Use of fish otoliths as a temporal biomarker of field uranium exposure.

This study aimed to determine uranium (U) pollution over time using otoliths as a marker of fish U contamination. Experiments were performed in field contamination (~20 µg L-1: encaged fish: 15d, 50d and collected wild fish) and in laboratory exposure conditions (20 and 250 µg L-1, 20d). We reported the U seasonal concentrations in field waterborne exposed roach fish (Rutilus rutilus), in organs and otoliths. Otoliths were analyzed by ICPMS and LA-ICP SF MS of the entire growth zone. Concentrations were measured on transects from nucleus to the edge of otoliths to characterize environmental variations of metal accumulation. Results showed a spatial and temporal variation of U contamination in water (from 51 to 9.4 µg L-1 at the surface of the water column), a high and seasonal accumulation in fish organs, mainly the digestive tract (from 1000 to 30,000 ng g-1, fw), the gills (from 1600 to 3200 ng g-1, fw) and the muscle (from 144 to 1054 ng g-1, fw). U was detected throughout the otolith and accumulation varied over the season from 70 to 350 ng g-1, close to the values measured (310 ng g-1) after high exposure levels in laboratory conditions. U in otoliths of encaged fish showed rapid and high U accumulation from 20 to 150 ng g-1. The U accumulation signal was mainly detected on the edge of the otolith, showing two U accumulation peaks, probably correlated to fish age, i.e. 2 years old. Surprisingly, elemental U and Zn signatures followed the same pattern therefore using the same uptake pathways. Laboratory, caging and field experiments indicated that otoliths were able to quickly accumulate U on the surface even for low levels and to store high levels of U. This study is an encouraging first step in using otoliths as a marker of U exposure.

Online monitoring and conditional regression tree test: Useful tools for a better understanding of combined sewer network behavior.

A good knowledge of the dynamic of pollutant concentration and flux in a combined sewer network is necessary when considering solutions to limit the pollutants discharged by combined sewer overflow (CSO) into receiving water during wet weather. Identification of the parameters that influence pollutant concentration and flux is important. Nevertheless, few studies have obtained satisfactory results for the identification of these parameters using statistical tools. Thus, this work uses a large database of rain events (116 over one year) obtained via continuous measurement of rainfall, discharge flow and chemical oxygen demand (COD) estimated using online turbidity for the identification of these parameters. We carried out a statistical study of the parameters influencing the maximum COD concentration, the discharge flow and the discharge COD flux. In this study a new test was used that has never been used in this field: the conditional regression tree test. We have demonstrated that the antecedent dry weather period, the rain event average intensity and the flow before the event are the three main factors influencing the maximum COD concentration during a rainfall event. Regarding the discharge flow, it is mainly influenced by the overall rainfall height but not by the maximum rainfall intensity. Finally, COD discharge flux is influenced by the discharge volume and the maximum COD concentration. Regression trees seem much more appropriate than common tests like PCA and PLS for this type of study as they take into account the thresholds and cumulative effects of various parameters as a function of the target variable. These results could help to improve sewer and CSO management in order to decrease the discharge of pollutants into receiving waters.

Assessment of erosion and sedimentation dynamic in a combined sewer network using online turbidity monitoring.

Eroded sewer sediments are a significant source of organic matter discharge by combined sewer overflows. Many authors have studied the erosion and sedimentation processes at the scale of a section of sewer pipe and over short time periods. The objective of this study was to assess these processes at the scale of an entire sewer network and over 1 month, to understand whether phenomena observed on a small scale of space and time are still valid on a larger scale. To achieve this objective the continuous monitoring of turbidity was used. First, the study of successive rain events allows observation of the reduction of the available sediment and highlights the widely different erosion resistance for the different sediment layers. Secondly, calculation of daily chemical oxygen demand (COD) fluxes during the entire month was performed showing that sediment storage in the sewer pipe after a rain period is important and stops after 5 days. Nevertheless, during rainfall events, the eroded fluxes are more important than the whole sewer sediment accumulated during a dry weather period. This means that the COD fluxes promoted by runoff are substantial. This work confirms, with online monitoring, most of the conclusions from other studies on a smaller scale.

Spatial and temporal variations in otolith chemistry and relationships with water chemistry: a useful tool to distinguish Atlantic salmon Salmo salar parr from different natal streams.

Otolith elemental (Sr:Ca, Ba:Ca, Mn:Ca, Mg:Ca and Rb:Ca) and isotopic (87Sr:86Sr) profiles from several annual cohorts of juvenile Atlantic salmon Salmo salar were related to the physico-chemical characteristics (chemical signatures, flow rate, temperature and conductivity) of their natal rivers over an annual hydrological cycle. Only Sr:Ca, Ba:Ca and 87Sr:86Sr in otoliths were determined by their respective ratios in the ambient water. Sr:Ca ratios in stream waters fluctuated strongly on a seasonal basis, but these fluctuations, mainly driven by water flow regimes, were not recorded in the otoliths. Otolith Sr:Ca ratios remained constant during freshwater residency at a given site and were exclusively related to water Sr:Ca ratios during low flow periods. While interannual differences in otolith elemental composition among rivers were observed, this variability was minor compared to geographic variability and did not limit classification of juveniles to their natal stream. Success in discriminating fish from different sites was greatest using Sr isotopes as it remained relatively constant across years at a given location.

