Anthropogenic legacy of potassium-40 in French large rivers reconstructed from sediment cores.

Environmental imprint of inorganic fertilizer uses was assessed over the last hundred years at the downstream part of large French rivers (Loire, Moselle, Rhine, Rhone, Meuse and Seine rivers) based on Potassium-40 (K) activity concentration data sets acquired from soil monitoring (1980-2022) and from sediment coes collected from 2020 to 2022 to reconstruct the temporal trajectories of K activity concentrations since the beginning of the last century. Cultivated soils were significantly enriched in K compared to non-cultivated ones in the 1980s and 1990s when they turned back to the contents of non-cultivated soils during the following decades. In riverine sediments, all the rivers displayed close K temporal trajectories with peaking K contents in fine grain size sediments in the 1980s.

Temporal trajectories of artificial radiocaesium Cs in French rivers over the nuclear era reconstructed from sediment cores.

Cs is a long-lived man-made radionuclide introduced in the environment worldwide at the early beginning of the nuclear Era during atmospheric nuclear testing's followed by the civil use of nuclear energy. Atmospheric fallout deposition of this major artificial radionuclide was reconstructed at the scale of French large river basins since 1945, and trajectories in French nuclearized rivers were established using sediment coring. Our results show that Cs contents in sediments of the studied rivers display a large spatial and temporal variability in response to the various anthropogenic pressures exerted on their catchment.

Identification of the origin of radiocesium released into the environment in areas remote from nuclear accident and military test sites using the Cs/Cs isotopic signature.

The isotopic signature of radionuclides provides a powerful tool for discriminating radioactive contamination sources and estimating their respective contributions in the environment. In this context, the Cs/Cs ratio has been tested as a very promising isotopic ratio that had not been explored yet in many countries around the world including France. To quantify the levels of radioactivity found in the environment, a new method combining a thorough radiochemical treatment of the sample and an efficient measurement by ICP-MS/MS has been recently developed.

Depositional environments and historical contamination as a framework to reconstruct fluvial sedimentary evolution.

In this study, we explore the variability of sedimentation conditions (e.g., grain-size, accumulation rate, contamination) according to fluvial depositional environments.

Behaviour of radiocaesium in coastal rivers of the Fukushima Prefecture (Japan) during conditions of low flow and low turbidity--Insight on the possible role of small particles and detrital organic compounds.

To investigate riverine transfers from contaminated soils of the Fukushima Prefecture in Japan to the marine environment, suspended sediments, filtered water, sediments and detrital organic macro debris deposited onto river beds were collected in November 2013 within small coastal rivers during conditions of low flow rates and low turbidity. River waters were directly filtered on the field and high efficiency well-type Ge detectors were used to analyse radiocaesium concentrations in very small quantities of suspended particles and filtered water (a few mg to a few g). For such base-flow conditions, our results show that the watersheds studied present similar hydro-sedimentary behaviours at their outlets and that the exports of dissolved and particulate radiocaesium are comparable.