ARCHIVE: e-Digest Statistics about: Radioactivity
Ingestion and inhalation of long-lived natural radionuclides are estimated to give rise to an average annual dose of 0.27 mSv, with around 60 per cent of the average annual dose estimated to come from potassium-40 (40K). The human body regulates its uptake of potassium hence the doses from 40K are relatively constant. Doses to individual members of the population from other natural radionuclides, for example polonium-210 (210Po), do, however, vary from 0.1 mSv to 1 mSv depending on the type and quantity of food and drink consumed. High rate consumers of shellfish, which contain elevated levels of 210Po, can receive annual doses up to 0.5 mSv. Among other foodstuffs, Brazil nuts contain some of the highest levels of natural radioactivity, in particular radium-226 (226Ra) and radium-228 (228Ra). The consumption of a 100g bag (about 30-40 nuts) per week throughout the year would give rise to an annual dose of 0.2 mSv.
In addition to food, another source of natural radionuclides is drinks of which water is a major component. Samples taken by water companies in England and Wales of various types of sources of water prior to treatment (and four treated water supplies) are monitored for Defra. These sources are chosen so as not to be near nuclear sites, which are monitored separately by the Environment Agency. Results of analyses for the years 1995 to 2001 for England and Wales are shown in the table 'Radiochemical and chemical analyses of treated and untreated water sources'. Results at all times were below the 1993 World Health Organisation's guideline values of 0.1 Bq/l for total alpha and 1 Bq/l for total beta activity, except for the Derbyshire groundwater where the total alpha activity exceeded the limit in 1996, 1998 and 1999. Detailed analysis of alpha emitting radionuclides for this source indicated natural uranium as the cause. One year's consumption of water from this source would have given a dose of about 0.001mSv. It is to be noted that, for all of these sources, although a number of the radionuclides detected are of natural origin, there are traces of artificial radionuclides present; these are mainly there as a result of fallout. Analyses did not reveal any iodine-125 (125I), which has been seen occasionally in the past and is associated with discharges from medical treatments. Similar analyses are organised in Scotland and Northern Ireland.
- Artificial Sources of radiation:
- Exposures from atmospheric effluents
- Exposure from liquid effluents
|3||Radiochemical and chemical analyses of treated and untreated water sources: 1995-2001|
- Internet Links:
- Food Standards Agency: Radioactivity in food
- Food Standards Agency: Radioactivity in Food and the Environment, 2001 (RIFE-7)
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Page last modified: 16 September 2003
Page published: 10 September 2003