Bioremediation mechanisms of combined pollution of PAHs and heavy metals by bacteria and fungi: A mini review

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) are predominant pollutants linked with anthropogenic activities across a host of environmental mediums. The level of pollution, ecological and health risk were assessed in surface water from Ekulu in Enugu metropolis, Nigeria for 17 PAHs and selected HMs (As, Cd, Cr, Cu, Pb, Ni, Zn) components. PAHs and HMs were determined using a gas chromatography-flame ionization detector (GC-FID) and atomic adsorption spectrophotometer (AAS). The total PAHs in station A (3.17mg/l), B (1.51mg/l), and C (1.83mg/l) were due to high molecular weight (HMW) PAHs than low molecular weight (HMW) PAHs. HMs contents were within USEPA and WHO minimum contamination levels (MCL) except Cr and Pb. The molecular diagnostics of PAHs showed that incomplete combustion of carbonaceous compounds was dominant, while petrogenic was insignificant across all samples. The ecological indices of PAHs and HMs varied from medium to high pollution due to anthropogenic activities that pose a threat to the ecosystem. The non-carcinogenic models showed that hazard index (HI) ranged from PAHs (0.027 – 0.083) and HMs (0.0067 – 0.087) which is less than unity implying no adverse health issues. The lifetime cancer risk (LCR) for PAHs (4.21×10–4 – 9.61×10–4) and HMs (1.72×10–5 – 3.98×10–5) suggested significant cancer risk is possible over some time for a population of 1 in 10,000 and 100,000 for both PAHs and HMs exposure for 70 years. Therefore, there is an urgent need for proper pollution control and mitigation plan to preserve both age groups from being continuously exposed to anthropogenic activities in the Ekulu River and further study should be carried out to monitor the available toxicants.

In this study, samples were taken of the surface dust of main roads in Xinxiang City, and the concentrations of five heavy metals (Cd, Pb, Cr, Cu and Zn) and fifteen polycyclic aromatic hydrocarbons (PAHs) were determined by inductively coupled plasma mass spectrometry (ICP-MS) and gas chromatography-mass spectrometry (GC-MS), respectively. Meanwhile, the effects of vehicle emissions on the pollution characteristics were investigated. The results showed that the concentrations of heavy metals and PAHs ranged from 2.58 to 1560 mg·kg-1 and ND to 1.30 mg·kg-1, respectively. Overall, the concentrations of heavy metals and PAHs increased with a decrease in dust particle size. In terms of composition, the heavy metals were dominated by Zn while the high-molecular-weight PAHs were mainly homologous. In spatial distribution, the concentrations of heavy metals and PAHs were different. The total concentrations of heavy metals in road dust near Renmin Road, Xiaodian Industrial Park, and Cement Plant were the highest, while the high concentrations of PAHs appeared in the dust of Renmin Road, Upper Expressway, and 107 National Highway. Pearson correlation analysis showed that there was no positive correlation between the five heavy metals and fifteen PAHs. Then cluster analysis and factor analysis indicated that the PAHs were greatly affected by vehicle emissions, while the heavy metals were basically unaffected.

