|Abstract: ||奈米科技由於可廣泛應用於各個領域，已被視為是二十一世紀最重要的新興科技之一。然而，近年來奈米材料的大量製造與利用逐漸使得這些奈米顆粒進入環境中的機率大增；不僅如此，這些奈米材料所具有的獨特高比表面積使其被歸類為高反應性和高物化動態的材料，易於環境和生物系統中發生許多轉化，特別是與自然界存在之天然有機物或人為有機污染物之間的吸附反應，而這些轉化作用終將改變奈米材料的宿命、傳輸以及毒性作用，因此實有必要在這些材料的生產製造有顯著進展前了解其轉化的性質和程度，以推估其所帶來的環境風險。有鑒於此，為了解具微生物毒性潛力的奈米碳管 (carbon nanotubes, CNTs) 在與常見的有機物質作用後，其物化特性的改變對其所引起的生物毒性的影響為何，本研究透過平板計數、OD600生長曲線、螢光染劑染色以及量測細胞ATP總量等方法，觀察改質前後與吸附有機質前後的多壁奈米碳管 (multiwalled carbon nanotubes, MWCNTs) 對模式生物E. coli所造成之細胞毒性效應（毒性的觀察以細胞致死或生長抑制的程度顯示）。結果顯示在暴露期間為震盪搖晃的條件下，裸露未吸附有機質的原始碳管A-MWCNTs (本身分散性差) 比裸露的改質碳管H-MWCNTs (本身分散性佳) 所造成的E. coli細胞毒性較強，可能是由於H-MWCNTs表面帶含有COO－等帶電官能基，故較A-MWCNTs不容易與菌接觸。此外，腐植酸 (humic acid, HA) 或鄰苯二甲酸二乙酯 (diethyl phthalate, DEP) 吸附於碳管表面所形成的高分子層空間位阻，除了能增加A-MWCNTs於水相中的分散穩定性外，亦能減緩其與E. coli的直接接觸，致使A-MWCNTs的細胞毒性減緩。H-MWCNTs吸附HA後在碳管表面形成之HA高分子層同樣能減輕H-MWCNTs的毒性，但在高濃度DEP溶液中之H-MWCNTs卻增加了碳管的微生物毒性，然其中的原因還無法確定。整體而言，這些結果顯示未改質之碳管在環境中與含苯環的有機物相互作用後，對於水生生態較為友善，但在評估環境風險時也不能忽視H-MWCNTs於較高DEP濃度的溶液中，些微增加微生物毒性此種特殊之現象。;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.