Past and emerging platinum contamination of sediments and oysters from the Gironde fluvial-estuarine system

Supervisor: Jörg Schäfer (Univ. Bordeaux)
This work presents the first historical record of platinum (Pt) content, sources, and bioaccumulation in sediments and oysters from the Gironde fluvial-estuarine system. Reservoir sediments were sampled in the Lot River, a main river in the Gironde watershed, upstream and downstream a former metallurgic industry. Upstream sediments have provided a first regional geochemical background Pt concentration corresponding to ~ 0.15 ng.g-1, i.e. a typical Thorium (Th)-normalised value of Pt/Th ~ 0.016. The downstream sediments displayed average Pt concentrations of ~ 0.75 ± 0.34 ng.g-1 (n=9; i.e. Thorium (Th)-normalised concentrations of ~ 0.05 ± 0.02). This corresponds to Enrichment Factors of up to 6 compared to background values in the years of full metallurgic activities (1952-1986), indicating moderately severe contamination by Pt. Platinum concentrations have been measured for the first time in wild oysters from the Gironde Estuary showing average levels of ~ 0.35 ± 0.08 ng.g-1 (n=20). Temporal variations of Pt concentrations in both sediments (from 1952 to 2001) and biological samples (from 1981 to 2013) have been attributed respectively to a former point source originating from metal industry in the Lot watershed and to recent diffuse sources due to the exponential increase in the use of Pt-based catalytic converters in cars. Platinum distribution in different tissues of wild oysters (organotropism) suggests direct uptake pathway as the major contamination pathway. The first estimated bioconcentration factor (BCF) of Pt for wild oysters corresponds to ~ 103 which is clearly lower than those of other trace metals (e.g. cadmium and silver) in the same system but still of concern considering its potential toxicity. Further work is necessary to assess the Pt behaviour in the marine food chain and more data on Pt in other systems is needed.

Keywords: platinum, sediments, wild oysters, sources, enrichment, bioaccumulation