children. The following are all probable outcomes: brain damage, muscle weakness, paralysis, hyperactivity, dyslexia, kidney failure, weight loss, coma, and death. Neurotoxic effects are especially dangerous to foetuses in the womb and children (Jaishankar et al., 2014).

Mercury

Metallic mercury is silver-white sparkling odourless liquid metal that turns into a colourless, odourless gas when heated. Mercury is found in thermometers, dental amalgams and batteries. Chemicals, metal-processing, electrical-equipment, construction and automotive industries use it. As mercury is in a gaseous state, it can be inhaled. Anthropogenic activities such as mining, agriculture, cremation, and discharges of municipal wastewater or effluent from industry may expose humans to mercury. When mercury reacts with other elements, it produces both inorganic and organic mercury. Metal, inorganic, and organic mercury in high concentrations can harm the kidneys, brain, and growing foetus. Methyl mercury is a carcinogen that increases the risk of cancer. Organic mercury is lipophilic by its nature. As a result, getting through cell membranes is simple. Thus, increased mercury exposure easily affects the nervous system altering brain activities. This condition causes tremors, hostility, memory problems, shyness and hearing problems. The environmental impact of mercury and its compounds is significant. Mercury poisoning during pregnancy can result in mental retardation, retention of basic reflexes, cerebellar symptoms, impaired motor neuron function, memory loss and speech difficulties in the offspring (Carocci et al., 2014).

 Cadmium

Paints, pigments, alloys, coatings, batteries, and plastics are among the products made with this metal. In alkaline batteries, about three-quarters of the cadmium is employed as an electrode component. Cadmium is a heavy metal that can persist for years in soils and sediments after being discharged into sewage sludge by industrial activity, cadmium smelters and fertilisers. This significant human cadmium exposure due to ingestion of tainted foods, such as cereals, grains, and fruits, as well as tainted beverages, fruits and green vegetables can cause severe illness. Humans may potentially be harmed by the combustion of municipal waste. Cadmium and its derivatives have a variety of detrimental health effects. The human body`s inability to eliminate cadmium compounds precipitates the negative effects of cadmium exposure. Inhalation of cadmium even for time can cause sickness. Its ingestion in high dosages can induce lung damage and respiratory irritation, while low levels can cause stomach irritation leading to vomition and diarrhoea. Cadmium accumulates in the bones and lungs of persons exposed to it for an extended period of time, causing damage to the bones and lungs. In both animals and humans, cadmium has the potential to promote bone calcification and osteoporosis. Cadmium is particularly harmful to the kidneys, where it accumulates in greater levels in the proximal tubular cells. As a result, cadmium poisoning can harm the kidneys. Cadmium has also been related to prostate cancer and male testicular atrophy (Engwa et al., 2019).

 Chromium

Coal, petroleum, chrome steel, oil well drilling, pigment oxidants, fertilisers, catalyst, and tanneries for metal plating contain chromium. Wood preservation, electroplating, and metal plating are just a few of the industries that use chromium. Metallurgy, paint, tanning, pigment manufacture, chemical production, pulp and paper production are examples of industries where chromium play a key role. These industrial and agricultural processes may contribute to chromium release into the environment due to anthropogenic activities, sewage disposal and fertiliser use. Significant skin redness and oedema are common adverse reactions to chromium. Chromium compounds in extremely high concentrations can cause major cardiovascular, pulmonary, and neurological disorders in humans, affecting the haematology, gastrointestinal, renal, hepatic, and neurological systems. Higher quantities of chromium compounds in the environment may cause cancer in humans. Exposure to chromium through drinking water leads to stomach tumours suggesting carcinogenicity of chromium. The corrosive characteristics of chromium causes allergy. As inhaling excessive levels of chromium irritates the nasal lining, chromium compounds produce nasal septum ulcers, which are prevalent among chromate workers (Teklay, 2016).

 Copper

Certain cookware, pipes, wires, cables etc. are made from this heavy metal. Birth control pills and intrauterine devices are also made using copper. Copper sulphate is used in swimming pools and drinking water for disinfection. It has the potential to accumulate in the soil and can be absorbed by plants. Copper is thus found in a number of foods such as wheat germ, almonds, bran, avocados, and so on. Copper toxicity can lead to fever, diarrhoea with black stool and long-term exposure can harm liver, kidney and brain (Nkwunonwo et al., 2020).

