Comparative bioremediation of heavy metals and petroleum hydrocarbons co-contaminated soil by natural attenuation, phytoremediation, bioaugmentation and bioaugmentation-assisted phytoremediation

Effects of root exudates on the activation and remediation of cadmium ion in contaminated soils

To screen out plants with hyperaccumulation of heavy metals and explore the effects of root exudates on the phytoremediation in contaminated soils. The germination rates of five plants including Lolium perenne L. (L. perenne), Sorghum sudanense (Piper) Stapf. (S. sudanense), Pennisetum alopecuroides (L.) Spreng. (P. alopecuroides), Medicago sativa L. (M. sativa), and Trifolium repens L. (T. repens) in different concentrations of cadmium ion solution (0-100 mg/kg) were determined. The growth adaptability of these five plants under conditions of contaminated soils with the above cadmium ion concentrations was also evaluated. S. sudanense and P. alopecuroides had higher germination rates and better growth than the three other plants and were selected as the latter experimental varieties. The activation amounts of cadmium ion in soils were measured using AAS in the presence of three types of root secretions (citric acid, glycine, and maltose) with different concentrations (10-500 mmol/L). The activation amounts decrease in the following order: citric acid > glycine > maltose. The effect of these three root exudates on the removal of cadmium-contaminated soils in combination with S. sudanense and P. alopecuroides was also tested. For S. sudanense and P. alopecuroides, the maximum biomass and removal rate reaches the maximum at 100 mmol/L of citric acid. Conversely, low concentrations (approximately 10-50 mmol/L) of glycine and maltose are more effective for plant growth and phytoremediation. The addition of citric acid at 100 mmol/L and approximately 10-50 mmol/L of glycine and maltose can effectively promote the transfer of cadmium ion from roots to leaves and the accumulation of cadmium ion in leaves.

Multi-criteria decision analysis of optimal planting for enhancing phytoremediation of trace heavy metals in mining sites under interval residual contaminant concentrations

As one of the most cost-effective and sustainable methods for contaminants' removal, sequestration and/or detoxification, phytoremediation has already captured comprehensive attention worldwide. Nevertheless, the accurate effects of various spatial pattern in enhancing phytoremediation efficiency is not yet clear, especially for the polluted mining areas. This study designed nine planting patterns (monocropping, double intercropping and triple intercropping) of three indigenous plant species (Setaria viridis (L.), Echinochloa crus-galli (L.) and Phragmites australis (Cav.) Trin. ex Steud.) to further explore the effects of plants spatial pattern on phytoremediation efficiency. Considering the uncertainties of the residual contaminants' concentration (RCC) caused by soil anisotropy, permeability and land types, the interval transformation was introduced into the plant uptake model to simulate the remediation efficiency. Then multi-criteria decision analysis (MCDA) were applied to optimal the planting patterns, with the help of criteria of (a) the amount of heavy metal absorption; (b) the concentration of residual contaminant in soil; (c) root tolerance of heavy metals; (d) the total investment cost. Results showed that (1) the highest concentrations of Zn, Cd, and Pb of the polluted area were 7320.02, 14.30, 1650.51 mg kg^-1 (2) During the 180 days simulation, the highest RMSE of residue trace metals in soil are 3.02(Zn), 2.67(Pb), 2.89(Cd), respectively. (3) The result of IMCDA shows that the planting patterns of Setaria viridis, Echinochloa crus-galli and Phragmites australis in alternative a9 (269 mg kg^-1 year^-1) had the highest absorption rate of heavy metals compared with a7 (235 mg kg^-1 year^-1) and a2 (240 mg kg^-1 year^-1). After 20 years of remediation, the simulated RCC in a9 is far below the national standard, and the root toxicity is 0.12 (EC ≤ EC₂₀). In general, the optimal alternative derived from interval residual contaminant concentration can effectively express the dynamic of contaminant distribution and then can be effectively employed to evaluate the sustainable remediation methods.

Cupriavidus sp. strain Cd02-mediated pH increase favoring bioprecipitation of Cd2+ in medium and reduction of cadmium bioavailability in paddy soil

This study investigated the effects of Cupriavidus sp. strain Cd02-mediated increase on biosorption and bioprecipitation of Cd²⁺ during the 144-h cultivation time as well as evaluated effectivenesses of changing soil pH and bioavailability of cadmium after bioaugmentation of strain Cd02 into Cd-contaminated paddy soil for 15 days. Results showed that strain Cd02-induced pH increase of the culture medium (from 7.40 to 8.68) facilitated biosorption of Cd²⁺ on Cd02 cell surface (4.82 mg/mg) and extracellular bioprecipitation in form of cadmium carbonate (3.07 mg/mg). Also, the pH values of Cd-contaminated paddy soil increased by 1.41 units after strain Cd02 was applied for 15 days, which thereby promoted the decrease of exchangeable fraction of Cd²⁺ by 6.5% in the tested paddy soil. Meanwhile, strain Cd02 could prosperously live in paddy soils after bioaugmentation. These results suggest that strain Cd02 may be applicable for bioremediation of the heavy metal-contaminated soils by bioaugmentation.

Bio-based remediation of petroleum-contaminated saline soils: Challenges, the current state-of-the-art and future prospects

Exploiting synergism between plants and microbes offers a potential means of remediating soils contaminated with petroleum hydrocarbons (PHCs). Salinity alters the physicochemical characteristics of soils and suppresses the growth of both plants and soil microbes, so the bioremediation of saline soils requires the use of plants and in microbes which can tolerate salinity. This review focuses on the management of PHC-contaminated saline soils, surveying what is currently known with respect to the potential of halophytes (plants adapted to saline environments) acting in concert with synergistic microbes to degrade PHCs. The priority is to identify optimal combinations of halophyte(s) and the bacteria present as endophytes and/or associated with the rhizosphere, and to determine what are the factors which most strongly affect their viability.

Remediation of Organically Contaminated Soil Through the Combination of Assisted Phytoremediation and Bioaugmentation

Here, we aimed to bioremediate organically contaminated soil with Brassica napus and a bacterial consortium. The bioaugmentation consortium consisted of four endophyte strains that showed plant growth-promoting traits (three Pseudomonas and one Microbacterium) plus three strains with the capacity to degrade organic compounds (Burkholderia xenovorans LB400, Paenibacillus sp. and Lysinibacillus sp.). The organically contaminated soil was supplemented with rhamnolipid biosurfactant and sodium dodecyl benzenesulfonate to increase the degradability of the sorbed contaminants. Soils were treated with organic amendments (composted horse manure vs. dried cow slurry) to promote plant growth and stimulate soil microbial activity. Apart from quantification of the expected decrease in contaminant concentrations (total petroleum hydrocarbons, polycyclic aromatic hydrocarbons), the effectiveness of our approach was assessed in terms of the recovery of soil health, as reflected by the values of different microbial indicators of soil health. Although the applied treatments did not achieve a significant decrease in contaminant concentrations, a significant improvement of soil health was observed in our amended soils (especially in soils amended with dried cow slurry), pointing out a not-so-uncommon situation in which remediation efforts fail from the point of view of the reduction in contaminant concentrations while succeeding to recover soil health.

