Selection of an appropriate aqueous nano-fullerene (nC60) preparation protocol for studying its environmental fate and behavior

Fullerene toxicity in the benthos with implications for freshwater ecosystem services

Production of engineered carbon-based nanomaterials (CNMs) is rising, with increased risk of release to the environment during production, use, and disposal. This trend highlights a need to understand potential impacts of CNMs on the natural environment. Fullerenes are an emerging class of CNMs that are insoluble in water, and form aggregates that settle quickly, suggesting higher relative vulnerability of aquatic benthic ecosystems. This study assessed eco-toxicity of fullerenes (C60, C70) and the functionalized derivative, phenyl-C61-butyric acid methyl ester (PCBM), on functionally representative benthic organisms in traditional laboratory assays, and evaluated how the potential lethal and sub-lethal effects of fullerenes may indirectly impact benthic ecosystem function, including decomposition, primary productivity and nutrient cycling in lake microcosms with natural sediments. Standard toxicity tests indicated that population growth of Lumbriculus variegatus was reduced at 25 to 150 mg C60 kg^-1, but C70 and PCBM did not affect growth or weight of organisms in artificial sediments at 25 mg kg^-1. Survivorship and growth were lower in natural sediments with historic contamination, but C60 did not exacerbate this effect. C60 inhibited photosynthesis by the benthic diatom Nitzschia palea, and at high exposure chlorophyll a increased, suggesting a shading response. L. variegatus had strong effects on benthic ecosystem function, especially metabolism and nitrogen cycling, but C60 ≤ 30 mg kg^-1 sediment did not influence the role of L. variegatus in driving benthic processes. These observations suggest that at moderate to high concentrations, C60 may directly impact benthic organisms. However, under natural conditions with low to moderate concentrations, C60 has little effect and does not indirectly impact the ecosystem processes maintained by such organisms. These results are a step further towards a better understanding of potential impacts of fullerenes on aquatic ecosystems, and can aid in the development of regulatory policies.

Ecotoxicological effects of carbon based nanomaterials in aquatic organisms

An increasing amount of carbon-based nanomaterials (CNM) (mostly fullerenes, carbon nanotubes and graphene) has been observed in aquatic systems over the last years. However, the potential toxicity of these CNM on aquatic ecosystems remains unclear. This paper reviews the existing literature on the toxic effects of CNM in aquatic organisms as well as the toxic effects of CNM through influencing the toxicity of other micro-pollutants, and outlines a series of research needs to reduce the uncertainty associated with CNMs toxic effects. The results show that environmental concentrations of CNM do not pose a threat on aquatic organisms on their own. The observed concentrations of CNM in aquatic environments are in the order of ngL^-1 or even lower, much below than the lowest observed effect concentrations (LOEC) on different aquatic organisms (in the order of mgL^-1). Toxic effects have been mainly observed in short-term experiments at high concentrations, and toxicity principally depends on the type of organisms, exposition time and CNM preparation methods. Moreover, we observed that CNM interact (establishing synergistic and/or antagonistic effects) with other micro-pollutants. Apparently, the resulting interaction is highly dependent on the chemical properties of each micro-pollutant, CNM acting either as carriers or as sorbents, thereby modifying the original toxicity of the contaminants. Results stress the need of studying the interactive effects of CNM with other micro-pollutants at environmental relevant concentrations, as well as their effects on biological communities in the long-term.

Improving the understanding of fullerene (nC60) aggregate structures: Fractal dimension characterization by static light scattering coupled to asymmetrical flow field flow fractionation

Fullerene (C₆₀) aggregation mechanisms in aqueous media require considerable attention in the near future due to the heavy use and application of fullerene-based products within the context of nanotechnology. Such intensive development will result in the release of massive amounts of C₆₀ in aqueous environmental systems in the aggregate form (nC₆₀). In that sense, the aggregation mechanisms need to be fully determined to better evaluate the environmental fate and behavior of C₆₀. To fulfil these needs, the aim of this work was to extensively characterize the aggregation mechanisms of fullerene aggregates in aqueous media by asymmetrical flow field fractionation (AF4) coupled to static light scattering (SLS). We developed a sequential ultrafiltration method that allows the fractionation of the whole nC₆₀ size distribution into different size classes (1-100-200-450-800nm). Following a preliminary analysis by dynamic light scattering (DLS), we optimized several AF4 separation methods to allow screening of these colloidal size classes of nC₆₀ with high efficiency and resolution. The fractal dimension (D_f) of this entire size class was characterized directly on-line according to the radius of gyration through a combination of angle-dependent light scattering and fractal dimension analysis. We demonstrate the possible formation and persistence of colloidal populations of nC₆₀ in aqueous media from a few nanometers up to 800nm. D_f values ranging from 1.2 to 2.8, based on the nC₆₀ colloidal size range, strongly depend on the method of the sample filtration.