Secondary radioactive contamination of the Black Sea after Chernobyl accident: recent levels, pathways and trends.

The recent radionuclide measurements have showed that concentrations of the Chernobyl-derived (137)Cs and (90)Sr in the surface Black Sea waters are still relatively high, reaching 56 and 32 Bq m(-3), respectively. This is comparable or even exceeds the pre-Chernobyl levels (∼16 Bq (137)Cs and 22 Bq (90)Sr per m(3) as the basin-wide average values). The measurements have revealed that the Black Sea continues to receive Chernobyl radionuclides, particularly (90)Sr, by the runoff from the Dnieper River. An additional source of (90)Sr and (137)Cs was found in the area adjacent to the Kerch Strait that connects the Black Sea and the Sea of Azov. This may be caused by the inflow of the contaminated Dnieper waters, which come to this area through the North-Crimean Canal. The long-term monitoring of (137)Cs and (90)Sr concentration in the Black Sea surface waters and in the benthic brown seaweed Cystoseira sp., in comparison with the earlier published sediment records of the radionuclides, have showed signs of a secondary radioactive contamination, which has started to increase since the late 1990's. This may be the result of the combined effect of a higher input of radionuclides from the rivers in 1995-1999 due to an increased runoff; and a slow transport of the particulate bound radionuclides from the watersheds followed by their desorption in seawater from the riverine suspended matter and remobilization from the sediments adjacent to the river mouths.

Distribution and migration of 9°Sr in components of the Dnieper River basin and the Black Sea ecosystems after the Chernobyl NPP accident.

The change in (90)Sr concentrations in hydrobionts, water and bottom sediments of the Chernobyl NPP pond-cooler, the Kievskoe and Kakhovskoe reservoirs, the Northern-Crimean canal and the Black Sea after the Chernobyl NPP accident was studied. The environmental half-times for the decrease of (90)Sr concentrations were determined: in water - 4.1-24.3 years; algae and flowering water plants - 3.6-7.7 years, in molluscs - 2.4-6.7 years, and in fish - 7.8-12.9 years. The time for (90)Sr concentrations to decrease to pre-accident levels were estimated: in freshwater reservoirs and the northwest part of the Black Sea this was 32-44 years, and in freshwater hydrobionts this was 25-73 years. The contribution of dose from (90)Sr to the hydrobionts, sampled from the Kakhovskoe reservoir, the Northern-Crimean canal and the Black Sea, has not reached values which could impact them during the entire post-accident period. This complex of comparative studies was carried out for the first time.

[Deep-sea research ground for the study of living matter properties in extreme conditions].

The Black Sea hollow bottom is a promising research ground in the field of deep-sea radiochemoecology and exobiology. It has turned out to be at the intersection of the earth and cosmic scientific interests such as deep-sea marine radiochemoecology from the perspective of the study of extreme biogeocenological properties of the Earth biosphere and exobiology from the standpoint of the study of life phenomena (living matter) outside the Earth biosphere, i.e. on other planets and during hypothetical transfer of spores in the outer space. The potential of this ground is substantiated with the data published by the author and co-workers on accumulation of 90Sr, 137Cs and Pu isotopes with silts of bathyal pelo-contour, on the quality of deep-sea hydrogen sulphide waters (after their contact with air) for vital functions of planktonic and benthic aerobes, as well as the species composition of marine, freshwater and terrestrial plants grown from the spores collected from the bottom sediments of the Black Sea bathyal. Discussion was based on V.I. Vernadsky's ideas about the living matter and biosphere, which allowed conclusions about the biospheric and outer space role of the described phenomena.

[Polonium-210 in fishes from the Black Sea].

The specific activity of naturally occurring radionuclide 210Po in main species of the Black Sea fishes and some their organs were used for the calculation of absorbed and equivalent dose rates. The values of the dose in investigated fish depend on their ecological belonging. Maximum values of equivalent dose rates for viscera and, first of all, liver exceed such for the whole body of fishes. But they are significantly lower than the dose rate limit recommended by IAEA for the protection of aquatic organisms from ionizing radiation.

[The criteria of identification of "critical" populations in aquatic radiochemoecology].

Data on chromosome mutagenesis levels in populations of aquatic organisms in the Black and the Aegean Seas, the Danube and the Dnieper Rivers, the 30-km zone of ChNPP are presented. The highest level of mutagenesis was observed in hydrobionts populations in the 10-km zone of the ChNPP. The obvious damaged effects of ionizing radiation were noted only in these populations. The comparison of the adaptation rate of aquatic crustaceans and worms populations with different reproduction modes was made. It is found that the studied species with sexual reproduction have higher rate of adaptation to the pollution in comparison with species with prevalent asexual reproduction. Hypothetic mechanisms of population adaptation are discussed. On the basis of species and populations characteristics, the criteria for the identification of "critical" populations (species) and an algoritm of ecological risk assessment for them are proposed.

