The critical importance of defined media conditions in Daphnia magna nanotoxicity studies

Abstract

Due to the widespread use of silver nanoparticles (AgNPs), the likelihood of them entering the environment has increased and they are known to be potentially toxic. Currently, there is little information on the dynamic changes of AgNPs in ecotoxicity exposure media and how this may affect toxicity. Here, the colloidal stability of three different sizes of citrate-stabilized AgNPs was assessed in standard strength OECD ISO exposure media, and in 2-fold (media2) and 10-fold (media10) dilutions by transmission electron microscopy (TEM) and atomic force microscopy (AFM) and these characteristics were related to their toxicity towards Daphnia magna. Aggregation in undiluted media (media1) was rapid, and after diluting the medium by a factor of 2 or 10, aggregation was reduced, with minimal aggregation over 24h occurring in media10. Acute toxicity measurements were performed using 7nm diameter particles in media1 and media10. In media10 the EC50 of the 7nm particles for D. magna neonates was calculated to be 7.46μgL(-1) with upper and lower 95% confidence intervals of 6.84μgL(-1) and 8.13μgL(-1) respectively. For media1, an EC50 could not be calculated, the lowest observed adverse effect concentration (LOAEC) of 11.25μgL(-1) indicating a significant reduction in toxicity compared to that in media10. The data suggest the increased dispersion of nanoparticles leads to enhanced toxicity, emphasising the importance of appropriate media composition to fully assess nanoparticle toxicity in aquatic ecotoxicity tests.

Preparation and characterization of three-layer, isotopically labelled core-shell nanoparticles; a tool for understanding mechanisms of bioavailability

“…Romer et al 26 Unlabeled NPs were synthesized primarily to allow the synthesis method to be validated on the relatively inexpensive unlabeled Ag starting material.…”

Response of biochemical biomarkers in the aquatic crustacean Daphnia magna exposed to silver nanoparticles

“…While it has been shown that media composition can influence particle stability Römer et al 2013), the aggregation behavior of 1 mg/L AgNPs was assessed at 0, 1, 4, 24, and 48 h to correspond to the duration of the toxicity exposure study (Fig. 1b).…”

“…1b) probably due to the settling of aggregates in SCM. The rate of aggregation is affected by both the collapse of the diffuse layer of counter ions around the particle and the frequency of particle-toparticle interactions, as a consequence of the higher concentration of AgNPs (Römer et al 2013). Therefore, it is possible that the AgNPs used in the bioassays were less aggregated than suggested by results presented in Table 1 and Fig.…”

“…Whether the Ag + release occurred in the concentration range of AgNPs used in this study (1-10 μg Ag/L) remains unclear. If one assumes that the dissolution properties of AgNPs would stay the same regardless of the applied concentrations, it may be concluded that there was no free Ag + in SCM after 48 h. Complex chemical and biological processes that constantly modify Ag speciation during the test, as well as different exposure pathways for tested silver to organisms, make the analysis of the contribution of Ag + ions to the net toxicity of AgNPs very complicated (Römer et al 2013). Moreover, the ingestion and excretion of AgNPs and adhesion of AgNP aggregates to the outer surface of test organisms (such as the exoskeleton of crustaceans) during the test may change the speciation of silver (Blinova et al 2013).…”

Understanding the fate and biological effects of Ag- and TiO2-nanoparticles in the environment: The quest for advanced analytics and interdisciplinary concepts

“…Publications dealing with this aspect (see also SI Table S4) underline the relevance of ionic strength for aggregation of TiO 2 NP and Ag NP (Dabrunz et al, 2011;Romer et al, 2013;Romer et al, 2011;Tejamaya et al, 2012;Zhao and Wang, 2012). Moreover, charge-stabilized EINP dispersions are less stable than EINP coated with polyethylene glycol or PVP (Tejamaya et al, 2012).…”