The colonization of an irradiated environment: the case of microbial biofilm in a nuclear reactor.

The investigation of the microbial community change in the biofilm, growing on the walls of a containment tank of TRIGA nuclear reactor revealed a thriving community in an oligotrophic and heavy-metal-laden environment, periodically exposed to high pulses of ionizing radiation (IR). We observed a vertical IR resistance/tolerance stratification of microbial genera, with higher resistance and less diversity closer to the reactor core. One of the isolated Bacillus strains survived 15 kGy of combined gamma and proton radiation, which was surprising. It appears that there is a succession of genera that colonizes or re-colonizes new or IR-sterilized surfaces, led by Bacilli and/or Actinobacteria, upon which a photoautotrophic and diazotrophic community is established within a fortnight. The temporal progression of the biofilm community was evaluated also as a proxy for microbial response to radiological contamination events. This indicated there is a need for better dose-response models that could describe microbial response to contamination events. Overall, TRIGA nuclear reactor offers a unique insight into IR microbiology and provides useful means to study relevant microbial dose-thresholds during and after radiological contamination.

Recovery after Running an "Everesting" Mountain Ultramarathon.

Blood markers of muscle microdamage and systemic inflammation do not adequately explain the reduced performance observed over a prolonged recovery after running a mountain ultramarathon. This case study aimed to determine whether the reduced performance after the Everesting mountain ultramarathon can be further assessed by considering cardiorespiratory and metabolic alterations determined via repeated incremental and continuous running tests. A single runner (age: 24 years, BM: 70 kg, BMI: 22, Vo2peak: 74 mL∙min-1∙kg-1) was observed over a preparatory period of two months with a one-month recovery period. The Everesting consisted of nine ascents and descents of 9349 vertical metres completed in 18:22 (h:min). During the first phase of the recovery, enhanced peak creatine kinase (800%) and C-reactive protein (44%) levels explained the decreased performance. In contrast, decreased performance during the second, longer phase was associated with a decreased lactate threshold and Vo2 (21% and 17%, respectively), as well as an increased energetic cost of running (15%) and higher endogenous carbohydrate oxidation rates (87%), lactate concentrations (170%) and respiratory muscle fatigue sensations that remained elevated for up to one month. These alterations may represent characteristics that can explain the second phase of the recovery process after Everesting.

Uranium isotopes as a possible tracer of terrestrial authigenic carbonate.

The concentration and isotopic composition of uranium (δ238U, 234U/238U activity ratio) in combination with traditional isotopes (δ18O, δ13C) were examined as potential tracers of authigenic carbonate formation in a karst aquifer. The U concentration and 234U/238U activity ratios in the tufa-precipitating sections of two connected karst rivers (Krka and Zrmanja, Croatia) decreased downstream in water and in precipitated carbonate due to active self-purification processes, i.e. adsorption of isotopically lighter U(VI) on mineral particles, sedimentation and co-precipitation with carbonate. The isotopic composition of carbonate in tufa mostly resembled the 234U/238U activity ratio and the δ238U values of dissolved U in water but was also affected by the presence of detrital carbonate flushed into the river from soil and weathered bedrock. This interpretation was supported by the δ18O and δ13C values of tufa, which were shifted out of equilibrium with river water and dissolved in organic carbon and in their isotopic signature, which showed the presence of lithic carbonate. Large fluctuations of the δ238U values of water, leachable U (eluted in acetic acid buffered with Na-acetate) and residual U fraction could not be fully explained by available data due to the overlapping U isotopic signatures of leachable (mainly carbonate) and residual fractions of soil, bedrock and tufa. Therefore, a long-term, systematic, seasonal and event-based observation of the isotopic composition of dissolved and suspended particulate U in water is necessary. Nevertheless, the U isotopes were found to have the potential to be used as identifiers of authigenic carbonate and the storage of CO2 in terrestrial river sediments, to improve knowledge on fluxes within local and global biogeochemical carbon cycle.

Geostatistical evaluation of the design of the precipitation stable isotope monitoring network for Slovenia and Hungary.

