Potential of four aquatic plant species to remove 60Co from contaminated water under changing experimental conditions.

This study aimed to compare the potential of Lemna minor, Spirodela sp., Eichhornia crassipes and Pistia stratiotes to remove 60Co from a realistic aquatic environment. Although all four plant species performed similarly well after 3 days of exposure to 50 kBq L-1 60Co, Lemna minor and Spirodela sp. came forward as having higher 60Co removal potential. This conclusion is, in first instance, based on the high 60Co removal percentage obtained after a short contact time (e.g. more than 95% could be removed after 6 h by Spirodela sp.). Additionally, Lemna minor and Spirodela sp. accumulated a high amount of 60Co per gram of biomass. For example, Lemna minor accumulated over three times more 60Co per gram of biomass compared to Pistia stratiotes and Eichhornia crassipes. Both plants also performed well in the pH range 5-9. We used Lemna minor to test the influence of the initial 60Co concentration (10, 50, 100 and 200 kBq L-1 60Co) on its phytoremediation capacity but no differences could be observed in removal percentage. In addition, it was shown that by optimising the initial amount of biomass, radioactive waste production can be minimised whilst maintaining high 60Co removal rates. Our study shows that these aquatic plants can be used for phytoremediation of 60Co from contaminated water and can be considered as a "green" addition or alternative for conventional remediation techniques.

Effects of ocean acidification on 109Cd, 57Co, and 134Cs bioconcentration by the European oyster (Ostrea edulis): Biokinetics and tissue-to-subcellular partitioning.

The uptake and depuration kinetics of dissolved 109Cd, 57Co and 134Cs were determined experimentally in the European flat oyster Ostrea edulis (Linnaeus, 1758) under different pH conditions (i.e., 8.1, 7.8 and 7.5) for 59 days. Uptake and depuration rates were variable within these elements; no effects were observed under different pH conditions for the uptake biokinetics of 109Cd and 57Co and depuration of 109Cd and 134Cs in oyster. The uptake and depuration rate constants of 134Cs differed during the exposure phase between treatments, while the steady state concentration factors (CFss) were similar. The resulting Cs activity that was purged during short- and long-term depuration phases differed, while the remaining activities after thirty-nine days depuration phase (RA39d) were similar. Co-57 depuration was affected by pCO2 conditions: RA39d were found to be significantly higher in oysters reared in normocapnia (pCO2 = 350 µatm) compared to high pCO2 conditions. Co-57 tissue distribution did not differ among the variable pCO2 conditions, while 109Cd and 134Cs accumulated in soft tissue of oysters were found to be higher under the highest pCO2. Additionally, Cd, Co and Cs were stored differently in various compartments of the oyster cells, i.e. cellular debris, metal-rich granules (MRG) and metallothionein-like proteins (MTLP), respectively. The subcellular sequestration of the elements at the end of the depuration phase did not differ among pH treatments. These results suggest that bioconcentration and tissue/subcellular distribution are element-specific in the oyster, and the effects of higher pCO2 driven acidification and/or coastal acidification variably influence these processes.

Comparing single-feeding and multi-feeding approaches for experimentally assessing trophic transfer of metals in fish.

Diet is an important pathway for metal uptake in marine organisms, and assimilation efficiency is one of the most relevant parameters to quantify trophic transfer of metals along aquatic food webs. The most commonly used method to estimate this parameter is pulse-chase feeding using radiolabeled food. This approach is, however, based on several assumptions that are not always tested in an experimental context. The present study aimed to validate the approach by assessing single-feeding and multiple-feeding approaches, using a model species (the turbot Scophthalmus maximus). Using the kinetic data obtained from the single-feeding experiment, the reconstruction of a multi-feeding experiment was tested for consistency with data provided by an actual multi-feeding performed under the same experimental conditions. The results validated the single-feeding approach. Environ Toxicol Chem 2017;36:1227-1234. © 2016 SETAC.

Cell Type-Specific Modulation of Cobalamin Uptake by Bovine Serum.

