Publicação
Eco-friendly potential of layered double hydroxides (LDHs) to remediate waters: ecotoxicity assessment towards freshwater species
| Resumo: | The nanotechnology field has been experiencing a remarkable expansion, characterized by the emergence of innovative nanomaterials (NMs) with unique properties and suitable for a wide range of applications. Layered double hydroxides (LDHs) are nanoclays composed of positive charged layers with divalent or trivalent metal cations and stabilized by anions and water molecules in the interlayers. In recent years, the use of LDHs have grown exponentially, much due to their properties, such as anion exchangeability, memory effect and high absorbing capacity. Therefore, it is critical to understand the environmental behaviour and toxicological effects of LDHs to address potential concerns caused by their subsequent release into the environment. Furthermore, ecotoxicological assessment of new materials and products is becoming a vital component for the implementation of safe and sustainable by design strategies. Considering this, the present thesis aimed to assess the ecotoxicological effects of two LDHs (MgAl-NO₃ LDH and ZnAl-NO₃ LDH) in aquatic species, with the future prospect for use in phosphate removal from eutrophicated waters. Ecotoxicity experiments were performed with four environmentally relevant freshwater species: the crustacean Daphnia magna, the macrophyte Lemna minor, the microalgae Raphidocelis subcapitata and the fish Danio rerio. Neonates of D. magna were exposed to MgAl-NO₃ (145 – 345 mg/L) and ZnAl-NO3 LDH (10 – 60 mg/L) to evaluate the immobilisation (OECD No. 202). No immobilisation was recorded in exposure to MgAl-NO₃ and a IC₅₀ of 31.99 mg/L was determined for the ZnAl-NO3 LDH exposure. To assess effects in reproduction (OECD No. 211), the crustacean was exposed to concentrations between 0.56 – 18 mg/L of MgAl-NO3 LDH and 0.5 – 12.5 mg/L of ZnAl-NO₃ LDH. For the total number of neonates were calculated EC₅₀ values > 18 mg/L and of 7.60 mg/L for MgAl-NO₃ and ZnAl-NO₃ LDHs, respectively. Growth inhibition tests (OECD No. 221) were performed exposing L. minor to a concentration range of 5 – 1215 mg/L of both LDHs. For MgAl-NO₃ LDH was determined an EC₅₀ > 1215 mg/L and dark fronds were observed in macrophytes exposed to the highest tested concentration. In turn, an EC₅₀ of 741 mg/L for ZnAl-NO₃ LDH was obtained and yellow fronds were observed. The toxicity of MgAl-NO₃ LDH and ZnAl-NO₃ LDH to R. subcapitata was assessed through growth inhibition tests (OECD No. 201). In line with the previous results, lower toxicity was observed in exposure to MgAl-NO₃ LDH (EC₅₀ > 210 mg/L), while for ZnAl-NO₃ LDH, an EC₅₀ = 108 mg/L was calculated. D. rerio embryos were exposed to MgAl-NO₃ and ZnAl-NO₃ LDHs (100 – 1300 mg/L) to assess hatching success, mortality and malformations, according to the OECD No. 236 protocol. No effects were observed for MgAl-NO₃ LDH, while it was determined a LC₅₀ of 1222 mg/L and an EC₅₀ of 801 mg/L for ZnAl-NO₃ exposure. In addition, the LDHs were characterized in the different test media used (ASTM, MBL, Steinberg and FSW) through the evaluation of the zeta potential and hydrodynamic particle size over time. Results revealed that both LDHs formed unstable dispersions in all test media. In summary, results demonstrated low to very low toxicity of MgAl-NO₃ and ZnAl-NO₃ LDHs to the test species, which is a positive indication that these LDHs have the potential to be used as an eco-friendly nanotechnology tool to remediate eutrophic wates. Furthermore, data presented in this thesis may also be used for nanoregulation purposes and support environmental risk assessment of NMs. |
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| Autores principais: | Lopes, Ana Filipa Pinheiro |
