How does iodine react with water

Iodine is naturally found in water. The concentration in seawater averages around 60 ppb, but is highly variable. Rivers generally contain around 5 ppb of iodine and mineral springs can even contain a few ppm. Iodine concentrations of up to 0.45% (dry matter) can accumulate in brown algae, and corals, sponges, mussels and fish also contain high concentrations of iodine in the form of thyroxine and triiodothyronine.

How and in which compounds does iodine react with water?

Even if to a lesser extent than the other halogens, iodine is also very reactive and does not come as an element, but in molecular form (I.2), as an ion (I.-) or as iodate (salt of iodic acid with the anion IO3-) in front.
When iodine is added to water, the following reaction takes place:

I.2(l) + H2O (l) -> OI-(aq) + 2H+(aq) + I.-(aq)

From I.2-Molecules and water molecules, among other things, hypoiodite (OI-). The equilibrium of this reaction depends heavily on the pH of the solution.
Other possibilities in which form iodine can occur in dissolved form are I.3-(aq), HIO (aq), IO-(aq) and HIO3(aq).
Iodine can form a wide variety of compounds, e.g. with other halogens, which also behave differently.

Water solubility of iodine and / or its compounds

The water solubility of iodine is 20OC and a bar at 1: 3500 and is therefore low. In contrast, iodine is more soluble in aqueous iodide solutions, whereby the following reaction takes place:

I.2 + I- -> [I.3]-

If iodine gets into surface water, it can be released back into the air as iodine gas. Most iodine compounds, on the other hand, are readily soluble in water or alcohol. For example, inorganic iodides have a high solubility in water.

Solubility and how it can be influenced

How can iodine get into water?

Often iodine gets into surface waters through rainfall and in coastal regions through water droplets that evaporate from the sea. So it can eventually seep into the groundwater. Other possibilities are the weathering of rocks containing iodine and volcanic activity (including underwater). In nature, iodine occurs in relatively large quantities, but only in the form of its compounds.
In addition to the iodine concentrations that may be naturally contained in water, additional exposure to humans can occur. This has various uses for iodine. An example are iodized X-ray contrast media, which are administered in very high doses (up to 200g) during X-ray examinations and are quickly excreted in the urine. These substances, like other pharmaceuticals, can even get into the groundwater through sewage. Iodine is also used for cleaning and disinfection and is found in facial soaps and bandages. The disinfecting effect is attributed to the splitting of oxygen from water.
In the chemical industry, colors and chemicals for photography, batteries, lubricants and the like are made with the help of iodine.
Radioactive iodine is used in medical examinations and in the treatment of thyroid cancer. It can be released in the event of a reactor accident.
Iodine often ends up in surface waters from sewage treatment plants. This can also apply to radioactive iodine isotopes. Only 2-25% of the iodine is retained in the sewage sludge. The rest remains in the water, so that the iodine content of the treated wastewater is often between one and sixteen micrograms per liter.
Iodine can occur in higher concentrations in the vicinity of hazardous waste landfills.

What environmental problems can iodine water pollution cause?

Iodine falls into the water hazard class (WGK) 1, so it is slightly hazardous to water. Nevertheless, dangerous reactions with e.g. alkali metals, aluminum, magnesium, mercury, fluorine or turpentine can occur. The harmfulness to the environment can be very different depending on the iodine compound.
The LD50Value, which indicates the dose of a substance at which half of a population is killed, is 14 g / kg for rats at an oral intake.
Probably the best-known example of the effects radioactive iodine can have is the 1986 Chernobyl nuclear accident 131I free in bulk. The isotope has a half-life of eight days, but can be ingested by grazing animals and in this way find its way into human milk and water supplies. In Ukraine, radioactive iodine is still a major problem in flowing water as most of the rivers flow south. During floods, radioactivity is washed away from the mainland.
Normally, people are almost never exposed to radioactive iodine unless they are working with it at work or undergoing medical treatment with the substance.

What are the health effects of iodine in water?

Iodine plays an important role in the production of thyroid hormones. There should be around 10-15 mg of this substance in the body. Most of these are then located in the thyroid gland. The daily recommended amount of iodine, a trace element, is between 150 and 200 μg, according to the World Health Organization. Since iodine is often added to table salt in Europe, this amount can normally be achieved without any problems.
The iodine intake varies widely around the world, as people in areas where a lot of fish is eaten, for example, consume a lot of iodine. It is between 50 μg and 10 mg daily. Too much iodine, in turn, can have negative effects on the thyroid. This is often associated with hyperactivity. Sensitive people react to too much iodine with iodism, which manifests itself in itching and sneezing, bronchitis, sleep disorders and a rash.
Skin contact with concentrated iodine can cause pigment loss and iodine fumes cause irritation to the eyes and lungs
As an element, iodine is toxic, 2 g can be fatal. Iodine tincture is fatal when taken orally from an amount of approx. 30 ml. Iodides, on the other hand, are relatively harmless. However, experiments with rats showed that they can have an impact on female fertility.
Children are particularly sensitive to too much or too little iodine intake because their thyroid is still growing.

Which water purification technologies can be used to remove iodine?

Iodine can be easily removed from the water by using activated charcoal.
Iodine itself is often used to purify water. It is mainly used for disinfection when preparing drinking water. For example, iodine tablets are available that can be added directly to the water. Iodine itself can be reprocessed. This is often done for economic reasons.

References

To the periodic table of the elements

To the overview of the elements and water