Bioavailability and microbial adaptation to elevated levels of uranium in an acid, organic topsoil forming on an old mine spoil.
An old mine spoil at a 19th-century mining site with considerable residues of uranium (400-800 mg U/kg) was investigated with respect to U concentrations in soil and plants and tolerance to U in the soil microbial community in order to describe the bioavailability of U. Measurements of soil fractions representing water-soluble U, easily exchangeable U, and U bound to humified organic matter showed that all fractions contained elevated concentrations of U. Plant U concentrations were only 10 times higher at the mine spoil site compared to the reference site (3 mg U/kg vs 0.3 mg U/kg), while the most easily available soil fractions contained 0.18 to 0.86 mg U/kg soil at the mine spoil. An ecotoxicity bioassay using incorporation of [3H]thymidine into the indigenous microbial communities of the two soils in the presence of increasing U concentrations showed that microorganisms at the mining site were sensitive to U but also that they had acquired a substantial tolerance toward U (EC50, the effective concentration reducing activity by 50% of UO2-citrate was approximately 120 microM as compared to 30 microM in the reference soil). In the assay, more than 40% of the microbial activity was maintained in the presence of 1 mM UO2-citrate versus 3% in the reference soil. We conclude that U-enriched mining waste can contain sufficiently elevated concentrations of bioavailable U to affect indigenous microorganisms and that bioavailable U imposes a selection pressure that favors the development of a highly uranium-tolerant microbial community, while plant uptake of U remains low.
Joner
Erik Jautris
EJ
BIOFORSK, Soil and Environment Division, Fredrik Dahls vei 20, N-1432 Aas, Norway. erik.joner@bioforsk.no
Munier-Lamy
Colette
C
Gouget
Barbara
B
D000143:Acids / Q000737:chemistry*; D001673:Biodegradation, Environmental; D001681:Biological Assay; D001682:Biological Availability; D005308:Fertilizers; D007220:Industrial Waste; D019216:Metals, Heavy / Q000032:analysis / Q000378:metabolism* / Q000633:toxicity; D008906:Mining; D012990:Soil Pollutants, Radioactive / Q000032:analysis / Q000378:metabolism* / Q000633:toxicity; D013936:Thymidine / Q000378:metabolism; D018675:Toxicity Tests; D014501:Uranium / Q000032:analysis / Q000378:metabolism* / Q000633:toxicity; D014875:Water Pollutants, Radioactive / Q000032:analysis / Q000378:metabolism* / Q000633:toxicity
D000143:Acids; D005308:Fertilizers; D007220:Industrial Waste; D019216:Metals, Heavy; D012990:Soil Pollutants, Radioactive; D014875:Water Pollutants, Radioactive; D014501:Uranium; D013936:Thymidine