– A step forward in development of selenium insolubilization technology that prevents environmental outflow of the pollutant selenium –
Researchers) AOYAGI Tomo, Researcher, and HORI Tomoyuki, Senior Researcher, Environmental Ecophysiology Research Group, Environmental Management Research Institute
- Discovery of microorganisms responsible for insolubilization (reduction) of selenium in rock mass produced by tunnel excavation etc.
- Provision of nutrients to selenium reducing microorganisms promotes selenium insolubilization.
- Expected to lead to development of a new environment purification technology with low environmental impact that prevents the elution of selenium from rock mass
Mechanism of selenium insolubilization by microorganisms in rock mass (excavation tailings) produced by tunnel excavation work
A part of the large quantities of rock mass (excavation tailings) produced by tunnel construction work such as for expressways and railways contains naturally originated heavy metals and metalloids such as selenium, arsenic, boron, palladium, cadmium, copper, and zinc. Ions of these heavy metals and metalloids may dissolve in groundwater etc., so measures such as insolubilization are needed. Hexavalent selenium in particular is difficult to reduce by chemical treatment, which makes insolubilization a challenge. However, microorganisms that reduce hexavalent selenium are widely present in natural environments such as soil and sediments, so there are expectations for bioremediation using these microorganisms. That said, it is not even clear whether such microorganisms are present in excavation tailings, and there are no known studies to date of insolubilization of the selenium in excavation tailings by microorganisms.
In collaboration with Taiheiyo Cement Corporation, the researchers discovered that living microorganisms are present in rock mass produced by tunnel construction work etc., and that those microorganisms insolubilize selenium, which is a harmful and difficult-to-treat heavy metalloid naturally contained in rock mass.
The metalloid selenium contained in rock mass produced by excavation may be ionized by rainwater etc. and dissolve out in concentrations that exceed environmental standards, thereby contaminating groundwater etc. Therefore, development of environmentally friendly bioremediation is demanded to prevent contamination. The researchers verified the presence of selenium reducing microorganisms surviving in rock mass. Furthermore, they also found for the first time that those microorganisms can be activated by providing lactic acid as a nutrient source, enabling efficient insolubilization of selenium. These results are expected to lead to the development of a new selenium insolubilization technology with low environmental impact using microorganisms, as well as prevention of groundwater contamination.