A detailed knowledge of the stable isotope signature of precipitation is the basis of investigations in a variety of scientific fields and applications. To obtain robust and reliable results, the representativity of the currently operating (at least, as of 2018) precipitation stable isotope monitoring stations across Slovenia (n = 8) and Hungary (n = 9) was evaluated on the basis of amount-weighted annual averages with the aim of revealing any redundantly (i.e. over-) represented or un(der)represented areas. In the case of the latter, optimal locations for additional sites were suggested in Slovenia and Hungary. The networks of both countries are design-based systems that need to be fine-tuned for long-term optimized operation. The evaluation of the monitoring network was performed taking into consideration the stations operating in Slovenia and Hungary, as well as closely situated ones operating in neighboring countries. The evaluation was carried out in nine different combinations, using spatial simulated annealing, with regression kriging variance as a quality measure. The results showed that (i) there are over- and un(der)represented areas in the network, an issue requiring remedial action, (ii) the mutual information exchange of the precipitation stable isotope monitoring networks of Slovenia and Hungary increases the precision of precipitation δ18O estimation by ~0.3‰ in a 15-30 km wide zone near the borders, and (iii) by an even greater degree in the neighboring countries' stations. The current research may be termed pioneering in the matter of the detailed geostatistical assessment of spatial representativity of a precipitation stable isotope monitoring network, and as such, can serve as an example for future studies aiming for the spatial optimization of other regional precipitation stable isotope monitoring networks.

Millennial climate oscillations controlled the structure and evolution of Termination II.

The controls that affect the structure and timing of terminations are still poorly understood. We studied a tufa deposit from the Iberian Peninsula that covers Termination II (T-II) and whose chronology was synchronized to speleothem records. We used the same chronology to synchronize ocean sediments from the North Atlantic to correlate major climate events in a common timescale. We identify two stages within T-II. The first stage started with the increase of boreal summer integrated solar insolation, and during this stage three millennial climate oscillations were recorded. These oscillations resulted from complex ocean-atmosphere interactions in the Nordic seas, caused by the progressive decay of Northern Hemisphere ice-sheets. The second stage commenced after a glacial outburst that caused the collapse of the Thermohaline Circulation, a massive Heinrich event, and the onset of the Bipolar Seesaw Mechanism (BSM) that eventually permitted the completion of T-II. The pace of the millennial oscillations during the first stage of T-II controlled the onset of the second stage, when the termination became a non-reversible and global phenomenon that accelerated the deglaciation. During the last the two terminations, the BSM was triggered by different detailed climate interactions, which suggests the occurrence of different modes of terminations.

Geographical Origin Characterization of Slovenian Organic Garlic Using Stable Isotope and Elemental Composition Analyses.

In the present research, the applicability of stable isotope (δ13C, δ15N, δ34S, δ18O) and multi-element (P, S, Cl, K, Ca, Zn, Br, Rb, Sr) data for determining the geographical origin of garlic (Allium sativum L.) at the scale of Slovenia was examined. Slovenia is a rather small country (20273 km2) with significant geological and biological diversity. Garlic, valued for its medicinal properties, was collected from Slovenian farms with certified organic production and analyzed by elemental analyzer isotope ratio mass spectrometry combined with energy dispersive X- ray fluorescence spectrometry. Multivariate discriminant analysis (DA) revealed a distinction between four Slovenian macro-regions: the Alpine, Dinaric, Mediterranean and Pannonian. The model was validated through a leave-10%, 20% and 25% out cross validation. The overall success rate of correctly reclassified samples was 77% (on average), indicating that the model and the proposed methodology could be a promising tool for rapid, inexpensive and robust screening to control the provenance of garlic samples.

Historical records of mercury in southern latitudes over 1600 years: Lake Futalaufquen, Northern Patagonia.

Mercury is released to the environment from natural and anthropogenic sources, and through atmospheric transport is distributed globally. Lake Futalaufquen (42.8°S) is an oligotrophic lake located in Los Alerces National Park (Northern Patagonia), providing a remote and unpolluted study system. A lacustrine sedimentary sequence revealed 1600 years of Hg deposition, identifying natural baselines and marked peaks not correlated with long-range atmospheric transport. Organic matter and catchment erosion were discarded as Hg drivers. Natural background, pre-1300 CE Hg concentrations, ranged between 27 and 47 ng g(-1) (accumulation rates from 8 to 15µg m(-2) y(-1)). From 1300 CE on, the Hg background profile did not follow the generally increasing Hg pattern observed in both Southern and Northern Hemisphere since pre-industrial times. It was not until the last century that a 1.6-fold increase is observed in the Hg accumulation rate, considered among the lowest increments in southern South America. Noteworthy local/regional sources of Hg for this area, along with global transport, are forest fires and volcanic activity. Between approx. 1340 and 1510 CE, sharp increase in Hg concentration and accumulation rate (up to 204 ng g(-1) and 51 µg m(-2) y(-1), respectively) were clearly associated with extended fire episodes. Furthermore, high Hg peaks during the last 300 years were associated with volcanic eruptions in northernmost Patagonia together with fairly irregular fire episodes, caused by anthropogenic burning by settling population in the Andes.

Influence of canopy drip on the indicative N, S and δ(15)N content in moss Hypnum cupressiforme.

Samples of Hypnum cupressiforme were collected at two types of site in forest areas: within the forest stand and within forest openings, and analyzed for N and S concentrations and δ(15)N. Mosses sampled within forest openings reflect the atmospheric N deposition; however, no influence of throughfall N deposition on the N in the moss that was sampled within the forest stand was found, nor was any influence of S deposition on the S in the moss found. For the N and S concentrations in the mosses sampled within forest openings, the within-site variability was comparable to the between-site variability, and for the δ(15)N, the within-site variability was lower than the between-site. The results showed that a short distance (<1 m) between the sampling location and the nearest tree canopy increases the N in the moss, and significantly higher values are found in mosses sampled in areas within the forest stand.

C and O stable isotopic signatures of fast-growing dripstones on alkaline substrates: reflection of growth mechanism, carbonate sources and environmental conditions.

Secondary carbonate precipitates (dripstones) formed on concrete surfaces in four different environments--Mediterranean and continental open-space and indoor environments (inside a building and in a karstic cave)--were studied. The fabric of dripstones depends upon water supply, pH of mother solution and carbonate-resulting precipitation rate. Very low δ(13)C (average-28.2‰) and δ(18)O (average-18.4‰) values showed a strong positive correlation, typical for carbonate precipitated by rapid dissolution of CO(2) in a highly alkaline solution and consequent disequilibrium precipitation of CaCO(3). The main source of carbon is atmospheric or biogenic CO(2) in the poorly ventilated karstic cave, which is reflected in even lower δ(13)C values. Statistical analysis of δ(13)C and δ(18)O values of the four groups of samples showed that the governing factor of isotope fractionation is not the temperature, but rather the precipitation rate.

Quality of white cabbage yield and potential risk of ground water nitrogen pollution, as affected by nitrogen fertilisation and irrigation practices.

BACKGROUND: The effect of different fertilisation (broadcast solid NPK application and fertigation with water-soluble fertiliser) and irrigation practices (sprinkler and drip irrigation) on yield, the nitrate content in cabbage (Brassica oleracea var. capitata L.) and the cabbage N uptake was detected, in order to assess the potential risk for N losses, by cultivation on sandy-loam soil. The N rate applied on the plots was 200 kg N ha(-1). RESULTS: The highest yield (93 t ha(-1)) and nitrate content (1256 mg kg(-1) DW) were found with treatments using broadcast fertilisation and sprinkler irrigation. On those plots the negative N balance (-30 kg N ha(-1)) was recorded, which comes mainly from the highest crop N uptake (234 kg N ha(-1)) indicating the lowest potential for N losses. CONCLUSION: In terms of yield quality and the potential risk for N losses, broadcast fertilisation combined with sprinkler irrigation proved to be the most effective combination among the tested practices under the given experimental conditions. The importance of adequate irrigation is also evident, namely in plots on which 50% drip irrigation was applied, the lowest yield was detected and according to the positive N balance, a higher potential for N losses is expected.

Nitrogen isotopic signature of vegetables from the Slovenian market and its suitability as an indicator of organic production.

