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The biological effect of soilborne nanoparticles (NPs) is a manifestation of soil-NMs-bio interactions. Soil factors are known to restructure NPs surfaces and thus influence the nanotoxicity. However, the mechanisms by which environmental factors affecting nano-bio interactions to aggravate or alleviate nanotoxicities are poorly understood. Herein, we compared the toxicity of TiO 2 NPs (nTiO 2 ) in five soils using the model nematode (Caenorhabditis elegans), and investigated the variation of nano-bio interactions under different conditions. A correlation analysis showed that pH and dissolved organic matter (DOM) were dominant regulators of nTiO 2 toxicity. At the nano-bio interface, low pH (5.0) led to nTiO 2 adhesion to micron-sized furrows and aggravated dermal wrinkling, while humid acid (HA) alleviated these impacts. Mechanically, low pH increased nTiO 2 adhesion through enhanced electrostatic attraction and subsequent stimulation of mucin and collagen synthesis, resulting in a positive feed cycle of pH-dependent contact nanotoxicity. HA not only prevented nTiO 2 adhesion onto the epidermis due to its negative charge, but also relieved the overstimulation of stress response pathways, thereby alleviating nanotoxicity. These findings broaden our knowledge of how NPs induce contact toxicity in soil invertebrates through specific biointerfacial interactions, and highlight the important role of DOM in alleviating the combined hazards of NPs and soil acidification., Competing Interests: Declaration of competing interest The authors declare that there are no conflicts of interest in the present experiment., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Titanium dioxide nanoparticles (nTiO 2 ) are widely used and their environmental occurrence has raised concerns about the potential toxicity to biota. However, few studies have investigated the effect of long-term exposure to nTiO 2 on soil invertebrates. This study therefore for the first time investigated the long-term (120 days) effect of nTiO 2 (0, 5, 50, and 500 mg/kg) on the phenotypes, transcriptomic, and metabolomic profiles of earthworm (Eisenia fetida) in soil. The results showed that the long-term exposure to nTiO 2 did not significantly affect the growth, reproduction, and Ti content of earthworms. However, 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 nTiO 2 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 nTiO 2 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 nTiO 2 exposure. The combination of transcriptomics and metabolomics reveals the global responses that cannot be observed by conventional toxicity endpoints, facilitating the assessment of long-term ecological effect of engineered nanoparticles in the environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)