ABSTRACT: 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 ¹⁴CO₂ production) when worms were present. An additional experiment investigated the fate of ingested particle-bound ¹⁴C-DEHP and measured the loss of ingested ¹⁴C-DEHP into ¹⁴CO₂, DO¹⁴C and PO¹⁴C pools. Less than 1% of ¹⁴C consumed during a 1 h ingestion period was ultimately respired as ¹⁴CO₂, while 10% was excreted as DO¹⁴C and 89% as PO¹⁴C. Approximately 1% of ingested ¹⁴C was retained in worm tissue 20 h after ingestion. Assuming density-independent feeding rates, worm respiration could account for 4.5% to 19.1% of the total microcosm ¹⁴CO₂ production, suggesting that microbial respiration to ¹⁴CO₂ was the dominant process. Pre-exposure of worms to DEHP (10 µg g^-1 sediment dry wt) for 1 wk had no effect on the fate of ingested DEHP and distribution into the respective pools. Worms exerted a strong effect on ultimate DEHP degradation (¹⁴CO₂ production) but the effect was manifest at the lowest worm density and did not increase with increasing population size. The lack of an increased effect at greater population densities may be due to population density-dependent factors acting to decrease such important parameters as individual worm ventilation and feeding rates. A density-dependent decrease in feeding rate is supported by the observation that measured ¹⁴C body burdens were highest at lowest worm densities.

KEY WORDS: Bioturbation · Capitella sp. I. · Phthalate esters · Sediment · Microbial degradation · Metabolism

Published in MEPS Vol. 182 (1999) on June 11
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1999