Responses of cytochrome P450, GST, and MXR in the mollusk Corbicula fluminea to the exposure to hospital wastewater effluents

Glutathione S-transferase activity facilitates rice tolerance to the barnyard grass root exudate DIMBOA

BACKGROUND

In paddy fields, the noxious weed barnyard grass secretes 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA) to interfere with rice growth. Rice is unable to synthesize DIMBOA. Rice cultivars with high or low levels of allelopathy may respond differently to DIMBOA.

RESULTS

In this study, we found that low concentrations of DIMBOA (≤ 0.06 mM) promoted seedling growth in allelopathic rice PI312777, while DIMBOA (≤ 0.08 mM) had no significant influence on the nonallelopathic rice Lemont. DIMBOA treatment caused changes in the expression of a large number of glutathione S-transferase (GST) proteins, which resulting in enrichment of the glutathione metabolic pathway. This pathway facilitates plant detoxification of heterologous substances. The basal levels of GST activity in Lemont were significantly higher than those in PI312777, while GST activity in PI312777 was slightly induced by increasing DIMBOA concentrations. Overexpression of GST genes (Os09g0367700 and Os01g0949800) in these two cultivars enhanced rice resistance to DIMBOA.

CONCLUSIONS

Taken together, our results indicated that different rice accessions with different levels of allelopathy have variable tolerance to DIMBOA. Lemont had higher GST activity, which helped it tolerate DIMBOA, while PI312777 had lower GST activity that was more inducible. The enhancement of GST expression facilitates rice tolerance to DIMBOA toxins from barnyard grass root exudates.

Chlorpromazine's impact on Mytilus galloprovincialis: a multi-faceted investigation

The antipsychotic chlorpromazine (Cpz) has raised concern as a pharmaceutical effluent due to its wide medical applications. Moreover, its potent pro-oxidant properties and impact on the cell viability of the marine mollusc Mytilus galloprovincialis, even at low concentrations (ng/L), have been noted. Based on this evidence, in this study, we investigated the physiological effects of Cpz on M. galloprovincialis, to elucidate its fate within the organism, in terms of bioaccumulation, biotransformation, byssus changes and stress responses of the cellular thiolome. Histological and indicators of vitality analyses were also performed to better evaluate the influence of the drug on the morphology and cell viability of the digestive gland. To this end, two different concentrations of Cpz (Cpz I (12 ng/L or 37 pM) and Cpz II (12 μg/L or 37 nM)) were administered to mussels over 14 days. Cpz accumulation in the digestive gland significantly increased with water concentration (BCF of Cpz I and Cpz II). Biochemical analyses indicated lysosomal dysfunction, reflected in elevated total Cathepsin D activity and compromised lysosomal membrane stability. Stress-related and metal-buffering proteins (GST and metallothionein) responded to both Cpz concentrations. Cpz I induced phase I biotransformation activity (CYP450-dependent EROD), while Cpz II triggered caspase-3 activation, indicative of detoxification overload. Histological analysis revealed digestive gland atrophy, epithelial thinning, haemocyte infiltration, and brown cell presence. Byssus analysis showed significant alterations. In conclusion, our study underscores Cpz-induced physiological and histological changes in M. galloprovincialis, posing potential implications for mussel health and confirming the utilisation of this mussel as an indication of Cpz ecotoxicity.

Triazophos-induced Respiratory and Behavioral Effects and Development of Adverse Outcome Pathway (AOP) for short-term Exposed Freshwater Snail, Bellamya Bengalensis

The physiological effects of triazophos were examined using respiratory and behavioral endpoints in Bellamya bengalensis under a 96-hour acute exposure regime. Physiological manifestation of respiratory stress was measured using the rate of oxygen consumption while behavioral toxicity was measured using crawling reflexes, touch response, and mucus production. The threshold effect values for LOEC (Lowest Observed Effect Concentration), NOEC (No Observed Effect Concentration), and MATC (Maximum Acceptable Toxicant Concentration) at 96 h were 0.40, 0.60, and 0.075 mg/l, respectively. Definitive 96 h acute exposures for both respiratory and behavioral endpoints tests were determined using a control group and concentrations ranging from 0.40 to 1.60 mg/l monitored for 24, 48, 72, and 96 h. Test organisms irrespective of exposure concentration demonstrated an initial rise in oxygen consumption rate after 24 h, followed by a progressive decrease in toxicant concentration and exposure period. The in silico structural analysis presents triazophos as having an electrophilic toxic structure similar to choline esterase inhibitors, and also capable of inducing oxidative stress. The AOP highlighted neurotoxicity and oxidative stress as plausible pathways of triazophos toxicity in mollusk species.

