Potential Risks of Radon in Soils to the Indigenous Microorganism: A Case Study of Ganghwa Island in South Korea

초록

This study was investigated on the metabolic activity of Bacillus velenzensis under the radon exposure, and soil bacterial isolates have been collected from Gang-Hwa island, Korea. B. velezensis exposed to a degree of different radon levels in the tightly sealed chamber equipped with radon reservoir at the various experimental conditions where their radon concentrations were varied from 200, 500, 800, 1,500 to 3,000 Bq/m3, each of which was temporally exposed for 1, 3, 5, 7, and 9 h. Thereafter, they were all commonly incubated in the fresh LB broth medium (containing Tryptone 10g/L; Yeast extract 5 g/L; and NaCl 10 g/L) to estimate the variation of the microbial population density (as of optical density at 600 nm), colony forming (CFU/mL), and dehydrogenase activity. Indigenous soil samples were analyzed with the same manner, and radon in soils was measured using FRD 400 (Radon FT Lab, Korea). As a result, dehydrogenase activity of B. velezensis was diminished when radiation intensity has been exceeded beyond the certain level; for example, at the 6th h of incubation, its microbial density was decreased to 22.4% (exposed to 200 Bq/m3), 67.6% (500 Bq/m3), 45.0% (800 Bq/m3), 42.7% (1,500 Bq/m3) and 41.8% (3,000 Bq/m3) compared to the control, respectively. Although this bacterial strain restored their own growth rate along with enzymatic activity as the incubation was prolonged, the extent of metabolic activity has been dwindled. It delineates that radon can be considered to be acted as for a potential environmental risk against the ecosystem. In the field survey, we have found such a consistency previously observed from the microbial exposure tests by the fact that the heterogenous microbial culture isolated from soil samples also have a higher metabolic activity in the medium level of radiation (i.e., 500 ? 1,500 Bq/m3) than other ranges of radon radiation either lower or higher.