Changes in metallothionein concentrations in response to variation in natural factors (salinity, sex, weight) and metal contamination in crabs from ametal-rich estuary

Intermoult male and female crabs Pachygrapsus marmoratus and Carcinus maena s were sampled from three sites between the mouth and 25 km upstream in the Gironde, the most Cd-contaminated estuary in France, in order to study the relative importance of natural factors (salinity, sex, weight) and accumul ated metal concentrations on metallothionein (MT) concentrations. In the tw o species studied, higher metal, total protein and MT concentrations were o bserved in the hepatopancreas than in the gills. In P. marmoratus, MT conce ntrations were mainly related to changes in the natural factors even if MT and Zn concentrations were positively correlated in the hepatopancreas wher eas in C. maenas, the main relationships were with accumulated metal levels . In the case of the natural factors, the most important ones were weight i n gills of both crab species, and salinity changes in both hepatopancreas a nd gills of P. marmoratus. Cd and Cu concentrations in both organs of the t wo species were inversely related to salinity. The same observation was fou nd for Zn concentrations in C. maenas but not in P. marmoratus. In the hepa topancreas of both species, the highest total protein concentrations were f ound in crabs from the site with the highest salinity, whereas there were n o such differences in the gills. It seems that changes in MT concentrations are linked more to changes in general protein metabolism than to changes i n metal accumulation. Thus it was important to examine the storage of metal s in other tissue compartments, particularly the insoluble fraction which i ncludes mineral granules which is known to also contribute to trace metal d etoxification in invertebrates. In the gills of the crabs, Zn was present m ainly in the insoluble fraction, whereas Cd was nearly equally distributed between soluble and insoluble fractions. In contrast, Cu in the gills and a ll three metals in the hepatopancreas of both species were mainly cytosolic , but. this does not necessarily imply a predominant role for MT since the cytosolic fraction also includes other macramolecules which may be the targ et binding site for accumulated trace metals. (C) 2000 Elsevier Science B.V . All rights reserved.