Science and Informations      Health effects of heavy metals on organism

Health effects of heavy metals on organism (As, Pb, Hg, Cd, Cr, etc.)

 

 

Heavy metal pollution pose a major problem worldwide. From an environmental and toxicological point of view, the term "heavy metals" is used to refer to metallic elements which have toxic effects on organisms and pollute the environment. This collective term refers to a group of metals and metalloids with an atomic density higher than 5 g/cm3. However, the term does not apply to aluminium (Al) and selenium (Se), so it is more suitable to use the term toxic metals. (Cibulka, 1991) Toxic metals is a relatively large group of non-degrading contaminants which includes 37 elements. They differ in terms of properties, effects and sources of origin.

Many metals belonging to the group of toxic metals exhibit toxic properties even at very low concentrations (even a few ppm). For this reason, these are labelled "trace elements". However, this group also includes non-metallic elements, essential elements, probably essential elements, non-essential elements and toxic elements. (Prousek, 2021) The first group includes elements which are indispensable (in low concentrations) for the normal growth of plants and animals but which are toxic in higher concentrations. These are referred to as "micronutrients": e.g. iron (Fe), copper (Cu), manganese (Mn). The second group includes those elements whose essentiality has not yet been clearly proven, in particular nickel (Ni), fluorine (F), bromine (Br), vanadium (V), barium (Ba) and strontium (Sr). The third group is made of elements which have demonstrable positive effects, but their absence does not cause pathological changes - chromium (Cr), thallium (Tl), uranium (U) are toxic when their concentration exceeds the threshold, but no adverse effects are known to result from their absence. For this reason, they were labelled as non-essential elements. (Alloway and Ayres, 1993) The fourth group of trace elements includes toxic elements: arsenic (As), cadmium (Cd), lead (Pb) and mercury (Hg). Their environmental significance is limited to their toxic properties at very low concentrations. The attention should be paid to the concentration of elements in the human body. Therefore, toxicity is evaluated mainly in terms of toxic elements concentration in the body. The toxicity series goes as follows: Hg> Cd> Ni> Pb> Cr.

Mercury (Hg), cadmium (Cd), nickel (Ni), lead (Pb), chromium (Cr) and arsenic (As) are considered to be the most harmful heavy metals for animals and humans alike

Usually, heavy metals enter the body with food. Their presence in food may be the result of genetically inherent bioaccumulation of a particular plant or animal (Suhaj and Kováč, 1996). Of all the elements which enter the food chain and cause food contamination, arsenic (As), cadmium (Cd), lead (Pb) and mercury (Hg) are considered to be the most toxic. Where soils are enriched in these elements, it is usually through the agricultural, industrial or urban activities of man. The propensity for plants to accumulate and translocate these contaminants to edible and harvested parts depends largely on soil and climatic factors, plant genotype and agronomic management. The bioavailability of contaminants generally also depends on the physical and chemical properties of the diet. There is a strong link between plant, animal and human microelement nutrition and the absorption and action of contaminants in these organisms (McLaughlin, Parker and Clarke, 1999). The presence of toxic elements in food is related, among other things, to environmental pollution. The main anthropogenic sources of heavy metal contamination include: burning of fossil fuels, transport, industrial metal production, excessive use of mineral fertilizers and other agrochemicals, penetration of sewage sludge to the soil. Natural sources of toxic elements in the environment include rock weathering, forest fires and volcanic activity. The content of toxic elements in food is one of the main indicators of health safety. From all toxic elements, limits for the presence of mercury (Hg), cadmium (Cd), aluminium (P b) and arsenic (As) in food are set the highest. (Velíšek, 2002).

Table 1: Maximum permitted amounts of mercury, cadmium, lead and arsenic in certain foods (VESTNÍK Ministerstva pôdohospodárstva Slovenskej republiky, 2006)

Chemický prvok

Maximum permitted amount in v µg/kg

Groceries

Mercury (Hg)

20

Potatoes

30

Fruits

30

Vegetables

500

Molluscs, crustaceans

100

Entrails

Cadmium (Cd)

10

Milk

20

Eggs and egg products

40

Fruit and vegetable foods for infants and young children with added cereals

50

Non-alcoholic beverages

100

Game animals

800

Poppy seeds

Lead (Pb)

50

Non-alcoholic beverages

100

Eggs

2 000

Cacao powder, glucose syrup

5 0000

Gelatin, yeast

10 000

Tea

1 000

Other foodstuffs except foodstuffs according to special regulations

Arsenic (As)

