Natural Attenuation Research Articles

How Do Fractures Influence Hyporheic Exchange in Sedimentary Rock Riverbeds?

AbstractBedrock rivers represent a hydrogeological environment in which surface water flows along an exposed bedrock surface. Studies of hyporheic exchange have exclusively involved rivers composed of unconsolidated fluvial sediments, leaving a critical knowledge gap. This study evaluates the conditions that could support bedform‐scale hyporheic exchange within a fractured sedimentary bedrock river based on field data collected near Guelph, Canada. Hyporheic exchange at the bedform‐scale was evaluated by numerically modeling the migration of a conservative solute tracer through a bedrock riverbed within a two‐dimensional vertical cross‐section along the flow direction. A stochastic discrete fracture‐matrix framework was developed to represent measured subsurface fractured bedrock properties, producing a probabilistic distribution of potential hyporheic exchange pathways. Flow and transport model results indicate that: (a) bedform‐scale hyporheic exchange within a bedrock river exists with high fluid flow velocities in fractures, yet long solute residence times due to diffusion across the fracture‐matrix boundary; (b) the coincidence of fractures and hydrodynamic head gradients across the riverbed controls the spatial extent of bedform‐scale hyporheic exchange; and (c) the potential variability in hyporheic exchange residence time is large (i.e., tens of years) due to the inherent variability in facture network properties. Our field‐based numerical study indicates that the average (median) residence time may not be a good proxy for the potential natural attenuation capacity of a fractured sedimentary bedrock riverbed and that hyporheic exchange has the potential to emplace surface water contaminants within the fractured porous rock matrix that could become a long‐term source of trace contaminants.

Microbial dynamics and physico-chemical properties of artisanal refinery polluted environment in Niger Delta

Artisanal refining of crude oil is a common practice in the Niger Delta region of Nigeria and this has continuously posed serious environmental and health risks. This was designed to investigate the microbial dynamics and physico-chemical properties of environmental (water, sediment and soil) matrix of impacted by artisanal refining activities. Three sampling locations (Bolo, River’s state; Ekpemu, Delta state; and Twon-Brass, Bayelsa state) were studied. Finding revealed that the total heterotrophic bacterial (THB) load of the recipient water from Twon-Brass had the least count of 2.0 ±0.2 x 104cfu/ml, followed by Ekpemu (2.1 ±0.3 x 103cfu/ml), then Bolo (2.35±0.6 x 104cfu/ml). In the contrary, recipient water body in Ekpemu had the least HUB load (1.8 ±0.1 x 103cfu/ml) followed by Bolo (2.0 ±0.3 x 104cfu/ml), and Twon-Brass (2.0 ±0.8 x 104cfu/ml). The bacterial load of the un-impacted aquatic matrix revealed a higher heterotrophic bacterial load (5.8+ 0.30 x 105cfu/ml) and low HUB load (0.2+ 0.21 x 103cfu/ml). In the sediment, Bodo had the least THB load of 2.1 ±0.2 x 105cfu/g, followed by Twon-Brass (2.3 ±0.6 x 105cfu/g), and Ekpemu (2.9 ±0.3 x 105cfu/g).Bolo and Twon-Brass soil were also highly impacted with hydrocarbons with a pollution index close to 1 (HUB/THB ratio = 0.9) while Ekpemu had a pollution index of 0.7. Bacterial species associated with the samples were Bacillus subtilis, Pseudomonas putida, and Pseudomonas aeruginosa were predominant in all the sample locations. Similarly, the artisanal refining activities also altered the physico-chemical properties of the various environmental matrix studied. Based on the finding of this study, it can be predicted that bioremediation various environmental matrix by natural attenuation is ongoing as most of the organisms isolated are hydrocarbon degraders. However, it is recommended that artisanal refining activities should be discouraged.