Tracking cellular 57Co-labelled cobalamin (57Co-Cbl) uptake is a well-established method for studying Cbl homeostasis. Previous studies established that bovine serum is not generally permissive for cellular Cbl uptake when used as a supplement in cell culture medium, whereas supplementation with human serum promotes cellular Cbl uptake. The underlying reasons for these differences are not fully defined. In the current study we address this question. We extend earlier observations by showing that fetal calf serum inhibits cellular 57Co-Cbl uptake by HT1080 cells (a fibrosarcoma-derived fibroblast cell line). Furthermore, we discovered that a simple heat-treatment protocol (95°C for 10 min) ameliorates this inhibitory activity for HT1080 cell 57Co-Cbl uptake. We provide evidence that the very high level of haptocorrin in bovine serum (as compared to human serum) is responsible for this inhibitory activity. We suggest that bovine haptocorrin competes with cell-derived transcobalamin for Cbl binding, and that cellular Cbl uptake may be minimised in the presence of large amounts of bovine haptocorrin that are present under routine in vitro cell culture conditions. In experiments conducted with AG01518 cells (a neonatal foreskin-derived fibroblast cell line), overall cellular 57Co-Cbl uptake was 86% lower than for HT1080 cells, cellular TC production was below levels detectable by western blotting, and heat treatment of fetal calf serum resulted in only a modest increase in cellular 57Co-Cbl uptake. We recommend a careful assessment of cell culture protocols should be conducted in order to determine the potential benefits that heat-treated bovine serum may provide for in vitro studies of mammalian cell lines.

Engineered Deinococcus radiodurans R1 with NiCoT genes for bioremoval of trace cobalt from spent decontamination solutions of nuclear power reactors.

The aim of the present work was to engineer bacteria for the removal of Co in contaminated effluents. Radioactive cobalt ((60)Co) is known as a major contributor for person-sievert budgetary because of its long half-life and high γ-energy values. Some bacterial Ni/Co transporter (NiCoT) genes were described to have preferential uptake for cobalt. In this study, the NiCoT genes nxiA and nvoA from Rhodopseudomonas palustris CGA009 (RP) and Novosphingobium aromaticivorans F-199 (NA), respectively, were cloned under the control of the groESL promoter. These genes were expressed in Deinococcus radiodurans in reason of its high resistance to radiation as compared to other bacterial strains. Using qualitative real time-PCR, we showed that the expression of NiCoT-RP and NiCoT-NA is induced by cobalt and nickel. The functional expression of these genes in bioengineered D. radiodurans R1 strains resulted in >60 % removal of (60)Co (≥5.1 nM) within 90 min from simulated spent decontamination solution containing 8.5 nM of Co, even in the presence of >10 mM of Fe, Cr, and Ni. D. radiodurans R1 (DR-RP and DR-NA) showed superior survival to recombinant E. coli (ARY023) expressing NiCoT-RP and NA and efficiency in Co remediation up to 6.4 kGy. Thus, the present study reports a remarkable reduction in biomass requirements (2 kg) compared to previous studies using wild-type bacteria (50 kg) or ion-exchanger resins (8000 kg) for treatment of ~10(5)-l spent decontamination solutions (SDS).

Pre-assessment of dose rates of (134)Cs, (137)Cs, and (60)Co for marine biota from discharge of Haiyang Nuclear Power Plant, China.

Haiyang Nuclear Power Plant to be built in China was selected as a case for the dose pre-assessment for marine biota in this study. The concentrations of Cs and Co in organisms (turbot, yellow croaker, swimming crab, abalone, sea cucumber, and sea lettuce), seawater, and bottom sediment sampled on-site were measured by neutron activation analysis, and the site-specific transfer parameters (concentration ratios and distribution coefficients) of Cs and Co were calculated. (134)Cs, (137)Cs, and (60)Co activity concentrations in the organisms and the sediment at the site were calculated with the site-specific transfer parameters and the anticipated activity concentrations in the liquid effluent of the nuclear power plant. The ERICA tool was used to estimate the dose rates of (134)Cs, (137)Cs, and (60)Co to the selected organisms based on the biological models developed. The total dose rates of (134)Cs, (137)Cs, and (60)Co to the six organisms were all <0.001 µGy h(-1).

Monitoring of tritium, 60Co and 137Cs in the vicinity of the warm water outlet of the Paks Nuclear Power Plant, Hungary.

