Mechanisms of (photo)toxicity of TiO2 nanomaterials (NM103, NM104, NM105): using high-throughput gene expression in Enchytraeus crypticus

Titanium dioxide (TiO2) based nanomaterials (NMs) are among the most produced NMs worldwide. When irradiated with light, particularly UV, TiO2 is photoactive, a property that is explored for several purposes. There is an increasingly number of reports on the negative effects of photoactivated TiO2 to non-target organisms. We have here studied the effect of a suite of reference type TiO2 NMs i.e. NM103, NM104, NM105 and compared these to the Bulk) with and without UV radiation to the oligochaete Enchytraeus crypticus. High-throughput gene expression was used to assess the molecular mechanisms, while also anchoring it to known effects at organism level (i.e., reproduction). Results showed that the photoactivity of TiO2 (UV exposed) played a major role in enhancing TiO2 toxicity, activating transcription of oxidative stress, lysosome damage and apoptosis mechanisms. For non-UV activated TiO2, where toxicity at organism level (reproduction) was lower, results showed the potential for long-term effects (i.e., mutagenic and epigenetic). NM specific mechanisms were identified: NM103 affected transcription and translation, NM104_UV negatively affected reproductive system/organs; and NM105_UV activated superoxide anion response. Results provided mechanistic information for UV-related phototoxicity of TiO2 materials and evidences of the potential long-term effects. Gene expression profile of Enchytraeus crypticus was analysed after 5 days of exposure to: i) TiO2 NMs under standard lab illumination (No-UV) and ii) TiO2 NMs + UV radiation. To maximise exposure, the test media was reconstituted water (ISO 1). The concentration tested was 1 mg/L (known to cause effects at reproduction - 3 weeks - after transference to clean soil). Three biological replicates per test treatment/NM and controls (standard laboratory light or UV) were used.