Publicação
Impacts of silver nanoparticles in freshwater detrital food-webs in a warming scenario
| Resumo: | The production and use of silver nanoparticles (AgNPs) has significantly grown over the last decade, increasing the risk that a fraction of NPs is transported to freshwater ecosystems. In these ecosystems, AgNPs and ionic silver released from dissolution of NPs can have toxic effects on aquatic species and compromise important ecosystem processes, such as plant litter decomposition. The research on the impacts of AgNPs on plant litter decomposition is scarce, rarely conducted under environmentally relevant conditions and not taking into account the physical and chemical properties of AgNPs that affect their toxicity. The general goal of this study was to assess the impacts of AgNPs under environmentally-realist concentrations, considering species interactions and the physical and chemical properties of AgNPs at increasing temperatures focusing on freshwater detrital food webs. Firstly, we assessed the impacts of AgNPs with different sizes and surface coating (100 nm PVP (polyvinylpyrrolidone)-dispersant, 50-60 nm and 35 nm uncoated) on freshwater decomposers of leaf litter by exposing leaf associated microbial assemblages to increasing concentrations of AgNPs and AgNO3. We further conducted a feeding preference experiment with a common invertebrate shredder, Limnephilus sp., which was allowed to feed on microbially-colonized leaves previously exposed to AgNPs and AgNO3. Leaf decomposition and microbial activity and diversity were inhibited when exposed to increased concentrations of 100 nm AgNPs, while microbial activity was stimulated by exposure to 35 nm AgNPs. Invertebrate shredders preferred leaves exposed to 35 nm AgNPs and avoided leaves exposed to AgNO3. The 100 nm AgNP coated with PVP-dispersant were more stable than the uncoated AgNPs, indicating more aggregation and probably leading to lower toxicity. Our results highlighted the importance of considering the physical and chemical properties of NPs when assessing their toxicity to litter decomposers in freshwaters. Secondly, we evaluated the effects of AgNPs at increased temperature on the activity and diversity of microbial decomposers of plant litter in streams and on the feeding behavior of invertebrate shredders. Litter-associated microbial communities were exposed in microcosms to increased concentrations of AgNPs/AgNO3 and kept for 21 days at 10ºC, 16ºC and at 23ºC. Contaminated leaves were subsequently used to fed the invertebrate shredders Limnephilus sp. under the same temperature range, and after 5 days, animals were released from the stressor (AgNPs or AgNO3) and allowed to feed on non-contaminated leaves. The increase in temperature stimulated leaf decomposition by microbial decomposers and shredders, and the activity of leaf degrading enzymes, while low temperature increased fungal biomass and diversity. Increased AgNP and AgNO3 concentrations reduced reproduction and diversity of fungi. The negative effects on microbial activity were more pronounced at 10ºC and 23ºC, suggesting that changes in temperature might promote a severe threat of AgNPs to aquatic organisms. Exposure of invertebrate shredders to leaves contaminated by AgNP induced oxidative stress in the animals. The activity of catalase (CAT) and superoxide dismutase (SOD) in the animals were associated with the total Ag accumulated, while glutationa transferase (GST) activity was strongly associated with treatments exposed to 23ºC. Results highlight the importance of considering different environmental scenarios when examining NP toxicity to freshwater biota. Microbial communities can develop adaptive mechanisms toward tolerance against metals, so tolerance acquisition by these communities can be used as specific indicator of nano and ionic metal pollution in freshwater ecosystems. We conducted a pollution-induced community tolerance (PICT) approach to test if microbial decomposers had the ability to evolve tolerance to AgNPs. After 21 days of exposure to low concentrations of AgNPs and AgNO3, microbial communities were able to acquire tolerance as measured via short-term bioassays using several microbial endpoints. Indeed, communities pre-exposed to AgNPs and AgNO3 showed higher tolerance as revealed by the lower effects on fungal sporulation and bacterial biomass production. The results showed that approaches at the community level, such as PICT, using microbial decomposers might provide a better understanding of the mechanisms of toxicity triggered by NPs, helping to assess potential impacts of AgNPs on freshwater ecosystems. Moreover, we assessed the impacts of environmentally-realistic concentrations of AgNPs and Ag+ across a food web. Specifically, we assessed the importance of direct (via water) and indirect (via diet) exposure routes towards a simplified detrital food web, comprising leaf litter, microbes, a shredder species and collector species using: (i) water contaminated with AgNPs or AgNO3), and (ii) leaves contaminated with AgNPs and AgNO3. Microbial decomposition was lower by direct exposure to AgNPs and Ag+, whereas leaf consumption by Gammarus pulex only decreased when leaves were contaminated with the lowest concentration of AgNPs. There were no effects on fine particulate organic matter produced by the shredder in both exposure routes. Changes in the activity of a key antioxidant enzyme, CAT, indicated AgNPs and Ag+ caused oxidative stress in both invertebrate species, mainly in response to direct exposure. Overall results demonstrated that ecological effects on different functional groups of stream invertebrates vary with exposure route of AgNPs. Thus, the route by which stream biota are exposed to AgNPs will influence the impacts of AgNPs on ecosystem processes. |
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| Autores principais: | Batista, Daniela Miranda |