 Manganese

Gasoline fumes have very dangerous manganese after addition of methylcyclopentadienyl manganese tricarbonyl (MMT) to gasoline. Manganese has the potential to be harmful to the nervous system. Accumulation of manganese in the brain causes manganism, a neurological condition. Memory and cognitive impairment, as well as gait issues, bradykinesia, micrographia, and depression, are all common. Manganism has symptoms like tremor, gait problems, postural instability, and cognitive impairment that are quite similar to Parkinson`s disease (Aschner et al., 2009).

 Nickel

Nickel plated jewellery, metallic objects, wire, batteries, machine components, steel, and electrical parts are the applications. It can also be found in foods like commercial peanut butter, milk, vegetable oils high in hydrogenated oils, unprocessed grains and cereals, tainted alcoholic beverages and cigarette. Long term exposure to nickel can cause fibrosis of the lungs, renal and cardiovascular problems and cancer (Genchi et al., 2020).

Human beings can be exposed to heavy metals by consuming contaminated foods including sea animals, drinking contaminated water, inhaling polluted air as dust fumes, or working in an environment that contains heavy metals. Heavy metal contamination enters the food chain in a cyclic order, starting with industry and ending with the environment, soil, water, and food, and finally to humans (Jarup, 2003). These heavy metals get access to various tissues of the body via transfer through blood. For example, red blood cells transfer lead to the liver and kidneys, where it is subsequently redistributed. Cadmium binds to calcium and then attaches to metallothionein in kidney and blood cells, as well as albumin in liver tissue. Manganese vapour diffuses to the central nervous system after passing via the bloodstream from the lungs (Peralta-Videa et al., 2009).

 Conclusion

Exposure to heavy metals in humans occurs due to eating contaminated food and drinking polluted water, skin contact, inhaling contaminated air, and most crucially occupational hazard. Despite the fact that some heavy metals like iron and manganese, are indispensable for specific biochemical and physiological roles in the body, heavy metals are toxic to the body when consumed in large quantities. Heavy metal poisoning can be acute or chronic, causing problems in the brain, lungs, liver and kidneys. The exposure to these heavy metals should therefore be minimized, and in case of poisoning chelation therapy and supportive treatment should be followed.

 References

 

Aschner, M., Erikson, K. M., Hernández, E. H. and Tjalkens, R. (2009). Manganese and its role in Parkinson’s disease: from transport to neuropathology. Neuromolecular medicine, 11(4): 252-266.

Carocci, A., Rovito, N., Sinicropi, M. S. and Genchi, G. (2014). Mercury toxicity and neurodegenerative effects. Reviews of environmental contamination and toxicology, 229:1-18.

Engwa, G. A., Ferdinand, P. U., Nwalo, F. N. and Unachukwu, M. N. (2019). Mechanism and health effects of heavy metal toxicity in humans. Poisoning in the modern world-new tricks for an old dog, 10.

 Genchi, G., Carocci, A., Lauria, G., Sinicropi, M. S. and Catalano, A. (2020). Nickel: Human health and environmental toxicology. International journal of environmental research and public health, 17(3): 679.

Jaishankar, M., Tseten, T., Anbalagan, N., Mathew, B. B. and Beeregowda, K. N. (2014). Toxicity, mechanism and health effects of some heavy metals. Interdisciplinary toxicology, 7(2): 60.

Jarup, L. (2003). Hazards of heavy metal contamination. British medical bulletin, 68(1):167-182.

Nkwunonwo, U. C., Odika, P. O. and Onyia, N. I. (2020). A review of the health implications of heavy metals in food chain in Nigeria. The Scientific World Journal, 2020.

Peralta-Videa, J. R., Lopez, M. L., Narayan, M., Saupe, G. and Gardea-Torresdey, J. (2009). The biochemistry of environmental heavy metal uptake by plants: implications for the food chain. The international journal of biochemistry & cell biology, 41(8-9):1665-1677.

Pyatt, F. B., Kennedy, R. D. P. and Kennedy, E. M. P. (2018). An appraisal of sample preparation, analysis and some toxicological implications of ancient industrial metalliferous pollution. International Journal of Environmental Studies, 75(3):518-531.

Teklay, A. (2016). Physiological effect of chromium exposure: A review. Int. J. Food Sci. Nutr. Diet. S, 7:1-11.

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Heavy Metals in the Food Chain Health Consequences_Food and Scientific Reports.pdf