Lead or cadmium co-contamination alters benzene and toluene degrading bacterial communities

A Mechanistic Insight in Cr (VI) Bioremediation by Bacillus spp. SSAU-2 Under Multi-Heavy Metal Contamination

Climate change has significantly contributed to high level of contamination of multi-pollutants in the environment. For instance, it increases the intensity of rainfall, leading to soil erosion and leaching of heavy metals, pesticides and other pollutants into the water bodies. Additionally, climate change intensifies both natural processes and anthropogenic activities resulting in the widespread release and dispersal of heavy metals (HMs) and other pollutants, posing great risk to environment and human health. Cr (VI) is the most hazardous metal contaminant in the ecosystem. In the environment, it often coexists with other heavy metal such as Fe (III), Zn (II), Pb (II), Hg (II), Cd (II) and Cu (II) which interferes with the Cr (VI) removal strategies and significantly influence the efficiency of bioremediating microbes. In this study, the Cr (VI) removal potential of the novel microbe Bacillus sp. SSAU-2 was explored in the presence of multi-heavy metal contaminations in various combinations. The tolerance against HM of the SSAU-2 was analyzed with minimum inhibition concentration (MIC) study and the mechanism was observed by analyzing the various types pf Siderophore production in the presence of HM. Revealed that the SSAU-2 exhibits multi-heavy metal tolerance, with the following MIC order Pb (II) > Fe (III) > Cu (II) > Cr (VI) > Zn (II) > Cd (II) > Hg (II). The presence of Zn (II), Fe (III) and Cu (II) acted as positive inducers, enhancing its growth and Cr (VI) removal efficiency. Although SSAU-2 demonstrates remarkable resistance to most heavy metals, it is highly susceptible to Hg (II) and Cd (II). However, Hg (II) proved to be the most toxic, reducing the Cr (VI) removal efficiency from 83 to 32% even at a concentration of 0.1 ppm concentration. The mechanism underlying its multi-heavy metal tolerance is linked to the production of siderophore, particularly catechol-type siderophore. Thus, this study highlights the potential of SSAU-2 as a robust microbe, capable of sustaining its Cr (VI) removal ability even in the presence of multiple heavy metals. Therefore, this microbe can tackle the adverse climate change phenomenon and environmental pollution altogether.

An in situ reactive zone approach using calcium peroxide for the remediation of benzene and chlorobenzene in groundwater: A field study

There is a gap in understanding the different contributions of biodegradation and free radical oxidation using calcium peroxide (CaO2) for the remediation of mixed contaminants of benzene and chlorobenzene in groundwater. In this study, the remedial efficiency and mechanisms of benzene and chlorobenzene co-contaminants using CaO2 were explored by an integrated approach of field study and laboratory validation. It was found that in the field demonstration program, the radius of influence for each injection point using Geoprobe direct-push was larger than the designed value of 0.75 m in the reactive zones created by CaO2 supplemented with a buffer solution (Area A) and CaO2 only (Area B). Both benzene and chlorobenzene were remediated to meet the cleanup goals within 5 months. The benzene and chlorobenzene concentration rebounds observed in monitoring wells were treated effectively with sustained effect of reagents. The laboratory validation experiments verified CaO2 with a buffer solution could maintain the pH values within the range of 6.05-7.69, and higher DO concentrations for prolonged period. The contributions of biodegradation for benzene were 43.47% and 42.02% in CaO2 group and CaO2 adjusted with buffer solutions group, respectively, while those for chlorobenzene were 16.87% and 19.61%. In addition, it was demonstrated in the laboratory that the application of CaO2 supplemented with a buffer solution had the best remediation efficiency for benzene and chlorobenzene, due to the contributions from both the free radicals HO• and the biodegradation of co-contaminants by the native microbial consortium. Furthermore, the intermediate byproducts, including phenol, 2-chlorophenol and pyruvate, were detected in groundwater collected in the field, and the biodegradation and oxidative degradation pathways of benzene and chlorobenzene with the application of CaO2 were proposed. The microbial composition analyses for groundwater samples revealed that multiple functional bacteria, which are capable of degrading benzene and chlorobenzene, were enriched. The findings of the current study take one step further for the understanding of the fundamentals of CaO2 as a slow oxygen releasing reagent, as well as its engineering applications for the remediation of organic contaminants in soil and groundwater.