| Assunto: | Aquatic species Ecotoxicity Layered double hydroxides Eutrophication Remediation Nanotechnology |
| Ano: | 2023 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | The nanotechnology field has been experiencing a remarkable expansion, characterized by the emergence of innovative nanomaterials (NMs) with unique properties and suitable for a wide range of applications. Layered double hydroxides (LDHs) are nanoclays composed of positive charged layers with divalent or trivalent metal cations and stabilized by anions and water molecules in the interlayers. In recent years, the use of LDHs have grown exponentially, much due to their properties, such as anion exchangeability, memory effect and high absorbing capacity. Therefore, it is critical to understand the environmental behaviour and toxicological effects of LDHs to address potential concerns caused by their subsequent release into the environment. Furthermore, ecotoxicological assessment of new materials and products is becoming a vital component for the implementation of safe and sustainable by design strategies. Considering this, the present thesis aimed to assess the ecotoxicological effects of two LDHs (MgAl-NO₃ LDH and ZnAl-NO₃ LDH) in aquatic species, with the future prospect for use in phosphate removal from eutrophicated waters. Ecotoxicity experiments were performed with four environmentally relevant freshwater species: the crustacean Daphnia magna, the macrophyte Lemna minor, the microalgae Raphidocelis subcapitata and the fish Danio rerio. Neonates of D. magna were exposed to MgAl-NO₃ (145 – 345 mg/L) and ZnAl-NO3 LDH (10 – 60 mg/L) to evaluate the immobilisation (OECD No. 202). No immobilisation was recorded in exposure to MgAl-NO₃ and a IC₅₀ of 31.99 mg/L was determined for the ZnAl-NO3 LDH exposure. To assess effects in reproduction (OECD No. 211), the crustacean was exposed to concentrations between 0.56 – 18 mg/L of MgAl-NO3 LDH and 0.5 – 12.5 mg/L of ZnAl-NO₃ LDH. For the total number of neonates were calculated EC₅₀ values > 18 mg/L and of 7.60 mg/L for MgAl-NO₃ and ZnAl-NO₃ LDHs, respectively. Growth inhibition tests (OECD No. 221) were performed exposing L. minor to a concentration range of 5 – 1215 mg/L of both LDHs. For MgAl-NO₃ LDH was determined an EC₅₀ > 1215 mg/L and dark fronds were observed in macrophytes exposed to the highest tested concentration. In turn, an EC₅₀ of 741 mg/L for ZnAl-NO₃ LDH was obtained and yellow fronds were observed. The toxicity of MgAl-NO₃ LDH and ZnAl-NO₃ LDH to R. subcapitata was assessed through growth inhibition tests (OECD No. 201). In line with the previous results, lower toxicity was observed in exposure to MgAl-NO₃ LDH (EC₅₀ > 210 mg/L), while for ZnAl-NO₃ LDH, an EC₅₀ = 108 mg/L was calculated. D. rerio embryos were exposed to MgAl-NO₃ and ZnAl-NO₃ LDHs (100 – 1300 mg/L) to assess hatching success, mortality and malformations, according to the OECD No. 236 protocol. No effects were observed for MgAl-NO₃ LDH, while it was determined a LC₅₀ of 1222 mg/L and an EC₅₀ of 801 mg/L for ZnAl-NO₃ exposure. In addition, the LDHs were characterized in the different test media used (ASTM, MBL, Steinberg and FSW) through the evaluation of the zeta potential and hydrodynamic particle size over time. Results revealed that both LDHs formed unstable dispersions in all test media. In summary, results demonstrated low to very low toxicity of MgAl-NO₃ and ZnAl-NO₃ LDHs to the test species, which is a positive indication that these LDHs have the potential to be used as an eco-friendly nanotechnology tool to remediate eutrophic wates. Furthermore, data presented in this thesis may also be used for nanoregulation purposes and support environmental risk assessment of NMs. |
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