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Formation and uses of negative ions

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Issues with Anions

Issues with Anions

Credit: Titus Tscharntke
Source: http://commons.wikimedia.org/wiki/File:Dried_seaweed.jpg
License: CC BY-NC 3.0

Tired, run-down, feeling not at your peak? Try eating some seaweed. This plant contains iodine, an essential component of thyroid hormone. Low levels of thyroid hormone can be the result of a low iodine intake. Seaweed will provide some of the dietary iodine needed to enhance thyroid hormone production.

News You Can Use

  • In the 1940s, scientists learned that small amounts of fluoride in the drinking water significantly reduced the incidence of tooth decay. Grand Rapids, Michigan, was the first city to introduce fluoride addition to the drinking water (in 1945). Optimum concentrations of fluoride in water are considered to be 0.7 ppm.
  • Chloride in water (don’t confuse this with the chlorine used to disinfect the water) can have some adverse effects. High chloride content could come from seepage from sea water in coastal areas, from mineral deposits, and from human and animal waste (indicating contamination of the water supply). Although the presence of chloride in water is not considered unhealthy, high levels can contribute to an unpleasant salty taste. In addition, excessive amounts of chlorides will help produce corrosion in hot water tanks and plumbing. Reverse osmosis and deionization are two common approaches to lowering the chloride content of water.
  • Bromide salts are commonly found in nature, as are chloride salts. In sea water, bromide concentrations are around 65 mg/L (compare that with chloride’s approximately 20,000 mg/L). In fresh water, bromide levels of up to 0.5 mg/L may be found. Studies in humans do not show any adverse effects from slight increases in bromine intake. However, it is known that extremely high intake on bromide (the anion was once used as a sedative and a treatment for convulsions) can produce nausea, vomiting, and abdominal pain, as well as coma and paralysis.
  • Iodide anion is an important component for the synthesis of thyroid hormone. This hormone helps regulate growth and development as well as the rate of body metabolism. Too little iodide in the diet can lead to low production of thyroid hormone (hypothyroidism), characterized by weight gain, lethargy, and depression. Intake of too much iodide is very rare, and is seen mainly in people who eat a lot of seaweed. Most commercial table salt products are “iodized”, meaning they are supplemented with iodide to provide an adequate intake of this anion.
  • Credit: John Lambert Pearson
    Source: http://www.flickr.com/photos/orphanjones/419121524/
    License: CC BY-NC 3.0

    Most common brands of table salt are now iodized [Figure2]

  • Watch a video about thyroid disease at the link below:


Show What You Know

Use the links below to learn more about anions in everyday life. Then answer the following questions.

  1. What research suggested that fluoride caused cancer?
  2. What does current research on fluoride and cancer show?
  3. What are some signs of bromine toxicity?
  4. Why were bromides withdrawn from the American market in 1975?
  5. What was David Cowie’s contribution to medical science?

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Image Attributions

  1. [1]^ Credit: Titus Tscharntke; Source: http://commons.wikimedia.org/wiki/File:Dried_seaweed.jpg; License: CC BY-NC 3.0
  2. [2]^ Credit: John Lambert Pearson; Source: http://www.flickr.com/photos/orphanjones/419121524/; License: CC BY-NC 3.0

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