穩定化奈米零價鐵及其氧化產物對青鱂魚苗的毒性效應

Toxicity assessments of stabilized nanoscale zero-valent iron and its oxidation products in medaka (Oryzias latipes) larvae

蘇志翔(Chih-Hsiang Su)

指導教授 ： 陳佩貞

國立臺灣大學/生物資源暨農學院/農業化學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.01827

摘要

奈米零價鐵（nanoscale zero-valent iron, nZVI）為具粒徑小（＜100 nm）、比表面積大與高氧化還原力等特性的奈米級材料，經常用於土壤及地下水污染的整治與廢水處理的程序中。近年來許多研究指出將穩定化之nZVI直接注入地下水污染場址可提升現地污染復育的成效。然而，目前對於nZVI在地下水體中的傳輸、宿命及對生態環境與人類健康的衝擊尚未釐清。本研究使用無毒性的羧甲基纖維素（carboxymethyl cellulose, CMC)合成穩定化之CMC-nZVI (平均粒徑約49.3±11.0 nm)，並利用青鱂魚（medaka, Oryzias latipes）為模式動物來評估CMC-nZVI、自然氧化之CMC-nZVI （nFe-oxide）與二價鐵離子（Fe(II)）對青鱂魚苗的急毒性（acute toxicity），並觀察存活之青鱂魚苗組織病理變化與鐵生物累積情況。我們同時測量暴露溶液中pH值、溶氧量、鐵物種與活性氧物種（reactive oxygen species, ROS）隨時間的變化。結果顯示三種鐵溶液（1-100 mg/L）對青鱂魚苗的急毒性為：Fe(II)＞CMC-nZVI＞nFe-oxide。CMC-nZVI在溶液中會快速氧化成Fe(II)與三價鐵離子（Fe(III)），並經由芬騰反應（fenton reaction）產生過氧化氫等ROS及消耗溶液中的溶氧。nFe-oxide溶液中的主要鐵物種為Fe(III)及奈米氧化鐵，Fe(II)溶液則沒有顯著的物種變化；此兩種鐵溶液中的溶氧與ROS量與控制組相比並無顯著變化。組織病理（histopathology）觀察發現，高濃度CMC- nZVI（100 mg/L）會造成青鱂魚苗鰓絲（gill filament）組織肥大、肝細胞（hepatocyte）排列不規則與腸壁（intestine wall）變薄。此外，我們發現CMC- nZVI與Fe(II)溶液對青鱂魚苗腸壁造成類似的組織變異，且在低濃度（25 mg/L）就足以使青鱂魚苗腸部組織受損；然而，相同濃度下的nFe-oxide溶液對青鱂魚腸部無顯著影響。經過長時間的暴露後（12天），低濃度CMC-nZVI 與nFe-oxide也將導致魚苗死亡或氧化壓力等毒性效應，綜合言之， CMC-nZVI對青鱂魚苗的毒性效應應來自溶液中氧氣缺乏、 Fe(II)的毒性與ROS誘發的氧化壓力（oxidative stress）等因子。鐵物種進入魚體後所造成的氧化還原反應及誘導的生物毒性，仍需進一步的研究。

關鍵字

奈米零價鐵 ； 青鱂魚 ； 急毒性 ； 芬騰反應 ； 活性氧化物種

並列摘要

Iron-based nanotechnologies are increasingly used for environmental remediation; however, the aqueous fate and toxicologic impacts of engineered iron nanoparticles (NPs) on the aquatic ecosystem remain poorly understood. We treated larvae of medaka fish (Oryzias latipes) with 1-100 mg/L doses of thoroughly characterized solutions containing carboxymethyl cellulose (CMC)-stabilized nanoscale zerovalent iron (nZVI), aged nanoscale iron oxides (nFe-oxides) or ferrous ion (Fe[II]) for 12-14 days’ aqueous exposure to assess the causal toxic effect(s) of iron NPs on the fish. Dosing solutions were daily renewed and temporal changes of the particle size, pH and dissolved oxygen (DO) and reactive oxygen species (ROS) of the dosing solutions were monitored. Results show that the particle size of nZVI was remained around 50 nm and pH of the dosing solutions was consistent between 6-8 within 24 hr. We found that approximately 50% of nZVI was dissociated to Fe(II) ions in 10 mins and Fe(II) ions was then immediately oxidized to Fe(III) oxidizes. Due to rapid oxidation reaction of nZVI in water, DO of nZVI solution (100 mg/L) was thus down to zero for 50 minutes, while DO of nZVI solution (1-25 mg/L) stayed at 2-3 mg/L for an hour. In the meantime, high nZVI (100 mg/L) resulted in acute toxicity (65% mortality) of medaka larvae after a 7-day exposure; however, low larval mortality (<15%) was found from nZVI exposure (1-25 mg/L). Compared to nZVI, Fe(II) ion (50 mg/L) resulted 55% larval mortality, while 25 mg/L Fe(II) only caused 2.5 % mortality to medaka larvae after 7-days exposure. Based on histopathological analyses, fish intestine from the treated groups (>25 mg/L nZVI) accumulated high amount of ferrous iron and their intestine wall was significantly thinner than the control fish. We discuss the modes of acute toxic action of CMC-nZVI and chronic toxic effects in terms of ROS, hypoxia and Fe(II) toxicity.

並列關鍵字

nanoscale zero-valent iron ； medaka ； acute toxicity ； fenton reaction ； reactive oxygen species

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