Danube water, sediment and various aquatic organisms (snail, mussel, predatory and omnivorous fish) were collected upstream (at a background site) and downstream of the outlet of the warm water channel of Paks Nuclear Power Plant. Gamma emitters, tissue free-water tritium (TFWT) and total organically-bound tritium (T-OBT) measurements were performed. A slight contribution of the power plant to the natural tritium background concentration was measured in water samples from the Danube section downstream of the warm water channel. Sediment samples also contained elevated tritium concentrations, along with a detectable amount of (60)Co. In the case of biota samples, TFWT exhibited only a very slight difference compared to the tritium concentration of the Danube water, however, the OBT was higher than the tritium concentration in the Danube, independent of the origin of the samples. The elevated OBT concentration in the mollusc samples downstream of the warm water channel may be attributed to the excess emission from the nuclear power plant. The whole data set obtained was used for dose rate calculations and will be contributed to the development of the ERICA database.

Vanadate-induced Ca(2+) and Co(2+) uptake in human red blood cells.

The vanadate-induced increase in passive uptake of calcium and cobalt and their interference were studied in human red cells using (45)Ca and (57)Co as tracers. Vanadate is a potent inhibitor of the Ca-pump in red cells, although in fed cells a residual pump activity remains that is highly significant compared to the passive influx, and even in cells that are both ATP-depleted and vanadate-treated the pump arrest is not complete. In the presence of vanadate the Ca(2+) uptake is increased due to inhibition of Ca-pump extrusion, but is further increased due to a vanadate-induced increment in passive influx. In order to measure the vanadate-induced increment in Ca(2+) influx, the total uptake in vanadate-treated cells is corrected for the basal influx, as recorded in ATP-depleted cells in the presence of tetrathionate (5mM) that has been shown to eliminate the residual Ca-pump activity in ATP-depleted cells. The (57)Co uptake is also increased by vanadate. (57)Co is not transported by the Ca-pump, and hence the uptake in vanadate-treated cells can be directly compared to the basal uptake, both in fed and in ATP-depleted cells. The vanadate effect shows rapid onset and appears to be irreversible. The vanadate-induced increment in uptake of both (45)Ca and (57)Co is reduced by about 50% in ATP-depleted cells compared to fed cells, suggesting a metabolism- or SH-group-dependent component. The influx of both (45)Ca (in ATP-depleted cells) and (57)Co (in fed cells) increases with the vanadate concentration, with a similar K(½) (0.4 and 0.3mM, respectively), and is nearly maximal at 5mM vanadate. The vanadate-induced increment in influx of both (45)Ca and (57)Co increases with the extracellular concentration as a saturable function, with K(½) estimated at, respectively, 700 and 80µM. In the case of (57)Co K(½) is similar in fed and in ATP-depleted cells. The vanadate-induced uptake of (45)Ca and of (57)Co shows interference. The uptake of (45)Ca is inhibited by Co(2+), and the uptake of (57)Co is inhibited by Ca(2+), although with an unexplained time course. The vanadate-induced uptake of (45)Ca and (57)Co are both inhibited, and to a similar degree, by the 1,4-dihydropyridine Ca(2+)-channel blocker nifedipine, although only at concentrations much higher than IC(50) for classical Ca-channels. The vanadate-induced increment in (57)Co uptake is electroneutral, in contrast to the basal uptake that is at least partially electrogenic. In experiments with resealed ghosts a vanadate-induced (57)Co uptake could not be detected. The vanadate-induced increment in (57)Co uptake amounts to nearly half the increment in (45)Ca uptake, both in fed and in ATP-depleted cells. It is speculated that the vanadate-induced Ca(2+) and Co(2+) uptake could be mediated by a putative common transporter, which appears to be separate and distinct from the putative common transporter for basal Ca(2+) and Co(2+) uptake.

Transfer of elements relevant to radioactive waste from soil to five boreal plant species.