A multi-biomarker approach for the early assessment of the toxicity of hospital wastewater using the freshwater organism Daphnia magna

Hospital wastewater (HWW) contains different hazardous substances resulting from a combination of medical and non-medical activities of hospitals, including pharmaceutical residues. These substances may represent a threat to the aquatic environment if they do not follow specific treatment processes. Therefore, we aimed to investigate the effects of the untreated effluent collected from a general hospital in Mahdia City (Tunisia) on neonatal stages of the freshwater crustacean Daphnia magna. Test organisms were exposed to three proportions (3.12%, 6.25%, and 12.5% v/v) of HWW. After 48 h of exposure, a battery of biomarkers was measured, including the quantification of antioxidant enzymes [catalase (CAT) and total and selenium-dependent glutathione peroxidase (total GPx; Se-GPx)], phase II biotransformation isoenzymes glutathione-S-transferases (GSTs), cyclooxygenases (COX) involved in the regulation of the inflammatory process, and total cholinesterases (ChEs) activities. Lipid peroxidation (LPO) was measured to estimate oxidative damage. The here-obtained results showed significant decreases of CAT and GSTs activities and also on LPO content in daphnids, whereas Se-GPx activity was significantly increased in a dose-dependent manner. Impairment of cholinesterasic and COX activities were also observed, with a significant decrease of ChEs and an increase of COX enzymatic activities. Considering these findings, HWW was capable of inducing an imbalance of the antioxidant defense system, but without resulting in oxidative damage in test organisms, suggesting that peroxidases and alternative detoxifying pathways were able to prevent the oxidant potential of several drugs, which were found in the tested effluents. In general, this study demonstrated the toxicity of hospital effluents, measured in terms of the potential impairment of key pathways, namely neurotransmission, antioxidant defense, and inflammatory homeostasis of crustaceans.

Generational sensitivity alteration in Chironomus yoshimatsui to carbamate and pharmaceutical chemicals and the effect on Catalase, CYP450, and hemoglobin gene transcription

To ascertain the tolerance mechanisms of aquatic organisms to artificial chemicals, intergenerational sensitivity changes of Chironomus yoshimatsui to a carbamate pesticide (pirimicarb) and pharmaceutical chemical (diazepam) were investigated. The larvae (<48-h-old) in each generation were exposed to both chemicals for 48 h and then the surviving chironomids were cultured until the fifth generation (F0-F4) without chemical addition. The 48-h 50% effective concentration (EC₅₀) value of chironomids was determined for each generation. In the pirimicarb treatment group, the EC₅₀ values significantly increased in F3 and F4, and those in the diazepam treatment group slightly increased. Catalase, Cytochrome P450 and hemoglobin (Hb) mRNA levels were monitored to see whether these were related to the trans-generational sensitivity. Although the generalized linear model results showed that the sensitivity to diazepam was slightly increased in the diazepam treatment, we could not find any mRNA levels related to sensitivity alteration. In contrast, the model approach showed that the chironomids exposed to pirimicarb trans-generationally became tolerant with increasing Hb mRNA levels. Therefore, they might decrease their chemical stress by modifying Hb gene transcription.

Effects of Au/TiO2 metallic nanoparticles on Unio ravoisieri: assessment through an oxidative stress and toxicity biomarkers

Several studies have been performed on the effects of nanoparticles on aquatic life. However, most of them investigated marine organisms, not freshwater organisms. This study investigated biomarker responses after exposure for 48 h and 7 days to newly made gold and titanium dioxide (Au/TiO₂) metallic nanoparticles (MNPs) (100 and 200 μg·L^-1) using the freshwater bivalve mussel Unio ravoisieri. Biochemical analysis of the gills and digestive glands showed induction of oxidative stress following exposure of the bivalve to Au/TiO₂ MNPs. After 2 or 7 days of exposure to Au/TiO₂ MNPs, both utilized concentrations of Au/TiO₂ MNPs induce an overproduction of H₂O₂. Catalase and glutathione S-transferase activities and the malonedialdehyde content significantly increased in the presence of Au/TiO₂ MNPs, depending on the concentration and target organ. In contrast, acetylcholinesterase activity was significantly inhibited, indicating a discernible disturbance of the cholinergic system in the presence of Au/TiO₂ MNPs. The behavior of the freshwater mussel was altered by reducing the clearance rate. Therefore, U. ravoisieri can be used as a model species in laboratory studies to mirror the presence of MNPs, and the biomarker approach is important for detecting the effects of Au/TiO₂ MNPs. In addition, digestive gland is the target organ of Au/TiO₂NPs contamination.

