Phytoremediation in mangrove sediments impacted by persistent total petroleum hydrocarbons (TPH's) using Avicennia schaueriana

Methods Using Marine Aquatic Photoautotrophs along the Qatari Coastline to Remediate Oil and Gas Industrial Water

Qatar and other Gulf States have a diverse range of marine vegetation that is adapted to the stressful environmental conditions of seawater. The industrial wastewater produced by oil and gas activities adds further detrimental conditions for marine aquatic photosynthetic organisms on the Qatari coastlines. Thus, these organisms experience severe stress from both seawater and industrial wastewater. This review discusses the biodiversity in seawater around Qatar, as well as remediation methods and metabolic pathways to reduce the negative impacts of heavy metals and petroleum hydrocarbons produced during these activities. The role of microorganisms that are adjacent to or associated with these aquatic marine organisms is discussed. Exudates that are released by plant roots enhance the role of microorganisms to degrade organic pollutants and immobilize heavy metals. Seaweeds may have other roles such as biosorption and nutrient uptake of extra essential elements to avoid or reduce eutrophication in marine environments. Special attention is paid to mangrove forests and their roles in remediating shores polluted by industrial wastewater. Seagrasses (Halodule uninervis, Halophila ovalis, and Thalassia hemprichii) can be used as promising candidates for phytoremediation or bioindicators for pollution status. Some genera among seaweeds that have proven efficient in accumulating the most common heavy metals found in gas activities and biodegradation of petroleum hydrocarbons are discussed.

Phytoremediation of pollutants in oil-contaminated soils by Alhagi camelorum: evaluation and modeling

Phytoremediation is a cost-effective and environmentally friendly method, offering a suitable alternative to chemical and physical approaches for the removal of pollutants from soil. This research explored the phytoremediation potential of Alhagi camelorum, a plant species, for total petroleum hydrocarbons (TPHs) and heavy metals (HMs), specifically lead (Pb), chromium (Cr), nickel (Ni), and cadmium (Cd), in oil-contaminated soil. A field-scale study spanning six months was conducted, involving the cultivation of A. camelorum seeds in a nursery and subsequent transplantation of seedlings onto prepared soil plots. Control plots, devoid of any plants, were also incorporated for comparison. Soil samples were analyzed throughout the study period using inductively coupled plasma-optical emission spectroscopy (ICP‒OES) for HMs and gas chromatography‒mass spectrometry (GC‒MS) for TPHs. The results showed that after six months, the average removal percentage was 53.6 ± 2.8% for TPHs and varying percentages observed for the HMs (Pb: 50 ± 2.1%, Cr: 47.6 ± 2.5%, Ni: 48.1 ± 1.6%, and Cd: 45.4 ± 3.5%). The upward trajectory in the population of heterotrophic bacteria and the level of microbial respiration, in contrast to the control plots, suggests that the presence of the plant plays a significant role in promoting soil microbial growth (P < 0.05). Moreover, kinetic rate models were examined to assess the rate of pollutant removal. The coefficient of determination consistently aligned with the first-order kinetic rate model for all the mentioned pollutants (R2 > 0.8). These results collectively suggest that phytoremediation employing A. camelorum can effectively reduce pollutants in oil-contaminated soils.

The effect of petroleum levels on some soil biological properties under phytoremediation and bioaugmentation

With the development of industries and excessive use of petroleum compounds, petroleum pollution has become a serious threat to the environment. The aim of this study was to the effect of petroleum levels on the biological activities of soil affected by phytoremediation and bioaugmentation. A surface soil sample was collected from the polluted areas around Bandar Abbas Oil Refinery Company, and the petroleum-degrading bacteria were isolated. M. yunnanensis (native) was selected among the isolated colonies for further experiment. The used soil in this study was a surface soil collected from Baghu region of Bandar Abbas, Sothern Iran, and treatments were added to soil samples. To evaluate removal of petroleum levels (0, 4, and 8%) from the soil by phytoremediation (control, sorghum, barley, and bermudagrass) and bioaugmentation (control, A. brasilense (non-native) and M. yunnanensis) and bioaugmented phytoremediation, a factorial pot experiment with completely randomized design and three replications was performed. The results demonstrated that sorghum and bermudagrass were more resistant than barley to the toxic effects of petroleum. Positive effect of bacteria on dry weight in polluted soil was greater than in the non-polluted soil. The degradation of petroleum reaches 77% in sorghum + M. yunanesis + 4% petroleum. Plants had stronger ability to degrade total petroleum hydrocarbon (TPH), while bacteria could better degrade polyaromatic hydrocarbons (PAHs). Application of bacteria and plants stimulated soil biological characteristics (dehydrogenase, arylsulfatase, lipase, bacterial population, and respiration) in polluted soil. Among measured enzymes, dehydrogenase exhibited a stronger response to petroleum levels. Four-percent level had greater irritating effect on soil biological properties. Plants and bacteria rely on differences in biological properties to attain synergy in petroleum degradation. Results indicated that M. yunnanensis has a high ability to remove petroleum from soil, and plants enhance the efficiency of this bacterium.

