Effects of silver nanoparticles on bacterioplankton in a boreal lake

Abstract

SUMMARY1. Silver nanoparticles (AgNPs) are widely used antimicrobial agents and a growing body of evidence suggests that their release into aquatic environments threatens natural bacterial communities and whole ecosystems. However, a knowledge gap exists between the toxic effects of AgNPs found in laboratory studies and their potential impacts in natural environments. 2. In an enclosure experiment conducted in a boreal lake, we exposed natural bacterial communities to AgNPs with two common types of coatings (polyvinylpyrrolidone (PVP) and citrate) under two different exposure regimes, a one-time (pulse) and a continuous (chronic) addition. AgNP additions increased Ag concentrations to nearly 50 lg L À1 in the highest treatments. We examined bacterial responses (abundance, biomass, production, chlorophyll-a content and nutrient stoichiometry) over the course of 6 weeks in the summer of 2012. 3. Bacterioplankton exposed to AgNPs initially accumulated Ag over the experimental period regardless of AgNP concentration or coating. After the initial period of increase, Ag in the bacterial size fraction changed largely in concert with bacterial biomass. 4. We found no toxic effects of AgNPs on bacterioplankton abundance, biomass, production or chlorophyll-a content throughout the experiment. Bacterial production was greater after the pulse addition of PVP-coated AgNPs and in the chronic addition of PVP-coated AgNPs at the highest concentrations. Furthermore, AgNPs produced no significant changes in nutrient stoichiometry of the bacterioplankton size fraction. 5. This lack of effects of AgNPs on lake bacterioplankton observed under the natural conditions studied here differs from results of short-term and laboratory studies of single-species bacterial cultures. Our results thus indicate AgNP effects in lakes may be less than expected based on standard laboratory experiments, and that additional studies are needed to understand AgNP toxicity under realistic natural conditions in lakes and other ecosystems.

Fostering integration of freshwater ecology with ecotoxicology

“…Blakelock et al . () investigated the effects of silver nanoparticles (AgNP) on bacterioplankton in large enclosures of a boreal lake. One of the main outcomes of this study is that no toxic effects of AgNP on bacterioplankton were observed.…”

“…() and Blakelock et al . () underline the importance of considering environmental context and the specific properties of particles, and especially the biological complexity within ecosystems, to assess toxicity of ENPs.…”

“…Another interesting finding of this work is that combined exposure to both stressors mitigated the adverse effects of the small and medium-sized nanoCuO. Blakelock et al (2016) investigated the effects of silver nanoparticles (AgNP) on bacterioplankton in large enclosures of a boreal lake. One of the main outcomes of this study is that no toxic effects of AgNP on bacterioplankton were observed.…”

“…temperature, pH, ionic strength, dissolved organic matter) that affect the stability of the ENPs and therefore their toxicity. Thus, the studies by Pradhan et al (2016) and Blakelock et al (2016) underline the importance of considering environmental context and the specific properties of particles, and especially the biological complexity within ecosystems, to assess toxicity of ENPs.…”

Muted responses to Ag accumulation by plankton to chronic and pulse exposure to silver nanoparticles in a boreal lake

“…Our primary goals were to compare the temporal patterns of the response of a boreal lake grazingbased food web (microbes, phytoplankton, and zooplankton) to trophic Ag accumulation following chronic or pulse AgNP exposure and to assess the corresponding response of plankton-driven ecosystem metabolism over time scales capturing plankton food web dynamics. These goals were part of a larger experiment investigating the response of plankton biomass, diversity, and production to AgNP exposure and the behaviour of AgNPs in natural waters, the results of which are published elsewhere (Furtado et al 2014(Furtado et al , 2015Blakelock et al 2016;Vincent et al 2017). We predicted that (i) Ag accumulation would predict biotic responses and (ii) ecosystem function would reflect these responses and be maintained or recover quickly when exposed to chronic AgNP addition but be impaired after exposure to a pulse of AgNPs.…”