Contamination characteristics of chlorinated hydrocarbons in a fractured karst aquifer using TMVOC and hydro-chemical techniques

In this study, we investigated a fractured karst aquifer polluted by chlorinated hydrocarbons to determine the contamination characteristics of the main hydrocarbon components. The natural attenuation processes of representative components were simulated and forecasted using TMVOC and hydro-chemical components (NO3−, SO42−, HCO3− Cl− and δ13CDIC). The impact of hydrocarbon compounds on the hydro-chemical ions were estimated, and their historical contamination characteristics were also reconstructed. Results showed that the dynamic characteristics of Trichloromethane and 1,1,2-Trichlorethane can indicate those of chlorinated hydrocarbons, where the rate of natural attenuation was observed to decrease with decreasing concentrations of hydrocarbon compounds. Additionally, the long-term variation characteristics in groundwater levels showed that the relatively stable hydrodynamic field conditions enabled the simulation of the natural attenuation processes of chlorinated hydrocarbons. The simulation which also considered the biodegradation processes showed that the use of TMVOC and hydro-chemical parameters may better describe natural attenuation processes. Over 3 years (from 2017 to 2019), the average percentage of biodegradation in the total natural attenuation was estimated to be 88.35%. Similarly, Trichloromethane and 1,1,2-Trichlorethane are forecasted to have no health hazards in 10 and 15 years, respectively. The contribution rates of biodegradation to HCO3− and Cl− in the fractured karst aquifer varied with the concentrations of chlorinated hydrocarbons. Overall, the findings and methods in this work have significant contributions for advancing remediation developments of petroleum hydrocarbons, especially in karst environments that are highly susceptible to contamination.

Soil quality changes in an Iberian pyrite mine site 15 years after land reclamation

Reclamation of highly degraded mine lands to a sustainable environmental quality has become a major policy concern in many countries with a long mining tradition. This paper reports the soil quality status of a historical mine site fifteen years after its reclamation, using indicators of chemical reactivity, soil fertility and health, and discusses the progress and effectiveness of the implemented measures by a comparative analysis between pre- and post-reclamation conditions. Twenty composite surface samples (0–20 cm depth) were obtained for physical and chemical characterization from the open pit mine and waste disposal area, using a stratified random sampling approach. Additionally seven sites were selected to collect topsoil samples for microbiological testing. Results showed that soil quality changed noticeably over the study period (2003–2018), with overall improvements in key properties, such as structural stability, cation exchange capacity, degree of base saturation, soil organic carbon, and available phosphorus. Prior to reclamation, the mine soil was unable to support vegetation due to hyperacidity coupled with elevated levels of toxic metals and nutrient deficiencies. The combined use of sugar beet lime and composted biosolids as a low-cost, locally available, soil amendment was effective in neutralizing both active and exchangeable acidity, and reducing the mobility, plant uptake and human bioaccessibility of trace elements. The amendment addition also enhanced soil fertility, carbon storage, nutrient availability and microbial biomass (bacteria and fungi). Revegetation with Pinus pinea and Nerium oleander has proven to be a successful strategy to create a vegetative cover aesthetically pleasant and environmentally compatible with the surrounding undisturbed landscape, although further efforts should be made to monitor over time the phytotoxic and bioaccessible levels of residual metals, notably Cd, Cu and Zn. The insights gained from this land reclamation experience provide success criteria for assisting natural attenuation in other abandoned mining sites worldwide.

Natural attenuation mechanism of hexavalent chromium in a wetland: Zoning characteristics of abiotic and biotic effects

Natural wetland has great retention effect on Cr(VI) migration due to its abiotic and biotic reduction abilities, however, the zoning characteristics of dominating reduction mechanism along Cr(VI) pollution plume in wetland is still unclear. In this study, a Cr(VI) contaminated natural wetland was explored to investigate the distributions of Cr and Fe in groundwater and sediment, and their relationship with microorganisms according to metagenomics, aiming to reveal the natural attenuation mechanism of Cr(VI) from the perspective of zoning characteristics of abiotic and biotic effects. The wetland was divided into contaminated zone, transition zone and uncontaminated zone according to the contamination states of groundwater and sediment. At the upstream of contaminated zone, Cr(VI) concentration in groundwater was as high as 26.7 mg L−1, which has significant inhibition effect on microbial growth, and thus chemical reduction of Cr(VI) by natural organic matters (NOMs) dominated in this area, leading to the increasing of H/C and O/C ratios of NOMs because of the oxidation of aromatic moieties. At the downstream of contaminated zone, Cr(VI) concentration in groundwater decreased to less than 4.46 mg L−1 resulting from dilution and attenuation, but the microbial community was altered substantially, chromate resistant bacteria with ChrA, ChrR, NemA and AzoR genes were enriched, such as Sphingomonas, Mesorhizobium and Comamonadaceae, and thus the direct microbial reduction of Cr(VI) dominated in this area. While at the transition zone, which is located at the front edge of the pollution plume, Cr(VI) could only reached in this area intermittently, and the microbial community remained similar to that of the uncontaminated zone, dominated by Chloroflexi and Acidobateria phylum with dissimilatory ferric iron reduction capacity, and thus Cr(VI) was indirectly reduced by Fe2+ intermediately in this area.