100

Edible fats and oils

200

Fruit juices and nectars

500

Fruit juices and nectars

1 000

Sugar and other natural sweeteners other than powdered sugar, cocoa powder

2 000

Baker's yeast, gelatin, powdered sugar

5 000

Spices

 

 

 

Mercury

Mercury (Hg) enters the environment through the combustion of fossil fuels, various wastes and in industrial and agricultural processes (Bencko, Cikrt and Lener, 1995). Fungi have a great ability to concentrate Hg, especially those from Agaricaceae and Tricholomataceae families (Zimmermannová, 2000). The primary source of Hg for humans is fish consumption (Toman, Massányi and Ducsay, 2000). From a toxicological point of view, the form in which Hg occurs is very important. Alkylmercury compounds are more toxic than inorganic compounds due to higher absorption and longer retention (Toman, Massányi and Ducsay, 2001). In addition, toxicity is directly affected by the length of exposure (Kafka and Punčochářová, 2002). Chronic mercury poisoning is caused by continuous or intermittent long-term contact with even a small amount of mercury - it causes damage to the brain and nervous system, liver and irreversible kidney damage. Symptoms of mercury poisoning include soft and spongy gums, gum recession, gingivitis. People with chronic mercury poisoning also often have major mood swings, are irritable, frightened, depressed, or get aroused very quickly for no apparent reason. Such people can become extremely upset in any situation, lose any self-confidence and become apathetic. Hallucinations, memory loss, and inability to concentrate may also occur. Damage to the nervous system is of major concern - shaking of the hands, loss of sensitivity in the hands and feet, difficulty walking or incomprehensible speech. Eventually, this can lead to balance and gait problems. In rare cases, mercury poisoning can cause paralysis and death.

 

Cadmium

 

Cadmium (Cd) is a common element of industrial pollution, so it easily enters the food chain. The main sources of Cd pollution are plants mining and processing zinc and lead ores, coal combustion, oil, waste and industrial fertilizers incinerators (Toman, Golian and Massányi, 2003). Mammal kidneys (up to 1,300 µg/kg), oysters (up to 5,000 µg/kg), crayfish and crabs are rich in Cd (Toman, Massányi and Ducsay, 2000) (Sokol et al., 1998). The content of Cd in food of animal origin is negligible when compared to plant food. The highest amount of Cd accumulates in the kidneys of both domestic and wild animals. Lower levels were observed in the livers of the animals. The muscle of animals accumulates only low amount of Cd and therefore its consumption is not very dangerous to human health (Toman, Massányi and Ducsay, 2000). Cd replaces zinc in the biochemical structures of the organism and can thus change their functionality (e.g. cause inactivation of some enzymes) (Kafka and Punčochářová, 2002). The most common source of Cd poisoning is tobacco smoking. The most serious consequence of chronic cadmium poisoning is cancer (lung and prostate). A smoker who smokes 20 cigarettes a day absorbs 2-4 micrograms of cadmium a day and accumulates up to 0.5 milligrams of cadmium in their body per year. It may not sound like much, but even a small amount of cadmium is very dangerous in the long run.

Cadmium is one of the key factors for osteoporosis. It is known to damage the kidneys and liver. Cadmium has a major effect on the testes and ovaries and can be a major cause of infertility. Cadmium also limits the body's ability to absorb essential minerals. Some recent research suggests that cadmium may be a major contributing factor for breast cancer.

Manifestations of acute cadmium intoxication are not specific and it is difficult to distinguish them from acute intoxication by other poisons (Ginter and Nagyová, 1991).

 

Nickel

Although it is the fifth most common element in the biosphere, Ni has been discovered when mining other metals. Nickel is also present in air, water and soil (Wang et al., 2009). Nickel allergy is a common cause of allergic contact dermatitis. Nickel allergy is often associated with earrings and other jewellery. Ni has many uses in industry and in the manufacture of consumer products such as stainless steel, magnets, coins and special alloys. Prolonged exposure to high concentrations of Ni and nickel compounds causes poisoning and health issues in humans. These include, but are not limited to, headache, dizziness, nausea, vomiting, epigastric pain, eye and respiratory tract irritation, cough, dyspnoea (hyperplasia), cyanosis, pulmonary edema (may be delayed), weakness, leukocytosis, pneumonitis, cerebral edema, convulsions, contact dermatitis and skin and lung sensitization (Yu, Tsunoda and Tsunoda, 2016). Ni and nickel compounds are known to be carcinogens (there is enough evidence to conclude that it can cause cancer in humans, including epidemiological studies suggesting a causal link between exposure to nickel compounds and cancer). An increased occurrence of cancer in workers exposed to Ni (also animals) supports the above-mentioned findings that exposure to a range of nickel compounds causes malignancies. Nickel sulphide fumes and dusts (also various other nickel compounds) are believed to be carcinogenic. Chronic exposure to Ni and nickel compounds is implicated in nickel-induced carcinogenic contact dermatitis (the most common harmful health effect of nickel in humans (Yu, Tsunoda and Tsunoda, 2016).