Study on the efficiency of phytoremediation of soils heavily polluted with PAHs in petroleum-contaminated sites by microorganism

The effects of Fire Phoenix (a mixture of Festuca L.) and Purple coneflower (Echinacea purpurea (L.) Moench) on the remediation of two different high concentrations of PAH-contaminated soils were studied under the effect of strain N12 (Mycobacterium sp.), and the changes in rhizosphere enzymatic activity were preliminarily studied. The results of three culture stages (60 d, 120 d, and 150 d) showed that N12 has a promotional effect on the biomass of Fire Phoenix and E. purpurea, and the effect of N12 on the biomass of Fire Phoenix is better. Under the strengthening of N12, the maximum removal rates of Fire Phoenix reached 86.77% and 67.82% at two high PAH concentrations (A and B, respectively). The activity of dehydrogenase (DHO) is positively correlated with the degradation rate of PAHs at the A concentration (P < 0.05). The activity of DHO in soil will continue to increase at a higher level of the B concentration, but the positive correlation between the activity of DHO and the degradation rate of PAH is weakened. In the rhizosphere soil of the two plants, the change in polyphenol oxidase (PPO) activity with time has a significant negative correlation with the degradation rate of PAHs (P < 0.05). The experiment proved that Fire Phoenix is more suitable for the remediation of heavy PAH-contaminated soil under the condition of microorganism-strengthening, and it can achieve a better degradation effect when the concentrations of PAHs are < 150 mg·kg^-1. Results provide a further scientific basis for the remediation of contaminated sites.

Phytoremediation of multi-metal contaminated mine tailings with Solanum nigrum L. and biochar/attapulgite amendments

A greenhouse experiment was conducted to investigate an enhanced phytoremediation technique for multi-metal contaminated mine tailings by Solanum nigrum L. and using biochar/attapulgite as soil amendments. The 10% attapulgite (MA₂) and 10% biochar (MB₂) were recommended as the optimum chemical proportions for amendment materials. Plant length and fresh weight in the MA₂/MB₂-applied treatments were significantly higher than that in the non-amended treatment, indicating MA₂ and MB₂ amendments could alleviate metal phytotoxicity. Metal uptake in plant leaves was lower with MA₂ and MB₂ application than that in the non-amended treatment. However, metal uptake in plant roots was significantly increased with MA₂ and MB₂ application from the fifth month, suggesting that MA₂ and MB₂ had significant enhancement on metal stabilization. Temporal variation of metal translocation in soil-to-plant system showed that the function of MA₂ and MB₂ reached the plateau nearly in the seventh month. The removal rates of metals were higher after the application of MA₂ than MB₂, and by the following order: Cu (39.6%) > Zn (35.0%) > Cd (34.1%) > Hg (32.1%) > Pb (31.8%) > Mn (19.1%). The synergistic effect between S. nigrum L. and MA₂/MB₂ appeared to be particularly effective in terms of metal phytostabilization, and MA₂ was superior to MB_2.

The Application of Different Biological Remediation Strategies to PCDDs/PCDFs Contaminated Urban Sediments

Our aim was to assess the efficacy of four different bioremediation strategies applied to soil treated with urban sediments for alleviating soil phytotoxicity (examined using Lepidium sativum), by removing polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), and mitigating the toxic effect on plants by the applied sediment: (1) Natural attenuation, (2) phytoremediation with the use of two plants Tagetes patula L. and Festuca arundinacea, (3) rhizobacterial inoculation with Massilia niastensis p87 and Streptomyces costaricanus RP92 strains, (4) rhizobacteria-assisted phytoremediation with both plants and strains. The applied sediment had a positive influence on L. sativum growth (90% higher than in the unamended soil), mostly due to its high content of nutrients, mainly Ca and Fe, which immobilize pollutants. The positive effect of sediments continued for up to 10-week duration of the experiment; however, the rhizobacterial inoculated samples were characterized by higher growth of L. sativum. The application of rhizobacteria-assisted phytoremediation further increased the growth of L. sativum, and was also found to improve the efficiency of PCDD/PCDF removal, resulting in a maximum 44% reduction of its content. This strategy also alleviated the negative impact of urban sediments on T. patula and F. arundinacea biomass, and had a beneficial effect on protein and chlorophyll content in the studied plants.

Effects of an Integrated Carbide Slag-Mushroom Dreg-Calcium Superphosphate Amendment on the Stabilization Process of Pb, Cu, Zn and Cd in Contaminated Soils

In the present study, the integrated use of organic and inorganic amendments (CS–MD–CSP) including carbide slag (CS), calcium superphosphate (CSP) and mushroom dreg (MD) are employed for the stabilization of heavy metals in contaminated soils. A response surface methodology combined with immobilization efficiency was employed to evaluate and optimize the proportion of the integration amendments on the stabilization process. The results predicted by a Box–Behnken design indicated that the maximum immobilization efficiencies of soil Pb, Cu, Zn and Cd could be achieve up to 99.88, 96.11, 99.78 and 87.88%, respectively, when the dosage of CS, CSP and MD were set as 4, 1 and 6%, respectively. European Community Bureau of Reference (BCR) speciation analysis indicated that the acid-soluble proportion of Pb, Cu, Zn and Cd in the soils decreased by 72.68, 37.03, 9.36 and 12.94%, respectively. Thus, this CS–MD–CSP integration amendment could potentially be used for the remediation of Pb, Cu, Zn and Cd in contaminated soils.

Role of Festuca rubra and Festuca arundinacea in determinig the functional and genetic diversity of microorganisms and of the enzymatic activity in the soil polluted with diesel oil

The objective of this study was to analyze the effect of two grass species, i.e. red fescue (Festuca rubra) and tall fescue (F. arundinacea), on the functional and genetic diversity of soil-dwelling microorganisms and on the enzymatic activity of soil not polluted and polluted with diesel oil. Grasses were examined for their effectiveness in accelerating degradation of PAHs introduced into soil with diesel oil. A growing experiment was conducted in Kick-Brauckman pots. The soil not polluted and polluted with diesel oil (7 cm3 kg-1 d.m.) was determined for the count of bacteria, colony development index, ecophysiological diversity index, functional diversity (using Biolog system), genetic diversity of bacteria (using NGS), enzymatic activity, and content of hydrocarbons. Study results demonstrated disturbed homeostasis of soil. The toxic effect of diesel oil on grasses alleviate with time since soil pollution. The yield of the first swath of red fescue decreased by 98% and that of tall fescue by 92%, whereas the yields of the second swath decreased by 82% and 89%, and these of the third swath by 50% and 47%, respectively. Diesel oil diminished also the functional and genetic diversity of bacteria. The use of grasses significantly decreased contents of C6-C12 (gasoline total), C12-C35 mineral oils, BTEX (volatile aromatic hydrocarbons), and PAHs in the soil, as well as enabled restoring the microbiological equilibrium in the soil, and increased functional and genetic diversity of bacteria. For this reason, both analyzed grass species, i.e. Festuca rubra and F. arundinacea, may be recommended for the remediation of soil polluted with diesel oil.

