Importance of bioturbation and feeding by the polychaete Capitella sp I inthe degradation of di(2-ethylhexyl)phthalate (DEHP)

A microcosm study of the effect of Capitella sp. I (Polychaeta) population density on the mineralization of a pulse addition of the plasticizer DEHP ( di[2-ethylhexyl]phthalate) demonstrated a 2-fold increase in mineralization (cumulative (CO2)-C-14 production) when worms were present. An additional experiment investigated the fate of ingested particle-bound C-14-DEHP and m easured the loss of ingested C-14-DEHP into (CO2)-C-14, (DOC)-C-14 and (POC )-C-14 pools. Less than 1% of C-14 consumed during a 1 h ingestion period w as ultimately respired as (CO2)-C-14, while 10% was excreted as (DOC)-C-14 and 89% as (POC)-C-14. Approximately 1% of ingested C-14 was retained in wo rm tissue 20 h after ingestion. Assuming density-independent feeding rates, worm respiration could account for 4.5% to 19.1% of the total microcosm (C O2)-C-14 production, suggesting that microbial respiration to (CO2)-C-14 wa s the dominant process. Pre-exposure of worms to DEHP (10 mu g g(-1) sedime nt dry wt) for 1 wk had no effect on the fate of ingested DEHP and distribu tion into the respective pools. Worms exerted a strong effect on ultimate D EHP degradation ((CO2)-C-14 production) but the effect was manifest at the lowest worm density and did not increase with increasing population size. T he lack of an increased effect at greater population densities may be due t o population density-dependent factors acting to decrease such important pa rameters as individual worm ventilation and feeding rates. A density-depend ent decrease in feeding rate is supported by the observation that measured C-14 body burdens were highest at lowest worm densities.