An ecological microsystem to treat waste oil contaminated soil: Using phytoremediation assisted by fungi and local compost, on a mixed-contaminant site, in a cold climate

A meta-analysis of influencing factors on soil pollution around copper smelting sites

Non-ferrous smelting activities have caused serious heavy metal(loid) pollution in soil which seriously threatens human health globally. A number of studies have been conducted to assess the characteristics and risks of soil heavy metal(loid) pollution around copper (Cu) smelting sites. However, the current research mainly focuses on soil pollution around a single smelter, and the global impact of Cu smelting on soil and its quantitative relationship with related factors need to be further studied. Meta-analysis can integrate a large amount of data and quantitatively analyze the relationship between multiple factors. To investigate the extent to which Cu smelting sites have contributed to heavy metal(loid) pollution in soils, a meta-analysis was conducted on 189 research publications from 1993 to 2023. Furthermore, a single meta regression was used to analyze the relationship between the soil heavy metal(loid)s (HMs) and influencing factors on a global scale. The results of meta-regression analysis showed that compared with the soil background value, Cu smelting significantly increased the concentration of HMs in soil (315%), with the concentration increase for each heavy metal(loid) being: Cu (1012%) > Cd (622%) > As (315%) > Pb (277%) > Zn (188%) > Cr (96%) > Ni (95%) > Mn (45%). Among these, Cu, Cd, and As were the major pollutants in soils around Cu smelting sites. Land use type was a key factor affecting HMs concentrations in surrounding soils, and the influence of non-agricultural land (381%) was greater than that of agricultural land (203%). In addition, the influence of Cu smelting on HMs were negatively correlated with distance (QM=9.86) and positively correlated with latitude (QM=10.7). There was no significant correlation between heavy metal(loid) pollution and soil chemical properties, average annual rainfall and temperature, longitude, or other factors. Our work may be meaningful to the risk control and remediation for Cu smelting sites.

Assembly and functional profile of rhizosphere microbial community during the Salix viminalis-AMF remediation of polycyclic aromatic hydrocarbon polluted soils

Arbuscular mycorrhizal fungi (AMF) are positive to the phytoremediation by improving plant biomass and soil properties. However, the role of AM plants to the remediation of polycyclic aromatic hydrocarbons (PAHs) is yet to be widely recognized, and the impact of AM plants to indigenous microbial communities during remediation remains unclear. In this work, a 90-day study was conducted to assess the effect of AMF-Salix viminalis on the removal of PAHs, and explore the impact to the microbial community composition, abundance, and function. Results showed that AMF-Salix viminalis effectively enhanced the removal of benzo[a]pyrene, and enriched more PAH-degrading bacteria, consisting of Actinobacteria, Chloroflexi, Sphingomonas, and Stenotrophobacter, as well as fungi including Basidiomycota, Pseudogymnoascus, and Tomentella. For gene function, AM willow enhanced the enrichment of genes involved in amino acid synthesis, aminoacyl-tRNA biosynthesis, and cysteine and methionine metabolism pathways. F. mosseae inoculation had a greater effect on alpha- and beta-diversity of microbial genes at 90 d. Additionally, AMF inoculation significantly increased the soil microbial biomass carbon and organic matter concentration. All together, the microbial community assembly and function shaped by AM willow promoted the dissipation of PAHs. Our results support the effectiveness of AM remediation and contribute to reveal the enhancing-remediation mechanism to PAHs using multi-omics data.

Current trends in bioremediation and bio-integrated treatment of petroleum hydrocarbons

Petroleum hydrocarbons and their derivatives constitute the leading group of environmental pollutants worldwide. In the present global scenario, petroleum and natural gas production, exploration, petroleum refining, and other anthropogenic activities produce huge amounts of hazardous petroleum wastes that accumulate in the terrestrial and marine environment. Due to their carcinogenic, neurotoxic, and mutagenic characteristics, petroleum pollutants pose severe risks to human health and exert ecotoxicological effects on the ecosystems. To mitigate petroleum hydrocarbons (PHs) contamination, implementing "green technologies" for effective cleanup and restoration of an affected environment is considered as a pragmatic approach. This review provides a comprehensive outline of newly emerging bioremediation technologies, for instance; nanobioremediation, electrokinetic bioremediation, vermiremediation, multifunctional and sustainably implemented on-site applied biotechnologies such as; natural attenuation, biostimulation, bioaugmentation, bioventing, phytoremediation and multi-process hybrid technologies. Additionally, the scope of the effectiveness and limitations of individual technologies in treating the petroleum hydrocarbon polluted sites are also evaluated.