Aged diesel and heavy metal pollution in the Arctic tundra (Yamal Peninsula, Russia)

Monitoring pollution in Arctic regions is a challenging and important task, regardless of the way these lands are used. The summer 2019 expedition to the Yamal Peninsula revealed historic petroleum pollution of the tundra area adjacent to “Yamalsky” natural reserve. Soil, surface water and bottom sediments from a downhill lake, and herbaceous plant Eriophorum scheuchzeri samples were collected to address the origin and the level of the aged pollution, and to investigate, if E. scheuchzeri species could be a potential phytoremediation agent. Compositional GC–MS analysis of the soil organic matter showed that diesel fuel spillage affected the study area and the territories nearby. Weathered diesel compounds penetrated the soil and reached the permafrost layer at 85 cm depth. Petroleum hydrocarbon level peaked at 11% (wt) in the topsoil at the polluted site and 3% (wt) in the bottom sediments of the downhill lake, demonstrating chronic ecosystem exposure. The following ICP-MS analysis showed presence of trace elements (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Ag, Cd, Ba, Pb, Bi, U) in the soil, water, and E. scheuchzeri samples. Observed concentrations of V, Cr, Cd, Pb, Ni, and Zn in the soil samples exceeded the background values by 3.6, 2.3, 9.7, 2.9, and 3.0 times, respectively. V (0.4 mg/L) and Cr (0.12 mg/L) levels in the lake water exceeded the established national limits by 40 and 2.4 times, respectively, which demonstrated the possibility of pollution migration with groundwater or surface water. The plant E. scheuchzeri tolerated diesel pollution and stimulated natural attenuation, bioaccumulating Mo, Cd, Ba, and Bi in its tissue from the soil. E. scheuchzeri is proposed for phytoremediation of Arctic soils polluted with petroleum and metals.

Efficiencies of selected biotreatments for the remediation of PAH in diluted bitumen contaminated soil microcosms.

Unconventional oils such as diluted bitumen from oil sands differs from most of conventional oils in terms of physiochemical properties and PAHs composition. This raises concerns regarding the effectiveness of current remediation strategies and protocols originally developed for conventional oil. Here we evaluated the efficiency of different biotreatment approaches, such as fungi inoculation (bioaugmentation), sludge addition (bioaugmentation/biostimulation), perennial grasses plantation (phytoremediation) and their combinations as well as natural attenuation (as control condition), for the remediation of soil contaminated by synthetic crude oil (a product of diluted bitumen) in laboratory microcosms. We specifically monitored the PAHs loss percentage (alkylated PAHs and unsubstituted 16 EPA Priority PAHs), the residue of PAHs and evaluated the ecotoxicity of soil after treatment. All treatments were highly efficient with more than ~ 80% of ∑PAHs loss after 60days. Distinctive loss efficiencies between light PAHs (≤ 3 rings, ~ 96% average loss) and heavy PAHs (4-6 rings, ~ 29% average loss) were observed. The lowest average PAHs residue (0.10 ± 0.02mg·kg-1, for an initial concentration of 0.29 ± 0.12mg·kg-1) was achieved with the "sludge-plants (grasses)" combination. Sludge addition was the only treatment that achieved significantly lower ecotoxicity (3% ± 4% of growth inhibition of L. sativa) than the control (natural attenuation, 13% ± 4% of inhibition). Sludge addition, grasses plantation and "sludge-fungi combination" treatments could result in lower PAH exposure (than other treatments) in post-treated soil when using the Canadian Soil Quality Guidelines for the protection of environmental and human health for potentially carcinogenic and other PAHs.

