Biogeochemical Cycle, Occurrence and Biological Treatments of Polycyclic Aromatic Hydrocarbons (PAHs)

Bioremediation experiments and dynamic model of petroleum hydrocarbon contaminated soil

Clarifying the occurrence and morphological characteristics of petroleum hydrocarbons (PHs) in soil can facilitate a comprehensive understanding of their migration and transformation patterns in soil/sediment. Additionally, by establishing the dynamic transformation process of each occurrence state, the ecological impact and environmental risk associated with PHs in soil/sediment can be assessed more precisely. The adsorption experiments and closed static incubation experiments was carried out to explore the PHs degradation and fraction distribution in aged contaminated soil under two remediation scenarios of natural attenuation (NA) and bioaugmentation (BA) by exogenous bacteria through a new sequential extraction method based on Tenax-TA, Hydroxypropyl-β-cyclodextrin and Rhamnolipid (HPCD/RL), accelerated solvent extractor (ASE) unit and alkaline hydrolysis extraction. The adsorption experiment results illustrated that bioaugmentation could promote the desorption of PHs in the adsorption phase, and the soil-water partition coefficient Kd decreased from 0.153 L/g to 0.092 L/g. The incubation experiment results showed that compared with natural attenuation, bioaugmentation could improve the utilization of PHs in aged soil and promote the generation of non-extractable hydrocarbons. On the 90th day of the experiment, the concentrations of weakly adsorbed hydrocarbons in the natural attenuation and bioaugmentation experimental groups decreased by 46.44% and 87.07%, respectively, while the concentrations of strongly adsorbed hydrocarbons and non-extractable hydrocarbons increased by 77.93%, 182.14%, and 80.91%, and 501.19%, respectively, compared their initial values. We developed a novel dynamic model and inverted the kinetic parameters of the model by the parameter scanning function and the Markov Chain Monte Carlo (MCMC) method based on the Bayesian approach in COMSOL Multiphysics® finite element software combined with experimental data. There was a good linear relationship between experimental interpolation data and model prediction data. The R2 for the concentrations of weakly adsorbed hydrocarbons ranged from 0.9953 to 0.9974, for strongly adsorbed hydrocarbons from 0.9063 to 0.9756, and for non-extractable hydrocarbons from 0.9931 to 0.9982. These extremely high correlation coefficients demonstrate the high accuracy of the parameters calculated using the Bayesian inversion method.

Unveiling the capacity of bioaugmentation application, in comparison with biochar and rhamnolipid for TPHs degradation in aged hydrocarbons polluted soil

Persistent, aged hydrocarbons in soil hinder remediation, posing a significant environmental threat. While bioremediation offers an environmentally friendly and cost-effective approach, its efficacy for complex contaminants relies on enhancing pollutant bioavailability. This study explores the potential of immobilized bacterial consortia combined with biochar and rhamnolipids to accelerate bioremediation of aged total petroleum hydrocarbon (TPH)-contaminated soil. Previous research indicates that biochar and biosurfactants can increase bioremediation rates, while mixed consortia offer sequential degradation and higher hydrocarbon mineralization. The present investigation aimed to assess whether combining these strategies could further enhance degradation in aged, complex soil matrices. The bioaugmentation (BA) with bacterial consortium increased the TPHs degradation in aged soil (over 20% compared to natural attenuation - NA). However, co-application of BA with biochar and rhamnolipid higher did not show a statistically prominent synergistic effect. While biochar application facilitated the maintenance of hydrocarbon degrading bacterial consortium in soil, the present study did not identify a direct influence in TPHs degradation. The biochar application in contaminated soil contributed to TPHs adsorption. Rhamnolipid alone slightly increased the TPHs biodegradation with NA, while the combined bioaugmentation treatment with rhamnolipid and biochar increased the degradation between 27.5 and 29.8%. These findings encourage further exploration of combining bioaugmentation with amendment, like biochar and rhamnolipid, for remediating diverse environmental matrices contaminated with complex and aged hydrocarbons.