Main Factors Determining the Scale-Up Effectiveness of Mycoremediation for the Decontamination of Aliphatic Hydrocarbons in Soil

Soil contamination constitutes a significant threat to the health of soil ecosystems in terms of complexity, toxicity, and recalcitrance. Among all contaminants, aliphatic petroleum hydrocarbons (APH) are of particular concern due to their abundance and persistence in the environment and the need of remediation technologies to ensure their removal in an environmentally, socially, and economically sustainable way. Soil remediation technologies presently available on the market to tackle soil contamination by petroleum hydrocarbons (PH) include landfilling, physical treatments (e.g., thermal desorption), chemical treatments (e.g., oxidation), and conventional bioremediation. The first two solutions are costly and energy-intensive approaches. Conversely, bioremediation of on-site excavated soil arranged in biopiles is a more sustainable procedure. Biopiles are engineered heaps able to stimulate microbial activity and enhance biodegradation, thus ensuring the removal of organic pollutants. This soil remediation technology is currently the most environmentally friendly solution available on the market, as it is less energy-intensive and has no detrimental impact on biological soil functions. However, its major limitation is its low removal efficiency, especially for long-chain hydrocarbons (LCH), compared to thermal desorption. Nevertheless, the use of fungi for remediation of environmental contaminants retains the benefits of bioremediation treatments, including low economic, social, and environmental costs, while attaining removal efficiencies similar to thermal desorption. Mycoremediation is a widely studied technology at lab scale, but there are few experiences at pilot scale. Several factors may reduce the overall efficiency of on-site mycoremediation biopiles (mycopiles), and the efficiency detected in the bench scale. These factors include the bioavailability of hydrocarbons, the selection of fungal species and bulking agents and their application rate, the interaction between the inoculated fungi and the indigenous microbiota, soil properties and nutrients, and other environmental factors (e.g., humidity, oxygen, and temperature). The identification of these factors at an early stage of biotreatability experiments would allow the application of this on-site technology to be refined and fine-tuned. This review brings together all mycoremediation work applied to aliphatic petroleum hydrocarbons (APH) and identifies the key factors in making mycoremediation effective. It also includes technological advances that reduce the effect of these factors, such as the structure of mycopiles, the application of surfactants, and the control of environmental factors.

Phytotoxicity of weathered petroleum hydrocarbons in soil to boreal plant species

Canada has extensive petroleum hydrocarbon (PHC) contamination in northern areas and the boreal forest region from historical oil and gas activities. Since the 2013 standardization of boreal forest species for plant toxicity testing in Canada, there has been a need to build the primary literature of the toxicity of weathered PHCs to these species. A series of toxicity experiments were carried out using fine-grained (<0.005-0.425 mm) background (100 total mg/kg total PHCs) and weathered contaminated soil (11,900 mg/kg total PHCs) collected from a contaminated site in northern Ontario, Canada. The PHC mixture in the contaminated site soil was characterized through Canadian Council of Ministers of the Environment Fractions, as indicated by the number equivalent normal straight-chain hydrocarbons (nC). The soil was highly contaminated with Fraction 2 (>nC10 to nC16) at 4790 mg/kg and Fraction 3 (>nC16 to nC34) at 4960 mg/kg. Five plant species (Elymus trachycaulus, Achillea millefolium, Picea mariana, Salix bebbiana, and Alnus viridis) were grown from seed in 0%, 25%, 50%, 75%, and 100% relative contamination mixtures of the PHC-contaminated and background soil from the site over 2-6 weeks. All five species showed significant inhibition in shoot length, shoot weight, root length, and/or root weight (Kruskal-Wallis Tests: p < 0.05, df = 4.0). Measurements of 25% inhibitory concentrations (IC25) following PHC toxicity experiments revealed that S. bebbiana was most significantly impaired by the PHC-contaminated soil (410-990 mg/kg total PHCs), where it showed <35% germination. This study indicates that natural weathering of Fraction 2- and Fraction 3-concentrated soil did not eliminate phytotoxicity to boreal plant species. Furthermore, it builds on the limited existing literature for toxicity of PHCs on boreal plants and supports site remediation to existing Canadian provincial PHC guidelines.

