Impact of effective microorganisms on the transfer of radioactive cesium into lettuce and barley biomass.

Soil microorganisms play an important role in determining the physical and chemical properties of soils. Soil microorganisms have both direct and indirect effects on the physical and chemical states of radionuclides and their availability for uptake by plant roots. Controlling the soil microorganisms to immobilize radionuclides is a promising strategy to reduce the content of radionuclides in the food chain. In this study, we evaluated the impact of effective microorganisms (EM) comprising lactic-acid bacteria, photosynthetic bacteria, and yeast on the transfer of 137 Cs into the aboveground biomass of barley and lettuce. The application of EM or fermented organic fertilizer (bokashi) alone to sod-podzolic sandy-loam soil significantly reduced the aggregated transfer factor of 137 Cs in barley by 37% and 44%, respectively. The combination of EM with bokashi or potassium fertilizer produced the largest reductions in 137 Cs transfer into barley biomass (50% and 63%, respectively). EM had a stronger effect on 137 Cs transfer into barley compared to lettuce. Laboratory experiments suggested that the effect of microorganisms on 137 Cs uptake can be attributed to a reduction in the proportion of bioavailable physicochemical forms of 137 Cs in the soils treated with EM and bokashi. This study, to the best of our knowledge, is the first to report the mechanism by which microbial fertilizers reduce the transfer of 137 Cs into plants.