Heavy metals contamination is a serious threat to all life forms. Long term exposure of heavy metals can lead to different life-threatening medical conditions including cancers of different body parts. Phytoremediation and bioremediation offer a potential eco-friendly solution to such problems. Different microbes can interact with heavy metals in a variety of ways such as biotransformation, oxidation/reduction, and biosorption. Phytoremediation of the heavy metals using plants mostly involves rhizofilteration, phytoextraction, phytovolatization, and Phyto stabilization. A synergistic approach using both plants and microbes has proven much more efficient as compared to the individual applications of microbes or plants. This article aims to highlight the synergistic methods used in bioremediation, emphasizing the potent collaboration between bacteria and plants for environmental cleaning, along with the discussion of the importance of site-specific variables and potential constraints. While identifying the necessity for all-encompassing solutions, this review places emphasis on the combination of methodologies as a multifarious rehabilitation approach. This discussion offers insightful suggestions for scholars, scientists and decision-makers about the sustainable recovery of heavy metal-contaminated environments using a comprehensive strategy. REFERENCES Ankit, Bauddh K, Korstad J (2022). Phycoremediation: Use of algae to sequester heavy metals. Hydrobiol. 1(3): 288-303. Arantza SJ, Hiram MR, Erika K, Chávez-Avilés MN, Valiente-Banuet JI, Fierros-Romero G (2022). Bio-and phytoremediation: Plants and microbes to the rescue of heavy metal polluted soils. SN Appl. Sci. 4(2): 59. Azubuike CC, Chikere CB, Okpokwasili GC (2016). Bioremediation techniques–classification based on site of application: principles, advantages, limitations and prospects. World J. Microbiol. Biotechnol. 32: 1-18. Berti WR, Cunningham SD (2000). Phytostabilization of metals. Phytoremediation of toxic metals: Using plants to clean up the environment. Wiley, New York. 71-88. Bingöl NA, Özmal F, Akın B (2017). Phytoremediation and biosorption potential of Lythrum salicaria for nickel removal from aqueous solutions. Pol. J. Environ. Stud. 26(6): 2479-2485. Chandra R, Saxena G, Kumar V (2015). Phytoremediation of environmental pollutants: an eco-sustainable green technology to environmental management, In Advances in biodegradation and bioremediation of industrial waste. 1-29. Chaudhary K, Agarwal S, Khan S (2018). Role of phytochelatins (PCs), metallothioneins (MTs), and heavy metal ATPase (HMA) genes in heavy metal tolerance, In Mycoremediation and Environmental Sustainability. Volume 2: 39-60. Choudhary M, Kumar R, Datta A, Nehra V, Garg N (2017). Bioremediation of heavy metals by microbes, In Bioremediation of salt affected soils: an Indian perspective. 233-255. Chugh M, Kumar L, Shah MP, Bharadvaja N (2022). Algal bioremediation of heavy metals: An insight into removal mechanisms, recovery of by-products, challenges, and future opportunities. Energy Nexus. 7:100129. Congeevaram S, Dhanarani S, Park J, Dexilin M, Thamaraiselvi K (2007). Biosorption of chromium and nickel by heavy metal resistant fungal and bacterial isolates. J. Hazard. Mat. 146(1-2): 270-277. Cristaldi A, Conti GO, Jho EH, Zuccarello P, Grasso A, Copat C, Ferrante M (2017). Phytoremediation of contaminated soils by heavy metals and PAHs. A brief review. Environ. Technol. Inno. 8: 309-326. Crusberg T, Mark S. (2000). Heavy metal remediation of wastewaters by microbial biotraps, In Springer. 123-137. Emenike CU, Jayanthi B, Agamuthu P, Fauziah S (2018). Biotransformation and removal of heavy metals: a review of phytoremediation and microbial remediation assessment on contaminated soil. Environ. Rev. 26(2): 156-168. Ghosh M, Singh S (2005). A review on phytoremediation of heavy metals and utilization of it’s by products. Asian J. Energy Environ. 6(4): 18. Guignardi Z, Schiavon M (2017). Biochemistry of plant selenium uptake and metabolism, In Selenium in plants: molecular, physiological, ecological and evolutionary aspects. 21-34. Hong-Bo S, Li-Ye C, Cheng-Jiang R, Hua L, Dong-Gang G, Wei-Xiang L (2010). Understanding molecular mechanisms for improving phytoremediation of heavy metal-contaminated soils. Crit. Rev. Biotechnol. 30(1): 23-30. Igiri BE, Okoduwa SI, Idoko GO, Akabuogu EP, Adeyi AO, Ejiogu IK (2018). Toxicity and bioremediation of heavy metals contaminated ecosystem from tannery wastewater: a review. J. Toxicol. 2018. Jabeen R, Ahmad A, Iqbal M (2009). Phytoremediation of heavy metals: physiological and molecular mechanisms. Bot. Rev. 75: 339-364. Joshi P, Swarup A, Maheshwari S, Kumar R, Singh N (2011). Bioremediation of heavy metals in liquid media through fungi isolated from contaminated sources. Indian J. Microbiol. 51: 482-487. Junaid M, Hashmi MZ, Tang YM, Malik RN, Pei,DS (2017). Potential health risk of heavy metals in the leather manufacturing industries in Sialkot, Pakistan. Sci. Rep. 7(1): 8848. Kapahi M, Sachdeva S (2019). Bioremediation options for heavy metal pollution. J. Health Pollut. 