An eco-sustainable approach towards heavy metals remediation by mangroves from the coastal environment: A critical review

Mangroves provide various ecosystem services, carbon sequestration, biodiversity depository, and livelihoods. They are most abundant in marine and coastal ecosystems and are threatened by toxic contaminants like heavy metals released from various anthropogenic activities. However, they have significant potential to survive in salt-driven environments and accumulate various pollutants. The adverse effects of heavy metals have been extensively studied and recognized as toxic to mangrove species. This study sheds light on the dynamics of heavy metal levels, their absorption, accumulation and transport in the soil environment in a mangrove ecosystem. The article also focuses on the potential of mangrove species to remove heavy metals from marine and coastal environments. This review concludes that mangroves are potential candidates to clean up contaminated water, soil, and sediments through their phytoremediation ability. The accumulation of toxic heavy metals by mangroves is mainly through roots with limited upward translocation. Therefore, promoting the maintenance of biodiversity and stability in the coastal environment is recommended as an environmentally friendly and potentially cost-effective approach.

Development of Rhizophora mangle (Rhizophoraceae) and Avicennia schaueriana (Avicenniaceae) in the presence of a hydrocarbon-degrading bacterial consortium and marine diesel oil

The development of Rhizophora mangle and Avicennia schaueriana seedlings impacted by marine diesel oil (MDO) was evaluated in the presence or absence of a hydrocarbon-degrading bacterial consortium (HBC). The bioassays were conducted in a greenhouse during 6 months and consisted of three different treatments (control, MDO only and MDO + HBC). The bacterial consortium was mainly composed of Bacillus spp. (73%), but Rhizobium spp., Pseudomonas spp., Ochrobactrum spp., and Brevundimonas spp. were also present. After 6 months, A. schaueriana seedlings showed higher mortality compared to those of R. mangle; R. mangle exhibited 68% (control), 44% (MDO alone) and 50% (MDO + HBC) seedlings survivorship compared to 42% (control), 0% (MDO alone) and 4% (MDO + HBC) for A. schaueriana. This variability may be due to differences in species physiology. Stem growth, diameter and number of leaves remained constant during the 6 months of the experiment with marine diesel oil and hydrocarbon-degrading bacterial consortium (MDO + BBC). For both mangrove species, bacterial enzymatic activity in the sediments was sufficient to maintain cell counts of 10⁷ cells cm^-3 in the rhizospheric soil and possibly synthetize the extracellular polymeric substances (EPS) that may emulsify and solubilize oil products.

Endophytes and Halophytes to Remediate Industrial Wastewater and Saline Soils: Perspectives from Qatar

Many halophytes are considered to be salt hyperaccumulators, adopting ion extrusion and inclusion mechanisms. Such plants, with high aboveground biomass, may play crucial roles in saline habitats, including soil desalination and phytoremediation of polluted soils and waters. These plants cause significant changes in some of the soil’s physical and chemical properties; and have proven efficient in removing heavy metals and metabolizing organic compounds from oil and gas activities. Halophytes in Qatar, such as Halopeplis perfoliata, Salicornia europaea, Salsola soda, and Tetraena qatarensis, are shown here to play significant roles in the phytoremediation of polluted soils and waters. Microorganisms associated with these halophytes (such as endophytic bacteria) might boost these plants to remediate saline and polluted soils. A significant number of these bacteria, such as Bacillus spp. and Pseudomonas spp., are reported here to play important roles in many sectors of life. We explore the mechanisms adopted by the endophytic bacteria to promote and support these halophytes in the desalination of saline soils and phytoremediation of polluted soils. The possible roles played by endophytes in different parts of native plants are given to elucidate the mechanisms of cooperation between these native plants and the associated microorganisms.

