Rapid assessments of metal bioavailability in marine sediments using coelomic fluid of sipunculan worms

A suitable test organism for assessing the bioavailability of sediment-bound metals should accumulate metals mainly from the sediment instead of other sources such as water. The deposit-feeding sipunculan worms, which indiscriminately ingest sediment particles and have a very low uptake rate of dissolved metals, appear to be such good candidates. The worms have additional advantage due to simple anatomy and are like little sacs full of liquid, that is, coelomic fluid, which can be easily collected for metal analysis after simple sample treatment. We measured the metal concentrations in a sipunculan worm, Phascolosoma arcuatum and in sediments collected from intertidal zones of Xiamen City, China. Significant correlations were found for the concentrations of chromium, nickel, copper, zinc, cadmium, and lead in sediments and their concentrations in both somatic tissue and coelomic fluid of the worms. Analyzing the metals in coelomic fluid led to similar results as the somatic-tissue metals for assessing the bioavailability of sediment-bound metals and the spatial pattern of sediment-bound metal contamination. Therefore, measuring coelomic-fluid metal concentrations can be used to provide a rapid assessment of metal bioavailability in marine sediments.