A study of environmental fate and application of commercially available carbon nanotubes
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Carbon nanotubes (CNTs) are a group of carbon-based nanomaterials which can be conceptualized as one or more micrometer-scale-graphene sheets rolled into a nanoscale-cylinder. With special properties, especially large aspect ratio and quantum effects, CNTs have been used widely in various areas, such as materials science, electronics, pharmaceutical, and environmental sciences. As exceptional CNT properties are the key to the promotion of CNT applications in many aspects of our lives, these same properties are also cause for concern regarding the toxicological effects on organisms and the environment. Recent toxicity studies with CNTs have raised attention to the risks associated with CNTs to the environment and humans. It has also been suggested that not only toxicity of CNTs but also the fate, especially possible interactions with other contaminants, in a real environment should be understood to better serve future risk assessments. Currently, there are limited studies focused on CNT fate in the environment. In this research, fate and application studies of CNTs were conducted. The effect of CNTs on the fate of polyaromatic hydrocarbons (PAHs) was investigated in a soil system. Through sorption and desorption studies, it was discovered that CNTs had a strong sorption capacity for PAHs, which was three orders of magnitude higher than that of natural soils. However, at a concentration of 2 mg/g, CNTs did not change PAH sorption capacity in soil. This study also proposed ‘the rule of mixtures’ as a tool for prediction of PAH sorption behaviors in CNT-contaminated soil. Through leaching studies, CNTs at a concentration of 5 mg/g significantly changed PAH leaching behavior in soil. Properties of both sorbent (CNTs) and sorbate (PAHs) influenced PAH retention behavior in soil. Overall, CNTs with different concentrations led to distinct PAH fate behavior in soil. Future studies are needed to investigate PAH fate behavior in a CNT concentration-dependent manner. Bioaccumulation of CNTs in earthworms was also investigated. A novel microwave-induced heating method to detect CNTs in plants was recently developed. In this study, this method was modified to detect CNTs in earthworms; this is the first available method for quantification of CNTs in earthworms. The method was used to assess bioaccumulation of CNTs in earthworms and the calculated bioaccumulation factor was 0.015 ± 0.004, which indicated that CNTs are not bioaccumulative. In addition to these studies related to the fate and interactions of CNTs in the environment, one study was conducted to evaluate one potential application of CNTs. No studies have investigated the application of CNTs in passive sampling devices (PSDs) for contaminants in soil. Two PSDs with different sorbents (C18 and CNTs) were developed. The C18-PSD was a good biomimetic tool for PAH accumulation in soil, with a rapid equilibrium rate and good correlation with PAH bioaccumulation. With a cheaper price and higher sensitivity, CNTs-PSDs are a promising tool for estimating bioavailable PAHs in soil. However, future studies are needed to improve PAH extraction efficiency from CNTs. In summary, this research provided critical fate data needed for future CNT environmental risk assessment and regulation in soil. In addition, this study also provided data regarding the use of C18-PSDs and MWNTs-PSDs as potential biomimetic tools in PAH risk assessment.