Development of rearing and testing protocols for a new freshwater sediment test species: the gastropod Valvata piscinalis

Single and joint oxidative stress-related toxicity of sediment-associated cadmium and lead on Bellamya aeruginosa

The biotoxicity of heavy metals in sediments toward benthic organisms has evoked great concern for the health of freshwater ecosystems. This study applied a sediment toxicity testing protocol to investigate the single and joint toxicity of cadmium (Cd) and lead (Pb) on Bellamya aeruginosa. B. aeruginosa were exposed to different concentrations of Cd (5, 25, and 100 mg/kg), Pb (20, 100, and 400 mg/kg), and their different concentration combinations. A suite of biomarkers, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), metallothionein (MT), malondialdehyde (MDA), and acetylcholinesterase (AChE), were measured after 7, 14, 21, and 28 days of exposure to evaluate their oxidative stress status. Cell apoptosis of soft tissue was also determined after exposure. Results revealed that these endpoints represented sensitive biomarkers for the characterization of the oxidative stress response induced by these metals. Specifically, a decrease of SOD and GPx and an increase of MDA were indicative of the potential failure of the antioxidant defense system in neutralizing the reactive oxygen species (ROS) generated in the exposure of the Pb-treated group. The integrated biomarker response (IBR) index revealed the most significant sub-lethal toxicity for Pb-spiked sediments, leading to the highest rate of cell apoptosis (70.8%). Exposure to Cd resulted in a time- and dose-dependent effect on MT levels, which suggested active detoxification of this metal. Exposure to the mixture resulted in amelioration of Pb toxicity, likely due to the competitive binding of Cd to active enzyme, with the result of an observed antagonistic interaction. This study indicated that B. aeruginosa represents a good biomonitor for assessing Cd and Pb contamination of sediments, and laid the foundation for their potential risk assessments in freshwater ecosystems.

Energetic endpoints provide early indicators of life history effects in a freshwater gastropod exposed to the fungicide, pyraclostrobin

Organismal energetics provide important insights into the effects of environmental toxicants. We aimed to determine the effects of pyraclostrobin on Lymnaea stagnalis by examining energy allocation patterns and life history traits. Juvenile snails exposed to pyraclostrobin decreased feeding rate and increased apparent avoidance behaviors at environmentally relevant concentrations. In adults, we found that sublethal concentrations of pyraclostrobin did not affect reproductive output, however, there were significant effects on developmental endpoints with longer time to hatch and decreased hatching success in pyraclostrobin-exposed egg masses. Further, there were apparent differences in developmental effects depending on whether mothers were also exposed to pyraclostrobin suggesting this chemical can exert intergenerational effects. Pyraclostrobin also affected protein and carbohydrate content of eggs in mothers that were exposed to pyraclostrobin. Significant effects on macronutrient content of eggs occurred at lower concentrations than effects on gross endpoints such as hatching success and time to hatch suggesting potential value for these endpoints as early indicators of ecologically relevant stress. These results provide important insight into the effects of a common fungicide on important endpoints for organismal energetics and life history.

Microscale Ecotoxicity Testing of Moselle River Watershed (Lorraine Province, France) Sediments

The ecotoxic potential of seven Moselle river watershed sediments was assessed with a battery of bioassays comprised of rapid phototrophic [LuminoTox solid phase (L-SPA) and elutriate (L-ELU) assays] and bacterial [Microtox solid phase assay (M-SPA)] exposure tests, as well as with two micro-invertebrate solid phase tests conducted with Hydra attenuata (lethal and sublethal effects solid phase assay, H_L-SPA and H_SL-SPA) and Chironomus riparius. Measured effects of sediments and their elutriates were varied and reflected responses that were ecotoxicity test-, endpoint- and site-dependent, suggesting some degree of risk toward benthic and water column organisms, respectively, at specific sites. Correlation analysis demonstrated that L-SPA and M-SPA ecotoxicity responses were significantly linked with the Hydra H_SL-SPA assay, indicating their ability to predict ecotoxicity towards an invertebrate taxonomic group representing secondary consumers. While the L-SPA and M-SPA assays hold promise as rapid screens for sediment ecotoxicity, correlation analysis with grain size (L-SPA: r=–0.795, P=0.033; M-SPA: r=–0.73, P=0.07) points out that their responses can be influenced by the presence of fines (i.e., sediment particles ≤0.063 mm in size) and that this information is essential to properly interpret ecotoxicity data generated with these assays. Finally, notable differences observed in trophic level sensitivities once again recall the importance of employing a test battery to adequately appraise the ecotoxicity of sediments.

