Historical records, sources, and spatial trends of PCBs along the Rhône River (France)

• We reconstructed spatial and temporal trends in PCBs using eight sediment cores.
• PCB concentrations in sediments of the Rhône increase exponentially in a downstream direction.
• Concentrations of PCBs at the downstream sites remained elevated into the 2000s.
• Hierarchical clustering of PCB congeners identified differences within and between sites.
• PCBs in sediment downstream from Lyon are unlikely to decrease over the short term.

Despite bans on PCB use since 1975 (open systems) and 1987 (closed systems), concentrations of PCBs in riverine fish in France continue to exceed regulatory levels. We present historical records of PCB concentrations in sediment cores from eight sites on the Rhône River, from Lake Geneva to the Mediterranean Sea. Maximum PCB concentrations (sum of seven indicator PCBs) increase downstream, from 11.50 μg/kg at the most upstream site to 417.1 μg/kg at the most downstream site. At some sites peak concentrations occur in sediment deposited as recently as the 2000s. Hierarchical clustering (five clusters) identified differences in PCB congener profiles within and between sites. Exponential models fit to decadal time windows indicate that rapid reductions in concentrations during about 1990–2000 have slowed, and that it might be decades before target concentrations in sediment that correspond to regulatory thresholds in fish will be reached at some sites.

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