Due to steady increase in use and mass production carbon nanotubes (CNTs) will inevitably end up in the environment. Because of their chemical nature CNTs are expected to be recalcitrant and biotransform only at very slow rates. Degradation of CNTs within days has recently been reported, but excluding one study, conclusions relied solely on qualitative results. We incubated 13 different types of CNTs and subjected them to enzymatic oxidation with horseradish peroxidase and concluded that the analytical methods commonly employed for studying degradation of CNTs did not have the sensitivity to unequivocally demonstrate degradation of these materials. To obtain unambiguous results with regard to the biotransformability of CNTs in the horseradish peroxidase system we incubated: (a) (14)C-labeled multiwalled CNTs, homologous to Baytubes CNTs; and (b) (13)C-depleted single-walled CNTs, used in previous studies. Our results show that (14)C-CO2 evolved linearly at a rate of about 0.02‰ per day, and at the end of the 30-day incubations the CO2 evolved amounted to about 0.5‰ of both initial substrates, the (14)C-labeled multiwalled and (13)C-depleted single-walled CNTs. These results clearly show that CNT material is oxidized in the horseradish peroxidase system but with half-lives of about 80 years and not a few days as has been reported before. Adequately addressing biotransformation rates of CNTs is key toward a better understanding of the fate of these materials in the environment.
No data on the bioaccumulation and distribution of multiwalled carbon nanotubes (MWCNTs) in aquatic vertebrates is available until now. We quantified uptake and elimination of dispersed radiolabeled MWCNTs ((14)C-MWCNT; 1 mg/L) by zebrafish (Danio rerio) over time. The influences of the feeding regime and presence of dissolved organic carbon (DOC) on accumulation of the nanomaterial were determined. The partitioning of radioactivity to different organs and tissues was measured in all experiments. A bioaccumulation factor of 16 L/kg fish wet weight was derived. MWCNTs quickly associated with the fish, and steady state was reached within 1 day. After transfer to clear medium, MWCNTs were quickly released to the water phase, but on average 5 mg of MWCNTs/kg fish dry weight remained associated with the fish. The nanomaterial mainly accumulated in the gut of all fish. Feeding led to lower internal concentrations due to facilitated elimination via the digestive tract. In the presence of DOC, 10-fold less was taken up by the fish after 48 h of exposure compared to without DOC. Quick adhesion to and detachment from superficial tissues were observed. Remarkably, little fractions of the internalized radioactivity were detected in the blood and muscle tissue of exposed fish. The part accumulated in these fish compartments remained constant during the elimination phase. Hence, biomagnification of MWCNTs in the food chain is possible and should be a subject of further research.
37The analysis of the potential risks of engineered nanomaterials (ENM) has so far been almost 38 exclusively focused on the pristine, as-produced particles. However, when considering a life-39 cycle perspective, it is clear that ENM released from genuine products during manufacturing, 40 use, and disposal is far more relevant. Research on release of materials from nano-products 41 is growing and the next necessary step is to investigate the behavior and effects of these 42 released materials in the environment and on humans. Therefore, sufficient amounts of 43 released materials need to be available for further testing. In addition, ENM-free reference 44 materials are needed since many processes not only release ENM but also nano-sized 45 fragments from the ENM-containing matrix that may interfere with further tests. The SUN 46 consortium (Project on "Sustainable Nanotechnologies", EU 7 th Framework funding) uses 47 methods to characterize and quantify nanomaterials released from composite samples that 48 are exposed to environmental stressors. Here we describe an approach to provide materials 49 in hundreds of gram quantities mimicking actual released materials from coatings and 50 polymer nanocomposites by producing what is called "Fragmented Products" (FP). These FP 51can further be exposed to environmental conditions (e.g. humidity, light) to produce 52 "Weathered Fragmented Products" (WFP) or can be subjected to a further size fractionation 53 to isolate "Sieved Fragmented Products" (SFP) that are representative for inhalation studies. 54In this perspective we describe the approach, and the used methods to obtain released 55 materials in amounts large enough to be suitable for further fate and (eco)toxicity testing. 56We present a case study (nanoparticulate organic pigment in polypropylene) to show 57 exemplarily the procedures used to produce the FP. We present some characterization data 58 of the FP and discuss critically the further potential and the usefulness of the approach we 59 developed. 60 61 62 This is a post-prinnt version of Nowack et al.
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