Radioecological modelling and the computer codes for calculations of doses to marine biota and man in the Arctic

Abstract

Methodology and computer code DOSBIO are described for assessment of radiation doses to Arctic marine biota, and model parameters are evaluated. The algorithm and computer code DOSMAN are described for assessment of dose to man from consumption of arctic seafood products (fish, crustaceans and molluscs). The computer codes DOSBIO and DOSMAN are user-friendly tools for assessing the radioecological situation in the marine environment and analyzing the impact of technogenic radionuclides to both man and biota. The calculated values of dose conversion factors for 15 key species of arctic marine biota from exposure to 35 radionuclides are presented; dose conversion factors are given for internal and external exposure of arctic marine biota. The doses to Arctic marine biota and man were calculated from model runs, using actual environmental activity levels.

Introduction

Several sources of radionuclides have contributed to the contamination of the Arctic Seas. Among these are atmospheric fallout from nuclear tests, the Chernobyl accident, the contaminated waters of Siberian rivers and sea currents carrying discharges from the West-European nuclear processing plants. For three decades Russia practised the dumping of solid radioactive wastes (RW) in the Kara Sea near the Novaya Zemlya archipelago. Since 1993, major international efforts have been directed to the evaluation of long-term radiological consequences of dumping in the shallow Arctic sea (Strand and Holm, 1993, Strand et al., 1994, Strand and Cooke, 1995, Strand, 1997, Strand and Jolle, 1999, AMAP, 1998, IAEA, 1998). Up to now the levels of the radioactive contamination of the Arctic Seas are relatively low compared to marine areas of Western Europe. However, accidental or continuous releases of radionuclides from the sources of potential hazards may lead to radioactive contamination of some discrete areas of the Arctic Seas.

The Barents Sea and the Norwegian Sea are characterized as highly productive fishing regions. Because of severe climatic conditions, many species of fish exhibit extensive feeding, wintering and spawning migrations during the year, thereby covering distances of over a thousand miles. Such long-distance migrations of commercial fish may lead to a biological transfer of artificial radionuclides from a highly contaminated local area to distant non-contaminated areas.

Until recently the radiation protection of biota was based on a general assumption that so long as levels of radioactivity in the environment were controlled sufficiently to protect man, the natural ecosystems were automatically protected. However, the living environment for non-human organisms in the natural ecosystems differ considerably from those for man, and the radiation dose rates to non-human organisms may be orders of magnitude higher than exposure of man.

There is a great body of information on environmental radioactivity in the Arctic, see Table 1, Table 2, Table 3 (Strand and Holm, 1993, Strand and Cooke, 1995, Strand, 1997, Strand and Jolle, 1999). However, only a few scientific papers are concerned with assessments of doses to Arctic biota and man (Kryshev and Sazykina, 1995, Sazykina and Kryshev, 1997).

Under natural conditions, organisms are exposed to various sources of ionizing radiation. The absorbed dose to aquatic organisms depends on a number of factors. Among them are type and energy of emitters (photons, beta particles, alpha particles, protons, neutrons, etc.), radiation source geometry (point or extended), space distribution and time evolution of radionuclide concentrations in components of aquatic ecosystems, ecological–physiological parameters and stage of ontogenesis of organisms (IAEA, 1976, IAEA, 1979, Kryshev and Sazykina, 1986, Kryshev and Sazykina, 1990, Kryshev and Sazykina, 1995, Amiro, 1997). In the marine environment, doses to biota are originated from external irradiation owing to the presence of radionuclides in the water column and bottom sediments, and from internal irradiation from incorporated radionuclides.

The objectives of this paper are the development of models and computer codes based on site-specific radioecological information, which can be used to calculate doses to Arctic marine biota and man.

The modelling of doses to humans and biota is an important tool in the assessment of the impact of radionuclides released into the environment. Input data on the concentrations of radionuclides in biota and abiotic marine environment (water, sediments) are required for the calculation of doses. This can be derived either directly from analysis of the monitoring data on the marine ecosystems contamination, or by modelling the transport and fate of radionuclides in marine ecosystems under different release scenarios.