On the use of 210Pb-based records of sedimentation rates and activity concentrations for tracking past environmental changes.

Lead-210 from natural atmospheric fallout is widely used in multidisciplinary studies to date recent sediments. Some of the 210Pb-based dating models can produce historical records of sediment accumulation rates (SAR) and initial activity concentrations (A0). The former have been profusely used to track past changes in the sedimentary conditions. Both physical magnitudes are differently affected by model errors (those arising for the partial or null accomplishment of some model assumptions). This work is aimed at assessing the effects on SAR and A0 of model errors in the CRS, CS, PLUM and TERESA dating models, due to random variability in 210Pb fluxes, which is a usual sedimentary condition. Synthetic cores are used as virtual laboratories for this goal. Independently of the model choice, SARs are largely affected by model errors, resulting in some large and spurious deviations from the true values. This questions their general use for tracking past environmental changes. A0 are less sensitive to model errors and their trends of change with time may reflect real changes in sedimentary conditions, as it is shown with some real cores from varved sediments.

Modelling the kinetic reactive transport of pollutants at the sediment-water interface. Applications with atmospheric fallout radionuclides.

Understanding the behaviour of particulate matter and chemicals at the sediment-water interface (SWI) is of interest in environmental studies and risk assessments. These processes are still poorly understood, and this work aims to gain relevant insights by using a kinetic reactive transport model. It merges early diagenetic processes and box models for the uptake kinetics. Numerical solutions have been found for synthetic scenarios and for studying real cases from the literature (210Pb and Chernobyl fallout radionuclides in Lake Sniardwy, Poland, and 7Be in sediments from Tema Harbour, Ghana). The study identifies a series of factors that dynamically interact to govern the final fate of tracers in the SWI region, leading to a wide diversity of behaviours. When a term of eddy diffusivity is included in the upper regions of the pore fluid, which seems feasible for some energetic scenarios, it is possible to explain the observed large penetration depths for Cs and Be, while high particle-reactive elements are retained in thinner sediment layers. Desorption from the sediment occurs through the pore fluid as diffusive fluxes. Transient depth profiles of tracer concentrations can last from months up to a year, and they can show subsurface maxima at positions unrelated with the accretion rate. In the application cases, the model explained a wide set of observational data that was beyond the capabilities of other approaches involving physical mixing of solids and equilibrium kd. This modelling study could provide useful guidance for future research works.

From floodplain to aquatic sediments: Radiogeochronological fingerprints in a sediment core from the mining impacted Sancho Reservoir (SW Spain).

The Sancho Reservoir (SW Spain) was built in 1962, about the time of maximum 137Cs fallout, and it has been affected by acid mine drainage (AMD) particularly since the mining cease in 2001. This is a unique scenario for studying the radiogeochronological fingerprints in AMD-affected sediments deposited over the former flood plain. A sediment core sampled in 2011 was analysed for bulk density, 137Cs, 239Pu, 240Pu, 210Pb, 226Ra, 228Ra, 234Th (238U) and 40K, and studied with various radiometric dating models. Bulk density revealed unsteady compaction and likely depositional events. The activity concentrations of 226Ra, 228Ra, 234Th (238U) and 40K were uniform down-core, but declining overall in the upper 0-25cm, revealing changes in provenance except for 238U, which increased in the top 10cm likely due to its supply by AMD. The AMD fingerprint was also found in the 239+240Pu/137Cs activity ratio, which increased in the top sediment layers. The 137Cs and 239+240Pu profiles show well defined peaks at the same depth, with inventories being about four times higher than the expected integrated atmospheric deposition in the area. The unsupported 210Pb (210Pbexc) showed a complex non-monotonic profile interrupted at several sections, particularly around the 137Cs peak. The whole dataset cannot be interpreted in terms of continuous sedimentation processes. Based upon correlated features in the bulk density and 210Pbexc profiles, a series of depositional events (likely linked to peaks in the rainfall records) have been identified in the core. These events date back to the period comprised since the construction of the dam until its increase in height in 1972, which likely displaced upstream the main depositional area of riverine loads, as inferred from sediment trap data. The CRS (with a reference date) and (a piecewise) CIC models have been used for complementing and discussing the chronology.

Radioecological assessment and radiometric dating of sediment cores from dynamic sedimentary systems of Pra and Volta estuaries (Ghana) along the Equatorial Atlantic.

