Nanotubes de carbone : quels risques pour l’environnement ?

Depuis le coup de projecteur sur les nanotubes de carbone au début des années 1990, les extraordinaires propriétés de ces nanoparticules ont déclenché un effort de recherche considérable qui s’est très rapidement traduit par la commercialisation de nombreux produits en contenant, comme souvent sans aucun recul quant à leur impact potentiel sur l’environnement

Environmental impact of engineered carbon nanoparticles: from releases to effects on the aquatic biota

Nano-ecotoxicology is an emerging science which aims to assess the environmental effect of nanotechnologies. The development of this particular aspect of ecotoxicology was made necessary in order to evaluate the potential impact of recently produced and used materials: nanoparticles (NPs). Among all the types of NPs, carbon nanoparticles (CNPs) especially draw attention giving the increasing number of applications and integration into consumer products. However the potential impacts of CNPs in the environment remain poorly known. This review aims to point out the critical issues and aspects that will govern the toxicity of CNPs in the environment

Écotoxicité des nanotubes de carbone dans l’environnement : contexte et état de l’art

Parmi les nombreux nanomatériaux existants, les nanotubes de carbone (NTC), dont la production mondiale annuelle atteint plusieurs centaines de tonnes, font partie d’une catégorie de matériaux à part, tant leur potentiel d’application est vaste et leurs propriétés exceptionnelles. La toxicité des NTC est depuis peu étudiée en santé humaine, avec pour preuve de nombreuses publications disponibles, à ce jour, sur des études in vitro et indique que leur innocuité n’est pas démontrée. En revanche, la bibliographie dénote incroyablement par ses lacunes au niveau de leur impact potentiel sur les écosystèmes et sur les espèces qui les peuplent. Or, il paraît raisonnable d’envisager la dissémination des NTC dans l’environnement à chacune des étapes de leur cycle de vie (conception, production, utilisation et fin de vie de produits finis). Par conséquent, il paraît tout aussi raisonnable d’en étudier les risques sur la composante biologique du milieu réceptacle et « concentrateur » de pollution tel que le compartiment aquatique. Dans ce contexte, cette synthèse a pour objectif premier de réaliser un état de l’art des connaissances disponibles concernant les effets écotoxiques des NTC chez divers organismes, et notamment aquatiques. Le contexte actuel souligne l’importance de ce type de synthèse, qui répond à de réels besoins d’information de la société. Cette synthèse se veut motrice dans un domaine encore peu exploré, celui de l’écotoxicité des NTC chez les organismes aquatiques. Les études disponibles indiquent divers effets toxiques liés à l’ingestion par les organismes des NTC présents dans les milieux d’exposition

Biocompatible polymer-assisted dispersion of multi walled carbon nanotubes in water, application to the investigation of their ecotoxicity using Xenopus laevis amphibian larvae

Carbon nanotubes (CNTs) tend to readily agglomerate and settle down in water, while the adsorption of compounds present in natural aquatic media could enhance their dispersion and stabilization in the water column. We designed a new exposure protocol to compare the biological responses of Xenopus laevis larvae exposed in semi-static conditions to size-reduced agglomerates of multi-walled carbon nanotubes (MWCNTs) in suspension in the water column and/or to larger agglomerates. Suspensions were prepared using a combination of a non-covalent functionalization with a non-toxic polymer (either carboxymethylcellulose, CMC, or gum arabic, GA) and mechanical dispersion methods (mainly ultrasonication). The ingestion of agglomerates which have settled down was incriminated in the disruption of the intestinal transit and the assimilation of nutrients, leading to acute and chronic toxicities at the highest tested concentrations. Rise in mortality, decrease in the growth rate and induction of genotoxicity from low concentrations (1 mg/L in the presence of CMC) were evidenced in presence of suspended MWCNTs in the water column. The biological responses seemed to be modulated when GA, a potential antioxidant, was used. We hypothesized that MWCNTs should interfere mainly at the surface of the gills, acting as a potential respiratory toxicant and generally inducing indirect effects

Assessment of the potential in vivo ecotoxicity of Double-Walled Carbon Nanotubes (DWNTs) in water, using the amphibian Ambystoma mexicanum

Because of their specific properties (mechanical, electrical, etc), carbon nanotubes (CNTs) are being assessed for inclusion in many manufactured products. Due to their massive production and number of potential applications, the impact of CNTs on the environment must be taken into consideration. The present investigation evaluates the ecotoxic potential of CNTs in the amphibian larvae (Ambystoma mexicanum). Acute toxicity and genotoxicity were analysed after 12 days of exposure in laboratory conditions. The genotoxic effects were analysed by scoring the micronucleated erythrocytes in the circulating blood of the larvae according to the French standard micronucleus assay. The results obtained in the present study demonstrated that CNTs are neither acutely toxic nor genotoxic to larvae whatever the CNTs concentration in the water, although black masses of CNTs were observed inside the gut. In the increasing economical context of CNTs, complementary studies must be undertaken, especially including mechanistic and environmental investigations