The aim of this study was to obtain preliminary data on δ(15)N values in organically and conventionally grown vegetables available on the Slovenian market to determine whether there are any characteristic differences in δ(15)N values, which could be used as a marker to differentiate between organically and conventionally grown vegetables, namely vegetables grown with synthetic or organic nitrogen fertilisers. Therefore, 14 different varieties of organically and conventionally grown vegetables were analysed. The results obtained show clear differences in mean δ(15)N values between organically and conventionally grown vegetables (up to 6.3\permil). However, due to overlapping results, it was not possible to differentiate between organically and conventionally grown counterparts in eight vegetable varieties, despite the differences in mean δ(15)N values. The results obtained indicate that the method has several limitations. Hence, δ(15)N could be a reliable indicator for organic production, but nevertheless, the conclusion has to be validated by background information.

Can δ(15)N in lettuce tissues reveal the use of synthetic nitrogen fertiliser in organic production?

BACKGROUND: The nitrogen isotopic fingerprint (δ(15)N) is reported to be a promising indicator for differentiating between organically and conventionally grown vegetables. However, the effect on plant δ(15)N of split nitrogen fertilisation, which could enable farmers to cover up the use of synthetic fertiliser, is not well studied. In this study the use of δ(15)N in lettuce as a potential marker for identifying the use of synthetic nitrogen fertiliser was tested on pot-grown lettuce (Lactuca sativa L.) treated with synthetic and organic nitrogen fertilisers (single or split application). The effect of combined usage of synthetic and organic fertilisers on δ(15)N was also investigated. RESULTS: The δ(15)N values of whole plants treated with different fertilisers differed significantly when the fertiliser was applied in a single treatment. However, additional fertilisation (with isotopically the same or different fertiliser) did not cause a significant alteration of plant δ(15)N. CONCLUSION: The findings of the study suggest that the δ(15)N value of lettuce tissues could be used as a rough marker to reveal the history of nitrogen fertilisation, but only in the case of single fertiliser application. However, if the difference in δ(15)N between the applied synthetic and organic nitrogen fertilisers was > 9.1 ‰, the detection of split and combined usage of the fertilisers would have greater discriminatory power.

Effects of fish farm loading on sea grass Posidonia oceanica at Vrgada Island (Central Adriatic): a nitrogen stable isotope study.

Analyses of nitrogen stable isotopes in the marine sea grass Posidonia oceanica were used to investigate the influence of fish farming on the coastal ecosystem of Vrgada Island in the Murter Sea, Central Adriatic. The results show a statistically significant 15N enrichment (up to 4.7 per thousand at p < 0.005) in P. oceanica leaf and shoot tissues from fish cage sites with respect to the unaffected offshore reference site of Lumbarda Reef Flat (Kornati Islands). Heavy nitrogen enrichment was also detected in other benthic organisms analysed during this study and is attributed to the absorption and assimilation of 15N-enriched fish farm derived nitrogen waste.

Nutrient fluxes and sulfur cycling in the organic-rich sediment of Makirina Bay (Central Dalmatia, Croatia).

Fluxes of dissolved nutrients in the organic-rich sediment of Makirina Bay (Croatia) were estimated in in-situ incubation experiments and compared to those calculated from a diagenetic model based on the concentration vs. depth profiles in the pore water extracted from a sediment core at the same sampling site. Benthic fluxes observed in the in-situ experiment were strongly influenced by the decomposition of sedimentary organic matter by bacterial sulfate reduction and precipitation of authigenic pyrite and calcite. Assimilation of dissolved nitrate and ammonia within the sediment resulted in peculiar nitrate and ammonia concentration profiles. Differences between the benthic and diffusive fluxes indicated that the effects of bioturbation and irrigation, which were not taken into account in the model calculation of diffusive fluxes, should not be considered as negligible. They are, however, extremely difficult to estimate because of the heterogeneity of the sediment. Sulfate reduction in the pore water could not be detected, although it was obvious from pyrite precipitation and the isotopic compositions of different sedimentary sulfur species. It is suggested that reoxidation of sulfide and upward diffusion of sulfate from the sediment layer accumulated during past salt production can account for the scattered sulfate vs. depth profile. The distribution and stable isotope compositions of sedimentary sulfur species were studied in more detail. The influx of sulfate was explained by rapid sulfate reduction in the sediment. The sulfate reduction rate was highest in the upper part of the sediment column, as concluded from delta(34)S values. In lower horizons, the concentration of organic sulfur increased, while concentrations of sulfide decreased. The mirror-imaged concentration vs. depth profiles of sulfide and organic sulfur, as well as their stable isotopic compositions, show that they were formed simultaneously, most probably in competitive processes.

