細胞密度於連續式藻類毒性試驗中之影響

Abstract

本研究延續Chen and Lin 於1997年所提出的連續式試驗方法進行藻類(Selenastrum capricornutum)重金屬毒性試驗。經由稀釋方法，將每次實驗時所需的藻液使用量由原系統的100 % 降為50 % 及6 % 後進行毒性試驗，以探討藻類細胞密度與試驗敏感度間之相對應關係。而由實驗結果發現: 當降低藻類細胞密度時，實驗所得之 EC50值、LOEC值及NOEC值皆隨之下降，亦即試驗敏感度隨之提高。而由於藻液使用量的降低，連續式試驗之實驗週期可由原系統的4天進一步縮短為2天甚至1天，可有效增加試驗頻率。 由於目前各藻類標準方法有逐漸禁止於試驗基質中添加螫合物的趨勢，因此在本研究中亦進行不含(或減量)螫合物-EDTA的相關實驗，藉以探討EDTA含量對連續式培養下之藻類生長及對連續式藻類毒性試驗結果所造成的影響。同時為對照之用，研究中亦操作不含EDTA的批次式藻類毒性實驗。根據結果顯示: 在將進流基質中的EDTA含量由30 μg/L降為15 μg/L後，連續式培養下之藻類在長時間下仍可維持正常之生長。而不含EDTA之批次式培養下，藻類細胞生長則明顯受到抑制。至於進行批次式及連續式藻類毒性試驗時，EDTA的減少將造成兩者在毒性試驗敏感度大幅提高。 最終，對各不同條件下之藻類毒性試驗進行參考毒物Cd2+之再現性比較。在50 % 細胞密度之連續式試驗中，實驗之再現性明顯優於批次式試驗。然而在6 % 之試驗中，由於由於藻類細胞數目較少，些微的細胞數量變動即可導致生長率產生大幅度變化，因此實驗之再現性較為不佳。

In this study , we performed the modified method of the continuous algal(Selenastrum capricornutum) toxicity test which was introduced by Chen & Lin in 1996 . By diluting , we decreased the use of algal cells per ml from 100 % to 50 %、6 % in each continuous experiment . We then researched the correlation between the algal cell density with the sensitivity of the continuous toxicity test . And we found that : When we lowered the algal cell density , the sensibility would be improved markedly i.e. the EC50 values 、NOEC values and LOEC values dropped off . In addition , the lower cell density could shorten the experimental period from 4 days to two or one day . The short period could increase the frequency of the operation of the experiment . Because the new algal standard batch method is intend to inhibit the use of the chelator-EDTA in the medium , we also proceeded the correlative experiments which not including (or reduced) EDTA . Then , we researched how the lack of EDTA could effect on the algal growth , and compared the results of the toxicity test from the exist of EDTA or not . Additionally , we proceeded the batch toxicity test without EDTA in comparison to the results from continuous toxicity test. Then we found that : when the EDTA , in the medium , was reduced from 30 μg/L to 15 μg/L , the culture of algae in the continuous incubator was still maintained in healthy condition for a long time . In the toxicity test , however, when we reduced the use of the EDTA , the sensibility would be increased . Finally , we compared the reproducibility in each different toxicity test .