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Question from Margaret

I have checked with the companies that sell clay plaster and they tell me kaolin clay is one of the ingredients. Since kaolin clay is somewhat radioactive, wouldn’t covering the walls of my home with it be ill advised? Or is it such a tiny amount that it is negligible? I have asked them this question and they won’t answer it (probably for liability reasons). I would love to know since clay plaster is beautiful and (apart from the radioactivity) nontoxic.

Debra’s Answer

Hmmm…I didn’t know about this. I clay-plastered my bathroom walls last year (photos coming soon) so I’ve got it on my walls–no warnings on the label, but there are no warnings on glossy magazines either, which use paper coated with kaolin…or ceramics, medicines, foods in which it is used as an additive, toothpaste, or cosmetics.

Kaolin is a naturally-occuring a clay, an aluminum silicate mineral. It is one of the most common found in sediments, soils, hydrothermal deposits, and sedimentary rocks. It is mined in Brazil, France, United Kingdom, Germany, India, Australia, Korea, the People’s Republic of China, and Georgia, Florida, and South Carolina.

Kaolinite can contain very small traces of uranium and thorium. While a single magazine made using kaolin does not contain enough radioactive material to be detected by a security monitor, radioactivitiy in a single magazine can be measured.

The EPA has a a whole page on uranium exposure. They say, “Uranium is a naturally-occurring element found at low levels in virtually all rock, soil, and water. Significant concentrations of uranium occur in some substances such as phosphate rock deposits, and minerals such as uraninite in uranium-rich ores.” My logic says that if it occurs in virtually all rock, soil, and water, and kaolin is found in soils and mineral deposits, kaolin probably has the same concentration of uranium as other naturally-occuring substances.

They also say, “A person can be exposed to uranium by inhaling dust in air, or ingesting water and food. The general population is exposed to uranium primarily through food and water. The average daily intake of uranium from food ranges from 0.07 to 1.1 micrograms per day. The amount of uranium in air is usually very small.” No mention is made of exposure from kaolin in consumer products.

My point here is, uranium is indeed very dangerous to health in very concentrated amounts, but at the other end of the spectrum, we are exposed to it every day from multiple sources. I always say it’s best to minimize exposure wherever possible, but I wouldn’t say that clay plaster is alarmingly radioactive. Our bathroom walls don’t glow in the dark and we haven’t noticed any ill health effects.

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