View source for Chemistry:Toxic heavy metal

{{Short description|Category of substances}}
[[File:Kingston-plant-spill-swanpond-tn2.jpg|thumb|A {{convert|25|ft|m|adj=on}} wall of coal [[Chemistry:Fly ash|fly ash]] contaminated with toxic heavy metals, resulting from the release of 5.4 million cubic yards of coal fly ash slurry into the Emory River, {{wipe|Tennessee}}, and nearby land and water features, in December 2008.<ref>Dewan 2008</ref> Testing showed significantly elevated levels of arsenic, copper, barium, cadmium, chromium, lead, mercury, nickel, and thallium in samples of slurry and river water.<ref>Dewan 2009</ref> Cleanup costs may exceed $1.2 billion.<ref>Poovey 2001</ref>]]

A '''toxic heavy metal''' is any relatively dense [[Chemistry:Metal|metal]] or [[Chemistry:Metalloid|metalloid]] that is noted for its potential toxicity, especially in environmental contexts.<ref>{{cite journal |last1=Zhang |first1=Hongling |last2=Walker |first2=Tony R. |last3=Davis |first3=Emily |last4=Ma |first4=Guofeng |title=Ecological risk assessment of metals in small craft harbour sediments in Nova Scotia, Canada |journal=Marine Pollution Bulletin |date=September 2019 |volume=146 |pages=466–475 |doi=10.1016/j.marpolbul.2019.06.068 |pmid=31426182 |s2cid=201095843 }}</ref><ref>Srivastava & Goyal 2010, p.&nbsp;2</ref> The term has particular application to [[Chemistry:Cadmium|cadmium]], [[Chemistry:Mercury (element)|mercury]] and [[Chemistry:Lead|lead]],<ref>Brathwaite & Rabone 1985, p.&nbsp;363</ref> all of which appear in the [[Organization:World Health Organization|World Health Organization]]'s list of 10 chemicals of major public concern. Other examples include [[Chemistry:Manganese|manganese]], [[Chemistry:Chromium|chromium]], [[Chemistry:Cobalt|cobalt]], [[Chemistry:Nickel|nickel]], [[Chemistry:Copper|copper]], [[Chemistry:Zinc|zinc]], [[Chemistry:Silver|silver]], [[Chemistry:Antimony|antimony]] and [[Chemistry:Thallium|thallium]].<ref>{{Cite web|title=10 chemicals of public health concern|url=https://www.who.int/news-room/photo-story/photo-story-detail/10-chemicals-of-public-health-concern|access-date=2021-10-09|website=www.who.int|language=en}}</ref>

[[Chemistry:Heavy metals|Heavy metals]] are found naturally in the earth. They become concentrated as a result of human caused activities and can enter plant and animal (including human) tissues via inhalation, diet, and manual handling. Then, they can bind to and interfere with the functioning of vital cellular components. The toxic effects of arsenic, mercury, and lead were known to the ancients, but methodical studies of the toxicity of some heavy metals appear to date from only 1868. In humans, heavy metal poisoning is generally treated by the administration of [[Chemistry:Chelation|chelating agents]]. Some elements otherwise regarded as toxic heavy metals are essential, in small quantities, for human health.

{{Periodic table (micro)|title=|caption=Examples of toxic heavy metals|mark=Cr, Co, Ni, Cu, Zn, As, Se, Ag, Cd, Sb, Hg, Tl, Pb}}

== Contamination sources ==
[[File:Tetraethyllead-3D-balls.png|thumb|Tetraethyl lead is one of the most significant heavy metal contaminants in recent use.<ref>Wright 2002, p.&nbsp;288</ref>]]