Effects of oil contamination on plant growth and development: a review

Oil spills generate several environmental impacts and have become more common with the increase in petroleum extraction, refining, transportation, and trade. In soil, oil contamination increases water and nutrient availability and compaction, directly affecting plant growth and development. Different aspects of phytotoxicity can be observed and will vary according to the characteristics of soil and plants. Oil-contaminated soil also results in negative effects on biomass and changes in leaves and roots. Investigating the effects of oil contamination on plant growth and development can aid in the conservation of plant species and in the development of techniques such as bioremediation and biomonitoring. Thus, this review aims to discuss the main effects of oil contamination on plants, such as environmental stress and morphological, physiological, and anatomical changes, and the strategies developed by plants to survive contamination, as well as to identify plants with phytoremediation potential that can assist in removing oil from the environment.

A preliminary study on the eco-environmental geological issue of in-situ oil shale mining by a physical model

As traditional methods of oil shale production emitting high levels of pollutants, in-situ exploitation has aroused great concerns. In order to study the effect of in-situ pyrolysis products on the underground environment, an in-situ oil shale exploitation of underground environment impact laboratory simulation system was designed. Based on the hydrogeological condition of oil shale area in Nong'an City, a physical simulation test was conducted. It was found the temperature of surrounding layers continued to be perturbed after heating of the formation had stopped. The time during which the temperature was perturbed was about 4-5 times the heating period. During the simulation test, stray gas migration through fractures and faults was considered a mechanism for groundwater contamination. In the test, the maximum TOC content in aquifer was the value of 97.0 mg/L. The maximum total petroleum hydrocarbon (TPH) content of the simulated formation was 129 mg/kg after oil pyrolysis.

Metagenomic analysis of microbial communities continuously exposed to Bisphenol A in mangrove rhizosphere and non-rhizosphere soils

Bisphenol A (BPA) is widely distributed in littoral zones and may cause adverse impacts on mangrove ecosystem. Biodegradation and phytoremediation are two primary processes for BPA dissipation in mangrove soils. However, the rhizosphere effects of different mangrove species on BPA elimination are still unresolved. In this study, three typical mangrove seedlings, namely Avicennia marina, Bruguiera gymnorrhiza (L.) and Aegiceras corniculatum, were cultivated in soil microcosms for four months and then subjected to 28-day continuous BPA amendment. Un-planted soil microcosms (as control) were also set up. The BPA residual rates and root exudates were monitored, and the metabolic pathways as well as functional microbial communities were also investigated to decipher the rhizosphere effects based on metagenomic analysis. The BPA residual rates in all planted soils were significantly lower than that in un-planted soil on day 7. Both plantation and BPA dosage had significant effects on bacterial abundance. A distinct separation of microbial structure was found between planted and un-planted soil microcosms. Genera Pseudomonas and Lutibacter got enriched with BPA addition and may play important roles in BPA biodegradation. The shifts in bacterial community structure upon BPA addition were different among the microcosms with different mangrove species. Genus Novosphingobium increased in Avicennia marina and Bruguiera gymnorrhiza (L.) rhizosphere soils but decreased in Aegiceras corniculatum rhizosphere soil. Based on KEGG annotation and binning analysis, the proposal of BPA degradation pathways and the quantification of relevant functional genes were achieved. The roles of Pseudomonas and Novosphingobium may differ in lower BPA degradation pathways. The quantity variation patterns of functional genes during the 28-day BPA amendment were different among soil microcosms and bacterial genera.

A photobioreactor using Nannochloropsis oculata marine microalgae for removal of polycyclic aromatic hydrocarbons and sorption of metals in produced water

The objective of the present work is to evaluate the potential of the removal of PAHs and metal sorption for the treatment of petroleum produced water using a photobioreactor system with Nannochloropsis oculata microalgae. A set of photobioreactors with different gradients of produced water concentration diluted in saline water was designed, establishing five gradients (v/v): 0, 25, 50, 75 and 100%. These concentrations were established to test the removal of PAHs. The microalgal growth was monitored daily, noting the adaptation of microalgae to the addition of produced water as a culture medium, with cell growth of 5.24 × 10⁷ cells mL^-1 from 25% (v/v), 4.09 × 10⁷ cells mL^-1 from 50% (v/v), 2.77 × 10⁷ cells mL^-1 from 75% (v/v), and 1.17 × 10⁷ cells mL^-1 from 100%. The total removal efficiency of PAHs in the produced water was 94%. Organic compounds such as naphthalene, benzo(a)pyrene, benzo(b)fluoranthene, and acenaphthylene showed higher removal percentages, between 89 and 99% efficiency in produced water. Iron and zinc were the metals detected in the water produced, and iron reduced from 1.57 ± 0.08 mg L^-1 to <0.1 mg L^-1 after 28 days of cultivation, whereas zinc increased by 0.23 ± 0.05 to 3.90 ± 0.46 mg L^-1. The PAHs removal may have occurred in two ways, by intracellular bioaccumulation or biodegradation by oxidoreductase enzymes. 0.2 g of dry biomass with maximum extraction of oil obtained 3.07% and generation of 3.70% of protein was considered as value-added products for biodiesel and bioplastics.

Remediation of petroleum contaminated saline water using value-added adsorbents derived from waste coconut fibres

Oil spill from petrochemical industries into marine areas has resulted in severe environmental pollution. The use of natural sorbents to clean marine areas affected by petroleum contaminants is a promising approach to alleviate this problem. Therefore, this study aims at developing an technique that uses waste coconut fibres (Cocos nucifera L.) pre-treated with a "green" solvent, viz. protic ionic liquid (PIL) [2-HEA][Ac], for the remediation of oil in saline water. Conventional chemical pre-treatments (mercerisation/acetylation) and the innovative treatment (using PIL), chemical characterisation, Scanning Electron Microscope, Fourier-transform infrared spectroscopy, and oil sorption tests in hydrodynamic simulation on a laboratory scale were conducted. The fibres treated with PIL[2-HEA][Ac] possessed more pores and hydrophobic content than the mercerised/acetylated coconut fibres, indicating the efficiency of sorption. The average sorption of the PIL[2-HEA][Ac] fibre was 1.40 ± 0.06 g/g and that of the mercerised/acetylated fibre was 1.32 ± 0.12 g/g. Although the difference in sorption results is not significant, according to the Tukey test, fibre pre-treatment with PIL[2-HEA][Ac] is more advantageous than conventional treatments because it exhibits better average sorption results; furthermore, the synthesis procedure for PIL[2-HEA][Ac] is simple, reusable and non-toxic. Therefore, the use of these petroleum biosorbents is a technology with environmental benefits, such as the availability of the biosorbent in the form of biodegradable waste and treated with a "green" solvent, both of which can be reused. Thus, it adds value for its use in industries with a circular economy product; that are environment-friendly and economical.

Phytoremediation of soil co-contaminated with zinc and crude oil using Ocimum gratissimum (L.) in association with Pseudomonas putida MU02

Soil adulteration by organic and inorganic contaminants chiefly in industrial and agricultural area is one of the major problems faced by the world today. Phytoremediation using aromatic plant such as Ocimum is a sound, economically reasonable and an eco-friendly approach. Besides, microbial assisted phytoremediation can bring about plant-promoted microbial degradation, plant uptake and phytodegradation of soil contaminants. In this study, the ability of Ocimum gratissimum in association with Pseudomonas putida MU02 to remediate zinc and crude oil contaminated soil (2,000 mg/kg, 1% w w^-1 crude oil) was investigated in a 60-day pot experiment. Four different treatments and a control (clean soil + plant) were employed for the study: co-contaminated soil only; co-contaminated soil with O. gratissimum; co-contaminated with P. putida inoculum; co-contaminated soil with O. gratissimum and P. putida. Comparatively, the highest TPH deduction efficiency (75.87%) was shown by the treatment comprising of O. gratissimum and P. putida while highest metal uptake was shown by the treatment with plant only. Better TPH removal associated with higher number of bacteria in the vegetated and inoculated pots could be attributed to the rhizopheric effect of the plants. Altogether, the association of O. gratissimum with P. putida can be a potential candidate for the remediation of co-contaminated soil.

