The role of ingestion as a route of contaminant bioaccumulation in a deposit-feeding polychaete

A mass-balance bioaccumulation model was used to examine the bioaccumulation of benzo[a]pyrene (BaP) from ingested sediment by the deposit-feeding polychaete Abarenicola pacifica over a series of experiments employing nine different sediments. Through selective ingestion of fine-grained material, the worm was able to increase the BaP content of ingested sediment by 10-35% above that of the bulk material. During digestion, an average of 5-21% of the ingested BaP was absorbed from gut contents. The relative importance of ingestion as a route of BaP uptake was dependent on the time period of observation. Initial uptake of BaP was postulated to come from absorption of dissolved BaP across the body wall since, after short periods of exposure (<24 h), only 3-38% of observed BaP tissue concentrations could have been derived from ingested material. With time and with increased feeding activity, however, ingested sediment became the major source of BaP to the organism. After 72 h of exposure, 36-119% of the tissue BaP (mean = 77%) was estimated to have been derived from dietary absorption of ingested material, and with continued exposure the dietary route is likely to be as great or greater as the relative significance of the initial uptake from the dissolved phase diminishes. This work and other studies indicate that for many deposit feeders, ingested sediment can be the primary source for the bioaccumulation of hydrophobic toxicants.