In Response : Views from research/academia on the challenges to detecting carbon‐based nanomaterials in environmental matrices—An academic perspective

Since the discovery of C60 fullerene by Kroto et al. [1] and the progress of nanotechnology, a great effort has been made with respect to the development of carbon-based nanomaterials. These new nano-sized allotropes, such as carbon nanotubes (single-walled andmultiwalled), nano-diamonds, and graphene, are currently in use in microelectronics, catalysis, battery and fuel cells, supercapacitors, conductive coatings, water-purification systems, plastics, and sensors, among other uses; and new formulations and applications are envisaged in the near future. Currently, however, the potential impact of nanotechnology in the environment and in human health remains unclear [2]. Previous reviews presented the state of the art in methods for the detection, quantification and characterization of nanomaterials, toxicology data, or toxicological evaluation. The present article aims to assess if current data and tools are appropriate in relation to the initial question: Are carbon-based nanomaterials wonder material or a new threat? To establish the basis of risk assessment for carbon-based nanomaterials, realistic scenarios of exposure should be defined. To date, however, there is a lack of knowledge on their fate, transport, and behavior. One of the main drawbacks is the variety of environmental transformations and processes that can occur. For example, pristine fullerenes are highly likely topartition out of the aqueous phase and become adsorbed by biomass, particulate, and organisms. Pristine fullerenes also can be solubilized in colloidal aggregates, which can undergo transformation by the presence of organic matter, electrolytes, pH, and sun irradiation. Meanwhile, functionalized fullerenes are suspected of being transformed into more stable forms such as pristine homologs. Carbon nanotubes also can be solubilized and transformed by oxidative processes that modify their physicochemical characteristics. Therefore, combined approaches to characterize, identify, and quantify their degradation products are highly required. To date, few analytical methods have been developed for the quantitation of carbon-based nanomaterials in the environment, and almost all of them were devoted to fullerenes. Most of these methods havebeen considered in different reviewarticles [3,4], but in brief they are based on a separation step, generally by liquid– liquid extraction [5–7], solid-phase extraction [5–7], or filtration followed by ultrasound-assisted extraction with toluene [8,9] and then liquid chromatography coupled to mass spectrometry or tandem mass spectrometry. First studies in assessing fullerenes in the environment have been published during recent years [8–12]. For other types of carbon nanomaterials, however, such as carbon nanotubes, similar analytical approaches are not feasible because of their variable lengths and structures. Quantification at trace levels in complex samples has not been solved yet. In these cases, nowadays, their fate, behavior, and prevention of potential environmental impacts can be estimated only bymeans of models. Nonetheless, other difficulties that should be overcome are the lack of standardized approaches to characterize the toxicological behavior of nanomaterials. Among them are potential impurities present in the standards, the methods to prepare test suspensions, and toxicity test procedures. For example, nanomaterial suspension preparations can change the surface properties of nanomaterials or change their aggregation states with, in both cases, an In This Issue: