Effects of natural factors (salinity and body weight) on cadmium, copper, zinc and metallothionein-like protein levels in resident populations of oysters Crassostrea gigas from a polluted estuary

Abstract

The Gironde estuary has been shown to be the most Cd-contaminated area In France. Oysters Crassostrea gigas of different size classes were sampled from 3 sites between the mouth and 25 km upstream, to study the relative importance of natural and contamination factors on metal accumulation and metallothionein-like protein (MTLP) induction. The highest metal and MTLP concentrations were observed in the digestive gland. In all organs, the 3 metals were mainly cytosolic. An inverse relationship was generally observed between weight of soft tissues and metals or MTLP concentrations in the whole soft tissues, whereas the influence of weight on metal distribution among cytosolic and insoluble fractions was small. When oysters with similar weight of soft tissues were considered, no influence of salinity at different sites was found for Cu and Zn whereas the lowest soluble and insoluble Cd concentrations were observed at the mouth of the river. Salinity did not influence Cu and Zn distribution among the cytosolic or insoluble fractions whereas cytosolic Cd in gills and digestive gland (%) was higher at the mouth of the estuary than upstream. MTLP and metal concentrations were generally positively correlated except at those sites where metal concentrations were lowest. However when multiple regression analyses were performed, weight appeared also as a major or an important factor to explain vanations of MTLP levels, the prevalence of this natural factor versus contan~ination factors being different at ddferent sites. KEY WORDS. Oyster. Heavy metals. Metallothionein

Comparative radiotracer study of cadmium uptake, storage, detoxification and depuration in the oyster Crassostrea gigas: potential adaptive mechanisms

“…The other fraction with a notable amount of Cd was the 'heavy' fraction, which contained the nuclei, heavy lysosomes and cellular debris. This latter fraction is comparable to the 'insoluble' fraction obtained by other authors using different methods (Mouneyrac et al 1998, Geffard et al 2001). In the BB oysters, the heaviest fractions -nuclei, heavy lysosomes and cellular debris or lysosomes and mitochondria -contained up to 47% of the total Cd.…”

Is the digestive gland of Mytilus galloprovincialis a tissue of choice for estimating cadmium exposure by means of metallothioneins?

“…Lower concentrations of trace metals in the gonadic tissues (George and Coombs, 1977;La Touche and Mix 1982;Lobel and Wright, 1982) cause "biological dilution" of trace metal concentrations in the digestive gland. As already stated by Bordin et al (1997), Amiard-Triquet et al (1998) and Mouneyrac et al (1998;2000), variation of soft tissue mass also influences MT concentration in bivalves. The "biological dilution" is, thus, a valid explanation for the MT concentration in the digestive gland, too.…”

Growth rate as a factor confounding the use of the dogwhelk Nucella lapillus as biomonitor of heavy metal contamination

“…Therefore it has been proposed that measurement of MT may provide information about potential health hazards of metals in exposed organisms (Benson et al 1990, Bebianno & Machado 1997, although MT may be influenced by various biotic and abiotic factors (Mouneyrac et al 1998, Leung & Furness 1999a, Leung et al 2000. The MT concentration observed in the Leiblein gland of Nucella lapillus from Largs was 5 times greater than that of the other 2 populations.…”