Development of Decision-Making Factors to Determine EMP Protection Level: A Case Study of a Brigade-Level EMP Protection Facility

This study developed decision-making factors to classify electromagnetic pulse (EMP) protection levels and determine various protection measures. We proposed three EMP protection levels of 80, 60, and 40 dB by considering the characteristics of military equipment and factors that determine EMP protection level, based on a Delphi study. We modeled EMP protection facilities for brigade-level troops to evaluate the derived decision-making factors and applicability of differential protection levels. The natural attenuation effect of soil was confirmed for structures installed underground. The shielding effect of wet soil was up to 30 dB. Considering the 20 dB EMP resistance of military equipment and the 30 dB of attenuation of wet soil, new materials with 30 dB of shielding efficiency could be used to meet an EMP protection level of 80 dB. Therefore, we confirmed that EMP protection measures could be established to build mobile, lightweight shelters. If lightweight shelters are constructed by applying the differential protection level scheme, they can be applied as a more effective EMP protection measure. Furthermore, differential protection measures can be adopted as a sustainable defense facility policy approach, wherein lightweight protection facilities replace conventional heavyweight facilities.

Effectiveness of biochar application and bioaugmentation techniques for the remediation of freshly and aged diesel-polluted soils

In order to contribute to a minimum impact on soil biocenosis during the application of in-situ bioremediation techniques, this work assessed the efficiency of a scarcely used combination of biochar and a bioaugmentation based on an autochthonous bacterial consortium. Bioaugmentation-biochar combination was assessed by using soil samples from a polluted site with two pollution scenarios: a) soil with aged diesel, and b) clean soil to which fresh diesel was later added simulating a recent pollution event. The autochthonous consortium, isolated from the aged-diesel soil, was genetically, taxonomically and functionally characterized by these authors in a previous work. The biochar used was obtained from tree pruning residues. In both scenarios, four treatments were carried out under short-term test conditions: i) natural attenuation, ii) biochar, iii) bioaugmentation, and iv) biochar-bioaugmentation combination. Our results show that the bioaugmentation-biochar combination was significantly more effective than the simple treatments. This combination produced more than 20% diesel degradation in both scenarios over twelve weeks. Simultaneously, an increase in bacterial diversity was observed in that period. Therefore, using biochar combined with bioaugmentation suggests synergies that lead to a highly efficient and environmentally friendly bioremediation processes.

Increasing electron donor concentration does not accelerate complete microbial reductive dechlorination in contaminated sediment with native organic carbon.

Experiments with Fe(III)-rich, chloroethene-contaminated sediment demonstrated that trichloroethylene (TCE) and vinyl chloride (VC) were completely reduced to ethene regardless of whether electron donor(s) were added at 1 × stoichiometry or 10 × stoichiometry relative to all-electron acceptors. Unamended controls uniformly reduced TCE to ethene with a mean time to complete dechlorination (operationally defined as the presence of stoichiometric ethene production) of 79days. Adding 1 × and 10 × acetate hindered the rate and extent of TCE and VC reduction relative to unamended controls, with several only partially reduced when the experiments were terminated. Adding high molecular mass (soybean oil derivative) substrates did not increase microbial reductive dechlorination relative to unamended incubations, and in many cases, hindered microbial dechlorination in favor of methanogenesis. The mean time to complete dechlorination was comparable between low (× 1) and high (× 10) electron donor concentration for all lipid-based electron donors tested. Those tested included Newman Zone® Standard without sodium lactate (96 vs. 75days, respectively), CAP 18 ME (85 vs. 94days, respectively), EOS 598B42 (68 vs. 72days, respectively), and acetate (134 vs. 125days, respectively). These data suggest that the addition of an electron donor does not always increase the rate and extent of reductive dechlorination but will increase costs. In particular, increasing the concentration of electron donors higher than the stoichiometric demand only decreased complete microbial reductive dechlorination, which is the opposite of most standard "more time and more electrons" approaches. These data argue that site-specific electron donor demands must be evaluated, and in some cases, a monitored natural attenuation (MNA) approach is most favorable.

