Effects of cadmium on the survival of three life-stages of the freshwater pulmonate Lymnaea stagnalis (Mollusca: Gastropoda)

A workflow to investigate the impacts of weathered multi-walled carbon nanotubes to the mud snail Lymnaea stagnalis

Although the development and application of nanomaterials is a growing industry, little data is available on the ecotoxicological effects on aquatic organisms. Therefore, we set up a workflow to address the potential uptake of weathered multi-walled carbon nanotubes (wMWCNTs) by a model organism, the pulmonary mud snail Lymnaea stagnalis (L. stagnalis), which plays an important role in the food web. It represents a suitable organism for this approach because as a grazer it potentially ingests large amounts of sedimented wMWCNTs. As food source for L. stagnalis, benthic biofilm was investigated by the use of a transmission electron microscope (TEM) and a scanning electron microscope (SEM) after exposure with wMWCNTs. In addition, isotopic labeling was applied with ¹⁴C-wMWCNTs (0.1 mg/L) to quantify fate, behavior, and enrichment of ¹⁴C-wMWCNTs in benthic biofilm and in L. stagnalis. Enrichment in benthic biofilm amounted to 529.0 µg wMWCNTs/g dry weight and in L. stagnalis to 79.6 µg wMWCNTs/g dry weight. A bioconcentration factor (BCF) for L. stagnalis was calculated (3500 L/kg). We demonstrate the accumulation of wMWCNTs (10 mg/L) in the digestive tract of L. stagnalis in an effect study. Moreover, the physiological markers glycogen and triglycerides as indicators for the physiological state, as well as the RNA/DNA ratio as growth indicator, were examined. No significant differences between exposed and control animals were analyzed for glycogen and triglycerides after 24 days of exposure, but a decreasing trend is recognizable for triglycerides. In contrast, the significant reduction in the RNA/DNA ratio of L. stagnalis indicated an inhibition of growth with a following recovery after depuration. The described workflow enables a comprehensive determination of the fate and the behavior of wMWCNTs specifically and in general all kinds of CNTs in the aquatic environment and therefore contributes to a holistic risk assessment of wMWCNTs.

Accumulation and histopathological effects of cadmium on the great pond snail Lymnaea stagnalis Linnaeus, 1758 (Gastropoda: Pulmonata)

Toxic metal ions are an important stress factor for a living organism. In this study, accumulation and histopathological changes in foot, mantle and hepatopancreas of great pond snail, Lymnaea stagnalis exposed to different Cadmium (Cd) concentrations in laboratory conditions were investigated. Great pond snails were exposed to sublethal concentrations of 7.92 μg/L, 15.85 μg/L, 31.7 μg/L and 63.4 μg/L Cd. At the end of 7, 14, 21 and 28 days, snail foot, mantle and hepatopancreas were removed to investigate and determine Cd accumulation and histopathological alterations by light microscopy. Cd levels determined in hepatopancreas were higher than those measured from the foot and the mantle of studied specimens. A positive correlation was found between Cd levels in tissues and exposure days. As a result of Cd application, we observed increase in the number of mucosit, pigment and protein cells and desquamation in the epithelium in the foot, atrophy in muscle fibrils, connective tissue cells and increase in the lipid vacuoles in the mantle, increase in the lipid vacuoles and amoebocyte in the hepatopancreas. The severity of the alterations resulting from Cd increased with dose-time dependent.

Accumulation of polybrominated diphenyl ethers and microbiome response in the great pond snail Lymnaea stagnalis with exposure to nylon (polyamide) microplastics

Microplastics attract widespread attention, including for their potential to transport toxic chemicals in the form of plasticisers and associated hydrophobic organic chemicals, such as polybrominated diphenyl ethers (PBDEs). The aims of this study were to investigate how nylon (polyamide) microplastics may affect PBDE accumulation in snails, and the acute effects of nylon particles and PBDEs on survival, weight change and inherent microbiome diversity and community composition of the pond snail Lymnaea stagnalis. Snails were exposed for 96 h to BDEs-47, 99, 100 and 153 in the presence and absence of 1% w/w nylon microplastics in quartz sand sediment. No mortality was observed over the exposure period. Snails not exposed to microplastics lost significantly more weight compared to those exposed to microplastics. Increasing PBDE concentration in the sediment resulted in an increased PBDE body burden in the snails, however microplastics did not significantly influence total PBDE uptake. Based on individual congeners, uptake of BDE 47 by snails was significantly reduced in the presence of microplastics. The diversity and composition of the snail microbiome was not significantly altered by the presence of PBDEs nor by the microplastics, singly or combined. Significant effects on a few individual operational taxonomic units (OTUs) occurred when comparing the highest PBDE concentration with the control treatment, but in the absence of microplastics only. Overall within these acute experiments, only subtle effects on weight loss and slight microbiome alterations occurred. These results therefore highlight that L. stagnalis are resilient to acute exposures to microplastics and PBDEs, and that microplastics are unlikely to influence HOC accumulation or the microbiome of this species over short timescales.

