應用Arthrobacter globiformis檢測底泥中銅之生物毒性

Abstract

水域環境中的底泥對許多化學物質具有沉澱、吸附與錯合等固定作用，因而常成為水中污染物的最終受體。然而，原本存在底泥中的污染物卻可能在環境擾動時再度被釋出並污染水質，產生龐大的環境風險。污染物對生物的毒性並不能單純從化學分析直接反映出來，相關的毒性研究與試驗仍是必須的。目前，國內公告的底泥污染物生物毒性檢測法只有一種，即端足蟲更水式法。而微生物的操作普遍具有成本較低、試驗時間較短與操作相對容易等特點。若能引進或開發利用微生物來進行水域底泥污染物的毒性檢測，勢必有助於提高國內環境風險評估的效益。 本研究欲探討德國DIN ISO 18187的「Arthrobacter globiformis固相接觸測試法」實際應用於評估國內現地環境底泥生物毒性的可能性與適用性。藉由添加硫酸銅作為代表性污染物，檢測當不同底泥環境因子（鹽度與有機質含量）存在下，不同濃度硫酸銅對A. globiformis的毒性影響。根據實驗結果，本研究建立出硫酸銅添加底泥的急毒性迴歸模型，並利用此模型成功將現地底泥的生物毒性加以量化。最後，經過量化的現地底泥生物毒性，也將與底泥中所含重金屬的實際濃度進行比對與討論。 在不同鹽度含量的硫酸銅添加底泥暴露實驗中，可發現隨著鹽度增加，相同硫酸銅濃度的底泥生物毒性也隨之增加。而在不同有機質含量的硫酸銅添加底泥暴露實驗中，隨著有機質增加，相同硫酸銅濃度的底泥生物毒性隨之減少。 在套用以鹽度為環境干擾因子所建立的急毒性迴歸模型後，觀察到現地底泥樣本的生物急毒性與其中重金屬實際濃度的相關性較低。這顯示，一方面來看，由鹽度擬合的模型對於底泥中生物毒性的詮釋性較低；另一方面，底泥中的鹽度雖然會影響其中重金屬的生物毒性，影響的效果仍不顯著。相反地，在套用以有機質為環境因子所建立的急毒性迴歸模型後，結果顯示出現地底泥的生物毒性與其中銅、鋅、鎳等三種重金屬及總金屬的實際濃度具高度正相關。這意謂著，底泥中的有機質含量確實是影響其生物毒性的重要環境因子。同時，底泥的污染狀況也能如實反映在其生物毒性上。綜合以上的結果顯示，在納入適當的環境因子考慮後，A. globiformis固相接觸測試法可以應用於國內現地底泥生物毒性的檢測與評估上。

Sediment in the aquatic environment can immobilization many chemical substances through precipitation, absorption and complexation, usually serving as the terminal acceptor of contaminants. However, pre-existing contaminants in sediments could be released and re-contaminate the water when disturbance occurs, raising significant environmental risk. Simply employing chemical analysis does not necessarily reflect the biological toxicity of the contaminants, which means the research regarding toxicology of the contaminants is essential. Currently, only one standard regarding biological toxicity assay for sediments exists and it uses Hyalella azteca as the test organism. Assay methods with microorganisms are generally low-cost, quick and easy-to-operate. Thus, developing a biological toxicity assay with microorganisms as the test organism for contaminants in aquatic sediments will help to enhance the efficiency of evaluating environmental risk in Taiwan. The purpose of this study is to evaluate the plausibility and suitability of the Germany standard: Soil Quality— Contact Test for Solid Samples using the Hydrogenase Activity of Arthrobacter globiformis (DIN ISO 18187: 2014-11 Draft) when this method is being applied to assess biological toxicity of natural sediments in Taiwan. By analyzing artificial sediments spiked with copper sulfate, which are used as the representative contaminant, this study discusses the toxic effects to A. globiformis caused by different concentration of copper sulfate when different environmental factors like salinity or organic matter are involved. The regression models of artificial sediments spiked with copper sulfate are established, and successfully applied to quantify biological toxicity of natural sediments. Finally, the outcomes of quantified biological toxicity are then employed to compare with the real content of heavy metals in natural sediments. Using artificial sediments spiked with copper sulfate under varying salinity, results show that with increasing salinity, the biological toxicity of sediments spiked with the copper sulfate increases as well. The artificial sediments spiked with copper sulfate under different concentrations of organic matter show that with increasing organic matter concentration, the biological toxicity of sediments spiked with the copper sulfate decreases. After applying the regression model of biological acute toxicity established by taking salinity as an environmental factor affecting natural sediments, results suggest that the correlation between the acute toxicity and the total amount of the eight regulated heavy metals in natural sediments is weak. In other words, the salinity regression model deviates from true biological toxicity of natural sediments. Despite that salinity content itself showed high correlation to biological toxicity, the effect of salinity content to biological is not significant. On the contrary, when implementing the regression model of biological acute toxicity established by taking organic matter as an environmental factor affecting natural sediments, the acute toxicity is highly correlated to copper, zinc, nickel concentrations and the total amount of the eight regulated heavy metals, indicating that the organic matter content is a significant factor related to biological toxicity in sediments. At the same time, the simulated concentration of contaminants with biological toxicity could reflect in situ contaminant levels. To summarize the results above, when involving appropriate environmental factors, this A. globiformis solid contact test can be applied to analyze and evaluate the environmental risk of natural sediments in Taiwan.