In long-term safety assessment models for radioactive waste disposal, uptake of radionuclides by plants is an important process with possible adverse effects in ecosystems. Cobalt-60, (59,63)Ni, (93)Mo, and (210)Pb are examples of long-living radionuclides present in nuclear waste. The soil-to-plant transfer of stable cobalt, nickel, molybdenum and lead and their distribution across plant parts were investigated in blueberry (Vaccinium myrtillus), May lily (Maianthemum bifolium), narrow buckler fern (Dryopteris carthusiana), rowan (Sorbus aucuparia) and Norway spruce (Picea abies) at two boreal forest sites in Eastern Finland. The concentrations of all of the studied elements were higher in roots than in above-ground plant parts showing that different concentration ratios (CR values) are needed for modelling the transfer to roots and stems/leaves. Some significant differences in CR values were found in comparisons of different plant species and of the same species grown at different sites. However, large within-species variation suggests that it is not justified to use different CR values for modelling soil-to-plant transfer of these elements in the different boreal forest plant species.

Accumulation of zirconium phosphate by a Serratia sp.: a benign system for the removal of radionuclides from aqueous flows.

Metal phosphate deposited enzymatically on Serratia sp. has been used successfully for the removal of radionuclides from aqueous flows. Previous studies using biogenic hydrogen uranyl phosphate (HUP) on Serratia sp. biofilm showed removal of 100% of (90)Sr, (137)Cs, and (60)Co via their intercalation into biogenic HUP crystals. Zirconium phosphates (ZrP) offer a potential non-toxic and non-radioactive alternative to HUP for water decontamination. A method was developed for biomanufacturing ZrP. Biogenic ZrP removed ca. 100% of Sr(2+) and Co(2+) (0.5 mM) from solutions to a molar ratio at saturation of ca. 1:0.6 for both Zr:Sr and Zr:Co. The potential for drinking water decontamination via bio-ZrP is discussed with respect to bio-HUP and also other commercially available materials.

Detection and temporal variation of (60)Co in the digestive glands of the common octopus, Octopus vulgaris, in the East China Sea.

(60)Co were detected in common octopus specimens collected in the East China Sea in 1996-2005. The source of (60)Co has remained unclear yet. Stable isotope analyses showed that there was no difference in stable Co concentrations between octopus samples with (60)Co and without (60)Co. This result showed that the stable Co in the digestive gland of octopus potentially did not include a trace amount of (60)Co and the source of (60)Co existed independently. Furthermore, investigations of octopus in other area and other species indicated that the origin of the source of (60)Co occurred locally in the restricted area in the East China Sea and not in the coastal area of Japan. Concentrations of (60)Co have annually decreased with shorter half-life than the physical half-life. This decrease tendency suggests that the sources of (60)Co were identical and were temporary dumped into the East China Sea as a solid waste.

[Soil sorption and transfer from it to plant of the radioactive and stable isotopes of chemical elements: methodology and experimental approach].

The adsorption of pair nuclides 60Co/Co and 65Zn/Zn by solid phase and their availability to plants were studied in soil suspension conditions and in the sod podzolic soil under controlled moisture. The situation when the radionuclide in constant activity is entered to system (surface water, soil) with different heavy metal contamination has been modeled. Was observed that soil contamination with heavy metal Co (Zn) significantly reduce sorption of the radionuclide 60Co (65Zn) by solid phase. As a result, the activity concentration of the 60Co or 65Zn in soil solution and, therefore, their mobility and potential availability to plants increases in 2-4 times with the total metal concentration increasing. The difference between two elements is that high Co concentration increase root uptake of the 60Co, whereas soil contamination with Zn reduce activity of 65Zn in the 14-days barley plants that may reflects diverse plant necessity of two elements and more important role of the isotopic exchange effect in the case of Zn.

137Cs, 60Co and 40K uptake by lettuce plants in two distributions of soil contamination.

(137)Cs and (60)Co, two of the radionuclides more representative of discharges from nuclear facilities, are of interest for radiological protections because of their great mobility in biosphere and affinity with biological systems. The aim of the present work is the investigation of the possible influence of the vertical distribution of (137)Cs and (60)Co in soil upon their uptake by lettuce as function of plant's growth. An experiment ad hoc has been carried out in field conditions. The results show that (i) the transfer of (137)Cs and (60)Co from soil to lettuce is independent by their distribution in soil, (ii) the soil-plant transfer factors of (137)Cs and (60)Co show a similar trend vs. growth stage, (iii) the (40)K transfer factor trend is different from those of anthropogenic radionuclides, and (iv) (137)Cs and (60)Co specific activities are about 1Bq/kg, in the mature vegetable with soil activity from 9 to 21kBq/m(2).

