Quantification of heavy metals and mercury-resistant bacteria in artisanal and small-scale gold mining sites, Maniema region, Democratic Republic of the Congo

The eastern region of the Democratic Republic of the Congo host large auriferous deposits that attracted artisanal and small-scale gold mining (ASGM) activities. In this study, soil and sediment samples from the Ulindi River in Maniema region, where Hg is used for ASGM activities, were analyzed for heavy metals contamination and Hg-resistance bacteria. Analysis by inductively coupled plasma-mass spectrometry showed high As concentrations in soil and sediment samples, ranging from 7.63 to 55.43 mg kg −1 . Except for As and Cr in soil samples, the concentrations of other metals (Ti, Co, Ni, Cu, Zn, As, Cd, Pb) were very low. The Hg concentrations determined with an advanced mercury analyzer, showed values ranging from 0.07 to 9.32 mg kg −1 . Hg-resistant bacteria in soil and sediment samples were counted using bacterial cultures, and the Hg-resistant strains were characterized through PCR amplification of 16S rDNA, restriction fragment length polymorphism, cloning, and sequencing. The densities of heterotrophic bacteria populations in soil and sediments ranged from 2.88 to 33.36 CFU 10 6 g −1 and from 0.10 to 14.26 CFU 10 6 g −1 , respectively. The isolated bacterial strains from different sites were capable to grow in medium containing up to 68.1 and 136.1 μg mL −1 of Hg 2+ in soil and sediment samples, respectively. Molecular analysis demonstrated the presence of bacterial strains from diverse groups which developed resistance to Hg: Bacillus sp. , Bacillus cereus, Lysinibacillus fusiformis , Paenibacillus alvei , Paenibacillus sp. , Arthrobacter sp. , Stenotrophomonas maltophilia , Acinetobacter sp. , Acinetobacter sp. , Aeromonas sp. , Pseudomonas sp. , Pseudomonas frederiksbergensis. The isolated strains of Hg-resistant bacteria will be the subject of further research to evaluate their potential in bioremediation of Hg-contaminated soil/sediments. Highlights Heavy Metal concentrations were assessed in soil/sediment samples collected along Ulindi River. ICP-MS and AAS indicated high concentrations of Cr, As and Hg. Hg-resistant bacteria in soil/sediment samples were assessed using PCR amplification, 16S rDNA, RFLP, cloning and sequencing.