Palanisami Thavamani

Microbial activity and diversity in long-term mixed contaminated soils with respect to polyaromatic hydrocarbons and heavy metals

The co-occurrence of polyaromatic hydrocarbons (PAHs) with heavy metals and their effect on soil microbial activity have not been systematically investigated. In this study a holistic approach was employed by combining physico-chemical, biological and advanced molecular methods to determine the soil microbial activities of long-term mixed contaminated soils collected from a former manufactured gas plant (MGP) site. Concentrations of PAHs in MGP soils ranged from 335 to 8645 mg/kg. Of the potentially toxic metals, concentrations of lead were found to be highest, ranging from 88 to 671 mg/kg, cadmium 8 to 112 mg/kg, while zinc varied from 64 to 488 mg/kg. The enzyme activities were severely inhibited in soils that were contaminated with both PAHs and heavy metals. The presence of heavy metals in PAH-contaminated soils not only reduced the diversity of microbial population but also showed a few distinctive species by exerting selective pressure. The multivariate analysis revealed that there is an association between PAHs and heavy metals which influenced biological properties in mixed contaminated soils. The findings of this study have major implications for the bioremediation of organic pollutants in metal-organic mixed contaminated sites.

Remediation approaches for polycyclic aromatic hydrocarbons (PAHs) contaminated soils: Technological constraints, emerging trends and future directions.

For more than a decade, the primary focus of environmental experts has been to adopt risk-based management approaches to cleanup PAH polluted sites that pose potentially destructive ecological consequences. This focus had led to the development of several physical, chemical, thermal and biological technologies that are widely implementable. Established remedial options available for treating PAH contaminated soils are incineration, thermal conduction, solvent extraction/soil washing, chemical oxidation, bioaugmentation, biostimulation, phytoremediation, composting/biopiles and bioreactors. Integrating physico-chemical and biological technologies is also widely practiced for better cleanup of PAH contaminated soils. Electrokinetic remediation, vermiremediation and biocatalyst assisted remediation are still at the development stage. Though several treatment methods to remediate PAH polluted soils currently exist, a comprehensive overview of all the available remediation technologies to date is necessary so that the right technology for field-level success is chosen. The objective of this review is to provide a critical overview in this respect, focusing only on the treatment options available for field soils and ignoring the spiked ones. The authors also propose the development of novel multifunctional green and sustainable systems like mixed cell culture system, biosurfactant flushing, transgenic approaches and nanoremediation in order to overcome the existing soil- contaminant- and microbial-associated technological limitations in tackling high molecular weight PAHs. The ultimate objective is to ensure the successful remediation of long-term PAH contaminated soils.

Finger printing of mixed contaminants from former manufactured gas plant (MGP) site soils: Implications to bioremediation.

Contaminants in general do not occur as single chemicals but as mixtures at any contaminated site. Gasworks sites are the typical mixed contaminated sites. These sites are not only subjected to PAH contamination but also varying degrees of heavy metal contamination. Bioremediation in these sites is often hindered by the presence of heavy metals. The co-occurrence of PAHs with heavy metals has not been systematically investigated. Metals are reported to inhibit the general soil microbiological processes. The total concentration of soluble metal in the system includes both free metal ion and complexed forms. Within bioavailable fraction, the most toxic form is the free metal species, which was not addressed well so far in gas works site characterisation. This study underpins the science and importance of metal bioavailability and speciation based site characterisation in mixed contaminated sites. In this study a detailed elemental chemistry of the gas works site soils are discussed using different methods. The PAH contamination was contributed by both low and high molecular weight PAHs. The total PAHs concentration ranged from 335 to 8645 mg/kg. Among most toxic metals Pb was found in high concentration ranging from 88 to 671 mg/kg, Cd 8 to 112 mg/kg and Zn varied from 64 to 488 mg/kg. Thermodynamic chemical equilibrium model VMINTEQ (Ver 2.52) was used to calculate the free metal species in gas works site soils. The percentage free metal species showed a different trend compared to total metal concentrations, free Zn species ranged 18-86%, free Cd was 26-87% and Pb showed lowest free metal percentage (0-17%). The bioavailable metal species and its implications to bioremediation have also been discussed.

