Phytotoxicity of silver nanoparticles to Lemna minor: Surface coating and exposure period-related effects

• Published in: The Science of the total environment Vol. 618; pp. 1389 - 1399
• Main Authors: Pereira, Susana P.P., Jesus, Fátima, Aguiar, Sara, de Oliveira, Rhaul, Fernandes, Marco, Ranville, James, Nogueira, António J.A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.03.2018
• Subjects: Aquatic plants; Exposure period; Oxidative stress; Silver nanoparticles; Surface coating; Exposure period; Oxidative stress; Surface coating; Silver nanoparticles; Aquatic plants
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2017.09.275

Silver nanoparticles (Ag NPs) exponential production raises concern about their environmental impact. The effects of Ag NPs to aquatic plants remain scarcely studied, especially in extended exposures. This paper aims to evaluate Ag NPs effects in Lemna minor at individual and sub-individual levels, focusing on three variables: Ag form (NPs versus ions – Ag+), NPs surface coating (citrate vs polyvinylpyrrolidone – PVP) and exposure period (7 vs 14days). Endpoints were assessed at individual level (specific growth rate, chlorosis incidence and number of fronds per colony) and sub-individual level (enzymatic activities of catalase (CAT), guaiacol peroxidase (GPx) and glutathione-S-transferase (GST)). Generally, plants exposed to all Ag forms underwent decays on growth rate and fronds per colony, and increases on chlorosis, GPX and GST, but no effects on CAT. The most sensitive endpoints were specific growth rate and GPx activity, showing significant effects down to 0.05mg/L for Ag NPs and 3μg/L for Ag+, after 14days. Ag+ showed higher toxicity with a 14d–EC50 of 0.0037mg Ag/L. Concerning surface coating, PVP-Ag NPs were more deleterious on growth rate and fronds per colony, whereas citrate-Ag NPs affected more the chlorosis incidence and GPx and GST activities. The exposure period significantly affected chlorosis: 14days triggered a chlorosis increase in Ag+-exposed plants and a decrease in Ag NPs-exposed plants when compared to 7days. Ag NPs induced an oxidative stress status in cells, thus ensuing upregulated enzymatic activity as a self-defense mechanism. Since Ag NPs dissolution might occur on a steady and continuous mode along time, and the average longevity of fronds, we propose longer exposures periods than the recommended by the OECD guideline. This approach would provide more relevant and holistic evidences on the overall response of freshwater plants to Ag NPs in an ecological relevant scenario. Lemna minor exposure to silver nanoparticles with two surface coatings (citrate and PVP) along 14days. Growth rate inhibition and GPx induction were the most significant effects. Chlorosis was the main phenotypic effect. [Display omitted] •Ag nanoparticles (NPs) and Ag+ reduced plants growth rate, more noticeably Ag+.•Citrate-Ag NPs effects were more pronounced on GPx and GST activities.•PVP-Ag NPs affected more distinctively the growth rate and fronds per colony.•GPx and GST were induced by citrate and PVP-Ag NPs, but CAT remained unaffected.•14days exposure alleviated chlorosis in Ag NPs, but the opposite occurred in Ag+.