Distribution, behavior, and erosion of uranium in vineyard soils

Abstract

Phosphate fertilization contributes to an input of uranium (U) in agricultural soils. Although its accumulation and fate in agricultural soils have been previously studied, its colloidal transport and accumulation along slopes through erosion have been studied to a lesser extent in viticulture soils. To bridge this gap, the contents and potential mobility of U were investigated in vineyard model soils in the Rhineland-Palatinate region, Germany. In addition to elevated U contents, U was expected to associate with colloids and subject to erosion, thus accumulating on slope foots and in soils with fine structure, and reflecting a greater variability. Moreover, another expectation was the favorable erosion/mobility of U in areas with greater carbonate content. This was tested in three regional locations, at different slope positions and through soil horizon depths, with a total of 57 soil samples. The results show that U concentrations (0.48–1.26 ppm) were slightly higher than proximal non-agricultural soils (0.50 ppm), quite homogenous along slope positions, and slightly higher in topsoils. Assuming a homogeneous fertilization, the vertical translocation of U in soil was most probably higher than along the slope by erosion. In addition, carbonate content and soil texture correlated with U concentrations, whereas other parameters such as organic carbon and iron contents did not. The central role of carbonate and soil texture for the prediction of U content was confirmed using decision trees and elastic net, although their limited prediction power suggests that a larger sample size with a larger range of U content is required to improve the accuracy. Overall, we did not observe neither U nor colloids accumulating on slope foots, thus suggesting that soils are aggregate-stable. Lastly, we suggested considering further soil parameters (e.g., Ca2+, phosphorus, alkali metals) in future works to improve our modelling approach. Overall, our results suggest U is fortunately immobile in the studied locations.

Uranium Dissemination with Phosphate Fertilizers Globally: A Systematic Review with Focus on East Africa

“…The applications of P fertilizers have been reported to enhance U concentrations in agricultural soils on different continents around the world. For instance, in Asia [15][16][17][18][19][20][21][22][23][24][25][26], similar in Europe [16][17][18][19][20], in Australia [21,22], in America [23][24][25][26], and in Africa [27][28][29][30][31]. This study revealed that from all reviewed articles, the concentration of U from Minjingu P fertilizers from Tanzania ranged from 200 to 600 mg kg −1 , which is similar to what is found in open-pit commercial uranium mines in Namibia.…”

“…Their study was also complemented by work from Liesch et al [73], who reported that P fertilizers can be a major source of U in agricultural soils together with background concentrations. In addition to U buildup in agricultural soils, Campos et al [15] investigated the possibility of U mobility in vineyard soils in Germany's Rhineland-Palatinate region. The findings demonstrated that U in fertilized soils varied from 0.48 to 1.26 mg kg −1 , which was slightly higher than nearby non-agricultural soils (0.50 mg kg −1 ), very homogeneous along slope positions, and slightly higher in top soils.…”

“…U is mostly found as UO 2 2+ in oxidative environments, and as the pH increases, more of it sticks to negatively charged soil particles [15]. However, the creation of soluble and negatively charged compounds with substances like carbonate improves the mobility of U [132].…”

“…Sedimentary PR accounts for approximately 80% of the PR mined globally, while in igneous PR, the U concentrations are typically much lower (around 30 mg kg −1 ) [11][12][13][14]. The application of P fertilizers can disseminate considerable amounts of U on agricultural soils that may leach from the soil to ground and surface waters [11,15].…”

Uranium in phosphate rocks and mineral fertilizers applied to agricultural soils in East Africa

“…It is suspected though, and part of an active scientific debate, that prolonged application of phosphate rock and phosphate fertilizer can cause uranium accumulation on agricultural soils (Takeda et al 2006;Yamaguchi et al 2009;Schipper et al 2011;Bigalke et al 2017;Ratnikov et al 2020;Campos et al 2021). It is further speculated that a high concentration of uranium in agricultural soil could influence its uptake by plants through the root system in a similar way that other essential elements such as nitrogen, phosphorous, potassium, calcium, and magnesium and other supplemented micronutrients are absorbed (Velasco et al 2009;Shtangeeva 2010;Sheppard 2011;Baumann et al 2014;Harguindeguy et al 2019;Semioshkina and Voigt 2021).…”