Improving the Bioremediation and in situ Production of Biocompounds of a Biodiesel-Contaminated Soil.

We aimed to produce simultaneously biosurfactants and lipases in solid state fermentation (SSF) using Aspergillus niger, followed by the use of the fermented media on the bioremediation of oily contaminated soil, in order to valuate agro industrial residuals and reduce the contamination. The biocompounds were produced using wheat bran and corncob (80:20), 5% of soybean oil and 0.5% of sugar cane molasses in SSF for 4 d, producing 4.58 ± 0.69 UE of emulsifying activity and 7.77 ± 1.52 U of lipolytic activity. This fermented media was used in the bioremediation of a 20% biodiesel contaminated soil, evaluating for 90 d microbial growth, contaminant degradation, and production of lipases and biosurfactants in soils. Six experimental strategies (natural attenuation; biostimulation + bioaugmentation + biocompounds; biostimulation + biosurfactant; biocompounds extract; biostimulation; adsorption of contaminant) were realized. The highest degradation of contaminant was verified in 90 d, of 74.40 ± 1.76%, and the production of biosurfactants and lipases in situ in the soil was found in 30 d (6.02 ± 0.24% of reduction in surface tension and 6.62 ± 0.17 UL of lipid activity in soil) for the same experiment (biostimulation + bioaugmentation + biocompounds). The addition of biostimulation + biosurfactant promotes higher biodegradation (66.00 ± 0.92%) of the contaminant than the biocompounds extract (59.58 ± 0.34%). The use of a solid fermented culture medium containing both biocompounds was feasible for the treatment of contaminants, demonstrating the potential for environmental application without the need for purification processes.

Natural Attenuation as a Decontamination Approach for SARS-CoV-2 on Library Materials

Based on the current scientific understanding regarding COVID-19, this article presents the results of new studies (Tests 4, 5, 6), conducted by the Institute of Museum and Library Services (IMLS) and the Online Computer Library Center (OCLC), in partnership with Battelle. The purpose of the experiments is to determine how long frequently circulated library, museum and archival materials should be quarantined before being put back into public circulation.Each test has been conducted by applying the virulent SARS-CoV-2 virus on various materials held at standard room temperature and relative humidity conditions, and then examining the rate of natural attenuation of the virus. The items were not sterilized before testing. Battelle propagated the clinical isolate of the SARS-CoV-2 virus in-house, followed by characterization and testing to establish a certified titer. The materials in Test 4 included binding and cover items placed in a stacked configuration to imitate the common practice that libraries employ when handling book/DVD returns, as well as expanded polyethylene foam, which is typically used in museums for storage and shipping. Test 5 focused on textiles, while Test 6 included building materials (glass, marble, brass, laminate, and powder-coated steel). Test coupons cut from the materials were inoculated with active virus, and then allowed to dry. The test coupons were then examined at the following timepoints: on the second, third, fourth and sixth day (Test 4); on the second, fourth, sixth and eighth day (Tests 5 and 6). The results of the tests showed how much virus was detectable at the selected timepoints. In Test 4, the virus was still detected on all the five materials after six days. In Test 5, the virus was still detected on leather and synthetic leather publication after eight days. In Test 6, the virus was not detected on the tested materials after six days.This publication is provided for informational purposes only, and readers are encouraged to review federal, regional, and local guidance. The authors, sponsors and researchers are not liable for any damages resulting from use, misuse, or reliance upon this information, or any errors or omissions herein.

