Biogeochemical fate of sediment-associated PAH: Effect of animal processing

Biotransformation and fate of polycyclic aromatic hydrocarbons (PAHs) in marine invertebrates and sediment have been studied. Invertebrates can accumulate and metabolize sediment-associated PAHs to polar and aqueous PAH-derived compounds. The objectives of this study are to identify metabolites of PAHs in species of deposit-feeding polychaetes and to examine biogeochemical fate and microbial degradation of the identified metabolites. Two metabolites, 1-hydroxypyrene and 1-hydroxypyrene glucuronide, were identified as the primary phase I and phase II metabolites of the tetra-cyclic PAH pyrene in Nereis diversicolor. Identification was performed using high pressure liquid chromatography with diode array and fluorescence detection (HPLC/DAD/F) and an ion-trap mass spectrometer for positive identification of 1-hydroxypyrene glucuronide. A fast synchronous fluorescence spectrometry (SFS) method was developed for detection of pyrene metabolites in polychaete tissue. A good correlation between 1-hydroxypyrene measured by SFS and HPLC/F was observed. 1-hydroxypyrene was identified as the single phase I metabolite in tissue of three additional polychaete species Nereis virens, Arenicola marina , and Capitella sp. I. A tentative aqueous metabolite identification scheme indicates that Nereid polychaetes predominantly make use of glucuronide conjugation whereas Capitella sp. I. and Arenicola marina appear to utilize sulfate and/or glucoside conjugation. Gut fluid from Nereis virens, Arenicola brasiliensis , and Arenicola marina and Parastichopus californicus could catalyze oxidative coupling of 1-hydroxypyrene in an apparent enzymatic reaction. Oxidative coupling will reduce subsequent bioavailability, toxicity, and transport of PAH metabolites in marine environments by formation of stable covalent bonds. An antioxidant enzyme, presumably a peroxidase, capable of oxidative coupling and with high oxyradical scavenging capacity was tentatively identified in gut fluid from Nereis virens . Nereis virens gut fluid could also catalyse formation of dityrosine, a marker of oxidative damage in proteins. Oxidative coupling of PAHs represents a new sink for organic contaminants in marine sediments and suggests a biological mechanism for the formation of aquatic humic material in general. Production of aqueous and polar metabolites by marine invertebrates does not enhance microbial degradation of pyrene either directly or in co-metabolic processes. The evidence suggests that enhanced degradation of larger PAHs in marine sediments is primarily due to bioturbation and irrigation processes of infauna.