Field observations of the effects of protracted low levels of ionizing radiation on natural aquatic population by using a cytogenetic tool.

In the present study, an effort is attempted to record the impact of chronic radiation on natural aquatic populations exposed to protracted doses (lower if compared to intervention levels but higher if compared to typical background) and to chemical pollution. The methodology is based on the analyses of chromosome aberrations observed in cells. Therefore, some preliminary research results on the cytogenetic effects on aquatic organisms of various taxa, in coastal ecosystems are presented, considering some selective regions of elevated natural gamma radiation and conventional pollution. These areas are the geothermal spring areas in the island of Ikaria-Eastern Aegean Sea and the port of Pireus, in Greece. The data are compared to the findings recorded in some organisms collected from the North Aegean Sea the early period after the Chernobyl accident. With regard to the different species examined, a first evaluation of the results is made using the reported field findings for the wide area of Chernobyl. The environmental assessment of the studied areas in terms of radiation impact is based on the cytogenetic injuries observed, and evidence of ecosystem disturbance is also pointed out. The final environmental assessment based on the quantified effects observed in the organisms from the studied areas takes into account a published conceptual model of zones of radiation dose rates and the resulting organism responses in a step function scale.

Environmental radioactivity in the South Urals 1990-1997. An international study supported by INTAS, EC and national funding.

Radioecological studies carried out in a joint co-operation between Russian, Ukrainian and Danish Laboratories are reported. The environmental impact of routine, discharges as well as accidental events, notably the Kyshtym accident in 1957 and the Karachay wind dispersion in 1968 have been studied. From measurements and based on model assumptions it has been estimated that the Ob river system outside Mayak, i.e. first of all the Techa and Iset rivers and their floodplains contain 0.1 PBq 90Sr, 0.3 PBq 137Cs and 0.8 TBq 239, 240Pu. The uncertainty of these estimates is a factor of 3-4. The present contamination from the Kyshtym accident outside the Mayak area is calculated to 0.1-0.5 PBq 90Sr and from the Karachay incident the contamination is 0.05-0.1 Bq 137Cs. The environmental contaminations with Pu from these two events are in the order of 1 TBq. The occurrence of 99Tc, 129I and 237Np in highly contaminated Techa river sediments collected outside Mayak is for the first time reported.

Ecological effects of various toxic agents on the aquatic microcosm in comparison with acute ionizing radiation.

The purpose of this study was an evaluation of the effect levels of various toxic agents compared with acute doses of ionizing radiation for the experimental model ecosystem, i.e., microcosm mimicking aquatic microbial communities. For this purpose, the authors used the microcosm consisting of populations of the flagellate alga Euglena gracilis as a producer, the ciliate protozoan Tetrahymena thermophila as a consumer and the bacterium Escherichia coli as a decomposer. Effects of aluminum and copper on the microcosm were investigated in this study, while effects of gamma-rays, ultraviolet radiation, acidification, manganese, nickel and gadolinium were reported in previous studies. The microcosm could detect not only the direct effects of these agents but also the community-level effects due to the interspecies interactions or the interactions between organisms and toxic agents. The authors evaluated doses or concentrations of each toxic agent which had the following effects on the microcosm: (1) no effects; (2) recognizable effects, i.e., decrease or increase in the cell densities of at least one species; (3) severe effects, i.e., extinction of one or two species; and (4) destructive effects, i.e., extinction of all species. The resulting effects data will contribute to an ecological risk assessment of the toxic agents compared with acute doses of ionizing radiation.

Radiological effects on populations of Oligochaeta in the Chernobyl contaminated zone.

A detailed investigation of 3 populations of Oligochaete species (Dero obtusa, Nais pseudobtusa and Nais pardalis) has been carried out in a contaminated lake of the close-in Chernobyl zone and in a control lake. Hydrochemical indices and concentrations of heavy metals, chloro-organic compounds and (90)Sr in bottom sediments have been measured. Absorbed doses were calculated on the basis of the results of radiochemical analysis and assessed directly with thermoluminescent dosimeters (TLD). Stimulation of paratomous division (asexual reproduction) was found in one species of worm (D. obtusa), and activation of sexual reproduction in the two other species studied. An increase in the amount of cytogenetic damage in the somatic cells of worms from the contaminated lake was found and an attempt was made to assess the relative contributions of radiation and chemical exposure on the basis of analyses of inter-cellular aberration distributions and the types of chromosome aberrations observed in the cells.