Natural attenuation of indicator bacteria in coastal streams and estuarine environments

One of the most significant causes of poor water quality is the presence of pathogens. To reduce the cost of human exposure to microbial contamination, monitoring of Fecal Indicator Bacteria (FIB), as a surrogate for the presence of pathogens in natural waters, has become the norm. A total maximum daily load (TMDL) framework is used to establish limits for microbial concentrations in impaired waterbodies. In order to meet microbial loads determined by the TMDLs, reductions in microbial sources varying from 50% to almost complete elimination are required. Such targets are fairly difficult, if not impossible, to achieve. A natural attenuation (NA) framework is proposed that takes into account the connectivity between freshwater streams and their receiving coastal estuaries. The framework accounts for destructive and non-destructive mechanisms and defines three regimes: NA 1 - reaction-dilution mixing at the freshwater-tidal interface, NA 2 - advection-reactions within the tidally influenced coastal stream, and NA 3 - dilution-discharge at the interface with the estuary. The framework was illustrated using the Houston Metropolitan area freshwater streams, their discharge into the Houston Ship Channel (HSC) and into Galveston Bay. FIB concentrations in Galveston Bay were much lower when compared to FIB concentrations in Houston streams. Lower enterococci concentrations in tributary tidal waters were found compared to their counterparts in fresh waters (NA1 regime). Additionally, 70% reduction in FIB loads within the HSC was demonstrated as well as a decreasing trend in enterococci geometric means, from upstream to downstream, on the order of 0.092 day^-1 (NA2 regime). Lower enterococci concentrations in Galveston Bay at the confluence with the HSC were also demonstrated (NA3 regime). Statistical testing showed that dilution, tide-associated processes, and salinity are the most important NA mechanisms and indicated the significant effect of ambient temperature and rainfall patterns on FIB concentrations and the NA mechanisms.

EFFECT OF NITROGEN AND HUMIC FERTILIZERS ON THE BIOCHEMICAL STATE OF OIL‐CONTAMINATED CHERNOZEM

Aim. In this paper, we aim to assess the effect of nitrogen and humic fertilizers on the biochemical state of oil‐contaminated chernozem.

Methods. In order to simulate the oil pollu‐ tion, chernozem was exposed to oil doses constituting 1, 5 and 10% of the soil mass for 30, 60 and 90 days. For simulating bioremediation of oil‐contaminated chernozem, the following fertilizers were used: potassium and sodium humates, urea and nitroammophos. Nitrogen fertilizers – urea and nitroammophos having a nitrogen content of 46% and 15%, respectively – were applied to the soil for the purposes of restoring the equilibrium between carbon and nitrogen. Humic fertilizers (potassium and sodium humates) were applied to the soil for stimulating the indigenous oil destructive microbiota. In order to assess the biological activity of the soil, we determined catalase activity, invertase activity, as well as CO2 emission intensity.

Results. The effect of urea, nitroammophos, potassium and sodium humates on the enzymatic activity and CO2 emissions of ordinary chernozem, which had been exposed to various doses of oil (1, 5 and 10% of the soil mass) for 90 days, was studied in a model experiment. Following the introduction of nitroammophos into soil with low levels of oil pollution, catalase activity decreased, whereas respiration and invertase activity increased. Urea introduced into the soil contaminat‐ ed with a 10% dose of oil stimulated catalase activity. At oil concentrations of 1 and 5%, the introduction of potassium and sodium humates had a stimulating effect on enzymic activity and carbon dioxide evolution.

Conclusions. It is advisable to use the intensity of CO2 emissions released from the soil, as well as the invertase activity for diagnosing the state of chernozem con‐ taminated with oil (5‐10%) following the introduction of nitrogen and humic ameliorants. At lower doses of oil, it is advisable to assess the state of the soil following the introduction of nitrogen fertilizers by catalase activity. 

The effect of oil sludge contamination on morphological and physiological characteristics of some tree species

Although petroleum plays an important part in world economy, its exploitation can bring about a great deal of contamination in soil. To select the tree species being tolerant to soil pollution, a pot experiment has been carried out to assess and compare the growth potential of the seedlings of black locust (Robinia pseudoacacia L.), Chinaberry (Melia azedarach L.), Ailantos (Ailanthus altissima Mill.) and Ash (Fraxinus rotundifolia Mill.) in petroleum-hydrocarbon contaminated soils. The seeds of the mentioned species were subjected to different oil sludge concentrations (0, 10, 20 and 40%) for a growth season of 240 days and then seedling emergence, growth performance, biomass production, photosynthetic parameters and heavy metal absorption were measured to find the species with higher resistantce. For all the species, seedling emergence was significantly reduced under the soil pollution among which F. rotundifolia exhibited a better performance. Besides, growth and biomass of F. rotundifolia and R. pseudoacacia were seldom influenced by oil sludge. In addition, seedlings of A. altissima accumulated higher percentage of the heavy metals (particularly Ni, Cu, Cd) in their leaves by virtue of their wider leaf surface area. This study provides valuable insights into phytoremediation of sites contaminated by oil sludge, using tree species.

Enhanced Cd transport in the soil-plant-atmosphere continuum (SPAC) system by tobacco (Nicotiana tabacum L.)

The optimal treatment designs of the heavy metal pollution sites and the calculation of the recovery capacity are important in recent studies. In this paper, we aimed to model the accumulation of heavy metals under different artificially Cd added concentrations, and analyzed the various tobacco solute adsorption and fluid flow properties. The finite difference method was used to simulate the heavy metals flux and root absorption in the soil, and the model simulation was compared with the measured values to quantify the uncertainty of the metal transport and modeling parameters. Treatments with different Cd levels were compared, e.g., control tillage (CT), low Cd tillage (LT, 2.0 mg/kg), high Cd tillage (HT, 20.0 mg/kg), ultra-high Cd tillage (UHT, 80.0 mg/kg). The predicted soil water content (SWC) was consistent with observed data. Predicted cumulative root water uptake (mm) ranked as follows: CT (196)>LT (178)>HT (134)>UHT (117). Potential transpiration rates (T r p) under HT and UHT were lower than that of other treatment, because of their lower leaf Area Index (LAI). The predicted root Cd uptake showed a strong correlation within the actual Cd uptake. The predicted root absorption of Cdmax was UHT (180.17)> HT (106.52)> LT (53.20) >CT (0.610). However, deviation of models was added by the Cd effluent trend and the performance of root exudates. This finding would be useful for further investigation into bio-remediation in the agricultural area, not only for Cd ion but for a range of other heavy metal contaminants.

Enhancement of heavy metal tolerance and accumulation efficiency by expressing Arabidopsis ATP sulfurylase gene in alfalfa

Transgenic alfalfa (Medicago sativa L.) plants overexpressing the Arabidopsis ATP sulfurylase gene were generated using Agrobacterium-mediated genetic transformation to enhance their heavy metal accumulation efficiency. The ATP sulfurylase gene was cloned from Arabidopsis, following exposure to vanadium (V) and lead (Pb), and transferred into an Agrobacterium tumefaciens binary vector. This was co-cultivated with leaf explants of the alfalfa genotype Regen SY. Co-cultivated leaf explants were cultured on callus and somatic embryo induction medium, followed by regeneration medium for regenerating complete transgenic plants. The transgenic nature of the plants was confirmed using PCR and southern hybridization. The expression of Arabidopsis ATP sulfurylase gene in the transgenic plants was evaluated through RT-PCR. The selected transgenic lines showed increased tolerance to a mixture of five heavy metals and also demonstrated enhanced metal uptake ability under controlled conditions. The transgenic lines were fertile and did not exhibit any apparent morphological abnormality. The results of this study indicated an effective approach to improve the heavy metal accumulation ability of alfalfa plants which can then be used for the remediation of contaminated soil in arid regions.

