Modelling and experimental studies on the transfer of radionuclides to fruit.

Although fruit is an important component of the diet, the extent to which it contributes to radiological exposure remains unclear, partially as a consequence of uncertainties in models and data used to assess transfer of radionuclides in the food chain. A Fruits Working Group operated as part of the IAEA BIOMASS (BIOsphere Modelling and ASSessment) programme from 1997 to 2000, with the aim of improving the robustness of the models that are used for radiological assessment. The Group completed a number of modelling and experimental activities including: (i) a review of experimental, field and modelling information on the transfer of radionuclides to fruit; (ii) discussion of recently completed or ongoing experimental studies; (iii) development of a database on the transfer of radionuclides to fruit; (iv) development of a conceptual model for fruit and (v) two model intercomparison studies and a model validation study. The Group achieved significant advances in understanding the processes involved in transfer of radionuclides to fruit. The work demonstrated that further experimental and modelling studies are required to ensure that the current generation of models can be applied to a wide range of scenarios.

The role of fruit in the diet.

Data on the production and consumption of fruit are reviewed in the context of modelling the transfer of radionuclides to fruit, and the assessment of the consequent risks to the consumers. Mean consumption rates vary widely from country to country, from 150 g per day fresh weight to about 500 g per day. Consumption also varies with age, socio-economic class, and climate. In some countries there is a trend towards increased consumption of fruit, associated with a growing interest in a healthy diet, and these trends have been associated with changes in the incidence of cardio-vascular diseases and some forms of cancer. Assessment of the effects of radionuclides in fruit needs to take into account the use of wild growing fruits, the increasing trade in fruit between countries, and the contribution from natural radionuclides in fruit.

Radiocaesium activity concentrations in the fruit-bodies of macrofungi in Great Britain and an assessment of dietary intake habits.

Radiocaesium activity concentrations in the fruit-bodies of some species of macrofungi are higher than in many other foodstuffs. The consumption of fruit-bodies contributes significantly to radiocaesium intake of humans in some countries. In the United Kingdom, the collection of wild fungi has generally been considered to be of minor importance and there are few data on consumption rates or radiocaesium activity concentrations in most edible species. Samples of commonly eaten species in Great Britain have been collected to assess radiocaesium contamination levels and geographical variation. Concurrently, surveys of consumption habits were conducted. A total of 425 samples representing 37 different species were collected. Significantly higher radiocaesium activity concentrations occurred in mycorrhizal compared to saprotrophic or parasitic species. The highest 137Cs activity concentration of 30.5 kBq kg-1 dry wt. was determined in a sample of Hydnum repandum collected in Wales. The transfer of radiocaesium from soil to fungal fruit-bodies was highly variable, ranging over three orders of magnitude within individual species. A number of approaches to quantifying radiocaesium transfer from soil to fungal fruit-bodies were used. Although these were in general agreement with previously measured values in other countries, all the approaches gave variable results. Over 200 people responded to the dietary habits questionnaire. The median intake rate was 0.75 kg year-1 (fresh wt.) and 60% of respondents consumed only one species (generally Agaricus campestris). However, intakes of up to 26 kg year-1 were recorded and a total of 82 species were consumed. The intake of 137Cs was determined by the amount of mycorrhizal fungi in the diet rather than the total intake of fungi. Assuming median recorded 137Cs activity concentrations in each fungal species, the estimated annual committed effective dose for over 95% of respondents was < 1 microSv. Hence, currently, the consumption of wild fungi in the UK would not be expected to significantly increase the dose above that attributable to the normal diet of most consumers. However, the results of this study demonstrate that, in the event of any future accidental release of radiocaesium, the potential ingestion dose received from the consumption of wild fungi would need to be considered.

Dose due to man-made radionuclides in terrestrial wild foods near Sellafield.

Radiological dose implications for consumers of wild foods around Sellafield have been assessed. Habits were surveyed from 72 households, mostly within a few kilometres of Sellafield. A few people were included who lived further away but collect wild foods close to Sellafield. Dose estimates were based on measured gamma emitters, as well as 239Pu, 241Am, 14C and 129I in selected samples. In all cases, doses were dominated by 137Cs. One infant was identified who consumed wild food, giving an estimated effective dose of 0.3 microSv a(-1). In the age group 2 to 10 years a mean dose of 0.51 microSv a(-1), and a maximum of 2.8 microSv a(-1), were estimated. Intakes by adults were higher and resulted in more radiologically significant doses. The extreme individual received a dose of 32 microSv a(-1) largely due to consumption of honey that included contributions from the Chernobyl accident, and hedgerow fruits. This is comparable to doses to the critical group for consumption of conventional agricultural produce close to the Sellafield site. The 97.5th percentile dose, for all age groups of consumers taken together, was 16.6 microSv a(-1), or 6.2 microSv a(-1) if the contributions from Chernobyl are excluded. Considering the contributions from different foods to the whole group of 181 wild food consumers, the rank order is honey, blackberries and venison.

The determination of 129I in milk and vegetation using neutron activation analysis.