Comparison of species sensitivity distributions based on population or individual endpoints

Species sensitivity distributions (SSDs) developed from individual and population endpoints were compared based on simulations and a case study. The simulations were performed with five invertebrate species accounting for the diversity of benthic macroinvertebrate communities in large European lowland rivers and for five benthic invertebrates used as laboratory species. Population growth rate 10% effective concentration (EC10) values were, in most of the simulations, higher than the lowest of the EC10 values at the individual level. However, for the set of ecologically representative species, the fifth percentile level of this distribution (HC5) was more protective for population endpoints than for individual endpoints. This was the opposite for the set of laboratory species. Population and individual SSDs were also compared based on existing data on Cu for the five laboratory invertebrate species. In this case, the calculated population HC5 value was almost twice the individual value, and the authors showed much reduced variability between species sensitivities at population level compared with individual level. They conclude that population-based HC5 would generally be more protective than individual-based HC5. However, the change of level could reveal higher homogeneity at population level than at individual level, supporting the use of population-based HC5 to avoid overprotection. The authors thus advise the derivation of population-based HC5, as soon as it is possible, to derive such value with a relevant panel of species.

Traits-based approaches in bioassessment and ecological risk assessment: strengths, weaknesses, opportunities and threats

We discuss the application of traits-based bioassessment approaches in retrospective bioassessment as well as in prospective ecological risk assessments in regulatory frameworks. Both approaches address the interaction between species and stressors and their consequences at different levels of biological organization, but the fact that a specific species may be less abundant in a potentially impacted site compared with a reference site is, regrettably, insufficient to provide diagnostic information. Species traits may, however, overcome the problems associated with taxonomy-based bioassessment. Trait-based approaches could provide signals regarding what environmental factors may be responsible for the impairment and, thereby, provide causal insight into the interaction between species and stressors. For development of traits-based (TBA), traits should correspond to specific types of stressors or suites of stressors. In this paper, a strengths, weaknesses, opportunities, and threats (SWOT) analysis of TBA in both applications was used to identify challenges and potentials. This paper is part of a series describing the output of the TERA (Traits-based ecological risk assessment: Realising the potential of ecoinformatics approaches in ecotoxicology) Workshop held between 7 and 11 September, 2009, in Burlington, Ontario, Canada. The recognized strengths were that traits are transferrable across geographies, add mechanistic and diagnostic knowledge, require no new sampling methodology, have an old tradition, and can supplement taxonomic analysis. Weaknesses include autocorrelation, redundancy, and inability to protect biodiversity directly. Automated image analysis, combined with genetic and biotechnology tools and improved data analysis to solve autocorrelation problems were identified as opportunities, whereas low availability of trait data, their transferability, their quantitative interpretation, the risk of developing nonrelevant traits, low quality of historic databases, and their standardization were listed as threats.

In vivo indirect measurement of cytochrome P450-associated activities in freshwater gastropod molluscs

The cytochrome P450 (CYP) system is widely distributed across phyla and plays a key role in the metabolism of xenobiotic compounds. However, most studies on CYP system were developed on vertebrates and among invertebrates, gastropod molluscs are rarely used. In this context, ethoxycoumarin-O-deethylase (ECOD), ethoxyresorufin-O-deethylase (EROD), and pentoxyresorufin-O-dealkylase (PROD) activities, which are indirect measurements of CYP system, were characterized in two freshwater gastropod molluscs, Potamopyrgus antipodarum, and Valvata piscinalis, to ascertain their potential interest as biomarkers of exposure to chemicals. Activities were measured using an in vivo non lethal method based on the measurement of formed product (resorufin or hydroxycoumarin). This in vivo assay allowed to measure the three activities in P. antipodarum and two of them (ECOD and PROD) in V. piscinalis. The detection of activities and the optimization of experimental design were carried out first and allowed to measure the selected activities for one individual. The modulation of the detected activities was secondly assessed using a polycyclic aromatic hydrocarbon (Benzo(a)pyrene). Based on this non destructive measurement, effect of BaP exposure could be detected on ECOD and EROD activity in P. antipodarum, as well on PROD activity of V. piscinalis after 96 h of exposure. Such an in vivo assay must be further developed to be valuably used to screen the exposure of gastropod species to CYP inducer chemicals and its consequences in terms of fitness of the organisms and of the population.

