Metal toxicity ormetal poisoning is thetoxic effect of certainmetals in certain forms and doses onlife. Some metals are toxic when they formpoisonous soluble compounds. Certain metals have no biological role, i.e. are not essential minerals, or are toxic when in a certain form.[1] In the case oflead, any measurable amount may have negative health effects.[2] There is a popular misconception that onlyheavy metals can be toxic, but lighter metals such asberyllium andlithium can be toxic too.[3] Not all heavy metals are particularly toxic, and some are essential, such asiron. The definition may also includetrace elements when abnormally high doses may be toxic. An option for treatment of metal poisoning may bechelation therapy, a technique involving the administration ofchelation agents to remove metals from the body.
Toxic metals sometimes imitate the action of an essential element, interfering with the metabolic processes resulting inillness. Many metals, particularlyheavy metals are toxic, but some are essential, and some, such asbismuth, have a low toxicity. Metals in an oxidation state abnormal to the body may also become toxic:chromium(III) is an essential trace element, butchromium(VI) is acarcinogen.
Only soluble metal-containing compounds are toxic. Soluble metals are calledcoordination complexes, which consist of a metal ion surrounded byligands. Ligands can range from water inmetal aquo complexes to methyl groups as intetraethyl lead. Usually metal complexes consist of a mixture of ligands.
Structure of ametal aquo complex, a typical soluble form for many metal ions in water.
Toxic metal complexes can be detoxified by conversion to insoluble derivatives or (ii) by encasing in rigid molecular environments using chelating agents. Alternatively, when very dilute, metal complexes are often innocuous.[4] This method uses plants to extract and lower the concentration of toxic heavy metals in the soil.[4] An aspirational method of decontamination of heavy metals isphytoremediation orbioremediation, but these approaches have solved few real world problems.
Toxic metals canbioaccumulate in the body and in thefood chain.[5] Therefore, a common characteristic of toxic metals is the chronic nature of their toxicity. This is particularly notable with radioactive heavy metals such asradium, which imitatescalcium to the point of being incorporated into human bone, although similar health implications are found inlead ormercury poisoning.
A dominant kind of metal toxicity is arsenic poisoning. This problem mainly arises fromground water that naturally contains high concentrations of arsenic. A 2007 study found that over 137 million people indicates that more than 70 countries may be affected by arsenic poisoning from drinking water.[6]
Lead poisoning, in contrast to arsenic poisoning, is inflicted by industry. Most lead on the planet is immobilized as minerals, which are relatively harmless. Two major sources of lead poisoning are leaded gasoline and lead leached from plumbing (from Latin, plumbus for lead). Use ofleaded gasoline has declined precipitously since the 1970s.[7][8] One lead-containing pigments islead chromate (the yellow-orange of U.S. school buses), but this material is so stable and so insoluble that little evidence exists for its toxicity.
No evidence for biological action in mammals, but essential or beneficial in some organisms
In the case of thelanthanides, the definition of an essential nutrient as being indispensable and irreplaceable is not completely applicable due to their extreme similarity. The stable early lanthanides La–Nd are known to stimulate the growth of various lanthanide-using organisms, and Sm–Gd show lesser effects for some such organisms. The later elements in the lanthanide series do not appear to have such effects.[15]
Many metal ions are required for life. Even in these cases, a large excess of these ions can prove toxic.
Selenium poisoning has been observed even though Se is an essentialtrace element. TheTolerable Upper Intake Level is 400 micrograms per day. Additional Se intake can lead to selenosis.[17] Signs and symptoms of selenosis include a garlic odor on the breath, gastrointestinal disorders, hair loss,sloughing of nails, fatigue, irritability, and neurological damage.
Zinc toxicity has been seen to occur at ingestion of greater than 225 mg of zinc.[18] Excessive absorption of zinc can suppress copper and iron absorption. The free zinc ion in solution is highly toxic to bacteria, plants, invertebrates, and even vertebrate fish.[19][20][21]
No global mechanism exists for the toxicities of these metal ions. Excessive exposure, when it occurs, typically is associated with industrial activities.
Beryllium poisoning is attributed to the ability of Be2+ to replace Mg2+ in some enzymes.[22] Be has been classified by one agency as a carcinogen.[23]
Cadmium poisoning came into focus with the discovery of theItai-itai disease due to cadmium contaminated waters resulting from mining in theToyama Prefecture starting around 1912.[24] The term refers to the severepains (Japanese: 痛いitai) people with the condition felt in the spine and joints. Cd2+ is thought to accumulate in the kidneys, where it tightly binds to the sulfur incysteine-containing proteins.[25]
Mercury poisoning came into sharp focus with the discovery ofMinamata disease, named for the Japanese city ofMinamata. In 1956, a factory in that city released ofmethylmercury in theindustrial wastewater resulting in thousands of deaths and many other health problems.[27] This incident alerted the world to the phenomenon ofbioaccumulation. While all mercury compounds are toxic,organomercury compounds are especially dangerous because they are more mobile.Methyl mercury and related compounds are thought to bind to the sulfur of cysteinyl residues in proteins.[28]
A 92-year-old Caucasian man (right) with pigmentary changes had used nose drops containing silver for many years. His skin biopsy showed silver deposits in the dermis, confirming the diagnosis of generalized argyria.[29]
Thallium poisoning has been observed on several occasions, and it is well known thatthallium compounds are highly toxic. Nonetheless, incidents of thallium poisoning are few.[32] Tl is located on the periodic table near two other highly toxic metals, mercury and lead.
Chelation therapy is a medical procedure that involves the administration ofchelating agents to remove or deactivate heavy metals from the body. Chelating agents are molecules that form particularly stablecoordination 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.[34] That diagnosis should be validated with tests done in appropriate biological samples.[35]
This section needs to beupdated. Please help update this article to reflect recent events or newly available information.(May 2024)
It is difficult to differentiate the effects of low level metal poisoning from the environment with other kinds of environmental harms, including nonmetal pollution.[36] Generally, increased exposure to heavy metals in the environment increases risk of developing cancer.[37]
^Nielsen, Forrest H. (1999). "Ultratrace minerals". In Maurice E. Shils; James A. Olsen; Moshe Shine; A. Catharine Ross (eds.).Modern nutrition in health and disease. Baltimore: Lippincott Williams & Wilkins. pp. 283–303.hdl:10113/46493.ISBN978-0683307696.
^Hedya, Shireen A.; Avula, Akshay; Swoboda, Henry D. (2019)."Lithium Toxicity".StatPearls. StatPearls Publishing.PMID29763168. Retrieved22 December 2019.
^Xiao, Zhiguang; Wedd, Anthony G.; "Coping with Toxic Metals", pp 271-298 in "Metals, Microbes and Minerals: The Biogeochemical Side of Life" (2021) pp xiv + 341. Walter de Gruyter, Berlin. "Metals, Microbes and Minerals: . Walter de Gruyter, Berlin. Editors Kroneck, Peter M.H. and Sosa Torres, Martha.Gruyter.com/document/doi/10.1515/9783110589771-009 DOI 10.1515/9783110589771-009
^Tabrez, Shams; Priyadarshini, Medha; Priyamvada, Shubha; Khan, Mohd Shahnawaz; NA, Arivarasu; Zaidi, Syed Kashif (2014). "Gene–environment interactions in heavy metal and pesticide carcinogenesis".Mutation Research/Genetic Toxicology and Environmental Mutagenesis.760:1–9.Bibcode:2014MRGTE.760....1T.doi:10.1016/j.mrgentox.2013.11.002.PMID24309507.
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