Few Layer Graphene sticking by biofilm of freshwater diatom Nitzschia palea as a mitigation to its ecotoxicity

Carbon-based nanoparticles such as graphene have many applications leading to their industrial production. Few-Layer Graphene (FLG) is thus likely to be found in the environment, and especially in rivers. In this study, the effect of FLG on the photosynthetic benthic diatom Nitzschia palea was assessed making distinction between the impact of a direct contact with FLG and a shading effect of FLG on diatoms. Growth inhibition of diatoms exposed to FLG at 50 mg L-1 was observed at 48 h of exposure associated with an increase in diatoms mortality. At 144 h, the growth rate was recovered. However, in shading condition, at 48 h of FLG exposure, a persistent growth inhibitionwas observed at 50 mg L-1. Microscopic observations and a monitoring of FLG concentration in the medium allowed to conclude that exopolymeric substances (EPS), naturally secreted by N. palea, strongly interact with FLG, sticking nanoparticles at the bottom of wells. Our results highlight the potential mechanisms of clarification of the water column by diatoms biofilms, by sticking FLG even at high concentration. Overall, these results suggest that one potential toxicity process of graphene could be a combination of direct and shading effect leading to a strong interaction between biofilm and nanoparticles

Surface area of carbon-based nanoparticles prevails on dispersion for growth inhibition in amphibians

The attractive properties of carbon-based nanoparticles such as graphene and its derivatives or carbon nanotubes lead to their use in many application fields, whether they are raw or functionalized, such as oxidized. These particles may finally contaminate the aquatic compartment, which is a major receptacle of pollutants. The study of their impact on aquatic organisms is thus essential. At the nano scale, recent studies have highlighted that specific surface area should be used as the most relevant descriptor of toxicity instead of the conventional mass concentration. By using a dose-response model, this work compares the chronic toxicity observed on Xenopus laevis larvae after 12-day in vivo exposure to raw, oxidized carbon allotropes, or in the presence of chemical dispersant. We show that chemical dispersion does not influence the observed chronic toxicity, whether it is through surface chemistry (oxidation state) or through the addition of a dispersant. The biological hypothesis leading to growth inhibition are discussed. Finally, these results confirm that surface area is the more suited metric unit describing growth inhibition

International standardized procedures forin vivoevaluation of multi-walled carbon nanotube toxicity in water

The classical approach in ecotoxicological evaluation of chemical substances consists of conducting standardized bioassays on organism models. In this work, the potential impact of industrial multiwalled carbon nanotubes was investigated by ecotoxicological standardized procedures using aquatic organisms of different trophic levels, namely bacteria, green algae, invertebrates, fish, and amphibians. The results indicated (1) inhibition of growth in amphibians at 50 mg L¡1 and higher, and (2) no effects on daphnia and fish up to 100 mg L¡1. With the exception of algae (for which Fe deficiency is measured), it seems that the observed toxicity may be due to physiological effects in relation to the ingestion of carbon nanotubes not necessarily related to their intrinsic effects

International amphibian micronucleus standardized procedure (ISO 21427-1) for in vivo evaluation of double-walled carbon nanotubes toxicity and genotoxicity in water

Considering the important production of carbon nanotubes (CNTs), it is likely that some of them will contaminate the environment during each step of their life cycle. Nevertheless, there is little known about their potential ecotoxicity. Consequently, the impact of CNTs on the environment must be taken into consideration. This work evaluates the potential impact of well characterized double-walled carbon nanotubes (DWNTs) in the amphibian larvae Xenopus laevis under normalized laboratory conditions according to the International Standard micronucleus assay ISO 21427-1:2006 for 12 days of half-static exposure to 0.1–1–10 and 50 mg L−1 of DWNTs in water. Two different endpoints were carried out: (i) toxicity (mortality and growth of larvae) and (ii) genotoxicity (induction of micronucleated erythrocytes). Moreover, intestine of larvae were analyzed using Raman spectroscopy. The DWNTs synthetized by catalytic chemical vapor deposition (CCVD) were used as produce (experiment I) and the addition of Gum Arabic (GA) was investigated to improve the stability of the aqueous suspensions (experiment II). The results show growth inhibition in larvae exposed to 10 and 50 mg L−1 of DWNTs with or without GA. No genotoxicity was evidenced in erythrocytes of larvae exposed to DWNTs, except to 1 mg L−1 of DWNTs with GA suggesting its potential effect in association with DWNTs at the first nonacutely toxic concentration. The Raman analysis confirmed the presence of DWNTs into the lumen of intestine but not in intestinal tissues and cells, nor in the circulating blood of exposed larvae