Abstract
Nanoparticles (NPs) are causing threats to the environment. Silver NPs (AgNPs) are increasingly used in commercial products and may end up in freshwater ecosystems. The freshwater organisms are vulnerable due to water-borne and dietary exposure to AgNPs. Surface properties play an important role in the fate and behavior of AgNPs in the aquatic environment and their effects on organisms. However, effects of surface properties of AgNPs on organisms are poorly understood. In this study, we explored the effects of AgNPs coated with three different ligands; Tyrosine (T-AgNP), Epigallocatechin gallate (E-AgNP) and Curcumin (C-AgNP) in relation to the toxicity to a key aquatic organism; Daphnia carinata. The study focused on how coatings determine fate of NPs in the medium, mortality, feeding behaviour, bioaccumulation and trophic transfer from the freshwater alga, Raphidocelis subcapitata to daphnids. NP stability tests indicated that T-AgNPs were least stable in the ASTM daphnia medium while C-AgNPs were most stable. 48 h EC50 values of AgNPs to D. carinata were in the order of E-AgNP (19.37 μg L-1) > C-AgNP (21.37 μg L-1) > T-AgNP (49.74 μg L-1) while the 48 h EC50 value of Ag+ ions was 1.21 μg L-1. AgNP contaminated algae significantly decreased the feeding rates of daphnids. However, no significant differences were observed in feeding rates between algae contaminated with differently coated AgNPs. Trophic transfer studies showed that AgNPs were transferred from algae to daphnids. The bioacumulation of AgNPs in algae and the diet-borne bioaccumulation of AgNPs in daphnids varied for differently coated AgNPs. Bioaccumulation of C-AgNPs in algae was 1.5 time higher than T-AgNPs. However, the accumulation of T-AgNPs in daphnids via trophic transfer was 2.6 times higher than T-AgNPs. The knowledge generated from this study enhances the understanding of surface property dependent toxicity, bioaccumulation and trophic transfer of AgNPs in aquatic environments.
Highlights
Engineered nanoparticles (ENPs) are man-made materials with a size range of 1 to 100 nm [1]
We studied the toxicity of AgNPs coated with different organic ligands; Tyrosine (T-AgNP), Curcurmin (C-AgNP) and Epigallocatechin gallate (E-AgNP) to the freshwater filter-feeding cladoceran, Daphnia carinata
The presence of NPs was further confirmed by transmission electron microscope (TEM) analysis (Fig 1B, 1C and 1D) which revealed spherical shaped NPs which were reasonably uniform in size
Summary
Engineered nanoparticles (ENPs) are man-made materials with a size range of 1 to 100 nm [1]. Global production of ENPs are increasing exponentially as they are widely being used in many applications such as healthcare, personal care, construction, energy, electronics, catalysts, packaging, textiles, environmental remediation and agriculture [2,3,4]. Despite their useful applications, the physicochemical characteristics that make NPs unique are causing possible threats to the health of the environment including humans. Complete assessment of health and environmental impacts of engineered nanomaterials is not possible due to lack of nanotoxicity and ecotoxicity data and it will take many more years to produce actionable information leaving all concerned parties with little guidance [7]. Further studies are required to minimize the harm caused by NPs considering the diversity of NP characteristics [16, 19,20,21,22]
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