 

Lead

 

Much of our exposure to lead comes from human activities including the use of fossil fuels (including past use of leaded gasoline). Lead is also found in some old paint and contaminated soil. The major source of Pb contamination in food is packaging material, cans, foils and food production equipment (Kirchhoff, 1999). Fruits and leafy vegetables, cereals and wine show the highest content of lead. The Pb concentration in animal meat is very low, about 0.1 mg / kg, in milk 0.002 mg / l. In general, there is no acute risk of high levels of Pb in food, but higher Pb levels in the liver and kidneys of animals should be taken into account. If these organs contain more than 3 mg / kg, they are not suitable for consumption (Toman, Golian and Massányi, 2003). Approximately 90% of the Pb taken up by the body accumulates in the bones, where it negatively affects hematopoiesis (interferes with hemoglobin synthesis) – this may lead to anemia (Kafka and Punčochářová, 2002).

Lead poisoning is very serious. Lead exposure can have serious consequences for the health of children.  Lead can be passed through a pregnant woman's placenta to the fetus. Any exposure to lead in the prenatal period impairs the development of the baby even after birth. Because children are not yet fully developed, lead poisoning affects many aspects of development and growth. Lead poisoning can result in delayed speech, hyperactivity, attention deficit, learning disabilities, behavioural disorders, neurological and renal impairment, anemia, hearing loss. Lead poisoning affects children under the age of six months because their brain and nervous system are still developing and lead is hindering this development. Lead can also negatively affect a child's IQ.

Symptoms of lead poisoning include irritability, stomach pain, loss of appetite, diarrhea, poor concentration and lethargy.

 

Chromium

Chromium is unique among regulated toxic elements in the environment. It has been commonly used in various alloys and compounds for more than 100 years. Chromium occurs in the environment primarily in three valence states, elemental chromium (Cr0), trivalent chromium (Cr3+) and hexavalent chromium (Cr6+). In recent decades, chromium has been widely used in chromium alloys and chromium plating. Several million workers worldwide are exposed to air vapor, mist and dust containing Cr or its compounds (Wang et al., 2009). A major source of worker exposure to hexavalent Cr6+ occurs during chromate production, welding, chromate pigment production, chromium plating and spraying. The major source of other forms of Cr is mining, ferrochrome and steel production, welding, cutting and grinding of chromium alloys. Hexavalent Cr6+ and trivalent Cr3+ are used for chrome plating, dyes and pigments, leather tanning and wood protection. Cr is released into the air mainly by combustion processes and the metallurgical industry. Cr exposure by inhalation is common in the stainless steel welding industry (Yu, Tsunoda and Tsunoda, 2016). Cr was recognized as a dangerous element in the first years after its discovery. Hexavalent Cr6+ is considered lethal at doses higher than 3 g for adults. The first symptoms include vomiting and persistent diarrhea. Hemorrhagic diathesis and epitasis are usually observed after one week. Convulsions occur during diarrhea. Repeated inhalation of hexavalent Cr compounds causes nasal septal perforations and skin ulcers. Acute irritating dermatitis or allergic eczematous dermatitis have often been reported with chronic exposure to chromic acid vapor, as well as an increased incidence of respiratory cancer. Many workers have experienced bronchial asthma due to chromium dust or chromic acid fumes. Compared to mercury or cadmium, environmental chromium contamination is trivial. Nevertheless, serious toxic effects on plants have been reported at hexavalent Cr6+ concentrations of approximately 0.5 mg / l. Several studies have shown that hexavalent chromium compounds may increase the risk of lung cancer. Animal studies have also shown an increased risk of cancer. The WHO has determined that hexavalent Cr6+ is a human carcinogen (Yu, Tsunoda and Tsunoda, 2016).

