Abstract
Despite their ubiquity in personal care products, the health implications of titanium dioxide (TiO2) nanomaterials (NMs) are under strenuous investigation for their potential as a carcinogen, whereas other evidence has shown links with premature ageing. Both potential hazards are manifested after chronic exposure. To explore the chronic effects of TiO2 NMs in the environment, a multigenerational study using the model test species Daphnia magna is conducted. Phenotypical characteristics associated with ageing are observed (loss or shortening of tails and lipid accumulation) with increased expression of highly conserved key stress response genes involved in inflammatory responses and oxidative stress. These responses are visible in continuously exposed daphnids over four generations and in daphnids removed from maternal exposure even three generations later. However, exposure to the “aged” variants of these NMs at the same concentrations significantly reduced these effects, and exposure in medium containing natural organic matter is less severe than in salt‐only medium.
Highlights
We hypothesized that the toxicity of pristine TiO2 NMs would vary with surface chemistry, with the medium type, and with environmental ageing of the NMs which would reduce their surface reactivity
Using four conditions, we have demonstrated that even where toxicity is apparently reduced, some lasting effects persist in the subsequent generations affecting their apparent age and their reproductive success
Identical exposures of the aged TiO2 NMs in the artificial river water representative resulted in dramatically decreased effects on the D. magna
Summary
Multigenerational health effects and life history parameters assessed included survival, growth, reproduction, morphological traits, TiO2 biodistribution, and expression of key stress response genes involved in compensational pathways that are highly conserved between species.[26]. The most severe effects were observed in Daphnia (F0) exposed to the pristine uncoated TiO2 in the Daphnia culturing medium, with increased mortality, reduced fitness, and reproduction, and no surviving offspring for multigenerational monitoring (Figure 1). The reproductive cycle was altered as their fifth were broods not observed until day 33 (Figure SI.3B, Supporting Information) with only an average of two neonates per daphnid (Table SI., Supporting Information) The results show inconsistences in the daphnid growth and development between the two differently coated TiO2 NM exposures in the salt-only Daphnia culturing medium. Daphnids exposed to pristine uncoated TiO2 NMs in artificial water with NOM had 86% survival for 25 days (Figure 1c), which correlated with reduced body burden of Ti (Tables SI. and SI., Supporting Information), and brood timings that were comparable with the controls (Table SI., Supporting Information). The PVP TiO2 NMs were the most toxic, further highlighting the codependant effects of medium composition and NM surface reactivity
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