Ecotoxicity evaluation of an amended soil contaminated with uranium and radium using sensitive plants

• Available soil concentrations of U and 226Ra represent high environmental risk.
• Soil contaminated with U and Ra was amended with bone meal and sheep manure.
• Amendments reduced U and Ra concentrations in soil available fraction and leachates.
• Urgeiriça soil toxicity bioassays using lettuce and maize
• No ecotoxicity exist in the Urgeiriça soil due to U and Ra contamination.

As a result of former uranium mining at Urgeiriça (central-northern Portugal), the studied adjacent agriculture soils (Fluvisols) had high total concentration of uranium (~ 660 mg/kg) and high radium-226 activity (~ 2310 Bq/kg). The environmental risk of these soils is also related to the high available concentrations (soluble + exchangeable fraction extracted with ammonium acetate) of uraniumtotal and radium-226, which represent 100% and 20% of their total concentrations, respectively. The objective of this work was to evaluate the effect of different amendments (sheep manure and bone meal) in the toxicity reduction from agricultural soils contaminated with uranium and radium, by bioassays using two sensitive plants (Lactuca sativa L. and Zea mays L.). Pot experiments (microcosm experiments), under controlled conditions, were undertaken during two months of incubation at 70% of the soil water-holding capacity. Bone meal at 40 Mg/ha, sheep manure at 70 Mg/ha, and two mixtures of bone meal and sheep manure (40 Mg/ha + 70 Mg/ha and 20 Mg/ha + 70 Mg/ha, respectively) were used as amendments. The amendments' application, independently of their type and concentration, reduced drastically the radionuclides concentrations in the soil available fraction and in the soil leachates. Bioassays using the two above plant species, in different matrices (filter test, soil test and hydroponic test), showed that the soil from Urgeiriça did not have any ecotoxic effect from the radionuclides.