Common and particular biochemical responses of Unio tumidus to herbicide, pharmaceuticals and their combined exposure with heating

The priority list of freshwater pollutants is increasingly amended by pharmaceuticals. Their impact on the aquatic biota can be modulated by the presence of typical pollutants, like pesticides, and/or abnormal heating. The aim of this study was to elucidate potentially hazardous impact of combined environmental factors on the freshwater mussels by analyzing various sets of biochemical markers. We treated the bivalve molluscs of Unio tumidus with non-steroidal anti-inflammatory drug diclofenac (Dc, 2 nM), calcium antagonist and antihypertensive drug nifedipine (Nf, 2 nM) or organophosphonate glyphosate-based herbicide Roundup MAX (Rn, 79 nM of glyphosate) at 18 °C as well as with the mixture of these substances at 18 °C (Mix) or 25 °C (MixT) during 14 days. The concentrations used were correspondent to the environmentally relevant levels. The biomarkers of stress and toxicity were evaluated in digestive gland, except the lysosomal membrane stability measured in hemocytes. Exposures caused an oxidative stress due to the decreased SOD and GST activities and GSH/GSSG ratio, increased levels of thiobarbituric acid-reactive substances and protein carbonyls (with some exceptions). Dc increased cathepsin D activity in lysosomes. Nf increased lysosomal membrane stability and caspase-3 activity. Rn caused a dramatic distortion of metallo-thiolome due to increased levels of GSH and metallothionein-related thiols (MTSH) as well as depletion of Zn, Cu and Cd in the composition of metallothioneins, and decreased Zn/Cu molar ratio in the tissue. The particular toxicity of Rn was also attested by decreased lysosomal membrane stability and cholinesterase activity. Canonical discriminant analysis separated Rn-, Mix- and MixT-groups from the joint set of C-, Dc- and Nf-groups. Generally, compound-specific effects were expressed in U. tumidus responses to the mixtures, but in MixT-group some effects were particular or extremely strong. Multi-marker approach and integrative analysis proved to be a useful tool for understanding possible future risks to freshwater mussels under a combination of xenobiotics and warming climate.

Elucidating multilevel toxicity response differences between tris(1,3-dichloro-2-propyl) phosphate and its primary metabolite in Corbicula fluminea

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and its primary metabolite, bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) are frequently detected in aquatic environments. However, information regarding the biotoxicity of these compounds to bivalves is limited. We explored the multilevel physiological responses of Corbicula fluminea to TDCIPP and BDCIPP. The results indicated that TDCIPP/BDCIPP bioaccumulation in bivalves was positively correlated with their hydrophobicity. Furthermore, the higher body burden of TDCIPP in digestive glands led to significantly higher levels of ethoxyresorufin-O-deethylase (EROD), glutathione S-transferase (GST), and P-glycoprotein (p < 0.05). Owing to different molecular structures of inducers, upregulations of cyp4, gstm1, and abcb1 mRNA exhibited different sensitivities to TDCIPP and BDCIPP. Although Phase-I and Phase-II biotransformation and the multixenobiotic resistance (MXR) system were activated to protect bivalves from TDCIPP or BDCIPP, digestive glands produced large amounts of reactive oxygen species (ROS). Moreover, oxidative stress, the percentage of apoptotic cells in digestive glands, and inhibition of siphoning behaviour in TDCIPP treatments were higher than those in BDCIPP treatments (p < 0.05), indicating that TDCIPP was more toxic to bivalves than BDCIPP. Lower bioaccumulation and rapid metabolism of BDCIPP in vivo may contribute to alleviating its toxicity. This research establishes a foundation for further understanding the differences between the toxic mechanisms of TDCIPP and its metabolites.

