ARSENIC MOBILIZATION FROM SEDIMENTS IN BAKER CREEK OUTFLOW FROM GIANT MINE, YELLOWKNIFE, CANADA
Fifty years of gold mining at the Giant Mine in Yellowknife on the Great Slave Lake Canada, left a tremendous unresolved arsenic contamination problem in the area. Mine waste, such as arsenic trioxide, has been stored in underground vaults and the arsenic contaminated decant from surface tailing ponds flows through Baker Creek into Yellowknife Bay. Microorganisms, surviving in that environment, could play a significant role in redox transformations of arsenic species leading to their mobilization from sediments. The focus of our study was quantification of two target genes, arsC and aroA, that are responsible for arsenate reduction and arsenite oxidation, respectively, in sediment samples obtained from Baker Creek upstream of the mine, the mine discharge station, and downstream of the mine including the marshes at the creek exit into Yellowknife Bay.
For monitoring the capacity for arsenic mobilization by microbes we used quantitative real-time PCR. The amplifiable DNA for analysis of both genes was purified directly from 36 wet and dry soil samples by a process we developed to prevent heavy metal, cyanide and chloride inhibition of enzymes in qPCR analyses. For the arsC gene three sets of primers we designed earlier for different groups of bacteria were used. For the aroA gene two sets of published primers were used. These five primer sets allowed us to probe a total of ~50 bacterial strains for their arsenic redox capacity.
The Baker Creek control site samples above Giant mine showed 28x104 aroA gene copies per 1 ng of total DNA and up to 180x104 at the discharge point. Downstream we find from 500 to 158x104 copies per 1 ng total DNA. The arsC numbers detected were generally very low. This is an indication that the arsenate reduction previously observed in Baker Creek is primarily by fungi, not bacteria.
Several species of predominating bacteria were identified by 16S rDNA analysis in these highly toxic samples, e.g red colonies of Sporosarcina aquimarina, a bacterium which is related to psychrophilic Bacillus psychrophillus; a very slow growing Actinomycete Oerskovia paurometabola; and abundant Bacilli species such as B.cereus were detected.