Lymnaea stagnalis as a freshwater model invertebrate for ecotoxicological studies

Lymnaea stagnalis, also referred to as great or common pond snail, is an abundant and widespread invertebrate species colonizing temperate limnic systems. Given the species importance, studies involving L. stagnalis have the potential to produce scientifically relevant information, leading to a better understanding of the damage caused by aquatic contamination, as well as the modes of action of toxicants. Lymnaea stagnalis individuals are easily maintained in laboratory conditions, with a lifespan of about two years. The snails are hermaphrodites and sexual maturity occurs about three months after egg laying. Importantly, they can produce a high number of offspring all year round and are considered well suited for use in investigations targeting the identification of developmental and reproductive impairments. The primary aims of this review were two-fold: i) to provide an updated and insightful compilation of established toxicological measures determined in both chronic and acute toxicity assays, as useful tool to the design and development of future research; and ii) to provide a state of the art related to direct toxicant exposure and its potentially negative effects on this species. Relevant and informative studies were analysed and discussed. Knowledge gaps in need to be addressed in the near future were further identified.

Biomphalaria alexandrina as a bioindicator of metal toxicity

Heavy metals are common environmental pollutants to the aquatic ecosystems. Several aquatic species have been used as bioindicators and biomonitoring subjects for heavy metals pollution. In the present study, the effects of cadmium (Cd) and manganese (Mn) on the survival, attachment, locomotion, and feeding behaviours of the gastropod snail Biomphalaria alexandrina were determined. The short-term (96 h) LC50 for Cd and Mn were found to be 0.219 and 154.2 mg/l, respectively. Long-term exposures (16-20 days) to ascending concentrations of Cd (0.01-1 mg/l) and Mn (50-500 mg/l) also caused gradual decreases in the survival rate of B. alexandrina in a dose-dependent manner. Attachment, locomotion and feeding behaviours of snails exposed to lethal and sublethal concentrations of Cd and Mn at acute (96 h) and chronic exposure (24 days) intervals, respectively, were also recorded. Compared to controls, a significant decrease (p ≤ 0.05) was recorded in the different behaviours of exposed snails. These changes in behaviour would potentially impact the snail's ability to survive in the wild. Although Cd caused a more severe decline in snail survivorship than Mn, the behavioural effects of Mn were much more severe than Cd when the metals were roughly matched for lethality. In sum, the present study demonstrates B. alexandrina to be a sensitive bioindicator and model organism to assess heavy metals risk factors for severe toxicity in freshwater ecosystems.

Transcriptional and biochemical effects of cadmium and manganese on the defense system of Octopus vulgaris paralarvae

Due to anthropogenic activities the relative concentrations of cadmium and manganese have increased in the marine environment. Cephalopods are able to accumulate such metals and, as inhabitant of coastal waters, Octopus vulgaris is continuously exposed to anthropogenic activities. Since no study is available on the effects of heavy metals at molecular level in developing octopuses, herein we exposed 1-day-old paralarvae for 24 h to 10, 100, and 1000 μg/L of CdCl2 or MnCl2. Cd exerted a concentration-dependent inhibition of survival and a reduction in growth rate was shown while Mn exposure did not affect the survival rate even at the highest concentrations. Gene expression profiles of hsp70, sod, cat, and gst genes were analyzed by quantitative real-time PCR and defined patterns of transcription were observed. Moreover posttranscriptional analyses were also performed suggesting the impairment of metabolic functions, under strong oxidative conditions (as occurred in paralarvae exposed to Cd) or the complete detoxification events (as occurred in paralarvae exposed to Mn).

How does human-induced environmental change influence host-parasite interactions?