Heavy metals are found naturally in the earth, and become concentrated as a result of human activities, or, in some cases geochemical processes, such as accumulation in peat soils that are then released when drained for agriculture.<ref>{{cite journal |last1=Qureshi |first1=Shabnam |last2=Richards |first2=Brian K. |last3=McBride |first3=Murray B. |last4=Baveye |first4=Philippe |last5=Steenhuis |first5=Tammo S. |title=Temperature and Microbial Activity Effects on Trace Element Leaching from Metalliferous Peats |journal=Journal of Environmental Quality |date=2003 |volume=32 |issue=6 |pages=2067–75 |doi=10.2134/jeq2003.2067|pmid=14674528 }}</ref> Common sources are mining and industrial wastes; vehicle emissions; motor oil; fuels used by ships and heavy machineries; construction works; fertilisers;<ref>{{cite web | url=https://archive.seattletimes.com/archive/?date=19970703&slug=2547772 | title=Fear In The Fields -- How Hazardous Wastes Become Fertilizer -- Spreading Heavy Metals On Farmland Is Perfectly Legal, But Little Research Has Been Done To Find Out Whether It's Safe}}</ref> pesticides; paints; dyes and pigments; renovation; illegal depositing of construction and demolition waste; open top roll-off dumpster; welding, brazing and soldering; glassworking;<ref>https://hazwastehelp.org/ArtHazards/glassworking.aspx Art Hazards</ref> concrete works; roadworks; use of recycled materials; DIY metal projects; burning of [[Biology:Joss paper|joss paper]]; open burning of waste in rural area; contaminated ventilation system; food contaminated by the environment or by the packaging; armaments; [[Chemistry:Lead–acid battery|lead-acid batteries]]; electronic waste recycling yard; treated woods; aging water supply infrastructure;<ref>Harvey, Handley & Taylor 2015</ref> and [[Earth:Microplastics|microplastics]] floating in the world's oceans.<ref>Howell et al. 2012; Cole et al. 2011, pp.&nbsp;2589‒2590</ref> Arsenic, cadmium and lead may be present in children's toys at levels that exceed regulatory standards. Lead can be used in toys as a [[Chemistry:Stabilizer|stabilizer]], color enhancer, or anti-corrosive agent. Cadmium is sometimes employed as a stabilizer, or to increase the mass and luster of toy jewelry. Arsenic is thought to be used in connection with coloring dyes.<ref>Finch, Hillyer & Leopold 2015, pp.&nbsp;849–850</ref> Regular imbibers of illegally distilled alcohol may be exposed to arsenic or lead poisoning the source of which is arsenic-contaminated lead used to [[Chemistry:Solder|solder]] the distilling apparatus. Rat poison used in grain and mash stores may be another source of the arsenic.<ref>Aggrawal 2014, p.&nbsp;680</ref>

Lead is the most prevalent heavy metal contaminant.<ref>Di Maio 2001, p.&nbsp;527</ref> As a component of tetraethyl lead, {{chem|(CH|3|CH|2|)|4|Pb}}, it was used extensively in [[Chemistry:Gasoline|gasoline]] during the 1930s–1970s.<ref>Lovei 1998, p.&nbsp;15</ref> Lead levels in the aquatic environments of industrialised societies have been estimated to be two to three times those of pre-industrial levels.<ref>Perry & Vanderklein 1996, p.&nbsp;336</ref> Although the use of leaded gasoline was largely phased out in North America by 1996, soils next to roads built before this time retain high lead concentrations. Lead (from [[Chemistry:Lead(II) azide|lead(II) azide]] or [[Chemistry:Lead styphnate|lead styphnate]] used in firearms) gradually accumulates at firearms training grounds, contaminating the local environment and exposing range employees to a risk of [[Medicine:Lead poisoning|lead poisoning]].<ref>Houlton 2014, p.&nbsp;50</ref>

== Entry routes ==

Heavy metals enter plant, animal and human tissues via air inhalation, diet, and manual handling. Motor vehicle emissions are a major source of airborne contaminants including arsenic, cadmium, cobalt, nickel, lead, antimony, vanadium, zinc, platinum, palladium and rhodium.<ref>Balasubramanian, He & Wang 2009, p.&nbsp;476</ref> Water sources (groundwater, lakes, streams and rivers) can be polluted by heavy metals leaching from industrial and consumer waste; [[Earth:Acid rain|acid rain]] can exacerbate this process by releasing heavy metals trapped in soils.<ref>Worsztynowicz & Mill 1995, p.&nbsp;361</ref> Transport through soil can be facilitated by the presence of preferential flow paths (macropores) and dissolved organic compounds.<ref>{{cite journal |last1=Camobreco |first1=Vincent J. |last2=Richards |first2=Brian K. |last3=Steenhuis |first3=Tammo S. |last4=Peverly |first4=John H. |last5=McBride |first5=Murray B. |title=Movement of heavy metals through undisturbed and homogenized soil columns |journal=Soil Science |date=November 1996 |volume=161 |issue=11 |pages=740–750 |doi=10.1097/00010694-199611000-00003|bibcode=1996SoilS.161..740C }}</ref> Plants are exposed to heavy metals through the uptake of water; animals eat these plants; ingestion of plant- and animal-based foods are the largest sources of heavy metals in humans.<ref>Radojevic & Bashkin 1999, p.&nbsp;406</ref> Absorption through skin contact, for example from contact with soil, or metal containing toys and jewelry,<ref>{{cite journal|last1=Guney|first1=Mert|last2=Zagury|first2=Gerald J.|title=Bioaccessibility of As, Cd, Cu, Ni, Pb, and Sb in Toys and Low-Cost Jewelry|journal=Environmental Science & Technology|date=4 January 2014|volume=48|issue=2|pages=1238–1246|doi=10.1021/es4036122|pmid=24345102|bibcode=2014EnST...48.1238G|doi-access=free}}{{open access}}</ref> is another potential source of heavy metal contamination.<ref>Qu et al. 2014, p.&nbsp;144</ref> Toxic heavy metals can bioaccumulate in organisms as they are hard to [[Biology:Metabolism|metabolize]].<ref>Pezzarossa, Gorini & Petruzelli 2011, p.&nbsp;94</ref>

