Christelle Lopes

Caged Gammarus fossarum (Crustacea) as a robust tool for the characterization of bioavailable contamination levels in continental waters: towards the determination of threshold values.

We investigated the suitability of an active biomonitoring approach, using the ecologically relevant species Gammarus fossarum, to assess trends of bioavailable contamination in continental waters. Gammarids were translocated into cages at 27 sites, in the Rhône-Alpes region (France) during early autumn 2009. Study sites were chosen to represent different physico-chemical characteristics and various anthropic pressures. Biotic factors such as sex, weight and food availability were controlled in order to provide robust and comparable results. After one week of exposure, concentrations of 11 metals/metalloids (Cd, Pb, Hg, Ni, Zn, Cr, Co, Cu, As, Se and Ag) and 38 hydrophobic organic substances including polycyclic aromatic hydrocarbons (PAHs), polychlorobiphenyles (PCBs), pentabromodiphenylethers (PBDEs) and organochlorine pesticides, were measured in gammarids. All metals except Ag, and 33 organic substances among 38 were quantified in G. fossarum, showing that this species is relevant for chemical biomonitoring. The control of biotic factors allowed a robust and direct inter-site comparison of the bioavailable contamination levels. Overall, our results show the interest and robustness of the proposed methodological approach for assessing trends of bioavailable contamination, notably for metals and hydrophobic organic contaminants, in continental waters. Furthermore, we built threshold values of bioavailable contamination in gammarids, above which measured concentrations are expected to reveal a bioavailable contamination at the sampling site. Two ways to define such values were investigated, a statistical approach and a model fit. Threshold values were determined for almost all the substances investigated in this study and similar values were generally derived from the two approaches. Then, levels of contaminants measured in G. fossarum at the 27 study sites were compared to the threshold values obtained using the model fit. These threshold values could serve as a basis for further implementation of quality grids to rank sites according to the extent of the bioavailable contamination, with regard to the applied methodology.

WHAT TO DO WITH NOECS/NOELS—PROHIBITION OR INNOVATION?

This study attempted to be as realistic as possible when evaluating third-hand PAH residues resulting from 1 cigarette. Smokers were not asked to change their smoking habits, except to continuously hold the cigarette in 1 hand during the entire duration of the cigarette’s burning. Hand size (that is, the adsorptive surface area), duration of smoking, and environmental conditions such as wind, temperature, and humidity, in addition to other factors, may potentially influence PAH concentration. We conducted our third-hand smoke studies outdoors under environmental conditions, and therefore hypothesize that a similar study conducted in the more stable conditions of an indoor environment may reveal higher levels of contaminant residues on surfaces and smokers’ bodies. Moir et al. (2008) quantified PAH concentrations in second-hand tobacco smoke, defined as environmental tobacco smoke that is inhaled involuntarily or passively by someone who is not smoking. Using their study and our data set, we carried out a ‘‘back of the envelope’’ calculation to estimate the percentage of sidestream smoke (i.e., secondhand smoke) that becomes third-hand smoke. We conclude that the PAH inventory on 1 hand of a smoker represents 0.1% to 6% of that emitted from sidestream smoke. Third-hand PAH residues on a smoker’s hand represent only a fraction of the total PAH reservoir for a smoker (compared to residues on all exposed skin and clothing). We have begun to quantify this load of chemicals as the first step in assessing the potential for smokers to act as vectors for impairment of indoor air quality. To completely capture the health risk posed by third-hand smoke, further studies from our research group and others need to address the off-gassing or desorption potential of these compounds and more fully evaluate the significance of third-hand smoke residues in impairing indoor air quality and/or increasing PAH exposure to subpopulations such as children. A thorough ranking of the importance of this exposure route compared to other exposures modes (e.g., release of PAHs from cooking methods such as open fires, incense burning, indoor tobacco smoking, etc.) also remain to be quantified.