9(24): 191203. Lebeau T, Jézéquel K, Braud A (2011). Bioaugmentation-assisted phytoextraction applied to metal-contaminated soils: state of the art and future prospects, In Microbes and Microbial Technology: Agricultural and Environmental Applications. 229-266. Leong YK, Chang JS (2020). Bioremediation of heavy metals using microalgae: Recent advances and mechanisms. Bioresour.Technol. 303: 122886. Limmer M, Burken J (2016). Phytovolatilization of organic contaminants. Environ. Sci. Technol. 50(13): 6632-6643. Ma Y, Oliveira RS, Freitas H, Zhang C (2016). Biochemical and molecular mechanisms of plant-microbe-metal interactions: relevance for phytoremediation. Front. Plant Sci. 7: 918. Manzoor M, Gul I, Ahmed I, Zeeshan M, Hashmi I, Amin BAZ, Kallerhoff J, Arshad M (2019). Metal tolerant bacteria enhanced phytoextraction of lead by two accumulator ornamental species. Chemosphere. 227: 561-569. Mueller B, Rock S, Gowswami D, Ensley D (1999). Phytoremediation decision tree. Prepared by-Interstate Technology and Regulatory Cooperation Work Group. 1-36. Nies DH (1999). Microbial heavy-metal resistance. Appl. Microbiol. Biotechnol. 51: 730-750. Nies DH, Silver S (1995). Ion efflux systems involved in bacterial metal resistances. J. Ind. 14: 186-199. Pande V, Pandey SC, Sati D, Bhatt P, Samant M (2022). Microbial interventions in bioremediation of heavy metal contaminants in agroecosystem. Front. Microbiol. 13: 824084. Pandey VC, Bajpai O (2019). Phytoremediation: from theory toward practice, In Phytomanagement of polluted sites. 1-49. Robinson BH, Leblanc M, Petit D, Brooks RR, Kirkman JH, Gregg PE (1998). The potential of Thlaspi caerulescens for phytoremediation of contaminated soils. Plant Soil. 203: 47-56. Romantschuk M, Lahti-Leikas K, Kontro M, Allen JA, Sinkkonen A (2023). Bioremediation of contaminated soil and groundwater by in situ Front. Microbiol. 14: 1258148. Sabreena, Hassan S, Bhat SA, Kumar V, Ganai BA, Ameen F (2022). Phytoremediation of heavy metals: An indispensable contrivance in green remediation technology. Plants. 11(9): 1255. Saha L, Tiwari J, Bauddh K, Ma Y (2021). Recent developments in microbe–plant-based bioremediation for tackling heavy metal-polluted soils. Front. Microbiol. 12: 731723. Sharma I. (2020). Bioremediation techniques for polluted environment: concept, advantages, limitations, and prospects, In Trace metals in the environment-new approaches and recent advances. IntechOpen. Sharma JK, Kumar N, Singh NP, Santal, AR (2023). Phytoremediation technologies and their mechanism for removal of heavy metal from contaminated soil: An approach for a sustainable environment. Front. Plant Sci. 14: 1076876. Shen X, Dai M, Yang J, Sun L, Tan X, Peng C, Ali I, and Naz I (2022). A critical review on the phytoremediation of heavy metals from environment: Performance and challenges. Chemosphere. 291: 132979. Silver S (2011). BioMetals: a historical and personal perspective. Biometals. 24(3): 379-390. Silver S, Phung LT (2005). A bacterial view of the periodic table: genes and proteins for toxic inorganic ions. J. Ind. Microbiol. Biotechnol. 32: 587-605. Singh N, Santal AR (2015). Phytoremediation of heavy metals: the use of green approaches to clean the environment, In Phytoremediation: Management of Environmental Contaminants. Volume 2: 115-129. Strong PJ, Burgess JE (2008). Treatment methods for wine-related and distillery wastewaters: a review. Bioremediation J. 12(2): 70-87. Syranidou E, Christofilopoulos S, Gkavrou G, Thijs S, Weyens N, Vangronsveld J, Kalogerakis N (2016). Exploitation of endophytic bacteria to enhance the phytoremediation potential of the wetland helophyte Juncus acutus. Front. Microbiol. 7: 1016. Umrania VV (2006). Bioremediation of toxic heavy metals using acidothermophilic autotrophes. Bioresour. Technol. 97(10): 1237-1242. Valls M, De Lorenzo V (2002). Exploiting the genetic and biochemical capacities of bacteria for the remediation of heavy metal pollution. FEMS Microbiol. Rev. 26(4): 327-338. Verma P, George K, Singh H, Singh S, Juwarkar A, Singh R (2006). Modeling rhizofiltration: heavy-metal uptake by plant roots. Environ. Model. Assess. 11: 387-394. Wu Y, Li Z, Yang Y, Purchase D, Lu Y, Dai Z (2021). Extracellular polymeric substances facilitate the adsorption and migration of Cu2+ and Cd2+ in saturated porous media. Biomolecules. 11(11): 1715. Wuana RA, Okieimen FE (2011). Heavy metals in contaminated soils: a review of sources, chemistry, risks and best available strategies for remediation. International Scholarly Research Notices. Yan A, Wang Y, Tan SN, Mohd Yusof ML, Ghosh S, Chen Z (2020). Phytoremediation: a promising approach for revegetation of heavy metal-polluted land. Front. Plant Sci. 11: 359. Zhang Y, Hu J, Bai J, Wang J, Yin R, Wang J, and Lin X (2018). Arbuscular mycorrhizal fungi alleviate the heavy metal toxicity on sunflower (Helianthus annuus) plants cultivated on a heavily contaminated field soil at a WEEE-recycling site. Sci. Total Environ. 628: 282-290.