[Identification of radiation, chemical and combined effects on natural populations of aquatic organisms]. / Identifikatsiia deistviia radioaktivnogo, khimicheskogo i sochetannogo zagriazneniia na prirodnye populiatsii gidrobiontov.

Approaches to the identification of radiation, chemical and combined effects on natural populations of aquatic organisms are proposed. These approaches are based on generalization of our previous experimental data concerning separate and combined effects of ionizing radiation and chemical mutagens (heavy metals and chlororganic compounds) on crustaceans and fishes embryos, as well as on results of field studies carried out before and after the Chernobyl NPP accident. For the identification of damaged factors it is proposed to use the following criteria: a comparison of cytogenetic effects in mutagen equivalent doses, a distribution of chromosome aberrations in cells and a number of aberrations per an aberrant cell.

[Cytogenetic and population effects in oligochaeta from the Chernobyl zone]. / Tsitogeneticheskie i populiatsionnye éffekty u oligokhet iz Chernobyl'skii zony.

Research on intensity and character of reproduction of Oligochaeta (Dero obtusa, Nais pseudobtusa and Nais pardalis) was carried out in 1995-1996 in two water-bodies: a) in the Chernobyl NPP zone near Yanov Village, with a dose rate of 14 microGy h-1 on the surface of the bottom sediment; b) at the Uzh River area (the control water-body). The changes in both intensity and reproduction type were observed in worms at the radioactively polluted water-body. Stimulation of paratomic division in D. obtusa as well as activation of sexual reproduction in two other species were found out along with increasing of amount of cytogenetic damages in somatic cells.

[The sequelae of the Kyshtym and Chernobyl accidents for hydrobionts]. / Posledstviia Kyshtymskoi i Chernobyl'skoi avarii dlia gidrobiontov.

The results of the works, published in the USSR and the CIS, on studies of the action of radioactive pollution upon hydrobionts in natural conditions were summarized and analyzed. Feasible causes of discrepancy of obtained data were considered.

Strontium-90 concentrations in human teeth in south Ukraine, 5 years after the Chernobyl accident.

Approximately 1000 human teeth, collected in South Ukraine, in 1990-1991, were measured for 90Sr concentration. The teeth were grouped into 18 samples according to the age and sex of the donors. Measured levels of 90Sr concentrations were lower by a factor of 10 than measurements taken in the mid-1960s and mid-1970s. An interesting feature of the data is a 3-fold enhancement of contamination levels in the 25-45 year-old age group of the male population. A possible explanation for this anomaly is that this age group contains a significant number of men who were mobilized immediately after the Chernobyl accident for clean-up operations within the 30-km zone around the damaged nuclear power plant.

[Patterns in the distribution of chromosome aberrations in the cells of hydrobionts under the action of ionizing radiation and environmental chemical mutagens]. / Zakonomernosti raspredeleniia aberratsii khromosom po kletkam gidrobiontov pri deistvii ioniziruiushchego izlucheniia i khimicheskikh mutagenov sredy.

In studying the pattern of chromosome aberration distribution among hydrobiont cells in experimental and natural populations, it has been found that the Poisson distribution of chromosomes among cells occurs under the effect of ionizing radiation and under the combined effect of radiation and a chemical mutagen with a higher efficiency of the former. With the comparable efficiencies of both factors and with the effect of a chemical mutagen alone distribution of chromosome aberrations among cells resembles the geometrical one to a greater extent.

[The radioecological problems of Eurasia and the sources of radioactive environmental contamination in the former USSR]. / Problemy radioékologii Evrazii, istochniki radioaktivnogo zagriazneniia okruzhaiushchei sredy v byvshem SSSR.

There is three major sites of radioactive environmental contamination in the former USSR: the Chelyabinsk region in the Urals, Chernobyl NPP in Ukraine and Novaya Zemlya in the Arctic Ocean. The first mentioned is the most important with regard to local (potential) contamination, the last one dominates the global contamination. A number of sites and sources are less well known with regard to environmental contamination. This is thus the case for the plutonium production factories at Tomsk and Dodonovo. More information on nuclear reactors in lost or dumped submarines is also needed. From a global point of view reliable assessment of the radioactive run-off from land and deposits of nuclear waste in the Arctic Ocean are in particular pertinent.