Aged TiO₂‑Based Nanocomposite Used in Sunscreens Produces Singlet Oxygen under Long-Wave UV and Sensitizes <i>Escherichia coli</i> to Cadmium

TiO₂-based nanocomposite (NC) are widely used as invisible UV protectant in cosmetics. These nanomaterials (NMs) end in the environment as altered materials. We have investigated the properties of T-Lite SF, a TiO₂–NC used as sunscreen, after weathering in water and under light. We have examined the formation of ROS and their consequences on cell physiology of <i>Escherichia coli</i>. Our results show that aged-T-Lite SF produced singlet oxygen under low intensity long wave UV and formed hydroxyl radicals at high intensity. Despite the production of these ROS, T-Lite SF had neither effect on the viability of <i>E. coli</i> nor on mutant impaired in oxidative stress, did not induce mutagenesis and did not impair the integrity of membrane lipids, thus seemed safe to bacteria. However, when pre-exposed to T-Lite SF under low intensity UV, cells turned out to be more sensitive to cadmium, a priority pollutant widely disseminated in soil and surface waters. This effect was not a Trojan horse: sensitization of cells was dependent on the formation of singlet oxygen. These results provide a basis for caution, especially on NMs that have no straight environmental toxicity. It is crucial to anticipate indirect and combined effects of environmental pollutants and NMs

Physico-chemical Control over the Single- or Double-Wall Structure of Aluminogermanate Imogolite-like Nanotubes

It is known that silicon can be successfully replaced by germanium atoms in the synthesis of imogolite nanotubes, leading to shorter and larger AlGe nanotubes. Beside the change in morphology, two characteristics of the AlGe nanotube synthesis were recently discovered. AlGe imogolite nanotubes can be synthesized at much higher concentrations than AlSi imogolite. AlGe imogolite exists in the form of both single-walled (SW) and double-walled (DW) nanotubes, whereas DW AlSi imogolites have never been observed. In this article, we give details on the physicochemical control over the SW or DW AlGe imogolite structure. For some conditions, an almost 100% yield of SW or DW nanotubes is demonstrated. We propose a model for the formation of SW or DW AlGe imogolite, which also explains why DW AlSi imogolites or higher wall numbers for AlGe imogolite are not likely to be formed

Thallium Long-Term Fate from Rock-Deposit to Soil: The Jas Roux Sulfosalt Natural Analogue

Inorganic contaminant release resulting from mining activities can impact surrounding ecosystems. Ores formed by primary sulfide minerals produce sulfuric acid after mineral oxidation, which is the driving force of metal release. Yet secondary metal sulfates may form and play a crucial role in controlling the metal fate. In the case of thallium (Tl), it has been shown that in natural Tl-rich sulfide deposits and those found in mining areas, Tl can be trapped by Tl-jarosite (Tl-rich iron sulfate) and dorallcharite (TlFe3(SO4)2(OH)6). Our Tl speciation characterization results have generated novel insight into the long-term behavior of this metal derived from a unique natural hotspot: the Jas Roux site (France). The biogeochemical cycle of the soil ecosystems of Jas Roux dates back almost 15000 years ago and has now reached a steady state. A chemical gradient was found in soils across the toposequence underlying the Jas Roux outcrop. X-ray absorption spectroscopy revealed that Tl was mainly present in secondary minerals at the top of the studied zone. Oxidative dissolution of Tl-rich sulfide minerals and pyrite accounts for the presence of Tl-jarosite in soils, either by direct formation in soils or by gravity erosion from the outcrop. The Tl-jarosite quantity was found to decrease from the top to the bottom of the toposequence, probably due to sulfate leaching. Released Tl likely adsorbed on phyllosilicates such as Illite or muscovite, and a fraction of Tl was found to have oxidized into Tl(III) along the toposequence

Molecular Insights of Oxidation Process of Iron Nanoparticles: Spectroscopic, Magnetic, and Microscopic Evidence

Oxidation behavior of nano-Fe⁰ particles in an anoxic environment was determined using different state-of-the-art analytical approaches, including high resolution transmission electron microscopy (HR-TEM) combined with energy filtered transmission electron microscopy (EFTEM), X-ray absorption spectroscopy (XAS), and magnetic measurements. Oxidation in controlled experiments was compared in standard double distilled (DD) water, DD water spiked with trichloroethene (TCE), and TCE contaminated site water. Using HR-TEM and EFTEM, we observed a surface oxide layer (∼3 nm) formed immediately after the particles were exposed to water. XAS analysis followed the dynamic change in total metallic iron concentration and iron oxide concentration for the experimental duration of 35 days. The metallic iron concentration in nano-Fe⁰ particles exposed to water, was ∼40% after 35 days; in contrast, the samples containing TCE were reduced to ∼15% and even to nil in the case of TCE contaminated site water, suggesting that the contaminants enhance the oxidation of nano-Fe⁰. Frequency dependence measurements confirmed the formation of superparamagnetic particles in the system. Overall, our results suggest that nano-Fe⁰ oxidized via the Fe⁰ – Fe­(OH)₂ – Fe₃O₄ – (γ-Fe₂O₃) route and the formation of superparamagnetic maghemite nanoparticles due to disruption of the surface oxide layer

Influence of the Length of Imogolite-Like Nanotubes on Their Cytotoxicity and Genotoxicity toward Human Dermal Cells

Physical–chemical parameters such as purity, structure, chemistry, length, and aspect ratio of nanoparticles (NPs) are linked to their toxicity. Here, synthetic imogolite-like nanotubes with a set chemical composition but various sizes and shapes were used as models to investigate the influence of these physical parameters on the cyto- and genotoxicity and cellular uptake of NPs. The NPs were characterized using X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and atomic force microscopy (AFM). Imogolite precursors (PR, ca. 5 nm curved platelets), as well as short tubes (ST, ca. 6 nm) and long tubes (LT, ca. 50 nm), remained stable in the cell culture medium. Internalization into human fibroblasts was observed only for the small particles PR and ST. None of the tested particles induced a significant cytotoxicity up to a concentration of 10^–1 mg·mL^–1. However, small sized NPs (PR and ST) were found to be genotoxic at very low concentration 10^–6 mg·mL^–1, while LT particles exhibited a weak genotoxicity. Our results indicate that small size NPs (PR, ST) were able to induce primary lesions of DNA at very low concentrations and that this DNA damage was exclusively induced by oxidative stress. The higher aspect ratio LT particles exhibited a weaker genotoxicity, where oxidative stress is a minor factor, and the likely involvement of other mechanisms. Moreover, a relationship among cell uptake, particle aspect ratio, and DNA damage of NPs was observed