Oxidative Stress Mechanisms Caused by Ag Nanoparticles (NM300K) are Different from Those of AgNO3: Effects in the Soil Invertebrate Enchytraeus Crypticus

Abstract

The mechanisms of toxicity of Ag nanoparticles (NPs) are unclear, in particular in the terrestrial environment. In this study the effects of AgNP (AgNM300K) were assessed in terms of oxidative stress in the soil worm Enchytraeus crypticus, using a range of biochemical markers [catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), glutathione reductase (GR), total glutathione (TG), metallothionein (MT), lipid peroxidation (LPO)]. E. crypticus were exposed during 3 and 7 days (d) to the reproduction EC20, EC50 and EC80 levels of both AgNP and AgNO3. AgNO3 induced oxidative stress earlier (3 d) than AgNP (7 d), both leading to LPO despite the activation of the anti-redox system. MT increased only for AgNP. The Correspondence Analysis showed a clear separation between AgNO3 and AgNP, with e.g., CAT being the main descriptor for AgNP for 7 d. LPO, GST and GPx were for both 3 and 7 d associated with AgNO3, whereas MT and TG were associated with AgNP. These results may reflect a delay in the effects of AgNP compared to AgNO3 due to the slower release of Ag+ ions from the AgNP, although this does not fully explain the observed differences, i.e., we can conclude that there is a nanoparticle effect.

Antioxidant Enzyme Activity and Lipid Peroxidation in Aporrectodea caliginosa Earthworms Exposed to Silver Nanoparticles and Silver Nitrate in Spiked Soil

“…Thus, the Ag + released from AgNPs can lead to LPO in earthworms, either A. caliginosa or E. fetida (Li et al 2014). Exposure of the soil invertebrate Enchytraeus crypticus to AgNPs showed that the oxidative stress mechanism caused by AgNPs may be somewhat different from that of Ag + , with AgNPs taking a longer time than Ag + to produce toxic effects (Ribeiro et al 2015).…”

“…Among the antioxidant enzymes, CAT appears to be the most induced (Ribeiro et al 2015). This agrees with our present study, which found a >2‐fold increase in CAT activity by Ag + .…”

“…A comparison of the antioxidant enzyme profiles in earthworms exposed to the same concentrations (0.3 and 3 mg/kg soil) of Ag + and AgNPs showed that the activities of antioxidant enzymes were markedly higher in earthworms exposed to Ag + . There are several reasons Ag + may be more toxic than AgNPs: 1) the solubility of Ag + is much higher than that of AgNPs because Ag + (from AgNO 3 ) is a salt, although AgNPs are considered to be a base that forms a colloidal solution in water; 2) on a molar basis, Ag + ions are some 5.6 × 10 14 times more concentrated than an equal mass of AgNPs; 3) Ag from AgNPs accumulates in the cell membranes, whereas Ag + is localized in the cytosolic fraction (Li et al 2014); and 4) the elimination rate of Ag when exposed to AgNPs is greater than that of Ag + (Ribeiro et al 2015). Schlich et al (2013) observed higher accumulation of Ag in the AgNP (sized 15 nm) group than in Eisenia andrei earthworms exposed to Ag + .…”

Nanomaterials in the Environment: Perspectives on in Vivo Terrestrial Toxicity Testing

“…It has been given considerable focus and has currently an extensive suite of tools available for hazard assessment, far beyond the standard ecotoxicity test battery of many other species. The tools cover bioaccumulation (Amorim et al, 2011), avoidance (Bicho et al, 2015a), full life cycle test (Bicho et al, 2015b(Bicho et al, , 2016(Bicho et al, , 2017aSantos et al, 2017), embryotoxicity (Gonçalves et al, 2015), full life span (Gonçalves et al, 2017), multigenerational (Bicho et al, 2017b), multispecies (mesocosm) system (SMS) (Menezes-Oliveira et al, 2013), full transcriptome and microarray tool (Castro-Ferreira et al, 2014;Gomes et al, 2017), oxidative stress biomarkers (Ribeiro et al, 2015), energy metabolism and cellular energy allocation , genotoxicity via the comet assay (Maria et al, 2017), and metabolomics and proteomics. This species has further potential as it can be exposed via water for a short period and hence allows the assessment of other routes of exposure (Gomes et al, 2015b).…”

Collembola Reproduction Decreases with Aging of Silver Nanoparticles in a Sewage Sludge-Treated Soil

“…The focus in ecotoxicological testing of AgNP in soil has, thus far, been more on microorganisms (Schlich et al, 2013b;Engelke et al, 2014;McKee and Filser, 2016), earthworms (Heckmann et al, 2011;Shoults-Wilson et al, 2011a;Schlich et al, 2013a;van der Ploeg et al, 2014;Novo et al, 2015), enchytraeids (Gomes et al, 2013(Gomes et al, , 2015Ribeiro et al, 2015;Bicho et al, 2016) and nematodes (Roh et al, 2009;Meyer et al, 2010). Collembola have received less attention.…”