Modelling the release to the Kara Sea of radioactive waste from the icebreaker Lenin: Version II

In progressing its work for the International Arctic Seas Assessment Project (IASAP), under the auspices of the International Atomic Energy Agency (IAEA), the Source Term Working Group has developed a FORTRAN model to predict a radiation release profile into the Kara Sea from reactor fuel and activated components of the nuclear icebreaker Lenin. The model accounts for the degradation of containment materials through corrosion and other mechanisms, and predicts annual release rates to 4500 years into the future. Version I of the model was developed as a spreadsheet program from the original data gathered by the Working Group and the results were published by Timms et al. (1994); revised information on the method of disposal necessitated a change to the program, which is presented in this paper as Version II. The model is being applied to other marine reactors dumped in the Kara Sea in a programme of work for the IASAP aimed at assessing the collective release profile from all significant dump sites in this region.     

Radionuclide adsorption to sediments from nuclear waste dumping sites in the Kara Sea

Environmental parameters (salinity, sediment concentration, equilibration time) affecting radionuclide partitioning between sediment and seawater were experimentally investigated for Kara Sea sediments collected from nuclear waste dumping sites in Abrosimov and Stepovogo Bays off Novaya Zemlya. Adsorption kinetics were examined and the influence of salinity and sediment concentration were evaluated over the range of concentrations expected in the bays for the following radionuclides: ^{110 m}Ag; ²⁴¹Am; ¹⁰⁹Cd; ⁶⁰Co; ⁵⁷Co-cobalamine; ¹³⁴Cs; ¹⁵²Eu; ⁵⁴Mn; ¹³³Ba; ¹⁰⁶Ru; and ⁸⁵Sr. The major findings of this investigation are that 1. radionuclide distribution coefficients (K_ds) were most sensitive to variations in sediment character (²⁴¹Am, ⁶⁰Co, ¹⁰⁹Cd) and concentration (⁵⁷Co-cobalamine, ⁸⁵Sr, and ¹³³Ba), 2. distribution coefficients generally decreased with increasing sediment concentration and 3. fast adsorption kinetics (near equilibrium ≈1 day) were observed only for ¹³⁷Cs and ^{110 m}Ag. The observed differences in K_ds for sediments from the two dumpsites exemplifies the importance of undertaking site-specific determinations of K_ds. For purposes of confining radioactive wastes to the dumpsites in Stepovogo and Abrosimov Bays, the findings of this study indicate that based on sediment character alone, Stepovogo Bay will be more effective at retaining radionuclides than Abrosimov Bay. This is unfortunate since less radioactive waste resides in Stepovogo Bay (0.6 PBq) than in Abrosimov Bay (1.4 PBq).     

Radiocaesium distribution in the bottom sediments of the Kara Sea

The article presents the results of radiogeochemical studies carried out by the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, RAS (IGEM RAS), in the Kara Sea and the estuaries of the Ob and Yenisei rivers in 1995–2003. The studies were carried out onboard the Akademik Boris Petrov research vessel, belonging to the Institute of Geochemistry, RAS. Based on studies of circa 1500 samples of bottom sediments, taken from 172 marine and river stations, a map of ¹³⁷Cs distribution in the surface sediments has been compiled. Four zones of radiocesium overactivity (>15 Bk/kg) have been identified: Novaya Zemlya Zone, Vaigach Zone, Ob Zone, and Yenisei Zone. The zones have different radiocesium concentration levels, as well as different input sources, but all of them have formed under the influence of complex geochemical barriers. Data from 47 sectioned cores of bottom sediments, sampled in Ob and Yenisei overactivity zones, demonstrate distinct differences in the vertical radiocesium distribution. These differences have been shown to be due to many-year oscillations of suspended silt discharge, which are main transfer agents of solvable and poorly solvable radiocesium forms and to be independent of sedimentation conditions and the geochemical characteristics of the deposition environment.     

PAH-profiles in sediment cores from the Baltic Sea

To document the historical input the PAH-profiles of sediment cores in two different basins of the Baltic Sea, the Gotland Basin (GB) and Arkona Basin (AB), were analysed by means of GC-MS. 35 PAHs were quantified in all samples, and additionally, several marker PAHs, like Cyclopenta[cd]phenanthrene (CCP) for combustion processes and retene for terrigenous input, were quantified in selected samples. The preindustrial sediments (older than 200-250 years) in the GB core illustrate concentrations <100 ng PAH15 g(-1) d.w. Calculated PAH-ratios indicated combustion processes as the main sources for both basins. The Perylene concentrations within the sediment cores decrease with increasing depth, along with an increase in relative percentage, indicating slow diagenetic processes. The preservation and enrichment of the introduced PAHs was more pronounced in the GB core.     

