We tested the effect of silver nanoparticles (AgNPs) on the ability of the pond snail, Lymnaea stagnalis, to learn and form long-term memory (LTM) following operant conditioning of aerial respiration. We hypothesized that the AgNPs would act as a stressor and prevent learning and LTM formation. We tested snails exposed for either 72 h or only during training and testing for memory (i.e. 0.5 h) and found no difference between those treatments. We found that at a low concentration of AgNPs (5 μg/L) neither learning and nor memory formation were altered. When we increased the concentration of AgNPs (10 μg/L) we found that memory formation was enhanced. Finally, at a higher concentration (50 μg/L) memory formation was blocked. To determine if the disassociation of Ag+ from the AgNPs caused the effects on memory we performed similar experiments with AgNO3 and found similar concentration-dependent results. Finally, we found that snails perceive the AgNPs differently from Ag+ as there was context specific memory. That is, snails trained in AgNPs did not show memory when tested in Ag+ and vice-versa. We believe that changes in memory formation may be a more sensitive determination of AgNPs on aquatic organisms than the determination of a LC50.

Nickel bioavailability is reduced in the presence of dissolved organic carbon (DOC), suspended solids (TSS), and other complexing ligands; however, no studies have examined the relative importance of Ni exposure through different compartments (water, sediment, food). Hyalella azteca and Lymnaea stagnalis were exposed to Ni-amended water, sediment, and food, either separately or in combination. Both organisms experienced survival and growth effects in several Ni compartment tests. The DOC amendments attenuated L. stagnalis Ni effects (survival, growth, and ⁶²Ni bioaccumulation), and presence of TSS exposures demonstrated both protective and synergistic effects on H. azteca and L. stagnalis. ⁶²Ni trophic transfer from food to H. azteca and L. stagnalis was negligible; however, bioaccumulating ⁶²Ni was attributed to ⁶²Ni-water (⁶²Ni flux from food), ⁶²Ni-TSS, and ⁶²Ni-food. Overall, H. azteca and L. stagnalis Ni compartment toxicity increased in the following order: Ni-water >> Ni-sediment >> Ni-all (water, sediment, food) >> Ni-food.

Understanding the behavior of engineered nanoparticles in the environment and within organisms is perhaps the biggest obstacle to the safe development of nanotechnologies. Reliable tracing is a particular issue for nanoparticles such as ZnO, because Zn is an essential element and a common pollutant thus present at elevated background concentrations. We synthesized isotopically enriched (89.6%) with a rare isotope of Zn (⁶⁷Zn) ZnO nanoparticles and measured the uptake of ⁶⁷Zn by L. stagnalis exposed to diatoms amended with the particles. Stable isotope technique is sufficiently sensitive to determine the uptake of Zn at an exposure equivalent to lower concentration range (<15 μg g⁻¹). Without a tracer, detection of newly accumulated Zn is significant at Zn exposure concentration only above 5000 μg g⁻¹ which represents some of the most contaminated Zn conditions. Only by using a tracer we can study Zn uptake at a range of environmentally realistic exposure conditions.

The amount of toxic metal accumulated by an organism is often taken as an indicator of potential toxicity. We investigated this relationship in the freshwater snail, Lymnaea stagnalis, exposed to 500 μg l⁻¹ Al over 30 days, either alone or in the presence of phosphate (500 μg l⁻¹ P) or a fulvic acid surrogate (FAS; 10 mg l⁻¹ C). Behavioural activity was assessed and tissue accumulation of Al quantified. Lability of Al within the water column was a good predictor of toxicity. FAS increased both Al lability and behavioural dysfunction, whereas phosphate reduced Al lability, and completely abolished Al-induced behavioural toxicity. Tissue accumulation of Al was not linked to toxicity. Higher levels of Al were accumulated in snails exposed to Al + P, compared to those exposed to Al alone, whereas FAS reduced Al accumulation. These findings demonstrate that the degree of tissue accumulation of a metal can be independent of toxicity. Total Al accumulation in the tissues of Lymnaea stagnalis does not provide a direct indication of its toxicity.

Azoxystrobin (AZ) is an aryloxy pyrimidine fungicide extensively applied in the agriculture field all over the world. There is a little information about the ecotoxicity of AZ fungicide on the freshwater snail Lymnaea luteola (L. luteola). The present study investigated the toxic effect of AZ fungicide on L. luteola by using various measures. We determined the mean LC₅₀ value―96 h of AZ fungicide (0.79 mg/L) for L. luteola, in a static system. Based on this value, three sublethal concentrations, viz., I (0.079 mg/L), II (~ 0.40 mg/L), and III (~ 0.53 mg/L), were determined. The snails were exposed to these three concentrations of AZ fungicide for 96 h, and hemolymph and digestive glands were collected after 24 and 96 h for assessment of oxidative stress, apoptosis, and histological and genotoxic changes. The induction of intracellular reactive oxygen species (ROS) and apoptosis in hemocyte cells was increased in a dose- and time-dependent manner. It was observed that lipid peroxide (LPO) and glutathione S transferase (GST) were increased, and glutathione and superoxide dismutase decreased in digestive glands. A similar trend was observed for the DNA damage as measured in terms of the percentage of tail DNA and olive tail moment in digestive gland cells. This study showed the collective use of oxidative stress, histological, and genotoxicity parameters in in vivo laboratory studies using snails that are useful for screening the toxic potential of environmental contaminants such as AZ fungicide.Graphical abstract