Growth of zinnia, Italian ryegrass, and alfalfa and their remediation effects in diesel oil-contaminated soils

Our objective in this study was to compare the growth of zinnia, Italian ryegrass, and alfalfa, and their remediation effects in oil-contaminated soils. The soils were prepared by mixing 2, 4, or 8% diesel oil by weight with soil. The plant height and dry weights of shoots and roots were highest for zinnia in the 2 and 4% oil treatments, and highest for Italian ryegrass in the 8% oil treatment. The reduction ratios in soil total petroleum hydrocarbons concentration (TPH) for 3 plants were lower in the 4 and 8% oil treatments than those in the 2% treatment. The reduction ratios for Italian ryegrass and zinnia contaminated with 2, 4, and 8% diesel oil treatments were significantly higher than those for alfalfa and the non-cultivation treatment at 45 days after sowing, and there were no significant differences in reduction ratios between Italian ryegrass and zinnia. The reduction ratio of soil TPH concentration brought about by zinnia was also comparable to that of Italian ryegrass. Therefore, we conclude that zinnia shows growth and remediation effects that are equivalent to those of Italian ryegrass, in soils contaminated with less than 8% oil.

The impact of nanoparticles zero-valent iron (nZVI) and rhizosphere microorganisms on the phytoremediation ability of white willow and its response

Soil contaminated with heavy metals (HMs) is a serious problem throughout the world that threatens all living organisms in the soil. Therefore, large-scale remediation is necessary. This study investigated a new combination of remediation techniques on heavy metal contaminated soil, phytoremediation, and soil amendment with nano-sized zero-valent iron (nZVI) and rhizosphere microorganisms. White willow (Salix alba L.) was grown for 160 days in pots containing Pb, Cu, and Cd and amended with 0, 150, and 300 (mg kg^-1) of nZVI and rhizosphere microorganisms, including the arbuscular mycorrhizal fungus (AMF), Rhizophagus irregularis, and the plant growth promoting rhizobacteria (PGPR), Pseudomonas fluorescens. The results showed that inoculation with PGPR and AMF, particularly dual inoculation, improved plant growth as well as the physiological and biochemical parameters of white willow, and increased the bioconcentration factor (BCF) of Pb, Cu, and Cd. The low dose of nZVI significantly increased the root length and the leaf area of the seedlings and increased the BCF of Cd. In contrast, the high dose of nZVI had negative effects on the seedlings growth and the BCF of Pb and Cu, about - 32% and - 63%, respectively. Our results demonstrate that nZVI at low doses can improve plant performance in a phytoremediation context and that the use of beneficial rhizosphere microorganisms can minimize nZVI stress in plants and make them less susceptible to stress even under high dose conditions.

Nano-based smart pesticide formulations: Emerging opportunities for agriculture

The incorporation of nanotechnology as a means for nanopesticides is in the early stage of development. The main idea behind this incorporation is to lower the indiscriminate use of conventional pesticides to be in line with safe environmental applications. Nanoencapsulated pesticides can provide controlled release kinetics, while efficiently enhancing permeability, stability, and solubility. Nanoencapsulation can enhance the pest-control efficiency over extended durations by preventing the premature degradation of active ingredients (AIs) under harsh environmental conditions. This review is thus organized to critically assess the significant role of nanotechnology for encapsulation of AIs for pesticides. The smart delivery of pesticides is essential to reduce the dosage of AIs with enhanced efficacy and to overcome pesticide loss (e.g., due to leaching and evaporation). The future trends of pesticide nanoformulations including nanomaterials as AIs and nanoemulsions of biopesticides are also explored. This review should thus offer a valuable guide for establishing regulatory frameworks related to field applications of these nano-based pesticides in the near future.

Relationships between root growth of Zinnia hybrid "profusion orange" flowers and phytoremediation of oil-contaminated soil

Relationships exist between plant root growth and the phytoremediation of oil-contaminated soils. In a previous study, we demonstrated that zinnia flowers are well suited for the remediation of oil-contaminated soil. In this study, our goal was to quantify the relationship between zinnia root growth and purification of oil-contaminated soils. Three treatments were used: (1) cultivation of zinnia in oil-contaminated soil (contaminated pots), (2) cultivation in non-contaminated soil (non-contaminated pots), and (3) contaminated soil with no cultivation and only irrigation (irrigated pots). Growth of the Zinnia plants, including their roots, was significantly reduced in the contaminated pots compared with the noncontaminated pots. The soil dehydrogenase activity increased between 45 and 90 days after planting in all parts of the contaminated pots, especially the upper parts. The soil total petroleum hydrocarbon (TPH) concentrations in the contaminated pots decreased throughout the study period. Interestingly, the soil dehydrogenase activity increased, and the soil TPH concentration decreased even in lower parts of the pots where there was very little root growth. Therefore, the cultivation of plants can have a remediative effect on oil-contaminated soil even below the depth reached by the plant roots.

Identification and comprehensive analysis of the characteristics and roles of leucine-rich repeat receptor-like protein kinase (LRR-RLK) genes in Sedum alfredii Hance responding to cadmium stress

Sedum alfredii Hance is a Zn/Cd co-hyperaccumulator and its underlying molecular mechanism of Cd tolerance is worthy to be elucidated. Although numerous studies have reported the uptake, sequestration and detoxification of Cd in S. alfredii Hance, how it senses Cd-stress stimuli and transfers signals within tissues remains unclear. Leucine-rich repeat receptor-like protein kinases (LRR-RLKs) are vital for plant growth, development, immunity and signal transduction. Till now, there is lack of comprehensive studies addressing their functions in S. alfredii Hance responding to Cd stress. In the present study, we identified 60 LRR-RLK genes in S. alfredii Hance based on transcriptome analysis under Cd stress. They were categorized into 11 subfamilies and most of them had highly conserved protein structures and motif compositions. The inter-family diversity provided evidence for their functional divergence, supported by their expression level and profile in tissues under Cd stress. Co-expression network analysis revealed that the most highly connected hubs, Sa0F.522, Sa0F.1036, Sa28F.115 and Sa1F.472, were closely related with other genes involved in metal transport, stimulus response and transcription regulations. Of the ten hub genes exhibiting differential expression dynamics under the short-term Cd stress (Sa0F.522, Sa0F.1036 and Sa28F.115) were dramatically induced in the whole plant. Among them, Sa0F.522 gene was heterologously expressed in a Cd-sensitive yeast cell line and its function in Cd signal perception was confirmed. For the first time, our findings performed a comprehensive analysis of LRR-RLKs in S. alfredii Hance, mapped their expression patterns under Cd stress, and identified the key roles of Sa0F.522, Sa0F.1036 and Sa28F.115 in Cd signal transduction.

Remediation approach for organic compounds and arsenic co-contaminated soil using the pressurized hot water extraction process

Successful remediation of soil with co-existing organics contaminants and arsenic (As) is a challenge as the chemical and remediation technologies are different for each group of pollutants. In this study, the treatment effectiveness of the pressurized hot water (PHW) extraction process was investigated for remediation of soil co-contaminated with phenol, crude oil, polycyclic aromatic hydrocarbons (PAHs), and As. An elimination percentage of about 99% was achieved for phenol, and in the range of 63-100% was observed for the PAHs at 260°C for 90 min operation. The performance of PHW extraction in the removal of total petroleum hydrocarbons was found to be 86%. Of the 87 mg/kg of As in untreated soil, 67% of which was eliminated after treatment. The removal of organic contaminants was mainly via desorption, dissolution and degradation in subcritical water, while As was eliminated probably by oxidation and dissolution of arsenic-bearing minerals. According to the experimental results, the PHW extraction process can be suggested as an alternative cleaning technology, instead of using any organic solvents for remediation of such co-contaminated soil.

