Microbiology of formation waters from the deep repository of liquid radioactive wastes Severnyi

Abstract

The presence, diversity, and geochemical activity of microorganisms in the Severnyi repository of liquid radioactive wastes were studied. Cultivable anaerobic denitrifiers, fermenters, sulfate-reducers, and methanogens were found in water samples from a depth of 162-405 m below sea level. Subsurface microorganisms produced methane from [2-(14)C]acetate and [(14)C]CO(2), formed hydrogen sulfide from Na(2) (35)SO(4), and reduced nitrate to dinitrogen in medium with acetate. The cell numbers of all studied groups of microorganisms and rates of anaerobic processes were higher in the zone of dispersion of radioactive wastes. Microbial communities present in the repository were able to utilise a wide range of organic and inorganic compounds and components of waste (acetate, nitrate, and sulfate) both aerobically and anaerobically. Bacterial production of gases may result in a local increase of the pressure in the repository and consequent discharge of wastes onto the surface. Microorganisms can indirectly decrease the mobility of radionuclides due to consumption of oxygen and production of sulfide, which favours deposition of metals. These results show the necessity of long-term microbiological and radiochemical monitoring of the repository.

Geomicrobial Processes and Biodiversity in the Deep Terrestrial Subsurface

“…Not surprisingly, the contamination often resulted in an apparent enrichment for microbes that could degrade or otherwise utilize the contaminants (e.g., Lowe et al 2002;de Lipthay et al 2003), or microbes that were comparatively resistant to highly toxic contaminants (e.g., Fredrickson et al 2004;Reardon et al 2004). Contamination has also been associated with increased cultivatability (de Lipthay et al 2003) or metabolic activity (Nazina et al 2004) of microbes within the contaminant plume. In contrast, some types of contaminants appeared to have little or no affect on subsurface • Viable bacterial numbers low (∼10 4 CFU g 2 ) but cultures recovered from 11 of 16 samples, including most radioactive (e.g., >10 µCi of 137 Cs/g) • Isolates/clones from contaminated sediments dominated by Gram-positive species; Arthrobacter most common but other high-G+C phyla present • Two isolates related to Deinococcus radiodurans able to survive doses of ionizing radiation up to 20 kGy; many Gram-positive isolates resistant to lower levels of gamma radiation Vadose-zone, nutrient-poor glacial melt water sand; influence of petroleum hydrocarbon vapors on microbial community structure…”

Physicochemical and biological monitoring of deep repositories for liquid radioactive wastes

“…In deep levels in Hungary (198-229 m), which are to be used for waste disposal [14], the population of aerobic microorganisms does not exceed 10 2 and anaerobic organisms 10 4 per 1 cm 3 . Close values were also found in waters in the deep liquid-wastes repository at the Severnyi site [6,7]. Investigations [6,7,12,13]have shown that microorganisms living in underground formations are capable of forming gasesmethane, carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and others -from possible macrocomponents of the liquid wastes.…”

“…Constant geological and hydrogeological monitoring (measurement of the temperature, pressure, piezolevels, and so forth) in injection and observation wells is performed on these sites, and the composition of the gases released from the injection wells is also analyzed [5]. In recent years, serious attention has been devoted to investigating the microflora in underground levels used for burying liquid wastes [6,7]. The main objects of investigation were samples of formation water from observational wells in the second level (Fig.…”

“…The population of microorganisms was determined on elective nutrient media [7]. The distribution of the population of microorganisms in the samples of formation liquids studied is presented in Table 3.…”

“…The rate of sulfate reduction and methane generation was measured in 2001-2004 in 11 samples of formation waters using tagged compounds (Na 2 35 SO 4 , NaH 14 CO 3 , and 14 CH 3 -COONa) [7]. The rate of both processes is extremely low (see Table 4).…”