Abstract
Inputs 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 species Chaetoceros curvisetus using 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.
Highlights
The increasing inputs of nanoparticles (NPs) into the environment constitutes a widespread pollution pressure[1]
As reported previously[6, 9, 11,12,13, 16], our results suggest that AgNPs have the potential to severely impact growth of marine diatoms, with the magnitude of the toxic effect strongly modulated by the supplied NP concentration
We found exposure of diatom cultures to AgNPs resulted in rapid declines in biomass, maximum relative electron transport rates, optimum light intensities, and an increased susceptibility to photoinhibition
Summary
The increasing inputs of nanoparticles (NPs) into the environment constitutes a widespread pollution pressure[1]. Silver NPs (AgNPs) in particular represent a dominant fraction of manufactured NPs because of their advantageous antibacterial, antiviral and antifungal properties[2] Despite their enhanced release rates into the marine environment, relatively little is known about the toxic effects of AgNPs on phytoplankton (photosynthetic algae), which are the base of the marine food chain. Formation of Ag-cysteine complexes is thought to prohibit phytoplankton uptake of Ag(I) ions[12]; the role of cysteine in the context of AgNPs is probably more complex, as whilst it can strongly bind and remobilise Ag(I), it can affect the aggregation and dissolution of AgNPs by adsorption onto their surfaces[32, 33] Such processes potentially have the capacity to enhance or reduce toxicity
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