Sediment quality in the Douro river estuary based on trace metal contents, macrobenthic community and elutriate sediment toxicity test (ESTT)

The aim of this study was to evaluate the sediment quality in the mesotidal Douro River estuarine environment, in order to identify areas where sediment contamination could cause ecosystem degradation. Samples were obtained in five locations and sediment characterised for grain size, total organic matter, total-recoverable metals (Al, Fe, Cu, Pb, Cr, Ni, Cd, Zn and Mn), as well as acid volatile sulfide (AVS) and simultaneously extracted metals (SEM). In situ effects were evaluated by examining the macrobenthic community structure. An elutriate sediment toxicity test (ESTT) was used to estimate the amount of metals and nutrients that could be exchanged with the water column through resuspension, and its positive or negative effects on the growth of the micro-alga Emiliania huxleyi in a 10 day test. Anthropogenic metal contamination was identified at the north bank of the Douro estuary, with deleterious effects on the macrobenthic community, namely decrease in number of species and diversity. This contamination could possibly also be toxic for water column organisms, in case of resuspension, as shown by the ESTT. Sediments from the salt marsh at the south bank showed an impoverished macrobenthic community and elutriate toxicity, which appeared to be due to anaerobic conditions. This study clearly shows the usefulness of the ESST approach to assess the biological effect of resuspension of estuarine sediments.     

Salt marsh plants as key mediators on the level of cadmium impact on microbial denitrification

The fate of excess nitrogen in estuaries is determined by the microbial-driven nitrogen cycle, being denitrification a key process since it definitely removes fixed nitrogen as N₂. However, estuaries receive and retain metals, which may negatively affect this process efficiency. In this study, we evaluated the role of salt marsh plants in mediating cadmium (Cd) impact on microbial denitrification process. Juncus maritimus and Phragmites australis from an estuary were collected together with the sediment involving their roots, each placed in vessels and maintained in a greenhouse, exposed to natural light, with tides simulation. Similar non-vegetated sediment vessels were prepared. After 3 weeks of accommodation, nine vessels (three per plant species plus three non-vegetated) were doped with 20 mg/L Cd²⁺ saline solution, nine vessels were doped with 2 mg/L Cd²⁺ saline solution and nine vessels were left undoped. After 10 weeks, vessels were dissembled and denitrification potential was measured in sediment slurries. Results revealed that the addition of Cd did not cause an effect on the denitrification process in non-vegetated sediment but had a clear stimulation in colonized ones (39 % for P. australis and 36 % for J. maritimus). In addition, this increase on denitrification rates was followed by a decrease on N₂O emissions and on N₂O/N₂ ratios in both J. maritimus and P. australis sediments, increasing the efficiency of the N₂O step of denitrification pathway. Therefore, our results suggested that the presence of salt marsh plants functioned as key mediators on the degree of Cd impact on microbial denitrification.     

Potential of the microbial community present in an unimpacted beach sediment to remediate petroleum hydrocarbons

The potential of the microbial communities present in the intertidal zone of an unimpacted beach (a beach that did not suffer any significant oil spill) to degrade hydrocarbons was investigated. For that, laboratory-based microcosms (50-ml flasks) were set up with sandy beach sediment spiked with crude oil and incubated with local seawater for 15 days in the dark. Three bioremediation treatments were tested (biostimulation (BS), autochthonous bioaugmentation (AB), and combined treatment of biostimulation + bioaugmentation (BS + AB)) and the results were compared with natural attenuation (NA). Visual inspection showed clearly an oil solubility increase (confirmed by a higher hydrocarbons concentration in supernatant solutions) for all tested treatments when compared to NA. Significant degradation of the oil, shown by different profiles of petroleum hydrocarbons, was also observed for the different treatments particularly for BS + AB. Therefore, the microbial community of this unimpacted beach sediment could respond to an oil spill, degrading hydrocarbons. But to increase the natural attenuation pace, obtained results indicated that BS + AB is an appropriate approach for the bioremediation of beaches recently impacted by an oil spill. The autochthonous microbial cultures can be obtained “before” or “after” the contamination of the target site, being inoculated into the site right after it contamination.     

