Oily waste containing natural radionuclides: does it cause stimulation or inhibition of soil bacterial community?

Abstract

Contamination with oily wastes containing natural radionuclides is a potential hazard for soil health and function. Our study aimed to reveal both structural and functional changes of the microbial community resistant to and able to decompose oily wastes in soil. To do this, we determined CO 2 efflux, microbial biomass (by the extraction-fumigation method), and community structure (by PCR-SSCP) for 120 d after application of radioactive oily wastes to the soil at the ratio 1:4. The addition of the waste resulted in an increase of the activity concentration of 226 Ra by 130 times (up to 643 Bq kg -1 ) and of 232 Th by 29 times (up to 254 Bq kg -1 ). The calculated weighted dose for the radionuclide 226 Ra was found to be below the values that are known to affect microorganisms. However, the cumulative effect of a repeated deposition of radioactive oily waste may result in an increase of the weighted dose up to an effective level. During the incubation, the hydrocarbon (HC) content of the waste-treated soil decreased from 156 to 54 g kg -1 of soil indicating intensive decomposition of added organics by soil microorganisms. The waste application, however, led to an inhibition of soil microbial biomass compared with the control (by 26-47%). Microbial respiration was stimulated in the first month of incubation and then decreased until the end of the incubation period (by up to 74% compared to the control). The qCO 2 was estimated to be 3-fold higher than the control on day 1 of incubation and equal to the control on day 120 of incubation. The bacterial diversity decreased in the contaminated soil compared with the control soil. The bacterial community structure was altered by domination of new oil degrader species belonging to the genera Dyella, Pseudoxanthomonas, Sinobacter, and Parvibaculum. Thus, disposal of radioactive petroleum waste strongly altered the structure of the microbial community resulting in the selection of resistant species able to decompose pollutants and also affected the community function (inhibition of microbial biomass and stimulation of respiration) which tended to stabilize after long-term incubation.

Biochar-carrying hydrocarbon decomposers promote degradation during the early stage of bioremediation

“…The bacterial community on day 28 reflects the end of active hydrocarbon decomposition in biochar-amended soil. All the bacterial taxa that were abundant at this time were previously described as efficient degraders of hydrocarbons (Abed et al, 2015;Agnello et al, 2015;Cappello et al, 2016;Dashti et al, 2015;Galitskaya et al, 2015b;Kauppi et al, 2011;Shahi et al, 2016). Therefore, we conclude that the higher decomposition rate in variant B is due to the stimulation of degraders by biochar.…”

“…Changes of metabolic activity of soil microbes may be a result of an altered microbial community structure, and in the process of bioremediation of oil pollution, bacteria play a more important role (Atlas, 1995;Galitskaya et al, 2015a;Qin et al, 2013). That is why, in the next stage of investigation, we estimated the structure of bacterial communities in remediating variants.…”

Di- and Mono-Rhamnolipids Produced by the Pseudomonas putida PP021 Isolate Significantly Enhance the Degree of Recovery of Heavy Oil from the Romashkino Oil Field (Tatarstan, Russia)

“…It has been exploited since 1948, and the oil recovery degree since then has decreased from 53% to 45%. Because of its high oil viscosity (2.6-4.5 mPa•s) and high sulfur and wax contents (1.3 and 3.2%, respectively), the Romashkino oil field urgently needs the development and implementation of new efficient methods for enhancing oil recovery [3,4].…”

Sequestration Specificity of Single or Co-existing Benzene, 1,3,5-Trimethylbenzene, and Naphthalene in Soil

“…Petroleum hydrocarbons, from the production, transportation, storage, and distribution of fuels, can affect soil ecosystems and result in significant deterioration of soil quality (Dindar et al 2017;Mendez et al 2017). The long-term contact of petroleum hydrocarbons with soil often leads to progressive immobilization or sequestration of compounds within contaminated soil; in addition, the bioavailability of contaminants will decrease the longer they remain in soil (Li et al 2016;Galitskaya et al 2016). Alexander (2000) proposed that the sequestration of contaminants resulting from diffusion into the solid portion of soil or entry into nanopores caused the aforementioned decline of bioavailability.…”