Bioremediation of trace cobalt from simulated spent decontamination solutions of nuclear power reactors using E. coli expressing NiCoT genes.

Removal of radioactive cobalt at trace levels (approximately nM) in the presence of large excess (10(6)-fold) of corrosion product ions of complexed Fe, Cr, and Ni in spent chemical decontamination formulations (simulated effluent) of nuclear reactors is currently done by using synthetic organic ion exchangers. A large volume of solid waste is generated due to the nonspecific nature of ion sorption. Our earlier work using various fungi and bacteria, with the aim of nuclear waste volume reduction, realized up to 30% of Co removal with specific capacities calculated up to 1 microg/g in 6-24 h. In the present study using engineered Escherichia coli expressing NiCoT genes from Rhodopseudomonas palustris CGA009 (RP) and Novosphingobium aromaticivorans F-199 (NA), we report a significant increase in the specific capacity for Co removal (12 microg/g) in 1-h exposure to simulated effluent. About 85% of Co removal was achieved in a two-cycle treatment with the cloned bacteria. Expression of NiCoT genes in the E. coli knockout mutant of NiCoT efflux gene (rcnA) was more efficient as compared to expression in wild-type E. coli MC4100, JM109 and BL21 (DE3) hosts. The viability of the E. coli strains in the formulation as well as at different doses of gamma rays exposure and the effect of gamma dose on their cobalt removal capacity are determined. The potential application scheme of the above process of bioremediation of cobalt from nuclear power reactor chemical decontamination effluents is discussed.

The effect of organic amendment on potential mobility and bioavailability of 137Cs and 60Co in tropical soils.

In this work the role of organic matter in the potential mobility and bioavailability of 137Cs and 60Co in Brazilian soil was investigated. Radish was cultivated in pots containing the top layer (0-20 cm) of a Histosol, Ferralsol and Nitisol spiked with 137Cs and 60Co. In the case of the Ferralsol and Nitisol samples, besides the control, two different rates of organic amendments were used. In these soils, a sequential extraction protocol was used to identify the main soil compartments that could be responsible for the variation of transfer factor values. Our results indicate that organic amendment could be suggested as a practical countermeasure for 137Cs and 60Co contamination, since it reduces bioavailability of radionuclides and, consequently, soil to plant transfer factor values by almost one order of magnitude in a short period of time.

Soil to plant transfer of 137Cs and 60Co in Ferralsol, Nitisol and Acrisol.

In this study, soil to plant transfer factor values were determined for 137Cs and 60Co in radish (Raphanus sativus), maize (Zea mays L.) and cabbage (Brassica oleracea L. var. capitata) growing in gibbsite-, kaolinite- and iron-oxide-rich soils. After 3 years of experiment in lysimeters it was possible to identify the main soil properties able to modify the soil to plant transfer processes, e.g. exchangeable K and pH, for 137Cs, and organic matter for 60Co. Results of sequential chemical extraction were coherent with root uptake and allowed the recognition of the role of iron oxides on 137Cs behaviour and of Mn oxides on 60Co behaviour. This information should provide support for adequate choices of countermeasures to be applied on tropical soils in case of accident or for remediation purposes.

Accumulation and transport behaviour of 241americium, 60cobalt and 134cesium by eggs of the spotted dogfish Scyliorhinus canicula.

An experimental study examined the 96-h net influx from seawater of the anthropogenic radionuclides (241)Am, (60)Co and (134)Cs through the egg-case of the spotted dogfish Scyliorhinus canicula. Net influx directly through the wall of the egg-case was greatest for (134)Cs, then (241)Am and lastly (60)Co. Within the egg-case wall itself the measured concentration factors (CFs) and their gradients in the external, median and internal layers showed that for both (241)Am and (60)Co they were >10(3) in the external layer and declined by an order of magnitude in the interior layer. In contrast (134)Cs had a CF of only about three in the external layer which declined by a factor of 2 towards the two more internal layers of the egg-case. The egg-case apertures, that open within the prehatching stage of embryological development, significantly (P<0.05) increased the net influx of (241)Am and (60)Co to the interior of the egg-case, although their water concentrations were still lower than those in the labelled seawater bath. In contrast, the aperture did not increase the net influx of (134)Cs whose water concentrations equilibrated with those in seawater. Together these results indicate that the egg-case wall is very permeable to (134)Cs, representing little barrier to its movement, and hence consistent with the lack of importance of the aperture in determining its internal water concentrations in the egg-case. In contrast, (241)Am and (60)Co show much higher rates of accumulation by the egg-case, consistent with the measured reduced permeability of its wall, and therefore giving greater prominence to its aperture in the net transfer of these two radionuclides to the egg case's interior. The presence of the embryo within its egg-case did not significantly (P>0.05) affect the rates of influx of radioisotopes, with the exception of an interactive effect for (60)Co with the egg-case aperture (P<0.05). The CF of only (241)Am in the embryo itself relative to the external seawater concentration was significantly (P<0.05) enhanced by the presence of the aperture.

