Mobility of trace elements in soil-water systems near a decommissioned uranium mine: influence of environmental factors

Resumen

Oligoelements are trace mineral substances that occur in minimal amounts in living organisms and can be either beneficial or toxic depending on their concentration and bioavailability. Understanding their mobility in soil and water systems is essential for assessing environmental and human health risks, particularly in areas affected by mining activities. This study evaluated the mobility of five trace elements—arsenic (As), selenium (Se), aluminum (Al), uranium (U), and molybdenum (Mo)—in soils near a decommissioned uranium mine in Salamanca, Spain. The soil was fractionated into three particle size classes and subjected to varying moisture levels (50%, 75%, 100%) and incubation times (one, seven, 30 days). Soil solutions were extracted by centrifugation at different speeds, simulating suction pressures associated with water availability in the soil. Concentrations in soil solutions ranged from As: 0.5–12.3 µg/L, U: 0.2–8.7 µg/L, Al: 0.8–15.4 µg/L, Mo: 0.3–6.2 µg/L, Se: 0.1–2.8 µg/L, depending on environmental conditions. Moisture increases from 50% to 100% raised As and U concentrations by up to 60%, while particle size shifts from coarse sand to silt/clay altered As levels by over 70%. Boxplot analysis revealed outliers for As, Al, U, and Mo, indicating strong sensitivity to soil texture and water availability. ANOVA confirmed particle size as the most influential factor (p < 0.05), followed by moisture and suction pressure, whereas incubation time showed no significant effect. These findings highlight rapid equilibrium and element-specific responses, with implications for groundwater contamination risk in post-mining landscape.

Keywords: environmental contamination, soil mobility, trace elements, uranium mine, water resources.