Enzymatic biomarkers can portray nanoCuO-induced oxidative and neuronal stress in freshwater shredders

Are tolerance processes limiting the responses of Hediste diversicolor to cadmium exposure? A multimarker approach

Cadmium (Cd) is considered a priority hazardous substance under the European Community Directive 2013/39 due to its ecotoxicity. The ragworm Hediste diversicolor (O.F. Müller, 1776), a common species in estuaries and coastal lagoons, plays an important ecological role in these ecosystems and is a suitable bioindicator of environmental chemical contamination. In this study, H. diversicolor was chosen as an ecotoxicological model with the aim of evaluating the responses to Cd contamination, considering a multi-biomarker approach (mortality, biometry, behaviour, Cd bioaccumulation, oxidative stress and damage, and energy metabolism). Also, the hypothesis of different tolerances resulting in different responses was evaluated, by collecting worms from three systems distinctly impacted by metal contamination (Mondego estuary, Óbidos Lagoon and Sado estuary - Portugal). Animals were exposed under laboratory conditions to cadmium (10, 50 and 100 µg/L), for 10 days. Significant differences were observed in responses amongst worms originating from the different sites. Organisms from the less impacted systems revealed greater effects on mortality, biomass decrease and burrowing behaviour, as well as higher bioaccumulation potential, after exposure to Cd. Biochemical and behaviour impairments were observed as a consequence of Cd exposure, although not in a concentration-dependant manner. The results obtained in this study reinforce the importance of integrating endpoint responses, at the individual and sub-individual levels, to assess potential changes induced by pollutants in the physiological status and fitness of H. diversicolor and help to predict what their ecological consequences might be.

Responses of submerged macrophyte Ceratophyllum demersum to the gradient concentrations of microcystin-LR (MC-LR)

The responses of Ceratophyllum demersum to gradient concentrations (0, 0.8, 3.2, and 10 µg/L) of microcystin-LR (MC-LR) were comprehensively investigated by laboratory simulation experiments. The high reduction and accumulation efficiency of MC-LR by C. demersum were verified in this study. Results showed that the reduction ratio of MC-LR in the cultivation medium was up to 99% after 14 days of exposure, and the accumulation of MC-LR in C. demersum was highest at an exposure concentration of 10 μg/L, the value of which was 0.9 ng/g fresh weight (FW). Meanwhile, a series of negative effects on C. demersum was detectable, accompanied by a significant biomass reduction of the plant and changes in microbial community composition. In particular, this study indicated that the amount of Flavobacteria was elevated under the stress of MC-LR, provoking great threats to aquatic ecosystems. Moreover, oxidative damage was evidenced by the changes in total antioxidant capacity, superoxide dismutase, and glutathione. The results also demonstrated significant increases in sugar (0.025 mg/g FW), protein (0.3 mg/g FW), and carotenoids (0.6 mg/g FW) in C. demersum stressed by 10 μg/L of MC-LR, compared with the control without microcystins, which were among the defense strategies for dealing with adverse conditions. These results verified the good potential of submerged macrophytes as an eco-friendly strategy for controlling cyanobacterial blooms. However, the negative effects of MC-LR on the macrophytes themselves were also demonstrated, which would be considered in future practice and management.

Evidence of micro and macroplastic toxicity along a stream detrital food-chain

Freshwater ecosystems are subjected to plastic extensive pollution because they are the direct link between plastic wastes and marine ecosystems. The aim of this study was to assess the impacts of different sizes of polyethylene plastics (micro: µPs and macroplastics: PBs) on freshwater decomposers of plant litter. We exposed leaf associated microbial assemblages to µPs (0.5 or 1.5 g L^-1) and discs of PBs as follows: green plastic bags (PB-G) alone or in mixtures with transparent plastic bags (PB-Mix). Then, we conducted a feeding preference experiment with the invertebrate shredder Limnephilus sp. to assess their capacity to distinguish leaf discs from PB discs of the same size (12 mm). Leaf decomposition, activities of fungal enzymes and sporulation were inhibited by µPs and PB-Mix, and shifts in fungal community composition were observed. The invertebrate shredders preferred to feed on leaves treated with µPs avoiding those exposed to PB-G/PB-Mix. Our results demonstrated that plastics can have a direct effect on stream-dwelling microbial decomposers and an indirect effect on higher trophic levels (shredders), highlighting that trophic transfer is a route of plastic exposure. The plastic properties (size, concentration, colour) appear to influence plastic toxicity to microbes and shredders, indicating the importance of considering physicochemical properties when assessing their risks to freshwater ecosystems.

Can microplastics from personal care products affect stream microbial decomposers in the presence of silver nanoparticles?

