Exposure pathway dependent effects of titanium dioxide and silver nanoparticles on the benthic amphipod Gammarus fossarum

Effects of nanoplastic exposure routes on leaf decomposition in streams

Polystyrene nanoparticles (PS NPs) released from plastic products have been demonstrated to pose a threat to leaf litter decomposition in streams. Given the multitrophic systems of species interactions, the effects of PS NPs through different exposure routes on ecosystem functioning remain unclear. Especially dietary exposure, a frequently overlooked pathway leading to toxicity, deserves more attention. A microcosm experiment was conducted in this study to assess the effects of waterborne and dietary exposure to PS NPs on the litter-based food chain involving leaves, microbial decomposers, and detritivores (river snails). Compared to waterborne contamination, dietary contamination resulted in lower microbial enzyme activities and a significantly higher decrease in the lipid content of leaves. For river snails, their antioxidant activity was significantly increased by 20.21%-69.93%, and their leaf consumption rate was significantly reduced by 16.60% through the dietary route due to the lower lipid content of leaves. Besides, the significantly decreased nutritional quality of river snails would negatively influence their palatability to predators. The findings of this study indicate that dietary exposure to PS NPs significantly impacts microbial and detritivore activities, thus affecting their functions in the detritus food chain as well as nutrient cycling.

Assessing the in vivo toxicity of titanium dioxide nanoparticles in Schmidtea mediterranea: uptake pathways and (neuro)developmental outcomes

Titanium dioxide nanoparticles (TiO2-NPs) in aquatic environments, originating from urban run-off, product use and post-consumer degradation, interact with aquatic organisms through water and sediments. Thorough toxicity assessment requires comprehensive data across all ecosystem compartments especially the benthic zone, which is currently lacking. Moreover, a proper physicochemical characterization of the particles is needed before and during toxicity assessment. In the present work, we used the planarian Schmidtea mediterranea to investigate the effects of TiO2-NPs (5 mg/L and 50 mg/L). Planarians are benthic organisms that play an important role in the food chain as predators. Our study integrated particle characterization with toxicokinetic and toxicodynamic parameters and showed that the uptake of TiO2-NPs of 21 nm occurred through the epidermis and intestine. Epidermal irritation and mucus production occurred immediately after exposure, and TiO2-NPs induced stronger effects in regenerating organisms. More specifically, TiO2-NPs interfered with neuroregeneration, inducing behavioral effects. A delay in the formation of the anterior commissure between the two brain lobes after seven and nine days of exposure to 50 mg/L was observed, probably as a result of a decrease in stem cell proliferation. Our findings underscore the need to incorporate multiple exposure routes in toxicity screenings. Additionally, we highlight the vulnerability of developing organisms and recommend their inclusion in future risk assessment strategies.

Assessing the effects of silver nanoparticles on the ecophysiology of Gammarus roeseli

Being part of the macrobenthic fauna, gammarids are efficient indicators of contamination of aquatic ecosystems by nanoparticles that are likely to sediment on the bottom. The present study investigates the effects of silver nanoparticles (nAg) on ecophysiological functions in Gammarus roeseli by using a realistic scenario of contamination. Indeed, an experiment was conducted during 72 h, assessing the effects of 5 silver nAg from 10 to 100 nm diluted at concentrations of maximum 5 µg L^-1 in a natural water retrieved from a stream and supplemented with food. The measured endpoints in gammarids were survival, silver concentrations in tissues, consumption of oxygen and ventilation of gills. Additionally, a set of biomarkers of the energetic metabolism was measured. After a 72-h exposure, results showed a concentration-dependent increase of silver levels in G. roeseli that was significant for the smallest nAg size (10 nm). Ecophysiological responses in G. roeseli were affected and the most striking effect was a concentration-dependent increase in oxygen consumption especially for the smallest nAg (10 to 40 nm), whereas ventilation of gills by gammarids was not changed. The potential mechanisms underlying these findings are discussed. Thus, we demonstrated the very low exposure concentration of 0.5 µg L^-1 for the small nAg size led to significant ecophysiological effects reinforcing the need to further investigate subtle effects on nanoparticles on aquatic organisms.

Importance of exposure route in determining nanosilver impacts on a stream detrital processing chain

The commercial use and spread of silver nanoparticles (AgNPs) in freshwaters have greatly increased over the last decade. Both AgNPs and ionic silver (Ag⁺) released from nanoparticles are toxic to organisms and compromise ecosystem processes such as leaf litter decomposition. Yet little is known about how AgNPs affect multitrophic systems of interacting species. Furthermore, past work has focused on waterborne exposure with scarce attention given to effects mediated by the consumption of contaminated food. We assessed the importance of direct (via water) and indirect (via diet) AgNP exposure to a processing chain comprising leaf litter, fungi, a shredder (Gammarus pulex) and a collector (Habroleptoides confusa) in microcosms. Direct exposure to contaminated water for 15 days impaired microbial leaf decomposition by ∼50% and leaf-associated fungal biomass by ∼10%. Leaf consumption was reduced by ∼20% but only when G. pulex was exposed to silver via contaminated leaves. There was no effect on FPOM production. Ag ⁺ could impose oxidative stress on the shredders and collectors independent of exposure route, as indicated by increased catalase and glutathione S-transferase activities and decreased superoxide dismutase activity. The activity of a neuronal enzyme (cholinesterase) in collectors, but not shredders, also decreased by almost 50% when the animals were indirectly exposed to AgNP. Our results show that AgNPs and Ag⁺ may disrupt detrital processing chains through direct and indirect exposure routes, even at low concentrations. This highlights the importance of AgNP exposure pathways to interconnected stream biota and ecosystem processes for realistic assessments of risks to freshwater ecosystems.