Responses of cytochrome P450, GST and MXR in the mussel Perna viridis to the exposure of Aureococcus anophagefferens

The brown tide formed by a microscopic alga called Aureococcus anophagefferens has a devastating effect on filter-feeding bivalves, however, the related toxic principle remains an open question. In this study, we found that A. anophagefferens cells could motivate detoxification associated genes including CYP450, GST, P-gp and MVP, and induce SOD activity in the mussel Perna viridis. D1-like and D2-like receptors were expressed at high level in the gills of P. viridis, however, D2-like receptor transcript was too low to detect in digestive gland. The exposure of A. anophagefferens did not lead to any significant alterations in the expression of D1-like and D2-like receptors in both gills and digestive gland. These findings suggested that A. anophagefferens exhibited cytotoxicity toward bivalves, but did not obviously disrupt the dopamine system at transcriptional level in the acute exposure. Further studies are warranted to explore the nature of toxic compounds in A. anophagefferens affected bivalves.

Application of Biomarker Tools Using Bivalve Models Toward the Development of Adverse Outcome Pathways for Contaminants of Emerging Concern

As contaminant exposures in aquatic ecosystems continue to increase, the need for streamlining research efforts in environmental toxicology using predictive frameworks also grows. One such framework is the adverse outcome pathway (AOP). An AOP framework organizes and utilizes toxicological information to connect measurable molecular endpoints to an adverse outcome of regulatory relevance via a series of events at different levels of biological organization. Molecular endpoints or biomarkers are essential to develop AOPs and are valuable early warning signs of the toxicity of pollutants, including contaminants of emerging concern. Ecological risk-assessment approaches using tools such as biomarkers and AOPs benefit from identification of molecular targets conserved across species. Bivalve models are useful in such approaches and integral to our understanding of ecological and human health risks associated with contaminant exposures. We discuss the value of using biomarker approaches in bivalve models to meet the demands of twenty-first-century toxicology. Environ Toxicol Chem 2020;39:1472-1484. © 2020 SETAC.

Transcriptomic responses of the clam Meretrix meretrix to the organophosphorus pesticide (dimethoate)

Organophosphorus pesticides (OPs) play a certain role in promoting the development of agriculture and forestry, but they may cause potential harm to aquatic life when entering rivers and polluting water sources. Previous researches have shown that OPs participate in the regulation mechanism of aquatic organisms. Here, our aim is to determine the underlying mechanisms of one OP (dimethoate) at the transcriptional level using the clam Meretrix meretrix. 4119 DEGs were obtained from high-throughput RNA sequencing data. Then, expression profiles of some genes were verified by qPCR, which showed a positive correlation with the RNA sequencing results. 14,481 simple sequence repeats were also identified and could be further used as molecular markers. In addition, some oxidative, immune, and stress-related genes were further discussed and could also be used as biomarkers to indicate the biological response of dimethoate. This study will help to better understand the clam's response mechanism to dimethoate stress.

Combined toxicity of organophosphate flame retardants and cadmium to Corbicula fluminea in aquatic sediments

Organophosphate flame retardants (OPFRs), as alternatives to polybrominated biphenyl ethers (PBDEs), are frequently detected in various environmental matrices. Owing to urbanization and industrial pollution, co-contamination of OPFRs and heavy metals is ubiquitous in the environment. The toxicity of OPFRs in aqueous phase is a significant concern, but uncertainty still exists regarding the co-toxicity to benthic organisms of OPFRs and metals in sediments. Hence, we explored the physiological response of Corbicula fluminea to OPFRs and Cd in sediments. The results indicated that the antioxidant system in the clams was stimulated in the presence of OPFRs and Cd, and the oxidative stress increased with increasing concentrations of OPFRs. In contrast, the cytochrome P450 (CYP450) content and acetylcholinesterase (AChE) activity were reduced by exposure to both OPFRs and Cd. The cytochrome P450 4 family (CYP4) mRNA expression and OPFR toxicity were lower than those in previously reported experiments conducted in the water phase. Moreover, the expression levels of metallothionein (MT) and AChE mRNA decreased when OPFRs and Cd were present together. The highest integrated biomarker response (IBR) index (IBR = 15.41) was observed in the presence of 45 mg kg^-1 Cd + 200 mg kg^-1 OPFRs, rather than the 45 mg kg^-1 Cd + 400 mg kg^-1 OPFRs treatment (IBR = 9.48). In addition, CYP450 and AChE in the digestive glands of C. fluminea exhibited significant correlations with the concentration of the OPFR/Cd mixture (p < 0.01) and could be effective biomarkers for OPFR and Cd co-contamination. The results potentially contribute to more realistic predictions and evaluations of the environmental risks posed by OPFRs in aquatic sediments contaminated with heavy metals, particularly with respect to the risk to benthic organisms.

