Caged mudsnail Potamopyrgus antipodarum (Gray) as an integrated field biomonitoring tool: exposure assessment and reprotoxic effects of water column contamination.

This study highlights the usefulness of gastropods for water quality monitoring. Gastropods were caged upstream and downstream of an effluent discharge. Exposure was assessed by measurement of organic contaminants in water. Contamination of the Potamopyrgus antipodarum mudsnail was also measured using innovative techniques at the end of the 42 days of exposure. Biological effects were measured at the individual level (growth, reproduction) and subindividual level (energy reserves, vitellin-like proteins, steroid levels, expression of genes involved in estrogen signaling pathways), thus providing a better understanding of reprotoxic effects. The effluent was mainly contaminated by pharmaceutical compounds, as was the mudsnail. The highest concentrations were measured for oxazepam and were higher than 2 mg/kg downstream of the effluent discharge. Alkylphenols, bisphenol A, and vertebrate-like sex-steroid hormones were also bioaccumulated by the mudsnail downstream of the effluent. The combined use of water and snail contamination provided a complete exposure assessment. Exposure was further linked to biological effects. The mudsnail was shown to be a better adapted species for in situ exposures than Valvata piscinalis. Reproduction was sharply decreased after 6 weeks of exposure in the mudsnail. Feeding issues were excluded, confirming the toxic origin. These effects were related to estrogen signaling pathways using genomic analysis. Genes coding for proteins involved in nongenomic signaling pathways were inhibited, and those of genomic pathway repressors were induced. These results suggest that the chemical contamination due to the effluent discharge altered steroid control of reproduction and blocked the transition between oocyte and unshelled embryo, resulting in a drastic decrease of embryo production, while survival was not affected.

Organic solvents impair life-traits and biomarkers in the New Zealand mudsnail Potamopyrgus antipodarum (Gray) at concentrations below OECD recommendations.

Potamopyrgus antipodarum is a gastropod mollusk proposed for use in the development of reproduction tests within the Organization for Economic Cooperation and Development (OECD). Numerous chemicals, including endocrine disrupters, are relatively water-insoluble, and water-miscible solvents are currently used for testing them. OECD recommends a maximum concentration of 100 µll(-1). As several studies highlighted effects of lower concentrations of solvents, this study assessed the effects of 20 µll(-1) acetone, ethanol, methanol and dimethylsulfoxide (DMSO) on juvenile and adult snails during 42 days. Ethanol decreased juvenile growth, while acetone increased the rate of embryonic development. All solvents increased estradiol-like levels in adult snails. DMSO only increased mRNA expression of vitellogenin-like gene, while acetone, ethanol and methanol decreased mRNA expression of three nuclear receptor (estrogen receptor-like, ecdysone-induced protein and chicken ovalbumin upstream promoter transcription factor) genes as well as of genes encoding proteins involved in genomic (prohibitin-2) and non-genomic (striatin) pathways of estrogens activity in vertebrates. This study highlights the confounding effects of low concentrations of solvents and recommends avoiding their use. Where solvent use is inevitable, their concentrations and type should be investigated for suitability for the measured endpoints prior to use in chemical testing strategies.

Non destructive in vivo measurement of ethoxyresorufin biotransformation by zebrafish prolarva: development and application.

Biotransformation enzymatic activities, such as the cytochrome P450 one, have been used as biomarkers for pollution assessment for a long time. Nevertheless, such biochemical tools are destructive processes, because they are performed on fish liver or total larvae homogenates. Moreover, the adaptation of this bioassay to some fish larvae, like Danio rerio ones, is ineffective because it needs a lot of organisms. We thus developed an original, nondestructive method to detect the induction of a biotransformation activity in the prolarva of the fish, Danio rerio, exposed to chemicals. This methodology is based on the assessment of EROD activity, by measurement in the culture medium of the fluorescence increase due to the excretion of resorufin by fish during an ethoxyresorufin exposure. After exposure of fish embryos to known inducers (BaP and beta-naphtoflavone), the prolarvae were exposed to the substrate (ethoxyresorufin), and the kinetic of the fluorescence increase was measured. A dose-effect relationship was observed, with a three to five fold increase of EROD basal activity. This methodology also allowed us to compare between EROD activity induction by different environmental samples. The proposed methodology thus allows to perform a simple, sensitive, and reproducible microbiotest for the detection of sublethal concentrations of AhR chemical inducers in environmental samples.

Expression and activity of a multixenobiotic resistance system in the Pacific oyster Crassostrea gigas.

The multidrug resistance (MDR) mechanism corresponds to a defence system relying on the expression of high molecular membrane proteins that can actively lower the intracellular concentration of a wide variety of toxins, thus maintaining them below their toxic level. Using RT-PCR, expression levels of a gene belonging to the class I of mammalian mdr genes, has been assessed in different developmental stages of the oyster Crassostrea gigas. While no expression was found in the oocyte or the trocophore stage, a rise of mRNA content was observed from the veliger stage to the juvenile stage, thus indicating the induction of the system as the animal is developing in the environment. The incubation of gill fragments in the dye rhodamine B and subsequent measurements of intracellular fluorescence using a microplate reader indicates that the system can effectively decrease the accumulation of the test compound in a competitive manner with known inhibitors or environmental contaminants as observed in vertebrate cells. The oyster MXR system is thus becoming active in adult oyster and could be of importance in environmentally contaminated areas.