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Property-toxicity relationships of azaarenes to the green alga Scenedesmus acuminatus

Vlaardingen, P.L.A. van, Steinhoff, W.J., Voogt, P. de., Admiraal, W.A.
Environmental toxicology and chemistry 1996 v.15 no.11 pp. 2035-2042
Scenedesmus, chlorophyll, ionization, isomers, mechanism of action, quinoline, surface area, toxicity
The toxicity of three two-ring and five three-ring azaarenes to the green alga Scenedesmus acuminatus and its relationship with molecular structure was investigated. Indole, quinoline, isoquinoline, and carbazole did not inhibit the growth rate of S. acuminatus in 96-h batch culture assays up to 10 mg/L. Chlorophyll-a content appeared to be a more sensitive response parameter than growth for five of six compounds. This parameter showed a relationship with hydrophobicity-related molecular descriptors like molecular surface area. Four benzoquinoline isomers showed notably different effects on growth rate and chlorophyll-a content. Median effect concentration (EC50) values obtained for growth rate were acridine, 0.32 mg/L; benzo[f]quinoline, 1.55 mg/L; phenanthridine, 5.24 mg/L; and benzo[h]quinoline, 6.65 mg/L. Similar differences existed in their EC50 values for chlorophyll-a content. The differences 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 importance discussed.