Sorption of heavy oil onto Jiaozhou Bay sediment

The sorption of heavy oil onto sediment collected from Jiaozhou Bay was studied in a series of kinetic and equilibrium experiments using NaCl solutions. The effects of temperature, salinity, and pH of the medium on sorption behavior were investigated.Sorption equilibrium of the heavy oil and sediment was established within 60 min. The process was shown to follow a pseudo-second-order kinetic rate model. The sorption rate decreased with increasing initial heavy oil concentration in the solution. Batch equilibrium experiments showed that the sorption isotherm could be described by the Freundlich model. The standard free energy change and enthalpy change at the temperatures studied (283, 288, 293, and 298 K) were negative. These findings indicated that the process was spontaneous and exothermic. Salinity, pH and temperature influenced sorption performance. Sorption was favored by higher concentrations of NaCl, by lower pH values and by lower temperatures.     

Summary of IAEA-MEL's investigation of Kara Sea radioactivity and radiological assessment

IAEA-MEL participated in five expeditions to the Kara Sea with the aim of assessing the radiological consequences of dumped radioactive wastes in the Novaya Zemlya Bays and Trough. The programme included sampling, in-situ underwater investigations, laboratory analyses of water, sediment and biota samples, the development of a marine radioactivity database, modelling and radiological assessment, the organization of intercomparison exercises and the evaluation of distribution coefficients. Radiometric investigations have shown that no radiologically significant environmental contamination has occurred. Leakages which have led to locally increased levels of radionuclides in sediment have only been observed in Stepovoy and Abrosimov Bays. Computer modelling results suggest that only radiological effects on local and regional scales may be of importance. The global radiological impact of the disposals in the Arctic Seas will be negligible.     

Burrowing responses of the short-neck clam Ruditapes philippinarum to sediment contaminants

The burrowing responses of a common tropical bivalve, the short-neck clam Ruditapes philippinarum, to cadmium (Cd)-spiked sediment, variations of sediment grain size and natural sediments collected from 15 locations in Hong Kong's inshore waters were investigated through a series of laboratory tests. Results showed that the burrowing response exhibited a negative relationship with an increase in Cd concentration in the spiked sediments. The level of Cd was also found to be directly proportional to the percent mortality of the clam. However, there was no significant difference (p>0.05) in the time elapsed for the clam to burrow into sediments with different grain size composition. The elapsed time for 50% of the test clams to burrow into the sediment (ET₅₀) over a period of 48 h was calculated for the sediment samples collected from the 15 locations. Results of ANOVA showed significant difference (p<0.05) among the sediment samples. Tukey's multiple comparison test revealed two groups of sediments: group 1 containing 3 sediment samples collected from Victoria Harbour and group 2 containing 12 samples obtained from other coastal areas of Hong Kong. The ET₅₀ value for group 1 sediments was found to be greater than 2880 min whilst the ET₅₀ for group 2 sediments had a mean of 173.9 min. Agglomerative classification of the sediment samples, based on metal content (As, Cd, Cr, Cu, Ni, Pb, Zn), also showed two similar groups, suggesting that the ET₅₀ values were correlated with the metal level of the sediment samples. Group 1 sediments collected from Victoria Harbour had greater concentrations of Cd, Cr, Cu, Ni and Zn as compared to that in group 2. The present study demonstrated that high metal content in the sediment tends to inhibit the burrowing responses of the clam and that there is potential to develop the burrowing responses of R. philippinarum as a sublethal sediment toxicity test.     

Hydrocarbons in water,sediment and mussels from the southern Baltic Sea

Samples of water, sediment and mussels (Mytilus edulis) from the southern Baltic Sea have been analysed for total hydrocarbons by fluorescence spectroscopy and capillary gas chromatography. The sediment and mussel samples have also been analysed for specific aliphatic and aromatic hydrocarbons by computerized capillary gas chromatography-mass spectrometry. The highest hydrocarbon concentrations in all samples occurred either inshore (particularly in Gdansk Bay) or in deep offshore basins where fine sediment accumulates.     

Environment and biology of the Kara Sea: a general view for contamination studies

The recent revelation that over the past 30 years there has been a history of dumping waste including high-level radioactive wastes in the shallow Kara Sea has caused wide-spread concern. The potential impact of these contaminants and other non-nuclear pollutants in the Arctic ecosystem and on human health need to be assessed and, thus, a better insight gained on radioecological processes in cold waters. The present paper proposes a general view on the biology and the environment of the Kara Sea, as a basic tool for the experimental and modelling assessments of the impact of these contaminants.     