Macrophyte assisted phytoremediation and toxicological profiling of metal(loid)s polluted water is influenced by hydraulic retention time

The present study reports findings related to the treatment of polluted groundwater using macrophyte-assisted phytoremediation. The potential of three macrophyte species (Phragmites australis, Scirpus holoschoenus, and Typha angustifolia) to tolerate exposure to multi-metal(loid) polluted groundwater was first evaluated in mesocosms for 7- and 14-day batch testing. In the 7-day batch test, the polluted water was completely replaced and renewed after 7 days, while for 14 days exposure, the same polluted water, added in the first week, was maintained. The initial biochemical screening results of macrophytes indicated that the selected plants were more tolerant to the provided conditions with 14 days of exposure. Based on these findings, the plants were exposed to HRT regimes of 15 and 30 days. The results showed that P. australis and S. holoschoenus performed better than T. angustifolia, in terms of metal(loid) accumulation and removal, biomass production, and toxicity reduction. In addition, the translocation and compartmentalization of metal(loid)s were dose-dependent. At the 30-day loading rate (higher HRT), below-ground phytostabilization was greater than phytoaccumulation, whereas at the 15-day loading rate (lower HRT), below- and above-ground phytoaccumulation was the dominant metal(loid) removal mechanism. However, higher levels of toxicity were noted in the water at the 15-day loading rate. Overall, this study provides valuable insights for macrophyte-assisted phytoremediation of polluted (ground)water streams that can help to improve the design and implementation of phytoremediation systems.

Bioaugmentation and vermicompost facilitated the hydrocarbon bioremediation: scaling up from lab to field for petroleum-contaminated soils

The biodegradation of total petroleum hydrocarbon (TPH) in soil is very challenging due to the complex recalcitrant nature of hydrocarbon, hydrophobicity, indigenous microbial adaptation and competition, and harsh environmental conditions. This work further confirmed that limited natural attenuation of petroleum hydrocarbons (TPHs) (15% removal) necessitates efficient bioremediation strategies. Hence, a scaling-up experiment for testing and optimizing the use of biopiles for bioremediation of TPH polluted soils was conducted with three 500-kg pilots of polluted soil, and respective treatments were implemented: including control soil (CT), bioaugmentation and vermicompost treatment (BAVC), and a combined application of BAVC along with bioelectrochemical snorkels (BESBAVC), all maintained at 40% field capacity. This study identified that at pilot scale level, a successful application of BAVC treatment can achieve 90.3% TPH removal after 90 days. BAVC's effectiveness stemmed from synergistic mechanisms. Introduced microbial consortia were capable of TPH degradation, while vermicompost provided essential nutrients, enhanced aeration, and, potentially, acted as a biosorbent. Hence, it can be concluded that the combined application of BAVC significantly enhances TPH removal compared to natural attenuation. While the combined application of a bioelectrochemical snorkel (BES) with BAVC also showed a significant TPH removal, it did not differ statistically from the individual application of BAVC, under applied conditions. Further research is needed to optimize BES integration with BAVC for broader applicability. This study demonstrates BAVC as a scalable and mechanistically sound approach for TPH bioremediation in soil.

In vitro analysis of iron oxide (Fe3O4) nanoparticle mediated degradation of polycyclic aromatic hydrocarbons (PAHs) and their antimicrobial activity

To degrade anthracene, magnetite nanoparticles were produced using a simple co-precipitation process. The fabricated nanoparticles have been analyzed for structural and optical properties. XRD examination revealed that the produced Fe3O4 nanoparticles were cubic phase, having a mean crystallite dimension of 18.84 nm. DLS determined the hydrodynamic diameter of Fe3O4 nanoparticles to be 182 nm. UV-Vis research revealed that Fe3O4 nanoparticles absorb at 390 nm. A peak at 895 cm-1 in the FT-IR study indicated the metal-oxygen connection. The synthesized Fe3O4 nanoparticles demonstrated an effective photocatalytic performance towards anthracene degradation and was found to be 86.55%. Furthermore, Fe3O4 nanoparticles showed the highest antimicrobial activity against Bacillus subtilis was 19.43 mm. The present study is the first and foremost study determining the dual role of Fe3O4 nanoparticles towards bioremediation and biomedical applications.

Genome sequence of Stenotrophomonas indicatrix CPHE1, a powerful phenanthrene-degrading bacterium

Environmental pollution caused by polycyclic aromatic hydrocarbons (PAHs) involves a high-risk and have received considerable attention due to their carcinogenic, teratogenic, and mutagenic properties. Phenanthrene (PHE) is a low molecular weight PAH, which has three benzene rings. It is one of the most common PAH found in contaminated environments mainly due to its low volatilization ability and hydrophobic character. A PHE degrading bacterium was isolated from an industrial contaminated soil using enrichment culture techniques. Based on macroscopic, microscopic examination and phylogenetic analysis, this bacterium was classified as Stenotrophomonas indicatrix and named strain CPHE1. Several authors have reported about bacteria stains, which can degrade PHE, but this is the first time where the ability of S. indicatrix to biodegrade and mineralize PHE has been demonstrated.

