Freshwater Snail Lymnaea Stagnalis Research Articles

Understanding the differential impacts of two antidepressants on locomotion of freshwater snails (Lymnaea stagnalis)

There is growing evidence of negative impacts of antidepressants on behavior of aquatic non-target organisms. Accurate environmental risk assessment requires an understanding of whether antidepressants with similar modes of action have consistent negative impacts. Here, we tested the effect of acute exposure to two antidepressants, fluoxetine and venlafaxine (0–50 µg/L), on the behavior of non-target organism, i.e., freshwater pond snail, Lymnaea stagnalis. As compounds interact with chemical cues in the aquatic ecosystems, we also tested whether the effects altered in the presence of bile extract containing 5α-cyprinol sulfate (5α-CPS), a characterized kairomone of a natural predator, common carp (Cyprinus carpio). Behavior was studied using automated tracking and analysis of various locomotion parameters of L. stagnalis. Our results suggest that there are differences in the effects on locomotion upon exposure to venlafaxine and fluoxetine. We found strong evidence for a non-monotonic dose response on venlafaxine exposure, whereas fluoxetine only showed weak evidence of altered locomotion for a specific concentration. Combined exposure to compounds and 5α-CPS reduced the intensity of effects observed in the absence of 5α-CPS, possibly due to reduced bioavailability of the compounds. The results highlight the need for acknowledging different mechanisms of action among antidepressants while investigating their environmental risks. In addition, our results underline the importance of reporting non-significant effects and acknowledging individual variation in behavior for environmental risk assessment.Graphical

Effects of acute exposure to environmentally realistic tebuconazole concentrations on stress responses of kidney and digestive gland of Lymnaea stagnalis

This study aimed to investigate the effects of 24 and 72 h exposure to environmentally relevant concentrations of tebuconazole (TEB) (10, 100 and 500 µg/L) fungicide on the freshwater snail Lymnaea stagnalis. The focus was induction of oxidative stress, alteration of gene expressions and histopathological changes in the kidney and digestive gland. TEB treatment induced a time- and concentration-dependent increase in intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) levels, while the total antioxidant capacity (TAC) was decreased. The activities of glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (CAT) also increased in a time- and concentration-dependent manner in both tissues. TEB exposure significantly increased the mRNA levels of CAT, GPx, GR, heat shock proteins HSP40 and HSP70. Histological analysis revealed nephrocyte degeneration and disrupted digestive cells. The study concludes that acute exposure to TEB induces oxidative stress, alters antioxidant defense mechanisms, and leads to histopathological changes in L. stagnalis.

The effects of temperature on nickel bioaccumulation and toxicity in the freshwater snail Lymnaea stagnalis

It is well known that temperature can have important effects on the toxicity of metals (and other contaminants) to aquatic organisms. To date, research has mostly focused on thermal effects on acute metal toxicity, and there is a data gap on thermal effects on chronic metal toxicity to sensitive organisms that are particularly relevant to environmental risk assessment. This latter research is especially needed in the context of increased global temperature and heat waves frequency associated with climate change. We investigated temperature effects on chronic nickel (Ni) bioaccumulation and toxicity to the metal-sensitive freshwater snail Lymnaea stagnalis. In the laboratory, we conducted a series of experiments with juvenile snails that were pre-acclimated to different temperatures since their embryonic stage. We found that temperature and nickel separately had strong effects on juvenile growth rate and survival. Rising temperature from 18 to 26 °C had no noticeable effect on Ni-induced growth inhibition and Ni bioaccumulation in juvenile L. stagnalis exposed over 40 days to 0, 30 and 60 μg L−1 of dissolved Ni. These results agreed with estimates of Ni uptake and elimination rates (ku and ke), which were either unaffected by temperature or increased by similar factors from 18 to 26 °C. On the other hand, a temperature increase from 18 to 26 °C appeared to exacerbate Ni lethality to juvenile snails in the 40-day toxicity test. This exacerbation might have been due to a combination of factors, including detrimental changes in metabolically available Ni pools and/or to sensitization of the organism under sub-optimal temperatures. Overall, our study shows that thermal effects on metal chronic toxicity are complex, with effects that can be response-specific and not directly related to metal toxicokinetic.

