On the possibility to produce again oysters Crassostrea gigas in the North Médoc salt marshes (Gironde estuary, Southwestern France): A comparison study of metals bioaccumulation in spats 13 years after

• Investigation of polymetallic accumulation in spat oysters in Gironde salt marshes
• The majority of metals accumulated in oysters decreased in salt marches.
• Cd concentrations in oysters decreased for 80% in 13 years in salt marshes.
• An opportunity to produce again oysters in the Gironde estuary is evidenced.

The Gironde Estuary is known for its historic poly-metallic contamination, leading to levels of Cd in oysters Crassostrea gigas above the human consumption limit. However, since 25 years, Cd concentrations progressively decreased in the estuary and the question is raised if the same evolution occurred in the North Médoc salt marshes. In this aim, we analyzed 12 metals in juveniles of oysters transplanted from a hatchery on a 12 months period in 2 salt marshes. Moreover, the comparison of four metals already measured 13 years ago was conducted.The major results showed an overall decrease of the metals in the salt marshes, with a significant decrease of Cd reaching 80% compared to the Gironde estuary where it occurs for only 50% between 2001 and 2014. The concentrations in 2014 remained below the human consumption threshold, suggesting the possibility to produce again oysters in the salt marshes.

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