Techno-economic analysis of phytoremediation: A strategic rethinking

Phytoremediation is a cost-effective and environmentally sound approach, which uses plants to immobilize/stabilize, extract, decay, or lessen toxicity and contaminants. Despite successful evidence of field application, such as natural attenuations, and self-purification, the main barriers remain from a "promising" to a "commercial" approach. Therefore, the ultimate goal of this paper is to examine factors that contribute to phytoremediation's underutilization and discuss the real costs of phytoremediation when the time and land values are considered. We revisit mechanisms and processes of phytoremediation. We synthesize existing information and understanding based on previous works done on phytoremediation and its applications to provide the technical assessment and perspective views in the commercial acceptance of phytoremediation. The results show that phytoremediation is the most suitable for remote regions with low land values. Since these regions allow a longer period to be restored, land vegetation covers can be established in more or less time like natural attenuation. Since the length of phytoremediation is an inherent limitation, this inherent disadvantage limits its adoption in developed business regions, such as growing urban areas. Because high land values could not be recovered in the short term, phytoremediation is not cost-effective in those regions. We examine the potential measures that can enhance the performance of phytoremediation, such as soil amendments, and agricultural practices. The results obtained through review can clarify where/what conditions phytoremediation can provide the most suitable solutions at a large scale. Finally, we identify the main barriers and knowledge gaps to establishing a vegetation cover in large-scale applications and highlight the research priorities for increased acceptance of phytoremediation.

Characterization and genome analysis of Acinetobacter oleivorans S4 as an efficient hydrocarbon-degrading and plant-growth-promoting rhizobacterium

Plant-growth-promoting rhizobacteria (PGPR) have received increasing attention for assisting phytoremediation. However, the effect of PGPR on total petroleum hydrocarbon (TPH) degradation and plant growth promotion and its underlying mechanism is not well understood. In this study, phenotypic analysis and whole genome sequencing were conducted to comprehensively characterize a newly isolated rhizobacterium strain S4, which was identified as Acinetobacter oleivorans, from a TPH-contaminated soil. The strain degraded 62.5% of initially spiked diesel (1%) in minimal media within six days and utilized n-alkanes with a wide range of chain length (i.e., C₁₂ to C₄₀). In addition, the strain showed phenotypic traits beneficial to plant growth, including siderophore production, indole-3-acetic acid synthesis and phosphate solubilization. Potential metabolic pathways and genes encoding proteins responsible for the phenotypic traits were identified. In a real TPH-contaminated soil, inoculation of Acinetobacter oleivorans S4 significantly enhanced the growth of tall fescue relative to the soil without inoculation. In contrast, inoculation of Bacillus sp. Z7, a hydrocarbon-degrading strain, showed a negligible effect on the growth of tall fescue. The removal efficiency of TPH with inoculation of Acinetobacter oleivorans S4 was significantly higher than those without inoculation or inoculation of Bacillus sp. Z7. These results suggested that traits of PGPR beneficial to plant growth are critical to assist phytoremediation. Furthermore, heavy metal resistance genes and benzoate and phenol degradation genes were found in the genome of Acinetobacter oleivorans S4, suggesting its application potential in broad scenarios.

What happens to gut microorganisms and potential repair mechanisms when meet heavy metal(loid)s

Heavy metal (loid) pollution is a significant threat to human health, as the intake of heavy metal (loid)s can cause disturbances in intestinal microbial ecology and metabolic disorders, leading to intestinal and systemic diseases. Therefore, it is important to understand the effects of heavy metal (loid)s on intestinal microorganisms and the necessary approaches to restore them after damage. This review provides a summary of the effects of common toxic elements, such as lead (Pb), cadmium (Cd), chromium (Cr), and metalloid arsenic (As), on the microbial community and structure, metabolic pathways and metabolites, and intestinal morphology and structure. The effects of heavy metal (loid)s on metabolism are focused on energy, nitrogen, and short-chain fatty acid metabolism. We also discussed the main solutions for recovery of intestinal microorganisms from the effects of heavy metal (loid)s, namely the supplementation of probiotics, recombinant bacteria with metal resistance, and the non-toxic transformation of heavy metal (loid) ions by their own intestinal flora. This article provides insight into the toxic effects of heavy metals and As on gut microorganisms and hosts and provides additional therapeutic options to mitigate the damage caused by these toxic elements.