Sulfate sensitivity of aquatic organism in soft freshwaters explored by toxicity tests and species sensitivity distribution

Elevated concentrations of sulfate in waterways are observed due to various anthropogenic activities. Elevated levels of sulfate can have harmful effects on aquatic life in freshwaters: sulfate can cause osmotic stress or specific ion toxicity in aquatic organisms, especially in soft waters where Ca2+ and Mg2+ concentrations are low. Formerly, chronic toxicity test data in soft water have been scarce. The chronic and acute sulfate toxicity tests conducted with aquatic organisms from 10 families across various trophic levels in this study multiplied the number of tests conducted in soft freshwater conditions and enabled derivation of the species sensitivity distribution (SSD) and sulfate hazardous concentrations for soft freshwaters. The cladoceran Daphnia longispina and freshwater snail Lymnaea stagnalis were the most sensitive to sulfate among the studied species. Harmful effects on the reproduction of D. longispina were observed at 49 mg SO4 /L while growth of L. stagnalis was inhibited at 217 mg SO4 /L. Most studied organisms tolerated high sulfate concentrations: the median of chronic effective concentrations (EC10 or LC10) was 1008 mg/L for all the species tested in this study. Based on the species sensitivity distribution of the studied species the hazardous concentration for 5 % of aquatic organism (HC5) in soft waters was 117–194 mg SO4/L. Different data set combinations were used to demonstrate the data variability in SSD-based HC5 estimates. The lowest values were produced from combining biotest results from the present study and earlier literature, while the highest values were calculated from the present study only. The derived chronic no-effect concentrations (PNEC) varied between 39 and 65 mg SO4/L.

Effects of Single and Combined Exposure to Environmentally Relevant Concentrations of Cyfluthrin and Copper on Digestive Gland Histology of Lymnaea stagnalis

Pyrethroid insecticides and heavy metals frequently co-exist in aquatic systems, due to intensive anthropogenic activities, and their effects on aquatic organisms are needed to be investigated. In the present work, single and combined effects of environmentally realistic concentrations of cyfluthrin and copper on the digestive gland histology of the freshwater pond snail (Lymnaea stagnalis) were evaluated. Snails were exposed to 1 µg/L cyfluthrin, 10 µg/L copper, and 1 µg/L cyfluthrin + 10 µg/L copper mixture for 96 h. Cyfluthrin-exposed samples showed apparent vacuolization, basal lamina separations, and disrupted digestive cells. Exposure to copper alone gave rise to enlargements of the tubule lumens and the intertubular area, degenerated tubules, atrophied basophilic cells, prominently disrupted and ruptured digestive cells, and nuclear enlargements in some basophilic cells. Cyfluthrin and copper mixture caused more severe histopathological changes in the digestive gland. General tissue appearance was altered by prominently degenerated, and fused tubules lacking cellular structure; tubule lumens filled with cellular content were noted. Increased intertubular regions were filled with connective tissue formations. Progressive disruption of digestive cells; and basophilic cell atrophy were also observed. The findings of the current study highlighted that cyfluthrin and copper at environmentally relevant concentrations caused a biological response in L. stagnalis; however, this response was more intense following their co-exposure.

Ecological determinants of variation in phenotypic selection on quantitative immune defence traits

Immune defence is an important determinant of organismal fitness. While theoretical models based on tradeoffs in resource allocation predict quantitative immune traits to be subject to stabilizing selection due to associated energetic costs and self‐harm, empirical studies report mainly positive directional selection. This discrepancy may arise from multiple ecological factors that vary in nature and could influence selection. We examined if selection on immune activity varies depending on immune challenge/infection risk, between immune traits and among populations in the freshwater snail Lymnaea stagnalis. We assessed selection on the phenoloxidase‐like and antibacterial activity of snail haemolymph while manipulating the level of immune challenge imposed by environmental microbes. We did this using snails from multiple populations and also quantified within‐population family‐level variation (i.e. evolutionary potential) in the snails' immune activity. We found that the strength of immune challenge and the examined immune trait determined selection on the snails' immune function. Thus, variation in infection risk can be an important factor in maintaining genetic variation in defence traits. Additionally, immune traits showed low among‐population differentiation but high within‐population genetic variation. This pattern could arise if natural snail populations are exposed to higher temporal than spatial variation in infection risk.

