Editing Cassava (section)

== Toxicity ==

[[File:Linamarin.svg|thumb|Raw cassava is dangerous to eat as it contains [[linamarin]] (illustrated) and other [[cyanogenic glycoside]]s, which are broken down to release poisonous [[hydrogen cyanide]].<ref name="Cereda 1996"/>]]

Cassava roots, peels and leaves are dangerous to eat raw because they contain [[linamarin]] and [[lotaustralin]], which are toxic [[cyanogenic glycoside]]s. These are decomposed by the cassava enzyme [[linamarase]], releasing poisonous [[hydrogen cyanide]].<ref name="Cereda 1996">{{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 (high in cyanogenic glycosides) or sweet (low in those bitter compounds). Sweet cultivars can contain as little as 20 milligrams of [[cyanide]] per kilogram of fresh roots, whereas bitter cultivars may contain as much as 1000 milligrams per kilogram. 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&nbsp;mg of pure cassava cyanogenic glucoside, which contains 2.5&nbsp;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 causes goiters and acute cyanide poisoning, and is linked to ataxia (a neurological disorder affecting the ability to walk, also known as ''[[konzo]]'').<ref name="FAO-1990" /> It has also been linked to tropical fibrocalcific [[pancreatitis]] in humans, leading to chronic pancreatitis.<ref>{{cite journal |author=Bhatia E |year=2002 |title=Tropical calcific pancreatitis: strong association with SPINK1 trypsin inhibitor mutations |journal=[[Gastroenterology (journal)|Gastroenterology]]|volume=123 |issue=4 |pages=1020–1025 |doi=10.1053/gast.2002.36028 |pmid=12360463|doi-access=free }}</ref><ref name="Harford-2019">{{cite web |last1=Harford |first1=Tim |date=September 4, 2019 |title=How do people learn to cook a poisonous plant safely? |url=https://www.bbc.com/news/business-48859333 |access-date=4 September 2019 |work=BBC News |archive-date=4 September 2019 |archive-url=https://web.archive.org/web/20190904023704/https://www.bbc.com/news/business-48859333 |url-status=live }}</ref>

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="ProMED-2017">{{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-1990"/>

Chronic, low-level exposure to cyanide may contribute to both goiter and [[tropical ataxic neuropathy]], also called [[konzo]], which can be fatal. The risk is highest in famines, when as many as 3 percent of the population may be affected.<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 root and tuber crops, both bitter and sweet varieties of cassava contain [[antinutrient|antinutritional]] factors and toxins, with the bitter varieties containing much larger amounts.<ref name="FAO-1990">{{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="ProMED-2017" /><ref name="FAO-1990"/> 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 may select bitter cultivars to reduce crop losses.<ref name="Jiggins-2002">{{cite magazine |author1=Chiwona-Karltun, Linley |author2=Katundu, Chrissie |author3=Ngoma, James |author4=Chipungu, Felistus |author5=Mkumbira, Jonathan |author6=Simukoko, Sidney |author7=Jiggins, Janice |year=2002 |title=Bitter cassava and women: an intriguing response to food security |magazine=LEISA Magazine |volume=18 |issue=4 |url=https://www.researchgate.net/publication/255687456 |access-date=22 September 2018 |archive-date=22 September 2018 |archive-url=https://web.archive.org/web/20180922101746/https://www.researchgate.net/publication/255687456 |url-status=live }}</ref>

Societies that traditionally eat cassava generally understand that 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-1990"/>

For some smaller-rooted, sweet varieties, cooking is sufficient to eliminate all toxicity. The cyanide is carried away in the processing water and the amounts produced in domestic consumption are too small to have environmental impact.<ref name="Cereda 1996"/> The larger-rooted, bitter varieties used for production of flour or starch must be processed to remove the cyanogenic glucosides. The large roots are peeled and then ground into flour, which is then soaked in water, squeezed dry several times, and toasted. The starch grains that flow with the water during the soaking process are also used in cooking.<ref>{{Cite journal |last1=Padmaja |first1=G. |last2=Steinkraus |first2=K. H. |year=1995 |title=Cyanide detoxification in cassava for food and feed uses |journal=[[Critical Reviews in Food Science and Nutrition]]|volume=35 |issue=4 |pages=299–339 |doi=10.1080/10408399509527703 |pmid=7576161}}</ref> The flour is used throughout South America and the [[Caribbean]]. Industrial production of cassava flour, even at the cottage level, may generate enough cyanide and cyanogenic glycosides in the effluents to have a severe environmental impact.<ref name="Cereda 1996"/>