Legacy-micropollutant contamination levels in major river basins based on findings from the Rhone Sediment Observatory

For more than half a century, chemical contamination has progressively spread to all the large river basins. Large river outlets integrate multiple anthropogenic pressures in watersheds, making them the largest source of sediment-bound contaminants to continental shelf areas. However, comparing particulate micropollutant contaminations between the large river basins is a challenging task, especially due to the scarcity of long-term river monitoring programs. Here we address this issue, with a focus on legacy particulate micropollutants (polychlorobiphenyls [PCBi], polycyclic aromatic hydrocarbons [PAHs] and trace metal elements [TME]) yields. For this purpose, we employed a bottom-up multiscale approach to chemical contamination in river basins that takes micropollutant yields measured in the Rhone River sub-basins (France) as a benchmark of other large river basins. Data on the Rhone River basin came from a unique 10-year-long monitoring program within the Rhone Sediment Observatory (OSR), and were compared to data gathered on 18 major worldwide river outlets. The Rhone River basin is far cleaner now than a few decades ago, likely due to environmental regulations. At a wider spatial scale, our results depict an overall contamination gradient splitting the most heavily contaminated river basins, located in developing and industrializing low-to-middle-income countries, from the least contaminated rivers located in developed high-income countries. We argue that chemical contamination levels of large river basins depend on their stage of economic development.

Automated summary

This article discusses the spread and impact of chemical contamination in large river basins, and explores the comparison of particulate micropollutants between different river basins. The research findings show that the chemical contamination levels of large river basins are related to their stage of economic development.