Multivariate analysis of mixed contaminants (PAHs and heavy metals) at manufactured gas plant site soils

Principal component analysis (PCA) was used to provide an overview of the distribution pattern of polycyclic aromatic hydrocarbons (PAHs) and heavy metals in former manufactured gas plant (MGP) site soils. PCA is the powerful multivariate method to identify the patterns in data and expressing their similarities and differences. Ten PAHs (naphthalene, acenapthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benzo[a]pyrene) and four toxic heavy metals — lead (Pb), cadmium (Cd), chromium (Cr) and zinc (Zn) — were detected in the site soils. PAH contamination was contributed equally by both low and high molecular weight PAHs. PCA was performed using the varimax rotation method in SPSS, 17.0. Two principal components accounting for 91.7% of the total variance was retained using scree test. Principle component 1 (PC1) substantially explained the dominance of PAH contamination in the MGP site soils. All PAHs, except anthracene, were positively correlated in PC1. There was a common thread in high molecular weight PAHs loadings, where the loadings were inversely proportional to the hydrophobicity and molecular weight of individual PAHs. Anthracene, which was less correlated with other individual PAHs, deviated well from the origin which can be ascribed to its lower toxicity and different origin than its isomer phenanthrene. Among the four major heavy metals studied in MGP sites, Pb, Cd and Cr were negatively correlated in PC1 but showed strong positive correlation in principle component 2 (PC2). Although metals may not have originated directly from gaswork processes, the correlation between PAHs and metals suggests that the materials used in these sites may have contributed to high concentrations of Pb, Cd, Cr and Zn. Thus, multivariate analysis helped to identify the sources of PAHs, heavy metals and their association in MGP site, and thereby better characterise the site risk, which would not be possible if one uses chemical analysis alone.

Bioremediation of high molecular weight polyaromatic hydrocarbons co-contaminated with metals in liquid and soil slurries by metal tolerant PAHs degrading bacterial consortium

Bioremediation of polyaromatic hydrocarbons (PAH) contaminated soils in the presence of heavy metals have proved to be difficult and often challenging due to the ability of toxic metals to inhibit PAH degradation by bacteria. In this study, a mixed bacterial culture designated as consortium-5 was isolated from a former manufactured gas plant (MGP) site. The ability of this consortium to utilise HMW PAHs such as pyrene and BaP as a sole carbon source in the presence of toxic metal Cd was demonstrated. Furthermore, this consortium has proven to be effective in degradation of HMW PAHs even from the real long term contaminated MGP soil. Thus, the results of this study demonstrate the great potential of this consortium for field scale bioremediation of PAHs in long term mix contaminated soils such as MGP sites. To our knowledge this is the first study to isolate and characterize metal tolerant HMW PAH degrading bacterial consortium which shows great potential in bioremediation of mixed contaminated soils such as MGP.

Nitrate removal efficiency of bacterial consortium (Pseudomonas sp. KW1 and Bacillus sp. YW4) in synthetic nitrate-rich water

The efficiency of bacterial isolates to reduce nitrate from synthetic nitrate-rich water was tested using a batch scale process. Two efficient nitrate reducing bacterial species were isolated from water samples collected from Kodaikanal and Yercaud lakes. Bacterial analysis of the samples revealed the presence of nitrate reducing bacteria belonging to the genera Pseudomonas, Bacillus, Micrococcus and Alcaligenes. Among the isolates, the consortium of Pseudomonas sp. KW1 and Bacillus sp. YW4 was found to be efficient in nitrate reduction. Influences of various carbon sources, incubation temperature and pH on nitrate reduction from synthetic wastewater were also studied. The results showed a rapid and efficient process of nitrate removal (99.4%) from synthetic wastewater supplemented with starch (1%), inoculated by bacterial consortium (Pseudomonas sp. KW1 and Bacillus sp. YW4) at incubation temperature of 30 degrees C at pH 7. This observation has led to the conclusion that the bacterial consortium was responsible for nitrate removal from synthetic nitrate-rich wastewater.

Pyrosequencing analysis of bacterial diversity in soils contaminated long-term with PAHs and heavy metals: Implications to bioremediation

Diversity, distribution and composition of bacterial community of soils contaminated long-term with both polycyclic aromatic hydrocarbons (PAHs) and heavy metals were explored for the first time following 454 pyrosequencing. Strikingly, the complete picture of the Gram positive (+ve) and Gram negative (-ve) bacterial profile obtained in our study illustrates novel postulates that include: (1) Metal-tolerant and PAH-degrading Gram -ves belonging to the class Alphaproteobacteria persist relatively more in the real contaminated sites compared to Gram +ves, (2) Gram +ves are not always resistant to heavy metal toxicity, (3) Stenotrophomonas followed by Burkholderia and Pseudomonas are the dominant genera of PAH degraders with high metabolic activity in long-term contaminated soils, (4) Actinobacteria is the predominant group among the Gram +ves in soils contaminated with high molecular weight PAHs that co-exist with toxic heavy metals like Pb, Cu and Zn, (5) Microbial communities are nutrient-driven in natural environments and (6) Catabolically potential Gram +/-ves with diverse applicability to remediate the real contaminated sites evolve eventually in the historically-polluted soils. Thus, the most promising indigenous Gram +/-ve strains from the long-term contaminated sites with increased catabolic potential, enzymatic activity and metal tolerance need to be harnessed for mixed contaminant cleanups.

