Search

Background: Several biomarkers developed from freshwater sentinel species are used to complement chemical assessment of freshwater ecosystems and improve the evaluation of their contamination levels. While active biomonitoring strategies allow to compare biological data in the field, the lack of assessment criteria to interpret biomarkers modulations restricts their application in freshwater biomonitoring surveys. For this purpose, the determination of threshold values emerges as a relevant approach to support the biomarker-based diagnosis within biomonitoring surveys. Based on the distribution of contamination baselines, a statistical approach was proposed to define threshold values of bioaccumulated concentrations in the sentinel species Gammarus fossarum. Although this methodology is limited to chemical databases, this approach could be adapted for defining threshold values at the biological level. This study aims to demonstrate the possibility of defining threshold values for different classes of biomarkers monitored in two freshwater sentinel species (Dreissena polymorpha, G. fossarum) and evidence the added value of such an approach in biomarker-based diagnosis. Results: For this purpose, the study benefited from exceptional environmental biomarker datasets acquired from mussels and gammarids caged in hundred environmental sites, representative of the diversity of French water bodies. Thanks to these environmental datasets, inhibition and/or induction thresholds could be defined for 8 biochemical, cellular, and molecular biomarkers of D. polymorpha and 25 peptide biomarkers of G. fossarum, not influenced by confounding factors. Threshold values were then applied to another biomarker dataset acquired from mussels and gammarids caged upstream and downstream four wastewater treatment plants (WWTPs). Several biomarkers were modulated both downstream and upstream of WWTPs, indicating a potential contamination not related to WWTPs. In contrast, some biomarkers were impacted exclusively downstream of the WWTPs, highlighting an impact of WWTP discharges on the aquatic fauna. Conclusions: This study demonstrates the possibility to define threshold values for a wide range of biomarkers (cellular, biochemical and molecular) monitored on different sentinel species. The definition of threshold values constitutes an attractive solution to support the application of biomarkers in active biomonitoring surveys and improve the biomarker-based diagnosis without the need of "reference sites". [ABSTRACT FROM AUTHOR]

The global dynamic spread of chemical contamination through the aquatic environment calls for the development of biomarkers of interest. Reproduction is a key element to be considered because it is related to the sustainability of species. Spermatogenesis is a complex process that leads to the formation of mature germ cells, whose steps and impairments need to be finely described in ecotoxicological analyses. The physiological process has been commonly described by histological analyses of gonads in different taxa. In the present paper, we describe the development of a novel technique to characterize spermatogenesis based on the analysis of the DNA content of germ cells by flow cytometry, using a DNA-intercalating agent. This new biomarker, referred to as an index of sexual maturity, proved relevant to describe the seasonal reproductive cycle of the zebra mussel, Dreissena polymorpha (Pallas, 1771), used as a sentinel species in the biomonitoring of continental waters and sensitive to highlight the reprotoxicity of carbamazepine (an anti-epileptic pharmaceutical) tested under ecosystemic conditions (mesocosms). [ABSTRACT FROM AUTHOR]

• OXPHOS and anaerobic metabolism-related markers varied between seasons in D. polymorpha. • Mussel responses to Cd and warming depended on the reproduction stage. • The reproductive cycle period accounted for 92 % of marker responses variance. Metal trace elements such as cadmium (Cd) are commonly present in ecosystems and could lead to impairment of mitochondrial functions and energy imbalance in aquatic organisms including molluscs. Combined exposure to increasing temperatures and Cd could enhance such an impact on animals. Seasonal fluctuations, such as temperature, and the corresponding reproduction cycle can affect biomarker responses. However, the reproduction cycle stage is rarely taken into account in ecotoxicological studies. Thus, this work aimed at understanding energy metabolism responses in a sentinel species, Dreissena polymorpha. Mussels were collected during the rest and the reproduction periods and were exposed to 10 μg.L−1 of cadmium (Cd) at two temperatures (in situ temperature and in situ temperature + 5°C) during 7 days. Energy metabolism was monitored by measuring reserves and energy nucleotides charge and by assessing aerobic and anaerobic metabolism markers, and upstream regulation pathways. Markers related to OXPHOS activity revealed seasonal variations under laboratory conditions. Conversely, adenylate nucleotides, glycogen, lipid and transcript levels of AMP-activated protein kinase, citrate synthase, ATP synthase and cytochrome b encoding genes remained steady after the acclimation period. No evident effect of Cd on energy metabolism markers was noticed for both exposures although the transcript level of succinate dehydrogenase and citrate synthase encoding genes decreased with Cd during the rest period. Cellular stress, revealed by lipid peroxidation and catalase mRNA levels, only occurred in Cd and warming co-exposed mussels during the reproduction period. These results suggest that contaminant impact might differ according to the reproduction cycle stage. The effect of confounding factors on biomarker variations should be further investigated to have a deeper knowledge of metabolism responses under laboratory conditions. [ABSTRACT FROM AUTHOR]

