Abstract
The bacterial, fungal and archaeal communities were characterized in 17 top soil organic and mineral layer samples and in top sediment samples of the Paukkajanvaara area, a former pilot-scale uranium mine, located in Eno, Eastern Finland, using amplicon sequencing and qPCR. Soil and sediment samples were in addition analyzed for radium (226Ra), sulfate (SO42−), nitrate (NO3−) and phosphate (PO43−) concentrations. New bacterial strains, representing Pseudomonas spp., were isolated from the mine and reference area and used in laboratory experiments on uptake and leaching of radium (Ra). The effect of these strains on the sulfate leaching from the soil samples was also tested in vitro. Between 6 × 106 and 5 × 108 copies g−1 DW (dry weight) of bacterial 16S rRNA genes, 5 × 105–1 × 108 copies g−1 DW archaeal 16S rRNA genes and 1 × 105–1 × 108 copies g−1 DW fungal 5.8S rRNA genes were detected in the samples. A total of 814, 54 and 167 bacterial, archaeal and fungal genera, respectively, were identified. Proteobacteria, Euryarchaeota and Mortiriella were the dominant bacterial, archaeal and fungal phyla, respectively. All tested Pseudomonas spp. strains isolates from Paukkajanvaara removed Ra from the solution, but the amount of removed Ra depended on incubation conditions (temperature, time and nutrient broth). The highest removal of Ra (5320 L/kg DW) was observed by the Pseudomonas sp. strain T5-6-I at 37 °C. All Pseudomonas spp. strains decreased the release of Ra from soil with an average of 23% while simultaneously increasing the concentration of SO42− in the solution by 11%. As Pseudomonas spp. were frequent in both the sequence data and the cultures, these bacteria may play an important role in the immobilization of Ra in the Paukkajanvaara mine area.
Highlights
Microorganisms have essential roles in soil biogeochemical cycles and microbiota readily respond to the changes occurring in the soil conditions due to toxic compound, including radionuclides, pollution (Marin et al, 2005; Tejada et al, 2008; Marcin et al, 2013; Li et al, 2013)
Despite the aftercare technologies used in the mining industry, increased radionuclide concentrations are found in many former mining areas, like in Paukkajanvaara (Finland), former pilot scale uranium (U) mine area sediments (Tuovinen et al, 2016)
The area is limited to the Iso Hiislampi pond in the North and to the small Fe dike stream flowing from the waste rock pile area, in the East
Summary
Microorganisms have essential roles in soil biogeochemical cycles and microbiota readily respond to the changes occurring in the soil conditions due to toxic compound, including radionuclides, pollution (Marin et al, 2005; Tejada et al, 2008; Marcin et al, 2013; Li et al, 2013). On the abandoned mine sites, the mobilization of radionuclides from mill tailings and other mine by-products may be amplified because of acidic runoffs (Acid Mine Drainage, AMD) (Robb, 1994; Mason, 2002), typical for sulfide ores in the presence of water and chemolithotrophic microorganisms. In addition to initial radionuclide concentrations and chemical forms of radionuclides in the ore, mining processes, such as the selection of the extraction procedure and enrichment methods, may contribute to the increased migration of radionuclides into the environment (Paschoa, 1998). Despite the aftercare technologies used in the mining industry, increased radionuclide concentrations are found in many former mining areas, like in Paukkajanvaara (Finland), former pilot scale uranium (U) mine area sediments (Tuovinen et al, 2016)
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