Heavy metals What we need to know

15.05.2023

Heavy metals exist naturally in the environment. They can be found in some medicines, foods, nutritional supplements. In normal amounts, some of them are necessary for conducting a number of biological processes. Chemicals for industrial use also contain heavy metals, the contact of which with soil, air, water - brings serious consequences for health.

Table of Contents

Heavy metal poisoning can cause organ damage, behavioral abnormalities, and mental problems. Heavy metal poisoning in children causes long-term, serious problems.

Mercury, lead, chromium, cadmium and arsenic are the most common toxic heavy metals. Intoxication with metals such as aluminum, copper, iron, manganese, nickel, selenium, silicon, thallium, zinc, beryllium, silver, cobalt and others is common. Contamination of air, water, and soil with these metals causes acute or chronic poisoning. Bioaccumulation of these elements in tissues causes toxic effects and damage and dysfunction of various organs. Heavy metals disrupt cellular processes, including: growth, reproduction, differentiation, recovery processes (reparation) and apoptosis (programmed cell death). The mechanisms of the pathological effects of these metals are similar and lead to a decrease in the body's antioxidant and enzyme activity and oxidative stress. In addition, some of them are characterized by selective binding to specific macromolecules. For example, the interaction of lead with aminolevulinic acid dehydratase and ferrochelatase leads to its accumulation and pathological effects on nervous tissue, also causes anemia and others. Chromium, cadmium, arsenic can cause genomic instability, resulting in oxidative stress and defects in DNA repair processes, resulting in the development of cancer and other pathological processes.

mercury (Hg, mercury)

CNS damage
Kidney dysfunction
Gastrointestinal ulcers
Hepatotoxicity

Mechanism

Thiol binding
Inactivation of enzymes
Origin of oxidative radicals
Reduction of water molecule transport proteins
Inhibition of glutathione peroxidase

Mercury exists in three forms: metallic (Hg0), inorganic (Hg+, Hg2+) and organic mercury (methyl or ethylmercury). Elemental (metallic) mercury is liquid at room temperature, volatile and produces vapors that are dangerous to health if inhaled in large concentrations. It crosses the blood-brain and placental barriers and is much more toxic than inorganic mercury.

The organic mercury methylmercury (Me-Hg) or ethylmercury (Et-Hg) is much more toxic than its inorganic compounds. It is easily absorbed from the gastrointestinal tract. Mercury compounds are widely used in metallurgy, especially gold mining, as well as in industrial processes, such as the production of fluorescent lamps.

Methyl and ethylmercury compounds are used as fungicides in plant protection products. In the past, mercury was used in the production of some medicinal drugs - diuretics and disinfectants, but today they have been replaced by safer means. Mercuric chloride is an active ingredient in skin lightening creams, soaps, and freckle removers. HgCl2 irreversibly inhibits melanin tyrosinase and ensures reduction of melanin accumulation.

Inorganic mercury compounds accumulate in the kidneys. They do not have the ability to cross the blood-brain and placental barriers.

lead (Pl)

CNS damage
Lung dysfunction
Anemia
Gastrointestinal colic
Liver damage
Cardiovascular injuries

Mechanism

Enhanced release of inflammatory cytokines IL-1β, TNF-α, and IL-6 in the CNS
Increasing serum ET-1, NO, and EPO concentrations
Inhibition of aminolevulinic acid ferrochelatase and dihydrogenase (violation of hemoglobin heme synthesis)
Reduction in the concentration of antioxidants GSH, SOD, CAT and GPx.

Lead is one of the most toxic heavy metals, which is quite abundant in the environment, and it can enter the body through the respiratory system, skin, and digestive system. Lead affects the nervous, genitourinary, cardiovascular, respiratory systems through immuno-modulating, oxidative and inflammatory mechanisms.

Anemia develops with long-term, chronic exposure to lead, which is due to the inhibition of two enzymes involved in heme synthesis - aminolevulinic acid dehydratase and ferrochelatase. Also, under the influence of lead, an imbalance between oxidants and antioxidants and oxidative stress develops. GPx, CAT and SOD are metalloproteins whose antioxidant and anti-free radical functions are reduced by lead exposure. Long-term intoxication with lead disrupts the functioning of the immune system, in particular suppresses the proliferation of lymphocytes and NK (natural killer) cells in drivers, battery production workers, and silverware specialists. There is some evidence of a relationship between long-term lead exposure and atherosclerosis and cardiovascular disease.

Chrome (CR)

Kidney dysfunction
Gastrointestinal disorders
skin diseases
Lung, kidney, bladder, bone, thyroid tumors

Mechanism:

DNA damage
Genomic instability
Oxidative stress and generation of oxidative radicals

Chromium is found in the earth's crust and seawater. Also related to industrial processes. The trivalent form of chromium in small amounts is necessary for the processes taking place in the body - the metabolism of lipids and proteins, as well as the activity of the cofactor of insulin. The 6-valent form of chromium is classified as a group XNUMX occupational carcinogen. Chromium affects the population by taking it with water, food, and medicines. Chromium has a high bioaccumulation ability in human organs and tissues, which is manifested by dysfunction and tumors of the skin, kidneys, nervous system, bones, endocrine glands, digestive and respiratory systems.

Chromium's carcinogenic properties are due to DNA transcriptional dysregulation and genomic instability.

Oxidative stress caused by hexavalent (6-valent) chromium and generated oxidative radicals on the one hand are aimed at breaking DNA and cellular lipid structures, and on the other hand, it inhibits apoptosis (programmed death) of damaged cells, which leads to the development of tumor processes as a result of genetic mutations.

