Cyberphysics - Radioactivity and Food

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Radioactivity and Food

An annual report is published jointly by MAFF and the Scottish Environment Protection Agency (SEPA) showed that consumers' exposure to radioactivity via the food-chain in 1999 remained well below nationally and internationally recommended limits of 1 millisievert per year.

An American study found that radioactivity of food is due mainly to accumulations of Ra²²⁶, Th²³², K⁴⁰, C¹⁴ and H³. These contribute about 0.2 mSv to the total annual dose from natural radiation sources.

Public water supplies are unlikely to contain significant amounts of radon. However, private supplies (such as from wells or boreholes) can contain high levels of dissolved radon. This can happen if ground waters have filtered though uranium or radium rich rocks. This is rare but can result in high levels of dissolved radon. Radon released from water usage in these cases then contributes to room air concentrations of the gas and may also increase intestinal cancer risks though direct ingestion of the water.

Radioactive Isotopes in food due to human activity

The accident at the Chernobyl nuclear plant made us very aware of how quickly radioisotopes are incorporated into the food chain. Almost immediately increased radiation levels were found in leafy green vegetables growing in contaminated fields and in cows' milk (due to the 'radioactive grass'). Radioactive particles that went up into the atmosphere fell down to Earth dissolved in raindrops, steadily increasing the radioactivity of the soil for several weeks. Early estimates of how quickly radiation levels would drop were found to be wrong. Instead of decreasing levels of radioactivity crops were found to have successively increased levels.

Animals grazing on contaminated fields concentrated radioisotopes in their tissues, and passed them on to the carnivore that eats them.

Humans eating the animals or vegetation that are contaminated then get a larger than normal dose of radioisotopes that produce ionizing radiation within their bodies. This can lead to DNA damage and mutations and cancers.

Discharges from nuclear power plants are carefully monitored and restricted by the Government departments that have responsibility for the environment and food. The highest estimated level of exposure to consumers from artificially produced radionuclides in food from around the Sellafield area is only 10% of the recommended limit compared to 14% in 1996. This is mainly due to the decreased consumption of some shellfish. However the report also demonstrates that natural radionuclides such as lead-210, polonium-210 and carbon-14 are by far the most important source of exposure in the average diet of consumers.



Carbon-14 C¹⁴	half life of 5700 years	Found in all organic matter (plant and animal)
Cesium-137 Cs¹³⁷	half-life of 33 years	Cesium-137 is produced in a fission reactor it is distributed throughout the body, taking the place of potassium.
Calcium 45 Ca⁴⁵	half-life of 164 days	Calcium-45 is produced in fission reactors Calcium supplements obtained from animal bones or oyster shells will contain environmental contaminants, including radioisotopes, but calcium obtained from limestone (dolomite) will not be contaminated by recent radioactive fallout.
Iodine 131 `I¹³¹`	half-life of 8 days	Iodine 131 is also produced in fission reactors it competes with dietary supplies of normal iodine, and may be concentrated and stored in the thyroid gland. concentration and storage of the isotope in the thyroid increases the risk of cell mutation, and the subsequent emergence of cancer. Immediate impairment of thyroid function may also occur. iodine supplements reduce the opportunity for the radioactive isotope to be taken up. Doses as high as 100 mg of potassium iodide for 7-10 days have been recommended for those directly exposed to radioactive fallout. This is a toxic dose of iodide under normal circumstances and should not be taken unless there is real danger.
Lead-210 Pb²¹⁰	half-life of 19 years	A decay product in the Uranium (4n+2) series
Polonium-210 Po²¹⁰	half-life of 138 days	A decay product in the Uranium (4n+2) series
Potassium-40	half-life of 1.3 x 10⁹ years	Constitutes 0.011% of naturally occurring potassium vital for transmission of bio-action potentials emits beta rays The "average" banana contains 400 mg of Potassium
Plutonium (all isotopes are radioactive)	half-life of 24,000 years	Plutonium is the most dangerous isotope produced in nuclear reactors. It is toxic but if inhaled or ingested the biggest danger is from radiotoxicity
Radium (all isotopes are radioactive)	half-life of 1600 years - for Ra-226	Brazil nuts contain Radium
Strontium 90 Sr⁹⁰	half-life of 20 years	Strontium-90 has got into the environment from weapon testing fall out. It gets into food supplies and then is concentrated in animal and fish bones. The slow accumulation of this isotope in human bone can be expected to increase the mutation rate in bone and bone marrow, increasing the incidence of bone cancer and leukaemia. Calcium supplements are useful as they may compete with strontium-90 and reduce its storage in bones.

: Useful URLs :

http://www.foodstandards.gov.uk/surv/rifeprevious.htm

http://www.maff.gov.uk/inf/newsrel/1998/980918b.htm

http://www.maff.gov.uk/inf/newsrel/fsa/fsa2099.htm

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