== Detrimental effects ==

Heavy metals "can bind to vital cellular components, such as [[Biology:Protein#Structural proteins|structural proteins]], [[Biology:Enzymes|enzymes]], and [[Biology:Nucleic acid|nucleic acid]]s, and interfere with their functioning".<ref>Lanids, Sofield & Yu 2000, p.&nbsp;269</ref> Symptoms and effects can vary according to the metal or metal compound, and the dose involved. Broadly, long-term exposure to toxic heavy metals can have carcinogenic, central and peripheral nervous system, and circulatory effects. For humans, typical presentations associated with exposure to any of the "classical"<ref>Neilen & Marvin 2008, p.&nbsp;10</ref> toxic heavy metals, or chromium (another toxic heavy metal) or arsenic (a metalloid), are shown in the table.<ref>Afal & Wiener 2014</ref>

{| class="wikitable" style="margin: 1em auto 1em auto;"
|-
| style="text-align:center; background:#f0f0f0" | '''Element'''
| style="text-align:center; background:#f0f0f0" | '''Acute exposure'''<br />''usually a day or less''
| style="text-align:center; background:#f0f0f0" | '''Chronic exposure'''<br />''often months or years''
|-
| [[Medicine:Cadmium poisoning|Cadmium]] || [[Medicine:Pneumonitis|Pneumonitis]] (lung inflammation) ||Lung cancer <br />[[Medicine:Osteomalacia|Osteomalacia]] (softening of bones)<br />Proteinuria (excess protein in urine; possible kidney damage)
|-
| [[Medicine:Mercury poisoning|Mercury]] || [[Medicine:Diarrhea|Diarrhea]]<br />[[Medicine:Fever|Fever]]<br />[[Medicine:Vomiting|Vomiting]] ||[[Medicine:Stomatitis|Stomatitis]] (inflammation of gums and mouth) <br />Nausea<br />[[Medicine:Nephrotic syndrome|Nephrotic syndrome]] (nonspecific kidney disorder)<br />[[Medicine:Neurasthenia|Neurasthenia]] (neurotic disorder)<br />Parageusia (metallic taste)<br />[[Medicine:Mercury poisoning#Infantile acrodynia|Pink Disease]] (pain and pink discoloration of hands and feet)<br />Tremor
|-
| [[Medicine:Lead poisoning|Lead]] || Encephalopathy (brain dysfunction)<br />Nausea<br />Vomiting || [[Medicine:Anemia|Anemia]]<br />Encephalopathy<br />[[Medicine:Foot drop|Foot drop]]/wrist drop (palsy)<br />Nephropathy (kidney disease)
|-
| Chromium || Gastrointestinal hemorrhage (bleeding)&nbsp;<br />[[Medicine:Hemolysis|Hemolysis]] (red blood cell destruction)<br />Acute renal failure|| [[Medicine:Pulmonary fibrosis|Pulmonary fibrosis]] (lung scarring)<br />Lung cancer
|-
| [[Medicine:Arsenic poisoning|Arsenic]] || Nausea<br />Vomiting<br />Diarrhea<br />Encephalopathy<br />Multi-organ effects<br />[[Medicine:Heart arrhythmia|Arrhythmia]]<br />Painful neuropathy || [[Medicine:Diabetes|Diabetes]]<br />Hypopigmentation/Hyperkeratosis<br />[[Medicine:Cancer|Cancer]]
|}