Host-parasite interactions are an integral part of ecosystems that influence both ecological and evolutionary processes. Humans are currently altering environments the world over, often with drastic consequences for host-parasite interactions and the prevalence of parasites. The mechanisms behind the changes are, however, poorly known. Here, we explain how host-parasite interactions depend on two crucial steps – encounter rate and host-parasite compatibility – and how human activities are altering them and thereby host-parasite interactions. By drawing on examples from the literature, we show that changes in the two steps depend on the influence of human activities on a range of factors, such as the density and diversity of hosts and parasites, the search strategy of the parasite, and the avoidance strategy of the host. Thus, to unravel the mechanisms behind human-induced changes in host-parasite interactions, we have to consider the characteristics of all three parts of the interaction: the host, the parasite and the environment. More attention should now be directed to unfold these mechanisms, focusing on effects of environmental change on the factors that determine encounter rate and compatibility. We end with identifying several areas in urgent need of more investigations.

Gene expression profiling of three different stressors in the water flea Daphnia magna

Microarrays are an ideal tool to screen for differences in gene expression of thousands of genes simultaneously. However, often commercial arrays are not available. In this study, we performed microarray analyses to evaluate patterns of gene transcription following exposure to two natural and one anthropogenic stressor. cDNA microarrays compiled of three life stage specific and three stressor-specific EST libraries, yielding 1734 different EST sequences, were used. We exposed juveniles of the water flea Daphnia magna for 48, 96 and 144 h to three stressors known to exert strong selection in natural populations of this species i.e. a sublethal concentration of the pesticide carbaryl, infective spores of the endoparasite Pasteuria ramosa, and fish predation risk mimicked by exposure to fish kairomones. A total of 148 gene fragments were differentially expressed compared to the control. Based on a PCA, the exposure treatments were separated into two main groups based on the extent of the transcriptional response: a low and a high (144 h of fish or carbaryl exposure and 96 h of parasite exposure) stress group. Firstly, we observed a general stress-related transcriptional expression profile independent of the treatment characterized by repression of transcripts involved in transcription, translation, signal transduction and energy metabolism. Secondly, we observed treatment-specific responses including signs of migration to deeper water layers in response to fish predation, structural challenge of the cuticle in response to carbaryl exposure, and disturbance of the ATP production in parasite exposure. A third important conclusion is that transcription expression patterns exhibit stress-specific changes over time. Parasite exposure shows the most differentially expressed gene fragments after 96 h. The peak of differentially expressed transcripts came only after 144 h of fish exposure, while carbaryl exposure induced a more stable number of differently expressed gene fragments over time.

Plasticity in offspring contaminant tolerance traits: developmental cadmium exposure trumps parental effects

Parental effects are non-genotypic influences on offspring phenotype that occur via parental phenotypes or environments, while developmental plasticity is phenotypic variation that arises during development in response to environmental cues. We evaluated the relative contribution of these two sources of phenotypic variation on offspring toxicant tolerance in Physa pomilia snails exposed to cadmium. We exposed adult snails to 0, 2, or 20 μg/L cadmium for 7 days, then exposed egg masses collected from these adults to 0 or 2 μg/L cadmium in a factorial design (adult cadmium exposure × egg mass cadmium exposure). Starting at 2 days old, we recorded time to death for hatchlings exposed to 150 μg/L cadmium for 72 h at 8 h intervals. Juveniles hatched from cadmium-exposed egg masses displayed higher cadmium tolerance than juveniles from unexposed egg masses. Among juveniles from egg masses not exposed to cadmium, offspring of parents exposed to 20 μg/L cadmium had higher cadmium tolerance than offspring of parents exposed to 0 or 2 μg/L cadmium. Our results show that both parental effects and developmental plasticity can impact offspring toxicant tolerance and point to the potential importance of both processes in understanding how offspring respond to chemical contaminants. When both parents and offspring are exposed to a toxicant, our results showed that the effects of parental exposure on offspring toxicant tolerance may be eclipsed by the effects of offspring exposure during development.

Contrasting sensitivities to fluoride toxicity between juveniles and adults of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca)

In contrast to aquatic vertebrates, there is scarce available information on the contrasting tolerance to fluoride of different life stages and/or sizes of aquatic invertebrates. The purpose of this study was to assess the likely differences in sensitivity between juveniles and adults of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca) to short-term (4 days) toxicity of fluoride ion (F(-)). LC50 and EC50 values for juveniles were significantly lower than those for adults at 24, 48, 72 and 96 h. Based on our results, the use of fluoride data of bioassays with juveniles should provide more protective water quality criteria than data from adult stage.

