D. V. Dementyev

Evidence of the radioactive fallout in the center of Asia (Russia) following the Fukushima Nuclear Accident.

It was recently reported that radioactive fallout due to the Fukushima Nuclear Accident was detected in environmental samples collected in the USA and Greece, which are very far away from Japan. In April-May 2011, fallout radionuclides ((134)Cs, (137)Cs, (131)I) released in the Fukushima Nuclear Accident were detected in environmental samples at the city of Krasnoyarsk (Russia), situated in the center of Asia. Similar maximum levels of (131)I and (137)Cs/(134)Cs and (131)I/(137)Cs ratios in water samples collected in Russia and Greece suggest the high-velocity movement of the radioactive contamination from the Fukushima Nuclear Accident and the global effects of this accident, similar to those caused by the Chernobyl accident.

Low doses of gamma-radiation induce SOS response and increase mutation frequency in Escherichia coli and Salmonella typhimurium cells.

This study addresses use of two bacterial test systems (the Ames test and the SOS chromotest) to estimate the effects of low doses of γ-radiation. The most substantial increases in induction of SOS response and mutation frequencies were observed in the first 24h of exposure to γ-radiation as compared to the cells in the exposure-free control. Gamma-radiation also impaired growth and survival of S. typhimurium cells in the first 24h. The effects were attenuated at lower exposure doses and at longer exposure times. In the experiments conducted in this study, at 96h of exposure, the values of some of the γ-radiation effects were lower than the MID (minimum inducing dose) detection limits and, thus, were neglected. Long-term exposure to γ-radiation could also result in combined effects of γ-radiation and the death of cells in the culture.

Use of the aquatic plant Elodea canadensis to assess toxicity and genotoxicity of Yenisei River sediments

The toxicity, cytotoxicity, and genotoxicity of bulk sediments from the Yenisei River (Siberia, Russia) were estimated in laboratory bioassays based on several endpoints in the aquatic plant Elodea canadensis. The bottom sediment samples were collected in the Yenisei River upstream and downstream of the sources of chemical and radioactive contamination. The testing revealed different sensitivities of Elodea endpoints to the quality of the bottom sediment: weight of shoots < length of shoots < mitotic index < length of roots < percentage of abnormal cells. The response of the genotoxicity endpoint (percentage of cells with chromosome abnormalities in roots of Elodea) was the highest in sediments with chemical pollution, whereas the highest inhibition of toxicity endpoints (shoot and root length) occurred in sediments with the highest level of radioactive pollution. The extreme response of Elodea endpoints to the quality of certain sediment samples may be regarded as related to the possible presence of unknown toxicants. The results show that E. canadensis can be used as an indicator species in laboratory contact testing of bottom sediment. The responses of shoot and root length growth endpoints of Elodea can be recommended as basic sensitivity indicators of bottom sediment toxicity. Analysis of cells carrying abnormal chromosomes in the apical root meristem of Elodea can be performed optionally in the same test to assess the genotoxicity of sediments.

Chromosomal abnormalities in roots of aquatic plant Elodea canadensis as a tool for testing genotoxicity of bottom sediments

Submersed freshwater macrophytes are considered as relevant indicators for use in bulk bottom sediment contact tests. The purpose of this study was to estimate the validity of endpoints of aquatic plant Elodea canadensis for laboratory genotoxicity testing of natural bottom sediments. The inherent level of chromosome abnormalities (on artificial sediments) in roots of E. canadensis under laboratory conditions was lower than the percentage of abnormal cells in bulk sediments from the Yenisei River. The percentage of abnormal cells in roots of E. canadensis was more sensitive to the presence of genotoxic agents in laboratory contact tests than in the natural population of the plant. The spectra of chromosomal abnormalities that occur in roots of E. canadensis under natural conditions in the Yenisei River and in laboratory contact tests on the bulk bottom sediments from the Yenisei River were similar. Hence, chromosome abnormalities in roots of E. canadensis can be used as a relevant and sensitive genotoxicity endpoint in bottom sediment-contact tests.

The effect of γ-radiation on resting eggs and life cycle of cladoceran Moina macrocopa.