 

Arsenic

Marine fish, marine crustaceans and molluscs contain high levels of arsenic (As). The majority of As is contained in almost non-toxic organic compounds. Of plant foods, higher amounts of As are found in oats and rice. Also, some wines may contain higher amounts of arsenic (Velíšek, 2002). It is likely that As in wine originates mainly from As-containing insecticides, which have been used to protect grapes from harmful insects (Rojas et al., 1999). As compounds are found in seafood, eggs and cheese (Caballero, Trugo and Finglas, 2003). It is also increasingly found in oats and cocoa beans (Suhaj and Kováč, 1996). As a considerable amount of As compounds has been used in agriculture, As is now widespread in the soil. As content in food other than seafood is generally less than 1 mg / kg. Marine fish contain on average less than 5 mg / kg. Most As in seafood is organic arsenic compounds soluble either in fats or water. The content of arsenic in drinking water differs across the world (Rojas et al., 1999). Organic arsenic compounds are predominant in food ingredients, especially in seafood, and these compounds are absorbed in the human gut but are not metabolised and are rapidly excreted. If arsenic is essential for humans, its recommended daily intake has not been estimated. The interactions of arsenic with other nutrients are largely unknown, with the exception of mutual antagonism with selenium (McLaughlin, Parker and Clarke, 1999). Because As compounds have been used as insecticides, herbicides and as animal feed additives, some soils, vegetation and poultry may be contaminated with As. Fortunately, As mostly occurs in organic compounds, which are rapidly excreted and are therefore relatively non-toxic to humans. As has also been found in mushrooms. The main sources of arsenic contamination of drinking water are natural sources. Velíšek (Velíšek, 2002) states that an acceptable daily dose for an adult is 140 µg at a body weight of 70 kg. Fish and drinks also play a significant role in the As intake.

 

Aluminium

 

Al levels in our environment and diet have been increasing over time. Many junk foods, aspirin and deodorants contain additives containing aluminium salts. Aluminium can also be released from aluminium cooking utensils. Aluminium is harmful to all life forms. It damages all types of fine tissue. Aluminium is neither required by biological systems nor is it known to participate in any essential biological processes. It tends to accumulate in the brain and bones. It is much less toxic than mercury, arsenic, lead or cadmium, but it seems to be more resistant than most.

The main symptoms of aluminium poisoning are loss of intellectual function, forgetfulness, inability to concentrate and, in extreme cases, dementia. It is also known to cause bone softening and even bone loss, kidney and other soft tissue damage, and can even cause heart failure.

 

 

Golian et al. (Golian, Sokol and Chovanec, 2004) in the years 2001 - 2003 they randomly took and processed a total of 600 samples from different categories and their results are summarized in the following table.

Values are given in µg / kg in parentheses are the highest permissible quantities (VESTNÍK Ministerstva pôdohospodárstva Slovenskej republiky, 2006)

  Cadmium (Cd) Lead (Pb) Mercury (Hg)
Bread 15,6 37,9 1,9
Pastries 10,6 50,5 1,9
Pasta 23,8 62,6 2,1
Sweet pastries 10,4 67,3 1,6
Non-alcoholic beverages 4,0 (50) 53,1 (50) 0,6
Tea 89,9 221,7 (10 000) 10,9
Vegetables 8,1 49,7 3,3
Spices 72,3 208,3 6,6
Mayonaise salads 6,6 20,6 7,5
Vegetable fats and oils 2,8 46,8 1,7
Dried fruits 7,0 235,9 3,0
Fish 10,4 79,5 108,9
Children’s nutrition 2,6 (40) 33,3 0,6
Oilseeds 244,7 45,1 2,7
Milk and dairy beverages 2,9 (10) 57,9 0,4

 

 

It is confirmed in the literature (Spark, Wells and Johnson, 1997; Ziółkowska, 2015; Vašková et al., 2019; Rong et al., 2020) that humic acids have a high affinity for toxic metals and, when bound by a chelate bond, prevent their resorption.

 

 

Použitá literatúra

Alloway, B. J. and Ayres, D. C. (1993) ‘Chemical principles of environmental pollution’, p. 291.

Bencko, V., Cikrt, M. and Lener, J. (1995) Toxické kovy v životním a pracovním prostředí člověka. Praha: Grada. Available at: https://www.databazeknih.cz/knihy/toxicke-kovy-v-zivotnim-a-pracovnim-prostredi-cloveka-276619 (Accessed: 6 October 2021).

