Nathalie Cottin

Historical Profiles of PCB in Dated Sediment Cores Suggest Recent Lake Contamination through the “Halo Effect”

We investigated the major sources of polychlorinated biphenyls (PCB) and interpreted the environmental fate processes of these persistent organic pollutants in the past and current PCB contamination of three large, urbanized, French peri-alpine lakes. Dated sediment cores were analyzed in order to reconstruct and compare the historical contamination in all three lakes. Stratigraphic changes of PCB contents and fluxes were considered as revealing the temporal dynamics of PCB deposition to the lakes and the distribution of the seven indicator congeners (further referred to as PCBi) as an indicator of the main contamination origin and pathway. Although located within a single PCB industrial production region, concentration profiles for the three lakes differed in timing, peak concentration magnitudes, and in the PCBi congeners compositions. PCBi fluxes to the sediment and the magnitude of the temporal changes were generally much lower in Lake Annecy (0.05-2 ng·cm(-2)·yr(-1)) as compared to Lakes Geneva (0.05-5 ng·cm(-2)·yr(-1)) and Bourget (5-290 ng·cm(-2)·yr(-1)). For all three lakes, the paramount contamination occurred in the early 1970s. In Lakes Annecy and Bourget, PCB fluxes have declined and plateaued at 0.5 and 8 ng·cm(-2)·yr(-1), respectively, since the early 1990s. In Lake Geneva, PCB fluxes have further decreased by the end of the XX(th) century and are now very low. For the most contaminated lake (Lake Bourget), the high PCBi flux (5-290 ng·cm(-2)·yr(-1)) and the predominance of heavy congeners for most of the time period are consistent with a huge local input to the lake. This still high rate of Lake Bourget is explained by transport of suspended solids from one of its affluents, polluted by an industrial point source. Intermediate historical levels and PCBi distribution over time for Lake Geneva suggest a mixed contamination (urban point sources and distant atmospheric transport), while atmospheric deposition to Lake Annecy explains its lowest contamination rate. The presently low contamination levels recorded in Lake Geneva correspond to atmospheric inputs, but the recent PCBi distribution of Lake Annecy, enriched in relatively heavy congeners, reveals a contamination by the neighboring Lake Bourget, following a halo effect of about 40 km radius.

Mass budget in two high altitude lakes reveals their role as atmospheric PCB sinks.

A mass budget of polychlorinated biphenyls (PCBs) was constructed for two altitude lakes located in the French Alps to (i) quantify inward and outward PCB flux over the entire year of 2012, (ii) hierarchize the dominant pathways of PCB transfers, and (iii) evaluate to what extent these pathways vary between both lakes. The annual PCB inputs were similar, and the glacial runoff and sediment-to-water exchange were negligible sources of PCBs to the water column relative to atmospheric deposition. The annual inputs were primarily introduced by snow deposition and transferred into the lakes during the few weeks of spring thaw. While the dominant deposition pathways were similar, the main processes by which the water column lost pollutants differed between the two lakes. Despite these differences, the mass budget revealed that PCB inputs exceeded outputs for both studied lakes and that the lakes acted as atmospheric PCB sinks for the surrounding mountain environment. The differences in the PCB distribution between the key compartments (sediment and water column) are most likely due to differences in the lacustrine internal processes.

Particle-Dissolved Phase Partition of Polychlorinated Biphenyls in High Altitude Alpine Lakes.

We investigated whether polychlorinated biphenyls (PCBs) partitioning between the dissolved and particulate phases in two high altitude alpine lakes was determined by the quantity, size structure, or composition of suspended particles. Within- and between-lakes differences in water-particulate phase partition coefficient (Kp) were not related to total suspended matter, phytoplankton biomass, or taxonomic composition. Yet, a seasonal relationship between Kp and Kow was detected for both lakes, revealing equilibrium of PCBs partition when lakes were ice covered. On the contrary, PCBs partitioning between particles and water appeared kinetically limited during the open water season. Partition is therefore mainly governed by thermodynamic laws during the ice-covered period, while none of the tested physical or biological parameters seemed to explain the distribution of these particle-reactive contaminants in the open water period. PCBs were always mainly associated with particulate matter, but partitioning within different particulate size-fractions varied between seasons and between years during open water periods. When ice cover is absent, PCBs were mainly adsorbed on microplankton, the largest phytoplanktonic size fraction, which is the least likely to get grazed by pelagic microconsumers.