Microplastics (MPs) are emerging contaminants of great concern due to their abundance and persistence over time in aquatic environments. However, studies on their impacts on freshwater organisms are scarce. In resemblance, silver nanoparticles (Ag-NPs) are incorporated into textiles and personal care products and are also classified as emerging contaminants. We used the leaf litter decomposition model system to investigate the effects of MPs from a commercially used personal care product, alone or in mixture with Ag-NPs, on the diversity and activities of freshwater microbial decomposers. We exposed stream microbial communities associated with leaf litter to increasing concentrations of MPs (polyethylene extracted from a personal care product; 100 μg L^-1 up to 1 g L^-1 5 concentrations plus 1 control) for 27 days in the absence or presence of Ag-NPs (0.1 mg L^-1 and 1 mg L^-1). The exposure to MPs, alone or in mixture with Ag-NPs, negatively affected fungal diversity and sporulation, with a reduction in leaf litter decomposition (Cohen's d > 1.5; r> 0.8; Bonferroni, P < 0.01). Shifts in community structure of sporulating fungi were observed, and effects were more pronounced in mixtures with Ag-NPs at the highest concentration. Mixtures of MPs with Ag-NPs (at the higher concentration) had the strongest impacts on extracellular enzymatic (β-glucosidase, Cohen's d > 1; r > 0.5; phenol oxidase, Cohen's d > 1; r > 0.4) activities (ANOVAs, P < 0.05). Apart from sporulation rates, observed toxicity in mixtures was lower than that expected based on individual toxicity effects, mainly for higher concentrations (Bonferroni, P < 0.05). Our study provided evidence of the potential harmful effects of MPs, alone or in mixtures with Ag-NPs, on the activities of aquatic fungi and on a key ecosystem process, determinant to organic matter turnover in streams.

Fire and rain: A systematic review of the impacts of wildfire and associated runoff on aquatic fauna

Climate and land-use changes are expected to increase the future occurrence of wildfires, with potentially devastating consequences for freshwater species and ecosystems. Wildfires that burn in close proximity to freshwater systems can significantly alter the physicochemical properties of water. Following wildfires and heavy rain, freshwater species must contend with complex combinations of wildfire ash components (nutrients, polycyclic aromatic hydrocarbons, and metals), altered light and thermal regimes, and periods of low oxygen that together can lead to mass mortality events. However, the responses of aquatic fauna to wildfire disturbances are poorly understood. Here we provide a systematic review of available evidence on how aquatic animals respond to and recover from wildfire disturbance. Two databases (Web of Science and Scopus) were used to identify key literature. A total of 83 studies from across 11 countries were identified to have assessed the risk of wildfires on aquatic animals. We provide a summary of the main ecosystem-level changes associated with wildfires and the main responses of aquatic fauna to such disturbances. We pay special focus to physiological tools and biomarkers used to assess how wildfires impact aquatic animals. We conclude by providing an overview of how physiological biomarkers can further our understanding of wildfire-related impacts on aquatic fauna, and how different physiological tools can be incorporated into management and conservation plans and serve as early warning signs of wildfire disturbances.

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.

Biochemical and functional responses of stream invertebrate shredders to post-wildfire contamination

Forests in Mediterranean Europe including Portugal are highly susceptible to wildfires. Freshwaters are often exposed to post-wildfire contamination that contains several toxic substances, which may impose risk to freshwater organisms and ecosystem functions. However, knowledge on the impacts of post-wildfire runoffs from different origins on freshwater biota is scarce. In forest streams, invertebrate shredders have a major contribution to aquatic detrital-based food webs, by translocating energy and nutrients from plant-litter to higher trophic levels. We investigated the leaf consumption behaviour and the responses of oxidative and neuronal stress enzymatic biomarkers in the freshwater invertebrate shredder Allogamus ligonifer after short-term exposure (96 h) to post-wildfire runoff samples from Pinus and Eucalyptus plantation forests and stream water from a burnt catchment in Portugal. Chemical analyses indicated the presence of various metals and PAHs at considerable concentrations in all samples, although the levels were higher in the runoff samples from forests than in the stream water. The shredding activity was severely inhibited by exposure to increased concentrations of post-wildfire runoff samples from both forests. The dose-response patterns of enzymatic biomarkers suggest oxidative and neuronal stress in the shredders upon exposure to increasing concentrations of post-wildfire runoffs. The impacts were more pronounced for the runoffs from the burnt forests. Moreover, the response patterns suggest that the energy from the feeding activity of shredders might have contributed to alleviate the stress in A. ligonifer. Overall, the outcomes suggest that the post-wildfire contamination can induce sublethal effects on invertebrate shredders with impacts on key ecological processes in streams.

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.

