Bioaccumulation of multi trace elements in spats of oysters Crassostrea gigas grown in the North Médoc salt marshes: a comparative study 13 years after

Supervisors: Magalie Baudrimont, Alexia Legeay (Univ. Bordeaux)
The Gironde Estuary, in south-west of France, is known for its poly-metallic contamination originating from waste-water discharges from the Umicore-Vieille Montagne industry, a former zinc ore treatment plant. This metal contamination was also observed in the North Médoc salt marshes which are fed by the estuary water at high tides. Oysters Crassostrea gigas cultivated in these marshes reflected the water contamination in metals, and have been unauthorized to human consumption since 1995. Our study focused on the evolution of 11 metals (Ag, As, Cd, Co, Cr, Cu, Mn, Ni, V, Pb, and Zn) in the juvenile C. gigas transplanted from a hatchery of the Ile de Ré on a 12 months period in two salt marshes of the North Médoc, FACEM and Eau Médoc. Moreover, the comparison of four metals’ concentration (Cd, Hg, Cu, and Zn) in the juvenile oysters over a 13 years period was conducted. The analyses of all elements, except mercury, were conducted by Inductively Coupled Plasma Optical Spectrometry (ICP-OES; Agilent Technologies, 700 Series ICP-OES), and Hg measurements were carried out using an Advanced Mercury Analyzer (LECO AMA-254, Altec, Prague, Czech Republic). The results showed that the juvenile oysters were contaminated by all the elements we studied at the time of the transplantation (T0). At this time, Cd concentration was even above the consumption safety level of 5 mg/kg (dry weight) in oysters. The results also showed some variations in the evolution of the metals’ concentration in the juvenile oysters depending on the site of the transplantation. Indeed, an overall decrease of the elements was observed in Eau Médoc, while four elements (Ag, Cu, Mn, and Zn) increased in FACEM. The comparison at 13 years showed a decrease of all four elements compared over time. The most significant decrease was observed in the Cd measurements with an 83% decrease in Eau Médoc between February 2001 and February 2013. The decreasing metals’ concentration in the juvenile oysters, and particularly the low Cd level in them, could induce the possibility to grow juvenile C. gigas in the North Médoc salt marshes.