Exploring the significance of nanomaterials and organic amendments - Prospect for phytoremediation of contaminated agroecosystem

Emerging micro-pollutants have rapidly contaminated the agro-ecosystem, posing serious challenges to a sustainable future. The vast majority of them have infiltrated the soil and damaged agricultural fields and crops after being released from industry. These pollutants and their transformed products are also transported in vast quantities which further exacerbate the damage. Sustainable remediation techniques are warranted for such large amounts of contaminants. As aforementioned, many of them have been detected at very high concentrations in soil and water which adversely affect crop physiology by disrupting different metabolic processes. To combat this situation, nanomaterials and other organic amendments assisted phytoremediation ware considered as a viable alternative. It is a potent synergistic activity between the biological system and the supplied organic or nanomaterial material to eliminate emerging contaminants and micropollutants from crop fields. This can be effectively be applied to degraded crop fields and could potentially embody a green technology for sustainable agriculture.

Understanding the Implications of Predicted Function for Assessment of Rapid Bioremediation in a Farmland-Oilfield Mixed Area

Farmland-oilfield mixed areas are fragile ecosystems that require dynamic remediation to counteract the undesirable impact of energy development. Practicable assessment methods are pivotal to a fast and accurate evaluation of the in situ bioremediation process. Petroleum pollutants impose component-dependent effects on autochthonous microbiota before and after remediation. Here, the predicted functional response of soil microbiomes to petroleum pollutants was analyzed in a historically polluted farmland-oilfield mixed area from the perspective of developing a set of feasible biomarkers for immediate post-bioremediation evaluation. An array of microbial, genetic, systematic, and phenotypic biomarkers was proposed. Our results showed that the biomarkers could proxy the stage of the bioremediation multidimensionally. We argue that functional diversity should be considered together with microbial community dynamic to evaluate the restoration status of the microbial communities in petroleum-contaminated farmland-oilfield mixed environments.

Salix purpurea and Eleocharis obtusa Rhizospheres Harbor a Diverse Rhizospheric Bacterial Community Characterized by Hydrocarbons Degradation Potentials and Plant Growth-Promoting Properties

Phytoremediation, a method of phytomanagement using the plant holobiont to clean up polluted soils, is particularly effective for degrading organic pollutants. However, the respective contributions of host plants and their associated microbiota within the holobiont to the efficiency of phytoremediation is poorly understood. The identification of plant-associated bacteria capable of efficiently utilizing these compounds as a carbon source while stimulating plant-growth is a keystone for phytomanagement engineering. In this study, we sampled the rhizosphere and the surrounding bulk soil of Salixpurpurea and Eleocharis obusta from the site of a former petrochemical plant in Varennes, QC, Canada. Our objectives were to: (i) isolate and identify indigenous bacteria inhabiting these biotopes; (ii) assess the ability of isolated bacteria to utilize alkanes and polycyclic aromatic hydrocarbons (PAHS) as the sole carbon source, and (iii) determine the plant growth-promoting (PGP) potential of the isolates using five key traits. A total of 438 morphologically different bacterial isolates were obtained, purified, preserved and identified through PCR and 16S rRNA gene sequencing. Identified isolates represent 62 genera. Approximately, 32% of bacterial isolates were able to utilize all five different hydrocarbons compounds. Additionally, 5% of tested isolates belonging to genera Pseudomonas, Acinetobacter, Serratia, Klebsiella, Microbacterium, Bacillus and Stenotrophomonas possessed all five of the tested PGP functional traits. This culture collection of diverse, petroleum-hydrocarbon degrading bacteria, with multiple PGP traits, represents a valuable resource for future use in environmental bio- and phyto-technology applications.

Rhizoremediation as a green technology for the remediation of petroleum hydrocarbon-contaminated soils

Rhizoremediation is increasingly becoming a green and sustainable alternative to physico-chemical methods for remediation of contaminated environments through the utilization of symbiotic relationship between plants and their associated soil microorganisms in the root zone. The overall efficiency can be enhanced by identifying suitable plant-microbe combinations for specific contaminants and supporting the process with the application of appropriate soil amendments. This approach not only involves promoting the existing activity of plants and soil microbes, but also introduces an adequate number of microorganisms with specific catabolic activity. Here, we reviewed recent literature on the main mechanisms and key factors in the rhizoremediation process with a particular focus on soils contaminated with total petroleum hydrocarbon (TPH). We then discuss the potential of different soil amendments to accelerate the remediation efficiency based on biostimulation and bioaugmentation processes. Notwithstanding some successes in well-controlled environments, rhizoremediation of TPH under field conditions is still not widespread and considered less attractive than physico-chemical methods. We catalogued the major pitfalls of this remediation approach at the field scale in TPH-contaminated sites and, provide some applicable situations for the future successful use of in situ rhizoremediation of TPH-contaminated soils.