== History ==

The toxic effects of arsenic, mercury and lead were known to the ancients but methodical studies of the overall toxicity of heavy metals appear to date from only 1868. In that year, Wanklyn and Chapman speculated on the adverse effects of the heavy metals "arsenic, lead, copper, zinc, [[Chemistry:Iron|iron]] and [[Chemistry:Manganese|manganese]]" in drinking water. They noted an "absence of investigation" and were reduced to "the necessity of pleading for the collection of data".<ref>Wanklyn & Chapman 1868, pp.&nbsp;73–8; Cameron 1871, p.&nbsp;484</ref> In 1884, Blake described an apparent connection between toxicity and the atomic weight of an element.<ref>Blake 1884</ref> The following sections provide historical thumbnails for the "classical" toxic heavy metals (arsenic, mercury and lead) and some more recent examples (chromium and cadmium).

[[File:Orpiment mineral.jpg|thumb|left|200px|[[Chemistry:Orpiment|Orpiment]], a toxic arsenic mineral used in the tanning industry to remove hair from hides.]]

=== Arsenic ===

[[Chemistry:Arsenic|Arsenic]], as [[Chemistry:Realgar|realgar]] ({{chem|As|4|S|4}}) and [[Chemistry:Orpiment|orpiment]] ({{chem|As|2|S|3}}), was known in ancient times. Strabo (64–50 BCE – c. AD 24?), a Greek geographer and historian,<ref>Dueck 2000, pp.&nbsp;1–3, 46, 53</ref> wrote that only slaves were employed in realgar and orpiment mines since they would inevitably die from the toxic effects of the fumes given off from the ores. Arsenic-contaminated beer poisoned over 6,000 people in the Manchester area of England in 1900, and is thought to have killed at least 70 victims.<ref>Dyer 2009</ref> Clare Luce, American ambassador to Italy from 1953 to 1956, suffered from [[Medicine:Arsenic poisoning|arsenic poisoning]]. Its source was traced to flaking arsenic-laden paint on the ceiling of her bedroom. She may also have eaten food contaminated by arsenic in flaking ceiling paint in the embassy dining room.<ref>Whorton 2011, p.&nbsp;356</ref> [[Earth:Arsenic contamination of groundwater|Ground water contaminated by arsenic]], as of 2014, "is still poisoning millions of people in Asia".<ref>Notman 2014</ref>

=== Mercury ===
[[File:Saint Isaac's Cathedral in SPB.jpeg|thumb|right|Saint Isaac's Cathedral, in Saint Petersburg, Russia. The gold-mercury amalgam used to gild its dome caused numerous casualties among the workers involved.]]

The first emperor of unified China, Qin Shi Huang, it is reported, died of ingesting [[Chemistry:Mercury (element)|mercury]] pills that were intended to give him eternal life.<ref>Zhao, Zhu & Sui 2006</ref> The phrase "mad as a hatter" is likely a reference to [[Medicine:Mercury poisoning|mercury poisoning]] among milliners (so-called "mad hatter disease"), as mercury-based compounds were once used in the manufacture of felt hats in the 18th and 19th century.<ref>Waldron 1983</ref> Historically, gold amalgam (an alloy with mercury) was widely used in [[Chemistry:Gilding|gilding]], leading to numerous casualties among the workers. It is estimated that during the construction of Saint Isaac's Cathedral alone, 60 workers died from the gilding of the main dome.<ref>Emsely 2011, p.&nbsp;326</ref> Outbreaks of [[Chemistry:Methylmercury|methylmercury]] poisoning occurred in several places in Japan during the 1950s due to industrial discharges of mercury into rivers and coastal waters. The best-known instances were in Minamata and Niigata. In Minamata alone, more than 600 people died due to what became known as Minamata disease. More than 21,000 people filed claims with the Japanese government, of which almost 3000 became certified as having the disease. In 22 documented cases, pregnant women who consumed contaminated fish showed mild or no symptoms but gave birth to infants with severe developmental disabilities.<ref>Davidson, Myers & Weiss 2004, p.&nbsp;1025</ref> Since the [[History:Industrial Revolution|Industrial Revolution]], mercury levels have tripled in many near-surface [[Earth:Seawater|seawater]]s, especially around Iceland and [[Earth:Antarctica|Antarctica]].<ref>New Scientist August 2014, p. 4</ref>

[[File:Dutch boy collier white lead.png|thumb|left|upright|Dutch Boy white lead paint advertisement, 1912.]]

