End of life cycle assessment for carbon nanotube (CNT) containing composites : release of CNT and ecotoxicological consequences
Year: 2014
Type: dissertation
Abstract: In the present study, for the first time, release rates for CNT from polycarbonate nanocomposites (containing 1 weight % CNT) were quantified by use of 14C-labeleled CNT material. Composites were produced by dispersing 14C-CNT in chloroform and adding polycarbonate pellets afterwards in order to produce CNT holding PC composites. After evaporation of the chloroform and surface improvement by hot pressing, round samples with a diameter of 18 mm were produced. Two different sample types were prepared for release quantification, composite plates previously degraded by artificial sunlight (1000 MJ/m2) and fresh prepared plates. Both were subjected to different degradation scenarios; i.e. water, heat, frost-thaw, humic acids, acid rain, disposal site effluent and abrasion, in series. The pre-degraded samples exhibited a much higher CNT release compared to the non-degraded ones (1% of the CNT material released compared to 0.03%). Release of the pre-degraded samples amounted to 18 mg per m2 and year regarding to Florida irradiation mean. Investigations of the pre-degraded surfaces showed an uncovering of CNT material and the formation of a dense CNT network at the surfaces. This surface decelerated the degradation rate of the matrix material beneath. In the second part of this work, CNT were shown to be bioavailable for the unicellular algae Desmodesmus subspicatus. Cells were exposed to 14C-CNT suspensions (1 mg/L) within their growth media to determine uptake and association, as well as elimination and dissociation in clear media, afterwards. Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was used to determine effects on algae biochemical composition. Differences between the spectra of control and CNT-exposed cells were detected. CNT-cell interactions were visualized by electron microscopy and related to alterations in their cell composition. A concentration factor (CF) of 5000 L/kg dry weight was calculated. However, most of the material agglomerated around the cells, but single tubes were detected in the cytoplasm as well. Computational analyses, i.e. principal component analysis (PCA) and subsequent linear discriminant analysis (LDA), of the ATR-FTIR data showed that CNT treated algae differed from the corresponding controls at all sampling times. No growth inhibition was observed, but CNT exposure changed the biochemical composition of cells. In the third research part of the present study, interactions between CNT and 17alpha-ethinylestradiol (EE2) and resulting alterations on EE2 bioavailability to zebrafish (Danio rerio) was taken into account. EE2 is a highly relevant xeno-estrogen, as it is used in livestock farming for contraception usages, in human birth control pills, and for other medical reasons. It has been detected in the ng/L range in surface waters of various streams. Ethinylestradiol has a high effective potency at its environmentally relevant concentration range and therefore poses a risk for aquatic organisms. The reported hazardous impacts to organisms range from direct toxicity to endocrine disruptor impacts on higher organisms, such as fish. Adsorption of the environmental relevant pollutant EE2 to CNT was observed in the water phase over time. This interaction might have been influenced by CNT reagglomeration and possible surface modifications as detected in TGA measurements, caused by the ultrasound dispersion of our samples. Further tests should be performed, to draw an entire picture of the interactions, as non predictable results were observed for low EE2 concentrations. Experiments with zebrafish showed the bioaccumulation of EE2 in males exposed to a 24 h aged mixture of 1µg 14C- EE2 and 1 mg CNT per litre for one week. Maximum EE2 concentration in the fish was reached after 48 h leading to a BCF of 280 L/kg fish wet weight. In a second experiment, with the same amounts, uptake of EE2 to different compartments of the fish, i.e. bile, gut, gills, skin and liver, was quantified. In this experiment uptake and effects of EE2 only and of CNT and EE2 in combination (24 h pre-aged dispersions) were evaluated. However, only slight differences in the uptake and elimination behaviour of fish exposed to EE2 with and without CNT material in the media could be outlined. Slightly increased uptake of EE2 was detected in the presence of CNT material after 48 h, but also better elimination within 72 h when fish were transferred to clear media. A last experiment aimed at the vitellogenin (VTG) induction in male zebrafish which is a reliable marker for estrogenic endocrine activity. EE2 alone induced a high level of VTG production at 6.6 ng EE2/L, but no induction could be observed in the fish-blood after they were exposed to 2.2 ng EE2/L alone. Remarkably, for both EE2 treatments (2.2 and 6.6 ng EE2/L, exposed for 14 d), the VTG induction was low and in the same range in presence of CNT material in the media.
Source: RWTH Publications (RWTH Aachen)
Authors: Stefan Rhiem, Andreas Schäffer
Language: English
Subfield: Environmental Engineering
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W982244159