Trace contaminant concentrations in the Kara Sea and its adjacent rivers, Russia.

Trace organic (chlorinated pesticides, PCBs, PAHs and dioxins/furans) and trace metal concentrations were measured in surficial sediment and biological tissues (i.e., worms, crustaceans, bivalve molluscs, and fish livers) collected from the Russian Arctic. Total DDT, chlordane, PCB and PAH concentrations ranged from ND to 1.2, ND to <0.1, ND to 1.5 and <20-810 ng g(-1), respectively, in a suite of 40 surficial sediment samples from the Kara Sea and the adjacent Ob and Yenisey Rivers. High sedimentary concentrations of contaminants were found in the lower part of the Yenisey River below the salt wedge. Total dioxins/furans were analysed in a subset of 20 sediment samples and ranged from 1.4 to 410 pg g(-1). The highest trace organic contaminant concentrations were found in organisms, particularly fish livers. Concentrations as high as 89 ng g(-1) chlordane; 1010 ng g(-1) total DDTs; 460 ng g(-1) total PCBs; and 1110 ng g(-1) total PAH, were detected. A subset of 11 tissue samples was analysed for dioxins and furans with total concentrations ranging from 12 to 61 pg g(-1). Concentrations of many trace organic and metal contaminants in the Kara Sea appear to originate from riverine sources and atmospheric transport from more temperate areas. Most organic contaminant concentrations in sediments were low; however, contaminants are being concentrated in organisms and may pose a health hazard for inhabitants of coastal villages.     

Organic carbon flow in the Ob, Yenisey Rivers and Kara Sea of the Arctic region

Stable carbon isotope and elemental C/N ratios of the organic fraction of a set of samples along a transect in the Ob and Yenisey Rivers into the Kara Sea in the Arctic were measured. Previously, the concentrations of 239,240Pu and 137Cs in these same samples had been determined. The coupled measurements were carried out to assess possible connectivity between organic carbon flow into the Kara Sea and transport of radioactive nuclides in this marine environment. Organic carbon flow into the Kara Sea is influenced significantly by terrigenous sources carried by the Ob and Yenisey Rivers. The carbon isotope-organic carbon relationship provides evidence that a rich source of terrigenous carbon exists in the riverine system. A weak, but significant relationship between stable carbon isotope ratio and 137Cs suggests that most of the 137Cs is derived from riverine particles, as compared to Pu which is also derived from in situ scavenging within the water column.     

Burrowing responses of the short-neck clam Ruditapes philippinarum to sediment contaminants

The burrowing responses of a common tropical bivalve, the short-neck clam Ruditapes philippinarum, to cadmium (Cd)-spiked sediment, variations of sediment grain size and natural sediments collected from 15 locations in Hong Kong's inshore waters were investigated through a series of laboratory tests. Results showed that the burrowing response exhibited a negative relationship with an increase in Cd concentration in the spiked sediments. The level of Cd was also found to be directly proportional to the percent mortality of the clam. However, there was no significant difference (p>0.05) in the time elapsed for the clam to burrow into sediments with different grain size composition. The elapsed time for 50% of the test clams to burrow into the sediment (ET₅₀) over a period of 48 h was calculated for the sediment samples collected from the 15 locations. Results of ANOVA showed significant difference (p<0.05) among the sediment samples. Tukey's multiple comparison test revealed two groups of sediments: group 1 containing 3 sediment samples collected from Victoria Harbour and group 2 containing 12 samples obtained from other coastal areas of Hong Kong. The ET₅₀ value for group 1 sediments was found to be greater than 2880 min whilst the ET₅₀ for group 2 sediments had a mean of 173.9 min. Agglomerative classification of the sediment samples, based on metal content (As, Cd, Cr, Cu, Ni, Pb, Zn), also showed two similar groups, suggesting that the ET₅₀ values were correlated with the metal level of the sediment samples. Group 1 sediments collected from Victoria Harbour had greater concentrations of Cd, Cr, Cu, Ni and Zn as compared to that in group 2. The present study demonstrated that high metal content in the sediment tends to inhibit the burrowing responses of the clam and that there is potential to develop the burrowing responses of R. philippinarum as a sublethal sediment toxicity test.     

Modelling the transport of sediment discharged by Colombian rivers to the southern Caribbean Sea

Ocean Dynamics - The three-dimensional transport of sediments released by the main rivers in the Colombian Caribbean basin is investigated using numerical model simulations. Different types of...     

