Perchorlate, in large amounts, has the ability to interfere with thyroid function as it interferes with iodine uptake, and individuals exposed to excessive amounts of perchlorate for a long time may develop a decreased production of thyroid hormones. However, the effects of perchlorate on the thyroid gland are reversible.

Children and developing foetuses are more likely to be affected by perchlorate than adults. This is because thyroid hormones are essential for normal growth and for brain development and the effects on brain development due to a lack of thyroid hormone are not reversible. Perchlorate has also been found in breast milk, so nursing mothers can transfer perchlorate to their babies. However, the beneficial aspects of breast-feeding outweigh any risks from exposure to perchlorate from mother’s milk, especially if the mother is consuming adequate iodine from food and supplements.

Perchlorate occurs naturally in the environment, in deposits of nitrate and potash, and can be formed in the atmosphere. Trace levels are found in rainfall and therefore perchlorate can be found in the soil and groundwater.

However, the majority of perchlorates are man-made. Manufactured perchlorates, some in large amounts, include perchloric acid, magnesium perchlorate, potassium perchlorate, ammonium perchlorate, sodium perchlorate, and lithium perchlorate. One, ammonium perchlorate, is used in rocket fuels. In addition, perchlorates are used in explosives. As they are used for some military applications, many countries consider the amounts they make confidential which is why no-one knows the exact amount of perchlorates produced or used.

Other uses of perchlorates include temporary adhesives, batteries, air bags in vehicles, fireworks, flares and matches. Perchlorate has also been found in some consumer products such as bleach, and a direct association between the storage time of bleach and higher levels of perchlorate has been noted. Perchlorate is also found in some dry food packaging – it is used to decrease static electricity and sprayed onto containers to stop statically charged food from clinging to the plastic or to the paper/cardboard surface. Perchlorate can also be formed during processes used to disinfect water and can therefore contaminate the water supply.

Perchlorates have been found in food and milk. Some plants, especially leafy green vegetables, can have elevated levels of perchlorate. Following the initial finding of perchlorate in fruits and vegetables produced in European Union, more extensive monitoring was undertaken which indicated that the presence of perchlorate was more widespread than initially expected. This resulted in the Commission Recommendation 2015/682 (EU), on the monitoring of perchlorate in food (including drinking water) in 2015 and in 2016 being adopted. From 2016 the setting of maximum levels for perchlorate in food/certain foods will be considered.

Further studies are needed to completely answer all questions about the potential toxicity of perchlorate.

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