Editing Lead (section)

== Biological effects ==
{{Main|Lead poisoning}}
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Lead has no confirmed biological role, and there is no confirmed safe level of lead exposure.{{sfn|World Health Organization|2018}} A 2009 Canadian–American study concluded that even at levels that are considered to pose little to no risk, lead may cause "adverse mental health outcomes".{{sfn|Bouchard|Bellinger|Weuve|Matthews-Bellinger|2009}} Its prevalence in the human body—at an adult average of 120&nbsp;mg{{efn|Rates vary greatly by country.{{sfn|World Health Organization|2000|pp=149–153}} }}—is nevertheless exceeded only by zinc (2500&nbsp;mg) and iron (4000&nbsp;mg) among the heavy metals.{{sfn|Emsley|2011|pp=280, 621, 255}} Lead [[Salt (chemistry)|salts]] are very efficiently absorbed by the body.{{sfn|Luckey|Venugopal|1979|pp=177–178}} A small amount of lead (1%) is stored in bones; the rest is excreted in urine and feces within a few weeks of exposure. Only about a third of lead is excreted by a child. Continual exposure may result in the [[bioaccumulation]] of lead.{{sfn|Toxic Substances Portal}}

=== Toxicity ===
Lead is a highly poisonous metal (whether inhaled or swallowed), affecting almost every organ and system in the human body.{{sfn|United States Food and Drug Administration|2015|p=42}} <!--The permitted daily exposure limit for lead of 5&nbsp;μg (five millionths of a gram) is a recommended test benchmark for pharmaceuticals.--> At airborne levels of 100&nbsp;mg/m<sup>3</sup>, it is [[Immediately dangerous to life or health|immediately dangerous to life and health]].{{sfn|National Institute for Occupational Safety and Health}} Most ingested lead is absorbed into the bloodstream.{{sfn|Occupational Safety and Health Administration}} The primary cause of its toxicity is its predilection for interfering with the proper functioning of enzymes. It does so by binding to the [[Thiol|sulfhydryl groups]] found on many enzymes,{{sfn|Rudolph|Rudolph|Hostetter|Lister|2003|p=369}} or mimicking and displacing other metals which act as [[cofactor (biochemistry)|cofactors]] in many enzymatic reactions.{{sfn|Dart|Hurlbut|Boyer-Hassen|2004|p=1426}} The essential metals that lead interacts with include calcium, iron, and zinc.{{sfn|Kosnett|2006|p=238}} High levels of calcium and iron tend to provide some protection from lead poisoning; low levels cause increased susceptibility.{{sfn|Luckey|Venugopal|1979|pp=177–178}}

=== Effects ===
Lead can cause severe damage to the brain and kidneys and, ultimately, death. By mimicking calcium, lead can cross the [[blood–brain barrier]]. It degrades the [[myelin]] sheaths of [[neuron]]s, reduces their numbers, interferes with [[neurotransmitter|neurotransmission]] routes, and decreases neuronal growth.{{sfn|Rudolph|Rudolph|Hostetter|Lister|2003|p=369}} In the human body, lead inhibits [[Delta-aminolevulinic acid dehydratase|porphobilinogen synthase]] and [[ferrochelatase]], preventing both [[porphobilinogen]] formation and the incorporation of iron into [[protoporphyrin IX]], the final step in [[heme]] synthesis. This causes ineffective heme synthesis and [[microcytic anemia]].{{sfn|Cohen|Trotzky|Pincus|1981|pp=904–906}}
<!--At lower levels, it acts as a calcium analog, interfering with ion channels during nerve conduction. This is one of the mechanisms by which it interferes with cognition.-->

[[File:Symptoms of lead poisoning (raster).png|thumb|left|Symptoms of lead poisoning|alt=A chart of a human body with arrows pointing pieces of text to different parts of the body]]

Symptoms of lead poisoning include [[Kidney disease|nephropathy]], [[colic]]-like abdominal pains, and possibly weakness in the fingers, wrists, or ankles. Small blood pressure increases, particularly in middle-aged and older people, may be apparent and can cause [[anemia]].{{citation needed|date=October 2022}} Several studies, mostly cross-sectional, found an association between increased lead exposure and decreased heart rate variability.{{sfn|Navas-Acien|2007}} In pregnant women, high levels of exposure to lead may cause miscarriage. Chronic, high-level exposure has been shown to reduce fertility in males.{{sfn|Sokol|2005|p=133, passim}}

