Non-parametric estimation of thresholds for radiation effects in vertebrate species under chronic low-LET exposures.

Databases on effects of chronic low-LET radiation exposure were analyzed by non-parametric statistical methods, to estimate the threshold dose rates above which radiation effects can be expected in vertebrate organisms. Data were grouped under three umbrella endpoints: effects on morbidity, reproduction, and life shortening. The data sets were compiled on a simple 'yes' or 'no' basis. Each data set included dose rates at which effects were reported without further details about the size or peculiarity of the effects. In total, the data sets include 84 values for endpoint "morbidity", 77 values for reproduction, and 41 values for life shortening. The dose rates in each set were ranked from low to higher values. The threshold TDR5 for radiation effects of a given umbrella type was estimated as a dose rate below which only a small percentage (5%) of data reported statistically significant radiation effects. The statistical treatment of the data sets was performed using non-parametric order statistics, and the bootstrap method. The resulting thresholds estimated by the order statistics are for morbidity effects 8.1 x 10(-4) Gy day(-1) (2.0 x 10(-4)-1.0 x 10(-3)), reproduction effects 6.0 x 10(-4) Gy day(-1) (4.0 x 10(-4)-1.5 x 10(-3)), and life shortening 3.0 x 10(-3) Gy day(-1) (1.0 x 10(-3)-6.0 x 10(-3)), respectively. The bootstrap method gave slightly lower values: 2.1 x 10(-4) Gy day(-1) (1.4 x 10(-4)-3.2 x 10(-4)) (morbidity), 4.1 x 10(-4) Gy day(-1) (3.0 x 10(-4)-5.7 x 10(-4)) (reproduction), and 1.1 x 10(-3) Gy day(-1) (7.9 x 10(-4)-1.3 x 10(-3)) (life shortening), respectively. The generic threshold dose rate (based on all umbrella types of effects) was estimated at 1.0 x 10(-3) Gy day(-1).

Model testing of radioactive contamination by 90Sr, 137Cs and 239,240Pu of water and bottom sediments in the Techa River (Southern Urals, Russia).

This paper presents results of testing models for the radioactive contamination of river water and bottom sediments by (90)Sr, (137)Cs and (239,240)Pu. The scenario for the model testing was based on data from the Techa River (Southern Urals, Russia), which was contaminated as a result of discharges of liquid radioactive waste into the river. The endpoints of the scenario were model predictions of the activity concentrations of (90)Sr, (137)Cs and (239,240)Pu in water and bottom sediments along the Techa River in 1996. Calculations for the Techa scenario were performed by six participant teams from France (model CASTEAUR), Italy (model MARTE), Russia (models TRANSFER-2, CASSANDRA, GIDRO-W) and Ukraine (model RIVTOX), all using different models. As a whole, the radionuclide predictions for (90)Sr in water for all considered models, (137)Cs for MARTE and TRANSFER-2, and (239,240)Pu for TRANSFER-2 and CASSANDRA can be considered sufficiently reliable, whereas the prediction for sediments should be considered cautiously. At the same time the CASTEAUR and RIVTOX models estimate the activity concentrations of (137)Cs and (239,240)Pu in water more reliably than in bottom sediments. The models MARTE ((239,240)Pu) and CASSANDRA ((137)Cs) evaluated the activity concentrations of radionuclides in sediments with about the same agreement with observations as for water. For (90)Sr and (137)Cs the agreement between empirical data and model predictions was good, but not for all the observations of (239,240)Pu in the river water-bottom sediment system. The modelling of (239,240)Pu distribution proved difficult because, in contrast to (137)Cs and (90)Sr, most of models have not been previously tested or validated for plutonium.

Modelling of effects due to chronic exposure of a fish population to ionizing radiation.

A dynamic model was developed for description of radiation effects in an isolated fish population chronically exposed at different dose rates. The induced effects were predicted based on damage created by the radiation, recovery by means of repair mechanisms, and natural growth of the population. Three types of radiation effects (umbrella endpoints) were simulated--decrease of population size, decrease of reproductive capacity, and effects on the morbidity of the population. The influence of ecological interactions on the irradiated fish population was simulated using the combined action of radiation and parasite infestation as an example (ecological interaction "host-parasite"). The model calculations demonstrate that influence of ecological interactions can considerably aggravate the effects of radiation to an exposed population. It was concluded that development of standards for wildlife protection against ionizing radiation requires consideration of possible ecological interactions and to take into account the ecological effects of radiation.