The arbuscular mycorrhizal fungus Rhizophagus irregularis MUCL 41833 increases the phosphorus uptake and biomass of Medicago truncatula, a benzo[a]pyrene-tolerant plant species

The accumulation of phosphorus (P) in plants increases their biomass and resistance/tolerance to organic pollutants. Both characteristics are mandatory for the utilization of plants in phytoremediation. Arbuscular mycorrhizal (AM) fungi improve plant P nutrition, and thus growth. However, only a few studies have focused on the dynamics of inorganic P (Pi) uptake in AM fungal-colonized plants in the presence of organic pollutants. Indeed, most of the results so far were obtained after harvesting the plants, thus by evaluating P concentration and content at a single time point. Here, we investigated the effects of the AM fungus Rhizophagus irregularis MUCL 41833 on the short-term Pi uptake dynamics of Medicago truncatula plants grown in the presence of benzo[a]pyrene (B[a]P), a polyaromatic hydrocarbon (PAH) frequently found in polluted soils. The study was conducted using a non-destructive circulatory semi-hydroponic cultivation system to investigate the short-term Pi depletion from a nutrient solution and as a corollary, the Pi uptake by the AM fungal-colonized and non-colonized plants. The growth, P concentration, and content of plants were also evaluated at harvest. The presence of B[a]P neither impacted the development of the AM fungus in the roots nor the plant growth and Pi uptake, suggesting a marked tolerance of both organisms to B[a]P pollution. A generally higher Pi uptake coupled with a higher accumulation of P in shoots and roots was noticed in AM fungal-colonized plants as compared to the non-colonized controls, irrespective of the presence or absence of B[a]P. Therefore, fungal-colonized plants showed the best growth. Furthermore, the beneficial effect provided by the presence of the AM fungus in roots was similar in presence or absence of B[a]P, thus opening the door for potential utilization in phytomanagement of PAH-polluted soils.

Molecular and Microbiological Insights on the Enrichment Procedures for the Isolation of Petroleum Degrading Bacteria and Fungi

Autochthonous bioaugmentation, by exploiting the indigenous microorganisms of the contaminated environment to be treated, can represent a successful bioremediation strategy. In this perspective, we have assessed by molecular methods the evolution of bacterial and fungal communities during the selective enrichment on different pollutants of a soil strongly polluted by mixtures of aliphatic and polycyclic hydrocarbons. Three consecutive enrichments were carried out on soil samples from different soil depths (0-1, 1-2, 2-3 m), and analyzed at each step by means of high-throughput sequencing of bacterial and fungal amplicons biomarkers. At the end of the enrichments, bacterial and fungal contaminants degrading strains were isolated and identified in order to (i) compare the composition of enriched communities by culture-dependent and culture-independent molecular methods and to (ii) obtain a collection of hydrocarbon degrading microorganisms potentially exploitable for soil bioremediation. Molecular results highlighted that for both bacteria and fungi the pollutant had a partial shaping effect on the enriched communities, with paraffin creating distinct enriched bacterial community from oil, and polycyclic aromatic hydrocarbons generally overlapping; interestingly neither the soil depth or the enrichment step had significant effects on the composition of the final enriched communities. Molecular analyses well-agreed with culture-dependent analyses in terms of most abundant microbial genera. A total of 95 bacterial and 94 fungal strains were isolated after selective enrichment procedure on different pollutants. On the whole, isolated bacteria where manly ascribed to Pseudomonas genus followed by Sphingobacterium, Bacillus, Stenothrophomonas, Achromobacter, and Serratia. As for fungi, Fusarium was the most abundant genus followed by Trichoderma and Aspergillus. The species comprising more isolates, such as Pseudomonas putida, Achromobacter xylosoxidans and Ochromobactrum anthropi for bacteria, Fusarium oxysporum and Fusarium solani for fungi, were also the dominant OTUs assessed in Illumina.

Effect of copper on diesel degradation in Pseudomonas extremaustralis

Environments co-contaminated with heavy metals and hydrocarbons have become an important problem worldwide, especially due to the effect of metals on hydrocarbon degrading microorganisms. Pseudomonas extremaustralis, a bacterium isolated from a pristine pond in Antarctica, showed high capabilities to cope with environmental stress and a very versatile metabolism that includes alkane degradation under microaerobic conditions. In this work, we analyzed P. extremaustralis' capability to resist high copper concentrations and the effect of copper presence in diesel biodegradation. We observed that P. extremaustralis resisted up to 4 mM CuSO₄ in a rich medium such as LB. This copper resistance is sustained by the presence of the cus and cop operons together with other efflux systems and porins located in a single region in P. extremaustralis genome. When copper was present, diesel degradation was negatively affected, even though copper enhanced bacterial attachment to hydrocarbons. However, when a small amount of glucose (0.05% w/v) was added, the presence of CuSO₄ enhanced alkane degradation. In addition, atomic force microscopy analysis showed that the presence of glucose decreased the negative effects produced by copper and diesel on the cell envelopes.

Impact of pyrometallurgical slags on sunflower growth, metal accumulation and rhizosphere microbial communities

Metallurgical exploitation originates metal-rich by-products termed slags, which are often disposed in the environment being a source of heavy metal pollution. Despite the environmental risk that this may pose for living organisms, little is known about the impact of slags on biotic components of the ecosystem like plants and rhizosphere microbial communities. In this study, metal-rich (Cu, Pb, Zn) granulated slags (GS) derived from Cu production process, were used for a leaching test in the presence of the soil pore solution, showing that soil solution enhanced the release of Cu from GS. A pot experiment was conducted using as growing substrate for sunflower (Helianthus annuus) a 50% w/w mix of an agricultural soil and GS. Bioavailability of metals in soil was, in increasing order: Pb < Zn < Cu. Sunflower was able to grow in the presence of GS and accumulated metals preferentially in above-ground tissues. Microbial diversity was assessed in rhizosphere and bulk soil using community level physiological profiling (CLPP) and 16S rRNA gene based denaturing gradient gel electrophoresis (DGGE) analyses, which demonstrated a shift in the diversity of microbial communities induced by GS. Overall, these results suggest that metallurgical wastes should not be considered inert when dumped in the soil. Implications from this study are expected to contribute to the development of sustainable practices for the management of pyrometallurgical slags, possibly involving a phytomanagement approach.

Remediation of saline soils contaminated with crude oil using the halophyte Salicornia persica in conjunction with hydrocarbon-degrading bacteria

The negative impact of salinity on plant growth and the survival of rhizosphere biota complicates the application of bioremediation to crude oil-contaminated saline soils. Here, a comparison was made between the remedial effect of treating the soil with Pseudomonas aeruginosa, a salinity tolerant hydrocarbon-degrading consortium in conjunction with either the halophyte Salicornia persica or the non-halophyte Festuca arundinacea. The effect of the various treatments on salinized soils was measured by assessing the extent of total petroleum hydrocarbon (TPH) degradation, the soil's dehydrogenase activity, the abundance of the bacteria and the level of phytotoxicity as measured by a bioassay. When a non-salinized soil was assessed after a treatment period of 120 days, the ranking for effectiveness with respect to TPH removal was F. arundinacea > P. aeruginosa > S. persica > no treatment control, while in the presence of salinity, the ranking changed to S. persica > P. aeruginosa > F. arundinacea > no treatment control. Combining the planting of S. persica or F. arundinacea with P. aeruginosa inoculation ("bioaugmentation") boosted the degradation of TPH up to 5-17%. Analyses of the residual oil contamination revealed that long chain alkanes (above C20) were particularly strongly degraded following the bioaugmentation treatments. The induced increase in dehydrogenase activity and the abundance of the bacteria (3.5 and 10 fold respectively) achieved in the bioaugmentation/S. persica treatment resulted in 46-76% reduction in soil phytotoxicity in a saline soil. The indication was that bioaugmentation of halophyte can help to mitigate the adverse effects on the effectiveness of bioremediation in a crude oil-contaminated saline soil.

