In conclusion it must be emphasised that following any credible accident at the Daya Bay reactor site water supplies will remain potable, however, a number of techniques are available which will reduce even any low level of contamination in the water still further and such techniques could have a worthwhile effect upon collective doses. In view of the principle that all doses should be kept as low as reasonably practical these technique must be considered and, where applicable, implemented.
9.6 Food
The Radiological Hazard
Radioactive material released from a reactor accident could be deposited on foodstuffs, crops or pastureland and hence there is the potential for radioactivity to enter the food chains. If an accident occurred at the Daya Bay plant, it is these food pathways which are likely to be of principal concern.
Hong Kong is far from being self-sufficient in food production and therefore imports the major portion of the foodstuffs it consumes, much coming from the People's Republic of China.
In the event of a major accident there will be a requirement to carry out monitoring of foodstuffs produced in Hong Kong to ensure that they may be safely consumed. The principal concern is likely to be milk produced from animals grazing on contaminated land although, at least initially, consideration will have to be given to the potential levels of radioactive contamination on, or in, all foodstuffs. Details of the requirement for monitoring are given in Chapter 8 and details of the levels of contamination at which the distribution, sale and consumption of foodstuff should be banned are given in Chapter 10.
There will also be a need to ensure that foodstuffs entering Hong Kong from the People's Republic of China are not contaminated to a level above the appropriate derived emergency reference level (DERL). It is therefore important to have agreements with the Chinese Authorities concerning the values of the DERLs which will be used. In this way foodstuffs contaminated to an unacceptable level will not be exported from the People's Republic of China into Hong Kong.
Consideration may still need to be given to the provision of monitoring equipment to check for contaminated foodstuffs entering Hong Kong at the ports of entry. It is unlikely that livestock will be significantly contaminated unless they had been grazing on contaminated pasture. Co-operation from the Chinese Authorities should ensure that any such animals may be identified and checked for contamination at the affected farm. As such, significantly contaminated livestock and meat should not reach Hong Kong, however checks on a few representative samples of any such imports may be helpful to provide public reassurance. It should be noted that the DERLs for contamination of meat which were used after the Chernobyl accident (typically 1 000 Bq kg ̄1) were designed to provide adequate protection for continuous consumption over long periods and as such are very conservative if the supply of the contaminated meat only lasts, say, a few weeks. Taking the annual dose limit for members of the public to be 5 mSv, ie the single-year dose limit set by the International Commission on Radiological Protection (refs 34 and 35) this gives a limit of intake for Cs-137 for adults of 400 000 becquerels, (derived from ref 33). It may be seen therefore that a DERL of 1 000 Bq kg for caesium-137 in meat is such that in order to exceed the 5 mSv limit a person would have to eat 400 kgm of such meat per year, equivalent to over 1 kgm per day. It is therefore justifiable to use a system of representative sampling of livestock and meat since even if livestock or meat enter Hong Kong with levels of contamination, say, ten times the DERL there will be no significant health hazard to the consumers even if they eat, say, 40 kgm of such meat. A suitable sampling system should be devised to ensure that it is highly unlikely that anyone could continually eat meat significantly above the DERL value.
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