Natural Attenuation as a Decontamination Approach for SARS-CoV-2 on Library Materials

Based on the current scientific understanding regarding COVID-19, this article presents the results of new studies (Tests 4, 5, 6), conducted by the Institute of Museum and Library Services (IMLS) and the Online Computer Library Center (OCLC), in partnership with Battelle. The purpose of the experiments is to determine how long frequently circulated library, museum and archival materials should be quarantined before being put back into public circulation.Each test has been conducted by applying the virulent SARS-CoV-2 virus on various materials held at standard room temperature and relative humidity conditions, and then examining the rate of natural attenuation of the virus. The items were not sterilized before testing. Battelle propagated the clinical isolate of the SARS-CoV-2 virus in-house, followed by characterization and testing to establish a certified titer. The materials in Test 4 included binding and cover items placed in a stacked configuration to imitate the common practice that libraries employ when handling book/DVD returns, as well as expanded polyethylene foam, which is typically used in museums for storage and shipping. Test 5 focused on textiles, while Test 6 included building materials (glass, marble, brass, laminate, and powder-coated steel). Test coupons cut from the materials were inoculated with active virus, and then allowed to dry. The test coupons were then examined at the following timepoints: on the second, third, fourth and sixth day (Test 4); on the second, fourth, sixth and eighth day (Tests 5 and 6). The results of the tests showed how much virus was detectable at the selected timepoints. In Test 4, the virus was still detected on all the five materials after six days. In Test 5, the virus was still detected on leather and synthetic leather publication after eight days. In Test 6, the virus was not detected on the tested materials after six days.This publication is provided for informational purposes only, and readers are encouraged to review federal, regional, and local guidance. The authors, sponsors and researchers are not liable for any damages resulting from use, misuse, or reliance upon this information, or any errors or omissions herein.

Anaerobic Benzene Biodegradation Linked to the Growth of Highly Specific Bacterial Clades.

Reliance on bioremediation to remove benzene from anoxic environments has proven risky for decades but for unknown reasons. Research has revealed a strong link between anaerobic benzene biodegradation and the enrichment of highly specific microbes, including Thermincola in the family Peptococcaceae and the deltaproteobacterial Candidate Sva0485 clade. Using aquifer materials from Canadian Forces Base Borden, we compared five bioremediation approaches in batch microcosms. Under conditions simulating natural attenuation or sulfate biostimulation, benzene was not degraded after 1-2 years of incubation and no enrichment of known benzene-degrading microbes occurred. In contrast, nitrate-amended microcosms reported benzene biodegradation coincident with significant growth of Thermincola spp., along with a functional gene presumed to catalyze anaerobic benzene carboxylation (abcA). Inoculation with 2.5% of a methanogenic benzene-degrading consortium containing Sva0485 (Deltaproteobacteria ORM2) resulted in benzene biodegradation in the presence of sulfate or under methanogenic conditions. The presence of other hydrocarbon co-contaminants decreased the rates of benzene degradation by a factor of 2 to 4. Tracking the abundance of the abcA gene and 16S rRNA genes specific for benzene-degrading Thermincola and Sva0485 is recommended to monitor benzene bioremediation in anoxic groundwater systems to further uncover growth-rate-limiting conditions for these two intriguing phylotypes.

Soil microbial response to silicate fertilization reduces bioavailable arsenic in contaminated paddies

Rice grown in arsenic (As)-contaminated soils will have an elevated As concentration in the edible parts and lower yield due to the stressful growing environment. Silicon fertilizer is a soil amendment that can prevent As bioaccumulation and increase rice yield. This may be due to chemical interactions between silicon and As, but we hypothesized that silicon fertilization would improve soil microbial functions that control the bioavailable As concentration and improve the growing environment for rice in As-contaminated agroecosystems. We tested the hypothesis on two geographically different rice varieties (Indica and Japonica) grown on As spiked soils. Rice grown in pots amended with slag-based silicon fertilizer (silicate fertilizer) at a rate of 2 Mg ha−1 had a significantly lower As concentration in the grain, with 28% less As in the grain of Indica rice and 30% less As in the Japonica rice grain. The rice grain yield was 20–22% greater in these rice varieties. There are several reasons that As uptake declined in the rice grain, including: (i) a reduction in As bioavailability, likely because As was absorbed to amorphous and crystalline iron oxides in the soil and on root Fe-plaque, (ii) an increase in As resistant and arsenite-oxidizing bacteria that likely contribute to the natural attenuation of As in soil, and (iii) an increase in the pore-water silicon concentration that competitively inhibited As uptake by plants. Adding silicate fertilizer improved the general soil fertility by increasing the abundance of microbial functional communities involved in nutrient (carbon, nitrogen, and phosphorus) cycling, nitrogen and carbon fixation, methane consumption, and heavy metals/metalloid detoxification, while decreasing the number of microorganisms involved in methane and nitrous oxide production. We conclude that silicate fertilizer amendments stimulate soil microbial functions that are beneficial for rice growth while controlling As bioavailability, and thus are a potential solution to allow rice production in As-contaminated paddy soils.