Phytoremediation of polycyclic aromatic hydrocarbons (PAHs) in mangrove sediments using Rhizophora mangle

A phytoremediation experiment was carried out in mesocosms to investigate the performance of Rhizophora mangle in the remediation of polycyclic aromatic hydrocarbons (PAHs) in mangrove sediment contaminated with crude oil. The water pH of the experiments (phytoremediation and natural attenuation) ranged from 4.9 to 8.4 at 0 and 90 days, respectively. The oxy-reduction potential (Eh) ranged from oxidising (108.0 mV, time 0) to reducing (approximately -110.0 mV, time 90) environments. Dissolved oxygen (DO) ranged from 5.7 mg L^-1 (time 0) to 4.5 mg L^-1 and 3.6 mg L^-1 (time 90) in phytoremediation and natural attenuation, respectively. The sediments had silty texture and an average concentration of 5% organic matter (OM). Phytoremediation (60.76%) showed better efficiency in the remediation of the 16 PAHs compared to natural attenuation (49.57%). Principal component analyses showed a correlation between the concentrations of PAHs with pH, Eh, OM and DO in both experiments.

Insights into the remediation of cadmium-pyrene co-contaminated soil by electrokinetic and the influence factors

The remediation of cadmium-pyrene co-contaminated soil by electrokinetic (EK) and the influence factors were investigated in this study. The artificial contaminated soils were treated for 20 days in EK experimental setups without electrolyte solution reservoirs, to simulate in-situ remediation of unsaturated soil. The results indicated that polarity-reversing electric field had maintained soil pH in the range of 7.27-7.67. Cadmium (Cd) contaminant would aggregate near electrodes, and the average Cd concentration in these areas had reached 72.21 mg/kg (original 51.6 mg/kg), while the value in soil farthest away from electrodes was 33.58 mg/kg. The reasons for Cd aggregated were: the insoluble hydroxide formations attribute to the frequently alternation of acid-base environment, and the decrease of pH and water holding capacity in soil away from electrodes would promote the dissolved Cd movement by electro-osmosis flow. Although the applied electric field could promote the growth and activity of pyrene-degrading microorganisms (PDM), the soluble Cd would be the restriction factor, especially in soil near electrodes. However, the highest (56.38%) pyrene removal efficiency (PRE) was achieved near electrodes due to the synergistic effect of electric filed and PDM, and PRE was positively correlated with the PDM number in soil away from electrodes.

Evaluation of accelerated biodegradation of oil-SPM aggregates (OSAs)

The studies of the formation of oil-Suspended Particulate Matter (SPM) aggregates (OSAs) have advanced significantly in the scientific community, however there is a need to accelerate oil biodegradation that was dispersed by the formation of OSAs. The present research presents a pioneering character regarding the addition of nutrients as biostimulus for autochthonous hydrocarboclastic bacteria in the biodegradation of Total Petroleum Hydrocarbons (TPH) dispersed by the formation of OSAs. Water aliquots were taken over 60 days from eight bioreactors to perform ionic species analysis, pH, salinity and temperature monitoring, liquid/liquid extraction, serial dilution methodology and filter membrane. TPH quantification was performed on the gas chromatograph with a flame ionisation detector (GC-FID). The addition of nutrients contributed positively to the rate and extent of biodegradation of TPH in association with field-collected SPM. The best result found was with the lowest nutrient concentration (Bio 1) with an average of 98.65% of TPH reduction.

Bioremediation of cadmium-trichlorfon co-contaminated soil by Indian mustard (Brassica juncea) associated with the trichlorfon-degrading microbe Aspergillus sydowii: Related physiological responses and soil enzyme activities

Soil co-contaminated with heavy metals and organics is often difficult to remediate. In this study, pot experiments were conducted to investigate the concurrent removal of cadmium (Cd, two levels: Cd_L [10 mg kg^-1] and Cd_H [50 mg kg^-1]) and trichlorfon (TCF, 100 mg kg^-1) from co-contaminated soil by comparing the following remediation methods: natural remediation (NR), soil inoculated with Aspergillus sydowii (AS), soil planted with Brassica juncea (BJ), and soil planted with B. juncea and inoculated with A. sydowii (BJ-AS). The physiological responses of B. juncea and soil enzyme activities after remediation were also studied. B. juncea grew well in co-contaminated soil at both Cd levels. The biomass and chlorophyll content of B. juncea in Cd_H soil were lower than those in Cd_L soil, whereas the malondialdehyde content and activities of catalase, peroxidase and superoxide dismutase of B. juncea in Cd_H soil were higher than those in Cd_L soil. Cd accumulation in B. juncea was high in Cd_H soil, whereas high Cd removal efficiency was observed in Cd_L soil. TCF could be thoroughly degraded within 35 days in NR at both Cd-level soils. AS, BJ and BJ-AS promoted TCF degradation and enhanced the activities of catalase, urease, sucrase and alkaline phosphatase in soil compared with the NR. BJ-AS showed the highest phytoextraction ratio (3.32% in Cd_L and 1.34% in Cd_H soil) and TCF degradation rate (half-life of 2.18 and 2.37 days in Cd_L and Cd_H soil, respectively). These results demonstrate that BJ-AS could effectively remove Cd and TCF from soil and is thus a feasible technology for the bioremediation of these co-contaminated soil.