Adverse effects of two pharmaceuticals acetaminophen and oxytetracycline on life cycle parameters, oxidative stress, and defensome system in the marine rotifer Brachionus rotundiformis

To investigate the adverse effect of two widely used pharmaceuticals, paracetamol (acetaminophen [APAP]) and oxytetracycline (OTC) on the marine rotifer Brachionus rotundiformis (B. rotundiformis), the animals were exposed to various environmentally-relevant concentrations. Up to date, acetaminophen and oxytetracycline have been considered as toxic, if used above threshold concentration, i.e. overdosed. However, this study demonstrated these two pharmaceuticals even at low concentration (i.e., μg/L scale) elicited oxidative stress through the generation of reactive oxygen species (ROS) along with the increased glutathione S-transferase activity, despite no-observed effect in in-vivo population growth. To validate the adverse effects of the two pharmaceuticals at relatively low concentrations, mRNA expression analysis was performed of the entire set of genes encoding 26 cytochrome P450s (CYPs) of phase I and 19 glutathione S-transferases (GSTs) of phase II of the rotifer B. rotundiformis. The mRNA expression analysis suggested specific genes CYP3045A2 and GSTσ1, GSTσ4, and GSTω1 take part in detoxification of APAP and OTC, resulting in no significant changes in the population growth and undetermined no observed effect concentration (NOEC) in the marine rotifer B. rotundiformis.

Evaluation of psychiatric hospital wastewater toxicity: what is its impact on aquatic organisms?

The primary source of pharmaceuticals to the aquatic environment is the discharge of wastewater effluents. Pharmaceuticals are a large and diverse group of compounds. Among them, psychotropic substances are particularly interesting to study due to their specific known mode of action. The present study was performed to investigate the effects of wastewater effluents from a psychiatric hospital wastewater treatment plant (WWTP) on several aquatic organisms. All the analyzed pharmaceuticals (10 compounds) were detected in WWTP effluents as well as in the receiving river. Although the environmental concentrations were generally at trace levels (ng L^-1 to μg L^-1), induce toxic effects were observed. This study showed the effects of the WWTP effluents on the oogenesis and/or embryogenesis of amphipod crustacean Gammarus fossarum, Japanese fish medaka Oryzias latipes, mollusk Radix peregra, and planarian Schmidtea polychroa. A decrease of the number of oocytes and produced embryos was observed for G. fossarum and S. polychroa. Similarly, the hatching rate of R. peregra was affected by effluents. In the receiving river, the macroinvertebrate community was affected by the wastewater effluents discharge.

Biological toxicity response of Asian Clam (Corbicula fluminea) to pollutants in surface water and sediment

As a typical test species, Asian Clam (Corbicula fluminea) is widely used in the identification and evaluation of freshwater toxicity. This study provides a summary of the research published from 1979 to 2018. The focus was on the bioaccumulation, morphological and behavioral changes, and biochemical index alterations of Corbicula fluminea to target pollutants (i.e., ammonia, metal(loid)s, and organic chemicals) in surface water and sediment. The applications on the evaluation of actual aquatic pollution, determination of toxicological mechanisms, prediction of toxicity, and bioremediation are also specifically discussed. The primary purpose is to facilitate the comprehensive understanding and accurate application of Corbicula fluminea in freshwater ecotoxicological studies.

Assessment of Lemna minor (duckweed) and Corbicula fluminea (freshwater clam) as potential indicators of contaminated aquatic ecosystems: responses to presence of psychoactive drug mixtures

The pharmaceutical products are emerging pollutants continuously released into the environment, because they cannot be effectively removed by the wastewater treatment plants. In recent years, questions have been raised concerning the environmental risks related to these pollutants. The goal of this research was to evaluate the responses in Lemna minor after 7 days and in Corbicula fluminea after differing durations (1, 3, 7, and 19 days) of exposure to the psychoactive drug mixture (valproic acid, citalopram, carbamazepine, cyamemazine, hydroxyzine, oxazepam, norfluoxetine, lorazepam, fluoxetine, and sertraline) in different concentrations (0, 0 + ethanol, drug concentration (DC) 1 = river water concentration, DC2 = effluent concentration, and DC3 = 10× effluent concentration). In this aim, growth parameters of L. minor, gluthathione S-transferase (GSTs), catalase (CAT), ethoxyresorufin-O-deethylase (EROD) and/or gene expressions (pi-gst, cat, cytochrome P450 4 (cyp4), multidrug resistant 1 (mdr1), and superoxide dismutase (sod)) were measured. GST activities increased significantly in L. minor exposed to DC3, but no changes were found in CAT activity. In C. fluminea, EROD activity was induced significantly in both gill and digestive gland tissues after 3 days' exposure to DC3, while a GST increase was observed only in digestive gland tissues, suggesting that these pharmaceuticals induced an oxidative effect. Gene expression analysis revealed transient transcriptomic responses of cyp4, sod, and mdr1 under drug concentrations 2 or 3 and no change of expression for the other genes (cat and pi-gst) or condition (environmental drug concentration) tested. Finally, the data reported in this study represent important ecotoxicological information, confirming that this enzyme family (cyp4, sod, and mdr1) may be considered as a sensible and early indicator of exposure to drugs and emphasizing the involvement of selected genes in detoxification pathways.