Sublethal cadmium exposure in the freshwater snail Lymnaea stagnalis meets a deficient, poorly responsive metallothionein system while evoking oxidative and cellular stress

The Great Pond snail Lymnaea stagnalis (Gastropoda, Hygrophila) is a wide-spread freshwater gastropod, being considered as a model organism for research in many fields of biology, including ecotoxicology. The aim of the present study was to explore the Cd sensitivity of L. stagnalis through the measurement of a biomarker battery for oxidative, toxic and cellular stress. The interpretation of biomarker parameters occurred against the background of a truncated metallothionein protein with a limited Cd-binding capacity. Individuals of L. stagnalis were exposed through 14 days to uncontaminated water (controls) or to low (30 μg · L−1) or high (50 μg · L−1) Cd concentrations. The digestive gland of control and low-Cd exposed snails was processed for transcriptional analysis of the Metallothionein (MT) gene expression, and for determination of biomarkers for oxidative stress, toxicity and cellular stress. Digestive gland supernatants of high-Cd exposed snails were subjected to chromatography and subsequent analysis by spectrophotometry. It was shown that the MT system of L. stagnalis is functionally deficient, with a poor Cd responsiveness at both, the transcriptional and the protein expression levels. Instead, L. stagnalis appears to rely on alternative detoxification mechanisms such as Cd binding by phytochelatins and metal inactivation by compartmentalization within the lysosomal system. In spite of this, however, traces of Cd apparently leak out of the pre-determined detoxification pathways, leading to adverse effects, which is clearly indicated by biomarkers of oxidative and cellular stress.

Effects of acute and chronic bendiocarb exposure during early life stages of the pond snail (Lymnaea stagnalis)

ABSTRACT Environmental pollution is a global concern, and anthropogenic activities have contaminated natural water sources. Pesticides are one of the most recognised pollutants worldwide. Carbamates are a widely used pesticide family, and bendiocarb is a broad-spectrum carbamate insecticide detected in surface and groundwater. In the present work, acute lethal and chronic effects of bendiocarb on the early life stages of freshwater snail Lymnaea stagnalis were investigated. 24-h LC50 of bendiocarb on L. stagnalis embryos and juveniles was estimated at 20.39 (18.30–22.71) mg/L and 38.35 (29.58–52.89) mg/L, respectively. Chronic tests were conducted for 21-d to evaluate the potential effects of the environmentally realistic concentrations of bendiocarb (5 and 100 µg/L) on the embryos. Mortality, development, growth (embryo: egg ratio and shell height), heart rate, and hatching success were investigated. The test results showed that mortality, developmental progression, embryo: egg ratio, shell height measurements and cumulative hatching rate were not significantly impaired by chronic bendiocarb exposure compared to the control. However, bendiocarb induced increased heart rate in the exposed snails.

Embryonic exposure to selenium nanoparticles delays growth and hatching in the freshwater snail Lymnaea stagnalis

Selenium nanoparticles (SeNPs) have been applied in the biomedical and biocidal domain which may have potential environmental risks for aquatic systems. However, the knowledge of its toxicity and the role of functionalization on aquatic invertebrates are scarce. Thus, the present study aimed to analyze the embryotoxicity of two types of SeNPs coated with Sodium carboxymethyl cellulose (CMC-SeNPs) and Chitosan (CS-SeNPs) to the freshwater snail Lymnaea stagnalis in lake water, focusing on embryonic development. The influence of surface coatings and ions release, on the embryonic development of SeNPs to freshwater snail L. stagnalis was investigated. For this end, the snails were exposed to different concentrations of SeNPs and Se ions (0.05–1 mg L−1) during 7 days and multiple endpoints were analyzed, including developmental stage frequency, morphological alterations, embryos mortality and hatching success. The results showed that both Se forms promoted the developmental delay, mortality, morphological changes, and hatching inhibition in snail embryos in a concentration-dependent manner. CMC-SeNPs are 2.6 times more embryotoxic compared to CS-SeNPs indicating the importance of surface coating on the embryotoxicity. Moreover, the results revealed that although both forms of Se inhibited the embryo development and reduced the hatching of L. stagnalis, the mode of action on the embryogenesis was different. SeNPs had a higher toxicity to snails’ embryos compared to their dissolved counterparts. Despite significant dissolution, by comparing the SeNPs with their dissolved fraction, the results suggest SeNPs inhibition effect on the snail development could be caused by both SeNPs and Se4+, and SeNPs might be the major development retardation driver rather than Se ions. The present study evidenced by the first time the toxicity effects of SeNPs on the snail embryogenesis, and highlighted how SeNPs intrinsic properties influence their transformation and toxicity in environmental relevant scenarios.