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.

Potential application of oil-suspended particulate matter aggregates (OSA) on the remediation of reflective beaches impacted by petroleum: a mesocosm simulation

This paper presents the oil-suspended particulate matter aggregate (OSA) resulted from the interaction of droplets of dispersed oil in a water column and particulate matter. This structure reduces the adhesion of oil on solid surfaces, promotes dispersion, and may accelerate degradation processes. The effects of the addition of fine sediments (clay + silt) on the formation of OSA, their impact on the dispersion and degradation of the oil, and their potential use in recovering reflective sandy beaches were evaluated in a mesoscale simulation model. Two simulations were performed (21 days), in the absence and presence of fine sediments, with four units in each simulation using oil from the Recôncavo Basin. The results showed that the use of fine sediment increased the dispersion of the oil in the water column up to four times in relation to the sandy sediment. There was no evidence of the transport of hydrocarbons in bottom sediments associated with fine sediments that would have accelerated the dispersion and degradation rates of the oil. Most of the OSA that formed in this process remained in the water column, where the degradation processes were more effective. Over the 21 days of simulation, we observed a 40 % reduction on average of the levels of saturated hydrocarbons staining the surface oil.

Environmental Life Cycle Assessment of marine sediment decontamination by citric acid enhanced-microwave heating

The potential ability of microwave heating (MWH) for the remediation of marine sediments affected by severe hydrocarbon (HC) contamination was investigated. Decontamination effectiveness and environmental sustainability through a comparative Life Cycle Assessment (LCA) were addressed. Main results revealed that the application of a 650-W MWH treatment resulted in a rapid (15min) HC removal. A citric acid (CA) dose of 0.1M led to enhanced-HC removals of 76.9, 96.5 and 99.7% after 5, 10 and 15min of MW irradiation, respectively. The increase in CA dose to 0.2M resulted in a shorter successful remediation time of 10min. The exponential kinetic model adopted showed a good correlation with the experimental data with R² values in the 0.913-0.987 range. The nature of the MW treatment was shown to differently influence the HC fraction concentration after the irradiation process. Achieved HC removals in such a short remediation time are hardly possible by other clean-up techniques, making the studied treatment a potential excellent choice. Removal mechanisms, which allowed the enhanced-MWH to operate as a highly effective multi-step technique (pure thermal desorption+chemical washing), undoubtedly represent a key factor in the whole remediation process. The LCA highlighted that the MW technology is the most environmentally sustainable alternative for sediment decontamination applications, with a total damage, which was 75.74% lower than that associated with the EK (0.0503pt).

Effect of planting and fertilization on lead partitioning in dredged sediment

Dredging has been practiced to remove sediment impacted by persistent contaminants, such as heavy metals. Of these metals, lead (Pb) is of particular concern due to its toxicity. Therefore, dredged sediment containing Pb requires further mitigation. One method for Pb mitigation is phytoremediation of dredged sediment. In this study, the partitioning of Pb in sediment during phytoremediation by willow (Salix integra) was assessed. The results showed that, in general, the bioavailable forms of Pb declined with increased application of the standard Hoagland nutrient solution, which appeared to enhance the Fe-Mn oxide fraction and residual inert fraction. In contrast, the addition of excess phosphorus decreased the bioavailable fractions of Pb. However, the bioavailable fractions of Pb increased with additional potassium addition. Planting Salix integra was shown to promote the stabilization of Pb in sediment and led to a transformation from bioavailable forms to non-bioavailable forms. The results suggest that planting Salix integra can remediate Pb-contaminated dredged sediment via Pb immobilization by the roots. During this process, the application of Hoagland nutrient solution and the application of nutrient solutions with excess phosphorus not only promote root growth of Salix integra which would reduce Pb bioavailability, but also further enhance the immobilization of Pb in contaminated sediment, likely through the formation of Pb-containing compounds with low bioavailability.

