Phototoxicity of azaarene isomers to the marine flagellate Dunaliella tertiolecta.
Many studies have shown that narcosis or baseline toxicity of polycyclic aromatic hydrocarbons (PAHs) is strongly related to their lipophilicity. For azaarenes, such relationships have also been demonstrated, but for some compounds, deviations from these relationships have been observed, even for closely related compounds such as isomers. In the present study, the toxicity of four azaarene isomer pairs to the marine flagellate Dunaliella tertiolecta was determined. For quinoline, isoquinoline, acridine, phenanthridine, benz[a]acridine, and benz[c]acridine, the 72-h median effective concentrations for growth were 571, 464, 2.10, 14.7, 0.50, and 0.11 microM, respectively. For the five-ringed isomers dibenz[a,i]acridine and dibenz[c,h]acridine, no effects were observed at the highest concentration tested (0.1 and 0.005 microM, respectively). Growth inhibition by the two-, three-, and four-ringed isomer pairs to D. tertiolecta was well described by molecular volume and log Kow, indicating a narcotic mode of action. However, the toxicity of acridine and benz[c]acridine was much higher than that of their respective isomers, phenanthridine and benz[a]acridine, suggesting an additional specific mode of action. Based on the differences in energies between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, acridine and benz[c]acridine are susceptible to ultraviolet (UV) radiation, in contrast to the other tested compounds. Because UV was present, it is therefore argued that the toxicity of both compounds was photoenhanced. Photoenhanced toxicity may increase the environmental hazard of azaarenes, indicating the importance of enlarging the present monitoring of PAHs with phototoxic N-heterocyclic PAHs and incorporating this mode of action in water-quality criteria.
Wiegman
S
S
Department of Aquatic Ecology and Ecotoxicology, ARISE, University of Amsterdam, Kruislaan 320, 1098 SM, Amsterdam, The Netherlands. wiegman@science.uva.nl
van Vlaardingen
P L
PL
Bleeker
E A
EA
de Voogt
P
P
Kraak
M H
MH
D000818:Animals; D056890:Eukaryota / Q000187:drug effects* / Q000502:physiology; D007536:Isomerism; D010777:Photochemistry; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry / Q000633:toxicity*; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000633:toxicity*
D011084:Polycyclic Aromatic Hydrocarbons; D014874:Water Pollutants, Chemical