We investigated the effects of γ-irradiation on the survival of resting eggs of the cladoceran Moina macrocopa and on the parameters of the life cycle of neonates hatched from the irradiated eggs. It was shown that γ-irradiation in a wide range of doses (from the background level to 100 Gy) had no effect on survival of eggs and mortality of neonates hatched from the irradiated eggs. However, exceeding the absorbed dose of 40 Gy sharply decreased the reproductive potential of the neonates hatched from irradiated eggs.

Bioaccumulation, inter-organ distribution, and retention of waterborne and dietary 241Am in silver crucian carp

The bioaccumulation of actinide 241Am from food and water in bodies of freshwater fish (Carassius auratus gibelio, silver crucian carp) has been investigated in laboratory experiments. Homogenized biomass of submerged macrophytes labeled with 241Am was injected into the fish gullet. Internal organs and tissues of crucian carp could be ranked according to activity concentration of dietary 241Am after depuration of the digestive tract as follows: liver > gonads > bones > muscles. Accumulation of waterborne 241Am in internal organs and tissues of crucian carp mainly occurred via the digestive tract. While the concentration of 241Am in liver of crucian carps decreased during depuration time, its concentration in bones increased indicating slower transfer of 241Am to skeleton compared to muscles and liver. The retention of dietary 241Am in the bodies of crucian carp reached 35%–46% of ingested 241Am: 20%–31% was retained in liver, 0.6%–0.8% in skeleton, and 1.4%–2.0% in muscles. The concentration factor of 241Am from water was 0.4 for the whole body, 0.3 for liver, 0.01 for muscles, and 0.01 for skeleton. Trace amounts of 241Am were recorded in viscera and muscles of a wild population of silver crucian carp inhabiting a radioactively contaminated part of the Yenisei River.

New data on the effect of ionizing radiation on the growth of the aquatic plant Elodea canadensis in the laboratory

Toxicological experiments with radioactive bottom sediments and extrinsic γ-irradiation have demonstrated that the growth of common elodea roots is suppressed by irradiation at doses several times lower than the established threshold dose. The effect of γ-irradiation on the growth of elodea stems has not been observed at any dose used. The data obtained show that elodea could be recommended for use as an indicator of biological effects of radiation in the range of low radiation doses.

Biosorption of 241Am from solution and its biochemical fractionation in the mycelium of macromycetes

Experiments with macromycetes Pleurotus ostreatus, Neonothopanus nambi, and Agaricus bisporus demonstrated for the first time that live mycelium of mushrooms, cultivated on a liquid culture medium, can efficiently take up dissolved 241Am in its biomass. Biochemical fractionation of the mycelium biomass demonstrated for the first time that the major fraction (up to 90%) of 241Am accumulated in the mycelium is bonded to structural polysaccharides of the cell walls. The sorption capacity of cell wall polysaccharides for 241Am is 2.7–3.6 times higher than that of the initial mycelium biomass, and the activity concentration of 241Am in the polysaccharides reached 950 Bq g–1 dry weight.

Age-dependent accumulation of (137)Cs by pike Esox lucius in the Yenisei River.

Age-dependent accumulation of 137Cs in the muscles and bodies of the pike Esox lucius (aged two to seven years) inhabiting a section of the Yenisei River polluted with artificial radionuclides has been studied. The content of 137Cs in muscles varied from 0.5 to 7.0 Bq/kg of fresh weight. The maximum content of the radionuclide has been found in juveniles. The content of 137Cs in pike muscles and body decreased considerably with age. The high content of 137Cs in the muscles of juveniles is probably a consequence of their higher intensity of feeding as compared to older individuals, which is due to the intense growth of juveniles.

Genotoxicity assessment of low-level doses of gamma radiation with the SOS chromotest and the Ames test

This is the first study to present data on the genotoxicity of low γ-irradiation doses for E. coli and S. typhimurium cells obtained using the SOS chromotest and the Ames test. The most pronounced effect was recorded in the first 24 h of γ-irradiation. After 72 h in the Ames test and after 96 h in the SOS chromotest, a significant effect of γ-irradiation on bacterial cells was detected. The absence of genotoxicity at the later stages can be explained by the adaptation of bacterial cells to the conditions of exposure. The findings allow the bacterial test system to be used for studying the effects of low doses at the early stages of exposure to radiation.