Multi-contamination (heavy metals, polychlorinated biphenyls and polycyclic aromatic hydrocarbons) of littoral sediments and the associated ecological risk assessment in a large lake in France (Lake Bourget)

The lake littoral sediment is exposed to a large array of contaminants that can exhibit significant spatial variability and challenge our ability to assess contamination at lake scale. In this study, littoral sediment contamination was characterized among ten different sites in a large peri-alpine lake (Lake Bourget) regarding three groups of contaminants: 6 heavy metals, 15 polycyclic aromatic hydrocarbons and 7 polychlorinated biphenyls. The contamination profiles significantly varied among sites and differed from those previously reported for the deepest zone of the lake. An integrative approach including chemical and biological analyses was conducted to relate site contamination to ecological risk. The chemical approach consisted in mean PEC quotient calculation (average of the ratios of the contaminants concentration to their corresponding Probable Effect Concentration values) and revealed a low and heterogeneous toxicity of the contaminant mixture along the littoral. Biological analysis including both laboratory (microcosm assays) and in situ (Acetylcholine Esterase (AChE) and Glutathione S-Transferase (GST) activity measurements) experiments highlighted significant differences among sites both in the field and in laboratory assays suggesting a spatial variation of the biota response to contamination. Linear regressions were performed between mean PEC quotients and biological results to assess whether littoral ecological risk was explained by the contamination profiles. The results highly depended on the study benthic or pelagic compartment. Regarding autochthonous Corbicula fluminea, no significant relationship between mean PEC quotients and biomarker activity was found while a significant increase in AChE was observed on autochthonous chironomids, suggesting different stress among benthic organisms. Both AChE and GST in caged pelagic Daphnia magna showed a significant positive relationship with mean PEC quotients. This study underlines the importance of accounting for spatial variations in lake littoral sediment contamination and the need for performing an integrative approach coupling chemical, field and laboratory analyses to assess the ecological risk.

Performance of a compost biofilter containing earthworms to treat cheese whey

A compost biofilter enriched in earthworms was adapted to treat cheese whey produced by a dairy in a mountainous area of the French pre‐Alps. Until now, this type of installation has only been developed in mountain pasture areas and therefore only functions during the months of mountain pasture grazing, from May to September. The main goal of this study was to follow up pollutant removal performance after more than one year of operation. During the experiment, cheese whey loading varied from a few litres to 40 L m−2 d−1. Despite variations in the physical properties of the support media after 460 days of operation, whey removal performance was good. For COD and BOD, 80–88% of the loading mass and 70–80% of nitrogen and phosphorus was removed. In this experiment, the treated effluent could not meet the standards for discharge into rivers, but was a very effective and simple pretreatment. This study confirms the observations of previous experiments in mountain pastures both in France and Switzerland: a cheese whey volume of 20 L m−2 d−1 could be a basis for design, although the process can treat up to 40 L m−2 d−1 for seven days according to our results.

Bioconcentration may be favoured over biomagnification for fish PCB contamination in high altitude lakes

Abstract Cold aquatic ecosystems such as high altitude alpine lakes are expected to act as long-term sinks of polychlorinated biphenyls (PCBs), the burden of which might even be intensified by global warming. Because the physical, chemical, and biological structures of high altitude lakes are highly responsive to climate change, both PCB exposure and bioaccumulation are likely to be strongly altered in the near future. Yet, in the absence of mechanistic knowledge of the processes regulating fish contamination with PCB in such ecosystems, their fate cannot be predicted. The aim of this study was to investigate the relative roles of biomagnification and bioconcentration on the individual, seasonal, and between-site variability of fish PCB contamination in 2 alpine, high altitude lakes. The intra- and within-lake variability of fish PCBs was not related to differences in fish physiology (size, age, or lipid content) and only marginally tied to fish feeding habitats (assessed from fatty acid composition and δ13C) or trophic position (δ15N). These results suggested that the trophic pathway and biomagnification contributed little to the observed differences in fish PCB concentrations between lakes, seasons, and individuals. Moreover, the fish PCB levels did not depend on the total PCB concentration in the water, but the fish contamination dynamics during the spring thaw pointed to a significant role of dissolved PCBs during this season in both lakes. In high altitude lakes, low temperatures might contribute to kinetically limit equilibrium with dietary PCBs, thereafter favouring bioconcentration over biomagnification pathways by which fish become contaminated with PCBs.