Effects of freshwater pollution on the genetics of zebra mussels (Dreissena polymorpha) at the molecular and population level

Mortality and toxicity of a commercial formulation of cypermethrin in Physalaemus gracilis tadpoles

This study evaluated the lethal, sublethal, and toxic of a commercial formulation of cypermethrin in the anuran species Physalaemus gracilis. In the acute test, concentrations of 100-800 μg L-1 were tested over 96 h. In the chronic test, cypermethrin concentrations recorded in nature (1, 3, 6, and 20 μg L-1) were tested for mortality and then used for the micronucleus test and erythrocyte nuclear abnormalities over a 7-days period. The LC50 determined for P. gracilis for the commercial cypermethrin formulation was 273.41 μg L-1. In the chronic test, a mortality of more than 50% was observed at the highest concentration (20 μg L-1), as it caused half of the tadpoles studied to die. The micronucleus test showed significant results at concentrations of 6 and 20 μg L-1 and recorded the presence of several nuclear abnormalities, indicating the genotoxic potential of the commercial cypermethrin formulation for P. gracilis. Cypermethrin presented a high risk to the species, indicating that it has the potential to cause several problems in the short and long term and to affect the dynamics of this ecosystem. Therefore, it can be concluded that the commercial formulation of cypermethrin had toxicological effects on P. gracilis.

Insights on the Organ-Dependent, Molecular Sexual Dimorphism in the Zebra Mussel, Dreissena polymorpha, Revealed by Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry Metabolomics

The zebra mussel, Dreissena polymorpha, is extensively used as a sentinel species for biosurveys of environmental contaminants in freshwater ecosystems and for ecotoxicological studies. However, its metabolome remains poorly understood, particularly in light of the potential molecular sexual dimorphism between its different tissues. From an ecotoxicological point of view, inter-sex and inter-organ differences in the metabolome suggest variability in responsiveness, which can influence the analysis and interpretation of data, particularly in the case where males and females would be analyzed indifferently. This study aimed to assess the extent to which the molecular fingerprints of functionally diverse tissues like the digestive glands, gonads, gills, and mantle of D. polymorpha can reveal tissue-specific molecular sexual dimorphism. We employed a non-targeted metabolomic approach using liquid chromatography high-resolution mass spectrometry and revealed a significant sexual molecular dimorphism in the gonads, and to a lesser extent in the digestive glands, of D. polymorpha. Our results highlight the critical need to consider inter-sex differences in the metabolome of D. polymorpha to avoid confounding factors, particularly when investigating environmental effects on molecular regulation in the gonads, and to a lesser extent in the digestive glands.

Spatial and seasonal use of biomarkers in dreissenids: implications for biomonitoring

In addition to pollution, organisms are exposed to natural variations of the biotic and abiotic factors of their environment. A battery of sub-cellular biomarkers has been measured seasonally in several populations of both Dreissena polymorpha and Dreissena rostriformis bugensis. To observe and understand the variability associated with biomarker responses, water physicochemistry, sediment contamination, and internal concentrations of contaminants in soft tissues were also considered. Results evidenced seasonal, inter-specific, and inter-populational variability of the measured responses, highlighting the needs (1) to acquire long-term data on the studied populations and (2) to incorporate environmental parameters and contamination in the interpretation of biological responses. From a biomonitoring perspective, significant relationships were identified between biomarkers, internal concentrations of contaminants in soft tissues, and sediment contamination in D. r. bugensis and, to a lesser extent, in D. polymorpha. The detailed interpretation of each biomarker of the battery measured is complex, but a global analysis of all biomarkers at once allows to obtain this signature of the contamination of the studied sites.

The toxic effects of in situ exposure of a native fish species (Anabas testudineus) to electronic waste pollution

In recent decades, crude recycling of electronic waste (e-waste) has caused serious pollution and threatened wild organisms in certain regions. It is therefore valuable to investigate the pollution-induced toxic effects in situ using native fish species. Unlike the death or decline observed in other species, Anabas testudineus can better adapt to severe e-waste pollution. Using it as a model, the true status of this wild organism was revealed. We collected A. testudineus from two polluted sites (st1 and st2) and conducted transcriptome analyses of the liver, gill, and kidney. Clear whole-transcriptome differences were found between polluted and clean sites and between differentially polluted sites (st1 and st2). Pathway analysis revealed that long-term e-waste pollution would cause significant hypoxia, oxidative stress, and potentially apoptosis. Accordingly, several defensive responses were elicited including 'oxidation-reduction' and the 'unfolded protein response'. Certain biological processes, including 'DNA repair' and 'endoplasmic reticulum stress response', were altered in a tissue- or burden-specific pattern suggesting transcriptome plasticity in response to distinct burdens. This study revealed the toxic impacts of e-waste pollution on wild organisms using a native fish species. Additionally, due to its highly adaptive nature, A. testudineus could be a suitable test species for such severe conditions in the wild or otherwise.

Micronucleus Experiments with Bivalve Molluscs

The micronucleus (MN) test, as an index of accumulated DNA damage during the lifespan of cells, is the most applied assay in aquatic animals to assess the exposure to a complex mixture of genotoxic pollutants. An increase in MN frequency was reported on mussels exposed to the most common environmental pollutants under laboratory conditions, such as heavy metals, polycyclic aromatic hydrocarbons, and ionizing radiation. The test was applied in a large number of biomonitoring studies in different geographic areas to identify the exposure to different classes of pollutants with good discrimination power and to evaluate the recovery effects after accidental pollution events. A standardized MN assay protocol in hemocytes and gill cells for use in bivalve species, including scoring of different cell types, necrotic and apoptotic cells and nuclear anomalies, was established following the “cytome approach”. The mussel MNcytome (MUMNcyt) assay, using the proposed detailed criteria for the identification of cell types, is suitable for application in experimental studies under controlled conditions and in biomonitoring programs in aquatic environments.