Vitellogenin-like protein measurement in caged Gammarus fossarum males as a biomarker of endocrine disruptor exposure: Inconclusive experience

A vitellogenin (Vg) mass spectrometry-based assay was recently developed to actively biomonitor and assess the exposure of the amphipod Gammarus fossarum to endocrine-disrupting chemicals in freshwater hydrosystems. This paper focuses on the appropriate use of this biomarker, which requires good knowledge of its basal level in males and its natural variability related to intrinsic biotic and environmental abiotic factors. To obtain the lowest biomarker variability, we first studied some of these confounding factors. We observed that the spermatogenesis stage did not have an impact on the Vg level, allowing flexibility in the choice of transplanted gammarids. In the second part of the study, males were transplanted in two clean stations for 21 days, with results indicating a spatial and temporal variability of Vg levels. These Vg changes could not be correlated to environmental factors (e.g., temperature, pH and hardness of waters). Vg induction was then assessed in 21 stations having various levels of contamination. Inductions were observed for only two of the impacted stations studied. Under reference and contaminated conditions, a high interindividual variability of Vg levels was observed in caged organisms, severely limiting the sensitivity of the biomarker and its ability to detect a significant endocrine-disruptor effect. This may be explained by unidentified environmental factors that should later be determined to improved the use of Vg as a biomarker in male G. fossarum. Moreover, as discussed in this paper, recent advancements regarding the pleiotropic functions of the Vg gene in some species may complicate the application of this biomarker in males of invertebrate species.

Toxicity of ivermectin on cladocerans: Comparison of toxic effects on Daphnia and Ceriodaphnia species

Interspecies differences in contaminant sensitivity are measured to assess environmental risk based on species sensitivity distribution. The present study was intended to demonstrate the importance of studying the effects of contaminants on the life-history traits of various species. To do this, we compared the effects of ivermectin on the survival, growth, and reproduction of two cladoceran species (Daphnia magna and Ceriodaphnia dubia) and two strains of D. magna (one Japanese and one European). Ivermectin is widely used against endo- and ectoparasites in livestock and pets and is known for its high toxicity. Local aquatic ecosystems can be contaminated due to direct excretion into surface waters, but few data are available about the chronic effects of ivermectin on aquatic organisms. Adult daphnids were exposed to concentrations from 0 to 1 ng/L. Our results show a significant effect on all the life-history traits measured and reveal inter- and intraspecies differences. The no-observed-effect concentration found for growth and reproduction is 0.0003 ng/L for D. magna versus 0.001 ng/L for C. dubia, and the lowest-observed-effect concentration is 0.001 ng/L for D. magna versus 0.01 ng/L for C. dubia. C. dubia is smaller than D. magna and appeared to be less sensitive to ivermectin. The European strain of D. magna exhibited less resistance than the Japanese strain. A bias in the sex ratio was observed for all strains tested.

Matrix Population Models as Relevant Modeling Tools in Ecotoxicology

Nowadays, one of the big challenge in ecotoxicology is to understand how individually measured effects can be used as predictive indices at the population level. A particular interesting aspect is to evaluate how individual measures of fitness and survival under various toxic conditions can be used to estimate the asymptotic population growth rate known as one of the most robust endpoint in population risk assessment. Among others, matrix population models are now widely recognized as a convenient mathematical formalism dedicated to the characterization of the population demographic health. They offer the advantage of simplicity, not only in the modeling process of underlying biological phenomena, but also in the sensitivity analyses and the simulation running. On the basis of different biological systems among aquatic animal species (from fish to zooplankton), we illustrate the use of matrix population models to quantify environmental stress effects of toxic type. We also show how critical demographic parameters for the population dynamics can be highlighted by sensitivity analyses. The first example will focus on coupled effects of food amount and exposure concentration on chironomid population dynamics in laboratory. The second example will exemplify the use of energy-based models coupled with matrix population ones to properly describe toxic effects on daphnid populations. Last, we will show how to introduce a spatial dimension in Leslie type models to describe space-specific aspects of contaminant induced population dynamics alteration with the case of brown trout population modeling at the river network scale.

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 bioaccumulation 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.

Cadmium sulfide quantum dots induce oxidative stress and behavioral impairments in the marine clam Scrobicularia plana

Cadmium sulfide (CdS) quantum dots have a number of current applications in electronics and solar cells and significant future potential in medicine. The aim of the present study was to examine the toxic effects of CdS quantum dots on the marine clam Scrobicularia plana exposed for 14 d to these nanomaterials (10 µg Cd L(-1) ) in natural seawater and to compare them with soluble Cd. Measurement of labile Cd released from CdS quantum dots showed that 52% of CdS quantum dots remained in the nanoparticulate form. Clams accumulated the same levels of Cd regardless of the form in which it was delivered (soluble Cd vs CdS quantum dots). However, significant changes in biochemical responses were observed in clams exposed to CdS quantum dots compared with soluble Cd. Increased activities of catalase and glutathione-S-transferase were significantly higher in clams exposed in seawater to Cd as the nanoparticulate versus the soluble form, suggesting a specific nano effect. The behavior of S. plana in sediment showed impairments of foot movements only in the case of exposure to CdS quantum dots. The results show that oxidative stress and behavior biomarkers are sensitive predictors of CdS quantum dots toxicity in S. plana. Such responses, appearing well before changes might occur at the population level, demonstrate the usefulness of this model species and type of biomarker in the assessment of nanoparticle contamination in estuarine ecosystems.

