Abstract

A radiotracer study was conducted to investigate bioaccumulation and subcellular partitioning of Cd and Zn in the different organs (gills, digestive glands and residue tissues) of the oyster (Crassostrea gigas) during 3-week exposure to water-borne source (with and without 20 μg Cd L-1 and 100 μg Zn L-1) and 3-week depuration in uncontaminated seawater. Cd and Zn in the whole soft tissue and individual organs continuously increased during 3-week exposure. Following 3-week exposure, metal concentrations in the gill tissue was 3.3-6 X Cd and 1.5-2.5 X Zn in two other organs while Cd and Zn in digestive glands was about twice the concentrations in residue tissues. The release rate of Zn (1.9% d-1) was a little faster than Cd (1.6% d-1) during 3-week depuration. Cd and Zn in the three organs was mostly in the detoxified form as metal rich granule, where > 60% in gills and residue tissues while > 30% in digestive glands. The Cd and Zn associated with metallothionein-like proteins was < 10% in the all organs. The potentially toxic and metabolically sensitive fractions (organelles and heat-sensitive protein) of Cd and Zn in the gill and residue tissues ranged 18-31%, while that in digestive glands was 47% for Cd and 36% for Zn. The trophically transferable fractions ranged 29-52% for Cd and 22-39% for Zn in the all organs. The results provide some clue to understand why oyster could accumulate unusually high concentrations of heavy metals and could habitat in metal contaminated environment.