In a child's developing brain, lead interferes with [[synapse]] formation <!-- "syaptic modeling" --> in the [[cerebral cortex]], [[neurochemical]] development (including that of neurotransmitters), and the organization of [[ion channel]]s.{{sfn|Mycyk|Hryhorczuk|Amitai|2005|p=462}} Early childhood exposure has been linked with an increased risk of sleep disturbances and excessive daytime drowsiness in later childhood.{{sfn|Liu|Liu|Pak|Wang|2015|pp=1869–1874}} High blood levels are associated with delayed puberty in girls.{{sfn|Schoeters|Den Hond|Dhooge|Van Larebeke|2008|pp=168–175}} The rise and fall in exposure to airborne lead from the combustion of tetraethyl lead in gasoline during the 20th century has been linked with historical increases and [[Lead–crime hypothesis|decreases in crime levels]].{{Citation needed|date=April 2025}}

=== Exposure sources ===
Lead exposure is a global issue since lead mining and smelting, and battery manufacturing, disposal, and [[Battery recycling#Lead.E2.80.93acid batteries|recycling]], are common in many countries. Lead enters the body via inhalation, ingestion, or skin absorption. Almost all inhaled lead is absorbed into the body; for ingestion, the rate is 20–70%, with children absorbing a higher percentage than adults.{{sfn|Tarragó|2012|p=16}}

Poisoning typically results from ingestion of food or water contaminated with lead, and less commonly after accidental ingestion of contaminated soil, dust, or lead-based paint.{{sfn|Toxicological Profile for Lead|2007|p=4}} Seawater products can contain lead if affected by nearby industrial waters.{{sfn|Bremner|2002|p=101}} Fruit and vegetables can be contaminated by high levels of lead in the soils they were grown in. Soil can be contaminated through particulate accumulation from lead in pipes, [[lead paint]], residual emissions from leaded gasoline.{{sfn|Agency for Toxic Substances and Disease Registry|2007}}

The use of lead for water pipes is [[plumbosolvency|a problem in areas with soft or acidic water]].{{sfn|Thornton|Rautiu|Brush|2001|p=17}} Hard water forms insoluble protective layers on the inner surface of the pipes, whereas soft and acidic water dissolves the lead pipes.{{sfn|Moore|1977|pp=109–115}} Dissolved [[carbon dioxide]] in the carried water may result in the formation of soluble lead [[bicarbonate]]; oxygenated water may similarly dissolve lead as [[lead(II) hydroxide]]. Drinking such water, over time, can cause health problems due to the toxicity of the dissolved lead. The [[hard water|harder the water]] the more [[calcium bicarbonate]] and [[calcium sulfate|sulfate]] it contains, and the more the inside of the pipes are coated with a protective layer of lead carbonate or lead sulfate.{{sfn|Wiberg|Wiberg|Holleman|2001|p=914}}

[[File:Kymographic recording of the effect of lead on frog heart..jpg|thumb|upright|right|[[Kymograph]]ic recording of the effect of lead acetate on frog heart experimental set up]]

Ingestion of applied lead-based paint is the major source of exposure for children: a direct source is chewing on old painted window sills. Additionally, as lead paint on a surface deteriorates, it peels and is pulverized into dust. The dust then enters the body through hand-to-mouth contact or contaminated food or drink. Ingesting certain [[Traditional medicine#Home remedies|home remedies]] may result in exposure to lead or its compounds.{{sfn|Tarragó|2012|p=11}}

Inhalation is the second major exposure pathway, affecting smokers and especially workers in lead-related occupations.{{sfn|Occupational Safety and Health Administration}} [[Tobacco smoke|Cigarette smoke]] contains, among other toxic substances, radioactive [[Isotopes of lead|lead-210]].{{sfn|Centers for Disease Control and Prevention|2015}} "As a result of EPA's regulatory efforts, levels of lead in the air [in the United States] decreased by 86 percent between 2010 and 2020."<ref name="EPSLAP">{{cite web |title=Lead (Pb) Air Pollution |url=https://www.epa.gov/lead-air-pollution |website=epa.gov |publisher=United States Environmental Protection Agency |access-date=July 22, 2022 |date=July 8, 2022 |quote=As a result of EPA's regulatory efforts, levels of lead in the air nationally decreased by 86 percent between 2010 and 2020.}}</ref> The concentration of lead in the air in the United States fell below the national standard of 0.15&nbsp;μg/m<sup>3</sup><ref name="EPAleadStandards">{{cite web |title=NAAQS Table |url=https://www.epa.gov/criteria-air-pollutants/naaqs-table#1 |website=epa.gov |publisher=United States Environmental Protection Agency |access-date=July 22, 2022 |date=April 5, 2022 |quote=National Ambient Air Quality Standards (40 CFR part 50) for six principal pollutants}}</ref> in 2014.<ref name="EPALeadTrends">{{cite web |title=Lead Trends |url=https://www.epa.gov/air-trends/lead-trends |website=epa.gov |publisher=United States Environmental Protection Agency |date=June 1, 2022}}</ref>

