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This study provides the first geographic and temporal large-scale analysis of Cu stable isotope compositions in indigenous oysters to biomonitor anthropogenic Cu inputs in aquatic systems. It includes oyster samples from French marine environments with distinct Cu-pollution levels and histories and extends over several decades of biomonitoring. Sample series composed of oysters from the same season and similar size/age intended to avoid biological biases. Oysters in macrotidal estuaries (Loire and Gironde, Western France) display fluctuating Cu concentrations without clear temporal trends, challenging to infer anthropogenic influence. Conversely, the time series of their Cu isotope ratios indicate a constant proportion of natural and anthropogenic Cu sources since the 1980s. In contrast, Cu isotope compositions in oysters from the progressively developing locales (urbanization and recreational boating) of Arcachon and Vilaine bays shift positively over time, along with increasing Cu concentrations. This finding suggests a gradual augmentation in the bioaccumulation of anthropogenic Cu over time. Thus, the time series of Cu isotope compositions in oysters is an unambiguous and robust approach to pinpoint anthropogenic Cu contamination. Furthermore, Cu concentrations combined with isotope compositions yield site-specific fingerprints allowing geographic discrimination among oysters. This two-dimensional Cu signature is promising as a tool for seafood traceability.

International audience; This study uses Cu and Zn isotopic compositions as proxies of sources and metal transfers in the planktonic food webs from the Mediterranean Sea. Plankton was collected in spring 2019 in the deep chlorophyll maximum (DCM) along a North-South transect including coastal and offshore zones (MERITE-HIPPOCAMPE campaign). δ65Cu and δ66Zn were determined on four planktonic size fractions from 60 to 2000 μm. Combined δ65Cu and δ66Zn with geochemical tracers (Ti, particulate organic phosphorus) showed that geogenic particles were ubiquitous with plankton assemblages. The δ15N ecological tracer showed that planktonic food web was enriched in heavy isotopes of Cu and Zn in the higher trophic levels. δ65Cu were correlated with picoplankton in the offshore zone, and with zooplankton in the southern coastal zone. Firmicutes bacteria were found correlated with δ66Zn in northern and southern coastal zones suggesting decomposition of particulate matter at the DCM. These findings suggest that biogeochemical process may impact Cu and Zn isotopy in the planktonic community.