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==Toxicity==
Cassava roots, peels and leaves are dangerous to eat raw because they contain two [[Cyanogenic glycoside|cyanogenic glucosides]], [[linamarin]] and [[lotaustralin]]. These are decomposed by [[linamarase]], a naturally occurring [[enzyme]] in cassava, liberating [[hydrogen cyanide]].<ref name="cereda">{{Cite journal |last1=Cereda |first1=M. P. |last2=Mattos |first2=M. C. Y. |year=1996 |title=Linamarin: the Toxic Compound of Cassava |journal=Journal of Venomous Animals and Toxins|volume=2 |pages=6–12 |doi=10.1590/S0104-79301996000100002 |doi-access=free}}</ref> Cassava varieties are often categorized as either bitter or sweet, signifying the presence or absence of toxic levels of cyanogenic glucosides, respectively. The so-called sweet (more accurately non-bitter) cultivars can produce as little as 20 milligrams of [[cyanide]] per kilogram of fresh roots, whereas bitter ones may produce more than 50 times as much (1 g/kg). Cassavas grown during [[drought]] are especially high in these toxins.<ref>{{cite journal |author1=Aregheore E. M. |author2=Agunbiade O. O. |year=1991 |title=The toxic effects of cassava (''Manihot esculenta'' Crantz) diets on humans: a review|journal=Veterinary and Human Toxicology|volume=33 |issue=3 |pages=274–275 |pmid=1650055}}</ref><ref>{{cite journal |author1=White W. L. B. |author2=Arias-Garzon D. I. |author3=McMahon J. M. |author4=Sayre R. T. |year=1998 |title=Cyanogenesis in Cassava, The Role of Hydroxynitrile Lyase in Root Cyanide Production |journal=[[Plant Physiol.]] |volume=116 |issue=4 |pages=1219–1225 |doi=10.1104/pp.116.4.1219 |pmc=35028 |pmid=9536038}}</ref> A dose of 25 mg of pure cassava cyanogenic glucoside, which contains 2.5 mg of cyanide, is sufficient to kill a rat.<ref>{{cite journal |year=2004 |title=Opinion of the Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food (AFC) on hydrocyanic acid in flavourings and other food ingredients with flavouring properties |url=http://www.efsa.europa.eu/en/efsajournal/pub/105 |journal=[[EFSA Journal]] |volume=105 |pages=1–28 |access-date=6 April 2013 |archive-date=29 September 2015 |archive-url=https://web.archive.org/web/20150929055532/http://www.efsa.europa.eu/en/efsajournal/pub/105 |url-status=live }}</ref> Excess cyanide residue from improper preparation
Symptoms of acute cyanide intoxication appear four or more hours after ingesting raw or poorly processed cassava: vertigo, vomiting, [[goiter]], [[ataxia]], partial paralysis, collapse, and death.<ref name="promedmail-4799579">{{cite web|url=https://www.promedmail.org/post/4799579|title=CASSAVA POISONING – VENEZUELA|date=29 January 2017|access-date=29 January 2017|publisher=[[ProMED-mail]]|archive-date=2 February 2017|archive-url=https://web.archive.org/web/20170202061550/https://www.promedmail.org/post/4799579}}</ref><ref>{{cite web |title=Cassava poisoning was integral to Episode 177 of Series 17 of the BBC drama 'Doctors' |publisher=BBC |date=5 February 2016 |url=https://www.bbc.co.uk/iplayer/episode/b06zn3j8/doctors-series-17-177-a-taste-of-home |access-date=13 February 2018 |archive-date=8 February 2016 |archive-url=https://web.archive.org/web/20160208105645/http://www.bbc.co.uk/iplayer/episode/b06zn3j8/doctors-series-17-177-a-taste-of-home |url-status=live }}</ref><ref>{{Cite journal |last1=Soto-Blanco |first1=Benito |last2=Górniak |first2=Silvana Lima |date=2010-07-01 |title=Toxic effects of prolonged administration of leaves of cassava (''Manihot esculenta'' Crantz) to goats |journal=Experimental and Toxicologic Pathology|language=en |volume=62 |issue=4 |pages=361–366 |doi=10.1016/j.etp.2009.05.011 |pmid=19559583 |bibcode=2010EToxP..62..361S |issn=0940-2993}}</ref><ref>{{Cite journal |last1=Suharti |first1=Sri |last2=Oktafiani |first2=Hafni |last3=Sudarman |first3=Asep |last4=Baik |first4=Myunggi |last5=Wiryawan |first5=Komang Gede |date=2021-12-01 |title=Effect of cyanide-degrading bacteria inoculation on performance, rumen fermentation characteristics of sheep fed bitter cassava (''Manihot esculenta'' Crantz) leaf meal|journal=Annals of Agricultural Sciences|language=en |volume=66 |issue=2 |pages=131–136 |doi=10.1016/j.aoas.2021.09.001 |s2cid=244191058 |issn=0570-1783|doi-access=free }}</ref> It can be treated easily with an injection of [[thiosulfate]] (which makes sulfur available for the patient's body to detoxify by converting the poisonous cyanide into thiocyanate).<ref name="fao.org"/>