This study assessed the heavy metals and polycyclic aromatic hydrocarbons (PAHs) pollutant in soil around petrol filling stations and automobile mechanic workshops. Samples of soil were acquired from the depth range of 0–15 cm. Toxic heavy metals were analyzed with atomic absorption spectrophotometry. The PAHs were analyzed using phytochemical chromatographic analysis by the Soxhlet extraction method. The soil tested was weakly acidic (6.12–6.81). The trend of the heavy metals’ mean levels in soil followed the order: lead (Pb) > nickel (Ni) > vanadium (V) > cadmium (Cd). The mean levels of PAHs were in the order: 1,2-benzanthracene pyrene > anthracene > fluorene > benzo(b)fluoranthene > 1,1,2-benzopyrelene (BghiP) > naphthalene (Naph) > Dibenz(a, h)anthracene > 1, 2 benzanthracene > benzo(k)fluoranthene > phenanthrene > pyrene > xylene > acenapthylene. Pearson correlation and principal component analysis (PCA) revealed the heavy metals were generated from automobile exhaust and parent rocks. Soil pollution index and Numerov composite pollution index revealed that the soil is safe, clean, and unpolluted with heavy metals. The mean levels of heavy metals were below the European Union (2006) permissible values for uncontaminated soil. The PAH mean values were within permissible standards for unpolluted agricultural, forest, and residential soils. The diagnostic ratios of PAHs, supported by PCA, showed that PAHs in soil were produced by pyrogenic and internal combustion of gasoline and kerosene. This method of soil contamination assessment by heavy metals and PAHs is invaluable for pollution assessors in Nigeria and another area in the world.

