Biosafety assessment of titanium dioxide nanoparticles in acutely exposed nematode Caenorhabditis elegans with mutations of genes required for oxidative stress or stress response

We used Caenorhabditis elegans to investigate whether acute exposure to TiO2-NPs at the concentration of 20 μg L(-1) reflecting predicted environmental relevant concentration and 25 mg L(-1) reflecting concentration in food can cause toxicity on nematodes with mutations of susceptible genes. Among examined mutants associated with oxidative stress and stress response, we found that genes of sod-2, sod-3, mtl-2, and hsp-16.48 might be susceptible for TiO2-NPs toxicity. Mutations of these genes altered functions of both possible primary and secondary targeted organs in nematodes exposed to 25 mg L(-1) of TiO2-NPs for 24-h. Mutations of these genes caused similar expression patterns of genes required for oxidative stress in TiO2-NPs exposed mutant nematodes, implying their similar mechanisms to form the susceptible property. Nevertheless, acute exposure to 20 μg L(-1) of TiO2-NPs for 24-h and 25 mg L(-1) of TiO2-NPs for 0.48-h or 5.71-h did not influence functions of both possible primary and secondary targeted organs in sod-2, sod-3, mtl-2, and hsp-16.48 mutants. Therefore, our results suggest the relatively safe property of acute exposure to TiO2-NPs with certain durations at predicted environmental relevant concentrations or concentrations comparable to those in food in nematodes with mutations of some susceptible genes.