Laëtitia Minguez

The integrated biomarker response revisited: optimization to avoid misuse.

The growing need to evaluate the quality of aquatic ecosystems led to the development of numerous monitoring tools. Among them, the development of biomarker-based procedures, that combine precocity and relevance, is recommended. However, multi-biomarker approaches are often hard to interpret, and produce results that are not easy to integrate in the environmental policies framework. Integrative index have been developed, and one of the most used is the integrated biomarker response (IBR). However, an analysis of available literature demonstrated that the IBR suffers from a frequent misuse and a bias in its calculation. Then, we propose here a new calculation method based on both a more simple formula and a permutation procedure. Together, these improvements should rightly avoid the misuse and bias that were recorded. Additionally, a case study illustrates how the new procedure enabled to perform a reliable classification of site along a pollution gradient based on biomarker responses used in the IBR calculations.

Early defense responses in the freshwater bivalve Corbicula fluminea exposed to copper and cadmium: Transcriptional and histochemical studies.

The aim of the present study was to measure the early effects of copper (10 and 50 μg L−1), cadmium (2, 10, and 50 μg L−1) and mixtures of these metals in the freshwater bivalve Corbicula fluminea exposed for 12 h in laboratory. Transcription levels of superoxide dismutase (SOD), catalase (CAT), selenium‐dependent glutathione peroxidase (Se‐GPx), pi‐class glutathione S‐transferase (pi‐GST), metallothionein (MT) in digestive gland and gills, and response of lysosomal system and neutral lipids in digestive gland were determined after the exposure period. Results showed that lysosomal system, neutral lipids content, and mRNA levels were modified, suggesting their early response against oxidative stress and their important role in cell integrity. The integrated biomarker response was calculated and showed that the effects of the combinations of Cu and Cd on the biomarker responses are additive. MT and pi‐GST mRNA expression correspond to the largest ranges of response. As efficient biomarkers should have an early warning capacity, SOD, CAT, Se‐GPx, pi‐GST, MT transcripts levels, lysosomal system, and neutral lipids could be used as biomarkers of metal contamination in the aquatic environment.

Toxicities of 48 pharmaceuticals and their freshwater and marine environmental assessment in northwestern France

A risk assessment for freshwater and marine ecosystems is presented for 48 pharmaceutical compounds, belonging to 16 therapeutic classes, and prescribed in northwestern France. Ecotoxicity data were obtained on two freshwater organisms, i.e., crustacean Daphnia magna and the green algae Pseudokirchneriella subcapitata, and on two marine organisms, i.e., the crustacean Artemia salina and the diatom Skeletonema marinoi. Measured environmental concentrations (MEC), in the Orne River and sea off Merville-Franceville in the Basse-Normandie region, were compared to the predicted environmental concentrations (PEC). Predicted no-effect concentrations (PNEC) were derived from acute data for each compound. Then, a risk assessment for each compound and the mixture was performed by calculating risk quotients (RQ as PEC or MEC/PNEC ratio). Results showed that no immediate acute toxicities were expected even if some compounds displayed strong toxicities at very low concentrations. Antibiotics, antidepressants, and antifungals would deserve attention because of their high or median ecological risk suspected on marine and freshwater ecosystems. Marine ecosystems would be more sensitive to pharmaceutical residues.

Interactions between parasitism and biological responses in zebra mussels (Dreissena polymorpha): Importance in ecotoxicological studies.

Given that virtually all organisms are hosts for parasites, the investigation of the combined effects of contamination and parasitism is important in the framework of aquatic bioindication procedures. To assess the impact of such multistresses at the host cellular level, we sampled parasitized zebra mussel (Dreissena polymorpha) populations from two sites in northeast France that presented different levels of contamination. Experimental groups were formed based on parasite species and host gender and tested by histochemistry and automated image analysis for biological responses, such as structural changes of the lysosomal system and neutral lipid accumulation. Infected organisms displayed smaller and more numerous lysosomes compared with uninfected congeners, and infection further elevated the effect of the chemical contamination on this biomarker. In contrast, co-infection of females with selected parasites did produce inverse results, i.e. a more developed lysosomal system and neutral lipid depletion. Our data, therefore, suggest that parasitism in zebra mussels represents a potential confounding factor in ecotoxicological studies and must be taken into account in environmental risk assessment studies.

Acute toxicity of 8 antidepressants: What are their modes of action?

Currently, the hazard posed by pharmaceutical residues is a major concern of ecotoxicology. Most of the antidepressants belong to a family named the Cationic Amphipathic Drugs known to have specific interactions with cell membranes. The present study assessed the impact of eight antidepressants belonging to selective serotonin reuptake inhibitors or serotonin norepinephrine reuptake inhibitors by the combination of multi-approaches (in vivo, in vitro, in silico) and gives some insights on the mode of action for these molecules. Antidepressants were from the most to the least toxic compound for Daphnia magna: Sertraline (EC50=1.15 mg L(-1))>Clomipramine (2.74 mg L(-1))>Amitriptyline (4.82 mg L(-1))>Fluoxetine (5.91 mg L(-1))>Paroxetine (6.24 mg L(-1))>Mianserine (7.81 mg L(-1))>Citalopram (30.14 mg L(-1)) and Venlafaxine (141.28 mg L(-1)). These acute toxicities were found correlated to Log Kow coefficients (R=0.93, p<0.001) and to cytotoxicity assessed on abalone hemocytes through the neutral red uptake assay (R=0.96, p<0.001). If narcosis as mode of action is typically expected during acute ecotoxicity bioassays, we showed by molecular modeling that particular interactions can exist between antidepressants and phosphatidylcholine, a major component of cell membranes, leading to a more specific mode of action corresponding to a potential acidic hydrolysis of ester functions.

