Factors that influence the absorption of uranium by indigenous plants on the spoil tip of an abandoned mine in western Spain

Highlights: • Vesicular arbuscular mycorrhizae reduce the passage of U into the food chain. • The concentration of U in plants was correlated with annual rainfall. • U is a non-essential element but could have a hormesis effect. • The size of the plant leaves was directly proportional to the quantity of U absorbed by the plant. The purpose of this work was to study the factors affecting the absorption of U by plants growing on the spoil tip of an abandoned mine in western Spain. The plant species were selected based on how palatable they were to livestock and were sampled for four consecutive years during which, we also recorded rainfall data. The factors related to the plants studied were the leaf size and the percentage and characteristics of the arbuscular mycorrhizae (AM) fungi present in their roots. Our results showed a correlation between the annual rainfall and the U concentration in the plants. The percentage of mycorrhization and AM vesicles is a predominant factor in the uptake of U by plants. Spergularia rubra (L.) J.Presl & C.Presl, which is resistant to mycorrhization, contained higher U concentrations relative to the plants that grew with AM mycorrhization. The absorption curves of the different plants studied indicated that these plants were tolerant to ²³⁸U from 875 Bq kg⁻¹ (70 mg kg⁻¹), with a hormesis effect below that concentration. The annual U removal was 0.068%, suggesting that AM are responsible for limiting the incorporation of U into the food chain, favouring its retention in the soil and preventing its dispersion.