Iron sulfides in the sediment cores from the Sea of Japan and their geophysical implications

Ferromagnetic iron sulfides have been identified by thermomagnetic, X-ray crystallographic and reflection-microscopic analyses of deep-sea sediment cores taken from the Sea of Japan. Occurrence of iron sulfides at certain depths of the cores seems to indicate that the paleoenvironment of the deep basin in the Sea of Japan was very stagnant, probably due to the enclosure by lands caused by the lowering of the sea level during the glacial periods. Oxidation of sulfides as well as sulfuration of oxides in the sedimentary layer may account for the abnormally high heat flow in the deep basin.     

Entrainment of fine-grained surface deposits into new ice in the southwestern Kara Sea,Siberian Arctic

The entrainment of bottom deposits (silt and clay) into newly formed ice was investigated in the Amderma/Vaygach flaw lead in the southwestern Kara Sea, Siberian Arctic. Fine-grained bottom deposits and sea ice sediments (SIS) were analyzed by granulometry, scanning electron microscopy and X-ray diffractometry. On average, SIS contain by a factor of four times more silt than the shelf deposits (66.7% vs. 16.3%), and the SIS clay percentage is more than three-fold of the bottom value (31.2% vs. 9.1%). Sand-sized particles are significantly less abundant in SIS compared to bottom sediment (2.1% vs. 74.6%). The preferred entrainment of silt into ice is underpinned by the enhanced silt-to-clay-ratio in SIS compared to bottom deposits. Though silt is preferably entrained into SIS, no evidence was found for preferential ice-entrainment of any silt sub-fraction (coarse, medium or fine). However, sub-angular- and angular-discoidal silt particles are favorably entrained into local sea ice. Clay mineral assemblages in SIS and shelf surface sediments match very well revealing that no individual clay mineral is preferably enriched in SIS or reduced at the bottom. The general textural, compositional and statistical match of fine-grained shelf surface deposits and SIS proves that bottom sediment is the principle source for ice-entrained material in the study area. We propose e.g. wave action and thermohaline convection to take sediment particles upward from the bottom nepheloid layer into the well-mixed 10–40 m deep water column of the Amderma/Vaygach flaw lead, and the turbulent process of suspension freezing to bring sediment particles and frazil crystals into contact, finally leading to the formation of sediment-laden ice. The role of SIS entrainment and export for local/regional shelf erosion and coastal retreat is of minor importance in the SW Kara Sea compared to other circum-Arctic shelf seas. However, the characteristic clay mineral assemblage of local SIS and bottom deposits can help identify the origin of SIS both on regional and Arctic-wide scales.     

Analyses of organic and inorganic contaminants in Salton Sea fish

Chemical contamination of fish from the Salton Sea, a quasi-marine lake in Southern California, could adversely impact millions of birds using the Pacific Flyway and thousands of humans using the lake for recreation. Bairdiella icistia (bairdiella), Cynoscion xanthulus (orangemouth corvina), and Oreochromis spp. (tilapia) were sampled from two river mouths and two nearshore areas of the Salton Sea. Muscle tissues were analyzed for a complete suite of 14 trace metals and 53 pesticides. Fish muscle tissues had concentrations of selenium ranging between 1.89 and 2.73 microg/g wet weight. 4,4'-DDE accounted for 94% of the total DDT metabolites. Total DDTs ranged between 17.1 and 239.0 and total PCBs between 2.5 and 18.6 ng/g wet weight. PCB congeners 132, 138, 153, 168, and 180 comprised over 50% of the total PCBs. Given the potential implementation of a commercial fishing at the Salton Sea in the future, the presence of persistent organic pollutants and selenium warrants further research into the effects of these mixtures on fish populations, and on wildlife and humans consuming fish.     

Distribution and sources of organochlorinated contaminants in sediments from Izmir Bay (Eastern Aegean Sea)

Eighteen surface sediment samples representative of the entire Izmir Bay were analyzed for organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). This was in order to provide extensive information concerning the recent deposition of these compounds in this area, together with levels, distribution, possible sources and potential biological risk. Sites that were contaminated by high concentrations of organochlorine compounds were associated with dense population, such as the harbour and the Gediz River estuary. Relatively higher ΣDDT concentrations and high DDT/DDE + DDD ratios in the Gediz River estuary indicated DDT usage, probably linked to public health emergencies. According to the established guidelines for sediment quality, the risk of adverse biological effects from such levels of OCPs and PCBs as recorded at most of the study sites was insignificant. But the higher concentrations in Inner bay and in the Gediz River estuary could cause biological damage.