Investigation of the correlation between dispersivity and microbial toxicity of multi-walled carbon nanotubes in aquesous phase

• Main Authors: Mu-fan Chi, 齊慕凡
• Other Authors: 林居慶
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/86546792431559050901

碩士 === 國立中央大學 === 環境工程研究所 === 102 === Recent advances in nanotechnology have created numerous and promising applications in all sectors of society, thus making nanotechnology been considered as one of the most important technologies in the 21st century. However, the rapid worldwide development of nanotechnology seems inevitably increase the likelihood of the release of engineered nanomaterials (ENMs) to the environment. As being classified as a highly reactive and dynamic type of materials, ENMs are expected to easily undergo a number of transformations once released to the environment, thereby ultimately influencing the fate, transport and toxicity of these materials in both environmental and biological systems. Given that organic matter (OM) is a key factor controlling the behavior of chemicals in aquatic settings and microbes are the foundation of many ecosystems, probing the “OM-nanomaterial reactions” and consequent effect on microbial toxicity is one step towards understanding the lifetimes of nanomaterials in the environment and their potential toxicity on organisms exposed to them. In this study, laboratory experiments that incorporated approaches of viable count, growth monitoring (through optical-density measurement), LIVE/DEAD fluorescent staining, as well as total cellular ATP analysis were carried out to investigate the toxic extent of multi-walled carbon nanotubes (MWCNTs) towards the model organism E. coli. Specifically, this study focused on the microbial toxicity comparison of “surface-modified vs. surface-unmodified” and “OM-adsorbed vs. OM-unadsorbed” MWCNTs. Results indicated that over the course of exposure in the absence of OM, agitation led to higher cytotoxicity in unmodified MWCNTs (designated as A-MWCNTs) solution than in modified MWCNTs (designated a H-MWCNTs), probably due to more quantities of charged COO- moieties on the surface of H-MWCNTs that eventually prevented direct contact between E. coli cells and H-MWCNTs. Similarly, although humic acid (HA)- and diethyl phthalate (DEP)-sorption increased the dispersivity of A-MWCNTs, adsorption of these OM on A-MWCNTs minimized the toxicity of A-MWCNTs on E. coli owing to the same steric-obstruction effect. However, such sheltering effects were only observed in the H-MWCNTs solution containing HA as opposed to DEP, because H-MWCNTs equilibrated with higher concentrations of DEP resulted in higher growth inhibition, instead of toxicity mitigation. Explanations for this observation were currently unavailable. Together, these results suggested that while the interaction of MWCNTs and phenolic OM may not significantly cause a deleterious effect in the aquatic ecosystem, care should be taken when assessing environmental risk arising from exposure of H-MWCNTs in the presence of higher DEP concentrations.