Effect of titanium dioxide nanoparticles in enzymatic activity of epigeic earthworm species “eudrilus eugenia”

Titanium dioxide nanoparticles (TiO2 NPs) are commonly used in different industries because of their physico-chemical properties. They are widely used and their environmental occurrence has raised concerns about the potential toxicity to biota as the release of nanoparticles to the soil directly or indirectly through air and water is gradually increasing. The soil is contaminated with nanoparticles in the long term and soil microorganisms can adversely be affected by these accumulated nanoparticles. Studies show that nanoparticles can have a lethal effect on soil microorganisms by causing the production of reactive oxygen species by damaging the membrane permeability, cell signaling processes, and the stability of enzymes and protein structures. This study investigated the effect of nTiO2 (0, 5, 50, and 500 mg/kg) on the phenotypes, transcriptomic, and metabolomic profiles of earthworm (Eudrilus eugenia) in soil. The results showed that the antioxidant system and the transcriptomic and metabolomic profiles of earthworms were significantly affected. The superoxide dismutase (SOD) activity and the reduced glutathione/oxidized glutathione (GSH/GSSG) ratio significantly decreased under the 500 mg/kg nTiO2 treatment. The metabolomics analysis showed that glycine and pyroglutamic acid contents involved in the GSH metabolism were significantly altered under the 500 mg/kg treatment. Moreover, transcriptomics and metabolomics data revealed that the long-term exposure to nTiO2 affected the synthesis of carbohydrates, proteins, and lipids. However, the transcriptomics results indicated that the genes involved in ribosome biogenesis in eukaryotes pathway and TGF-beta signaling pathway were upregulated, which could explain why the growth and reproduction of earthworms were apparently not affected by the nTiO2 exposure.