A new method has been developed to measure 129I in the environment with detection limits below 10 mBq/kg of vegetation and 10 mBq/l of cows' milk. The method is based on extraction of 129I from the milk or vegetation sample, onto an ion exchange resin. An inactive carrier of 127I is added to the sample before separation, to monitor losses throughout the entire procedure. The ion exchange resin is irradiated for 7.5 h in a neutron flux of 10(16) n m-2 s-1 to induce the 129I(n, gamma) 130I reaction with thermal neutrons. The 127I carrier undergoes a (n,2n) reaction with fast neutrons to produce 126I. Iodine is extracted from the ion exchange resin after irradiation with an elution scheme which removes contamination from the radionuclide 82Br, the main interference in the analysis. Finally iodine is precipitated as AgI for gamma ray analysis. The sample is counted for 3 h on a Ge semiconductor detector to measure the radionuclide 130I, which has a half life of 12.4 h and 126I, which has a half life of 13.0 days. The measured 130I activity is compared to a known standard to deduce the amount of 129I in the sample, and the concentrations are corrected for losses during processing using the measured activity of 126I. The detection limits for 129I by this method are below 10 mBq/l for milk samples and 10 mBq/kg for vegetation. In addition to routine monitoring of milk and grass samples the method has been used to measure 129I deposition on grass and soils in a field near the Sellafield plant. Results of these analyses, along with measurements of 129I in air and rainfall using the same methodology, have been used to determine deposition velocity and retention coefficients of 129I to grass.

Transfer of radiocaesium from grass and silage to cows' milk.

The transfer of Cs137 from grass and silage to milk has been followed in detail for one farm in West Cumbria over the year following the deposition from the Chernobyl reactor accident. At this farm about 40% of the Cs137 in milk was attributed to the feeding of silage during the following winter. A wider study of an additional 14 farms showed considerable variations in the contributions from grazing and silage. The transfer quotient from silage to milk was comparable with the values measured for grass over the first few weeks and lower than values reached later in the grazing season.

The influence of different agricultural practices on the transfer of radionuclides from pasture to milk after the Chernobyl accident.

Deposition of radionuclides from the Chernobyl nuclear reactor in the Ukraine occurred over much of the United Kingdom. The magnitude of the deposition varied considerably, depending on the prevailing weather, but even in areas of low deposition, iodine-131, caesium-134 and caesium-137 were measurable on pasture and in cows' milk. The accident provided an opportunity to study the influence of differences in herd management and in climate upon transfer to cows' milk. In this paper, results from a small mixed farm in Cumbria are compared with those from a large dairy farm in Berkshire for the first few weeks after deposition. The contrasting herd management practices in operation at these farms result in very different temporal variations in activity concentrations in milk, although in neither case were the maximum concentrations in milk sufficient to warrant restrictions on distribution or consumption.

Vascular and glomerular changes in the ageing kidney.

Glomerular size, shape and number were examined in 44 human kidneys obtained at necropsy. Intrarenal vascular appearances were assessed histologically and by post-mortem angiography. The mean cross-sectional area of glomeruli varied nearly three-fold and glomerular number varied more than three-fold when kidneys from different adult subjects were compared but kidneys from the same subject resembled one another in glomerular size and number. A significant negative correlation existed in the adult between glomerular number and dimensions. Glomerular numbers in the few immature kidneys studied were similar to those in adult kidneys but glomeruli were smaller. Glomerular numbers tended to decline as age and severity of age-related vascular changes increased but correlation was poor. The possibility remains that glomerular involution in the senescent kidney occurs independently of events in the vessels. In men, but not in women, totally hyalinised glomeruli were observed more frequently with increasing age but their presence did not appear to be related to the degree of vascular change. In the senescent kidney, glomerular lobulations tended to disappear. This, together with glomerular loss, must result in a reduction in the area available for filtration. Assessments of total glomerular surface area should take account of glomerular shape and dimensions as well as numbers.

Estimation of glomerular size and number from radiographs of the kidney.

In 32 adult human kidneys obtained at necropsy, renal demensions, measured from radiographs, were correlated with the number and cross-sectional area of glomeruli, determined by point-counting and computerized image analysis. Cortical area, measured from post-mortem angiograms, was poorly correlated with glomerular area and was not significantly correlated with glomerular number per kidney. The area of the whole kidney was poorly correlated with the number of glomeruli per kidney and was not significantly correlated with glomerular area. However renal dimensions, particularly total renal area, were highly significantly correlated with the product of glomerular area and number. This may allow glomerular numbers to be estimated in life but will not assess loss of glon the ageing kidney, the number of glomeruli per unit volume increased.

Serum transaminase levels after experimental paracetamol-induced hepatic necrosis.

The relationship between serum transaminase levels and the extent of paracetamol-induced liver necrosis has been investigated in the rat. Three methods of histological quantitation were used to assess of necrosis--arbitrary grading, point counting, and the image-analysis computer. Highly significant correlations were obtained between the three methods and all were found to be reproducible. A close correlation was found between the extent of hepatic necrosis and the serum ASAT and ALAT 24 hours after a large dose (4 g/kg) of paracetamol. Likewise, the mean grade of necrosis correlated reasonably well with the serum enzyme levels in the recovery phase at 36 and 72 hours, although the transaminase level for a given degree of necrosis was considerably lower at 72 hours than at 24 hours. These findings suggest that serum transaminase levels gives a reliable indication of the severity of hepatic necrosis if the time of ingestion of the paracetamol is known and taken into account.