Cadmium (Cd)

Degenerative bone diseases
Kidney diseases
Liver damage
Gastrointestinal injuries
lung damage
Disruption of zinc and copper metabolism

Mechanism:

Dysregulation of gene expression
inhibition of apoptosis
Suppression of reparative (restorative) processes
Oxidative stress
Formation of oxidative radicals
Disruption of phosphorylation chain reactions
Parathyroid hormone decrease in the blood

Cadmium is found in soil and water in the form of sulfates, sulfides, chlorides, carbonates and other salts. An increase in its concentration in the environment is usually the result of improper management of industrial processes. Cadmium entering the body through contaminated water, food or air causes both short-term and long-term toxic effects - depending on the exposure time and dose. Cadmium, like chromium, is classified as a carcinogen of the first group. Cadmium dust causes much more severe intoxication than ingestion through contaminated food or water. As a result of chronic inhalation of cadmium dust, diseases and tumors of lung, kidney, bone and other organ systems develop in people working in glass production, metal alloys, electric batteries and galvanizing processes.

Cases of mass contamination of food and water reservoirs with cadmium (in Japan) have been described, after which the patients developed bone degenerative processes, kidney failure, lung and gastrointestinal system injuries.

The concentration of cadmium in the blood of smokers is almost twice as high as that of non-smokers, which is probably related to the accumulation of cadmium (and other heavy metals) in tobacco leaves.

In the body, cadmium is bound by metalloproteins, which in this way ensure their "harmlessness". But, with high concentration of cadmium in the body, the concentration of unbound cadmium also increases and its toxic effect is revealed. Bioaccumulation of cadmium mainly occurs in the liver and kidneys, which leads to carcinogenic processes in these organs. Like other metals, cadmium has the ability to connect with plasma protein - albumin; This disturbs the balance of calcium, zinc and iron in the plasma and causes the development of diseases associated with it. The pronounced osteotoxicity of cadmium (toxic effect on bone tissue) should be due to parathyroid hormone dysfunction and related calcium metabolism disorders.

Arsenic (As)

Cardiovascular dysfunction
Skin and hair damage
Damage to the CNS
Gastrointestinal disorders
Injuries of liver cells and erythrocytes

Mechanism:

Damage to the capillary endothelium
Impairment of glutathione conjugation (impairment of antioxidant function)
Violation of ATP synthesis
Disturbance of neurotransmitter homeostasis

Arsenic is historically the strongest poison. It is known as the "king of poisons and the poison of kings". It exists in nature as metalloid (As0), inorganic (As3+ and As5+), organic arsenic and arsine (AsH3).

Arsenic is absorbed from the small intestine. It is also possible to contaminate it through the skin and respiratory tract. It spreads to: lungs, heart, kidneys, liver, muscles, nervous tissue.

Acute and chronic arsenic poisoning is associated with the inactivation of a number of vital enzymes. By inactivating pyruvate dehydrogenase, the Krebs cycle is blocked and, as a result, ATP synthesis is delayed, which leads to cell cycle disruption and cell necrosis. The toxic effect of arsenic on the endothelium of blood vessels leads to increased permeability of blood vessels, expansion of blood vessels and circulatory collapse. In case of chronic intoxication, arsenic can cross the placental barrier and initiate miscarriage, stillbirth or premature birth in the early gestational period.

Arsenic accumulates in skin cells and causes keratosis and hyperpigmentation. Decreased expression of keratinocytes is accompanied by apoptosis aberration and skin tumorigenesis.

Hepatocellular carcinoma and angiosarcoma are associated with arsenic intoxication.

Oxidative stress-induced lipid peroxidation leads to DNA damage and CNS cell death.

Research material

The research material is selected depending on which metal is being tested and how long it was exposed to (short-term, long-term). Urine and blood are the most common test materials. To diagnose chronic intoxication, it is sometimes necessary to study nails and hair.

How to prepare for the test?

Some foods (fish, crustaceans) and medicines may contain heavy metals, so it is not recommended to take such products and medicines for 48 hours before the study.

Interpretation of answers

A higher than normal concentration of heavy metals in the blood may be a sign of severe intoxication, but not always. Even in the absence of symptoms, it is necessary to find a source of intoxication to reduce toxic exposure. Depending on the need, chelation (binding) therapy is also prescribed. Chelation therapy is usually accompanied by serious side effects, so the question of treatment should be decided by a doctor based on an assessment of risks and benefits.

A normal or low concentration of heavy metals in the blood indicates the absence of intoxication. However, some heavy metals quickly leave the bloodstream and accumulate in tissues. Therefore, in the presence of symptoms, despite the detection of a low concentration of heavy metals in the blood, sometimes additional studies are necessary - skin, hair, nails and other tissues.

Symptoms

Symptoms depend on: the type of metal, its concentration in the body, the age of the patient, although the general clinical picture includes more or less similar complaints of intoxication.

Nausea-vomiting
stomach-ache
Diarrhea
Tingling sensation in hands and feet - ants
increased breathing
Chills
muscle weakness
Changes in memory and behavior
Heart rhythm disorder and others

In the presence of risk factors for lead exposure (walls painted with old paint, furniture, proximity to industrial production, possibility of contamination of food and water with heavy metals, etc.), children under 6 years of age are recommended to be tested for heavy metals, for timely detection of intoxication and prevention of further complications, even in the absence of symptoms. Even a very small dose of lead has the ability to damage a child's (developing) nervous system, causing learning and other mental problems.