Photoactive titanium dioxide nanoparticles modify heterotrophic microbial functioning

Nanoparticulate titanium dioxide (nTiO₂) is frequently applied, raising concerns about potential side effects on the environment. While various studies have assessed structural effects in aquatic model ecosystems, its impact on ecosystem functions provided by microbial communities (biofilms) is not well understood. This is all the more the case when considering additional stressors, such as UV irradiation - a factor known to amplify nTiO₂-induced toxicity. Using pairwise comparisons, we assessed the impact of UV (UV-A = 1.6 W/m²; UV-B = 0.7 W/m²) at 0, 20 or 2000 μg nTiO₂/L on two ecosystem functions provided by leaf-associated biofilms: while leaf litter conditioning, important for detritivorous invertebrate nutrition, seems unaffected, microbial leaf decomposition was stimulated (up to 25%) by UV, with effect sizes being higher in the presence of nTiO₂. Although stoichiometric and microbial analyses did not allow for uncovering the underlying mechanism, it seems plausible that the combination of a shift in biofilm community composition and activity together with photodegradation as well as the formation of reactive oxygen species triggered changes in leaf litter decomposition. The present study implies that the multiple functions a microbial community performs are not equally sensitive. Consequently, relying on one of the many functions realized by the same microbial community may be misleading for environmental management.

Sub-chronic effects of AgNPs and AuNPs on Gammarus fossarum (Crustacea Amphipoda): From molecular to behavioural responses

The aim of the present study was the assessment of the sub-chronic effects of silver (AgNPs) and gold nanoparticles (AuNPs) of 40 nm primary size either stabilised with citrate (CIT) or coated with polyethylene glycol (PEG) on the freshwater invertebrate Gammarus fossarum. Silver nitrate (AgNO₃) was used as a positive control in order to study the contribution of silver ions potentially released from AgNPs on the observed effects. A multibiomarker approach was used to assess the long-term effects of AgNPs and AuNPs 40 nm on molecular, cellular, physiological and behavioural responses of G. fossarum. Specimen of G. fossarum were exposed for 15 days to 0.5 and 5 µgL^-1 of CIT and PEG AgNPs and AuNPs 40 nm in the presence of food. A significant uptake of both Ag and Au was observed in exposed animals but was under the toxic threshold leading to mortality of G. fossarum. Silver nanoparticles (CIT-AgNPs and PEG-AgNPs 40 nm) led to an up-regulation of Na⁺K⁺ATPase gene expression. An up-regulation of Catalse and Chitinase gene expressions due to exposure to PEG-AgNPs 40 nm was also observed. Gold nanoparticles (CIT and PEG-AuNPs 40 nm) led to an increase of CuZnSOD gene expression. Furthermore, both AgNPs and AuNPs led to a more developed digestive lysosomal system indicating a general stress response in G. fossarum. Both AgNPs and AuNPs 40 nm significantly affected locomotor activity of G. fossarum while no effects were observed on haemolymphatic ions and ventilation.

The Increase in Temperature Overwhelms Silver Nanoparticle Effects on the Aquatic Invertebrate Limnephilus sp

The effects of silver nanoparticles (AgNPs) have been largely explored, but there is still a lack of knowledge on their effects under the predicted changes in temperature as a consequence of climate change. The aim of the present study was to determine how leaf consumption by invertebrate shredders is affected by dietary exposure to AgNPs and AgNO₃ and whether changes in temperature alter such effects. Also, responses of antioxidant enzymes were examined. In microcosms, the invertebrate shredder Limnephilus sp. was allowed to feed on alder leaves treated with AgNPs (5, 10, and 25 mg L^-1 ) and AgNO₃ (1 mg L^-1 ) at 10, 16, and 23 °C (6 replicates). After 5 d, the animals were transferred to clean water and allowed to feed on untreated leaves. The higher leaf consumption by the shredder was related to temperature increase and to the contamination of leaves with AgNPs and AgNO₃ . Results from enzymatic activities demonstrated that AgNP contamination via food induce oxidative and neuronal stress in the shredder: the activities of catalase and superoxide dismutase were positively correlated with total Ag accumulated in the animal body. Moreover, glutathione S-transferase activity was strongly associated with higher temperature (23 °C). Overall results indicated that the effects of toxicants on consumption rates and enzymatic activities are modulated by temperature and suggested that increases in temperature changes the AgNP effects on invertebrate shredder performance. Environ Toxicol Chem 2020;39:1429-1437. © 2020 SETAC.

Silver nanoparticles: Toxicity in model organisms as an overview of its hazard for human health and the environment

Silver nanoparticles (AgNPs) have attracted remarkable attention due to their powerful antimicrobial action as well as their particular physicochemical properties. This has led to their application in a wide variety of products with promising results. However, their interaction with the environment and toxicity in live terrestrial or aquatic organisms is still a matter of intense debate. More detailed knowledge is still required about the toxicity of AgNPs, their possible uptake mechanisms and their adverse effects in live organisms. Several studies have reported the interactions and potential negative effects of AgNPs in different organisms. In this review, we report and discuss the current state of the art and perspectives for the impact of AgNPs on different organisms present in the environment. Recent progress in interpreting uptake, translocation and accumulation mechanisms in different organisms and/or living animals are discussed, as well as the toxicity of AgNPs and possible tolerance mechanisms in live organisms to cope with their deleterious effects. Finally, we discuss the challenges of accurate physicochemical characterization of AgNPs and their ecotoxicity in environmentally realistic conditions such as soil and water media.