Within the project “Environmental Modelling for Radiation Safety” (EMRAS) organized by the IAEA in 2003 experimental data of 131I measurements following the Chernobyl accident in the Plavsk district of Tula region, Russia were used to validate the calculations of some radioecological transfer models. Nine models participated in the inter-comparison. Levels of 137Cs soil contamination in all the settlements and 131I/137Cs isotopic ratios in the depositions in some locations were used as the main input information. 370 measurements of 131I content in thyroid of townspeople and villagers, and 90 measurements of 131I concentration in milk were used for validation of the model predictions. A remarkable improvement in models performance comparing with previous inter-comparison exercise was demonstrated. Predictions of the various models were within a factor of three relative to the observations, discrepancies between the estimates of average doses to thyroid produced by most participant not exceeded a factor of ten.

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Abstract. In 2003 IAEA launched the EMRAS Programme aiming at evaluating the predictive power of radiological models. The programme continued work of previous international radioecological modelling programmes and comprised several working groups focusing on different aspects of environmental modelling. The Iodine Working Group reassessed the impact of the release of 131 I during the Chernobyl accident with the aim of comparing model predictions with environmental data and inter-comparing the model predictions. Measurement data and detailed geographic and demographic descriptions were available for three regions: Plavsk, Warsaw and Prague. As for the Prague Scenario, milk supply regions of three big dairies were chosen for the model validation. Apart from geographic, demographic and agricultural descriptions (e.g. gathering regions of the dairies, feeding regime), the modellers were provided with information on the weather conditions and measurement data of iodine contamination. The most important peculiarities of Prague Scenario were keeping milk cattle in sheds and a special feeding regime during May 1986. The modellers were asked to assess the 131 I content in the thyroid of the local population and the resulting dose. The assessments were compared with measurement data. The results of these model calculations and their comparison with experimental data are presented.

Aquatic toxicity information is critical to provide scientifically defensible estimates of ecological impact and natural resource injury to aquatic organisms resulting from a petroleum spill. For most crude oils, the availability of aquatic toxicity information is a significant data gap. As part of Chevron's oil-specific properties summary sheet project, a series of marine fish (silversides, top smelt) and invertebrate (mysid shrimp) acute toxicity tests on five crude oils with extensive chemical analysis (e.g., VPH C6–C9, CROSERF VOCs, EPH C10–C32, PAHs) of exposure concentrations have been performed. Acute toxicity studies were conducted under standard test guidelines. ASTM D 6081 procedures were used to prepare individual water extracts, also called water-accommodated fractions (WAFs), of each test concentration to which the test organisms were exposed. WAF preparation and testing was done in tightly closed containers with minimal headspace to reduce volatilization and maintain stable exposure levels of dissolved hydrocarbons as much as possible. Also, WAFs were replenished daily with fresh test solution. Since toxicity results are expressed as the mean exposure concentration of a particular subset of the petroleum compounds in the WAF that resulted in 50% lethality in the test species, the LC50 values in μg/L will vary depending on which subset is used to describe the effect of the oil on the aquatic organisms. Additionally, since the aquatic organisms are exposed to a mixture of hydrocarbons in the WAF, LC50 values expressed as one subset's concentration are not independent of the presence of other petroleum constituent types. The results indicate that generally invertebrates (i.e., mysid) are more sensitive than fish. LC50s expressed as total polycyclic hydrocarbons (PAHs) showed the least variability—96-hour LC50s for total PAHs ranged from 19–36 μg/L and 30–128 μg/L for mysid and fish, respectively.

Decision makers must react in a prompt and appropriate manner in various emergency situations. The bases for decisions are often predictions produced with decision support systems (DSS). Actual radiation measurement data can be used to improve the reliability of the predictions. Data assimilation is an important link between model calculations and measurements and thus decreases the overall uncertainty of the DSS predictions. However, different aspects have to be taken into account for the optimal use of the data assimilation technique: different countries may have differing measurement strategies and systems as well as differing calculation models. The scenario and the amount and composition of radionuclides released may vary. In this paper we analyse the situation during and after an accident and draw up a list of recommendations that can help modellers to take into account the measurements that are best suited for data assimilation.