=== Lead ===

The adverse effects of [[Chemistry:Lead|lead]] were known to the ancients. In the 2nd century BC the Greek botanist Nicander described the [[Medicine:Colic|colic]] and [[Engineering:Paralysis|paralysis]] seen in lead-poisoned people.<ref>Pearce 2007; Needleman 2004</ref> Dioscorides, a Greek [[Medicine:Physician|physician]] who is thought to have lived in the 1st century CE,<ref>Rogers 2000, p.&nbsp;41</ref> wrote that lead "makes the mind give way". Lead was used extensively in Roman aqueducts from about 500 BC to 300 AD.<ref>Gilbert & Weiss 2006</ref> Julius Caesar's engineer, Vitruvius, reported, "water is much more wholesome from earthenware pipes than from lead pipes. For it seems to be made injurious by lead, because [[Chemistry:White lead|white lead]] is produced by it, and this is said to be harmful to the human body."<ref>Prioreschi 1998, p.&nbsp;279</ref> During the Mongol period in China (1271−1368 AD), lead pollution due to silver smelting in the Yunnan region exceeded contamination levels from modern mining activities by nearly four times.<ref>Hillman et al. 2015, pp.&nbsp;3353–3354</ref>{{#tag:ref|Up to one-sixth of China's arable land might be affected by heavy metal contamination.<ref>Hillman et al. 2015, p.&nbsp;3349</ref>|group=n}} In the 17th and 18th centuries, people in [[Earth:Devon|Devon]] were afflicted by a condition referred to as Devon colic; this was discovered to be due to the imbibing of [[Medicine:Lead poisoning|lead-contaminated]] cider. In 2013, the [[Organization:World Health Organization|World Health Organization]] estimated that lead poisoning resulted in 143,000 deaths, and "contribute[d] to 600,000 new cases of children with intellectual disabilities", each year.<ref>World Health Organization 2013</ref> In the U.S. city of Flint, Michigan, lead contamination in drinking water has been an issue since 2014. The source of the contamination has been attributed to "corrosion in the lead and iron [[Engineering:Lead service line|pipes that distribute water]] to city residents".<ref>Torrice 2016</ref> In 2015, the lead concentration of drinking water in north-eastern Tasmania, Australia, reached a level over 50 times the prescribed national drinking water guidelines. The source of the contamination was attributed to "a combination of dilapidated drinking water infrastructure, including lead jointed pipelines, end-of-life polyvinyl chloride pipes and household plumbing".<ref>Harvey, Handley & Taylor 2015</ref>

=== Chromium ===
[[File:Potassium-chromate-sample.jpg|thumb|right|[[Chemistry:Potassium chromate|Potassium chromate]], a carcinogen, is used in the dyeing of fabrics, and as a tanning agent to produce leather.]]

[[Chemistry:Chromium(III)|Chromium(III)]] compounds and [[Chemistry:Chromium|chromium]] metal are not considered a health hazard, while the toxicity and carcinogenic properties of [[Chemistry:Chromium(VI)|chromium(VI)]] have been known since at least the late 19th century.<ref>Barceloux & Barceloux 1999</ref> In 1890, Newman described the elevated cancer risk of workers in a [[Chemistry:Chromate ion|chromate]] dye company.<ref>Newman 1890</ref> Chromate-induced dermatitis was reported in aircraft workers during [[Social:World War II|World War II]].<ref>Haines & Nieboer 1988, p.&nbsp;504</ref> In 1963, an outbreak of dermatitis, ranging from [[Medicine:Erythema|erythema]] to exudative eczema, occurred amongst 60 automobile factory workers in England. The workers had been wet-sanding chromate-based primer paint that had been applied to car bodies.<ref>National Research Council 1974, p.&nbsp;68</ref> In Australia, chromium was released from the Newcastle Orica explosives plant on August 8, 2011. Up to 20 workers at the plant were exposed as were 70 nearby homes in Stockton. The town was only notified three days after the release and the accident sparked a major public controversy, with Orica criticised for playing down the extent and possible risks of the leak, and the state Government attacked for their slow response to the incident.<ref>Tovey 2011; Jones 2011; O'Brien & Aston</ref>

[[File:Cadmium-crystal bar.jpg|thumb|left|99.999% purity cadmium bar and 1 cm<sup>3</sup> cube.]]