Zebra mussel (Dreissena polymorpha) parasites: Potentially useful bioindicators of freshwater quality?

In environmental quality bioassessment studies, analysis of host-parasite interactions may well be a valuable alternative to classical macroinvertebrate sampling approaches. Herein, we investigated whether zebra mussel (Dreissena polymorpha) parasites could be useful biomonitoring tools. Mussel populations were sampled twice at two sites in northeastern France representing different levels of contamination and were characterized for parasite infection following standard histological methods. Our results indicated that sites of different environmental quality (i.e. chemical contamination) exhibited different parasite communities characterized by different trematode species and parasite associations. An additional significant finding was the positive correlation established between the prevalence of Rickettsiales-like organisms and metal contamination. Multivariate analyses were valuable in examining parasite communities.

Towards a better understanding of biomarker response in field survey: A case study in eight populations of zebra mussels

In order to provide reliable information about responsiveness of biomarkers during environmental monitoring, there is a need to improve the understanding of inter-population differences. The present study focused on eight populations of zebra mussels and aimed to describe how variable are biomarkers in different sampling locations. Biomarkers were investigated and summarised through the Integrated Biomarker Response (IBR index). Inter-site differences in IBR index were analysed through comparisons with morphological data, proteomic profiles and genetic background of the studied populations. We found that the IBR index was a good tool to inform about the status of sites. It revealed higher stress in more polluted sites than in cleaner ones. It was neither correlated to proteomic profiles nor to genetic background, suggesting a stronger influence of environment than genes. Meanwhile, morphological traits were related to both environment and genetic background influence. Together these results attest the benefit of using biological tools to better illustrate the status of a population and highlight the need of consider inter-population difference in their baselines.

Parasitism can be a confounding factor in assessing the response of zebra mussels to water contamination.

Biological responses measured in aquatic organisms to monitor environmental pollution could be also affected by different biotic and abiotic factors. Among these environmental factors, parasitism has often been neglected even if infection by parasites is very frequent. In the present field investigation, the parasite infra-communities and zebra mussel biological responses were studied up- and downstream a waste water treatment plant in northeast France. In both sites, mussels were infected by ciliates and/or intracellular bacteria, but prevalence rates and infection intensities were different according to the habitat. Concerning the biological responses differences were observed related to the site quality and the infection status. Parasitism affects both systems but seemed to depend mainly on environmental conditions. The influence of parasites is not constant, but remains important to consider it as a potential confounding factor in ecotoxicological studies. This study also emphasizes the interesting use of integrative indexes to synthesize data set.

Different Host Exploitation Strategies in Two Zebra Mussel-Trematode Systems: Adjustments of Host Life History Traits

The zebra mussel is the intermediate host for two digenean trematodes, Phyllodistomum folium and Bucephalus polymorphus, infecting gills and the gonad respectively. Many gray areas exist relating to the host physiological disturbances associated with these infections, and the strategies used by these parasites to exploit their host without killing it. The aim of this study was to examine the host exploitation strategies of these trematodes and the associated host physiological disturbances. We hypothesized that these two parasite species, by infecting two different organs (gills or gonads), do not induce the same physiological changes. Four cellular responses (lysosomal and peroxisomal defence systems, lipidic peroxidation and lipidic reserves) in the host digestive gland were studied by histochemistry and stereology, as well as the energetic reserves available in gonads. Moreover, two indices were calculated related to the reproductive status and the physiological condition of the organisms. Both parasites induced adjustments of zebra mussel life history traits. The host-exploitation strategy adopted by P. folium would occur during a short-term period due to gill deformation, and could be defined as “virulent.” Moreover, this parasite had significant host gender-dependent effects: infected males displayed a slowed-down metabolism and energetic reserves more allocated to growth, whereas females displayed better defences and would allocate more energy to reproduction and maintenance. In contrast, B. polymorphus would be a more “prudent” parasite, exploiting its host during a long-term period through the consumption of reserves allocated to reproduction.

Involvement of Apoptosis in Host-Parasite Interactions in the Zebra Mussel

The question of whether cell death by apoptosis plays a biological function during infection is key to understanding host-parasite interactions. We investigated the involvement of apoptosis in several host-parasite systems, using zebra mussels Dreissena polymorpha as test organisms and their micro- and macroparasites. As a stress response associated with parasitism, heat shock proteins (Hsp) can be induced. In this protein family, Hsp70 are known to be apoptosis inhibitors. Mussels were diagnosed for their respective infections by standard histological methods; apoptosis was detected using the TUNEL methods on paraffin sections and Hsp70 by immunohistochemistry on cryosections. Circulating hemocytes were the main cells observed in apoptosis whereas infected tissues displayed no or few apoptotic cells. Parasitism by intracellular bacteria Rickettsiales-like and the trematode Bucephalus polymorphus were associated with the inhibition of apoptosis whereas ciliates Ophryoglena spp. or the trematode Phyllodistomum folium did not involve significant differences in apoptosis. Even if some parasites were able to modulate apoptosis in zebra mussels, we did not see evidence of any involvement of Hsp70 on this mechanism.