Editing Group 12 element (section)

==Biological role and toxicity==
The group 12 elements have multiple effects on biological organisms as cadmium and mercury are toxic while zinc is required by most plants and animals in trace amounts.

Zinc is an essential [[trace element]], necessary for plants,<ref name=Broadley2007>{{cite journal|last1=Broadley|first1=M. R.|last2=White|first2=P. J.|last3=Hammond|first3=J. P.|last4=Zelko|first4=I.|last5=Lux|first5=A.|title=Zinc in plants|journal=New Phytologist|volume=173|year=2007|pmid=17286818|doi=10.1111/j.1469-8137.2007.01996.x|issue=4|pages=677–702|doi-access=free}}</ref> animals,<ref>{{cite journal|author=Prasad A. S.|title=Zinc in Human Health: Effect of Zinc on Immune Cells|journal=Mol. Med.|volume=14|year=2008|pmid=18385818|pmc=2277319|doi=10.2119/2008-00033.Prasad|issue=5–6|pages=353–7}}</ref> and [[microorganism]]s.<ref>Zinc's role in microorganisms is particularly reviewed in: {{cite journal|author=Sugarman, B.|title=Zinc and infection|journal=Reviews of Infectious Diseases|volume=5|year=1983|pmid=6338570|issue=1|pages=137–47|doi=10.1093/clinids/5.1.137}}</ref> It is "typically the second most abundant transition metal in organisms" after [[iron]] and it is the only metal which appears in all [[Enzyme#Naming conventions|enzyme classes]].<ref name=Broadley2007/> There are 2–4&nbsp;grams of zinc<ref name=Rink2000>{{cite journal|last1=Rink|first1 =L.|last2=Gabriel|first2=P.|title=Zinc and the immune system|journal=Proc Nutr Soc|volume=59|year=2000|pmid=11115789|doi=10.1017/S0029665100000781|issue=4|pages=541–52|doi-access=free}}</ref> distributed throughout the human body,<ref>{{cite book|last=Wapnir|first=Raul A.|title=Protein Nutrition and Mineral Absorption|publisher=CRC Press|location=Boca Raton, Florida|year=1990|isbn=978-0-8493-5227-0|url=https://books.google.com/books?id=qfKdaCoZS18C}}</ref><!-- page 131 --> and it plays "ubiquitous biological roles".<ref name=Hambridge2007>{{Cite journal|author1=Hambidge, K. M.|author2=Krebs, N. F.|title=Zinc deficiency: a special challenge|journal=J. Nutr.|volume=137|year=2007|pmid=17374687|issue=4|pages=1101–5|doi=10.1093/jn/137.4.1101|doi-access=free}}</ref> A 2006 study estimated that about 10% of human proteins (2800) potentially bind zinc, in addition to hundreds which transport and traffic zinc.<ref name=Broadley2007/> In the U.S., the [[Recommended Dietary Allowance]] (RDA) is 8&nbsp;mg/day for women and 11&nbsp;mg/day for men.<ref name=rda>{{cite book|author1=Connie W. Bales|author2=Christine Seel Ritchie|title=Handbook of Clinical Nutrition and Aging|url=https://books.google.com/books?id=jtsBbP2087wC&pg=PA151|access-date=23 June 2011|date=21 May 2009|publisher=Springer|isbn=978-1-60327-384-8|pages=151–}}</ref> Harmful excessive supplementation may be a problem and should probably not exceed 20&nbsp;mg/day in healthy people,<ref>{{Cite journal|last1 =Maret|first1=W.|last2=Sandstead|first2=H. H.|title=Zinc requirements and the risks and benefits of zinc supplementation|journal=[[Journal of Trace Elements in Medicine and Biology]]|volume=20|year=2006|pmid=16632171|doi=10.1016/j.jtemb.2006.01.006|issue =1|pages =3–18|bibcode=2006JTEMB..20....3M }}</ref> although the U.S. National Research Council set a Tolerable Upper Intake of 40&nbsp;mg/day.<ref>{{cite book|url=http://books.nap.edu/openbook.php?record_id=10026&page=442|title=Zinc – Summary|access-date=2010-03-30|publisher=[[Institute of Medicine]], Food and Nutrition Board|work=Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2001)|year=2001 |doi=10.17226/10026 |pmid=25057538 |isbn=978-0-309-07279-3 |author1=Institute of Medicine (US) Panel on Micronutrients }}</ref>

Mercury and cadmium are toxic and may cause environmental damage if they enter rivers or rain water. This may result in contaminated crops<ref>{{cite journal|title = Environmental cadmium exposure, adverse effects, and preventative measures in Japan|first1 = Koji|last1 = Nogawa|journal = Biometals|year = 2004|volume = 17|issue = 5|pages =581–587|doi = 10.1023/B:BIOM.0000045742.81440.9c|pmid = 15688869|last2 = Kobayashi|first2 = E.|last3 = Okubo|first3 = Y.|last4 = Suwazono|first4 = Y.|s2cid = 8053594}}</ref> as well as the [[bioaccumulation]] of mercury in a food chain leading to an increase in illnesses caused by [[mercury poisoning|mercury]] and [[cadmium poisoning]].<ref name="Mozaffarian D, Rimm EB 2006 1885–99">{{cite journal |journal=JAMA |year=2006 |volume=296 |issue=15 |pages=1885–99 |title= Fish intake, contaminants, and human health: evaluating the risks and the benefits |vauthors=Mozaffarian D, Rimm EB |pmid=17047219 |doi=10.1001/jama.296.15.1885|doi-access=free }}</ref>