Radiation and Food Safety
2.1 How can the radioactive substances be dispersed in a nuclear power plant accident?
If a nuclear power plant does not function properly, radioactivity may be released into the surrounding area by a mixture of products generated inside the reactor. The main radionuclides representing health risk are radioactive caesium and radioactive iodine. If radioactive fission products are released into the atmosphere, some of the gaseous and volatile radioactive isotopes could be carried by wind. The invisible radioactive material would behave in a way similar to a plume or cloud of smoke dispersing into the atmosphere, with some of its contents deposited onto the ground. The concentration of radioactive materials in the plume decreases as they move further away from the relevant site. Hong Kong is 3000 km from Japan . The plume will be much diluted when it reaches Hong Kong .
2.2 How can the radioactive materials contaminate our food?
When radioactive substances in the plume are deposited on plants, soil or water, they might enter the food chain. In the first instance, plants and animals could become surface contaminated and tissue contamination could occur after inhalation or after intake or ingestion of radiologically contaminated nutrients (animals eating a large quantity of contaminated items can concentrate radioactivity in their tissues). This tissue contamination will reduce over time. While surface contamination can be largely removed by washing, tissue contamination cannot be so removed. People can ingest the substances directly or indirectly through eating the products of animals (including fish) which have themselves eaten contaminated substances. Through this Ingestion Pathway, people may still become radiologically contaminated even they are not living in areas under the plume or after a lengthy period of time from the incident by consuming radiologically contaminated foodstuffs.
2.3 What are the possible health effects of consuming radioactively contaminated foodstuffs?
Naturally occurring radioactivity is actually present in the environment. Potential damage caused by low levels of radioactivity may be repaired by normal body metabolic processes. In a nuclear power plant accident, the general population is not likely to be exposed to high radiation doses. In general, foodstuffs available on markets are unlikely to be contaminated with very high levels of radioactive substances after a nuclear emergency. The chance of acute health effect is not common. If people are exposed to high dose of radiation, radiation sickness with acute symptoms like nausea, vomiting, extreme tiredness, hair loss, skin burns and diminished organ function will occur and immediate medical attention is required. In addition, prolonged consumption of radioactively contaminated foodstuffs may increase the risk of cancer in exposed persons.
2.4 Can I reduce the level of radionuclides in food through food preparation?
Possible residual surface radioactive contamination on food may be reduced by suitable food preparation such as washing, brushing, scrubbing, or peeling. It is also possible to store contaminated food for prolonged times to allow radioactive decay of short-lived radionuclides. On the contrary, cooking in general cannot reduce the level of radioactive contamination in food.
2.5 Is there any international standard on radioactive substances in foodstuff?
Codex Alimentarius Commission has established guideline levels for different radionuclides in foods destined for human consumption and traded internationally, which have been contaminated following a nuclear or radiological emergency. These guideline levels apply to food after reconstitution or as prepared for consumption. As far as generic radiological protection of food consumers is concerned, when radionuclide levels in food do not exceed the corresponding guideline levels, the food should be considered as safe for human consumption. The guideline levels are defined for two separate categories "infant foods" and "other foods" due to the fact that, for a number of radionuclides, the sensitivity of infants could pose a problem.
2.6 Do iodine-131 (I-131), caesium-134 (Cs-134) and caesium-137 (Cs-137) naturally occur in food?
I-131, Cs-134 and Cs-137 are artificially produced fission products* which do not naturally occur in food. However, these radionuclides can get into food after it has been discharged into the environment from civil (e.g. nuclear reactor operations) or military nuclear operations (e.g. above-ground nuclear testing) and then passes through the food chain. Therefore, low levels of I-131, Cs-134 and Cs-137 may be present in food due to possible contamination from the environment. The detection of high levels of these radionuclides in food may suggest possible radioactive contamination from a nuclear emergency.
* Nuclides produced either directly by nuclear fission or by the radioactive decay of such nuclides. For example, I-131 from the nuclear fission of uranium-235 (U-235).
2.7 Under what circumstances will the CFS apply the section 78B of the Public Health and Municipal Services Ordinance to prohibit food import?
The Director of Food and Environmental Hygiene may make an order under section 78B of Cap. 132 if he has reasonable grounds to believe that the making of the order is necessary to prevent or reduce a possibility of danger to public health or to mitigate the adverse consequence of a danger to public health. The order may prohibit the import and supply of problem food and order the recall of such food.
2.8 According to current risk assessment results, are there any health effects from consuming the contaminated spinach and radish?
Based on the assessment results, the radiation dose received by average consumers in Hong Kong due to prolonged consumption (1 year) of the contaminated radish was approximately 0.03 mSv, which equals to the radiation dose received from 2/3 chest X-ray examination or 1/256 CT scan, or one-third of the radiation dose received from air travel for a round trip from Hong Kong to the West Coast of the United States. As for spinach, the radiation dose received by average consumers in Hong Kong due to prolonged consumption (1 year) of the contaminated spinach was approximately 0.5 mSv, which equals to the radiation dose received from 10 chest X-ray examinations or 1/16 CT scan, or about 5 times the radiation dose received from air travel for a round trip from Hong Kong to the West Coast of the United States.