Phytoremediation of sewage sludge contaminated by trace elements and organic compounds

Phytoremediation is a green technique being increasingly used worldwide for various purposes including the treatment of municipal sewage sludge (MSS). Most plants proposed for this technique have high nutrient demands, and fertilization is often required to maintain soil fertility and nutrient balance while remediating the substrate. In this context, MSS could be a valuable source of nutrients (especially N and P) and water for plant growth. The aim of this study was to determine the capacity willow (Salix matsudana, cv Levante), poplar (Populus deltoides × Populus nigra, cv Orion), eucalyptus (Eucalyptus camaldulensis) and sunflower (Helianthus annuus) to clean MSS, which is slightly contaminated by trace elements (TEs) and organic pollutants, and to assess their physiological response to this medium. In particular, we aimed to evaluate the TE accumulation by different species as well as the decrease of TEs and organic pollutants in the sludge after one cropping cycle and the effect of MSS on plant growth and physiology. Since MSS did not show any detrimental effect on the biomass yield of any of the species tested, it was found to be a suitable growing medium for these species. TE phytoextraction rates depended on the species, with eucalyptus showing the highest accumulation for Cr, whereas sunflower exhibited the best performance for As, Cu and Zn. At the end of the trial, some TEs (i.e. Cr, Pb and Zn), n-alkanes and PCBs showed a significant concentration decrease in the sludge for all tested species. The highest Cr decrease was observed in pots with eucalyptus (57.4%) and sunflower (53.4%), whereas sunflower showed the highest Cu decrease (44.2%), followed by eucalyptus (41.2%), poplar (16.2%) and willow (14%). A significant decrease (41.1%) of Pb in the eucalyptus was observed. Zn showed a high decrease rate with sunflower (59.5%) and poplar (52%) and to a lesser degree with willow (35.3%) and eucalyptus (25.4%). The highest decrease in n-alkanes concentration in the sludge was found in willow (98.3%) and sunflower (97.3%), whereas eucalyptus has the lowest PCBs concentration (91.8%) in the sludge compared to the beginning of the trial. These results suggest new strategies (e.g. crop rotation and intercropping) to be adopted for a better management of this phytotechnology.

Environmental parameters altered by climate change affect the activity of soil microorganisms involved in bioremediation

Bioremediation, based on the use of microorganisms to break down pollutants, can be very effective at reducing soil pollution. But the climate change we are now experiencing is bound to have an impact on bioremediation performance, since the activity and degrading abilities of soil microorganisms are dependent on a series of environmental parameters that are themselves being altered by climate change, such as soil temperature, moisture, amount of root exudates, etc. Many climate-induced effects on soil microorganisms occur indirectly through changes in plant growth and physiology derived from increased atmospheric CO2 concentrations and temperatures, the alteration of precipitation patterns, etc., with a concomitant effect on rhizoremediation performance (i.e. the plant-assisted microbial degradation of pollutants in the rhizosphere). But these effects are extremely complex and mediated by processes such as acclimation and adaptation. Besides, soil microorganisms form complex networks of interactions with a myriad of organisms from many taxonomic groups that will also be affected by climate change, further complicating data interpretation.

Insight Into the Variation of Bacterial Structure in Atrazine-Contaminated Soil Regulating by Potential Phytoremediator: Pennisetum americanum (L.) K. Schum

Although plants of the genus Pennisetum can accelerate the removal of atrazine from its rhizosphere, the roles played by this plant in adjusting the soil environment and soil microorganism properties that might contribute to pollutant removal are incompletely understood. We selected Pennisetum americanum (L.) K. Schum (P. americanum) as the test plant and investigated the interaction between P. americanum and atrazine-contaminated soil, focusing on the adjustment of the soil biochemical properties as well as bacterial functional and community diversity in the rhizosphere using Biolog EcoPlates and high-throughput sequencing of the 16S rRNA gene. The results demonstrate that the rhizosphere soil of P. americanum exhibited higher catalase activity, urease activity and water soluble organic carbon (WSOC) content, as well as a suitable pH for microorganisms after a 28-day incubation. The bacterial functional diversity indices (Shannon and McIntosh) for rhizosphere soil were 3.17 ± 0.04 and 6.43 ± 0.86 respectively, while these indices for non-rhizosphere soil were 2.95 ± 0.06 and 3.98 ± 0.27. Thus, bacteria in the P. americanum rhizosphere exhibited better carbon substrate utilization than non-rhizosphere bacteria. Though atrazine decreased the richness of the soil bacterial community, rhizosphere soil had higher bacterial community traits. For example, the Shannon diversity indices for rhizosphere and non-rhizosphere soil were 5.821 and 5.670 respectively. Meanwhile, some bacteria, such as those of the genera Paenibacillus, Rhizobium, Sphingobium, and Mycoplana, which facilitate soil nutrient cycling or organic pollutants degradation, were only found in rhizosphere soil after a 28-day remediation. Moreover, redundancy analysis suggests that the soil biochemical properties that were adjusted by the test plant exhibited correlations with the bacterial community composition and functional diversity. These results suggest that the soil environment and bacterial properties could be adjusted by P. americanum during phytoremediation of atrazine-contaminated soil.

Use of bacterial acc deaminase to increase oil (especially poly aromatic hydrocarbons) phytoremediation efficiency for maize (zea mays) seedlings

Oil presence in soil, as a stressor, reduces phytoremediation efficiency through an increase in the plant stress ethylene. Bacterial 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, as a plant stress ethylene reducer, was employed to increase oil phytoremediation efficiency. For this purpose, the ability of ACC deaminase-producing Pseudomonas strains to grow in oil-polluted culture media and withstand various concentrations of oil and also their ability to reduce plant stress ethylene and enhance some growth characteristics of maize and finally their effects on increasing phytoremediation efficiency of poly aromatic hydrocarbons (PAHs) in soil were investigated. Based on the results, of tested strains just P9 and P12 were able to perform oil degradation. Increasing oil concentration from 0 to 10% augmented these two strains population, 15.7% and 12.9%, respectively. The maximum increase in maize growth was observed in presence of P12 strain. Results of high-performance liquid chromatography (HPLC) revealed that PAHs phytoremediation efficiency was higher for inoculated seeds than uninoculated. The highest plant growth and PAHs removal percentage (74.9%) from oil-polluted soil was observed in maize inoculated with P12. These results indicate the significance of ACC deaminase producing bacteria in alleviation of plant stress ethylene in oil-polluted soils and increasing phytoremediation efficiency of such soils.

