Comparative metabolism of phenanthridine by carp (Cyprinus carpio) and midge larvae (Chironomus riparius)

Abiotic transformation of azaarenes in the environment has been analysed extensively, but metabolism is less well described. To further elucidate preliminary observations of interspecific differences in azaarene metabolism by aquatic organisms, phenanthridine biotransformation by midge larvae and carp was studied. In both experiments, 6(5H)-phenanthridinone (phenanthridone) was found as an important metabolite. The fish were clearly capable of metabolising phenanthridine, but in the midge experiment the metabolite was principally formed by bacteria growing on the food and not by the midges. Phenanthridone itself was further degraded to non-observed compounds in both experiments, due to bacteria and midges acting together in the midge experiment, and by carp in the fish experiment. Internal concentrations of phenanthridine and phenanthridone were non-detectable in the midge larvae, but concentrations of both compounds in carp organs suggested a major role of bile and liver. Since phenanthridone did not account for all phenanthridine loss, it was suggested that, apart from phenanthridone degradation, other metabolic pathways may play a role. This study clearly demonstrates the importance of interspecies differences in metabolism, which should not be neglected in risk assessment.