Laboratory culture of the freshwater benthic gastropod Bellamya aeruginosa (Reeve) and its utility as a test species for sediment toxicity

This study aimed to develop original laboratory culture and sediment toxicity testing protocols for the freshwater gastropod Bellamya aeruginosa (Reeve), a new potential species for sediment toxicity testing. B. aeruginosa was successfully cultured with an effective culture system under proposed laboratory conditions. Optimal ad libitum feeding levels for larvae, juveniles, and adults were 2.0, 6.0, and 16.0 mg fish food/(snail x day), respectively. Mean survival rates of juveniles were higher than 90%. The snails could be sexed at 9 weeks of age, and their generation time is approximately 4 months. Reproduction continued all year around; the mean fecundity was 0.55 newborn/(female x day). The utility of this species for bioassays was evaluated in both 10-day and 28-day case studies with artificial sediments. The 10-day LC50 of Cu for larvae was 480 gg/g dry weight (dw), and the lowest observed effects concentration of Cu for survival and growth of larvae was 195 microg/g dw. Survival and growth are reliable indicators of acute toxicity. Larvae accumulated more Cu than adults. B. aeruginosa exhibited a higher sensitivity to Cu exposure than standard test species (Hyalella azteca and Chironomus tentans). The 28-day test of sediment toxicity with adults showed that fecundity was a robust endpoint indicator of reproductive toxicity, and the biochemical endpoints of superoxide dismutase, catalase, and glutathione could be used as sensitive biomarkers for Cu-induced oxidative damage. B. aeruginosa can be therefore recommended as a candidate for the standardization of the freshwater sediment toxicity test protocol.

Effects of fluoxetine on the reproduction of two prosobranch mollusks: Potamopyrgus antipodarum and Valvata piscinalis

Fluoxetine is a widely used antidepressant, frequently found in aquatic ecosystems. We investigated its effects on two freshwater prosobranch gastropods: Valvata piscinalis (European valve snail) and Potamopyrgus antipodarum (New Zealand mudsnail), which have different reproductive modes. The fecundity of V. piscinalis (cumulate number of eggs at day 42) was not affected with an NOEC of 100 mvg/L nominal concentration (69 microg/L measured concentration). The mudsnail P. antipodarum responded in a biphasic dose-effect curve at low concentrations. The cumulate number of neonates at day 42 had an LOEC of 100 microg/L (69 microg/L) and an NOEC of 33.3 microg/L (13 microg/L), whereas the embryos in the brood pouch at day 42 only showed an LOEC of 3.7 microg/L (1 microg/L). We also observed histological effects in P. antipodarum (gonadal thickness). Among the sexual steroids we measured only testosterone which varied, independent of reproduction. Moreover the use of two closely related species highlights the interspecific variability.

Spatial and temporal structure of the trematode component community in Valvata macrostoma (Gastropoda, Prosobranchia)

We conducted the first comprehensive study on the spatiotemporal structure of trematode communities in the large-mouthed valve snail, Valvata macrostoma. A total of 1103 snails were examined monthly between May and October 2007 from Lake Konnevesi, Central Finland, from a shallow (1-2 m deep) and an offshore site (5-6 m deep), located ca. 50-70 m apart. Snails were infected by 10 trematode species. The species composition and prevalence were strikingly different between the sites with high species diversity in the shallow site (all 10 species; total prevalence of sporocysts/rediae 12.1%, metacercariae 55.4%) compared to the deeper site (3 species; prevalence 15.0% and 1.9%, respectively). This difference persisted throughout our study and is probably related to the spatial distribution of bird definitive hosts, whereas the seasonal parasite dynamics are likely to be affected by changes in the age-structure of the snail population. The probability of sporocyst infections increased with snail size, but no such trend was observed in redial or metacercarial infections which decreased with host size. Our results show that generally well-described spatiotemporal differences in trematode infection of molluscs can emerge in very narrow spatial and temporal scales, which emphasizes the importance of these factors in community studies.