以密閉式藻類毒性試驗方法評估苯甲酸類之毒性與結構-活性關係之研究

Abstract

此篇研究以月芽藻 (Pseudokirchneriella subcapitata)對20種苯甲酸類進行之48小時密閉式毒性試驗。實驗所得到之結果，將利用△DO、Final yield及Growth rate做為觀測終點，藉由Probit模式求出半致死濃度 (50% Effect concentration，EC50)，其後將毒性試驗後所得到的log(1/EC50)，與logKOW與NOH(苯環上烴基取代基所接的數目)迴歸，為此篇研究之最佳方程式(R2=0.915~0.965)。結果顯示，鹵素取代基接於苯甲酸之鄰位取代基毒性較間位、對位低；但烴類取代基接於苯甲酸之鄰位毒性卻較間位、對位高，而三烴基苯甲酸雖為低pKa及logKOW之化學結構，但與藻類有很好之親合性而導致較高的毒性。針對低影響濃度進行敏感性之比較，(△DO、Final yield及Growth rate)，其敏感度為 NOEC > EC10。而在本研究之三種反應終點當中對於苯甲酸類之敏感性最高者為細胞密度變化量，其次為溶氧產生量，而敏感性最差之反應終點為生長率。與其他生物種進行比較可以發現本研究之海洋性發光菌敏感性最高、其他依序為月芽藻、水蚤，敏感性最差者為纖毛蟲。

The objective of this study is to study the toxic effect of benzoic acids on Pseudokirchneriella subcapitata using a closed system test. The effects of benzoic acids were evaluated by three kinds of response endpoints, i.e., cell density, algal growth rate, and the dissolved oxygen production. Median effective concentratons (EC50s) were estimated using the Probit model with a test duration of 48hr. The quantitative structure-activity relationships (QSARs) were established based on the 1-octanol/water partition coefficient (logKow) and the numbers of benzene substituted with hydroxyl revealed a good relationship (R2=0.915~0.965). Benzoic acids with halogens at the meta- and para- positions were more toxic than benzoic acids with halogens at the ortho- position. As for the hydroxylated benzoic acids considered here, the results indicate that ortho- hydroxylated benzoic acids have lower pKa values, but the resluts showed higher toxicities than the meta- and/or para- hydroxylated ones, indicating that the hydroxybenzoate derivatives behaved differently from the halobenzoates. Especially, Tri-hydroxybenzoates may have higher affinity to algae than expected from their low logKow and pKa values. The results also reveal that the value of the lower effect concentration of the benzoic acids (cell density, algal growth rate, and the dissolved oxygen production). This demonstrates that the relative sensitivity is NOEC >EC10>. Besides, the experiment results (EC50) are compared with literature data derived by various toxicity tests. The order of the relative sensitivity is then obtained as follows : Microtox> algae(Final yield)> algae(DO production)> algae(Grwoth rate)> Daphnia magna> Tetrahymena pyriformis.