Limited Phosphorous Supply Improved Lipid Content of Chlorella vulgaris That Increased Phenol and 2-Chlorophenol Adsorption from Contaminated Water with Acid Treatment

Phenolic compounds are toxic and ominously present in industrial effluents, which can end up in water bodies, causing potential damage to living organisms. This study employed the dried biomass of freshwater green microalgae Chlorella vulgaris to remove phenol and 2-chlorophenol from an aqueous environment. C. vulgaris was grown under different phosphorus- (P) starved conditions, and biomass was treated with sulfuric acid. It was observed that reducing the P level enhanced the lipid content by 7.8 times while decreasing protein by 7.2 times. P-starved C. vulgaris dried biomass removed phenol and 2-chlorophenol by 69 and 57%, respectively, after 180 min from the contaminated water. Acid-treated P-starved C. vulgaris dried biomass removed phenol and 2-chlorophenol by 77 and 75%, respectively, after 180 min. Thus, an economical and eco-friendly P-starved and acid treated C. vulgaris biomass has better potential to remove phenol and 2-chlorophenol from contaminated ground water and industrial wastewater.

Evaluation of biostimulation, bioaugmentation, and organic amendments application on the bioremediation of recalcitrant hydrocarbons of soil

In the present work, the operational conditions for improving the degradation rates of Total Petroleum Hydrocarbons (TPHs) in contaminated soil from a machinery park were optimized at a microcosms scale along a 90-days incubation period. In this study, bioremediation strategies and an organic amendment have been tested to verify the remediation of soil contaminated with different hydrocarbons, mineral oils, and heavy metals. Specifically, designed biostimulation and bioaugmentation strategies were compared with and without adding vermicompost. The polluted soil harboring multiple contaminants, partially attenuated for years, was used. The initial profile showed enrichment in heavy linear alkanes, suggesting a previous moderate weathering. The application of vermicompost increased five and two times the amounts of available phosphorus (P) and exchangeable potassium (K), respectively, as a direct consequence of the organic amendment addition. The microbial activity increased due to soil acidification, which influenced the solubility of P and other micronutrients. It also impacted the predominance and variability of the different microbial groups and the incubation, as reflected by phospholipid fatty acid (PLFA) results. An increase in the alkaline phosphatases and proteases linked to bacterial growth was displayed. This stimulation of microbial metabolism correlated with the degradation rates since TPHs degradation' efficiency after vermicompost addition reached 32.5% and 34.4% of the initial hydrocarbon levels for biostimulation and bioaugmentation, respectively. Although Polycyclic Aromatic Hydrocarbons (PAHs) were less abundant in this soil, results also decreased, especially for the most abundant, the phenanthrene. Despite improving the degradation rates, results revealed that recalcitrant and hydrophobic petroleum compounds remained unchanged, indicating that mobility, linked to bioavailability, probably represents the limiting step for further soil recovery.

Petroleum-contaminated soil: environmental occurrence and remediation strategies

Soil is an environmental matrix that carries life for all living things. With the rise of human activities and the acceleration of population, the soil has been exposed in part to pollution by the discharge of various xenobiotics and persistent pollutants into it. The disposal of toxic substances such as polycyclic aromatic hydrocarbons (PAHs) alters soil properties, affects microbial biodiversity, and damages objects. Considering the mutagenicity, carcinogenicity, and toxicity of petroleum hydrocarbons, the restoration and clean-up of PAH-polluted sites represents an important technological and environmental challenge for sustainable growth and development. Though several treatment methods to remediate PAH-polluted soils exist, interesting bacteria, fungi, and their enzymes receive considerable attention. The aim of the present review is to discuss PAHs' impact on soil properties. Also, this review illustrates physicochemical and biological remediation strategies for treating PAH-contaminated soil. The degradation pathways and contributing factors of microbial PAH-degradation are elucidated. This review also assesses the use of conventional microbial remediation compared to the application of genetically engineered microorganisms (GEM) that can provide a cost-effective and eco-friendly PAH-bioremediation strategy.

