Legacy‐micropollutant contamination levels in major river basins based on findings from the Rhône Sediment Observatory

Abstract

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 Rhône River sub‐basins (France) as a benchmark of other large river basins. Data on the Rhône River basin came from a unique 10‐year‐long monitoring program within the Rhône Sediment Observatory (OSR), and were compared to data gathered on 18 major worldwide river outlets. The Rhône 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.

Sources, Transport, and accumulation of Mercury in the northwestern Mediterranean margin sediments during the Industrial Era and influence of turbiditic events

“…In brief, the Hg concentrations measured in the sediments of the six cores collected in the Rhône prodelta exhibit a 1.6-2 % annual decrease during the last 50 years. They also show that the most recently deposited sediments (AD 2008(AD -2011 have a similar Hg concentration range (0.13-0.27 µg g -1 ) as the annual mean of Hg concentrations in the RR suspended particles collected near the river mouth (Arles), which consistently ranged from 0.1 to 0.2 µg g -1 for the period 2011-2016 AD (Poulier et al, 2019;Delile et al, 2022), in agreement with the Hg content of recent deposits at RR mouth (RDP: 0.16 ± 0.03 µg g -1 , Table 2).…”

Beyond just floodwater

“…In addition to hazards linked to landscape change, historically contaminated sediments remobilized during floods of various magnitude can raise significant issues for human health 9,10 . Although the supply of sediment and nutrients to floodplains is vital for their ecological functioning, erosion of contaminated sediments may lead to long-lasting problems through remobilization of pollutants such as polychlorinated biphenyls (PCBs), polychlorinated dibenzop-dioxins (PCDD's) and radionuclides 9,10 . Such contaminants may pose risks to human and animal health through a range of carcinogenic, neurotoxic, genotoxic and immunotoxic effects 10 .…”

“…Although the supply of sediment and nutrients to floodplains is vital for their ecological functioning, erosion of contaminated sediments may lead to long-lasting problems through remobilization of pollutants such as polychlorinated biphenyls (PCBs), polychlorinated dibenzop-dioxins (PCDD's) and radionuclides 9,10 . Such contaminants may pose risks to human and animal health through a range of carcinogenic, neurotoxic, genotoxic and immunotoxic effects 10 . For example, the levels of PCB's and PCDD's in beef cattle have been found to be greater in farms with flood-prone fields 11 , with contaminants sourced from legacy pollutants linked to previous industrialization and recent combustion activities.…”

“…Consequently, amplified flooding may generate substantial increases in the yield of riverine microplastics. Observational data and modelling 10 reveal the role of suspended sediment as a host for particulate-bound contaminants, the direct mobilization of particulate pollutants, and how contaminant yields relate to economic development and urbanization. There is thus a need to map the spatial distribution of contaminated legacy sediments and monitor their potential remobilization as affected by changing flood frequency and magnitude.…”