Comparative ecotoxicity of NPAHs to larvae of the midge Chironomus riparius

Abstract

Acute toxicity of seven azaarenes (NPAHs) has been determined using larvae of the midge Chironomus riparius. Clear dose-response relationships for mortality of first instar larvae were observed, but surviving larvae grew as equally well as the controls. LC 50 values (96 h) for a two-ringed structure (quinoline), four three-ringed structures (acridine, phenanthridine, benzo[ f]quinoline and benzo[ h]quinoline) and two four-ringed structures (benz[ a]acridine and benz[ c]acridine) were generally one order lower than the few values reported for other aquatic species in the literature. Dibenz[ a,i]acridine, a five-ringed structure, was not acutely toxic at its maximum dissolved concentration. Acute toxicity increased with increasing number of aromatic rings of the compound; accordingly, correlations between the LC 50 values and size, shape and topology-related molecular properties were strong. However, between the four benzoquinoline isomers tested also differences in toxicity were observed: acridine was significantly more toxic than the other benzoquinoline isomers tested. This is most likely caused by transformation of acridine under UV light, indicated by a HOMO–LUMO gap in the highly phototoxic region, a high correlation between isomer toxicity and heat of formation and a low recovery of acridine in the water during the experiment.