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AbstractInputs of silver nanoparticles (AgNPs) to marine waters continue to increase yet mechanisms of AgNPs toxicity to marine phytoplankton are still not well resolved. This study reports a series of toxicity experiments on a representative coastal marine diatom speciesChaetoceros curvisetususing the reference AgNP, NM-300K. Exposure to AgNPs resulted in photosynthetic impairment and loss of diatom biomass in proportion to the supplied AgNP dose. The underlying mechanism of toxicity was explored via comparing biological responses in parallel experiments. Diatom responses to AgNP, free Ag(I) species, and dialysis bag-retained AgNP treatments showed marked similarity, pointing towards a dominant role of Ag(I) species uptake, rather than NPs themselves, in inducing the toxic response. In marked contrast to previous studies, addition of the organic complexing agent cysteine (Cys) alongside Ag only marginally moderated toxicity, implying AgCys−complexes were bioavailable to this diatom species. A preliminary field experiment with a natural phytoplankton community in the southeast Atlantic Ocean showed no significant toxic response at a NM-300 K concentration that resulted in ~40% biomass loss in the culture studies, suggesting a modulating effect of natural seawaters on Ag toxicity.

AbstractInputs of silver nanoparticles (AgNPs) to marine waters continue to increase yet mechanisms of AgNPs toxicity to marine phytoplankton are still not well resolved. This study reports a series of toxicity experiments on a representative coastal marine diatom speciesChaetoceros curvisetususing the reference AgNP, NM-300K. Exposure to AgNPs resulted in photosynthetic impairment and loss of diatom biomass in proportion to the supplied AgNP dose. The underlying mechanism of toxicity was explored via comparing biological responses in parallel experiments. Diatom responses to AgNP, free Ag(I) species, and dialysis bag-retained AgNP treatments showed marked similarity, pointing towards a dominant role of Ag(I) species uptake, rather than NPs themselves, in inducing the toxic response. In marked contrast to previous studies, addition of the organic complexing agent cysteine (Cys) alongside Ag only marginally moderated toxicity, implying AgCys−complexes were bioavailable to this diatom species. A preliminary field experiment with a natural phytoplankton community in the southeast Atlantic Ocean showed no significant toxic response at a NM-300 K concentration that resulted in ~40% biomass loss in the culture studies, suggesting a modulating effect of natural seawaters on Ag toxicity.

This is an accepted version of the published document. [Abstract] Marine macroalgae represent an excellent raw material for the production of bioactives, adsorbents, plant biostimulants, soil fertilizers and biogas. The success in the exploitation of seaweeds depends on their characteristics, and the approach used to separate their specific active components. In the context of circular economy, invasive species are a good candidate for exploitation, and biorefinery a key valorization technique. Here we investigate a novel biorefinery scheme for an integral valorization of Sargassum muticum. An initial pressing stage allowed the production of a Sap fraction, which showed potential as a plant biostimulant, increasing both root development and shoot/root ratio, especially when used at a dose of 0.1 g/L lyophilized Sap. The solids after pressing were processed by non isothermal autohydrolysis, using pressurized hot water (up to 120-210 °C), a process previously optimized to solubilize the fucoidan and phlorotannin fractions. The residual solids remaining after pressing and autohydrolysis stages were evaluated for the production of biogas. The obtained value (150 mL CH4/g residual solids at 150 °C) was significantly higher than that found for the raw seaweed. The optimal autohydrolysis temperature (150 °C) is compatible with the production of the fucoidan fraction, although the phenolic content is favoured under more severe operation conditions. We also discuss the possibility of preparing adsorbents for pollutant removal and mineral amendments from the autohydrolysis waste solids. The authors are grateful to the Spanish Ministry of Education and Science (CTM2009-12664) and to Xunta de Galicia (CINBIO Centro singular de investigación de Galicia accreditation 2019-2022) with partial financial support from the European Regional Development Fund – ERDF (Ref. ED431G2019/06). M.D.T. thanks Spanish Ministry of Economy and Competitiveness for her postdoctoral grant (IJCI-2016-27535 and RYC2018-024454-I). N.F.F. thanks CINBIO and Xunta de Galicia for her postdoctoral contract (ED481B 2018/071) Xunta de Galicia; ED431G2019/06 Xunta de Galicia; ED481B 2018/071

This is an accepted version of the published document. [Abstract] Marine macroalgae represent an excellent raw material for the production of bioactives, adsorbents, plant biostimulants, soil fertilizers and biogas. The success in the exploitation of seaweeds depends on their characteristics, and the approach used to separate their specific active components. In the context of circular economy, invasive species are a good candidate for exploitation, and biorefinery a key valorization technique. Here we investigate a novel biorefinery scheme for an integral valorization of Sargassum muticum. An initial pressing stage allowed the production of a Sap fraction, which showed potential as a plant biostimulant, increasing both root development and shoot/root ratio, especially when used at a dose of 0.1 g/L lyophilized Sap. The solids after pressing were processed by non isothermal autohydrolysis, using pressurized hot water (up to 120-210 °C), a process previously optimized to solubilize the fucoidan and phlorotannin fractions. The residual solids remaining after pressing and autohydrolysis stages were evaluated for the production of biogas. The obtained value (150 mL CH4/g residual solids at 150 °C) was significantly higher than that found for the raw seaweed. The optimal autohydrolysis temperature (150 °C) is compatible with the production of the fucoidan fraction, although the phenolic content is favoured under more severe operation conditions. We also discuss the possibility of preparing adsorbents for pollutant removal and mineral amendments from the autohydrolysis waste solids. The authors are grateful to the Spanish Ministry of Education and Science (CTM2009-12664) and to Xunta de Galicia (CINBIO Centro singular de investigación de Galicia accreditation 2019-2022) with partial financial support from the European Regional Development Fund – ERDF (Ref. ED431G2019/06). M.D.T. thanks Spanish Ministry of Economy and Competitiveness for her postdoctoral grant (IJCI-2016-27535 and RYC2018-024454-I). N.F.F. thanks CINBIO and Xunta de Galicia for her postdoctoral contract (ED481B 2018/071) Xunta de Galicia; ED431G2019/06 Xunta de Galicia; ED481B 2018/071