Radioactivity testing of imported food items

M.C.S. Seneviratne, P. S. Shanaka Paranahewage-Atomic Energy Authority

Do you know that the imported food such as milk powder, chilled fish and canned fish items you purchase from the market, are screened to check whether they are contaminated with radioactive elements? The Atomic Energy Authority (AEA) which functions under the Ministry of Power and Energy is engaged in screening all the above food items imported to Sri Lanka, to find out whether they are contaminated or not with radioactive elements. The scientific method used to measure the radioactive level of food items is called Gamma Ray Spectrometry.

Nuclear power plant

The only institution having this facility in Sri Lanka is the Atomic Energy Authority and these tests are done in the Nuclear Analytical Laboratory of the Life Sciences Division (LSD) of AEA. This laboratory has been accredited by the Sri Lanka Accreditation Board (SLAB) for radioactivity measurement (TL 012-01) under the requirement of ISO/IEC 17025. If the radioactivity level is below a certain standard level, AEA issues a certificate to the Ministry of Health which gives its approval to release the food consignment from the customs for the consumption of the people.

All living beings in this world are exposed to naturally occurring radiation continuously due to (1) natural radioactive elements such as Thorium (Th), Uranium (U), Potassium-40 (40K) etc. present on earth and (2) cosmic rays which come from outer space continuously. This naturally occurring radiation is not harmful to human being. Other than naturally occurring radiation, all living beings are exposed to man-made radiation too. Man-made radiation includes (1) radiation due to radioactive sources used in medicine, industry, research etc. and (2) radioactive elements released to the environment due to nuclear weapon testing and nuclear power plant accidents. The radioactive elements released to the environment will spread all over the world through the atmosphere and finally falls on to the ground and enter human bodies through food chains as shown in the diagram.

The two major power plant accidents Chernobyl accident on April 26,1986 and Fukushima Daiichi accident on March 11, 2011 have caused lot of radioactive material to be leaked to the environment.

Contaminated milk food products

Testing of nuclear weapons in developed countries has also caused the release of radioactive material to the environment. These radioactive material cause contamination of our food products such as milk, fish, etc. Thus imported food items are tested for radioactive contamination in both developed countries and a few developing countries. Therefore Atomic Energy Authority tests imported food items such as milk powder, infant milk food, canned fish and chilled fish using gamma ray spectrometry for radioactive contamination in order to make sure that Sri Lankan public are not exposed to unnecessary harmful radiation.

According to the International Atomic Energy Agency (IAEA) during the Chernobyl nuclear accident in 1986, the total radioactive material released was 12×1018 Bq (Becqueral - Bq is a unit used to measure radioactivity) and the amount of radioactive Cesium isotopes, 137Cs and 134Cs released were 0.05×1018 Bq and 0.09×1018 Bq respectively. This radioactivity was released to the atmosphere and as a result of the meteorological conditions these radioactive material has got deposited on the surface of the countries in the Northern Hemisphere.

From the Fukushima Daiichi nuclear power plant accident in 2011, the total radioactive material released was 4.7×1015 Bq and the amount of radioactive Cesium isotopes, 137Cs released was 2.5×1015 Bq according to the NHK news published after the nuclear accident. Unlike the Chernobyl accident after the Fukushima nuclear accident lot of water used to cool the reactor core was also released to the Pacific Ocean and this contaminated water was spread all over the Pacific and Indian Oceans with the sea currents.

Since 1997, the AEA has launched a project to determine the radioactive levels of imported milk food items to protect the general public from undue exposure to radiation by consumption of contaminated milk food products. This project was extended in April 2011 to test imported sea food (chilled fish and canned fish). Considerable number of import and export food samples are tested per annum in this manner.

According to the Sri Lankan regulations, allowed maximum radioactivity level is 20 Bq/kg for milk foods and 100 Bq/kg for all other food items (Act 19 at 1969 and Gazette notification LD-B/73-1995). The AEA is maintaining very low radioactivity levels for food items as standard, for radioactive contamination, while some other developed countries use high radioactive levels as standards to measure the level of radioactivity. Very recently the Japanese government has set safety levels as 50 Bq/kg for milk based products, 100 Bq/kg for rice and vegetable and 500 Bq/Kg for all other food items due to the environment contamination from Fukushima Daiichi nuclear power plant accident.