Exposure to the environmentally-persistent insecticide chlordecone induces detoxification genes and causes polyp bail-out in the coral P. damicornis

Marine ecosystems are both stressed and threatened by pesticides that are used on land. Nevertheless, research on the impact of pesticides on coral reefs and the underlying mechanisms is still in its infancy. The insecticide chlordecone is a persistent organic pollutant with carcinogenic effects in rats and mice. Chlordecone has been detected in diverse marine organisms in the Caribbean, but unexpectedly, also in French Polynesia. We combined transcriptomic and morphologic analyses of analyses the response of the coral Pocillopora damicornis to chlordecone stress. We compared chlordecone stress with thermal stress to determine a chlordecone-specific response. We found eight transcripts related to the P450-1A or P450-3A families that were specifically overexpressed in response to chlordecone. There was also sequential overexpression of transcripts involved in apoptosis and degradation of cellular matrix proteins. Finally, we report the first observation of chlordecone-induced P. damicornis polyp bail-out. Altogether, these results strongly suggest that apoptosis and expression of genes belonging to the cathepsin family are sequentially regulated processes leading to coenosarc dissociation and loss.

ATP-binding cassette (ABC) proteins in aquatic invertebrates: Evolutionary significance and application in marine ecotoxicology

The ATP-binding cassette (ABC) protein superfamily is known to play a fundamental role in biological processes and is highly conserved across animal taxa. The ABC proteins function as active transporters for multiple substrates across the cellular membrane by ATP hydrolysis. As this superfamily is derived from a common ancestor, ABC genes have evolved via lineage-specific duplications through the process of adaptation. In this review, we summarized information about the ABC gene families in aquatic invertebrates, considering their evolution and putative functions in defense mechanisms. Phylogenetic analysis was conducted to examine the evolutionary significance of ABC gene families in aquatic invertebrates. Particularly, a massive expansion of multixenobiotic resistance (MXR)-mediated efflux transporters was identified in the absence of the ABCG2 (BCRP) gene in Ecdysozoa and Platyzoa, suggesting that a loss of Abcg2 gene occurred sporadically in these species during divergence of Protostome to Lophotrochozoa. Furthermore, in aquatic invertebrates, the ecotoxicological significance of MXR is discussed while considering the role of MXR-mediated efflux transporters in response to various environmental pollutants.

De novo transcriptome sequencing and analysis of freshwater snail (Radix balthica) to discover genes and pathways affected by exposure to oxazepam

Pharmaceuticals are increasingly found in aquatic ecosystems due to the non-efficiency of waste water treatment plants. Therefore, aquatic organisms are frequently exposed to a broad diversity of pharmaceuticals. Freshwater snail Radix balthica has been chosen as model to study the effects of oxazepam (psychotropic drug) on developmental stages ranging from trochophore to hatching. In order to provide a global insight of these effects, a transcriptome deep sequencing has been performed on exposed embryos. Eighteen libraries were sequenced, six libraries for three conditions: control, exposed to the lowest oxazepam concentration with a phenotypic effect (delayed hatching) (TA) and exposed to oxazepam concentration found in freshwater (TB). A total of 39,759,772 filtered raw reads were assembled into 56,435 contigs having a mean length of 1579.68 bp and mean depth of 378.96 reads. 44.91% of the contigs have at least one annotation. The differential expression analysis between the control condition and the two exposure conditions revealed 146 contigs differentially expressed of which 144 for TA and two for TB. 34.0% were annotated with biological function. There were four mainly impacted processes: two cellular signalling systems (Notch and JNK) and two biosynthesis pathways (Polyamine and Catecholamine pathways). This work reports a large-scale analysis of differentially transcribed genes of R. balthica exposed to oxazepam during egg development until hatching. In addition, these results enriched the de novo database of potential ecotoxicological models.