Recent advances in the synthesis of inorganic nano/microstructures using microbial biotemplates and their applications

Biotemplates from microbial origin have been a new source of inspiration for designing and fabricating intricate, high surface area structures that possess potent applications in nanotechnology. Microbial biotemplates are useful for synthesizing nano/micro structural materials based on a bottom up approach. Being from nature, microbial biotemplates with their extraordinarily molecular machinery have been reported to be considerably superior and cost effective for fabricating complex and heterogeneous structures when compared to the conventional and advanced lithographic techniques. The advantage of speedy growth and multiplication along with controlled shape, structure and size, make microorganisms a viable template for preparing nanomaterials of defined size and shape. In this review, we have consolidated the recent advances in the synthesis of nano/micro structures using biotemplates obtained from various types of microorganisms like bacteria, fungi, algae and virus, and have highlighted its possible applications. This review excludes biomolecules like DNA, protein and lipid based biotemplates extracted from various microorganisms.

Abandoned metalliferous mines: ecological impacts and potential approaches for reclamation

The lack of awareness for timely management of the environment surrounding a metal mine site results in several adverse consequences such as rampant business losses, abandoning the bread-earning mining industry, domestic instability and rise in ghost towns, increased environmental pollution, and indirect long-term impacts on the ecosystem. Although several abandoned mine lands (AMLs) exist globally, information on these derelict mines has not been consolidated in the literature. We present here the state-of-the-art on AMLs in major mining countries with emphasis on their impact towards soil health and biodiversity, remediation methods, and laws governing management of mined sites. While reclamation of metalliferous mines by phytoremediation is still a suitable option, there exist several limitations for its implementation. However, many issues of phytoremediation at the derelict mines can be resolved following phytostabilization, a technology that is effective also at the modern operational mine sites. The use of transgenic plant species in phytoremediation of metals in contaminated sites is also gaining momentum. In any case, monitoring and efficacy testing for bioremediation of mined sites is essential. The approaches for reclamation of metalliferous mines such as environmental awareness, effective planning and assessment of pre- and post-mining activities, implementation of regulations, and a safe and good use of phytostabilizers among the native plants for revegetation and ecological restoration are discussed in detail in the present review. We also suggest the use of microbially-enhanced phytoremediation and nanotechnology for efficient reclamation of AMLs, and identify future work warranted in this area of research. Further, we believe that the integration of science of remediation with mining policies and regulations is a reliable option which when executed can virtually balance economic development and environmental destruction for safer future.

Kinetics of PAH degradation by a new acid-metal-tolerant Trabulsiella isolated from the MGP site soil and identification of its potential to fix nitrogen and solubilize phosphorous

Development of an efficient bioinoculum is considered as an appropriate remedial approach to treat the PAHs-metal mixed contaminated sites. Therefore, we aimed to isolate a degrader able to exert an outstanding PAH catabolic potential with added traits of pH-metal-resistance, N-fix or P-solubilization from a manufactured gas plant site soil. The identified strain (MTS-6) was a first low and high molecular weight (LMW and HMW) PAHs degrading Trabulsiella sp. tolerant to pH 5. MTS-6 completely degraded the model 3 [150mgL(-1) phenanthrene (Phe)], 4 [150mgL(-1) pyrene (Pyr)] and 5 [50mgL(-1) benzo[a]pyrene (BaP)] ring PAHs in 6, 25 and 90 days, respectively. Presence of co-substrate (100mgL(-1) Phe) increased the biodegradation rate constant (k) and decreased the half-life time (t1/2) of HMW PAHs (100mgL(-1) Pyr or 50mgL(-1) BaP). The strain fixed 47μgmL(-1)N and solubilized 58μgmL(-1)P during PAH metabolism and exhibited an EC50 value of 3-4mgL(-1) for Cu, Cd, Pb and Zn. Over 6mgL(-1) metal levels was lethal for the microbe. The identified bacterium (MTS-6) with exceptional multi-functional traits opens the way for its exploitation in the bioremediation of manufactured gas plant sites in a sustainable way by employing bioaugmentation strategy.