Condition‐dependent immune function in a freshwater snail revealed by stable isotopes

Abstract The immune system is costly to maintain and use because it requires a lot of energy. This can make parasite resistance dependent on host nutritional state. The dependence of immune function on host condition can have broad ecological (e.g., disease dynamics) and evolutionary (e.g., expression of trade‐offs related to parasite resistance) consequences. Research on the dependence of immune function on host condition is typically conducted in laboratory experiments that manipulate either the quantity or composition of available resources. Such studies are essential in establishing conceptual frameworks, but their results are difficult to generalise to natural populations because the experimental treatments may deviate from natural variation in host resource level and use. We examined the condition dependence of immune function in a generalist freshwater snail Lymnaea stagnalis by relating the activity of two immune parameters of snail haemolymph, phenoloxidase (PO)‐like and antibacterial activity, to snail resource level and use using field‐collected individuals. We measured several variables that reflect the snails’ quality based on their recent (i.e., within the past few days; amount and stable isotope composition [δ15N and δ13C] of produced faeces) and longer‐term (i.e., weeks to months; stable isotope composition of tissues) resource use. The PO‐like activity of the snails’ haemolymph was condition‐dependent. Snails that had recently consumed food from higher trophic levels, presumably including more animal protein (high δ15N values of faeces), had a stronger defence. Additionally, snails with low energy (i.e., lipid) reserves in their tissues (high δ13C values of tissues) showed higher PO‐like activity. The antibacterial activity of the snails’ haemolymph was not condition dependent. The finding of the importance of the composition of recently consumed food on immune function (namely PO‐like activity) suggests that the parasite resistance of snails may change rapidly depending on the type of resources available in their environment. Thus, environmental variation may influence the outcome of host–parasite interactions on fine spatial and temporal scales. Furthermore, the negative relationship between the snails’ energy reserves and PO‐like activity suggests substantial energetic costs of immune activity in L. stagnalis.

Embryonic Exposure to Selenium Nanoparticles Delays Growth and Hatching in the Freshwater Snail Lymnaea Stagnalis

Embryonic Exposure to Selenium Nanoparticles Delays Growth and Hatching in the Freshwater Snail Lymnaea Stagnalis

Toll like receptors and their evolution in the lymnaeid freshwater snail species Radix auricularia and Lymnaea stagnalis, key intermediate hosts for zoonotic trematodes

One of the major evolutionarily conserved pathways in innate immunity of invertebrates is the toll-like receptor (TLR) pathway. However, little is known of the TLR protein family in gastropod molluscs despite their role in the transmission of human diseases, especially the common lymnaeid freshwater snail species Radix auricularia and Lymnaea stagnalis, key intermediate hosts of zoonotic trematodes. Using comparative genomics and gene prediction approaches utilising the freshwater snail Biomphalaria glabrata genome as a reference ten putative TLR proteins were identified in both R. auricularia and L. stagnalis. Phylogenetic analyses revealed that unlike other molluscs the lymnaeid species also possessed class 1 TLRs, previously thought to be unique to B. glabrata. Gene duplication events were also seen across the TLR classes in the lymnaeids with several of the genes appearing to exist as potential tandem elements in R. auricularia. Each predicted TLR was shown to possess the typical the leucine-rich repeat extracellular and TIR intracellular domains and both single cysteine clusters and multiple cysteine clusters TLRs were identified in both lymnaeid species. Principle component analyses of 3D models of the predicted TLRs showed that class 1 and 5 proteins did not cluster based on similarity of structure, suggested to be potential adaptation to a range of pathogens. This study provides the first detailed account of TLRs in lymnaeids and affords a platform for further research into the role of these proteins into susceptibility and compatibility of these snails with trematodes and their role in transmission.

What can we teach Lymnaea and what can Lymnaea teach us?

ABSTRACTThis review describes the advantages of adopting a molluscan complementary model, the freshwater snail Lymnaea stagnalis, to study the neural basis of learning and memory in appetitive and avoidance classical conditioning; as well as operant conditioning of its aerial respiratory and escape behaviour. We firstly explored ‘what we can teach Lymnaea’ by discussing a variety of sensitive, solid, easily reproducible and simple behavioural tests that have been used to uncover the memory abilities of this model system. Answering this question will allow us to open new frontiers in neuroscience and behavioural research to enhance our understanding of how the nervous system mediates learning and memory. In fact, from a translational perspective, Lymnaea and its nervous system can help to understand the neural transformation pathways from behavioural output to sensory coding in more complex systems like the mammalian brain. Moving on to the second question: ‘what can Lymnaea teach us?’, it is now known that Lymnaea shares important associative learning characteristics with vertebrates, including stimulus generalization, generalization of extinction and discriminative learning, opening the possibility to use snails as animal models for neuroscience translational research.

