Fractionating Nanosilver: Importance for Determining Toxicity to Aquatic Test Organisms

Abstract

This investigation applied novel techniques for characterizing and fractionating nanosilver particles and aggregates and relating these measurements to toxicological endpoints. The acute toxicity of eight nanosilver suspensions of varying primary particle sizes (10-80 nm) and coatings (citrate, polyvinylpyrrolidone, EDTA, proprietary) was assessed using three aquatic test organisms (Daphnia magna, Pimephales promelas, Pseudokirchneriella subcapitata). When 48-h lethal median concentrations (LC50) were expressed as total silver, both D. magna and P. promelas were significantly more sensitive to ionic silver (Ag(+)) as AgNO(3) (mean LC50 = 1.2 and 6.3 μg/L, respectively) relative to a wide range in LC50 values determined for the nanosilver suspensions (2 -126 μg/L). However, when LC50 values for nanosilver suspensions were expressed as fractionated nanosilver (Ag(+) and/or <4 nm particles), determined by ultracentrifugation of particles and confirmed field-flow-fractograms, the LC50 values (0.3-5.6 μg/L) were comparable to the values obtained for ionic Ag(+) as AgNO(3). These results suggest that dissolved Ag(+) plays a critical role in acute toxicity and underscores the importance of characterizing dissolved fractions in nanometal suspensions.

Chronic toxicity of silver nanoparticles to Daphnia magna under different feeding conditions

“…While a substantial number of studies describe the lethal toxicity of various forms of silver, including silver nitrate (AgNO3) and silver nanoparticles (AgNP) (Allen et al, 2010, Hoheisel et al, 2012, Kennedy et al, 2010, the information on chronic toxicity to aquatic organisms is scarce. Also the mechanisms of nanosilver toxicity are poorly understood.…”

Both released silver ions and particulate Ag contribute to the toxicity of AgNPs to earthwormEisenia fetida

“…AgNPs have emerged as a topic of environmental concern as they could have unintended detrimental ecological impacts, due to their effective biocidal properties. Research regarding the potential mechanisms of toxicity of AgNPs is still emerging, with most of the available data involving freshwater species (Kennedy et al, 2010;Laban et al, 2010;Scanlan et al, 2013;Yang et al, 2012), prokaryotic and eukaryotic microorganisms (Ivask et al, 2014;Morones et al, 2005), as well as some mammalian cell lines and viruses (Cha & Myung, 2007;Kittler et al, 2010). Unfortunately, few studies have involved soil-dwelling organisms, even fewer specifically used AgNPs (Shoults-Wilson et al, 2011a,b,c;Tsyusko et al, 2012).…”

A metabolomic study on the responses of daphnia magna exposed to silver nitrate and coated silver nanoparticles

“…This confirmed that the Ag þ released from the AgNPs induced significant metabolic alterations. Kennedy et al (2010) indicated the importance of free silver ions as a major source of toxicity of AgNPs to D. magna and Pimephales promelas. Zhao and Wang (2012) also attributed toxicity of AgNPs to daphnids mainly to the release of soluble Ag, as similar 48 h LC50s were obtained for lactate-coated AgNPs, PVPcoated AgNPs and AgNO 3 , when the daphnids were exposed to the soluble Ag released from AgNPs.…”