Metal Excess and Toxicity
Metal toxicity or metal poisoning is the toxic effect of certain metals in certain forms and doses on life. Some metals are toxic when they form poisonous soluble compounds. Not all heavy metals are particularly toxic, and some are essential, such as iron. Heavy metals are naturally occurring elements that have a high atomic weight and a density at least 5 times greater than that of water.
Toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals.
Metal toxicity can also occur from exposure to other heavy metals such as aluminum, antimony, beryllium, cadmium, chromium, cobalt, copper, iron, manganese, nickel, selenium, silicon, and thallium. However, toxicities from these heavy metals are observed less frequently than from lead, mercury, and arsenic poisoning. The definition may also include trace elements when in abnormally high doses may be toxic.
Toxic metals sometimes imitate the action of an essential element in the body, interfering with the metabolic process resulting in illness.
Many metals, particularly heavy metals are toxic, but some heavy metals are essential, and some, such as bismuth, have a low toxicity.
Toxicity is a function of solubility. Insoluble compounds as well as the metallic forms often exhibit negligible toxicity.
The toxicity of any metal depends on its ligands. In some cases, organometallic forms, such as methylmercury and tetraethyl lead, can be extremely toxic. In other cases, organometallic derivatives are less toxic such as the cobaltocenium cation.
Radioactive metals have both radiological toxicity and chemical toxicity.
Metals in an oxidation state abnormal to the body may also become toxic: chromium(III) is an essential trace element, but chromium(VI) is a carcinogen.
Toxic metals can bioaccumulate in the body and in the food chain. Therefore, a common characteristic of toxic metals is the chronic nature of their toxicity.
Metal toxicity can also occur from exposure to other heavy metals such as aluminum, antimony, beryllium, cadmium, chromium, cobalt, copper, iron, manganese, nickel, selenium, silicon, and thallium. However, toxicities from these heavy metals are observed less frequently than from lead, mercury, and arsenic poisoning.
Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure.
In recent years, there has been an increasing ecological and global public health concern associated with environmental contamination by these metals. Also, human exposure has risen drastically as a result of an exponential increase of their use in several industrial, agricultural, domestic and technological applications.
Although heavy metals are naturally occurring elements that are found throughout the earth’s crust, most environmental contamination and human exposure result from anthropogenic activities such as mining and smelting operations, industrial production and use, and domestic and agricultural use of metals and metal-containing compounds.
Environmental contamination can also occur through metal corrosion, atmospheric deposition, soil erosion of metal ions and leaching of heavy metals, sediment re-suspension and metal evaporation from water resources to soil and ground water.
Industrial sources include metal processing in refineries, coal burning in power plants, petroleum combustion, nuclear power stations and high tension lines, plastics, textiles, microelectronics, wood preservation and paper processing plants.
Metals such as cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se) and zinc (Zn) are essential nutrients that are required for various biochemical and physiological functions . Inadequate supply of these micro-nutrients results in a variety of deficiency diseases or syndromes.
1).COBALT (Co) EXCESS AND TOXICITY
Cobalt (Co) is a solid, silver color like element.
Cobalt poisoning is intoxication caused by excessive levels of cobalt in the body. Cobalt is an essential element for health in animals in minute amounts as a component of Vitamin B12.
A deficiency of cobalt, which is very rare, is also potentially lethal, leading to pernicious anemia.
Exposure to cobalt occurs during its production, diamond polishing , dentistry materials, soil and natural dust, seawater spray, volcanic eruptions, forest fires, marine biogenic emissions.
Moreover, airport and highway traffic pollution may also become a cause of cobalt exposure.
Cobalt enters into the body through inhalation (pulmonary), ingestion (gastrointestinal) and contacts (skin) and is excreted in urine and feces .
The excessive inhalation of cobalt may cause panic-anxiety attacks, coughing, and difficulty in breathing, interstitial lung disease, allergic alveolitis, respiratory deficiency, impaired lung function, bronchial asthma and pneumoconiosis.
It may also cause goiter and reduced thyroid activity .
Toxicity of ingested cobalt includes nausea, vomiting, abdominal pain, and congestive cardiomyopathy .
Cardiovascular toxicity of cobalt includes angina, congestive cardiomyopathy.
Plants, animals, and humans can all be affected by high cobalt concentrations in the environment.
For plants, the uptake and distribution of cobalt is entirely species-specific. In some species of plants, the over accumulation of cobalt can lead to an iron deficiency.
This in turn leads to poor growth of the plant as well as leaf loss which overall decreases the amount of oxygen produced by plants during photosynthesis. Eventually the deficiency would lead to plant death.
The LD50 value for soluble cobalt salts has been estimated to be between 150 and 500 mg/kg. Thus, for a 100 kg person the LD50 would be about 20 grams.
2). NICKEL(Ni) EXCESS AND TOXICITY
Nickel is a chemical element with the symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile.
The major source of nickel exposure is oral consumption, as nickel is essential to plants.
Nickel is found naturally in both food and water, and may be increased by human pollution.
For example, nickel-plated faucets may contaminate water and soil; mining and smelting may dump nickel into waste-water;
Nickel–steel alloy cookware and nickel-pigmented dishes may release nickel into food.
The atmosphere may be polluted by nickel ore refining and fossil fuel combustion.
Humans may absorb nickel directly from tobacco smoke and skin contact with jewelry, shampoos, detergents, and coins.
A less-common form of chronic exposure is through hemodialysis as traces of nickel ions may be absorbed into the plasma from the chelating action of albumin.
Most of the nickel absorbed every day by humans is removed by the kidneys and passed out of the body through urine or is eliminated through the gastrointestinal tract without being absorbed. Nickel is not a cumulative poison, but larger doses or chronic inhalation exposure may be toxic, even carcinogenic, and constitute an occupational hazard.
Sensitized individuals may show a skin contact allergy to nickel known as a contact dermatitis. Highly sensitized individuals may also react to foods with high nickel content.
Nickel is the top confirmed contact allergen worldwide, partly due to its use in jewelry for pierced ears. Nickel allergies affecting pierced ears are often marked by itchy, red skin. Many earrings are now made without nickel or with low-release nickel to address this problem.
An option for treatment of metal poisoning may be chelation therapy, which is a technique which involves the administration of chelation agents to remove metals from the body.
Chelation therapy is a medical procedure that involves the administration of chelating agents to remove heavy metals from the body. Chelating agents are molecules that have multiple electron-donating groups, which can form stable coordination complexes with metal ions. Complexation prevents the metal ions from reacting with molecules in the body, and enable them to be dissolved in blood and eliminated in urine. It should only be used in people who have a diagnosis of metal intoxication. That diagnosis should be validated with tests done in appropriate biological samples.
Chelation therapy is administered under very careful medical supervision due to various inherent risks. Even when the therapy is administered properly, the chelation drugs can have significant side effects. Chelation administered inappropriately can cause neurodevelopmental toxicity, increase risk of developing cancer, and cause death; chelation also removes essential metal elements and requires measures to prevent their loss.
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