Given the increasing use of carbon nanotubes (CNT) in composite materials and their possible expansion to new areas such as nanomedicine which will both lead to higher human exposure, a better understanding of their potential to cause adverse effects on human health is needed. Like other nanomaterials, the biological reactivity and toxicity of CNT were shown to depend on various physicochemical characteristics, and length has been suggested to play a critical role. We therefore designed a comprehensive study that aimed at comparing the effects on murine macrophages of two samples of multi-walled CNT (MWCNT) specifically synthesized following a similar production process (aerosol-assisted CVD), and used a soft ultrasonic treatment in water to modify the length of one of them. We showed that modification of the length of MWCNT leads, unavoidably, to accompanying structural (i.e. defects) and chemical (i.e. oxidation) modifications that affect both surface and residual catalyst iron nanoparticle content of CNT. The biological response of murine macrophages to the two different MWCNT samples was evaluated in terms of cell viability, pro-inflammatory cytokines secretion and oxidative stress. We showed that structural defects and oxidation both induced by the length reduction process are at least as responsible as the length reduction itself for the enhanced pro-inflammatory and pro-oxidative response observed with short (oxidized) compared to long (pristine) MWCNT. In conclusion, our results stress that surface properties should be considered, alongside the length, as essential parameters in CNT-induced inflammation, especially when dealing with a safe design of CNT, for application in nanomedicine for example.

Background: Carbon nanotubes (CNT) are a family of materials featuring a large range of length, diameter, numbers of walls and, quite often metallic impurities coming from the catalyst used for their synthesis. They exhibit unique physical properties, which have already led to an extensive development of CNT for numerous applications. Because of this development and the resulting potential increase of human exposure, an important body of literature has been published with the aim to evaluate the health impact of CNT. However, despite evidences of uptake and long-term persistence of CNT within macrophages and the central role of those cells in the CNT-induced pulmonary inflammatory response, a limited amount of data is available so far on the CNT fate inside macrophages. Therefore, the overall aim of our study was to investigate the fate of pristine single walled CNT (SWCNT) after their internalization by macrophages.Methods: To achieve our aim, we used a broad range of techniques that aimed at getting a comprehensive characterization of the SWCNT and their catalyst residues before and after exposure of murine macrophages: X-ray diffraction (XRD), High Resolution (HR) Transmission Electron Microscopy (TEM), High Angle Annular Dark Field-Scanning TEM (HAADF-STEM) coupled to Electron Energy Loss Spectroscopy (EELS), as well as micro-X-ray fluorescence mapping (μXRF), using synchrotron radiation.Results: We showed 1) the rapid detachment of part of the iron nanoparticles initially attached to SWCNT which appeared as free iron nanoparticles in the cytoplasm and nucleus of CNT-exposed murine macrophages, and 2) that blockade of intracellular lysosomal acidification prevented iron nanoparticles detachment from CNT bundles and protected cells from CNT downstream toxicity.Conclusions: The present results, while obtained with pristine SWCNT, could likely be extended to other catalyst-containing nanomaterials and surely open new ways in the interpretation and understanding of CNT toxicity.

This survey of the marine ichthyofauna of the Piton de La Fournaise volcano at Reunion Island is the first explanatory study of fish community structures in this area. It describes and analyses the main qualitative descriptors of the fish communities (i.e. species richness, diet, life history and geographical distribution) and their spatio‐temporal organization. This investigation in 2011 examined lava flows of different ages, including the most recent flows that entered the ocean between 1977 and 2007. In all, 263 species belonging to 45 families were observed. Overall, the fish community was notable for an absence of top predators and a predominance of opportunistic small‐bodied species, with dietary flexibility and high reproductive rates, characteristic of the early stages of ecological succession. Between‐site analysis indicated that the fish assemblages differed essentially according to the intensity of the last volcanic disturbances. Fish communities in the most disturbed sites showed the highest numbers of Serranidae and the highest proportions of omnivores and small‐bodied opportunistic carnivores, including a high proportion of endemic south‐western Indian Ocean species. The spatial pattern of this last category of species could be the result of convergent biological traits, and their adaptation to unstable environments at the expense of their competitiveness in more biodiverse, mature communities. Conversely, fish communities in the less disturbed sites showed the highest number of Holocentridae and the highest proportion of browsers of sessile invertebrates. This last characteristic could be a consequence of higher ecological maturity, illustrated by a more specialized trophic network, for assemblages in areas with less intense disturbances. Otherwise, high structural complexity, either in unconsolidated lava boulders, rocks and rubble or high coral‐covered sites, could favour the increase of the total number of species independent of disturbance intensity. Regarding the broader effects, this study helps better understand how ecosystems can resist or recover from acute disturbances and the process of ecological succession that leads to the establishment of fish communities in newly submerged habitats.