Comparative metabolism of nitroaromatic compounds in freshwater, brackish water and marine decapod crustaceans

Abstract

1. The metabolic pathways of p-nitroanisole, 4-nitro-m-cresol and methyl parathion in Malaysian prawns (Macrobrachium rosenbergii), ridgeback prawns (Sicyonia ingentis) and crayfish (Procambarus clarkii) were compared.

2. The Malaysian prawns and ridgeback prawns were shown to O-demethylate 29% and 11%, respectively, of an accumulated level of p-nitroanisole, while crayfish were able to O-demethylate 98% of the accumulated level of nitroanisole. 4-Nitro-m-cresol oxidation was not detected in either prawn species. In contrast, 5-hydroxy-2-nitrobenzaldehyde was the major metabolite formed from nitrocresol metabolism by crayfish.

3. Both prawn species readily dearylated methyl parathion to form p-nitrophenol and p-nitrophenyl conjugates. Crayfish displayed a similar trend in methyl parathion metabolism.

4. Nitroreduction was observed in the metabolism of 4-nitro-m-cresol by ridgeback prawns, which excreted 4-nitroso-m-cresol as a minor product. Reduction products were not observed in the metabolism of the three substrates by Malaysian prawns or crayfish.

5. Conjugation was overall the dominant detoxication pathway observed in the decapods. Malaysian prawns conjugated p-nitrophenol and 4-nitro-m-cresol to form the corresponding β-D-glucosides and sulphate monoesters. Ridgeback prawns formed β-D-glucosides in small quantities, preferring conjugation of p-nitrophenol and 4-nitro-m-cresol to form sulphates and unknown conjugates through a unique conjugation pathway. Crayfish conjugated the phenolic substrates to form exclusively the β-glucosides.

6. The unknown conjugates formed by ridgeback prawns had chromatographic properties similar to the corresponding β-D-glucosides but were refractory to the deconjugation by α- or β-glucosidase, β-galactosidase, aryl sulphatase and β-glucuronidase. Phenolic conjugation ability appeared to follow the order of ridgeback prawns > Malaysian prawns > crayfish.