Skin exposure may be significant for people working with organic lead compounds. The rate of skin absorption is lower for inorganic lead.{{sfn|Wani|Ara|Usman|2015|pp=57, 58}}

==== Lead in foods ====
Lead may be found in food when food is grown in soil that is high in lead, airborne lead contaminates the crops, animals eat lead in their diet, or lead enters the food either from what it was stored or cooked in.<ref>{{cite book |last1=Castellino |first1=Nicolo |last2=Sannolo |first2=Nicola |last3=Castellino |first3=Pietro | name-list-style = vanc |title=Inorganic Lead Exposure and Intoxications|date=1994|publisher=CRC Press|isbn=9780873719971|page=86|url=https://books.google.com/books?id=059oObc8X48C&pg=PA86|url-status=live|archive-url=https://web.archive.org/web/20171105194927/https://books.google.com/books?id=059oObc8X48C&pg=PA86|archive-date=2017-11-05}}</ref> Ingestion of lead paint and batteries is also a route of exposure for livestock, which can subsequently affect humans.<ref>{{Cite journal |last1=Hesami |first1=Reza |last2=Salimi |first2=Azam |last3=Ghaderian |first3=Seyed Majid |date=2018-01-10 |title=Lead, zinc, and cadmium uptake, accumulation, and phytoremediation by plants growing around Tang-e Douzan lead–zinc mine, Iran |url=http://dx.doi.org/10.1007/s11356-017-1156-y |journal=Environmental Science and Pollution Research |volume=25 |issue=9 |pages=8701–8714 |doi=10.1007/s11356-017-1156-y |pmid=29322395 |bibcode=2018ESPR...25.8701H |s2cid=3938066 |issn=0944-1344}}</ref> Milk produced by contaminated cattle can be diluted to a lower lead concentration and sold for consumption.<ref>{{Cite journal |last1=Mielke |first1=Howard W. |last2=Reagan |first2=Patrick L. |date=February 1998 |title=Soil Is an Important Pathway of Human Lead Exposure |journal=Environmental Health Perspectives |volume=106 |issue=Suppl 1 |pages=217–229 |doi=10.2307/3433922 |jstor=3433922 |pmid=9539015 |pmc=1533263 |issn=0091-6765 }}</ref>

In Bangladesh, lead compounds have been added to [[turmeric]] to make it more yellow.<ref name=Stan2019>{{cite news |last1=Jordan |first1=Rob |title=Lead found in turmeric |url=https://news.stanford.edu/2019/09/24/lead-found-turmeric/ |access-date=25 September 2019 |work=Stanford News |date=24 September 2019}}</ref> This is believed to have started in the 1980s and continues {{as of|2019|lc=y}}.<ref name=Stan2019/> It is believed to be one of the main sources of high lead levels in the country.<ref>{{cite news |title=Researchers find lead in turmeric |url=https://phys.org/news/2019-09-turmeric.html |date= September 24, 2019  |access-date=25 September 2019 |work=phys.org}}</ref> In Hong Kong the maximum allowed lead level in food is 6&nbsp;parts per million in solids and 1&nbsp;part per million in liquids.<ref>{{cite web |title=Maximum Permitted Concentration of Certain Metals Present in Specified Foods |url=https://www.elegislation.gov.hk/hk/cap132V!en@2019-09-19T00:00:00?INDEX_CS=N&xpid=ID_1438402695833_003 |work= Cap. 132V Food Adulteration (Metallic Contamination) Regulations [Past Version] |publisher=Hong Kong e-Legislation |access-date=15 April 2020}}</ref>

