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Listen to this siteTuesday 6 November 2001
Food Survey Information Sheet
Key Facts
Summary
This survey supplements routine surveillance in the vicinity of the Cardiff area to increase our understanding of the unexpectedly high levels of tritium found in fish and shellfish from Cardiff Bay and the River Taff. These levels result from authorised discharges of radioactive waste by Nycomed Amersham plc at Whitchurch, Cardiff to atmosphere and the public sewer system. The company produces a large range of radioactive labelled compounds principally for life science research.
The survey demonstrated that in terms of radioactive contamination by tritium and carbon-14, terrestrial foodstuffs and seafood produced in and around the Cardiff area are safe to eat. Doses to consumers from radioactive discharges incorporated into the foodchain are well below the statutory United Kingdom principal annual dose limit to members of the public of 1 milliSievert (mSv) for all artificial sources of radiation (excluding medical sources).
Introduction
Food produced around UK nuclear sites is routinely monitored for radioactivity by the Food Standards Agency (FSA). These results are reported in Radioactivity in Food and the Environment (RIFE) report 1which the Agency jointly publishes with the Scottish Environment Protection Agency (SEPA).
This survey was carried out as part of the Agency's work to increase its understanding of the unexpected high levels of tritium found in fish and shellfish from Cardiff Bay and the River Taff. These levels result from authorised discharges of radioactive waste by Nycomed Amersham plc at Whitchurch, Cardiff to atmosphere and the public sewer system. The company produces a range of radioactive labelled compounds principally for life science research.
This study was designed to obtain further data on the distribution of tritium and carbon-14 in aquatic biota and locally grown foodstuffs in the Cardiff area.
Materials and Method
Marine biota
Eight samples of marine biota were collected from the Cardiff beach and offshore fishing area as follows. The average weight of each of the samples was 150 grammes wet weight.
Freshwater fish
The river Taff flows immediately to the west of the laboratories, through the western outskirts of Cardiff and enters the sea at Cardiff Bay. The fish were netted from the river at Llandaff, approximately five kilometres downstream from the laboratories.
The six individual species of fish collected were:
Each sample consisted of fish fillets weighing between 100 and 400 grammes wet weight.
All aquatic samples were frozen after collection and transported to the CEFAS, Lowestoft laboratory for analysis for total tritium, organically bound tritium (OBT) and carbon-14 content. Standard analytical techniques as used for our routine surveillance programme were employed.1
Terrestrial samples
Fifty-six samples of locally grown fruit, vegetables and free-range eggs were collected from eight separate sites around Cardiff. Each sample collected weighed approximately 500 grammes with the exception of one sample of carrots which weighed 250 grammes, this being all that was available on the allotment. The foodstuffs were obtained from local allotment holders, 'pick your own' smallholdings, and farm shops with local produce. Two samples of blackberries were also collected from the wild.
The geographical positions of the sampling sites were determined by hand held Global Positioning System (GPS) instruments and recorded. The eight sites varied in distance from the laboratories, with A being the nearest and H the furthest away (Annex 1).
The terrestrial samples were transported by overnight courier service to the Radiochemistry Laboratory of the Veterinary Laboratory Agency, Weybridge for analysis. The samples were prepared and analysed for total tritium, organically bound tritium (OBT), tritiated water (HTO), carbon-14 and sulphur-35 using standard analytical and preparation techniques.1
Results
Aquatic samples
The results for the radioactivity in marine biota are given in Annex 2. Total tritium concentrations ranged from 39,500 to 59,500 Becquerels per kilogramme (Bq.kg-1) wet weight for crustacea (shore crab and shrimp) 4,000 to 73,900 Bq.kg-1 wet weight for molluscs (mussels, whelk and winkles) and 450 to 69,500 Bq.kg-1 wet weight for fish. The accepted range for values of natural tritium concentrations in sea water in open ocean waters is between 0.02 to 0.5 Bq.kg.-1 (2) Fish and seawater will have the same tritium concentration due to the water content of the fish flesh equilibrating with the surrounding seawater.
Over 90 percent of the total tritium concentration was present in the organically bound form. In general, these results are similar to those that have been reported in the 1999 RIFE report for the Cardiff area. Levels of carbon-14 activity were considerably lower than those for tritium, with the highest levels being found in whelks (1,100 Bq.kg-1 wet weight) and the lowest level in grey mullet (90 Bq.kg-1). These results are similar to those reported in the 1999 RIFE report. 1
Freshwater fish
The results for freshwater fish samples are given in Annex 3. Levels were generally lower than those in marine biota. Total tritium levels ranged from 8,000 to 30,000 Bq.kg-1 wet weight in barbel and brown trout respectively. Carbon-14 was detected in all freshwater samples in the range of 130 to 490 Bq.kg-1 wet weight. This range is similar to that reported for marine fish.
Terrestrial samples
The results for terrestrial results are given in Annex 4. Tritium and carbon-14 were present in virtually all of the samples analysed; results for sulphur-35 were all below the limit of detection. Results for total tritium ranged from less than 4 to 631 Bq.kg-1 fresh weight. The highest tritium content was found in foodstuffs grown nearest to the laboratories and concentrations were found to decrease sharply with distance from the site. There was little correlation between carbon-14 and distance from the laboratories. These results were all at or very close to the expected natural carbon-14 values for each foodstuff.
