Comparative toxicity of a food additive TiO, a bulk TiO, and a nano-sized P25 to a model organism the nematode C. elegans.

To help fill the knowledge gap regarding the potential human health impacts of food pigment TiO, a comparative toxicity study was performed on a food-grade TiO (f-TiO), a bulk TiO (b-TiO), and a nano-sized TiO (Degussa P25), and in the nematode Caenorhabditis elegans. Acute phototoxicity and chronic toxicity effects including reproduction, lifespan, and vulval integrity were evaluated. The f-TiO, b-TiO, and P25 had a primary particle size (size range) of 149 (53-308) nm, 129 (64-259) nm, and 26 (11-52) nm, respectively. P25 showed the greatest phototoxicity with a 24-h LC50 of 6.0 mg/L (95% CI 5.95, 6.3), followed by the f-TiO (LC50 = 6.55 mg/L (95% CI 6.35, 6.75)), and b-TiO was the least toxic. All three TiO (1-10 mg/L) induced concentration-dependent effects on the worm's reproduction, with a reduction in brood size by 8.5 to 34%. They all caused a reduction of worm lifespan, accompanied by an increased frequency of age-associated vulval integrity defects (Avid). The impact on lifespan and Avid phenotype was more notable for P25 than the f-TiO or b-TiO. Ingestion and accumulation of TiO particles in the worm intestine was observed for all three materials by light microscopy. These findings demonstrate that the food pigment TiO induces toxicity effects in the worm and further studies are needed to elucidate the human health implication of such toxicities.