An evidence of chemically and physically mediated migration of 238U and its daughter isotopes in the vicinity of a former uranium mine

An integrated approach combining soil profile, records and tree ring analysis to identify the origin of environmental contamination in a former uranium mine (Rophin, France)

“…Two hypothesis can be formulated: i) a slow dissolution of U particles contained in the WSL layers over decades, followed by an accumulation in the topsoil layer associated with a seasonal change of water level in the wetland; or ii) a regular inflow over the decades of U dissolved by water from the Gourgeat creek altered by mine water effluent even after ICPE site rehabilitations. Such an accumulation mechanism in the wetland has been detected and similarly described for other sites affected by U mining (Bister et al, 2015;Mangeret et al, 2018). At the same time, the fact that U concentrations quickly decrease below the WSL in cores D1 and D2 suggests that the mobility of the U deposited by diffusion has been rather low under the conditions prevailing during the last 50 years.…”

“…In the vicinity of U mines, wetlands prove to be particular natural zones since they act as physical particle and metal traps. Numerous studies have indeed found highly increased U concentrations in wetlands, extending into the several thousand mg.kg -1 ; this observation has been recorded in areas affected by mining activities (Li et al, 2014;Mangeret et al, 2018;Schöner et al, 2009;Wang et al, 2014) as well as areas with granitic bedrock subjected to naturally elevated U concentrations in groundwater (Mikutta et al, 2016;Owen and Otton, 1995;Regenspurg et al, 2010;Zielinski et al, 1986). The accumulation of U is explained by complexation with organic matter (OM) present at high concentrations in wetlands (Bordelet et al, 2018) and/or by reduction of U(VI) to scarcely soluble U(IV) due to strongly reducing conditions related to the bacterial degradation of plant material (Alessi et al, 2012;Cumberland et al, 2016;Lovley et al, 1991;Nakashima et al, 1984;Newsome et al, 2015).…”

“…In addition to the environmental monitoring of storage sites, it is also critical to consider the environment potentially contaminated near the mines. This consideration becomes even more important since the land may now be privately owned (Mangeret et al, 2018).…”

Climate-driven fluxes of organic-bound uranium to an alpine lake over the Holocene

“…Radio-elements (238U (from 234Th), 230Th, 228Th, 228Ra, 226Ra, 210Pb, 137Cs, 40K) were measured on core NEG18-05 by gamma spectrometry at IRSN using a HP Ge detector (EGPC 20, Intertech) according to the protocol described in Mangeret et al (2018) and a well-type highpurity/low-noise Ge ORTEC GWL Series detector following Reyss et al (19 9 5). 238U activities measured by gamma spectrometry (in Bq/kg) were converted to U concentrations (in pg/g) using the 238U mass activity (12.44 kBq/g).…”

Experimental redox transformations of uranium phosphate minerals and mononuclear species in a contaminated wetland

“…Uranium mining operations and legacies have been shown to be responsible for local increases of U contaminations in surrounding surface environments. For instance, U concentrations exceeding the geochemical background were found in aquifer sediments [4], lacustrine sediments [5], soils [6] and wetlands [7][8][9][10] in the vicinity of former U mining sites.…”