Macrobenthic community in the Douro estuary: relations with trace metals and natural sediment characteristics

The relationship between macrobenthic community structure and natural characteristics of sediment and trace metal contamination were studied in the lower Douro estuary (Portugal, NW, Iberian Peninsula), using an innovative threefold approach (SQG, Sediment Quality Guidelines), metal normalization to Fe, and macrobenthic community structure. This study allowed detection of a clear signature of anthropogenic contamination, in terms of Zn, Cu, Pb, and Cr in the north bank of the estuary, which experiences high urban pressure. Using the SQG approach, metal concentrations above ERM (effects range-median) were observed only at one sampling station, but several stations had levels above ERL (effects range-low). The macrobenthic community had a low diversity, with only 19 species found in the entire estuarine area, dominated by opportunistic species. The granulometric distribution of the sediments (estimated from the combination of organic matter, Fe and Al) seemed to be the major structuring factor for the communities, establishing the natural macrobenthic distribution pattern. The metals (Zn, Cu, Pb, and Cr) seemed to act as a disturbing factor over the natural distribution, with deleterious consequences for the macrobenthic communities.     

The Role of a Salt Marsh Plant on Trace Metal Bioavailability in Sediments. Estimation By Different Chemical Approaches * (7 pp)

Goal, Scope and Background The presence or absence of vegetation can condition sediment characteristics. The main aim of this work was to investigate the influence of the sea rush Juncus maritimus on metal (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) availability to organisms living on or in estuarine sediments, from Douro River (NW Portugal), by comparing the characteristics and chemical behaviour of rhizosediments (collected within the plant assemblage) and those of sediment (collected around the plant). In order to evaluate whether and how sediment characteristics condition the role of plants on metal availability, sandy and muddy sediments colonised by J. maritimus were studied in parallel. Methods Metal availability was estimated by enzymatic digestion with pepsin (ED), which may provide an estimate of metal availability to organisms living at estuarine sediments. Nevertheless, since no consensus exists yet on the most suitable methodologies to estimate metal bioavailability in sediments, two more conventional approaches, BCR sequential extraction (SE) and AVS/SEM model, were also used, in parallel, and the information these approaches provided was compared with that provided by ED. Total-recoverable metal contents were determined by atomic absorption spectrophotometry after sediment digestion using a high-pressure microwave system. Results and Discussion Plants could concentrate metals around its roots and rhizomes. In addition, they were capable of oxidizing (release of oxygen by the roots) the anaerobic medium surrounding their roots in muddy sediment (reducing AVS). As sulphide oxidation renders metals (Cd, Cu, Ni, Pb and Zn) into more soluble forms, according to the AVS/SEM model, metals from muddy sites would be more available in rhizosediment than in sediment. The SE approach led to a similar conclusion. Nevertheless, the results provided by ED pointed at opposite conclusion, particularly for Cd and Zn, indicating less availability at rhizosediments than in the surrounding sediment. ED results were interpreted as a consequence of an enrichment of the rhizosediment in organic ligands exuded by the roots or liberated by dead plants. The effect of complexation of metals by organic compounds, which ED could not decompose/dissolve, seemed to overcome that caused by sediment oxidation. In general, a comparison of the information about metal availability by ED, SE, AVS/SEM, showed that it did not always match and in few cases it was even contradictory. Conclusion and Outlook Therefore, a thorough evaluation of the metal availability in sediments requires a combination of different chemical approaches, so as to take into consideration differences in ways of organism exposure (interstitial water and/or ingestion of sediment particles). - * The basis of this peer-reviewed paper is a presentation at the 9th FECS Conference on 'Chemistry and Environment', 29 August to 1 September 2004, Bordeaux, France.     

