Abstract
SUMMARY: The metallothionein levels and metal concentrations in whole body, digestive gland and gills of Crassostrea angulata were analyzed in field samples collected from the River Guadalquivir estuary over several years following a mining waste spill upstream. The subcellular distribution of metals was analyzed to determine the mechanisms involved in the detoxification process. The highest metallothionein levels were reported in the digestive gland shortly after the mining contamination event. In this organ, metals are stored preferentially in the non-cytosolic fraction when increased bioaccumulation takes place. In the cytosol of the gills, metals are associated with metallothionein, whereas in the digestive gland, the distribution of metals between metallothioneins and high molecular weight proteins is similar. Metallothionein variation cannot be explained by metals alone; other abiotic factors must be taken into account. In order to use metallothionein as a metal exposure biomarker in field studies, natural variability needs to be taken into account for the correct interpretation of results.
Highlights
Coastal ecosystems of estuaries are vulnerable because they are subjected to both diffusive and periodic contamination from agricultural, industrial and urban activities
Metallothionein-like proteins (MTLPs) are metalloproteins, which play a role in the homeostasis of the essential metals Zn and Cu and are involved in detoxification processes for non-essential trace metals such as Ag, Cd and Hg (Mason and Jenkins, 1995; Mouneyrac et al, 2001)
Fig. 2. – Seasonal evolution of MTLP concentrations in digestive gland and gills of oysters collected at both stations (Montijo, black columns; Piletas, white columns)
Summary
Coastal ecosystems of estuaries are vulnerable because they are subjected to both diffusive and periodic contamination from agricultural, industrial and urban activities. The Guadalquivir is the principal river in the SW of the Iberian Peninsula and its estuary is an important area in which many marine species are reared This river has been impacted by metal contamination as a result of agricultural and mining activities and. Numerous studies have shown that levels of MTPLs are influenced by several factors of an environmental (salinity, season, location in the intertidal zone, etc.) and biological (sexual maturity, weight, etc.) nature (Hamza-Chaffay et al, 1999; Mouneyrac et al, 1998) This is especially relevant in field studies where changes in the concentration of MTPLs due to metal contamination need to be distinguished from those related to natural variations
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