The potential use of metallothionein in the clam Ruditapes decussatus as abiomarker of in situ metal exposure

This work aimed to validate the relationship between metallothioneins (MTs) and metals (Cd, Cu and Zn) in field conditions. Specimens of the marine bi valve Ruditapes decussatus (Linne, 1758) from Gargour were transferred in t wo sites: Gargour and Sidi Mansour, both situated along the south-eastern c oast of Tunisia. The bivalves were removed from pairs of cages at day 0 (da te of transplantation), day 62 and day 132. Metals (Cd, Cu and Zn) and MTs were determined in the subcellular fractions of the digestive gland. In Gar gour, metal and MT levels increased significantly after 62 days of transpla ntation. However, they showed modest and non-significant variations in Sidi Mansour. Zn was mainly associated with the insoluble fraction, whereas Cd and Cu percentages in the soluble and the insoluble fractions were equivale nt. Simple correlation analysis showed a positive and significant relations hip between MTs and each metal. If all metals were taken together, multiple correlations showed that MTs were significantly correlated with Cd and Zn, with an important coefficient for Cd, but no significant relationship was observed for Cu. Gel filtration chromatography showed that in the heat stab le fraction, the only cytosolic -SH rich compounds have an apparent low mol ecular mass (about 15 kDa), which could correspond to metallothioneins. In the digestive gland of R. decussatus MTs responded to moderate increases of metal contamination, without interference with other factors, and could be a promising biochemical indicator of metal exposure. (C) 2000 Elsevier Sci ence Inc. All rights reserved.