THE CONTRIBUTION OF METAL SHELL-WEIGHT INDEX IN TARGET-TISSUES TO METAL BODY BURDEN IN SENTINEL MARINE MOLLUSKS .2. MYTILUS-GALLOPROVINCIALIS/

The tissue distribution of Zn in mussels collected from a Zn-polluted site and the changes in the pattern of distribution for Zn and Cu in r esponse to experimental exposures to Cu, Zn and Cd, as well as the tis sue distribution of Cd have been studied. The organs of mussels were a ccurately separated avoiding mixtures except the kidney area that was included within the remainder tissues. Mussels exposed to intermediate dose (ID)-Cd showed the highest Cd burden first in gills and then mor e or less equally distributed between the various tissues examined wit h a dominance of the digestive gland. Mussels exposed to high dose (HD )-Cd, showed Cd equally distributed through all the organs at both exp osure times. Below 0.8 mu g Cd/l seawater, the gills of Zn-polluted mu ssels were able to either protect against Cd entry or mobilise uptaken Cd towards other tissues. On the other hand, Zn- and Cu-burdens did n ot rise in gill tissue, although in depurating mussels Zn-levels were higher than in any other exposure group. Similar conclusions were obta ined for the digestive gland. However, the accumulative capacity of th e digestive gland tissue for Cd was not exhausted and Cu burdens were depressed on exposure to Cd. Interactions between metals in the variou s organs studied could be explained by redistribution of haemocytes or brown cells and by enhanced release of metal-bearing digestive lysoso mes in response to metal exposure. It is suggested that (a) the patter n of metal accumulation and tissue distribution as well as a part of t he interactions between Cu, Zn and Cd cannot be explained solely by th e availability of metallothioneins in specific organs; and (b) the spe cific cell type in which these ligands occur as well as the relative a bundance and distribution of these cells are relevant factors controll ing metal burdens in organs of mussels. Therefore, in addition to the chemical and the biochemical approaches, investigations on tissue sect ions are required to better understand these phenomena. Meanwhile, the digestive gland of mussels could be used as the target organ to monit or metal pollution, including essential and non-essential metals, on t he basis of metal/shell-weight indices. (C) 1997 Elsevier Science B.V.