Agronomic and economic evaluation of Vetiver grass (Vetiveria zizanioides L.) as means for phytoremediation of diesel polluted soils in Israel

Soil pollution in Israel, due to diesel contamination, is a major concern, with gas stations, factories and refineries being the main polluters (>60%). Vetiver grass (Vetiveria zizanioides L.) is a perennial grass belonging to the Poaceae family, and is recognized world-wide for its potential as a plant with phytoremediation traits to contaminated soils. It is demonstrated here to decrease diesel contamination in field and court-yard trials. Chemical soil analysis indicated up to a 79% decrease (P < .05) in diesel pollution of contaminated soil planted with Vetiver; and at high soil contamination levels of 10 L/m², a significant (P < .05) reduction of 96, 96 and 87% was recorded at soil depths of 0-20, 20-40 and 40-60 cm, respectively. Furthermore, in field plots contaminated with diesel and planted with Vetiver, weeds' biomass recovered to non-polluted levels following 8 to 9 months of Vetiver treatment. An economic evaluation conducted based on the cost-benefit analysis (CBA) principles, utilizing the Net Present Value (NPV) compared phytoremediation to other currently used decontamination procedures. The economic comparison showed that phytoremediation cleanup costs are lower and more beneficial to society at large, primarily from an ecosystem services perspective. Combining the results of the agronomic examination with the economic valuation, this research pointed out that phytoremediation with Vetiver has a non-negligible potential, making it a good solution for cleansing diesel from soils on a state-wide scale in Israel and worthy of further research and development.

Rhizospheric microorganisms as a solution for the recovery of soils contaminated by petroleum: A review

Petroleum is currently the world's main energy source, and its demand is expected to increase in coming years. Its intense exploitation can lead to an increase in the number of environmental accidents, such as spills and leaks, and an increase in the generation of environmental liabilities resulting from refining. Due to its hydrophobic characteristics and slow process of biodegradation, petroleum can remain in the environment for a long time and its toxicity can cause a negative impact on both terrestrial and aquatic ecosystems, with the main negative effects related to its carcinogenic potential for both animals and humans. The objective of the present review is to discuss environmental contamination by oil, conventional treatment techniques and bioremediation an alternative tool for recovery petroleum-contaminated soils, focusing on the rhizodegradation process, plant growth-promoting rhizobacteria (PGPR), a phytoremediation strategy in which the microorganisms that colonize the roots of phytoremediatior plants are responsible for the biodegradation of petroleum. These microorganisms can be selected and tested individually or in the form of consortia to evaluate their potential for oil degradation, or even to measure the use of biosurfactants produced by them to constitute tools for the development of environmental recovery strategies and biotechnological application.

Brassica napus has a key role in the recovery of the health of soils contaminated with metals and diesel by rhizoremediation

Contaminated soils are frequently characterized by the simultaneous presence of organic and inorganic contaminants, as well as a poor biological and nutritional status. Rhizoremediation, the combined use of phytoremediation and bioremediation, has been proposed as a Gentle Remediation Option to rehabilitate multi-contaminated soils. Recently, newer techniques, such as the application of metallic nanoparticles, are being deployed in an attempt to improve traditional remediation options. In order to implement a phytomanagement strategy on calcareous alkaline peri-urban soils simultaneously contaminated with several metals and diesel, we evaluated the effectiveness of Brassica napus L., a profitable crop species, assisted with organic amendment and zero-valent iron nanoparticles (nZVI). A two-month phytotron experiment was carried out using two soils, i.e. amended and unamended with organic matter. Soils were artificially contaminated with Zn, Cu and Cd (1500, 500 and 50mgkg^-1, respectively) and diesel (6000mgkg^-1). After one month of stabilization, soils were treated with nZVI and/or planted with B. napus. The experiment was conducted with 16 treatments resulting from the combination of the following factors: amended/unamended, contaminated/non-contaminated, planted/unplanted and nZVI/no-nZVI. Soil physicochemical characteristics and biological indicators (plant performance and soil microbial properties) were determined at several time points along the experiment. Carbonate content of soils was the crucial factor for metal immobilization and, concomitantly, reduction of metal toxicity. Organic amendment was essential to promote diesel degradation and to improve the health and biomass of B. napus. Soil microorganisms degraded preferably diesel hydrocarbons of biological origin (biodiesel). Plants had a remarkable positive impact on the activity and functional diversity of soil microbial communities. The nZVI were ineffective as soil remediation tools, but did not cause any toxicity. We concluded that rhizoremediation with B. napus combined with an organic amendment is promising for the phytomanagement of calcareous soils with mixed (metals and diesel) contamination.

A comparative study to evaluate natural attenuation, mycoaugmentation, phytoremediation, and microbial-assisted phytoremediation strategies for the bioremediation of an aged PAH-polluted soil

Biological treatments are considered an environmentally option to clean-up polluted soil with polycyclic aromatic hydrocarbons (PAHs). A pot experiment was conducted to comparatively evaluate four different strategies, including natural attenuation (NA), mycoaugmentation (M) by using Crucibulum leave, phytoremediation (P) using maize plants, and microbial-assisted phytoremediation (MAP) for the bioremediation of an aged PAH-polluted soil at 180 days. The P treatment had higher affinity degrading 2-3 and 4 ring compounds than NA and M treatments, respectively. However, M and P treatments were more efficient in regards to naphthalene, indeno[l,2,3-c,d]pyrene and benzo[g,h,i]perylene degradation respect to NA. However, 4, 5-6 rings undergo a strong decline during the microbe-assisted phytoremediation, being the treatment which determined the highest rates of PAHs degradation. Sixteen PAH compounds, except fluorene and dibenzo[a,h]anthracene, were found in maize roots, whereas the naphthalene, phenanthrene, anthracene, fluoranthene, and pyrene were accumulated in the shoots, in both P and MAP treatments. However, higher PAH content in maize biomass was achieved during the MAP treatment respect to P treatment. The bioconversion and translocation factors were less than 1, indicating that phystabilization/phytodegradation processes occurred rather than phytoextraction. The microbial biomass, activity and ergosterol content were significantly boosted in the MAP treatment respect to the other treatments at 180 days. Ours results demonstrated that maize-C. laeve association was the most profitable technique for the treatment of an aged PAH-polluted soil when compared to other bioremediation approaches.

Hydrocarbon- and metal-polluted soil bioremediation: progress and challenges

The problem of soil contamination with petroleum hydrocarbons and heavy metals is becoming particularly acute for large oil-producing countries, like the Russian Federation. Both hydrocarbon and metal contaminants impact negatively the soil biota and human health, thus requiring efficient methods for their detoxification and elimination. Bioremediation of soil co-contaminated with hydrocarbon and metal pollutants is complicated by the fact that, although the two components must be treated differently, they mutually affect the overall removal efficiency. Heavy metals are reported to inhibit biodegradation of hydrocarbons by interfering with microbial enzymes directly involved in biodegradation or through the interaction with enzymes involved in general metabolism. Here we discuss recent progress and challenges in bioremediation of soils co-contaminated with hydrocarbons and heavy metals, focusing on selecting metal-resistant biodegrading strains and biosurfactant amendments.

Resistance of aerobic microorganisms and soil enzyme response to soil contamination with Ekodiesel Ultra fuel

This study determined the susceptibility of cultured soil microorganisms to the effects of Ekodiesel Ultra fuel (DO), to the enzymatic activity of soil and to soil contamination with PAHs. Studies into the effects of any type of oil products on reactions taking place in soil are necessary as particular fuels not only differ in the chemical composition of oil products but also in the composition of various fuel improvers and antimicrobial fuel additives. The subjects of the study included loamy sand and sandy loam which, in their natural state, have been classified into the soil subtype 3.1.1 Endocalcaric Cambisols. The soil was contaminated with the DO in amounts of 0, 5 and 10 cm³ kg^-1. Differences were noted in the resistance of particular groups or genera of microorganisms to DO contamination in loamy sand (LS) and sandy loam (SL). In loamy sand and sandy loam, the most resistant microorganisms were oligotrophic spore-forming bacteria. The resistance of microorganisms to DO contamination was greater in LS than in SL. It decreased with the duration of exposure of microorganisms to the effects of DO. The factor of impact (IF_DO) on the activity of particular enzymes varied. For dehydrogenases, urease, arylsulphatase and β-glucosidase, it had negative values, while for catalase, it had positive values and was close to 0 for acid phosphatase and alkaline phosphatase. However, in both soils, the noted index of biochemical activity of soil (BA) decreased with the increase in DO contamination. In addition, a positive correlation occurred between the degree of soil contamination and its PAH content.