Development and characterization of biofilms on stainless steel and titanium in spent nuclear fuel pools.

The aim of the present research was to study the biofilms developed in a Spanish nuclear power plant and their ability to entrap radionuclides. In order to carry this out, a bioreactor, which was then submerged in a spent nuclear fuel pool, was designed. To characterise the biofilm on two different metallic materials (stainless steel and titanium), standard culture microbiological methods and molecular biology tools, as well as epifluorescence and scanning electron microscopy were used. The bacterial composition of the biofilm belongs to several phylogenetic groups (alpha, beta, and gamma-Proteobacteria, Actinobacteridae, and Firmicutes). The radioactivity of the biofilms was measured by gamma-ray spectrometry. Biofilms were able to retain radionuclides from radioactive water, especially (60)Co. The potential use of these biofilms in bioremediation of radioactive water is discussed.

Composite organization of the cobalamin binding and cubilin recognition sites of intrinsic factor.

Intrinsic factor (IF(50)) is a cobalamin (Cbl)-transporting protein of 50 kDa, which can be cleaved into two fragments: the 30 kDa N-terminal peptide IF(30) and the 20 kDa C-terminal glycopeptide IF(20). Experiments on binding of Cbl to IF(30), IF(20), and IF(50) revealed comparable association rate constants (k(+)(Cbl) = 4 x 10(6), 14 x 10(6), and 26 x 10(6) M(-1) s(-1), respectively), but the equilibrium dissociation constants were essentially different (K(Cbl) = 200 microM, 0.2 microM, and

Bioremediation of 60Co from simulated spent decontamination solutions.

Bioremediation of 60Co from simulated spent decontamination solutions by utilizing different biomass of (Neurospora crassa, Trichoderma viridae, Mucor recemosus, Rhizopus chinensis, Penicillium citrinum, Aspergillus niger and, Aspergillus flavus) fungi is reported. Various fungal species were screened to evaluate their potential for removing cobalt from very low concentrations (0.03-0.16 microM) in presence of a high background of iron (9.33 mM) and nickel (0.93 mM) complexed with EDTA (10.3 mM). The different fungal isolates employed in this study showed a pickup of cobalt in the range 8-500 ng/g of dry biomass. The [Fe]/[Co] and [Ni]/[Co] ratios in the solutions before and after exposure to the fungi were also determined. At micromolar level the cobalt pickup by many fungi especially the mutants of N. crassa is seen to be proportional to the initial cobalt concentration taken in the solution. However, R. chinensis exhibits a low but iron concentration dependent cobalt pickup. Prior saturating the fungi with excess of iron during their growth showed the presence of selective cobalt pickup sites. The existence of cobalt specific sorption sites is shown by a model experiment with R. chinensis wherein at a constant cobalt concentration (0.034 microM) and varying iron concentrations so as to yield [Fe/Co]initial ratios in solution of 10, 100, 1000 and 287000 have all yielded a definite Co pickup capacity in the range 8-47 ng/g. The presence of Cr(III)EDTA (3 mM) in solution along with complexed Fe and Ni has not influenced the cobalt removal. The significant feature of this study is that even when cobalt is present in trace level (sub-micromolar) in a matrix of high concentration (millimolar levels) of iron, nickel and chromium, a situation typically encountered in spent decontamination solutions arising from stainless steel based primary systems of nuclear reactors, a number of fungi studied in this work showed a good sensitivity for cobalt pickup.