Per kilogram of fresh mass, Brazil nuts can contain activities of several tens of bequerels of radium-226 and radium-228, respectively. This means that one kilogram of Brazil nuts can have a radium content that is about 1,000 times higher than one kilogram of one’s total diet in Germany.

In addition to radium, other natural radionuclides are found in Brazil nuts:

Brazil nut tree Source: Imago Photo/Stock.adobe.com

Natural radioactive substances can be found everywhere in our environment, for example in the soil and in the rocks of the earth’s crust. Because radioactive substances can have similar chemical properties to nutrients, plants actively take up radioactive substances along with the nutrients they need to grow. Along with the vital water, plants also passively absorb radioactive substances dissolved in it.

This means that plants, like all foods, contain natural radioactive substances that emit radiation. Some plant species (or their parts) accumulate certain radionuclides to a high degree. This also includes Brazil nuts.

Why can Brazil nuts contain high levels of radium?

In addition to the nutrients essential for plants, all soils contain natural radionuclides, including radium. Brazil nut trees grow in the tropical rainforests of South America, the soils of which are usually highly weathered and poor in nutrients. Their radium content can vary greatly and can particularly be high in some cases.

One approach to explaining why Brazil nut trees in particular take up more radium is the presumed high calcium requirement of the jungle giants. Because the nutrient-poor soil of the tropical rainforests of South America is usually poor in calcium, Brazil nut trees instead absorb radioactive radium, which is chemically similar to the calcium they need, from different soil layers via their widely branched root system.

Within the Brazil nut tree, the absorbed radium can easily be transferred to the Brazil nut. This leads to the remarkably high radium contents of Brazil nuts. Researchers suspect that the formation of organic radium complexes is responsible for this.

Source: Matthieu/Stock.adobe.com

Radioactive radium is chemically quite similar to the mineral calcium. Because of this chemical similarity, radium behaves like calcium in the human body.

For the most, radium that enters the human body with food is excreted again immediately. Only a small proportion is absorbed into the body via the gastrointestinal tract. About one quarter to one third of this is initially stored in the bones and then slowly released. The absorption of radium is particularly unfavourable when bones are growing and radium is deposited in the forming bones.

Because the metabolism in the human body changes with age, during pregnancy, and during breastfeeding, the behaviour of radium in the human body is also different for different age groups.

The radioactive decay of radium in the human body produces other radionuclides that behave according to their respective chemical properties in the human body.

Pregnancy

During pregnancy, calcium is important for the bone growth of the unborn child. Among other things, bone remodelling intensifies in the expectant mother’s body during this time. Calcium (and thus also the chemically similar radium) is now increasingly absorbed into the body via the gastrointestinal tract.

The amount (activity) of radium that the expectant mother ingests with food and the time of ingestion by the mother are decisive for the health consequences of the unborn child. If the expectant mother has ingested radionuclides before pregnancy that are still in her body at the beginning of pregnancy, these can also contribute to the radiation dose to the child.

Breastfeeding

Calcium is also important for the bone growth of the infant. During breastfeeding, a small amount of the radium that the mother ingests with food passes into the breast milk and can then be passed to the infant through breastfeeding.

The maximal proportion is about half a percent and depends on when the mother ingested radium. Radium intake is particularly unfavourable one week after birth because the composition of breast milk changes after birth and the “mature milk” forms only gradually.

Both the amount (activity) of radium ingested by the mother with food and the time of ingestion by the mother are decisive for the health consequences of the infant. If the expectant mother has ingested radionuclides before breastfeeding that are still in her body at the beginning of breastfeeding, these can also contribute to the radiation dose to the child.

Brazil nuts Source: jchizhe/Stock.adobe.com

When people eat Brazil nuts, they ingest the radioactive substances contained in the Brazil nut. As a result they receive a radiation dose. Unborn or breastfed children whose mother has consumed Brazil nuts also receive a radiation dose.

These radiation doses are referred to as the committed effective dose. If radioactive substances are absorbed into the body, radiation protection experts calculate the resulting dose for a person until the fictitious end of their life. When people talk about a “dose per year” when consuming Brazil nuts, strictly speaking, the committed dose resulting from the Brazil nut consumption of the current year until the end of life is meant.

The amount (activity) of radium ingested by a person is decisive for the radiation dose (committed effective dose) received and thus also for possible health consequences. Thus, in addition to the radium content of Brazil nuts, the quantity of Brazil nuts that a person consumes is decisive. To a lesser extent, other natural radionuclides also contribute to the radiation dose.

Model calculations give an impression of how high a radiation dose can typically be for adults and children as a result of consuming Brazil nuts. The calculations are based on the average consumption in Germany as well as the occasional consumption recommendations (critically viewed by the BfS) to improve selenium supply.

• According to the World Health Organisation (WHO), an average of 0.1 gram of Brazil nuts per person per day are consumed in Germany.
• If people consume two Brazil nuts a day (as is sometimes recommended), this corresponds to around 8 grams of Brazil nuts a day. In individual cases, much higher quantities seem to be consumed – as can be seen from enquiries from citizens addressed to the BfS.

Based on these data, the personal radiation dose can be estimated for even higher consumption: For example, twice as much consumption would result in twice the annual committed effective dose.

Because the human body and its metabolism change with age, higher annual committed effective doses are to be expected in children compared to adults at the same consumption levels.

For comparison of the calculated values:

• Natural radionuclides in food result in an annual radiation dose of around 300 microsievert for adults in Germany under average dietary conditions.
• The annual effective dose from natural sources to which we are exposed in everyday life averages 2,100 microsievert in Germany. It varies between 1,000 and 10,000 microsievert depending on local conditions and lifestyle.

Source: sp4764/Stock.adobe.com

Model calculations give an impression of how high a radiation dose can typically be for unborn children and infants if the (expectant) mother ingests Brazil nuts.

If people consume two Brazil nuts a day (as is sometimes recommended), this corresponds to around 8 grams of Brazil nuts a day.

Based on these data, the radiation dose to the child can be estimated for lower or higher consumption by the mother: To the same extent that the average daily amount consumed by the mother increases or decreases, the radiation dose to her child also increases or decreases. For example, twice as much Brazil nut consumption by the mother would result in twice as much committed effective dose for the child.

For comparison of the calculated values:

• Natural radionuclides in food result in an annual radiation dose of around 300 microsievert for adults in Germany under average dietary conditions.
• The annual effective dose from natural sources to which we are exposed in everyday life averages 2,100 microsievert in Germany. It varies between 1,000 and 10,000 microsievert depending on local conditions and lifestyle.