| Summary: | 碩士 === 國立交通大學 === 環境工程系所 === 95 === 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.
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