Benz(a)anthracene in benthic marine environments : bioavailability, metabolism, and physiological effects on the polychaete Neries virens

Abstract

The fate of [14C- 121 benz(a)anthracene (BA) was followed in benthic microcosm experiments in the presence and absence of the polychaete Nereis virens. In concert with chemical analysis of BA and its metabolites in all components of the system, physiological and biochemical effects of exposure on Nereis were investigated. BA was introduced in three ways: already sorbed to the entire sediment reservoir; directly into the water column; or incorporated into a gelatin-based diet. Experiments ran from 4 to 25 days. Activity of BA and BA metabolic products was followed in sediments, worm tissue, and in the water column. 14CO2 activity in the water column was also measured. Growth, oxygen consumption, ammonia excretion, adenylate nucleotide pools, and mixed function oxygenase activity of the worms were also monitored. The presence of worms and the mode of introduction had significant effects on the fate of BA in this system. In experiments with sediments uniformly labeled with BA, worms increased flux of BA from the sediment, and after nine days, their presence lead to increased rates of microbial mineralization of BA to CO2. In experiments where BA was added directly to the water column, worms mixed BA into the sediment, but had no net effect on removal of BA in the sediment to the water column. BA added to the water column and deposited at the sediment-water interface was more available for uptake by worms, microbial mineralization to CO2, and removal to the water column than BA sorbed to bulk sediments. Regardless of mode of introduction, worms were able to accumulate BA. However, bioavailability of BA previously sorbed to sediments was less than BA added to the water column and allowed to settle at the sediment-water interface. Of the three modes of introduction studied, BA ingested in a geletin-based diet was most available for accumulation by Nereis. Length of exposure and mode of introduction had significant effects on accumulation and metabolism of BA by Nereis. Of total activity accumulated, the proportion remaining as parent compound decreased with time, and was inversely correlated with relative efficiency for accumulation. The relative amounts of different metabolic products were also affected by time and mode of exposure. In all experiments, most activity recovered from worms was present as metabolic products with only 2 to 23% remaining as parent compound. A significant portion (from 33 to 51%) of total activity was not extractable, indicating incorportation into macromolecular components. Physiological and biochemical effects of BA exposure on Nereis were minimal. Subtle alterations in adenylate nucleotide pools were observed after 6 days in experiments with either sediment-sorbed BA or BA added directly to the water column. After 25 days of exposure to sediment-sorbed BA, worms showed increased rates of oxygen consumption and ammonia excretion. No significant changes in growth or activity of the mixed function oxygenase system were observed. These experiments demonstrated: (1) that the presence of a large burrowing polychaete can have significant effects on the fate of PAH in the benthos; (2) that source can have significant effects on both fate and metabolism of PAH in the benthos; (3) that Nereis virens is capable of accumulating and metabolizing BA from the sediment, water column, or ingested food; and (4) that incorporation into cellular macromolecules is a major fate of accumulated BA.