Release of Metal Impurities from Carbon Nanomaterials Influences Aquatic Toxicity

Abstract

Few studies have considered the environmental impacts of impurities and byproducts associated with low-efficiency nanomanufacturing processes. Here, we study the composition and aquatic toxicity of low-purity, as-produced fullerenes (C60) and metallofullerene waste solids, both of which were generated via arc-discharge synthesis. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and inductively coupled plasma mass spectroscopy (ICP-MS) were used to characterize the metals composition of the solid test materials and of aqueous leachates prepared by mixing test materials with waters of varying pH, hardness, and salinity. The aquatic toxicity of the leachates was determined using U.S. Environmental Protection Agency recommended aquatic bioassay protocols with two standard test organisms-Pimephales promelas and Ceriodaphnia dubia. Results indicated that metals associated with the solid test materials became mobilized in our test system upon interaction with waters of circumneutral pH and reached concentrations sufficient to induce toxicity in both test species. Acute (48 h) LC50 values for P. promelas and C. dubia exposed to leachates prepared from metallofullerene waste solids were 54 and 5% (as % leachate in diluent), respectively. Toxicity was eliminated after adding the chelator EDTA to the leachates, implicating divalent transition metals as the toxicity source. Our results demonstrate the aquatic toxicity of metals mobilized from products and byproducts of nanomanufacturing, and they emphasize the need for a global review of nanomanufacturing wastes and low-purity products.

Methodological considerations for testing the ecotoxicity of carbon nanotubes and fullerenes: Review

“…Characterizing starting materials is essential, because CNPs can contain substances (including chemicals known to be toxic) in addition to the CNPs themselves [34][35][36] and because the purity of the CNP material is frequently unreliable, based only on the manufacturer's information. Large differences in reported toxicity of CNPs in the literature are likely a consequence of investigators actually testing different materials, starting materials containing varying amounts of contamination, and variable aggregation of the NPs occurring in the test solution.…”

“…Nevertheless, unpurified CNTs and to a lesser extent purified CNTs are likely to leach metals in the test media. In addition, byproducts from as-prepared fullerenes and metallofullerenes were shown recently to leach toxic concentrations of metals [36]. Assays such as the toxicity characteristic leaching procedure [44] or bioaccessibility tests [45][46][47] coupled with relevant analytical techniques can be used to measure ecologically relevant concentrations of the impurities.…”

Surface-associated metal catalyst enhances the sorption of perfluorooctanoic acid to multi-walled carbon nanotubes

“…This chemical is inevitably released into environmental compartments with the large-scale production of PFOA and its precursors, such as fluorotelomer alcohols and perfluoroalkyl sulfonamides [3,4]. The distribution of even after acid washing at high temperature CNTs may contain residual metal catalyst [41], which can be released into the aquatic environment [48]. The role of metal catalyst impurities, which released into the solutions during the sorption, in the sorption of Pb(II) on CNTs has recently been investigated [49].…”

Assessing nanomaterial exposures in aquatic ecotoxicological testing: Framework and case studies based on dispersion and dissolution

“…ENMs that agglomerate and settle to the bottom of test vessels can potentially entrain test organisms (Arndt et al, 2013;Petersen et al, 2015). ENM settling may also result in a predominance of smaller suspended particles and released ions or other constituent substances in the water column (Hull et al, 2009, Kennedy et al, 2015b, suggesting a need to test three different fractions of the exposure; the entire ENM exposure, the suspended fraction and the settled fraction (Potthoff et al, 2015). The focus of this study was on basic water-column assays, which use test organisms that are highly sensitive to ENMs (Coll et al, 2016;Garner et al, 2015).…”