A. G. Gillett

Predicting the transfer of radiocaesium from organic soils to plants using soil characteristics

A model predicting plant uptake of radiocaesium based on soil characteristics is described. Three soil parameters required to determine radiocaesium bioavailability in soils are estimated in the model: the labile caesium distribution coefficient (kd1), K+ concentration in the soil solution [mK] and the soil solution-->plant radiocaesium concentration factor (CF, Bq kg-1 plant/Bq dm-3). These were determined as functions of soil clay content, exchangeable K+ status, pH, NH4+ concentration and organic matter content. The effect of time on radiocaesium fixation was described using a previously published double exponential equation, modified for the effect of soil organic matter as a non-fixing adsorbent. The model was parameterised using radiocaesium uptake data from two pot trials conducted separately using ryegrass (Lolium perenne) on mineral soils and bent grass (Agrostis capillaris) on organic soils. This resulted in a significant fit to the observed transfer factor (TF, Bq kg-1 plant/Bq kg-1 whole soil) (P < 0.001, n = 58) and soil solution K+ concentration (mK, mol dm-3) (P < 0.001, n = 58). Without further parameterisation the model was tested against independent radiocaesium uptake data for barley (n = 71) using a database of published and unpublished information covering contamination time periods of 1.2-10 years (transfer factors ranged from 0.001 to 0.1). The model accounted for 52% (n = 71, P < 0.001) of the observed variation in log transfer factor.

Spatial modelling of transfer of long-lived radionuclides from soil to agricultural products in the Chernigov region, Ukraine.

Abstract Within the RESTORE project (‘restoration strategies for radioactive contaminated ecosystems’) funded by the European Commission Nuclear Fission Safety Programme, environmental models are being developed to identify regions that are vulnerable to increased radionuclide transfer as a consequence of the Chernobyl nuclear power plant accident and nuclear weapons testing at the Semipalatinsk test site in Kazakhstan. Since radionuclide transfer varies in space and time depending on deposition processes, soil type, land use, and resulting contamination in food products, the radionuclide transfer through food chains derived from a variety of ecosystems is analysed by the use of models embedded in a Geographical Information System. The Chernigov region in northern Ukraine was affected by the Chernobyl fallout resulting in deposition levels ranging from 15 to 300 kBq m −2 . GIS-based steady state and dynamic transfer models within an environmental decision support system (EDSS) were run for this region to model radiocaesium transfer from soil to various agricultural products on a collective farm level and on a district level within this region using spatial data sets of soil attributes, soil contamination and land use. Observed agricultural product contamination was available for comparison with model predictions. This paper presents examples of radiocaesium transfer from soil to fodder grass and potatoes to make an initial assessment of the radioecological situation in the Chernigov region to identify critical gaps in the model structure and data required for model input and validation. It highlights the feasibility of applying spatial and temporal data sets to make predictions of the present radioecological situation, as an alternative to approaches commonly used which categorise such data sets, thereby losing valuable information.

Self-help countermeasure strategies for populations living within contaminated areas of Belarus, Russia and Ukraine

Countermeasures have been effectively employed within intensive agricultural systems in areas of the Former Soviet Union (FSU) affected by the Chernobyl accident. However, ingestion doses continue to be elevated in some areas as a result of few foodstuffs which are collected from the wild or produced by the household. Forest fungi and berries, and milk from privately owned cattle are the most notable contributors to 137Cs intakes amongst these foodstuffs. In this paper we consider advice which would help affected populations to both understand the importance of these exposure routes and to reduce their exposure. In addition to the potential radiological benefits, self-help schemes are highly cost-effective and likely to have a positive psychological influence on populations living within contaminated areas of the FSU. Evidence to suggest that the transfer of radiocaesium to cow milk is considerably higher in the FSU than within western Europe and North America is discussed.

Simple winter wheat green area index model under UK conditions

A simple model of canopy expansion and senescence with accumulated thermal time from sowing was used to describe differences in canopy development and potential size across a range of sites in the UK between 1992 and 1995. The principal model inputs were nitrogen, temperature and sowing date. The model was calibrated across six sites within the major wheat growing areas using canopy data collected during the 1992/93 and 1993/94 growing seasons and was validated using data collected in the 1994/95 season. The model was able to predict the time course of green area index (GAI) over a season with an r 2 [ges ]0·87 for the five English sites, and an r 2 =0·68 for the single Scottish site. This model may prove to be a useful approach to forecasting the potential canopy size, based upon an estimate or measure of the total nitrogen available to the crop (both from applied fertilizer and the soil).

Prediction of leaf and internode development in wheat

Functions which predict rate of leaf emergence and final number of leaves, used in a model to predict the date at which growth stages occur, were tested in an experiment on winter wheat cv. Mercia grown with standardized husbandry at six sites in 1992/93, 1993/94 and 1994/95. A study of the number of detectable nodes on the culm and leaf length was also made. The predicted rate of leaf emergence was mostly within 5% of the observed value. The difference between observed and predicted final number of leaves was mostly less than half a leaf but suspected errors in leaf counts resulted in some differences of more than two leaves. Variable extension of the basal internode impaired confidence in the detection of nodes. The mean number of detectable nodes differed significantly among sites and between seasons from 3·7 to 4·8 but could not be related to sowing date or final number of leaves. Further information on factors affecting extension of the basal internode is desirable to standardize node detection and improve prediction of culm leaf appearance. Culm leaves showed successively longer laminae up to the penultimate leaf. There was a significant relationship between length of the flag leaf and the final number of leaves, but it was positive in 1993/94 and negative in 1994/95. This may have been due to greater water stress in 1994/95.

Reducing the Consumption of 137Cs Via Forest Fungi-Provision of ‘Self-Help’ Advice

Since the Chernobyl accident it has been recognised that agriculturally produced foods are not the only important food types which contribute to the radiation dose received by man. The transfer of radiocaesium to ‘wild food’ products (e.g. edible fungi, freshwater fish, game animals) is often much greater than that to agriculturally produced foodstuffs. The accumulation of radiocaesium by certain species of edible fungi for instance, results in radiocaesium levels that are far in excess of most other foods consumed by man.