Proteomic responses to silver nanoparticles vary with the fungal ecotype

Enhanced commercial application of silver nanoparticles (AgNPs) is increasing the chance of their release into aquatic environments, potentially putting non-target microorganisms at risk. Impacts of AgNPs and Ag⁺ on two fungal ecotypes of Articulospora tetracladia, collected from a metal-polluted (At61) and a non-polluted (At72) stream, were assessed based on antioxidant enzymatic and proteomic responses. At61 showed more tolerance to AgNPs than At72 (EC₂₀, 158.9 vs 7.5 µg L^-1, respectively). Antioxidant enzyme activities were induced by AgNPs or Ag⁺ in both fungal ecotypes. Proteomic responses to AgNPs or Ag⁺ revealed that 41.3% of the total altered proteins were common in At72, while 27.3% were common in At61. In At72, gene ontology enrichment analyses indicated that Ag⁺ increased mainly the content of proteins involved in proteostasis and decreased the content of those related to vesicle-mediated transport; whereas the key group of proteins induced by AgNPs had functions in DNA repair and energy production. In At61, AgNPs induced proteins involved in energy production and protein biosynthesis, while both Ag forms induced proteins related to cell-redox and protein homeostasis, ascospore formation, fatty acid biosynthesis and nucleic acids metabolism. Both Ag forms induced stress-responsive proteins, and this was consistent with the responses of antioxidant enzymes. The negligible quantity of Ag⁺ released from AgNPs (<0.2 μg L^-1) supported a minor role of dissolved ionic form in AgNP-induced toxicity to both fungal ecotypes. Overall, results unraveled distinct mechanisms of toxicity and cellular targets of nanoparticulate and ionic silver in aquatic fungi with different environmental background, and constitutes a proof of concept that toxicants induce adaptive responses in microbes to face emergent contaminants.

Phytoremediation: green technology for the removal of mixed contaminants of a water supply reservoir

The Iraí Reservoir, a water supply in Brazil, is constantly impacted by anthropogenic activities such as waste inputs from agriculture, hospitals and urbanization, resulting toxic cyanobacterial blooms causing economic, social and environmental problems. This study assessed the concentration of some common contaminants of the Iraí Reservoir, namely paracetamol, diclofenac and microcystin-LR and tested whether a laboratory scale Green Liver System^® would serve as a suitable technology to remove these contaminants. Further, the study investigated whether the pollutants caused adverse effects to the macrophytes using catalase as a biomarker for oxidative stress and investigated whether biotransformation (glutathione S-transferase) was a main route for detoxification. Egeria densa, Ceratophyllum demersum and Myriophyllum aquaticum were exposed to a mixture of the three contaminants for 14 days in a concentration range similar to those detected in the reservoir. The plants removed 93% of diclofenac and 100% of MC-LR after 14 days. Paracetamol could not be detected. Catalase and glutathione S-transferase enzyme activities remained unaltered after the 14-day exposure, indicating that the mixture did not cause oxidative stress. The study showed that the aquatic macrophytes used are suitable tools to apply in a Green Liver System^® for the remediation of mixed pollutants.

Organic matter modifies biochemical but not most behavioral responses of the clam Ruditapes philippinarum to nanosilver exposure

Adsorption of dissolved organic matter (DOM) can alter the environmental fate, bioavailability and toxicity of silver nanoparticles (Ag NPs). However, a number of questions remain about DOM's ability to modify nanotoxicity. Here, we examine the impact of humic acid (HA, as a model DOM) on the toxicity of Ag NPs (10 μg L^-1) in the marine clam Ruditapes philippinarum. Results showed that DOM additions to Ag NP treatments reduce clam silver tissue burdens and the oxidative stress response. However, HA does not significantly affect the impact of Ag NPs on clam acetylcholinesterase activity and feeding behavior (measured as filtration rate). Overall, the integrated biological response index supports the conclusion that humic acid reduces the toxicity of Ag NPs, clearly indicating the importance of considering environmental factors when assessing potential risks posed by nanomaterials in natural settings.

Ecotoxicity of two organic UV-filters to the freshwater caddisfly Sericostoma vittatum

Organic ultraviolet filters (UV-filters) used for protection against radiation in personal care products and other materials (e.g. textiles, plastic products) are considered emerging contaminants of aquatic ecosystem. Benzophenone-3 (BP3) and 3-(4-methylbenzylidene)camphor (4-MBC) are the most commonly used organic UV-filters and have been reported in freshwater environments due to contamination through discharges from wastewater treatment plants and swimming pools or by direct contamination from recreational activities. Our aim was to evaluate the ecotoxicological effects of these UV-filters using the freshwater caddisfly Sericostoma vittatum' biochemical biomarkers and energy processing related endpoints (feeding behaviour, energy reserves and cellular metabolism). In laboratory trials, both compounds induced feeding inhibition of S. vittatum at 3.55 mg/kg of BP3 and at concentrations ≥2.57 mg/kg of 4-MBC, decreased carbohydrates content at 3.55 and 6.95 mg/kg of BP3 and 4-MBC respectively, and increased total glutathione levels at concentrations ≥1.45 and 1.35 mg/kg of BP3 and 4-MBC respectively. No significant effects were observed on endpoints associated with oxidative stress, antioxidant defences, phase II biotransformation or neurotoxicity after exposure to the two UV-filters. Our results show that environmental relevant concentrations of BP3 and 4-MBC, can negatively impact freshwater insects and demonstrate the importance of monitoring the ecological effects of organic UV-filters using non-model invertebrate species.