Influence of chloride and sediment matrix on the extractability of HgS (cinnabar and metacinnabar) by nitric acid.

The extractability of metacinnabar and cinnabar, alone or in the presence of some sediment components, with various concentrations of HNO3 (1, 4, 6, and 14 M) was studied. Both forms of HgS (0.2-0.3 mg HgS in 10-20 mL of acid) were insoluble in all HNO3 concentrations as pure compounds. The presence of FeCl3 enhanced solubility of both cinnabar and metacinnabar, especially when concentrated HNO3 was used for the extraction. As the same effect was not obtained in the presence of FeOOH, we concluded that chloride and not Fe3+ was responsible for HgS dissolution. In fact, addition of very low chloride concentration to concentrated HNO3 provoked partial (Cl>10(-4) M) or even total dissolution (Cl>10(-2) M) of HgS. In dilute HNO3 (4-6 M) cinnabar was much less affected by chloride addition than metacinnabar. Extraction of HgS by concentrated HNO3 in the presence of sediment of various salinities demonstrated that the amount of dissolved HgS increased with the increase of the sediment salinity (from freshwater to estuarine and marine sediment), confirming that chloride enhances dissolution of HgS. Removal of chloride by washing the sediment with Milli-Q water significantly reduced dissolution of added HgS during extraction by concentrated HNO3. These results demonstrate that conclusions based on the extraction schemes using concentrated HNO3 as single extractant or as the first extractant in the sequential extraction procedures can be biased. A verification of artifactual oxidation of HgS, when using more concentrated HNO3 as extractant, would help to verify reliability of the applied extraction procedure.

Total mercury, methylmercury and selenium in mercury polluted areas in the province Guizhou, China.

The province of Guizhou in Southwestern China is currently one of the world's most important mercury production areas. Emissions of mercury from the province to the global atmosphere have been estimated to be approximately 12% of the world total anthropogenic emissions. The main objective of this study was to assess the level of contamination with Hg in two geographical areas of Guizhou province. Mercury pollution in the areas concerned originates from mercury mining and ore processing in the area of Wanshan, while in the area of Quingzhen mercury pollution originates from the chemical industry discharging Hg through wastewaters and emissions to the atmosphere due to coal burning for electricity production. The results of this study confirmed high contamination with Hg in soil, sediments and rice in the Hg mining area in Wanshan. High levels of Hg in soil and rice were also found in the vicinity of the chemical plant in Quingzhen. The concentrations of Hg decreased with distance from the main sources of pollution considerably. The general conclusion is that Hg contamination in Wanshan is geographically more widespread, due to deposition and scavenging of Hg from contaminated air and deposition on land. In Quingzhen Hg contamination of soil is very high close to the chemical plant but the levels reach background concentrations at a distance of several km. Even though the major source of Hg in both areas is inorganic Hg, it was observed that active transformation of inorganic Hg to organic Hg species (MeHg) takes place in water, sediments and soils. The concentration of Hg in rice grains can reach up to 569 microg/kg of total Hg of which 145 microg/kg was in MeHg form. The percentage of Hg as MeHg varied from 5 to 83%. The concentrations of selenium can reach up to 16 mg/kg in soil and up to 1 mg/g in rice. A correlation exists between the concentration of Se in soil and rice, indicating that a portion of Se is bioavailable to plants. No correlation between Hg and Se in rice was found. Exposure of the local population to Hg may occur due to inhalation of Hg present in air (in particular in Hg mining area) and consumption of Hg contaminated food (in particular rice and fish) and water. Comparison of intake through these different routes showed that the values of Hg considerably exceed the USA EPA Reference Concentration (RfC) for chronic Hg exposure (RfC is 0.0004 mg/m(3)) close to the emission sources. Intake of Hg through food consumption, particularly rice and fish, is also an important route of Hg exposure in study area. In general, it can be concluded that the population mostly at risk is located in the vicinity of smelting facilities, mining activities and close to the waste disposal sites in the wider area of Wanshan. In order to assess the real level of contamination in the local population, it is recommended that biomonitoring should be performed, including Hg and MeHg measurements in hair, blood and urine samples.