PROPERTY-TOXICITY RELATIONSHIPS OF AZAARENES TO THE GREEN-ALGA SCENEDESMUS-ACUMINATUS

The toxicity of three two-ring and five three-ring azaarenes to the gr een alga Scenedesmus acuminatus and its relationship with molecular st ructure was investigated. Indole, quinoline, isoquinoline, and carbazo le did not inhibit the growth rate of S. acuminatus in 96-h batch cult ure assays up to 10 mg/L. Chlorophyll-a content appeared to be a more sensitive response parameter than growth for five of six compounds. Th is parameter showed a relationship with hydrophobicity-related molecul ar descriptors like molecular surface area. Four benzoquinoline isomer s showed notably different effects on growth rare and chlorophyll-a co ntent. Median effect concentration (EC50) values obtained for growth r ate were acridine, 0.32 mg/L; benzo[f]quinoline, 1.55 mg/L; phenanthri dine, 5.24 mg/L; and benzo[h]quinoline, 6.65 mg/L. Similar differences existed in their EC50 values for chlorophyll-a content. The differenc es in toxicity between these isomers correlates with two electronical molecular descriptors, viz, the ionization potential and the homo-lumo gap. Several modes of action are put forward and their relative impor tance discussed.