Multiple metal tolerance and biosorption of cadmium by Candida tropicalis isolated from industrial effluents: glutathione as detoxifying agent

The ability of cadmium uptake by metal-resistant yeast, Candida tropicalis, from the liquid medium and wastewater was evaluated. The minimum inhibitory concentration of Cd(2+) against C. tropicalis was 2,500 mg L(-1). The yeast also showed tolerance toward Zn(2+) (1,400 mg L(-1)), Ni(2+) (1,000 mg L(-1)), Hg(2+) (1,400 mg L(-1)), Cu(2+) (1,000 mg L(-1)), Cr(6+) (1,200 mg L(-1)), and Pb(2+) (1,000 mg L(-1)). The yeast isolate showed typical growth curves, but lag and log phases extended in the presence of cadmium. The yeast isolate showed optimum growth at 30°C and pH 8. The metal processing ability of the isolate was determined in a medium containing 100 mg L(-1) of Cd(2+). C. tropicalis could decline Cd(2+) 70%, 85%, and 92% from the medium after 48, 96, and 144 h, respectively. C. tropicalis was also able to remove Cd(2+) 40% and 78% from the wastewater after 6 and 12 days, respectively. Cd produced an increase in glutathione (GSH) and nonprotein thiol levels by 135% and 134% at 100-mg L(-1) concentration, respectively. An increase in the synthesis of GSH is involved in metal tolerance, and the presence of increasing GSH concentrations may be a marker for high metal stress in C. tropicalis. C. tropicalis, which is resistant to heavy metal ions and is adaptable to the local environmental conditions, may be employed for metal detoxification operations.

Comprehensive biological effects of a complex field poly-metallic pollution gradient on the New Zealand mudsnail Potamopyrgus antipodarum (Gray)

The Lot River is known to be contaminated by metals, mainly cadmium and zinc, due to a former Zn ore treatment plant in the watershed of the Riou-Mort, a tributary of the Lot River. Many studies have been performed to characterize contamination, but few have assessed its consequences on the biological responses of organisms along the gradient. We exposed adult and juvenile New Zealand freshwater mudsnails Potamopyrgus antipodarum at several sites along the gradient of metal contamination for 28 days. Biological responses were monitored at different levels: individual (survival, growth and fecundity), tissue and biochemical (energy status and vertebrate-like sex steroid levels) to better understand the toxicity mechanisms involved. Accumulation of Cd and Zn was high during exposure. Most of the biological effects observed could be linked to this contamination and were concentration-dependent. Histological lesions of the digestive gland were observed, with hypertrophy of calcium cells and vacuolization of digestive cells. Such effects are likely to explain the decrease of energy status (triglycerides and proteins), juvenile growth and adult fecundity observed at the most polluted site. However the magnitude of the fall in fecundity cannot be attributed only to these tissular effects, indicating another mode of action of Cd or possible confounding factors. Steroid accumulation in snails indicated only organic pollution. Histopathological effects proved the most sensitive endpoint to metal (Cd and Zn) contamination.

Contrasting sensitivities to toxicants of the freshwater amphipods Gammarus pulex and G. fossarum

Amphipods are an important component of freshwater ecosystems. They are very often used in ecotoxicology, particularly the freshwater amphipod Gammarus pulex. However, there is scarce information on the sensitivity to toxicants of other species within the genus Gammarus. The present study aims to: (1) to compare sensitivities to ivermectin and cadmium between two species of freshwater amphipods (G. pulex and G. fossarum); (2) to compare sensitivities to these toxicants between juveniles and adults within each species; and (3) to assess whether the sensitivity to toxicants of these co-generic species is related with the wideness of their natural distribution area. Eight independent short-term bioassays (96 h) were conducted to assess sensitivity for ivermectin and cadmium for juvenile and adult life stages for each species. The LC50 (mortality) and EC50 (mortality plus immobility) were calculated to 48 and 96 h of continuous exposure. Our results showed that G. pulex was less tolerant to ivermectin than G. fossarum, the reverse being true for cadmium. In general, juveniles of both species were less tolerant to cadmium than adults. In the case of ivermectin, only for G. fossarum EC50 values were different between life stages. These results suggest that the risk assessment of toxicants to freshwater amphipods should include bioassays with the most sensitive species and life stage.