Different biological strategies for the bioremediation of naturally polluted soils

Finding an appropriate method with the highest rate of polycyclic aromatic hydrocarbon (PAH) removal from naturally polluted soils is an important research issue. A pot factorial experiment (using contaminated soil samples from the Isfahan Refinery, Iran) was conducted in a 90-day period to compare the following bioremediation strategies: (1) natural attenuation (NA): the inherent ability of soil for bioremediation; (2) bioaugmentation (BA): inoculating soil with PAH degrading microbes Marinobacter hydrocarbonoclasticus; (3) biostimulation (BS): using N, P and K nutrients for the stimulation of bioremediating soil bacteria to achieve the C : N : P ratio of 100 : 10 : 1, and(4) bioaugmentation + biostimulation (BS + BA). Treatments NA (22.8%) and BA + BS (63.9%) resulted in the least and the highest rate of PAH removal from the soil. The 2–4 ring compounds had a significantly (P ≤ 0.05) higher rate of degradation than the 5–6 ring compounds. The highest rates were resulted by fluorene (76.41%) and acenaphthylene (72.28%) using the BA + BS treatment. However, the lowest degradation rates were resulted by indeno (1,2,3-cd) pyrene (10.05%), benzo [b] fluoranthene (10.17%), benzo (g, h, i) perylene (12.53%), and benzo [k] fluoranthene (13.67%), using NA treatment. The BA + BS treatments are the most effective method for the bioremediation of PAH polluted soils.

Toluene Bioremediation by Using Geotextile-Layered Permeable Reactive Barriers (PRBs)

Sources of contamination in a subsurface environment are petrol, diesel fuel, gasoline at oil refineries, underground storage tanks, transmission pipelines, and different industries. The permeable reactive barrier (PRB) is a promising technology to remediate groundwater in-situ. In this study, synthetic groundwater samples containing toluene are treated in three reactor columns by biological processes. PRB-1 consisted of sand and gravel as reactor media, microbial inoculum (bioaugmentation—BA), and nutrients (biostimulation—BS); PRB-2 consisted of sand and gravel as reactor media, microbial inoculum, nutrients, and 12 layers of nonwoven geotextile fabrics; and PRB-3 consisted of only sand and gravel as reactor media (natural attenuation—NA). This study was conducted to assess the impact of geotextile fabric filter, bioaugmentation, and biostimulation on toluene degradation efficiency. After 167 days of treatment, toluene biodegradation efficiencies varied between 88.2% and 93.8% for PRB 1, between 98.0% and 99.3% for PRB 2, and between 14.2% and 68.6% for PRB 3. The effluent toluene concentrations for PRB-2 were less than the guideline value (0.7 mg/L) of the World Health Organization. Reaction rate data were fitted with a first-order kinetic reaction rate model. This study showed that the toluene removal efficiency in the geotextile layered PRB combined with BA and BS process was significantly higher compared to the other processes tested. This lab-scale study introduced a new PRB configuration suitable for the remediation of sites contaminated with toluene.

Effect of biostimulation and bioaugmentation on hydrocarbon degradation and detoxification of diesel-contaminated soil: a microcosm study.