=== Cadmium ===

[[Chemistry:Cadmium|Cadmium]] exposure is a phenomenon of the early 20th century, and onwards. In Japan in 1910, the Mitsui Mining & Smelting Company began discharging cadmium into the Jinzū River, as a byproduct of mining operations. Residents in the surrounding area subsequently consumed rice grown in cadmium-contaminated irrigation water. They experienced [[Chemistry:Itai-itai disease|softening of the bones and kidney failure]]. The origin of these symptoms was not clear; possibilities raised at the time included "a regional or bacterial disease or lead poisoning".<ref>Vallero & Letcher 2013, p.&nbsp;240</ref> In 1955, cadmium was identified as the likely cause and in 1961 the source was directly linked to mining operations in the area.<ref>Vallero & Letcher 2013, pp.&nbsp;239–241</ref> In February 2010, cadmium was found in [[Company:Walmart|Walmart]] exclusive Miley Cyrus jewelry. Wal-Mart continued to sell the jewelry until May, when covert testing organised by Associated Press confirmed the original results.<ref>Pritchard 2010</ref> In June 2010 cadmium was detected in the paint used on promotional drinking glasses for the movie ''Shrek Forever After'', sold by McDonald's Restaurants, triggering a recall of 12 million glasses.<ref>Mulvihill & Pritchard 2010</ref>

== Remediation ==
[[File:Metal-EDTA.svg|thumb|right|170px|A metal EDTA anion. Pb displaces Ca in {{chem|Na|2|[CaEDTA]}} to give {{chem|Na|2|[PbEDTA]}}, which is passed out of the body in [[Biology:Urine|urine]].<ref>Cs uros 1997, p.&nbsp;124</ref>]]

In humans, heavy metal poisoning is generally treated by the administration of [[Chemistry:Chelation|chelating agent]]s.<ref>Blann & Ahmed 2014, p.&nbsp;465</ref>
These are chemical compounds, such as {{chem|link=Sodium calcium edetate|CaNa|2|EDTA}} (calcium disodium ethylenediaminetetraacetate) that convert heavy metals to chemically inert forms that can be excreted without further interaction with the body. Chelates are not without side effects and can also remove beneficial metals from the body. Vitamin and mineral supplements are sometimes co-administered for this reason.<ref>American Cancer Society 2008; National Capital Poison Center 2010</ref>

Soils contaminated by heavy metals can be remediated by one or more of the following technologies: isolation; immobilization; toxicity reduction; physical separation; or extraction. ''Isolation'' involves the use of caps, membranes or below-ground barriers in an attempt to quarantine the contaminated soil. ''Immobilization'' aims to alter the properties of the soil so as to hinder the mobility of the heavy contaminants. ''Toxicity reduction'' attempts to oxidise or reduce the toxic heavy metal ions, via chemical or [[Earth:Phytoremediation|biological means]] into less toxic or mobile forms. ''Physical separation'' involves the removal of the contaminated soil and the separation of the metal contaminants by mechanical means. ''Extraction'' is an on or off-site process that uses chemicals, high-temperature volatization, or electrolysis to extract contaminants from soils. The process or processes used will vary according to contaminant and the characteristics of the site.<ref>Evanko & Dzombak 1997, pp.&nbsp;1, 14–40</ref>

== Benefits ==

Some elements otherwise regarded as toxic heavy metals are essential, in small quantities, for human health. These elements include vanadium, manganese, iron, cobalt, copper, zinc, selenium, strontium and molybdenum.<ref>Bánfalvi 2011, p.&nbsp;12</ref> A deficiency of these essential metals may increase susceptibility to heavy metal poisoning.<ref>Chowdhury 1987</ref>

== See also ==
* Bento Rodrigues dam disaster
* Heavy metal detoxification
* Kingston Fossil Plant coal fly ash slurry spill
* [[Chemistry:Light metal|Light metal]]
* [[Chemistry:Metal toxicity|Metal toxicity]]

== Explanatory notes ==
{{Reflist|group=n|colwidth=60em}}

== Citations ==
{{Reflist|30em}}

== General references ==
{{refbegin|30em}}
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* {{cite web |title=Chelation: Therapy or "Therapy"? |date=2010 |publisher=National Capital Poison Center |url=http://www.poison.org/current/chelationtherapy.htm }}
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{{refend}}

{{Wastewater}}
{{Poisoning and toxicity}}

[[Category:Sets of chemical elements]]
[[Category:Toxicology]]

{{Sourceattribution|Toxic heavy metal}}