It is a challenging issue to investigate the combined pollution of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in urban soils. The purpose of this study was to determine the concentrations of these two pollutants in soils in Shenyang, Fushun, and Fushun New District, to analyze their distribution, their interaction, and co-contamination levels. The concentrations of heavy metals were measured by inductively coupled plasma mass spectrometry (ICP-MS), while the concentrations of 21 kinds of PAH were analyzed by gas chromatography-mass spectrometry (GC-MS). Based on the analysis of pollution concentrations and distribution patterns, the intrinsic links between heavy metals and PAHs in three different cities were assessed using a variety of multivariate analysis methods. Compared to Shenfu New District, the concentration of pollutants in Shenyang and Fushun shows a higher level. Moreover, the results of redundancy analysis (RDA) of samples may quantify the possibility of combined pollution of different heavy metal elements and PAHs. This study also affirms the important role of multivariate analysis in being used to reveal the complex interactions and spatial distribution of different pollutants.

Distribution pattern and ecological risk assessment of heavy metals and PAHs in sediments of the entrance of Musa estuary, Persian Gulf to establish desalination plant

With increased urbanization and industrialization, modern life has led to an anthropogenic impact on the biosphere. Heavy metals pollution and pollutants from black liquor (BL) have caused severe effects on environment and living organisms. Bacterial biofilm has potential to remediate heavy metals and remove BL from the environment. Hence, this study was planned to investigate the potential of microbial biofilms for the bioremediation of heavy metals and BL polluted environments. Eleven biofilm forming bacterial strains (SB1, SB2, SC1, AF1, 5A, BC-1, BC-2, BC-3, BC-4, BC-5 and BC-6) were isolated and identified upto species level via 16S rRNA gene sequencing. Biofilm strains belonging to Bacillus and Lysinibacillus sphaericus were used to remediate heavy metals (Pb, Ni, Mn, Zn, Cu, and Co). Atomic absorption spectroscopy showed significantly high (P ≤ 0.05) bioremediation potential by L. sphaericus biofilm (1462.0 ± 0.67µgmL-1) against zinc (Zn). Similarly, Pseudomonas putida biofilm significantly (P ≤ 0.05) decolourized (65.1%) BL. Fourier transform infrared (FTIR) analysis of treated heavy metals showed the shifting of major peaks (1637 & 1629-1647, 1633 & 1635-1643, and 1638-1633cm-1) corresponding to specific amide groups due to C = O stretching. The study suggested that biofilm of the microbial flora from tanneries and pulp paper effluents possesses a strong potential for heavy metals bioremediation and BL decolourization. To our knowledge, this is the first report showing promising biofilm remediation potential of bacterial flora of tanneries and pulp-paper effluent from Kasur and Sheikhupura, Punjab, Pakistan, against heavy metals and BL.

Co-toxicity and co-contamination remediation of polycyclic aromatic hydrocarbons and heavy metals: Research progress and future perspectives

Improved microbial-plant soil bioremediation of PAHs and heavy metal through in silico methods

Sedimentary records of polycyclic aromatic hydrocarbons from three enclosed lakes in China: Response to energy structure and economic development

The frequent incidents of oil spills and other forms of pollution arising from crude oil exploration and exploitation (OEE) in the Niger Delta have caused several investigations on Polycyclic Aromatic Hydrocarbons (PAHs) pollution. This study aimed at developing a comprehensive report on PAH pollution and its human health risks recorded in the Niger Delta. Studies were extracted from Google Scholar, PubMed, and ResearchGate using a defined selection criterion. The quality of each study was assessed using the Newcastle – Ottawa Scale. Thirty-eight studies were selected with the majority reporting on PAH pollution in aquatic environments. Across all the selected studies, the total number of PAHs recorded ranged from 7 to 28 PAH congeners. Also, PAH potential sources reported in the studies were of pyrogenic and petrogenic sources. PAH concentrations recorded in water, sediment, aquatic organisms (fish and shrimp), soil, dust, and crop samples ranged from below detection limit (BDL) to 450 ± 117.9 mg/L, BDL to 1821.5 mg/kg, 0.005 to 1.098 mg/kg, ND to 4154 ± 3461 mg/kg, 165.1 to 1012 mg/kg, and 0.020 to 3.37 mg/kg, respectively. The majority of the selected studies reported PAH levels which were higher than the permissible limits. Incremental Lifetime Cancer Risk (ILCR) assessment of PAHs in samples ranged from low to high via ingestion and dermal routes of exposure to humans. It is recommended that the Federal Government of Nigeria promotes environmentally friendly operations of OEE. Future studies should focus on PAH pollution in farmlands, ambient air, and the associated human and ecological health risks.

Combined pollution of heavy metals and polycyclic aromatic hydrocarbons in non-ferrous metal smelting wastewater treatment plant: Distribution profiles, removal efficiency, and ecological risks to receiving river.