Soil contamination with diesel oil is quite common during processes of transport and storage. Bioremediation is considered a safe, economical, and environmentally friendly approach for contaminated soil treatment. In this context, studies using hydrocarbon bioremediation have focused on total petroleum hydrocarbon (TPH) analysis to assess process effectiveness, while ecotoxicity has been neglected. Thus, this study aimed to select a microbial consortium capable of detoxifying diesel oil and apply this consortium to the bioremediation of soil contaminated with this environmental pollutant through different bioremediation approaches. Gas chromatography (GC-FID) was used to analyze diesel oil degradation, while ecotoxicological bioassays with the bioindicators Artemia sp., Aliivibrio fischeri (Microtox), and Cucumis sativus were used to assess detoxification. After 90 days of bioremediation, we found that the biostimulation and biostimulation/bioaugmentation approaches showed higher rates of diesel oil degradation in relation to natural attenuation (41.9 and 26.7%, respectively). Phytotoxicity increased in the biostimulation and biostimulation/bioaugmentation treatments during the degradation process, whereas in the Microtox test, the toxicity was the same in these treatments as that in the natural attenuation treatment. In both the phytotoxicity and Microtox tests, bioaugmentation treatment showed lower toxicity. However, compared with natural attenuation, this approach did not show satisfactory hydrocarbon degradation. Based on the microcosm experiments results, we conclude that a broader analysis of the success of bioremediation requires the performance of toxicity bioassays.

Zooplankton functional diversity as an indicator of a long‐term aquatic restoration in an Amazonian lake

Mining is an important economic activity that can have severe impacts on aquatic ecosystems. Plankton communities are commonly used as bioindicators of human‐related threats to freshwater environments due to their rapid response to environmental conditions changes. Here, we used zooplankton functional diversity to understand the recovery patterns of an Amazonian lake impacted by mining activity (input of bauxite tailings) after 30 years of natural attenuation and active restoration processes. Zooplankton species richness and functional diversity (Rao's quadratic entropy—FDQ and community‐level weighted means of trait values—CWM) were compared in impacted and reference areas during the flood period, in March 2015. We found a significant negative influence of turbidity on zooplankton FDQ, and similar FDQ and CWM values between the active restoration area and the reference area. These results suggest a positive effect of vegetation restoration efforts for the zooplankton community of Batata Lake. We demonstrated the utility of zooplankton functional diversity metrics as bioindicators of freshwater restoration, the response of the aquatic ecosystem to vegetation restoration and, consequently, water quality.

Natural attenuation along subsurface flow paths based on modeling and monitoring of a pesticide metabolite from three case studies

BackgroundGroundwater—especially for the use as drinking water—is a strictly protected resource in the existing guidelines for pesticide registration and drinking water protection in the EU. One aspect that has hardly played a role in this context so far is the attenuation of pesticide concentrations along the flow path from the regulatory leaching concentration at a depth of 1 m below the applied field to raw water abstraction systems. The soil metabolite N,N-dimethylsulfamide (DMS) is formed from two fungicidal substances: tolylfluanid and dichlofluanid. According to the EU guidance document on relevant metabolites in groundwater, DMS is a “non-relevant” metabolite. However, long-term application of the two active substances on permanent crops has resulted in elevated and quantifiable amounts of DMS in groundwater catchment areas of water supplying plants. Therefore, in the case of DMS, substantial monitoring data is available. This enables in combination with groundwater modeling, a quantitative analysis of the natural attenuation of DMS concentrations over time and distance. To this end, extensive real-world data from three case studies of drinking water catchment areas in Germany were analyzed.ResultsThe environmental fate of DMS in soil and groundwater was evaluated according to the respective data determined at the study sites. Analyses using monitoring data and combined modeling approaches as well, were performed to obtain comparable results. These merged outcomes from monitoring and modeling show total attenuation factors of 12–93 from leachate at 1 m depth down to monitoring wells—close to raw water collection. If concentration attenuation further downwards to collected raw water is considered, the overall attenuation factor is even higher (40–246).ConclusionsThe conditions at the catchment areas of the three case studies are very diverse, thus providing a wide range of attenuating conditions. When following the path of DMS from its formation in soil below a treated field, to its leaching into the aquifer, and within the aquifer down to the raw water collection site, its concentration in water is continuously and consistently decreasing. The results from DMS represent conservative estimations due to non-sorptive, quick transport processes. Extended to other sorptive solutes, it represents the lower end of expected attenuation. Therefore, natural pesticide concentration attenuation processes are suggested for the consideration in regulatory pesticide risk assessments for a more realistic yet still protective evaluation of expected concentrations in raw water.