Enrichment and characterization of hydrocarbon-degrading bacteria from petroleum refinery waste as potent bioaugmentation agent for in situ bioremediation

Intrinsic biodegradation potential of bacteria from petroleum refinery waste was investigated through isolation of cultivable strains and their characterization. Pseudomonas and Bacillus spp. populated the normal cultivable taxa while prolonged enrichment with hydrocarbons and crude oil yielded hydrocarbonoclastic bacteria of genera Burkholderia, Enterobacter, Kocuria, Pandoraea, etc. Strains isolated through enrichment showed assemblages of superior metabolic properties: utilization of aliphatic (C6-C22) and polyaromatic compounds, anaerobic growth with multiple terminal electron acceptors and higher biosurfactant production. Biodegradation of dodecane was studied thoroughly by GC-MS along with detection of gene encoding alkane hydroxylase (alkB). Microcosms bioaugmented with Enterobacter, Pandoraea and Burkholderia strains showed efficient biodegradation (98% TPH removal) well fitted in first order kinetic model with low rate constants and decreased half-life. This study proves that catabolically efficient bacteria resides naturally in complex petroleum refinery wastes and those can be useful for bioaugmentation based bioremediation.

Functional Diversity of Fungal Communities in Soil Contaminated with Diesel Oil

The widespread use and consumption of crude oil draws the public's attention to the fate of petroleum hydrocarbons in the environment, as they can permeate the soil environment in an uncontrollable manner. Contamination of soils with petroleum products, including diesel oil (DO), can cause changes in the microbiological soil properties. The effect of diesel oil on the functional diversity of fungi was tested in a model experiment during 270 days. Fungi were isolated from soil and identified. The functional diversity of fungal communities was also determined. Fungi were identified with the MALDI-TOF method, while the functional diversity was determined using FF-plates made by Biolog®, with 95 carbon sources. Moreover, the diesel oil degradation dynamics was assessed. The research showed that soil contaminated with diesel oil is characterized by a higher activity of oxireductases and a higher number of fungi than soil not exposed to the pressure of this product. The DO pollution has an adverse effect on the diversity of fungal community. This is proved by significantly lower values of the Average Well-Color Development, substrates Richness (R) and Shannon-Weaver (H) indices at day 270 after contamination. The consequences of DO affecting soil not submitted to remediation are persistent. After 270 days, only 64% of four-ringed, 28% of five-ringed, 21% of 2-3-ringed and 16% of six-ringed PAHs underwent degradation. The lasting effect of DO on communities of fungi led to a decrease in their functional diversity. The assessment of the response of fungi to DO pollution made on the basis of the development of colonies on Petri dishes [Colony Development (CD) and Eco-physiological Diversity (EP) indices] is consistent with the analysis based on the FF MicroPlate system by Biolog®. Thus, a combination of the FF MicroPlate system by Biolog® with the simultaneous calculation of CD and EP indices alongside the concurrent determination of the content of PAHs and activity of oxireductases provides an opportunity to achieve relatively complete characterization of the consequences of a long-term impact of diesel oil on soil fungi.

Evaluation methods for assessing effectiveness of in situ remediation of soil and sediment contaminated with organic pollutants and heavy metals

Soil and sediment contamination has become a critical issue worldwide due to its great harm to the ecological environment and public health. In recent years, many remediation technologies including physical, chemical, biological, and combined methods have been proposed and adopted for the purpose of solving the problems of soil and sediment contamination. However, current research on evaluation methods for assessing these remediation technologies is scattered and lacks valid and integrated evaluation methods for assessing the remediation effectiveness. This paper provides a comprehensive review with an environmental perspective on the evaluation methods for assessing the effectiveness of in situ remediation of soil and sediment contaminated with organic pollutants and heavy metals. The review systematically summarizes recent exploration and attempts of the remediation effectiveness assessment based on the content of pollutants, soil and sediment characteristics, and ecological risks. Moreover, limitations and future research needs of the practical assessment are discussed. These limitations are not conducive to the implementation of the abatement and control programs for soil and sediment contamination. Therefore, more attention should be paid to the evaluation methods for assessing the remediation effectiveness while developing new in situ remediation technologies in future research.

Bioremoval of lead using Pennisetum purpureum augmented with Enterobacter cloacae-VITPASJ1: A pot culture approach

Lead is a toxic heavy metal discharged into the ecosystem from various industries. Biological remediation strategies have been effective in the bioremoval of lead. In our current study, a phytobacterial system using Pennisetum purpureum along with lead-resistant bacterium (LRB) was employed for the uptake of lead. The LRB was obtained from lead-contaminated sites. The isolate VITPASJ1 was found to be highly tolerant to lead and was identified as an effective plant growth-promoting bacterium. The 16S rRNA sequencing revealed VITPASJ1 to be the closest neighbour of Enterobacter cloacae. The lead-resistant gene pbrA in the plant and the bacterium were amplified using a specific primer. The uptake of lead was studied by phytoremediation and rhizoremediation set-ups where the soil was supplemented with various concentrations of lead (50, 100, 150 mg/kg). The plants were uprooted at regular intervals, and the translocation of lead into the plant was determined by atomic absorption spectroscopy. The root length, shoot height and chlorophyll content were found to be higher in the rhizoremediation set-up when compared to the phytoremediation set-up. The scanning electron microscopic micrographs gave a clear picture of increased tissue damage in the root and shoot of the phytoremediation set-up as compared to the rhizoremediation set-up with LRB.

Soil bioremediation approaches for petroleum hydrocarbon polluted environments

Increasing industrialisation, continued population growth and heavy demand and reliance on petrochemical products have led to unprecedented economic growth and development. However, inevitably this dependence on fossil fuels has resulted in serious environmental issues over recent decades. The eco-toxicity and the potential health implications that petroleum hydrocarbons pose for both environmental and human health have led to increased interest in developing environmental biotechnology-based methodologies to detoxify environments impacted by petrogenic compounds. Different approaches have been applied for remediating polluted sites with petroleum derivatives. Bioremediation represents an environmentally sustainable and economical emerging technology for maximizing the metabolism of organic pollutants and minimizing the ecological effects of oil spills. Bioremediation relies on microbial metabolic activities in the presence of optimal ecological factors and necessary nutrients to transform organic pollutants such as petrogenic hydrocarbons. Although, biodegradation often takes longer than traditional remediation methods, the complete degradation of the contaminant is often accomplished. Hydrocarbon biodegradation in soil is determined by a number of environmental and biological factors varying from site to site such as the pH of the soil, temperature, oxygen availability and nutrient content, the growth and survival of hydrocarbon-degrading microbes and bioavailability of pollutants to microbial attack. In this review we have attempted to broaden the perspectives of scientists working in bioremediation. We focus on the most common bioremediation technologies currently used for soil remediation and the mechanisms underlying the degradation of petrogenic hydrocarbons by microorganisms.