底泥中多環芳香烴對青鱂魚胚胎生物有效性及毒性效應之探討

Abstract

多環芳香烴（polycyclic aromatic hydrocarbons, PAHs）為持久性有機污染物（persistent organic pollutants, POPs）之一，也是常見之關切底泥污染物，這些污染物易與水體懸浮顆粒或有機質吸附而沉積在底泥中，而成了PAHs的蓄積庫。如水體及生物擾動常使吸附於底泥的PAHs重新釋放到表層水中，提高水生生物的暴露風險，也使得底泥污染對水生生物造成衝擊。然而目前底泥生物毒性檢測標準方法於台灣還屬開發階段。因此本研究（1）以青鱂魚（Oryzias latipes）胚胎做為模式生物，並以外添加PAH苯駢厄（Fluoranthene, Fl）（50-350 mg/kg dw）於人造底泥中進行全底泥暴露（whole sediment exposure），以評估底泥中Fl對胚胎毒性反應; （2）比較全底泥暴露法及以離心方式所取得之底泥孔隙水暴露法，探討底泥中Fl於胚胎的生物有效性及毒性效應; 以及（3）探討底泥中腐植酸（humic acid, HA）含量（0、0.1、1 g/kg dw）對底泥Fl（100 mg/kg dw）於胚胎生物有效性和毒性之影響。結果顯示，在全底泥Fl 50-350 mg/kg dw暴露下，胚胎受精後第20天（day post fertilization, dpf）的死亡率為35-67%，呈顯著劑量反應關係。此外胚胎發育毒性如心搏數與孵化後魚苗之體幹畸形率，皆隨底泥中Fl劑量上升而增加。相較於全底泥暴露，以離心方式所取得的水相暴露結果，以Fl暴露的胚胎經20天後仍無法順利孵化。且以水相暴露無法觀察到如全底泥暴露中，Fl對魚苗造成體幹畸形等毒性效應。因此以此離心條件方式所萃取的水相進行暴露，似乎無法有效的反應底泥中PAHs對胚胎的生物有效性。此外，底泥中Fl對胚胎死亡毒性效應，隨底泥中HA含量的增加而上升，可能原因為HA增加了Fl於水相中的溶解度，使得Fl對胚胎的生物有效性上升，而導致死亡率的上升。因此在底泥POPs胚胎毒性試驗中以全底泥暴露方式進行較佳，並需考慮HA對POPs毒性影響。本研究利用青鱂魚胚胎作為模式生物，藉由添加PAH（Fluoranthene, Fl）於人造底泥中，藉此建立出脊椎生物青鱂魚胚胎底泥毒性檢測方法，並發現底泥中腐質酸將顯著的影響了底泥中Fl傳輸及其對胚胎生物有效性的影響。

Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic persistent organic pollutants (POPs) with emerging concerns in sediment contamination. PAHs easily bind to the organic matter and/or particle matter in water and finally deposit in sediment as a pollutant source. Disturbance by aquatic organisms or water flow may release the PAHs to water column from sediment and the risk of aquatic organisms being exposed to PAHs is therefore enhanced. Indeed there are several standard sediment toxicity tests available for invertebrates, but very limited for vertebrates such as fish. Fish embryo toxicity (FET) assay is particularly suitable for chemical test because the embryonic stage is the most sensitive period to toxicants. The objectives of this research include (1) establishing a whole sediment exposure system with medaka (Oryzias latipes) embryos to evaluate toxicity of sediment PAHs (e.g. fluoranthene, Fl); (2) comparing two sediment exposure methods (whole sediment exposure vs. water phase exposure extracted from centrifuged sediment) on the effect of bioavailability and toxicity of Fl in medaka embryos; and (3) assessing the effect of sediment humic acid (HA) on bioavailability of Fl to medaka embryos with the whole sediment exposure. The results showed that Fl in sediment caused dose-dependent mortality and sublethal effects (e.g. malformation of hatchlings) in medaka embryos with whole sediment exposure, indicating medaka embryos could be a suitable vertebrate model used for sediment toxicity test. As compared with the whole sediment exposure, using water phase exposure from sediment centrifugation may not well express bioavailability of sediment pollution to medaka embryos because it caused lower embryonic mortality and no developmental abnormality was observed. The research also showed that sediment humic acid would enhance the bioavailability of Fl in sediment to medaka embryos, possibly due to enhanced the solubility of Fl in pore water by HA.