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

Abstract

To disentangle the contribution of ionic and nanoparticulate Ag to the overall toxicity to the earthworm Eisenia fetida, a semi-permeable membrane strategy was used to separate Ag + released from silver nanoparticles (AgNPs) in an aqueous exposure. Internal Ag fractionation, activities of antioxidant enzymes and metabolites in E. fetida were determined after 96 h of exposure to two sizes of polyvinylpyrrolidone-coated AgNPs. The response of the antioxidant system combined with the content of malondialdehyde indicated that the Ag + released from AgNPs induced significant oxidative stress to the earthworms. Ag accumulated from AgNPs was predominantly associated with the granules and cell membrane compartments, whereas dissolved Ag was localized in the cytosol-containing fraction. In both Ag + exposures, two intermediates in the Krebs cycle, succinate and fumarate, were significantly elevated and depleted, respectively. A similar alteration pattern was seen in groups exposed to both smaller AgNPs (S AgNP, 10 nm) and larger AgNP (L AgNP, 40 nm), indicating that these effects in E. fetida were induced by exposure to released Ag + . In addition, unique metabolic responses including decreased malate and glucose levels in S AgNP-exposed earthworms could be associated with exposure to nanoparticulate silver. Increased leucine and arginine and decreased ATP and inosine levels were observed in L AgNP exposures only, which clearly demonstrated a size-specific effect of AgNPs. Collectively, this study provided strong evidence that nanosilver acts by a different mechanism than ionic silver to cause acute toxicity to E. fetida, but further verification under different environmental conditions is needed.

On the nature of citrate-derived surface species on Ag nanoparticles: Insights from X-ray photoelectron spectroscopy

“…Conversely, no ketones were found at all the Ag surfaces, and no surface C=O groups have been revealed with in situ SERS for the iron-free media too [9,10], probably because of stabilization of alcohol group bound to silver. Li et al [10] have interpreted the SERS spectra by a silver impact [43,44] implying that AgNPs may disturb the biochemical enzymatic oxidation of citrate by stabilizing the alcohol group as one of the mechanisms of silver toxicity.…”

Uptake, translocation and physiological effects of magnetic iron oxide (γ-Fe2O3) nanoparticles in corn (Zea mays L.)

“…However, Qian et al (2013) compared the toxicity of silver nanoparticles and silver ions on the growth of terrestrial plant model Arabidopsis thaliana and found that Ag NPs showed stronger toxicity to A. Thaliana compared with Ag þ , demonstrating that growth inhibition and cell damage of plants can be directly attributed to the nanoparticles themselves, not only the dissolved silver released from Ag NPs. And other authors reported that both silver ions and Ag NPs contribute to the toxicity (Kawata et al, 2009;Li et al, 2015;Navarro et al, 2008).…”

A metabolomic study on the biological effects of metal pollutions in oysters Crassostrea sikamea

“…In the oysters from BJ, choline and phosphocholine were significantly elevated, which suggested that this reaction was enhanced in oysters. Li et al (2015) reported that the phosphocholine was also elevated in Ag + -exposed Eisenia fetida. Since the oysters from BJ site accumulated the highest concentration of Ag, the elevation of phosphocholine might be the metabolic biomarker of Ag.…”