Effect of Nanoparticle Size and Natural Organic Matter Composition on the Bioavailability of Polyvinylpyrrolidone-Coated Platinum Nanoparticles to a Model Freshwater Invertebrate.

The bioavailability of dissolved Pt(IV) and polyvinylpyrrolidone-coated platinum nanoparticles (PtNPs) of five different nominal hydrodynamic diameters (20, 30, 50, 75, and 95 nm) was characterized in laboratory experiments using the model freshwater snail Lymnaea stagnalis. Dissolved Pt(IV) and all nanoparticle sizes were bioavailable to L. stagnalis. Platinum bioavailability, inferred from conditional uptake rate constants, was greater for nanoparticulate than dissolved forms and increased with increasing nanoparticle hydrodynamic diameter. The effect of natural organic matter (NOM) composition on PtNP bioavailability was evaluated using six NOM samples at two nanoparticle sizes (20 and 95 nm). NOM suppressed the bioavailability of 95 nm PtNPs in all cases, and DOM reduced sulfur content exhibited a positive correlation with 95 nm PtNP bioavailability. The bioavailability of 20 nm PtNPs was only suppressed by NOM with a low reduced sulfur content. The physiological elimination of Pt accumulated after dissolved Pt(IV) exposure was slow and constant. In contrast, the elimination of Pt accumulated after PtNP exposures exhibited a triphasic pattern likely involving in vivo PtNP dissolution. This work highlights the importance of PtNP size and interfacial interactions with NOM on Pt bioavailability and suggests that in vivo PtNP transformations could yield unexpectedly higher adverse effects to organisms than dissolved exposure alone.

Impact of colchicine on morphology of different developmental stages of Lymnaea stagnalis

The molluscicidal effect of colchicine was evaluated against various stages of the freshwater snail Lymnaea stagnalis, immature, young mature and adults. Calculated values of lethal concentrations (LC50and LC100 ) showed colchicine as toxic against eggs, immature and adults. Results revealed that colchicine could be used to control harmful snails, as it significantly controls reproduction of these snails. The colchicine reduces fecundity, prolongs hatchability period and reduces survival of the newly hatched snails in a snail population, when exposed to a concentration lower than LC50. So, this investigation was made to know more about the intoxication of alkaloids of colchicines on the mortality and survivality of hatched young snail of pest snail.

The effect of trematode infection on the markers of oxidative stress in the offspring of the freshwater snail Lymnaea stagnalis.

Most invertebrate species exhibit immunological responses that can inactivate and eliminate penetrating parasites. Such immune responses in particular involve the formation of potentially toxic reactive oxygen species (ROS). We explored the immune capabilities of the first-generation (F1) offspring of naturally infected freshwater snails, Lymnaea stagnalis, in response to infection by trematode cercariae under laboratory conditions. The rates of ROS formation and peroxidase activity in the hemolymph of the F1 offspring of L. stagnalis parents infected by an asexual stage of trematodes were significantly higher than in F1 offspring of uninfected parents. Compared to offspring from uninfected parents, the growth rate of F1 snails from infected parents was higher, but survival was lower. After infection of F1 snails by trematode cercariae of Echinoparyphium aconiatum under laboratory conditions, the rate of ROS formation and peroxidase activity in the hemolymph of F1 offspring of uninfected parents increased compared to control snails. This pattern persisted throughout the entire 3-week observation period. In contrast, the rate of ROS formation in the hemolymph of F1 snails from infected parents after experimental infection by E. aconiatum cercariae did not differ from controls, and peroxidase activity even decreased. Thus, trematode parthenitae infection of parents could alter the immune response of their offspring.

The development of CRISPR for a mollusc establishes the formin Lsdia1 as the long-sought gene for snail dextral/sinistral coiling.

The establishment of left-right body asymmetry is a key biological process that is tightly regulated genetically. In the first application of CRISPR/Cas9 to a mollusc, we show decisively that the actin-related diaphanous gene Lsdia1 is the single maternal gene that determines the shell coiling direction of the freshwater snail Lymnaea stagnalis Biallelic frameshift mutations of the gene produced sinistrally coiled offspring generation after generation, in the otherwise totally dextral genetic background. This is the gene sought for over a century. We also show that the gene sets the chirality at the one-cell stage, the earliest observed symmetry-breaking event linked directly to body handedness in the animal kingdom. The early intracellular chirality is superseded by the inter-cellular chirality during the 3rd cleavage, leading to asymmetric nodal and Pitx expression, and then to organismal body handedness. Thus, our findings have important implications for chiromorphogenesis in invertebrates as well as vertebrates, including humans, and for the evolution of snail chirality. This article has an associated 'The people behind the papers' interview.