A Review of Microalgae- and Cyanobacteria-Based Biodegradation of Organic Pollutants

This review proposes a new bioremediation method based on the diverse functionalities of algae. A greenway for cleansing wastewater is more ecologically friendly and environmentally sustainable than prior methods with other bacteria. New bioremediation technology employing algae and cyanobacteria for the removal of a wide range of organic contaminants is reasonable and has great potential. The prevalence of organic contaminants in aquatic habitats may endanger the health and well-being of several marine creatures. Agriculture, industry, and household trash are just a few of the human-caused sources of organic pollutants that contaminate waterways around the world. Before wastewater can be released into waterways, it must be cleaned. Algae-based wastewater treatment systems are becoming increasingly popular because of their environmental sustainability and lack of secondary pollutants. According to the kind of pollutant, the physicochemical properties of wastewater, and the algal species, algae and cyanobacteria can absorb and accumulate a wide spectrum of organic pollutants at different rates. In addition, phytoremediation is a cost-effective alternative to conventional treatments for degrading organic contaminants. Phycoremediationally produced algal biomass may also be an important part of the bioenergy value chain. This article focuses on microalgae and cyanobacteria species, which may remove many organic contaminants from water systems.

Soil conditioners improve rhizodegradation of aged petroleum hydrocarbons and enhance the growth of Lolium multiflorum

Bioremediation and phytoremediation have demonstrated potential for decontamination of petroleum hydrocarbon-impacted soils. The total petroleum hydrocarbons (TPHs) are known to induce phytotoxicity, reduce water retention in soil, associate hydrophobic nature and contaminants' in situ heterogeneous distribution, limit soil nutrient release and reduce soil aeration and compaction. The ageing of TPHs in contaminated soils further hinders the degradation process. Soil amendments can promote plant growth and enhance the TPH removal from contaminated aged soil. In the present experiment, remediation of TPH-contaminated aged soil was performed by Italian ryegrass, with compost (COM, 5%), biochar (BC, 5%) and immobilized microorganisms' technique (IMT). Results revealed that significantly highest hydrocarbon removal (40%) was noted in mixed amendments (MAA) which contained BC + COM + IMT, followed by COM (36%), compared to vegetative control and other treatments. The higher TPH removal in aged soil corresponds with the stimulated rhizospheric effects, as evidenced by higher root biomass (85-159% increase), and bacterial count compared to NA control. Phyto-stimulants actions of biochar and IMT improved seed germination of Italian ryegrass. The compost co-amendment with other treatments showed improvement in plant physiological status. These results suggested that plant growth and TPH removal from aged, contaminated soils using BC, COM and IMT can improve bioremediation efficiency.

Interactive effect of biochar and compost with Poaceae and Fabaceae plants on remediation of total petroleum hydrocarbons in crude oil contaminated soil

The current study was dedicated to finding the effect of soil amendments (biochar and compost) on plants belonging to Poaceae and Fabaceae families. Plants selected for the phytoremediation experiment included wheat (Triticum aestivum), maize (Zea mays), white clover (Trifolium repens), alfalfa (Medicago sativa), and ryegrass (Lolium multiflorum). The physiological and microbial parameters of plants and soil were affected negatively by the 4 % TPHs soil contamination. The studied physiological parameters were fresh and dried biomass, root and shoot length, and chlorophyll content. Microbial parameters included root and shoot endophytic count. Soil parameters included rhizospheric CFUs and residual TPHs. Biochar with wheat, maize, and ryegrass (Fabaceae family) and compost with white clover and alfalfa (Poaceae family) improved plant growth parameters and showed better phytoremediation of TPHs. Among different plants, the highest TPH removal (68.5 %) was demonstrated by ryegrass with compost, followed by white clover with biochar (68 %). Without any soil amendment, ryegrass and alfalfa showed 59.55 and 35.21 % degradation of TPHs, respectively. Biochar and compost alone removed 27.24 % and 6.01 % TPHs, respectively. The interactive effect of soil amendment and plant type was also noted for studied parameters and TPHs degradation.

