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, animals, and microorganisms. It is "typically the second most abundant transition metal in organisms" after iron and it is the only metal which appears in all enzyme classes. There are 2–4 grams of zinc distributed throughout the human body, and it plays "ubiquitous biological roles". A 2006 study estimated that about 10% of human proteins (2800) potentially bind zinc, in addition to hundreds which transport and traffic zinc. In the U.S., the Recommended Dietary Allowance (RDA) is 8 mg/day for women and 11 mg/day for men. Harmful excessive supplementation may be a problem and should probably not exceed 20 mg/day in healthy people, although the U.S. National Research Council set a Tolerable Upper Intake of 40 mg/day.
Mercury and cadmium are toxic and may cause environmental damage if they enter rivers or rain water. This may result in contaminated crops as well as the bioaccumulation of mercury in a food chain leading to an increase in illnesses caused by mercury and cadmium poisoning.
Read more about this topic: Group 12 Element
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