The Impact of Gamma Radiation on Sediment Microbial Processes

Abstract

cMicrobial communities have the potential to control the biogeochemical fate of some radionuclides in contaminated land scenarios or in the vicinity of a geological repository for radioactive waste. However, there have been few studies of ionizing radiation effects on microbial communities in sediment systems. Here, acetate and lactate amended sediment microcosms irradiated with gamma radiation at 0.5 or 30 Gy h ؊1 for 8 weeks all displayed NO 3 ؊ and Fe(III) reduction, although the rate of Fe(III) reduction was decreased in 30-Gy h ؊1 treatments. These systems were dominated by fermentation processes. Pyrosequencing indicated that the 30-Gy h ؊1 treatment resulted in a community dominated by two Clostridial species. In systems containing no added electron donor, irradiation at either dose rate did not restrict NO 3 ؊ , Fe(III), or SO 4 2؊ reduction. Rather, Fe(III) reduction was stimulated in the 0.5-Gy h ؊1 -treated systems. In irradiated systems, there was a relative increase in the proportion of bacteria capable of Fe(III) reduction, with Geothrix fermentans and Geobacter sp. identified in the 0.5-Gy h ؊1 and 30-Gy h ؊1 treatments, respectively. These results indicate that biogeochemical processes will likely not be restricted by dose rates in such environments, and electron accepting processes may even be stimulated by radiation. In many countries, including the United Kingdom, the current policy for the long-term disposal of intermediate-level radioactive waste is to a deep geological disposal facility (GDF). In UK disposal concepts for higher-strength rocks and lower-strength sedimentary rocks, much of the intermediate-level radioactive waste is immobilized with a cementitious grout in stainless steel containers that are then surrounded with a cementitious backfill prior to closure of the facility (1). The vicinity of a GDF will not be a sterile environment, and microbial activity in the surrounding geosphere could have important implications for the evolution of biogeochemical processes, including microbial gas generation and utilization, microbially induced corrosion of waste containers and contents, and the mobility of radionuclides (2). In addition, there will be elevated concentrations of potential electron donors in and around the repository, including organics from the degradation of cellulose in the waste (3), and also molecular hydrogen from the radiolysis of water and the anaerobic corrosion of steel drums (4). Indeed, the availability of alternative electron acceptors will likely not be limited, since nitrate can be present in nuclear waste materials (5), and Fe(III) will be present due to aerobic corrosion of waste components and engineered infrastructure during the operational phase of the GDF.The stimulation of an Fe(III)-reducing community due to an increase in electron donors and acceptors is of particular interest since this may promote the reduction and precipitation of redoxactive radionuclides via the production of biogenic Fe(II)-bearing phases (2, 6). Indeed, many key Fe(III)-reducin...

Microbial Communities of the Drinking Water With Gradient Radon Concentration Are Primarily Contributed by Radon and Heavy Metal Content

“…At the family level, significantly dominant sequences obtained from contaminated sites are Moraxellaceae (under Proteobacteria), Chitinophagaceae (Bacteroidetes), unclassified Candidatus Azambacteria (Parcubacteria), unclassified Candidatus Moranbacteria (Parcubacteria), unclassified Candidatus Collierbacteria (Microgenomates), and unclassified Gammaproteobacteria (Proteobacteria), while Comamonadaceae (Proteobacteria), Rhodocyclaceae (Proteobacteria), Nitrospirales Incertae Sedis (Nitrospirae), cvE6 (Chlamydiae), unclassified Woesearchaeota (DHVEG-6) (Woesearchaeota), and Holophagaceae (Acidobacteria) are abundant in control sites (t-test; p < 0.05). The bacterial assemblages mentioned above were found to be dominated in contaminated radon water and were reported to be abundantly inhabitant in radiation and chemolithotrophic environments (Poirel et al, 2008;Brown et al, 2015;Rao et al, 2016;Danczak et al, 2017), thus supporting our finding. On the other side, dominant families present in the control water were generally reported to be present in natural soil and drinking water (Li et al, 2016;Deja-Sikora et al, 2019).…”

“…Nitrospira is a chemolithotrophic nitrite-oxidizing bacterium that shows the highest phylogenetic diversity and widest environmental distribution but is majorly found in fresh water and salt water (Daims et al, 2016) probably because of its reduced survival and adaptation strategies with a higher radionuclide-contaminated water. Meanwhile, Bacteroidetes was previously reported to be dominant in uranium-contaminated soils and γ-irradiated sediments (Brown et al, 2015;Yan et al, 2016), so it must have better survival strategies in such harsh environments. It is also reported that Bacteroidetes utilizes the catalase gene in order to show a resistance phenotype against oxidative stress (Rocha et al, 1996).…”

“…While most of the higher organisms are labile against this toxicity of radon and other radionuclides, the inhabitant microorganisms show resistance due to their protective mechanisms that are provided by extremozymes and extremolytes (Shukla et al, 2007). The radiation survival pure culture may not be effective in the relatively nutrient-limited different amounts of radiation-contaminated environments for bioremediation purposes due to community competition and other selective stress (Brown et al, 2015). However, indigenous microbial-based biostimulation or bioaugmentation is a more efficient approach than others that can be exploiting (Hassanshahian et al, 2014;Shukla et al, 2017).…”

Enhanced microbial degradation of irradiated cellulose under hyperalkaline conditions

“… 2014 ) and also stimulated Fe(III) reduction in more complex sediment microcosms (Brown et al . 2015 ).…”

Microbial corrosion of metallic materials in a deep nuclear-waste repository

“…Předběžné výpočty pro český koncept udávají dávkový příkon na povrchu UOS pod 0,4 Gy h -1 [39]. Např.v práci Brown et al [40] se zabývali vlivem dvou různých dávkových příkonů gama záření 30 Gy h -1 a 0.5 Gy h -1 po dobu 8 týdnů na životnost různých typů bakterií. V prostředí bez organických nutrientů nebyl pozorován žádný vliv IZ na životnost bakterií, naopak Geothrix fermentans a Geobacter sp.…”