Transfer of PCBs from bottom sediment to freshwater river fish: a food-web modelling approach in the Rhône River (France) in support of sediment management.

Since 2005, restrictions have been because of fish consumption along the Rhone River because of high polychlorobiphenyl (PCB) concentrations, which have resulted inadverse economic consequences for professional fisheries in affected areas. French environmental authorities have expended considerable efforts to research sediment remediation strategies and development of sediment quality guidelines designed to protect the health of humans consuming Rhône River fish. Here we: (1) develop a bioaccumulation food-web model that describes PCB concentrations in three common freshwater fish species of the Rhône River, using Bayesian inference to estimate the input parameters; (2) test the predictive power of the model in terms of risk assessment for fish consumption; and (3) discuss the use of this approach to develop sediment quality guidelines that protect the health of humans consuming Rhône River fish. The bioaccumulation model predictions are protective for human consumer of fish and are efficient for use in risk assessment. For example, 85% of the predicted values were within a factor of 5 of measured CB153 concentrations in fish. Using sensitivity analyses, the major role played by sediment and diet behaviors on bioaccumulation process is illustrated: the parameters involved in the respiratory process (contamination from water) have little impact on model outputs, whereas the parameters related to diet and digestion processes are the most sensitive. The bioaccumulation model was applied to derive sediment concentrations compatible with safe fish consumption. The resulting PCB sediment thresholds (expressed as the sum of seven PCB indicator congeners) that are protective for the consumption of the fish species ranged from 0.7 to 3 ng/g (dw).

Statistical handling of reproduction data for exposure-response modeling.

Reproduction data collected through standard bioassays are classically analyzed by regression in order to fit exposure-response curves and estimate ECx values (x% effective concentration). But regression is often misused on such data, ignoring statistical issues related to (i) the special nature of reproduction data (count data), (ii) a potential inter-replicate variability, and (iii) a possible concomitant mortality. This paper offers new insights in dealing with those issues. Concerning mortality, particular attention was paid not to waste any valuable data-by dropping all the replicates with mortality-or to bias ECx values. For that purpose we defined a new covariate summing the observation periods during which each individual contributes to the reproduction process. This covariate was then used to quantify reproduction-for each replicate at each concentration-as a number of offspring per individual-day. We formulated three exposure-response models differing by their stochastic part. Those models were fitted to four data sets and compared using a Bayesian framework. The individual-day unit proved to be a suitable approach to use all the available data and prevent bias in the estimation of ECx values. Furthermore, a nonclassical negative-binomial model was shown to correctly describe the inter-replicate variability observed in the studied data sets.

Modelling algae–duckweed interaction under chemical pressure within a laboratory microcosm

Contaminant effects on species are generally assessed with single-species bioassays. As a consequence, interactions between species that occur in ecosystems are not taken into account. To investigate the effects of contaminants on interacting species dynamics, our study describes the functioning of a 2-L laboratory microcosm with two species, the duckweed Lemna minor and the microalgae Pseudokirchneriella subcapitata, exposed to cadmium contamination. We modelled the dynamics of both species and their interactions using a mechanistic model based on coupled ordinary differential equations. The main processes occurring in this two-species microcosm were thus formalised, including growth and settling of algae, growth of duckweeds, interspecific competition between the two species and cadmium effects. We estimated model parameters by Bayesian inference, using simultaneously all the data issued from multiple laboratory experiments specifically conducted for this study. Cadmium concentrations ranged between 0 and 50 μg·L(-1). For all parameters of our model, we obtained biologically realistic values and reasonable uncertainties. Only duckweed dynamics was affected by interspecific competition, while algal dynamics was not impaired. Growth rate of both species decreased with cadmium concentration, as well as competition intensity showing that the interspecific competition pressure on duckweed decreased with cadmium concentration. This innovative combination of mechanistic modelling and model-guided experiments was successful to understand the algae-duckweed microcosm functioning without and with contaminant. This approach appears promising to include interactions between species when studying contaminant effects on ecosystem functioning.