Is PCBs concentration variability between and within freshwater fish species explained by their contamination pathways?

Many chemical, physiological, and trophic factors are known to affect ioaccumulation of polychlorinated biphenyls (PCBs) in biota. Understanding the primary factors affecting fish contamination is critical for predicting and assessing risks to upper-trophic level consumers, including humans. Here we identify PCB contamination pathways that could explain within- and between-species variability in fish concentration levels. Three freshwater river fish species (barbel, chub and bream) were sampled at three sites along the Rhone River (France) where fish consumption is partially prohibited because of PCB levels exceeding the European health-based benchmark. The trophic position was assessed using an innovative approach based on stable isotope analyses and Bayesian inference, which takes into account both isotope data variability and parameter uncertainty. The effect of foraging habitat on fish contamination was addressed using stable isotope mixing models. The fish trophic position and PCB concentrations were found to be unrelated while the exploitation of sediment detrital carbon as a food source appeared to be a critical factor affecting fish contamination. Fish length, PCB concentration of the sediment, and individual fish foraging habitat (exploitation of detrital versus planktonic carbon sources) explained 80% of within- and between-species variability observed in PCB concentrations. These results, obtained for species that have overlapping TPs and exploit different carbon sources, reveal that the important factor in fish PCB contamination is not only what fish consume, but also and essentially the feeding location

Using the delta 13 C and delta 15 N of whitefish scales for retrospective ecological studies : changes in isotope signatures during the restoration of lake Geneva, 1980-2001

International audienc

Transfert des PCB du sédiment au biote: développement d'un modèle de bioaccumulation dans une perspective d'évaluation du risque

International audienceMany chemical, physiological and trophic factors are known to be important in the bioaccumulation processes and trophic transfer of PCB in the biota. Understanding the primary factors influencing PCB contamination of fishes is critical for predicting and assessing risks to upper-trophic levels consumers including humans. We proposed here to (1) identify PCB contamination pathways that could explain between and within species variability in fish concentration levels; and (2) describe PCB transfer along fish food chain. Three freshwater river fishes (Barbel, Bream and Chub) were sampled in three sites along the Rhone river (France), where fish consumption is partially prohibited because of many exceeding of the European sanitary level. We showed that diet habitat exploitation is an essential factor, the sediment compartment playing a central role in the contamination process. By combining stable isotope mixing models and stepwise regression, it appeared that fish length, PCB concentration in the sediment and foraging habitat (exploitation of detrital carbon sources) explained around 80% of the within- and between species variability observed in PCB concentrations. The main important factor in fish PCB contamination is thus not what fishes eat but rather how contaminated the food they consume is, suggesting that spatial gradients of contamination are more important than the type of food consumed and its trophic status. A bioaccumulation food-web model, based on physiological processes, was then developed in order to describe PCB transfer along the food chain of these fish species. The use of Bayesian Inference to calibrate the functions involved allowed to pass on data variability and parameter uncertainty to model predictions and provided a credibility interval around them. Results concerning model predictions and sensibility analyses are presented and discussed in a risk assessment perspective. By linking sediment to fishes contamination, our model can help in determining sediment management guidelines in the future

Trophic position and individual feeding habits as drivers of differential PCB bioaccumulation in fish populations

International audienceDespite PCBs being banned since the 1980's, some European peri-alpine lakes, and consequently their fish populations, are still contaminated by these xenobiotics. We investigated the relative contribution of physiological and trophic factors that could be implicated in fish PCB bioaccumulation in Lake Bourget (France), one of the most contaminated in Europe, by collecting Arctic char (n = 55) and European whitefish (n = 89) from 2013 to 2016. Concentrations of 7 indicator PCBs were 9–168 ng.g w.w−1 in whitefish and 90–701 ng.g w.w−1 in Arctic char. The fish trophic positions calculated from δ 15N values were positively correlated with PCB concentrations (r2 = 0.45; p < 0.001). A biomagnification model relying on TP and lipid content of fish was then designed, and it confirmed this result. A Bayesian mixing model based on δ 13C and δ 15N values was used to estimate the relative contribution of preys in the fish diet, which explained a significant proportion of the biomagnification model residuals (i.e., 17%). Zooplankton consumption was negatively correlated with PCB concentrations, whereas consumption of chironomids enhanced the PCB burden in fish. Correction of the biomagnification model for individual diets of fish increased the correlation between the predicted and measured fish PCB contents (R2 = 0.71; p < 0.001), highlighting the importance of fish feeding habits in the bioaccumulation process

What can high frequency measurements tell us about mixing events in lakes?

The dynamics of lake temperature structure, driven by the interplay of surface wind and heat fluxes, are crucial to many aspects of ecology. It has long been observed that this temperature structure is characterised by an isothermal ‘mixed’ layer at the top of a lake, varying in depth from centimetres to the full lake depth across different lakes and through different seasons. While the concept of this mixed layer is ubiquitous and the importance of rapid changes in it is acknowledged, there is no unique quantitative definition of a mixing depth or event. This hampers comparisons and also raises questions about definitiondependence of results. Widespread, multi-year, high frequency studies examining mixed depths and mixing events have not previously been possible. The recent proliferation in deployment of high resolution temperature sensors provides an exciting opportunity to compare differences in these physical features across many different lakes at both short and long time-scales to improve understanding of extrinsic and intrinsic drivers of mixing. It also highlights the need to understand the implications of the use of a wide variety of definitions of mixed depth and mixing events. Here we show data from three very different European lakes, to demonstrate the importance of considering the diel cycle in mixing, the large interannual variability in mixing and the influence that definition has on the interpretation of mixing. These results provide a starting point for a large-scale analysis of mixing across European lakes

A 4D sedimentological approach to reconstructing the flood frequency and intensity of the Rhône River (Lake Bourget, NW European Alps)

A high-resolution sedimentological study of Lake Bourget was conducted to reconstruct the flood frequency and intensity (or magnitude) in the area over the last 350 years. Particular emphasis was placed on investigating the spatio-temporal distribution of flood deposits in this large lake basin. The thicknesses of deposits resulting from 30 flood events of the Rhoˆne River were collected over a set of 24 short sediment cores. Deposit thicknesses were compared with instrumental data for the Rhoˆne River discharge for the period from 1853 to 2010. The results show that flood frequency and intensity cannot be reliably reconstructed from a single core because of the inhomogeneous flood-deposit geometry in such a large lake. From all documented flood-deposit thicknesses, volumes of sediment brought into the lake during each flood event were computed through a Kriging procedure and compared with the historical instrumental data. The results show, in this study, that reconstructed sediment volumes are well correlated to maximal flood discharges. This significant correlation suggests that the increase of embankment and dam settlements on the Rhoˆne River during the last 150 years has not significantly affected the transport of the smallest sediment fraction during major flood events. Hence, assessment of the flood-sediment volumes deposited in the large Lake Bourget is the only way to reliably reconstruct the flood frequency and intensity