Ornamental plants for the phytoremediation of heavy metals: Present knowledge and future perspectives

Environmental matrices are polluted with the plethora of contaminants, and among these, the concerns related to heavy metals (HMs) are also included. Due to the low cost in a long-term application and environmental friendliness, the use of biological remediation has gained significant attention in recent decades. The use of ornamental plants (OPs) in the field of phytoremediation is scarcely reported, and the impacts of HMs on OPs have also not been investigated in great depth. The OPs mediated HMs remediation can simultaneously remove contaminants and bring improvement in aesthetics of the site. The biomass of OPs produced after such activities can be used and sold as pot plants, cut flowers, essential oils, perfumes, air fresheners production, metal phytomining, and feedstock in silk production. The OPs also present a lower risk of HMs bioaccumulation compared to crop plants. This review focuses on the current knowledge of HMs toxicity to OPs, their applicability advantages, methods to improve the tolerance of OPs with incremented HMs uptake, challenges in the field, and future application perspectives. The case studies realted to practical application of OPs, from China, Iran, India, Oman, Pakistan, and Turkey, were also discussed. This work fetches the inter-disciplinary features and understanding for the sustainable treatment of HMs in a new novel way, to which no previous review has focused.

Review of polycyclic aromatic hydrocarbons (PAHs) in fish and fisheries products; a Sri Lankan perspective

Polycyclic aromatic hydrocarbons (PAHs) are emerging as important contaminants in smoked and smoke-dried fish and fish products. The smoking techniques and different parameters contribute to the PAH load in smoked fish. This review paper provides insight into the PAHs and their sources and pathways to fish, effects on human health, smoking parameters and PAHs, regulations, available information, gaps in present knowledge, and future prospects in smoked fish from Sri Lanka. Based on the very few available research reports on PAH levels in smoked fish from Sri Lanka, it is concluded that the smoked fish are not safe for human consumption according to the regulation limits published by the European Union (EU). It is therefore important to implement proper guidelines and produce a safe product to ensure that hazards are managed as appropriate Hazard Analysis and Critical Control Points (HACCP). Graphical abstract.

Respuestas fisiológicas y capacidad antioxidante de <i>Chlorella vulgaris</i> (Chlorellaceae) expuesta a fenantreno

Los hidrocarburos aromáticos tienen un alto potencial toxicológico, por lo que su evaluación en organismos acuáticos es de gran importancia. La microalga Chlorella vulgaris fue seleccionada, por ser una de las especies de algas más dominantes en el agua y por su potencial para degradar o absorber diferentes xenobióticos. El objetivo fue evaluar la toxicidad en C. vulgaris expuesta a fenantreno (PHE), evaluando parámetros fisiológicos como la densidad celular, contenido de clorofila a y clorofila b y actividad enzimática de superóxido dismutasa (SOD) y catalasa (CAT) que definan respuestas tóxicas a corto plazo. Se evaluaron cinco diferentes concentraciones (0,1; 1,0; 10; 100 y 1000 µg PHE. L-1), un tratamiento control solvente (acetona) y control (sin aditamentos) durante siete días. En todas las respuestas fisiológicas se observó un comportamiento dosis dependiente, disminuyendo progresivamente con el incremento de las concentraciones de PHE. La densidad celular, tasa de crecimiento, diámetro celular y clorofila pueden ser considerados biomarcadores de toxicidad. La actividad de CAT y SOD en C. vulgaris disminuyó considerablemente durante todo el periodo de estudio, posiblemente a causa de una excesiva producción de especies reactivas de oxígeno generadas por la exposición a fenantreno provocando la inhibición de estas enzimas antioxidantes. A pesar de la toxicidad de este hidrocarburo evidentemente observada en este estudio, C. vulgaris presenta una alta resistencia y adaptación a este contaminante, por lo que se puede decir que este microorganismo tiene la capacidad de evidenciar efectos toxicológicos en un entorno con este contaminante en un corto periodo de tiempo.

Critical review of micro-extraction techniques used in the determination of polycyclic aromatic hydrocarbons in biological, environmental and food samples

Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous environmental contaminants and their accurate determination is very important to human health and environment safety. In this review, sorptive-based micro-extraction techniques [such as Solid-Phase Micro-extraction (SPME), Stir Bar Sorptive Extraction (SBSE), Micro-extraction in Packed Sorbent (MEPS)] and solvent-based micro-extraction [Membrane-Mediated Liquid-Phase Micro-extraction (MM-LPME), Dispersive Liquid-Liquid Micro-extraction (DLLME), and Single Drop Micro-extraction (SDME)] developed for quantification of PAHs in environmental, biological and food samples are reviewed. Moreover, recent micro-extraction techniques that have been coupled with other sample extraction strategies are also briefly discussed. The main objectives of these micro-extraction techniques are to perform extraction, pre-concentration and clean up together as one step, and the reduction of the analysis time, cost and solvent following the green chemistry guidelines.