利用全底泥暴露系統探討銅於不同環境底泥中之釋出能力、生物有效性及毒性

Using medaka embryos coupled with a whole sediment exposure strategy to assess copper releasing, bioavailability and toxicity in sediment

李偉(Wei Lee)

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/NTU201702608

摘要

當金屬汙染物進入自然水體後，容易和水中的各種離子、無機物、有機物或生物作用而沉降到底泥中並累積，由於底泥容易成為汙染物蓄聚的地方，底泥汙染問題在近期愈發受到重視。這些累積在底泥中的汙染物不僅會對底棲生物產生危害，底泥中汙染物亦可能因為環境的擾動或化學狀態改變再度被釋放到水中，進而影響水域生態安全。根據環保署對全台重點河川底泥的重金屬分析資料顯示，台灣諸多河川的底泥都受到重金屬汙染，銅是汙染出現頻率最高的其中一種金屬。由於銅有高的底泥汙染頻率且具有高生物毒性，而水生生物相對於其他生物對銅毒性更為敏感，因此受銅汙染底泥之生態風險是一項重要的環境議題。本研究以青鱂魚胚胎作為模式生物，最佳化前人建立之全底泥暴露系統，用以評估不同特性之環境底泥受銅汙染之生物有效性及毒性表現。本研究選用四種不同特性的底泥進行為期6天的全底泥暴露試驗，並測量系統中覆蓋水及孔隙水中溶解態銅濃度、樹脂吸附銅量及序列萃取底泥不同銅物種等方法，以評估底泥特性對銅的移動性、釋出潛勢、鍵結型態以及和生物累積及毒性之關係。最後使用化學分析方法作為預測因子 (如底泥中銅的總量、水相溶解態銅濃度和樹脂吸附銅量等) 與生物反應 (死亡率及生物累積量) 進行相關性分析，尋找能準確預測銅在性質各異環境底泥中的生物有效性及毒性。結果顯示底泥的特性 (如有機質含量、陽離子交換容量和酸鹼值等) 對銅在底泥中的鍵結型態和釋出能力影響極大，底泥中的鐵錳氧化物及有機質容易與銅離子產生鍵結，底泥pH值較高時容易使銅沉澱。環境底泥中以夢湖底泥的銅最容易由底泥釋出到水相，在覆蓋水或孔隙水中可測得較高濃度的溶解態銅，進而對青鱂魚胚胎造成較高的毒性效應。四種底泥水相中溶解態銅濃度的表現和胚胎死亡率趨勢相似，且使用覆蓋水或孔隙水進行水相暴露之結果與全底泥暴露的胚胎死亡率無顯著差異，證明全底泥暴露系統對胚胎主要的毒性來源為溶解在水相中的銅。在毒性預測方面，底泥中總銅量與胚胎死亡率相關性差，證明底泥中汙染物的總量不能代表汙染物在環境中的風險。水相 (覆蓋水或孔隙水) 中溶解態銅濃度與樹脂吸附銅量兩者和胚胎死亡率的相關性高 (R2 > 0.93)，具有預測環境底泥中銅毒性的潛力。在使用生物累積量做為生物指標時，所有的預測因子與其相關性均不佳，顯示這些化學分析方法無法預測底泥中銅的生物有效性。由水相溶解態銅濃度、生物累積量及胚胎死亡率三者間關係發現，四種底泥中以夢湖底泥及淡水河底泥水相中溶解態銅的生物有效性較低但毒性較高。由分析水相中溶解態銅物種的結果發現四種底泥的溶解態銅物種在種類及比例上具有差異，溶解態銅物種不同可能是造成四種底泥環境暴露下的銅生物有效性和毒性差異之原因。本研究所建立的方法與研究結果在評估受汙染底泥中重金屬的生物有效性與毒性具貢獻。

關鍵字

重金屬銅 ； 青鱂魚胚胎 ； 全底泥暴露 ； 生物有效性 ； 毒性

並列摘要

Sediment pollution has been an important environmental issue for decades. When contaminants, especially heavy metals, enter aquatic environments such as rivers, lakes or ocean, most metals would be settled down with water matrices (e.g., dissolved matters or suspended particles) into sediment. If the polluted sediment is disturbed or changed its chemical condition, the sediment heavy metals could be released to the water column again. Copper (Cu) is a commonly detected sediment contaminants, and its concentration can reach to hundreds to thousands mg/L in sediment. Aquatic organisms are very sensitive to Cu ion, which at μg/L level can cause lethal effect to some species. In this study, we used embryos of medaka fish (Oryzias latipes) as a model organism to optimize whole sediment exposure system, and used this system to evaluate the bioavailability and toxicity of Cu in sediments with different characteristics. The dissolution, mobility, sepciation, bioavailability and toxicity of Cu in different Cu-contaminated environmental sediments were investigated by measuring Cu concentrations in the overlaying water and pore water, resin adsorbed Cu amount, sequential extracted Cu and Cu bioaccumulation. The correlation of chemical analysis (Cu concentration in sediment, dissolved Cu concentration in water phases, resin adsorbed Cu, etc.) and biomarkers (Cu bioaccumulation and mortality) was performed to predict the bioavailability or toxicity of Cu-contaminated sediment. Our results demonstrated that sediment characteristics (such as organic matter contents, cation exchangeable capacity, pH value, etc.) strongly affected the chemical bounding and releasing. Sediment with lower levels of pH values, cation exchangeable capacity or organic matter tended to release more Cu ion into pore and overlaying water, thus causing higher copper toxicity (e.g., embryos mortality). The trend of the dissolved Cu concentration in water phases of 4 sediments was similar to that of mortality of embryos, which indicated the toxicity of Cu in sediment was mainly contributed from the dissolved Cu in water phases. As to results of predicting toxicity, the correlation of the Cu concentration in sediment versus mortality was poor, which indicated that the whole metal concentration in sediment is not a good index to evaluate environmental risk. Either dissolved Cu concentrations in water phases or resin adsorbed Cu amounts had good correlation with mortality, which were potential to be used for predicting the toxicity of Cu in sediment. However, Cu-bioaccumulation of hatchlings appeared not a suitable biomarker in this study as it could not correlate well with the mortality. Moreover, we found that the dissolved Cu in MH and DS had lower bioavailability but higher toxicity, which may be ascribed to different speciation of Cu in water phases. Overall, the established sediment toxicity assay with medaka embryos and whole sediment exposure strategy is reliable and effective for assessing bioavailability and toxicity of heavy metal-contaminated sediment.

並列關鍵字

copper ； whole sediment exposure ； medaka embryos ； bioavailability ； toxicity

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