2.9 How to assess the internal radiation dose (internal dose) received through our diet?
Internal dose is the radiation doses received by an individual through consumption of radioactively contaminated food products or inhalation of the contaminated air. In our risk assessment, internal dose refers to the radiation dose received from our diet. We calculate the internal dose by the formula adopted by the Codex Alimentarius Commission.
= Radiation level in food x Mass of food consumed x Age dependent ingestion dose coefficient (i.e. specific factor for different radionuclides and different age group) x Import/production factor (i.e. proportion of food being contaminated)
2.10 What are the health impacts of consuming the contaminated food?
Based on the test results, these food samples are mainly contaminated with radionuclide of iodine-131. Radioactive iodine, if ingested, will accumulate in thyroid, thus significantly increasing the risk of thyroid cancer. Children and young people with an exposure to radiation have a higher risk of getting thyroid cancer.
2.11 What kind of food are likely to be contaminated after a nuclear accident and why?
Foods can be contaminated with radioactive materials as a result of a nuclear emergency. The surface of foods like fruits and vegetables or animal feed can become radioactive by deposit of radioactive materials falling on it from the air or through rain water. Under such circumstances, the large leafy areas of leafy vegetables can effectively intercept the radioactive contaminants that deposited from the atmosphere, making them more susceptible to radioactive contamination. On the other hand, when lactating cows graze on contaminated herbages of the early fallout, the radionuclides will soon transfer and appear in their milk. Therefore, in general, foods consumed fresh, such as milk, leafy vegetables, and fruit, are initially more likely to be contaminated after a nuclear accident.
Depending on the agricultural practices in the area of contamination and the stage of growing or harvest season at the time of the accident, grains, root crops, other produce, and animal-derived food products may become contaminated at later stage.
2.12 Is radioactive plutonium presence in food extremely dangerous? Will the Government monitor the level of radioactive plutonium in food?
Radioactive plutonium mainly enters the body through inhalation. In general, only minute amount of radioactive plutonium will be absorbed by the gastro-intestinal tract from the contaminated food. Most of them will be excreted. Although radioactive plutonium is a human carcinogen, exposure to very low levels of radioactive plutonium will not pose a significant risk to human health.
During the early stage of a nuclear accident, monitoring should be focused on radionuclides that have a greater impact on human health including iodine-131, caesium-134 and caesium-137. For the monitoring of plutonium in food, we will keep in view the latest development on the issue and the recommendations by the international organizations (e.g.the International Atomic Energy Agency and the World Health Organization) and make necessary actions.
2.13 Is it safe to consume radioactively contaminated vegetables from Guangdong province?
According to Guangdong authority, the radiation levels detected in the vegetables concerned were very low and would not cause any health concerns. Washing can effectively reduce the level of radioactive contaminants on the surface of vegetables. Repeated washing can obtain a better effect.
In Hong Kong, the Centre for Food Safety (CFS) has been conducting a routine surveillance system to monitor the radioactivity in food to ensure food available on market is fit for human consumption. CFS will keep close communication with Mainland authorities, monitor the latest testing results in the Mainland and make necessary action based on risk assessment results.
2.14 Seawater in vicinity of the damaged nuclear power plant in Japan has been found to be contaminated with radioactive substances. Will seafood sourced from waters around Japan and other areas be affected? Is it safe to eat?
Radioactive contamination of the Pacific Ocean following the nuclear incident in Japan has raised public concerns about seafood safety. Based on currently available information, some seafood in the direct vicinity of the nuclear power plant has been found to be contaminated. The radionuclides found are mainly I-131, Cs-134 and Cs-137.
I-131 has a short half-life of eight days. Its level will drop significantly through natural radioactive decay and is not expected to be transported over long distances by ocean currents. Therefore, I-131 is not expected to pose long-term impact in marine pollution.
On the other hand, the longer lived radiocaesium (Cs-134, 2 years half-life and Cs-137, 30 years half-life) could be transported over long distances by ocean currents. The great quantity of water in the Pacific Ocean , however, will rapidly disperse and dilute the released radioactive materials. Levels of radioactivity in seafood collected away from the waters surrounding Japan are expected to remain significantly below levels of any public health concern.
In view of the radiation leak at the Fukushima nuclear plant, a prohibition order has been issued to control the import and supply of a variety of Japanese food products from five prefectures of Japan . Import and supply of chilled or frozen aquatic products from the five prefectures are prohibited, unless they are accompanied by a certificate issued by the competent authority of Japan stating that the radiation levels do not exceed the guideline levels laid down by Codex. On the other hand, radioactivity of food, including aquatic products, produced locally or imported from areas other than Japan is being monitored through the CFS's routine surveillance programme. Surveillance results and information obtained so far did not suggest that is an area of concern. With effective measures in place, seafood available on market is not likely to be contaminated with high level of radioactivity.