Heavy metals and organochlorinated compounds in the European eel (Anguilla anguilla) from the Adour estuary and associated wetlands (France).

Heavy metals and organic pollutants were investigated in the Adour estuary (South West France) and associated wetlands using the European eel (Anguilla anguilla) as a bioindicator. Heavy metals (Cu, Cd, Zn, Pb, and Ag) were measured in soft tissue of yellow eels. Mercury (total Hg and MeHg) and organochlorinated compounds (7 PCBs, 11 OCPs) were analysed in muscle. Concentrations in muscle were in agreement with moderately contaminated environments in Europe and were below the norms fixed for eel consumption for heavy metals and OCPs. Analyses of liver showed a higher pressure of Ag and Zn in the downstream estuary than in the freshwater sites whereas Cd was lower in the estuary probably because of the salinity influence. According to quality classes 100% of eels from freshwater sites indicated clean or slightly polluted environments. However, total mercury concentrations were close to the thresholds fixed by the European Community in the downstream estuary, whereas the sum of PCBs was found to be greatly above the fixed value. 100% of the individuals from the estuary were classified in quality classes corresponding to polluted or highly polluted sites. These first results highlight the need of further investigations focused on mercury and PCBs in this area taking the seasonal temperature influence into account for a better understanding of the pollution distribution and the possible threat on the eel population from the Adour basin.

Simultaneous use of strontium:calcium and barium:calcium ratios in otoliths as markers of habitat: application to the European eel (Anguilla anguilla) in the Adour basin, South West France.

Sr:Ca and Ba:Ca ratios in water from the Adour estuary show a clear relationship with the salinity of the surrounding water for salinities <20, while ratios are almost constant above this level of salinity. A positive relationship was observed for the Sr:Ca ratio, whereas it was inverse for the Ba:Ca ratio. These two elemental ratios were measured in the otoliths of the European eels (Anguilla anguilla L.) using femtosecond laser ablation linked to an ICP-MS (fs-LA-ICP-MS). There was a direct relationship between the elemental ratios recorded in eel otoliths and those found in water from fresh and marine areas, suggesting that Sr:Ca and Ba:Ca ratios in eel otoliths can be used as markers of habitat in this estuary. Continuous profiling allowed the determination of three behaviour patterns in terms of habitat: freshwater, estuary and migratory individuals. Finally, the above results support the simultaneous use of both ratios for a better understanding of the migratory contingents and also as a relevant method to avoid a misidentification of environmental migratory history due to the presence of vaterite crystal in the otolith matrix.

Mercury methylation by a microbial community from sediments of the Adour Estuary (Bay of Biscay, France).

In order to study the influence of microorganisms on the mercury biogeochemistry, the metal content and the structure of microbial communities were determined in sediments from stations along the Adour Estuary. The comparison of the bacterial communities and their distribution in function of the environmental parameters by Canonical Correspondence Analysis (CCA) revealed the influence of metals on the bacterial communities structure. Sediments where the bacterial communities are mostly influenced by methylmercury were incubated in slurries with or without mercury, under oxic and anoxic conditions. Methylmercury production was detected in the anoxic biotic slurries with a net methylation yield of 0.3% after 24 h. CCA based on T-RFLP profiles revealed the impact of mercury addition on the bacterial communities structure. In addition, 17 bacterial strains, mainly sulphate-reducing bacteria involved in mercury methylation, were isolated and identified.

Multielemental speciation of trace elements in estuarine waters with automated on-site UV photolysis and resin chelation coupled to inductively coupled plasma mass spectrometry.

An integrated approach for the accurate determination of total, labile and organically bound dissolved trace metal concentration in the field is presented. Two independent automated platforms consisting of an ultraviolet (UV) on-line unit and a chelation/preconcentration/matrix elimination module were specifically developed to process samples on-site to avoid sample storage prior to inductively coupled plasma mass spectrometry (ICP-MS) analysis. The speciation scheme allowed simultaneous discrimination between labile and organic stable dissolved species of seven trace elements including Cd, Cu, Mn, Ni, Pb, U and Zn, using only 5ml of sample with detection limits ranging between 0.6ngl(-1) for Cd and 33ngl(-1) for Ni. The influence of UV photolysis on organic matter and its associated metal complexes was investigated by fluorescence spectroscopy and validated against natural samples spiked with humic substances standards. The chelation/preconcentration/matrix elimination procedure was validated against an artificial seawater spiked sample and two certified reference materials (SLRS-4 and CASS-4) to ensure homogenous performance across freshwater, estuarine and seawater samples. The speciation scheme was applied to two natural freshwater and seawater samples collected in the Adour Estuary (Southwestern, France) and processed in the field. The results indicated that the organic complexation levels were high and unchanged for Cu in both samples, whereas different signatures were observed for Cd, Mn, Ni, Pb, U and Zn, suggesting organic ligands of different origin and/or their transformation/alteration along estuarine water mixing.