| Assunto: | Ciências Naturais::Ciências Biológicas |
| Ano: | 2017 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | português |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The production and use of silver nanoparticles (AgNPs) has significantly grown over the last decade, increasing the risk that a fraction of NPs is transported to freshwater ecosystems. In these ecosystems, AgNPs and ionic silver released from dissolution of NPs can have toxic effects on aquatic species and compromise important ecosystem processes, such as plant litter decomposition. The research on the impacts of AgNPs on plant litter decomposition is scarce, rarely conducted under environmentally relevant conditions and not taking into account the physical and chemical properties of AgNPs that affect their toxicity. The general goal of this study was to assess the impacts of AgNPs under environmentally-realist concentrations, considering species interactions and the physical and chemical properties of AgNPs at increasing temperatures focusing on freshwater detrital food webs. Firstly, we assessed the impacts of AgNPs with different sizes and surface coating (100 nm PVP (polyvinylpyrrolidone)-dispersant, 50-60 nm and 35 nm uncoated) on freshwater decomposers of leaf litter by exposing leaf associated microbial assemblages to increasing concentrations of AgNPs and AgNO3. We further conducted a feeding preference experiment with a common invertebrate shredder, Limnephilus sp., which was allowed to feed on microbially-colonized leaves previously exposed to AgNPs and AgNO3. Leaf decomposition and microbial activity and diversity were inhibited when exposed to increased concentrations of 100 nm AgNPs, while microbial activity was stimulated by exposure to 35 nm AgNPs. Invertebrate shredders preferred leaves exposed to 35 nm AgNPs and avoided leaves exposed to AgNO3. The 100 nm AgNP coated with PVP-dispersant were more stable than the uncoated AgNPs, indicating more aggregation and probably leading to lower toxicity. Our results highlighted the importance of considering the physical and chemical properties of NPs when assessing their toxicity to litter decomposers in freshwaters. Secondly, we evaluated the effects of AgNPs at increased temperature on the activity and diversity of microbial decomposers of plant litter in streams and on the feeding behavior of invertebrate shredders. Litter-associated microbial communities were exposed in microcosms to increased concentrations of AgNPs/AgNO3 and kept for 21 days at 10ºC, 16ºC and at 23ºC. Contaminated leaves were subsequently used to fed the invertebrate shredders Limnephilus sp. under the same temperature range, and after 5 days, animals were released from the stressor (AgNPs or AgNO3) and allowed to feed on non-contaminated leaves. The increase in temperature stimulated leaf decomposition by microbial decomposers and shredders, and the activity of leaf degrading enzymes, while low temperature increased fungal biomass and diversity. Increased AgNP and AgNO3 concentrations reduced reproduction and diversity of fungi. The negative effects on microbial activity were more pronounced at 10ºC and 23ºC, suggesting that changes in temperature might promote a severe threat of AgNPs to aquatic organisms. Exposure of invertebrate shredders to leaves contaminated by AgNP induced oxidative stress in the animals. The activity of catalase (CAT) and superoxide dismutase (SOD) in the animals were associated with the total Ag accumulated, while glutationa transferase (GST) activity was strongly associated with treatments exposed to 23ºC. Results highlight the importance of considering different environmental scenarios when examining NP toxicity to freshwater biota. Microbial communities can develop adaptive mechanisms toward tolerance against metals, so tolerance acquisition by these communities can be used as specific indicator of nano and ionic metal pollution in freshwater ecosystems. We conducted a pollution-induced community tolerance (PICT) approach to test if microbial decomposers had the ability to evolve tolerance to AgNPs. After 21 days of exposure to low concentrations of AgNPs and AgNO3, microbial communities were able to acquire tolerance as measured via short-term bioassays using several microbial endpoints. Indeed, communities pre-exposed to AgNPs and AgNO3 showed higher tolerance as revealed by the lower effects on fungal sporulation and bacterial biomass production. The results showed that approaches at the community level, such as PICT, using microbial decomposers might provide a better understanding of the mechanisms of toxicity triggered by NPs, helping to assess potential impacts of AgNPs on freshwater ecosystems. Moreover, we assessed the impacts of environmentally-realistic concentrations of AgNPs and Ag+ across a food web. Specifically, we assessed the importance of direct (via water) and indirect (via diet) exposure routes towards a simplified detrital food web, comprising leaf litter, microbes, a shredder species and collector species using: (i) water contaminated with AgNPs or AgNO3), and (ii) leaves contaminated with AgNPs and AgNO3. Microbial decomposition was lower by direct exposure to AgNPs and Ag+, whereas leaf consumption by Gammarus pulex only decreased when leaves were contaminated with the lowest concentration of AgNPs. There were no effects on fine particulate organic matter produced by the shredder in both exposure routes. Changes in the activity of a key antioxidant enzyme, CAT, indicated AgNPs and Ag+ caused oxidative stress in both invertebrate species, mainly in response to direct exposure. Overall results demonstrated that ecological effects on different functional groups of stream invertebrates vary with exposure route of AgNPs. Thus, the route by which stream biota are exposed to AgNPs will influence the impacts of AgNPs on ecosystem processes. |
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