The Integrated Biomarker Response (IBR) is one of the most used index in biomonitoring, especially the IBRv2 integrating a reference condition. However, some limitations remain for its routine and large-scale use. The IBRv2 is proportional to the total number of biomarkers, is dependent on the nature of biomarkers and considers all biomarkers modulations, even small and biologically non-significant. In addition, IBRv2 relies on reference values but the references are often different between each study, making it difficult to compare results between studies and/or campaigns. To overcome these limitations, the present work proposed a new index called IBR-T ("Integrated Biomarker Response – Threshold") which considers the threshold values of biomarkers by limiting the calculation of the IBR value to biomarkers with significant modulations. The IBRv2 and the IBR-T were calculated and compared on four datasets from active biomonitoring campaigns using Dreissena polymorpha, a bivalve widely used in freshwater biomonitoring studies. The comparison between indices has demonstrated that the IBR-T presents a better correlation (0.907 < r2 < 0.998) with the percentage of biomarkers significantly modulated than the IBRv2 (0.002 < r2 < 0.759). The IBRv2 could not be equal to 0 (0.915 < intercept <1.694) because the value was dependent on the total number of biomarkers, whereas the IBR-T reached 0 when no biomarker was significantly modulated, which appears more biologically relevant. The final ranking of sites was different between the two index and the IBR-T ranking tends to be more ecologically relevant that the IBRv2 ranking. This IBR-T have shown an undeniable interest for biomonitoring and could be used by environmental managers to simplify the interpretation of large datasets, directly interpret the contamination status of the site, use it to decision-making, and finally to easily communicate the results of biomonitoring studies to the general public. [Display omitted] • A new Integrative biomarker response index – IBR-T – is proposed to improve IBRv2. • IBR-T integrates reference and threshold values. • IBR-T improves site classification and includes biological variation of biomarkers. • IBR-T appears more ecologically relevant and allows comparing studies and years. [ABSTRACT FROM AUTHOR]

• Dreissena polymorpha showed a short-term tolerance to warm stress. • A metabolic rate depression was highlighted in D. polymorpha exposed to hypoxia. • Time is crucial to consider to characterise tolerance windows to natural factors. Dreissena polymorpha is a sentinel freshwater mussel providing key functional ecosystemic services like nutrient recycling and suspended matter filtration. Global warming and especially extreme events imply rapid fluctuations of environmental parameters that sessile organisms could not escape. The increase occurrence of heat waves and the subsequent expansion of hypoxic areas could challenge the survival of mussels. This study provided a deeper knowledge of energy management and cellular function during thermal (+15 °C) or hypoxic (30% of dissolved oxygen saturation) stress for 7 days. A potential metabolic rate depression was highlighted in D. polymorpha under hypoxia through a decline in the mitochondrial activity and a constant AMP content over time. A contrasted pattern of response was observed in thermal-stressed mussels between 24 h and 7 days of exposure. A global increase of metabolic activity was noticed in mussels after 24 h while a return to control level was noticed at the end of the experiment. Although D. polymorpha is considered as a temperature tolerant species, a significant increase of ADP:ATP ratio, related to a decrease of mitochondrial activity and density, suggested an overwhelming of organisms. This study pointed to the importance of considering time of exposure to natural factor variations in tolerance window of organisms in a long-term changing environment. The apparent short-term tolerance of D. polymorpha could hide much more deleterious consequences, i.e. mortality, if abiotic stresses persist, as suggested by climate change models. [ABSTRACT FROM AUTHOR]