Interpretation
Calculations of radiation exposure or doses to members of the public from authorised discharges from Nycomed Amersham plc laboratories have been estimated. These doses can be compared with the statutory United Kingdom principal annual dose limit to members of the public of 1 mSv (millisievert) for all artificial sources of radiation (excluding medical sources). 3
Three factors are required to estimate doses
Marine foodstuffs
The amounts of seafood consumed are determined by site-specific habits surveys. Data are collected primarily by direct interviews with potential high-rate consumers who are often found in fishing communities.5 Children are rarely found to eat large quantities of seafood and their resulting dose is invariably less than those for adults. The calculations presented in table 1, and shown graphically in annex 5, are representative of adult seafood consumers.
The total dose from consumption of marine biota was 0.012 mSv, this being approximately 1 percent of the principal dose limit for members of the public of 1mSv, with fish contributing the greatest proportion. Marine fish contained the highest concentrations of radionuclides. These results are lower than those that were found during the 1999 RIFE monitoring programme in which doses to high-rate adult seafood consumers were estimated to be 0.053 mSv.
Terrestrial foodstuffs
For the terrestrial foodstuffs monitored (local fruit, vegetables and free range eggs), the amounts of food consumed are derived from national dietary surveys and are given for four age groups: adults, 15-year-old children, 10-year-old, and 1-year-old infants.4 For each food group, the 97.5th percentile consumption rate has been taken to represent those people who consume a particular foodstuff at a high level. The dose assessments are based on the assumption that all foods consumed are from local sources. The dose calculations have also been based on just the terrestrial foodstuffs sampled and for tritium and carbon-14 radioactivity. Other components of the diet such as milk and meat are regularly monitored as part of the RIFE (Radioactivity in Food and the Environment) programme and have not been assessed in this survey. Previous monitoring in 1998 has found that the combined dose from lamb, beef and offal is 0.0004 mSv.6
Table 2 indicates that there is a correlation between the distance from the laboratories and dose (site A being the closest and H the furthest away). The highest doses are received by consumers who eat produce grown around site A. The highest doses are received by the 1 year old age group, (mean 0.0008 mSv, s.d plus or minus 0.0008 mSv); mean 0.0004 mSv s.d plus or minus 0.0004 mSv for 10 year old age group; both adults and 15 year olds have the same mean dose 0.0002 mSv plus or minus 0.0003. This data is shown graphically in annex 6. The 1 year olds have a much greater exposure in comparison with other age groups since the dose per unit intake of radioactivity co-efficients for this group reflect their higher radio-sensitivity. The most exposed group of adults from the RIFE 1999 monitoring programme received 0.015mSv.1 The largest contribution was from carbon-14 in milk (which was not monitored in this survey).
Conclusions
This study provided further analytical data on the distribution of tritium and carbon-14 in aquatic biota and locally grown foodstuffs in the Cardiff area. It investigated additional samples to those that are routinely monitored for the RIFE report. The data for marine biota are similar to that reported for marine biota generally from the Cardiff offshore area. The differences in total tritium content can be attributed to the species ecological differences: mullet, which contained lowest concentrations of tritium, is a pelagic and herbivorous feeder; sole, with the highest concentrations, is a benthic and omnivorous feeder. The sole is higher in the foodchain than the mullet and bioaccumulation is one of the main reasons for the differences.
Freshwater fish contained considerably lower concentrations of tritium than marine biota. However the concentrations recorded are higher than those that would be expected since there is no authorised discharges from the laboratories directly to the river. There is evidence however, that the Cardiff sewage system can overflow into the Taff following surges after heavy rain. Authorised discharges of radioactivity to the sewage system could thus be transferred to fresh water biota after periods of heavy rainfall.
The terrestrial data found that tritium concentrations decreased with distance from the laboratories. The highest tritium concentrations were found in fruit and vegetables from the sampling site closest to the laboratories.
This survey demonstrates that in terms of radioactive contamination, terrestrial foodstuffs and seafood produced in and around the Cardiff area are safe to eat. Doses to consumers from radioactive discharges incorporated into the foodchain are well below the statutory United Kingdom principal annual dose limit to members of the public of 1mSv for all artificial sources of radiation (excluding medical sources).
Units of Measurement
The unit of measurement of radioactivity is the Becquerel and describes the rate at which a radionuclide decays. 1 Becquerel is equivalent to 1 radioactive event per second. The unit of measurement for radiation exposure, or dose, is the Sievert. This is a large unit and it is more usual to use millisievert, or one thousandth of a Sievert.
References
Further Information
Further information on this survey can be obtained from:
Mr Nick Wood
Food Standards Agency
Radiation Protection and Research Management Division
Room 715B, Aviation House
125 Kingsway
London WC2B 6NH
Tel: +44 (0) 20 7276 8767
Fax: +44 (0) 20 7276 8751
E-mail:
nick.wood@foodstandards.gsi.gov.uk
Terrestrial sampling sites and positions
Total tritium, organically bound tritium (OBT) and 14C in Cardiff marine fauna Bq kg-1 (wet) ¿ 1 sd*
* ¿ 1 standard deviation counting error
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Total tritium, organically bound tritium (OBT) and 14C in Cardiff freshwater
fish Bq kg-1 (wet) ¿ 1 sd*
*¿ 1standard deviation counting error
Back to topSee below
Back to topAdult Doses from Tritium and C-14 in Cardiff Marine Biota
Back to topMean Dose to the Four Age Groups (adult, 15yrs, 10yrs, 1yr) from Tritium and C-14 in Cardiff Terrestrial Foodstuffs
Back to topAdult doses from Cardiff marine biota
Dose received by consumers from terrestrial foodstuffs at the eight sampling sites. (A being closest to laboratories and H being the furthest away)
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