Ectomycorrhizal Fungal Inoculation of Sphaerosporella brunnea Significantly Increased Stem Biomass of Salix miyabeana and Decreased Lead, Tin, and Zinc, Soil Concentrations during the Phytoremediation of an Industrial Landfill

Fast growing, high biomass willows (Salix sp.) have been extensively used for the phytoremediation of trace element-contaminated environments, as they have an extensive root system and they tolerate abiotic stressors such as drought and metal toxicity. Being dual mycorrhizal plants, they can engage single or simultaneous symbiotic associations with both arbuscular mycorrhizal (AM) fungi and ectomycorrhizal (EM) fungi, which can improve overall plant health and growth. The aim of this study was to test the effect of these mycorrhizal fungi on the growth and trace element (TE) extraction potential of willows. A field experiment was carried out where we grew Salix miyabeana clone SX67 on the site of a decommissioned industrial landfill, and inoculated the shrubs with an AM fungus Rhizophagus irregularis, an EM fungus Sphaerosporella brunnea, or a mixture of both. After two growing seasons, the willows inoculated with the EM fungus S. brunnea produced significantly higher biomass. Ba, Cd and Zn were found to be phytoextracted to the aerial plant biomass, where Cd presented the highest bioconcentration factor values in all treatments. Additionally, the plots where the willows received the S. brunnea inoculation showed a significant decrease of Cu, Pb, and Sn soil concentrations. AM fungi inoculation and dual inoculation did not significantly influence biomass production and soil TE levels.

Plant-assisted remediation of hydrocarbons in water and soil: Application, mechanisms, challenges and opportunities

Due to the increasing importance of diesel and petroleum for industrial development during the last century, petrochemical effluents have significantly contributed to the pollution of aquatic and soil environments. The contamination generated by petroleum hydrocarbons can endanger not only humans but also the environment. Phytoremediation or plant-assisted remediation can be considered one of the best technologies to manage petroleum product-contaminated water and soil. The main advantages of this method are that it is environmentally-friendly, potentially cost-effective and does not require specialised equipment. The scope of this review includes a description of hydrocarbon pollutants from petrochemical industries, their toxicity impacts and methods of treatment and degradation. The major emphasis is on phytodegradation (phytotransformation) and rhizodegradation since these mechanisms are the most favourable alternatives for soil and water reclamation of hydrocarbons using tropical plants. In addressing these issues, this review also covers challenges to retrieve the environment (soil and water) from petroleum contaminations through phytoremediation, and its opportunities to remove or reduce the negative environmental impacts of petroleum contaminations and restore damaged ecosystems with sustainable ways to keep healthy life for the future.

Mycoremediation: Expunging environmental pollutants

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Mycoremediation of polycyclic aromatic hydrocarbons, challenges, and strategies to overcome.

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Role of the fungi in eradicating heavy metal contamination from the polluted sites.

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Mycoremediation of agricultural wastes including pesticides, herbicides, and cyanotoxins.

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Pharmaceutical wastes and strategies for its remediation using white-rot and ligninolytic fungus.

The ever-increasing population, rapid rate of urbanization, and industrialization are exacerbating the pollution-related problems. Soil and water pollution affect human health and the ecosystem. Thus, it is crucial to develop strategies to combat this ever-growing problem. Mycoremediation, employing fungi or its derivatives for remediation of environmental pollutants, is a comparatively cost-effective, eco-friendly, and effective method. It has advantages over other conventional and bioremediation methods. In this review, we have elucidated the harmful effects of common pollutants on public health and the environment. The role of several fungi in degrading these pollutants such as heavy metals, agricultural, pharmaceutical wastes, including polycyclic aromatic hydrocarbons, is enumerated. Future strategies to improve the rate and efficiency of mycoremediation are suggested. The manuscript describes the strategies which can be used as a future framework to address the global problem of pollution.