Predictive modeling of diazinon residual concentration in soils contaminated with potentially toxic elements: a comparative study of machine learning approaches

The widespread use of pesticides, including diazinon, poses an increased risk of environmental pollution and detrimental effects on biodiversity, food security, and water resources. In this study, we investigated the impact of Potentially Toxic Elements (PTE) including Zn, Cd, V, and Mn on the degradation of diazinon in three different soils. We investigated the capability and performance of four machine learning models to predict residual pesticide concentration, including adaptive neuro-fuzzy inference system (ANFIS), support vector regression (SVR), radial basis function (RBF), and multi-layer perceptron (MLP). We employed a 10-fold cross-validation mechanism to evaluate the models. Moreover, performance validation of selected algorithms through the coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE) and mean square error (MSE) confirm that the SVR and ANFIS with lower RMSE, MSE, and a higher R2 can simulate the degradation process better than other models. The result showed that both SVR and ANFIS approaches worked well for the data set, but the SVR technique is more accurate than the fuzzy model for estimating pesticide concentration in soil in the presence of PTE. Vanadium appeared to be the best option for the degradation of diazinon. The models predicted the performance of V2+ for diazinon degradation with R2 and RMSE of 0.99 and 2.18 m g . k g - 1 for SVR and, 0.99, and 1.30 for the ANFIS model for the training set. Finally, the high accuracy of the models was confirmed.

In situ bioaugmented phytoremediation of cadmium and crude oil co-contaminated soil by Ocimum gratissimum in association with PGPR Micrococcus luteus WN01

Heavy metals and petroleum oil are the two most important contaminants in the environment. Currently, phytoremediation is regarded as an effective and affordable solution that allows the attenuation of toxic pollutants through the use of plants. Not many studies are carried out regarding the use of aromatic plants capable of remediating soil that is co-contaminated by heavy metal and petroleum hydrocarbons. A pot experiment was conducted to investigate the influence of cadmium-resistant PGPR Micrococcus luteus on the phytoremediation efficiency of Ocimum gratissimum in Cd and petroleum co-contaminated soil. The plants were harvested after 60 days of treatment and their growth and biomass were determined. The accumulation of Cd in plant shoots and roots was determined. The residual petroleum hydrocarbon concentration during the 60 days of the phytoremediation experiment was determined using GC-FID. O. gratissimum with M. luteus showed the highest Cd accumulation (14.05 mg kg-1) and the highest reduction of TPH (46.64%). M. luteus ameliorated contaminant toxicity and promoted biomass production of O. gratissimum. These results demonstrated that O. gratissimum in combination with M. luteus can be efficiently used to remediate Cd and petroleum-co-contaminated soils.

Exploring the microbe-mediated biological processes of BTEX and toxic metal(loid)s in aging petrochemical landfills

Aging petrochemical landfills serve as reservoirs of inorganic and organic contaminants, posing potential risks of contamination to the surrounding environment. Identifying the pollution characteristics and elucidating the translocation/ transformation processes of typical contaminants in aging petrochemical landfills are crucial yet challenging endeavors. In this study, we employed a combination of chemical analysis and microbial metagenomic technologies to investigate the pollution characteristics of benzene, toluene, ethylbenzene, and xylene (BTEX) as well as metal(loid)s in a representative aging landfill, surrounding soils, and underlying groundwater. Furthermore, we aimed to explore their transformations driven by microbial activity. Our findings revealed widespread distribution of metal(loid)s, including Cd, Ni, Cu, As, Mn, Pb, and Zn, in these environmental media, surpassing soil background values and posing potential ecological risks. Additionally, microbial processes were observed to contribute significantly to the degradation of BTEX compounds and the transformation of metal(loid)s in landfills and surrounding soils, with identified microbial communities and functions playing key roles. Notably, co-occurrence network analysis unveiled the coexistence of functional genes associated with BTEX degradation and metal(loid) transformation, driven primarily by As, Ni, and Cd. These results shed light on the co-selection of resistance traits against BTEX and metal(loid) contaminants in soil microbial consortia under co-contamination scenarios, supporting microbial adaptive evolution in aging petrochemical landfills. The insights gained from this study enhance our understanding of characteristic pollutants and microbial transformation processes in aging landfills, thereby facilitating improved landfill management and contamination remediation strategies.

Anaerobic treatment of groundwater co-contaminated by toluene and copper in a single chamber bioelectrochemical system

Addressing the simultaneous removal of multiple coexisting groundwater contaminants poses a significant challenge, primarily because of their different physicochemical properties. Indeed, different chemical compounds may necessitate establishing distinct, and sometimes conflicting, (bio)degradation and/or removal pathways. In this work, we investigated the concomitant anaerobic treatment of toluene and copper in a single-chamber bioelectrochemical cell with a potential difference of 1 V applied between the anode and the cathode. As a result, the electric current generated by the bioelectrocatalytic oxidation of toluene at the anode caused the abiotic reduction and precipitation of copper at the cathode, until the complete removal of both contaminants was achieved. Open circuit potential (OCP) experiments confirmed that the removal of copper and toluene was primarily associated with polarization. Analogously, abiotic experiments, at an applied potential of 1 V, confirmed that neither toluene was oxidized nor copper was reduced in the absence of microbial activity. At the end of each experiment, both electrodes were characterized by means of a comprehensive suite of chemical and microbiological analyses, evidencing a highly selected microbial community competent in the biodegradation of toluene in the anodic biofilm, and a uniform electrodeposition of spherical Cu2O nanoparticles over the cathode surface.