Purpose Submerged macrophyte Vallisneria spiralis and sediment microbial fuel cell (SMFC) systems are cost-effective methods for the remediation of polycyclic aromatic hydrocarbon (PAH)-polluted sediments. This study evaluates whether the combination of these two ecological approaches could further improve the removal efficiency of PAHs from sediments and investigates the possible mechanisms of removal. Materials and methods Sediments, macrophytes, electrodes, and plexiglass columns were used to construct an experimental microcosm. A 65-day comparative study was performed with six treatments as follows: SMFC without PAH (SMFC); PAH only (PAH); SMFC with PAH (SMFC-PAH); V. spiralis without PAH (macrophyte); V. spiralis with PAH (macrophyte-PAH); V. spiralis with SMFC and PAH (M-SMFC-PAH). Pyrene and phenanthrene were added to raw sediments to obtain initial PAH concentrations of 10 mgkg(-1) dry sediment. The monitored parameters were sediment oxidation-reduction potential (ORP); low molecular weight organic acids (LMWOAs) and Fe (II) concentrations in pore water; electron acceptor (sulfate and Fe (III)), humic acid (HA), and PAH concentrations in sediments; and plant morphology and root physiology. High-throughput 16S rRNA gene sequencing was also performed to assist mechanistic understanding. Results and discussion The M-SMFC-PAH treatment obtained the highest sediment ORP and PAH removal efficiency. The average ORP level in M-SMFC-PAH was increased by 57.2, 59.1, and 168.4 mV, compared with the SMFC-PAH, macrophyte-PAH, and PAH-only treatments, respectively, with a mean value of 121.7 mV observed during the whole experimental period. The pyrene (phenanthrene) dissipation ratios at the end of the experimental period were 29.1% (35.4%), 45.5% (56.3%), 59.8% (67.3%), and 79.4% (88.2%) for PAH only, SMFC-PAH, macrophyte-PAH, and M-SMFC-PAH treatments, respectively. The highest correlation was observed between PAH concentration and sediment ORP value, in the coupled M-SMFC-PAH system. Conclusions Results suggest that the interactions between the anode and rhizosphere of V. spiralis were synergistic during PAH removal. The coexistence of anodic and rhizospheric oxygen loss in sediments had a synergistic effect on PAH degradation. Plant presence facilitated the electrogenic degradation of PAHs. The inhibited growth of V. spiralis due to PAH toxicity was reduced by electrogenesis, thus facilitating the removal of vegetable PAHs from sediments. Coordinated growth of anaerobic and aerobic PAH degrading bacteria on the anode was a key factor in the optimal removal of PAHs in coupled systems.

BOOK REVIEW article Front. Microbiol., 11 January 2016Sec. Microbiotechnology Volume 6 - 2015 | https://doi.org/10.3389/fmicb.2015.01555

The presence of soils contaminated with polycyclic aromatic hydrocarbons and heavy metals presents a widespread environmental challenge in industrial areas. Unlike single-pollutant systems, co-pollution by polycyclic aromatic hydrocarbons and heavy metals exhibits synergistic toxicity that weakens traditional remediation technologies. This review systematically examines microbial remediation strategies for such co-polluted soils, focusing on three levels of intervention: functional microorganisms, compost-based enhancement, and engineered microbial solutions. We highlight the role of noncovalent interactions, especially cation-π bonding and hydrophobic partitioning, in decreasing pollutant bioavailability and increasing co-toxicity. Functional microbes improve pollutant removal through intracellular transformation, extracellular secretion of biosurfactants and chelators, and surface adsorption. Compost-enhanced systems incorporating biochar, vermicompost, and mycorrhizal fungi demonstrate improved pollutant breakdown and soil health. Engineered microbes offer advanced remediation capabilities but face challenges related to metabolic load, ecological safety, and regulation. Despite promising laboratory results, field implementation remains limited by low pollutant bioavailability, biosafety concerns, and uncertain cost efficiency. We propose critical future research directions to bridge this gap and enable practical remediation of soils co-contaminated with polycyclic aromatic hydrocarbons and heavy metals.