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"Chronic, low-level cyanide exposure is associated with the development of [[goiter]] and with tropical ataxic neuropathy, a nerve-damaging disorder that renders a person unsteady and uncoordinated. Severe cyanide poisoning, particularly during famines, is associated with outbreaks of a debilitating, irreversible paralytic disorder called [[konzo]] and, in some cases, death. The incidence of konzo and [[tropical ataxic neuropathy]] can be as high as three percent in some areas."<ref>{{cite web |last=Wagner |first=Holly |title=Cassava's cyanide-producing abilities can cause neuropathy |url=http://www.cidpusa.org/cassava.htm |archive-url=https://web.archive.org/web/20100924054056/http://cidpusa.org/cassava.htm |archive-date=24 September 2010 |access-date=21 June 2010 |publisher=cidpusa.org}}</ref><ref>{{cite journal |author1=Siritunga D |author2=Sayre RT |date=September–October 2007 |title=Transgenic approaches for cyanogen reduction in cassava |journal=[[J AOAC Int]] |volume=90 |issue=5 |pages=1450–1455 |doi=10.1093/jaoac/90.5.1450 |pmid=17955993 |doi-access=free}}</ref>
Like many other roots and tubers, both bitter and sweet varieties of cassava contain [[antinutrient|antinutritional]] factors and toxins, with the bitter varieties containing much larger amounts.<ref name="fao.org">{{cite book |publisher=[[Food and Agriculture Organization]] of the United Nations (FAO) |year=1990 |title=Roots, tubers, plantains and bananas in human nutrition |chapter=Ch. 7 Toxic substances and antinutritional factors |chapter-url=http://www.fao.org/docrep/t0207e/T0207E08.htm#Cassava%20toxicity |place=Rome |isbn=9789251028629|url-access=registration |url=https://archive.org/details/rootstubersplant0000unse}}</ref> The more toxic varieties of cassava have been used in some places as [[famine food]] during times of [[food insecurity]].<ref name="promedmail-4799579" /><ref name="fao.org"/> For example, during the [[shortages in Venezuela]] in the late 2010s, dozens of deaths were reported due to Venezuelans resorting to eating bitter cassava in order to curb starvation.<ref>{{cite news |last1=Castro |first1=Maolis |date=6 March 2017 |title=La yuca amarga alimenta la muerte en Venezuela |language=es |work=[[El País]] |url=https://elpais.com/internacional/2017/03/05/america/1488744764_611719.html |access-date=25 February 2018 |archive-date=12 February 2018 |archive-url=https://web.archive.org/web/20180212184804/https://elpais.com/internacional/2017/03/05/america/1488744764_611719.html |url-status=live }}</ref><ref>{{cite news |date=22 February 2018 |title=Estragos de la crisis: Ocho niños han muerto en Aragua por consumir yuca amarga |language=es-ES |work=[[La Patilla]] |url=https://www.lapatilla.com/site/2018/02/22/estragos-de-la-crisis-ocho-ninos-han-muerto-en-aragua-por-consumir-yuca-amarga/ |access-date=25 February 2018 |archive-date=23 February 2018 |archive-url=https://web.archive.org/web/20180223022727/https://www.lapatilla.com/site/2018/02/22/estragos-de-la-crisis-ocho-ninos-han-muerto-en-aragua-por-consumir-yuca-amarga/ |url-status=live }}</ref> Cases of cassava poisoning were also documented during the famine accompanying the [[Great Leap Forward]] (1958–1962) in China.<ref>{{cite book |author=Zhou Xun |title=The Great Famine in China, 1958-1962: A Documentary History |publisher=Yale University Press |year=2012 |chapter=Ch. 3 Seasons of death}}</ref> Farmers
Societies that traditionally eat cassava generally understand that some processing (soaking, cooking, fermentation, etc.) is necessary to avoid getting sick. Brief soaking (four hours) of cassava is not sufficient, but soaking for 18–24 hours can remove up to half the level of cyanide. Drying may not be sufficient, either.<ref name="fao.org"/>
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