The Challenge
of Studying TiO<sub>2</sub> Nanoparticle
Bioaccumulation at Environmental Concentrations: Crucial Use of a
Stable Isotope Tracer
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Abstract
The
ecotoxicity of nanoparticles (NPs) is a growing area of research
with many challenges ahead. To be relevant, laboratory experiments
must be performed with well-controlled and environmentally realistic
(i.e., low) exposure doses. Moreover, when focusing on the intensively
manufactured titanium dioxide (TiO<sub>2</sub>) NPs, sample preparations
and chemical analysis are critical steps to meaningfully assay NP’s
bioaccumulation. To deal with these imperatives, we synthesized for
the first time TiO<sub>2</sub> NPs labeled with the stable isotope <sup>47</sup>Ti. Thanks to the <sup>47</sup>Ti labeling, we could detect
the bioaccumulation of NPs in zebra mussels (D<i>reissena polymorpha</i>) exposed for 1 h at environmental concentrations via water (7–120
μg/L of <sup>47</sup>TiO<sub>2</sub> NPs) and via their food
(4–830 μg/L of <sup>47</sup>TiO<sub>2</sub> NPs mixed
with 1 × 10<sup>6</sup> cells/mL of cyanobacteria) despite the
high natural Ti background, which varied in individual mussels. The
assimilation efficiency (AE) of TiO<sub>2</sub> NPs by mussels from
their diet was very low (AE = 3.0 ± 2.7%) suggesting that NPs
are mainly captured in mussel gut, with little penetration in their
internal organs. Thus, our methodology is particularly relevant in
predicting NP’s bioaccumulation and investigating the factors
influencing their toxicokinetics in conditions mimicking real environments