Caballero, B., Trugo, L. and Finglas, P. M. (eds) (2003) Encyclopedia of Food Sciences and Nutrition.

Cibulka, J. (1991) Pohyb olova, kadmia a rtuti v biosféře. Academia.

Ginter, E. and Nagyová, A. (1991) ‘Kadmium. Metabolizmus a mechanizmus toxického pôsobenia’, Čs. fyziologie, 40(6), pp. 575–582.

Golian, J., Sokol, J. and Chovanec, M. (2004) Kadmium, olovo a ortuť - riziko surovín a potravín v spoločnom stravovaní. Nitra.

Kafka, Z. and Punčochářová, J. (2002) ‘Ťežké kovy v přírodě a jejich toxicita’, Chemické listy, 96(7), pp. 611–617.

Kirchhoffová, A. (1999) ‘Rizikovosť chemických prvkov v potravinách’, Výživa a zdravie, 44(3), pp. 53–54.

McLaughlin, M. J., Parker, D. R. and Clarke, J. M. (1999) ‘Metals and micronutrients – food safety issues’, Field Crops Research, 60(1–2), pp. 143–163. doi: 10.1016/S0378-4290(98)00137-3.

Prousek, J. (2021) Rizikové vlastnosti látok. STU Bratislava.

Rojas, E. et al. (1999) ‘Are metals dietary carcinogens?’, Mutation Research/Genetic Toxicology and Environmental Mutagenesis, 443(1–2), pp. 157–181. doi: 10.1016/S1383-5742(99)00018-6.

Rong, Q. et al. (2020) ‘Humic acid reduces the available cadmium, copper, lead, and zinc in soil and their uptake by tobacco’, Applied Sciences (Switzerland), 10(3), p. 1077. doi: 10.3390/app10031077.

Sokol, J. et al. (1998) Kadmium a jeho výskyt v organizmoch živočíchov. Štátna veterinárna správa SR.

Spark, K. M., Wells, J. D. and Johnson, B. B. (1997) ‘The interaction of a humic acid with heavy metals’, Australian Journal of Soil Research, 35(1), pp. 89–101. doi: 10.1071/S96008.

Suhaj, M. and Kováč, M. (1996) Prírodné toxikanty a antinutričné látky v potravinách. Bratislava: Bratislava: VÚP. Available at: https://arl4.library.sk/arl-sllk/sk/detail-sllk_un_cat-e003411-Prirodne-toxikanty-a-antinutricne-latky-v-potravinach/ (Accessed: 6 October 2021).

Toman, R., Golian, J. and Massányi, P. (2003) Toxikológia potravín. 1st edn. Nitra.

Toman, R., Massányi, P. and Ducsay, L. (2000) ‘Kadmium – kontaminant potravinového reťazca človeka’, in Cudzorodé látky v životnom prostredí: 3 medzinárodná konferencia. Nitra, pp. 208–212.

Toman, R., Massányi, P. and Ducsay, L. (2001) ‘Ortuť v potravinovom reťazci’, Trendy v potravinárstve, 8(4), pp. 3–4.

Vašková, J. et al. (2019) ‘Effects of Humic Acids in Chronic Lead Poisoning’, Biological Trace Element Research, 187(1), pp. 230–242. doi: 10.1007/s12011-018-1375-1.

Velíšek, J. (2002) Chemie potravin. 2nd edn. OSSIS. Available at: https://is.muni.cz/publication/520167/cs/Chemie-potravin-2/Velisek (Accessed: 6 October 2021).

VESTNÍK Ministerstva pôdohospodárstva Slovenskej republiky (2006).

Wang, L. K. et al. (eds) (2009) Heavy Metals in the Environment. CRC Press. doi: 10.1201/9781420073195.

Yu, M.-H., Tsunoda, H. and Tsunoda, M. (2016) Environmental Toxicology. CRC Press. doi: 10.1201/b11677.

Zimmermannová, M. (2000) ‘Koncentrácia ťažkých kovov v jedlých hubách’, Výživa a zdravie, XLV(3), pp. 63–64.

Ziółkowska, A. (2015) ‘The role of humic substances in detoxification process of the environment’, Ochrona Srodowiska i Zasobów Naturalnych, 26(4), pp. 1–5. doi: 10.1515/oszn-2015-0013.

 

 

Privacy policy settings

We use cookies so that we can provide you with the best user experience possible. More info...