MP9 Metals and Bioaccumulation
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(ZHO-1117-191751) Influences of contact time on the bioavailability of sediment-bound Cd and Zn.

Zhong , H¹, Wang, WX², ¹ Atmospheric, Marine and Coastal Environment (AMCE) Program, Hong Kong, China² Department of Biology, Hong Kong, China

ABSTRACT- We employed the radiotracer technique to assess the bioavailability of sediment-bound Cd and Zn by quantifying the metal assimilation efficiency in two deposit-feeding invertebrates: the sipunculan Sipunculus nudus and the soldier crab Mictyris longicarpus, and the extraction of metals from sediment by the gut juice of sipunculans. The sediments were spiked with the radiotracers for different durations (3 days, 3 months, 0.5 year, and 2 years) and the bioavailability and speciation (determined by the sequential extraction method) were tested. Sediment contact time longer than 3 months did not significantly influence the assimilation efficiency and speciation of Cd, but it affected the distribution of Zn in different geochemical phases. We found a positive correlation between the gut juice extraction and the assimilation efficiency (AE) for both sipunculans and crabs, while a relatively weaker correlation between normal seawater extraction and AE was documented. There was a positive relationship between the Cd in the exchangeable and the carbonate fractions and the AE, and a negative relationship between the Cd in the reducible phase and the AE. Similar trends were also found between the Cd speciation and the gut juice extraction. Overall, it is possible to combine gut juice extraction, assimilation efficiency measurement, and sequential extraction to predict the bioavailability of Cd in deposit-feeding invertebrates. It is important to consider the sediment-metal contact time when using spike technique to assess the bioavailability and toxicity of sediment-bound metals, especially for Zn.

Key words: Contact time, Bioavailability, Sediment, Metals