Lead-containing dust can settle on drying cocoa beans when they are set outside near polluting industrial plants.<ref>{{Cite web |date=2023-02-01 |title=Dark chocolate is high in cadmium and lead. How much is safe to eat? |url=https://www.wbur.org/hereandnow/2023/02/01/dark-chocolate-lead-cadmium |website=Here & Now |publisher=WBUR |first1=Robin |last1=Young |first2=Karyn |last2=Miller-Medzon  |language=en |url-status=live |archive-url=https://web.archive.org/web/20240208134257/https://www.wbur.org/hereandnow/2023/02/01/dark-chocolate-lead-cadmium |archive-date= Feb 8, 2024 }}</ref> In December 2022, [[Consumer Reports]] tested 28 [[dark chocolate]] brands and found that 23 of them contained potentially harmful levels of lead, [[cadmium]] or both. They have urged the chocolate makers to reduce the level of lead which could be harmful, especially to a developing fetus.<ref>{{Cite web |title=Consumer Reports urges dark chocolate makers to reduce lead, cadmium levels |url=https://www.yahoo.com/lifestyle/consumer-reports-urges-dark-chocolate-155747068.html |access-date=2023-01-28 |website=Yahoo Life |agency=Reuters |first1=Jonathan |last1=Stempel |date=23 January 2023 |language=en-US}}</ref>

In March 2024, the US [[Food and Drug Administration]] recommended a voluntary recall on 6 brands of [[cinnamon]] due to contamination with lead,<ref>{{Cite web|url=https://www.fda.gov/food/alerts-advisories-safety-information/fda-alert-concerning-certain-cinnamon-products-due-presence-elevated-levels-lead|title=FDA Alert Concerning Certain Cinnamon Products Due to Presence of Elevated Levels of Lead|website=[[Food and Drug Administration]] |date=6 March 2024|access-date=27 May 2024}}</ref> after 500 reports of child lead poisoning.<ref>{{Cite news|url=https://apnews.com/article/cinnamon-lead-applesauce-wanabana-fda-344066a22a729d176c0c732180f48247|title=Lead-tainted cinnamon has been recalled. Here's what you should know|last=Aleccia|first=Jonel|date=8 March 2024|access-date=27 May 2024}}</ref> The FDA determined that cinnamon was adulterated with [[lead chromate]].<ref>{{Cite web|url=https://www.fda.gov/food/outbreaks-foodborne-illness/investigation-elevated-lead-chromium-levels-cinnamon-applesauce-pouches-november-2023|title=Investigation of Elevated Lead & Chromium Levels: Cinnamon Applesauce Pouches (November 2023)|website=[[Food and Drug Administration]] |date=16 April 2024|access-date=27 May 2024}}</ref>

==== Lead in plastic toys ====
According to the United States [[Centers for Disease Control and Prevention|Center for Disease Control]], the use of lead in plastics has not been banned as of 2024. Lead softens the plastic and makes it more flexible so that it can go back to its original shape. Habitual chewing on colored plastic insulation from stripped electrical wires was found to cause elevated lead levels in a 46-year-old man.<ref>{{Cite web |title=Lead Intoxication Associated with Chewing Plastic Wire Coating – Ohio |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/00020984.htm |access-date=8 June 2024 |website=www.cdc.gov |language=en-us}}</ref>  Lead may be used in plastic toys to stabilize molecules from heat. Lead dust can be formed when plastic is exposed to sunlight, air, and detergents that break down the chemical bond between the lead and plastics.<ref>{{Cite web |date=16 April 2024 |title=About Lead in Consumer Products {{!}} Exposure {{!}} CDC |url=https://www.cdc.gov/lead-prevention/prevention/consumer-products.html |access-date=8 June 2024 |website=www.cdc.gov |language=en-us}}</ref>

=== Treatment ===
{{See also|Chelation therapy}}
Treatment for lead poisoning normally involves the administration of [[dimercaprol]] and [[succimer]].{{sfn|Prasad|2010|pp=651–652}} Acute cases may require the use of [[Sodium calcium edetate|disodium calcium edetate]], the calcium [[Chelation|chelate]], and the disodium salt of ethylenediaminetetraacetic acid ([[Ethylenediaminetetraacetic acid|EDTA]]). It has a greater affinity for lead than calcium, with the result that lead chelate is formed by exchange and excreted in the urine, leaving behind harmless calcium.{{sfn|Masters|Trevor|Katzung|2008|pp=481–483}}