Use of native mosses as biomonitors of heavy metals and nitrogen deposition in the surroundings of two steel works

A biomonitoring survey using the moss species Hypnum cupressiforme Hedw. was conducted in the surroundings of two steel plants located in the North of Spain. Levels of V, Cr, Ni, Cu, Zn, As, Cd, Hg, Pb and N were determined. Very high concentrations in the areas of study were detected when compared to nearby unaffected regions. Similar trends were observed for all the elements in the differently orientated transects, showing an appreciable influence of the NW prevailing winds of the region in the dispersion of pollutants, as well as a clear decreasing gradient in the concentrations of metals in mosses within a distance of 1500 meters from the facilities. A differentiation between the elements emitted by the chimney as result of the industrial activity (V, Cr, Ni, Cu and As) and those with a high presence in steel slag deposits (Zn, Cd, Hg and Pb) was observed. The range of contamination was also established by means of the Contamination Factor, indicating a category 4 out of 6 categories, which shows the high levels reported in the areas of study. A different dynamic was registered for nitrogen regarding the rest of the heavy metals analysed except for Hg, probably due to the elevated volatility and mobility of both elements, as well as their high persistence in the atmosphere.     

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.     

Future intensification of summer hypoxia in the tidal Garonne River (SW France) simulated by a coupled hydro sedimentary-biogeochemical model

Projections for the next 50 years predict a widespread distribution of hypoxic zones in the open and coastal ocean due to environmental and global changes. The Tidal Garonne River (SW France) has already experienced few episodic hypoxic events. However, predicted future climate and demographic changes suggest that summer hypoxia could become more severe and even permanent near the city of Bordeaux in the next few decades. A 3D model, which couples hydrodynamic, sediment transport, and biogeochemical processes, is applied to assess the impact of factors submitted to global and regional climate changes on oxygenation in the turbidity maximum zone (TMZ) of the Tidal Garonne River during low-discharge periods. The model simulates an intensification of summer hypoxia with an increase in temperature, a decrease in river flow or an increase in the local population, but not with sea level rise, which has a negligible impact on dissolved oxygen. Different scenarios were tested by combining these different factors according to the regional projections for 2050 and 2100. All the simulations showed a trend toward a spatial and temporal extension of summer hypoxia that needs to be considered by local water authorities to impose management strategies to protect the ecosystem.     

Some physical and chemical features of the variability of kd distribution coefficients for radionuclides

k_d distribution coefficients are widely used as a first approach to the understanding and determination of the eventual fate of metals and radionuclides released into the aquatic environment. For some radionuclides, k_d varies within a range of more than two orders of magnitude. Based on some physical and chemical aspects of the interactions between the dissolved and the particulate phases, some mathematical equations have been developed to explain some features of the observed k_d variability quantitatively. Thus, we have studied the decrease in particle size of k_d in the case of man-made radionuclides interacting with natural particles, and its increase in the case of naturally occurring radionuclides. For the latter, the dependence of k_d on the instantaneous water state has also been investigated. The study also shows the competition effects, particularly the dependence of k_d on pH and salinity. Finally, the effects produced by the size distribution of a given population of particles or the mixture of different populations, are also included. The present work provides for each situation, experimental support from literature data and/or modelling exercises.     

Phosphogypsum amendment effect on radionuclide content in drainage water and marsh soils from southwestern Spain

Phosphogypsum (PG) is a residue of the phosphate fertilizer industry that has relatively high concentrations of 226Ra and other radionuclides. Thus, it is interesting to study the effect of PG applied as a Ca amendment on the levels and behavior of radionuclides in agricultural soils. A study involving treatments with 13 and 26 Mg ha(-1) of PG and 30 Mg ha(-1) of manure was performed, measuring 226Ra and U isotopes in drainage water, soil, and plant samples. The PG used in the treatment had 510 +/- 40 Bq kg(-1) of 226Ra. The 226Ra concentrations in drainage waters from PG-amended plots were similar (between 2.6 and 7.2 mBq L(-1)) to that reported for noncontaminated waters. Although no significant effect due to PG was observed, the U concentrations in drainage waters (200 mBq L(-1) for 238U) were one order of magnitude higher than those described in noncontaminated waters. This high content in U can be ascribed to desorption processes mainly related to the natural adsorbed pool in soil (25 Bq kg(-1) of 238U). This is supported by the 234U to 238U isotopic ratio of 1.16 in drainage waters versus secular equilibrium in PG and P fertilizers. The progressive enrichment in 226Ra concentration in soils due to PG treatment cannot be concluded from our present data. This PG treatment does not determine any significant difference in 226Ra concentration in drainage waters or in plant material [cotton (Gossipium hirsutum L.) leaves]. No significant levels of radionuclides except 40K were found in the vegetal tissues.     

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 H?rsvatten Lake (Sweden).     

The development and application of remote sensing to monitor sand dune habitats

Sand dunes are complex systems that contain several habitats, often as mosaics or transitions between types. Several of these habitats are afforded protection under European Legislation and in the UK nationally within Special Areas of Conservation (SAC) and Sites of Special Scientific Interest (SSSI). Natural England has a statutory duty to report to Europe on the conservation status and condition of sand dunes; and is required to report to the UK Government on designated sites. To achieve this we have sought ways of capturing, analysing and interpreting data on the extent and location of sand dune habitats. This requires an ability to be able to obtain data over large areas of coastline in an efficient way. Natural England and Environment Agency Geomatics have worked collaboratively for over 16 years, sharing data and ecological knowledge. In 2012 work started to evaluate the use of remote sensing to map UK BAP and Annex I sand dune habitats. A methodology has now been developed and tested to map sand dune habitats. The key objective was to provide an operational tool that will help to map these habitats and understand change on sites around England. This has been achieved through analysis of LIDAR and Compact Airborne Spectrographic Imager (CASI) data using Object Orientated Image Analysis. Quality Control (QC) and accuracy assessments have shown this approach to be successful and 11 sites have been mapped to date. These techniques are providing a new approach to monitoring change in coastal vegetation communities and informing management of protected sites.     

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 ± 40 Bq kg⁻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 25 t PG ha⁻¹ with three replicates (each 0.5 ha 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 3.3 × 10² μBq m⁻³, implying negligible dose increment for exposed workers.