Molecular characterization and toxicological effects of citrate-coated silver nanoparticles in a terrestrial invertebrate, the earthworm (Eisenia fetida)

Silver is one of the most popular metals for use in synthesizing metal-based nanoparticles. Silver nanoparticles (AgNPs) are intensively applied within many industrial sectors. Previously, we observed unusual avoidance behavior in earthworms (Eisenia fetida) exposed to AgNPs. To understand the molecular basis of this abnormality, earthworms were exposed to AgNPs (1, 10, 100 mg/kg) or AgNO3 (100 mg/kg, positive control) via the soil to evaluate reactive oxygen species generation, genotoxicity, and transcriptional levels of stress-related genes (catalase, glutathione-S-transferase, heat shock protein 70, metallothionein, and superoxide dismutase). Earthworms exhibited a low propensity to accumulate silver, indicating a reduced mobility of AgNPs in the soil environment. Although abnormal behaviors were not found at low AgNPs concentrations, oxidative stress-related indicators were present, illustrating the importance of molecular responses as sensitive initial biomarkers of AgNP terrestrial contamination. The current study suggests that AgNPs may regulate oxidative stress-related mechanisms and provides an improved understanding of the environmental health effects of AgNPs on species in soil ecosystems.