The Volta and Pra estuaries (Ghana, West Africa) are dynamical sedimentary systems whose natural equilibrium is being affected by anthropogenic activities. This paper reports depth-distributions of 210Pb, 226Ra, 234Th, 40K, 228Ra and 137Cs for two sediment cores from these estuaries. Bulk densities were not steady-state and well correlated with 40K (p < 0.00005). Unsupported 210Pb profiles were incomplete, non-monotonic and showed large fluctuations. The assumptions involved in the common 210Pb-based dating models were not meet in these dynamical scenarios, and the use of 137Cs as a time-marker is difficult in Equatorial and South-Hemisphere countries due to its low fallout rates. Chronologies have been solved with the new 210Pb-based TERESA model, which operates with varying but statistically correlated fluxes and sediment accumulation rates (SAR). The core from the Volta reflects the conditions prevailing after the construction of the Akosombo Dam, with a mean SAR of 1.05 ± 0.03 g cm-2·y-1, while a higher value of 2.73 ± 0.06 g cm-2·y-1 was found in the Pra, affected by intense gold mining activities along its course. Radiological and radioecological assessments have been conducted by applying the UNSCEAR protocols and the ERICA model, respectively. The measured radionuclide concentrations do not pose any significant risk for the environment and human health.

Occupational dosimetric assessment (inhalation pathway) from the application of phosphogypsum in agriculture in South West Spain.

Phosphogypsum (PG) has been traditionally applied as Ca-amendment in saline marsh soils in SW Spain, where available PG has 710+/-40Bqkg(-1) of 226Ra. This work assesses the potential radiological risk for farmers through 222Rn exhalation from PG-amended soils and by inhalation of PG-dust during its application. A three-year field experiment was conducted in a commercial farm involving two treatments: control and 25tPGha(-1) with three replicates (each 0.5ha plots). The 222Rn exhalation rate was positively correlated with potential evapotranspiration, which explained 67% of the variability. Statistically significant differences between the control and PG treatments were not found for 222Rn exhalation rates, and mean values were within the lowest quartile of the typical range for 222Rn exhalation from soils. Airborne dust samples were collected during the application of PG and sugar-beet sludge amendments. The highest PG-attributable 226Ra concentration in the dust samples was 3.3x10(2)microBqm(-3), implying negligible dose increment for exposed workers.

Kinetic box models for the uptake of radionuclides and heavy metals by suspended particulate matter: equivalence between models and its implications.

In recent years an increasing experimental effort has been paid to the study of the sorption process of radionuclides and heavy metals by particulate matter in aquatic environments. This has led to the development of different kinetic box models. Most of them are variations of two basic approaches: one containing several (up to three) parallel reactions while the other involves consecutive reactions. All the reactions are reversible (irreversibility is contained as a particular case) with concentration independent coefficients. The present work provides analytical solutions and demonstrates that both approaches are mathematically equivalent. That is, both models produce the same analytical solution for the uptake curve (time course of the concentrations in the dissolved phase), which is illustrated using literature data. This result unifies the description of the observed behaviour, but it brings up the question of the physical meaning of the involved coefficients. Finally, the mathematical relationship developed here serves to discuss some limitations found in recent attempts in literature devoted to distinguish the actual uptake mechanism.

The importance of recording physical and chemical variables simultaneously with remote radiological surveillance of aquatic systems: a perspective for environmental modelling.

Modern nuclear metrological tools allow the remote surveillance of the radiological status of the aquatic systems, providing an important advance in the protection of the environment. Nevertheless, the significance of the radiological data could be highly improved through simultaneous recording of physical and chemical variables that govern the behaviour and bioavailability of radionuclides in these aquatic systems. This work reviews some of these variables from the point of view of the environmental modelling. The amount, nature and dynamics of the suspended loads and bottom sediments strongly influence the behaviour of particle-reactive radionuclides. The kinetics of this process has a very fast component, as it is shown from our recent studies with 241Am, 239Pu and 133Ba in several aquatic systems from southern Spain. Changes in pH, temperature and in the electrical conductivity are influencing the uptake kinetics and the final partitioning of the radioactivity. Water currents govern the radionuclide transport and dispersion. These points are illustrated with modelling exercises in the scenarios of the Suez Canal (Egypt) and the Härsvatten Lake (Sweden).

Trends of radionuclide sorption by estuarine sediments. Experimental studies using 133Ba as a tracer.

Sediments play an important (but still poorly understood) role in the dispersion and final fate of radionuclides and other hazardous materials in aquatic systems. Adopting an experimental point of view, the present work deals with the transfer of a radioactive tracer from water to sediments. Sediments and waters were sampled in the Odiel and Tinto estuaries (South-West Spain) with anthropogenic-enhanced 226Ra concentrations. 133Ba was used as a tracer since it is a gamma emitter and a good analogue of the environmental behaviour of 226Ra. Laboratory experiments have been carried out to quantify the uptake kinetics of 133Ba by sediments in aqueous suspensions and by sediment cores under a water column at rest. Depth distributions of 133Ba in sediments have been studied with different contact times and using sediment samples with different grain sizes. The results reveal an important and fast uptake by suspended sediments (up to 40% in 10 min with a 20 g l(-1) suspension) and sediment cores (up to 70% in a few minutes). The kinetics of the uptake by suspended sediments could be reasonably described by a model of two parallel and reversible reactions followed by a weakly-reversible reaction. The total uptake and the rate of reaction decreased with the increment of grain size. Furthermore, uptake following diffusion through the interstitial water was hardly detectable beyond 1 cm depth. For the case with more experimental results, the depth distribution could be reasonably described by the analytical solution based on the use of an effective diffusion coefficient (4.2 x 10(-12) m2 s(-1)) and the measured intrinsic distribution coefficient (kd = 63 +/- 6 l kg(-1)).