An assessment of the risks associated with PCDDs and PCDFs following the application of sewage sludge to agricultural land in the UK

A model has been developed to describe the transfer of PCDDs and PCDFs from sludge-amended soils to the human foodchain. The model is conservative and assumes that all foods consumed by an individual are derived from sludge-amended soils. Predicted concentrations of PCDDs and PCDFs in potatoes, cereals, root vegetables and leafy vegetables were in close agreement with mean concentrations reported in the food survey conducted by MAFF in the UK. Predicted concentrations in milk were well below the Maximum Tolerable Concentration adopted by MAFF. Assuming a half-life of ten years in sludge-amended soils, the maximum estimated incremental daily intake (IDI) predicted by the model following ten applications of sludge to agricultural land was 0.80 pg I-TEQ kg⁻¹ day⁻¹, representing an increase of approximately 45% on current levels of background exposure. For an individual whose diet is solely derived from sludge-amended soils, the total exposure is predicted to be approximately 181 pg I-TEQ day⁻¹ or 2.6 pg I-TEQ kg⁻¹ day⁻¹. This compares with an average background exposure of approximately 2 pg I-TEQ kg⁻¹ day⁻¹, well within the TDI of 10 pg I-TEQ kg⁻¹ day⁻¹ and indicates that the application of sewage sludge to agricultural land under the conditions assumed would not appear to present a significant health risk under the conservative scenarios considered in this assessment.     

Submicron particle-bound polycyclic aromatic hydrocarbons in the Polish teaching rooms: Concentrations, origin and health hazard

The goal of the work was to investigate the concentrations of the 16 US EPA priority polycyclic aromatic hydrocarbons(PAH) bound to submicrometer particles(particulate matter, PM_1) suspended in the air of university teaching rooms and in the atmospheric air outside. Two teaching rooms were selected in two Polish cities, Gliwice, southern Poland,and Warsaw, central Poland, differing with regard to the ambient concentrations and major sources of PM and PAH. The variabilities of indoor and outdoor 24-hr concentrations of PM_1-bound PAH, the ratio(I/O) of the indoor to outdoor 24-hr concentrations of PM_1-bound PAH, probable sources of PAH and the level of the hazard from the mixture of the 16 PAH(ΣPAH) to humans at both sites were analyzed. In both Warsaw and Gliwice, the mean concentrations of PM_1-bound ΣPAH were slightly higher in the atmospheric air than in the rooms. The indoor and outdoor concentrations of individual PAH in Gliwice were correlated,in Warsaw – they were not. Most probably, the lack of the correlations in Warsaw was due to the existence of an unidentified indoor source of gaseous PAH enriching PM_1 in phenanthrene, fluorene, and pyrene. Although the ambient concentrations of PM_1-bound PAH were low compared to the ones observed earlier at both sites, they were much higher than in other urbanized European areas. However, because of low mass share of heavy PAH in ΣPAH, the various indicators of the health hazard from the 16 PAH mixture were low compared to other regions.     

Applying deep learning to right whale photo identification

Photo identification is an important tool for estimating abundance and monitoring population trends over time. However, manually matching photographs to known individuals is time-consuming. Motivated by recent developments in image recognition, we hosted a data science challenge on the crowdsourcing platform Kaggle to automate the identification of endangered North Atlantic right whales (Eubalaena glacialis). The winning solution automatically identified individual whales with 87% accuracy with a series of convolutional neural networks to identify the region of interest on an image, rotate, crop, and create standardized photographs of uniform size and orientation and then identify the correct individual whale from these passport-like photographs. Recent advances in deep learning coupled with this fully automated workflow have yielded impressive results and have the potential to revolutionize traditional methods for the collection of data on the abundance and distribution of wild populations. Presenting these results to a broad audience should further bridge the gap between the data science and conservation science communities.     

Comparison of the role of the sea club-rush Scirpus maritimus and the sea rush Juncus maritimus in terms of concentration, speciation and bioaccumulation of metals in the estuarine sediment

The capability of Scirpus maritimus and of Juncus maritimus to accumulate metals and the role of each plant on the physico-chemical composition of sediments, from Douro river estuary (NW Portugal), were investigated through a year of plants' life. The contents of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were determined (by atomic absorption spectrophotometry) in sediment, rhizosediments (those in contact with each plant roots and rhizomes) and different tissues of S. maritimus and of J. maritimus. Both plants influenced the sediment composition (concentrating metals around its roots) and were able to bioaccumulate Cd, in spite of some seasonal variations in the metal levels in the system (both in rhizosediments and plants' roots). Therefore, both plants showed to have potential for Cd phytostabilization. S. maritimus could also concentrate Pb in its roots, probably by sorption on the root surface in (hydr)oxide forms, therefore, denoting capability for Pb phytostabilization.