Relative importance of chemical attractiveness to parasites for susceptibility to trematode infection.

While the host immune system is often considered the most important physiological mechanism against parasites, precontact mechanisms determining exposure to parasites may also affect infection dynamics. For instance, chemical cues released by hosts can attract parasite transmission stages. We used the freshwater snail Lymnaea stagnalis and its trematode parasite Echinoparyphium aconiatum to examine the role of host chemical attractiveness, physiological condition, and immune function in determining its susceptibility to infection. We assessed host attractiveness through parasite chemo‐orientation behavior; physiological condition through host body size, food consumption, and respiration rate; and immune function through two immune parameters (phenoloxidase‐like and antibacterial activity of hemolymph) at an individual level. We found that, although snails showed high variation in chemical attractiveness to E. aconiatum cercariae, this did not determine their overall susceptibility to infection. This was because large body size increased attractiveness, but also increased metabolic activity that reduced overall susceptibility. High metabolic rate indicates fast physiological processes, including immune activity. The examined immune traits, however, showed no association with susceptibility to infection. Our results indicate that postcontact mechanisms were more likely to determine snail susceptibility to infection than variation in attractiveness to parasites. These may include localized immune responses in the target tissue of the parasite. The lack of a relationship between food consumption and attractiveness to parasites contradicts earlier findings that show food deprivation reducing snail attractiveness. This suggests that, although variation in resource level over space and time can alter infection dynamics, variation in chemical attractiveness may not contribute to parasite‐induced fitness variation within populations when individuals experience similar environmental conditions.

Using the Biotic Ligand Model framework to investigate binary metal interactions on the uptake of Ag, Cd, Cu, Ni, Pb and Zn in the freshwater snail Lymnaea stagnalis

There is growing interest in the development of mechanistically-based models, such as the Biotic Ligand Model (BLM), for assessing the environmental risk of metal mixtures. However, the derivation of such models requires insights into the mechanisms of multimetal interactions that are often lacking for aquatic organisms. In the present study, we investigated how binary mixtures of six metals (Ag, Cd, Cu, Ni, Pb and Zn) interact for uptake in the great pond snail Lymnaea stagnalis, a freshwater species particularly sensitive to metals in chronic exposure. For each metal, short-term (2–3 h) uptake experiments on juvenile snails were performed with the metal alone and in combination with a second metal, at concentrations encompassing the chronic toxicity concentration range. These experiments showed significant binary metal interactions for 7 out of 15 mixtures. Most interactions were inhibitory in nature, not reciprocal and caused by either Ag or Cu. They led to relative changes of uptake that did not exceed 50% within the range of metal chronic toxicity. The BLM proved to be successful at explaining most of the interactions, via competitive inhibition. This study is in support of using bioavailability-based models, such as the BLM, to model metal mixture interactions in L. stagnalis.

Chronic Toxicity of Binary Mixtures of Six Metals (Ag, Cd, Cu, Ni, Pb, and Zn) to the Great Pond Snail Lymnaea stagnalis.

Although metal-mixture toxicity has recently received increasing attention, there is still insufficient knowledge on joint effects occurring in chronic exposures to relatively low metal concentrations. We characterized the chronic toxicity of binary mixtures of six metals (Ag, Cd, Cu, Ni, Pb, and Zn) in 14 day growth tests with juveniles of the metal-sensitive freshwater snail Lymnaea stagnalis. Observations were compared with predictions from individual metals and from the two most frequently used mixture models: concentration addition (CA) and independent action (IA). Predictions based on measured total dissolved concentrations and on calculated free-ion activities did not differ greatly because multimetal geochemical interactions in the tests were limited. In around half of the tests, mixture toxicity was higher than the greatest effect caused by the individual metals, arguing in favor of considering joint effects. When the additive models were used, the great majority of interactions were either additive or less than additive (i.e., antagonism). In general, the IA model was the most accurate, while the CA model was the most conservative. Along with other studies, these findings suggest that, at least for binary combinations, the simple CA model may provide satisfactory protection from the chronic metal toxicity of metal mixtures to aquatic organisms.