Experimental and modelling study on the uptake and desorption kinetics of 133Ba by suspended estuarine sediments from southern Spain.

Dispersion of pollutants in aquatic environments depends on their uptake by suspended solids. This work deals with the uptake kinetics of 133Ba (gamma-emitter and a good analogue of 226Ra) by suspended estuarine sediments (which can be resuspended into the water column under certain conditions). This study presents a wide set of tracing experiments, including second tracing, decantation and desorption processes. The purpose is to characterize 133Ba uptake by sediments and to investigate the use and limitations of box models in order to describe the uptake kinetics. Water and sediment samples were collected in the Huelva estuary (Spain), where environmental 226Ra concentrations have been increased by two phosphate fertilizer industries. Samples were characterized by granulometric, organic carbon content, cation exchange capacity and XRF-EP analyses. Results revealed three-step kinetics, with characteristic times of minutes, hours and days. These results enabled the selection and calibration of a suitable box model and facilitated the testing of its use as a fully predictive tool.

Constraints on the use of 137Cs as a time-marker to support CRS and SIT chronologies.

CRS and SIT are two (210)Pb-based models widely used in the radiometric dating of recent sediments. (210)Pb chronologies should be validated using at least one independent tracer, such as (137)Cs. This paper demonstrates that simple methods based on the identification of (137)Cs fallout peaks cannot provide a definitive support for CRS and SIT chronologies. Two main arguments will support this assertion: Firstly, the (137)Cs time-marks cannot support a CRS or SIT chronology if the derived sedimentation rates cannot explain the whole (137)Cs activity profile without postulating mixing. Secondly, the support by the (137)Cs time-marks for a given CRS or SIT chronology cannot be considered as definitive if other dating models can equally explain the whole set of data, thereby producing a different chronology. Several case studies selected from the literature are used to support the present discussion.

Experimental and modelling study of plutonium uptake by suspended matter in aquatic environments from southern Spain.

Kinetic transfer coefficients are important parameters to understand and reliably model the behaviour of non-conservative radionuclides in aquatic environments. This report pertains to a series of five radiotracer experiments on Pu uptake in natural aqueous suspensions of unfiltered waters from three aquatic systems in the south of Spain (Gergal reservoir, the Guadalquivir river, and the estuary of the Tinto river). The experimental procedure ensured the simulation of environmental conditions. Pu activity was measured by a liquid scintillation technique. The uptake curves, covering a period up to one week, are discussed with respect to numerical uptake kinetics models. The data suggest that in our experimental setting the main pathways for Pu uptake consist of two parallel and reversible reactions followed by a consecutive non-reversible reaction. Kinetic transfer coefficients were estimated by a fitting procedure and a comparative study was followed.

Intestinal obstruction in the elderly. Prognostic factors of mortality.

OBJECTIVES: To analyze mortality-related factors in elderly patients who were operated on for intestinal obstruction, and to determine whether advanced age worsened the morbidity and mortality rates. METHODS: In this prospective study we analyzed 188 patients older than 69 years who were operated on for intestinal obstruction. Group 1 consisted of 82 patients aged between 70 and 79 years, and group 2 consisted of 106 patients aged 80 years and older. We compared the distribution of clinical features and outcomes between the two groups, and determined factors related with mortality (chi-squared test with Yates' correction, Student's t test and multiple logistic regression analysis). RESULTS: The incidence of heart disease was 11% in group 1 and 35% in group 1 (p = 0.0003). There was no difference between the groups in any of the other factors analyzed. Univariate analysis identified as mortality-related factors perianesthetic risk (American Society of Anesthesiologists' Physical Status classification) (p = 0.0005), presence of metastases (p = 0.0001) and delay in surgery (t value = 3.043, p = 0.0027). CONCLUSIONS: Mortality due to surgery for intestinal obstruction in elderly patients is related to perianesthetic risk and delay in surgery. Older age does not increase the morbidity or mortality rates for this type of surgery.

La intervención o prevención secundaria del suicidio / Intervention or secondary prevention on suicide

Se analizan las posibilidades de intervenir para prevenir la conducta suicida dentro del marco de la prevención secundaria, planteada en tres puntos fundamentales: detectar a las personas acudan a algún centro donde se les preste ayuda y se les dé un tratamiento adecuado, tanto si aún no han intentado suicidarse, como si lo han hecho sin lograr sus propósitos. Se sistematizan veinte características principales para evaluar el riesgo de suicidio, y se plantea una serie de medidas fundamentales de aplicación clínica, encaminadas a la prevención secundária del suicidio