長期暴露於鄰苯二甲酸二(2-乙基己基)酯汙染底泥對青鱂魚幼魚之生物效應探討

Chronic Effects of Di(2-ethylhexyl)phthalate-contaminated Sediment on Larvae of Medaka Fish (Oryzias latipes)

吳柏成(Po-Cheng Wu)

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(2017年)

https://doi.org/10.6342/NTU201700025

摘要

鄰苯二甲酸酯類 (Phthalate esters, PAEs) 為常見的人造化合物，常被添加於塑膠產品以增強其彈性、強度及耐久性，其中鄰苯二甲酸二(2-乙基己基)酯 [Di(2-ethylhexyl)phthalate, DEHP] 為全世界產量最大、用途最廣的塑化劑，在世界各地皆有觀察到DEHP的流布。由於DEHP的水溶解度低，容易會被水中黏土礦物或有機物質等基質所吸附而沉降至底泥，使得底泥成為DEHP主要的蓄積庫。被吸附在底泥中的DEHP可能會因自然、人為或生物擾動而再度的移動到水體中，進而提高水中生物之暴露風險及危害效應。然而DEHP為生物急毒性低的新興汙染物，且目前臺灣對於底泥新興汙染物毒性評估的檢測方法較少，底泥中塑化劑汙染對水生生物的長期毒性效應所知有限。因此，本研究先以青鱂魚幼魚進行自動更水式底泥暴露系統干擾因子測試，選定275 mL燒杯中有100 mL飽和底泥，上層含有175 mL覆蓋水並每24小時更換一次水作後續暴露條件。再將DEHP添加的人造底泥進行21天青鱂魚幼魚毒性暴露試驗，並觀察底泥的DEHP汙染對於青鱂魚幼魚之生物毒性；最後利用擋網的有無 (隔絕青鱂魚直接接觸底泥) 來比較青鱂魚攝入汙染物的途徑差異，並觀察底泥DEHP對幼魚之生物毒性效應。結果顯示，DEHP底泥 (250、500、1000 mg/kg) 處理組其存活率與控制組間沒有明顯差異，但其幼魚的體長與體重隨底泥DEHP濃度升高而有降低的趨勢。此外，氧化壓力方面，暴露高濃度DEHP底泥 (500、1000 mg/kg) 顯著降低魚體GST酵素 (Gultathione S-transferases) 活性。底泥中DEHP在暴露前後約減少35-41 %，表層水於暴露期間皆無檢測到DEHP殘留。由暴露途徑實驗結果顯示，處理組幼魚存活率與控制組間沒有明顯差異，但隨著擋網隔絕幼魚直接接觸底泥，體長與體重減少的狀況有抑制的情形，氧化壓力酵素測定結果中，與控制組相比底泥暴露高濃度DEHP (500 mg/kg) 的幼魚體內GST酵素活性顯著降低。魚體中DEHP累積結果顯示，以擋網隔絕底泥也會減少青鱂魚對於DEHP之累積。底泥中DEHP在暴露前後約減少28-53 %，表層水也無檢測到DEHP含量，但發現表層水中懸浮物質中DEHP含量與底泥相近，表示底泥中的DEHP會隨著擾動而帶到水體中因而增加對於生物體暴露DEHP的風險。綜上所述，青鱂魚幼魚會透過直接攝入底泥而增加底泥汙染物的暴露途徑。青鱂魚幼魚長期暴露於受DEHP汙染之底泥中不會造成顯著之死亡效應，但會抑制GST酵素活性及幼魚成長情形 (體長及體重減少)。

關鍵字

自動更水式全底泥試驗系統 ； 鄰苯二甲酸酯類 ； 鄰苯二甲酸二(2-乙基己基)酯 ； 青鱂魚 ； 慢毒性

並列摘要

Phthalate esters (PAEs) are plasticizers commonly used in industries to enhance the flexibility, strengthening and softness of plastic products. Among these PAEs, di(2-ethylhexyl)phthalate (DEHP) is the most commonly used plasticizer in the world. It is easily leached into the environment and ubiquitously detected in surface water and sediment in the worldwide. The DEHP has low solubility, and is easily bound to the organic matter or clay minerals in water and DEHP will finally be deposited in sediment as a pollutant source. Sediment-bound DEHP may be remobilized by bioturbation or flood events and become more available and hazardous to aquatic biota. However, studies directly linking to the sediment toxicity tests with long term sediment chronic toxicity and using fish as a sediment model are still limited. The impact of DEHP contaminded sediment for fish (e.g., medaka larvae) is still unclear at present. The objectives of this study are to establish a sediment testing intermittent water renewal (STIR) system with larvae of medaka (Orzyias latipes) fish and to assess the chronic effect of DEHP-contaminated sediments. We also aim to investigate whether medaka larvae would directly uptake sediments through oral digestion, so we placed a mesh between the interface of sediment and water to seperate fish from directly exposing to sediment. We then compared the DEHP concentration and toxic effects in fish at different exposure tanks with and without the mesh. The results showed that a 21-days exposure of DEHP-contaminated sediment (250、500 and 1000 mg/kg) inhibited the growth (e.g., body weight and length) of medaka larvae and glutathione S-transferase (GST) activity were decreased at high concentrations of DEHP-contaminated sediment (500、1000 mg/kg) exposures. Our research also showed that the mesh placed between sediment and water lessened DEHP toxicity (e.g., growth and antioxidant enzymes decreases) and also declined the accumulation of DEHP in medaka larvae as compared to the fish from the beakers without the mesh. We also found that the DEHP-induced oxidative stress in larvae may obstruct the growth. In conclusion, DEHP-contaminated sediment caused developmental toxicity in growth and oxidative stress of medaka larvae. Pollutant in sediment might be taken by medaka fish via oral uptake. The established chronic sediment toxicity test of medaka larvae in a water renewal system has a potential to evaluate the risk of sediment DEHP contamination to ecosystems.

並列關鍵字

Sediment testing intermittent water renewal system ； Phthalate esters ； Di(2-ethylhexyl)phthalate ； Medaka ； Chronic toxicity

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