Heavy metal uptake by Euplotes mutabilis and its possible use in bioremediation of industrial wastewater

A ciliate protozoan, Euplotes mutabilis, isolated from heavy metal laden industrial wastewater, has been shown to tolerate multiple heavy metals thus suggesting its significance in bioremediation of industrial effluents. This ciliate tolerated Zn(2+) up to 33 microg/mL, Cd(2+) up to 22 microg/mL and Ni(2+) up to 18 microg/mL. The ciliate could uptake 85% Zn(2+), 84% of Cd(2+) and 87% of Ni(2+) after 96 h of inoculation of growth medium containing 10 microg/mL of Zn(2+) and 5 microg/mL of Cd(2+) and Ni(2+), with actively growing ciliates. After 6 days of incubation the ciliate removed 87% Cd(2+), 92% Ni(2+), and 93% Zn(2+) from the wastewater. The heavy metal uptake capability of Euplotes mutabilis may be employed for metal detoxification operations.

Effect of cadmium, lead and arsenic on the oviposition, hatching and embryonic survival of Biomphalaria glabrata

Biomphalaria glabrata is a widespread freshwater gastropod mollusc. The easy aquaculture of these organisms allow its use as an accessible tool for contamination bioassays. B. glabrata showed marked metabolic responses when exposed to cadmium, lead and arsenic. Those responses could also affect the reproduction of the snails. Taking into account this hypothesis, B. glabrata were exposed for 96 h (acute laboratory bioassays) to different concentrations of cadmium (0.1, 0.05 and 0 mg/L), lead (0.5, 0.1, 0.05 and 0 mg/L) and arsenic (0.5, 0.1, 0.05 and 0 mg/L). Snails were removed from the aquaria while eggs were left in the same contaminant concentrations. The effect of the assayed toxicants on snail reproduction was registered as the alterations of the total number of laid eggs (TNLE), hatching time and embryonic survival. At 0.10 mg/L cadmium significantly decreased the TNLE (p<0.05) and no embryos survived. The lowest assayed level (0.05 mg/L) of cadmium, delayed the hatching time twice when it was compared with the control group (p<0.01). Lead decreased the TNLE at 0.5 mg/L level (p<0.01). The other assayed doses (0.05 and 0.10 mg/L) also decreased embryonic survival significantly (p<0.05 and p<0.01 respectively) and extended twice the time to hatching (p<0.01). The 0.50 mg/L level killed all embryos. Arsenic at all studied concentrations decreased the TNLE (p<0.05) while the hatching time was increased by 50%. Embryo survival only decreased at the highest level (0.5 mg/L) of arsenic assayed. In summary, the acute exposure (96 h) to cadmium lead and arsenic, altered the reproduction of B. glabrata, modifying the TNLE, hatching time and embryonic survival.

Effects of cadmium exposure on embryogenesis of Stagnicola elodes (Mollusca, Gastropoda): potential consequences for parasite transmission

Experiments on the toxicity of cadmium (Cd(2+)) to the embryonic development of Stagnicola elodes (Mollusca, Gastropoda), obligatory first intermediate host of numerous trematodes of pathogenic importance, were carried out as part of a study on the effects of metal pollution on host-parasite relationships. Freshly laid snail eggs were exposed to Cd concentrations of 0, 0.02, 0.2, and 2.0 mg Cd(2+)/L, and survival and embryogenesis were examined for 30 days. Mean survival time (+/- SD) of the control group was 23.1 (+/- 5.3) days compared with 10.1 (+/- 3.2) at 0.02 mg Cd(2+)/L, 3.9 (+/- 0.7) at 0.2 mg Cd(2+)/L, and 1.1 (+/- 0.08) at 2.0 mg Cd(2+)/L. Mortality patterns of all test groups differed significantly from each other, demonstrating that the percentage of surviving individuals at any given time was inversely related to Cd concentration. Concentration-dependent effects of Cd exposure on snail embryogenesis were noted. While embryos of the control group developed properly and started hatching on day 16, eggs exposed to 0.02 mg Cd(2+)/L exhibited a prolonged gastrula period and failed to hatch. Eggs in the 0.2 mg Cd(2+)/L group were blocked in the gastrula stage on day 5, whereas individuals exposed to 2.0 mg Cd(2+)/L died in the morula stage on the second day. Data showed that Cd severely affects S. elodes embryogenesis. By implication, Cd contamination at concentrations >or=0.02 mg Cd(2+)/L will thus decrease transmission success of various trematodes by decreasing intermediate host snail abundance.