Abstract
Individual and whole-body soft tissues of bivalves, Cyclina sinensis and Crassostrea gigas, collected from tidal flats in Mikawa and Ise Bay, Aichi Prefecture, were analyzed for twelve metal concentrations (Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd, Sn, Hg, Pb) by ICP-MS, in order to clarify the degree of metal element enrichment into individual soft tissues from ambient environments. Among individual soft tissues of C. sinensis, mantle, gills and mid-gut gland show high metal concentrations compared to other parts and whole-body soft tissue. Three patterns of seasonal change of metal concentrations are found for individual soft tissues: 1) constant through spring to winter, 2) a decreasing trend from spring to winter, and 3) enrichment in summer. Mid-gut grand shows a relatively small deviation compared to other parts and can be a bio-indicator of metal pollution for Hg, Sn, Mn and As in seasonal scale. Whole-body soft tissue of C. sinensis shows smaller seasonal change of metal concentrations than those of individual soft tissues and can be a bio-indicator of longer-term environmental change of As and Pb in annual scale. Whole-body soft tissue of C. gigas shows extremely high concentrations of Cu, Zn and Cd and constant metal concentrations through summer to winter. Comparing individual soft tissues of C. sinensis collected from Shiokawa and Fujimae tidal flats and Okuda coast, samples from Fujimae tidal flat show high Mn concentration, those from Okuda coast show high Sn and low Mn concentrations and those from Fujimae tidal flat do high Pb concentration compared to the other two localities. This study suggests the possible use of soft tissues of C. sinensis as an environmental bio-indicator of metal pollution in tidal flats. In order to evaluate this possibility, we need to analyze specimens from other areas with various degrees of metal pollution and conduct culture experiment of C. sinensis under metal-doped conditions.