Capability of Paraguaçu estuary (Todos os Santos Bay, Brazil) to form oil-SPM aggregates (OSA) and their ecotoxicological effects on pelagic and benthic organisms

For experiments concerning the formation of oil-suspended particulate matter (SPM) aggregates (OSA), oil and sediment samples were collected from Campos Basin and six stations of Paraguaçu estuary, Todos os Santos Bay, Brazil, respectively. The sediments samples were analyzed for organic matter determined by the EMBRAPA method, nitrogen determined by the Kjeldahl method, and phosphorus determined by the method described by Aspila. The oil trapped in OSA was extracted following the method described by Moreira. The experiment showed a relationship between the amount of organic matter and OSA formation and consequently the dispersion of the studied oil. On the basis of the buoyancy of OSA and the ecotoxicological effects on pelagic and benthic community, the priority areas for application of remediation techniques are Cachoeira, Maragogipe, and Salinas da Margarida because of the large amount of oil that accumulated at the bottom of the experiment flask (5.85%, 27.95%, and 38,98%; 4.2%, 17.66%, and 32.64%; and 11.82%, 8.07%, and 10.91% respectively).

Phytoremediation of fuel oil and lead co-contaminated soil by Chromolaena odorata in association with Micrococcus luteus

Phytoremediation is widely promoted as a cost-effective technology for treating heavy metal and total petroleum hydrocarbon (TPH) co-contaminated soil. This study investigated the concurrent removal of TPHs and Pb in co-contaminated soil (27,000 mg kg(-1) TPHs, 780 mg kg(-1) Pb) by growing Siam weed (Chromolaena odorata) in a pot experiment for 90 days. There were four treatments: co-contaminated soil; co-contaminated soil with C. odorata only; co-contaminated soil with C. odorata and Micrococcus luteus inoculum; and co-contaminated soil with M. luteus only. C. odorata survived and grew well in the co-contaminated soil. C. odorata with M. luteus showed the highest Pb accumulation (513.7 mg kg(-1)) and uptake (7.7 mg plant(-1)), and the highest reduction percentage of TPHs (52.2%). The higher TPH degradation in vegetated soils indicated the interaction between the rhizosphere microorganisms and plants. The results suggested that C. odorata together with M. luteus and other rhizosphere microorganisms is a promising candidate for the removal of Pb and TPHs in co-contaminated soils.

A comprehensive guide of remediation technologies for oil contaminated soil - Present works and future directions

Oil spills result in negative impacts on the environment, economy and society. Due to tidal and waves actions, the oil spillage affects the shorelines by adhering to the soil, making it difficult for immediate cleaning of the soil. As shoreline clean-up is the most costly component of a response operation, there is a need for effective oil remediation technologies. This paper provides a review on the remediation technologies for soil contaminated with various types of oil, including diesel, crude oil, petroleum, lubricating oil, bitumen and bunker oil. The methods discussed include solvent extraction, bioremediation, phytoremediation, chemical oxidation, electrokinetic remediation, thermal technologies, ultrasonication, flotation and integrated remediation technologies. Each of these technologies was discussed, and associated with their advantages, disadvantages, advancements and future work in detail. Nonetheless, it is important to note that no single remediation technology is considered the best solution for the remediation of oil contaminated soil.

CAPSULE

This review provides a comprehensive literature on the various remediation technologies studied in the removal of different oil types from soil.

Phytoremediation of petroleum hydrocarbons-contaminated soil using Desmodium incanum DC., Fabaceae

The current research aimed to investigate both the tolerance and the phytoremediation potential of Desmodium incanum DC. on petroleum-contaminated soil. There were analyzed D. incanum seeds germination, surviving, growth and development cultivated at different contaminants concentrations as well as the pollutant degradation rate by gas chromatography and rhizosphere community. The experiment was carried out on a greenhouse containing non-contaminated soil (NCS), vegetated contaminated soil (VCS) and non-vegetated contaminated soil (NVCS) at the following petroleum concentrations (petroleum per of dry soil): 50 g kg-1 and 100 g kg-1. The experiments were performed during 90 days. The germination was more evident as it was observed higher petroleum concentrations. After 90 days, the surviving rate of the both groups 100%, and the soil samples were extracted and analyzed by gas chromatography. The VCS (100 g kg-1) group growth was reduced when compared to the NVCS (100 g kg-1). The petroleum influenced the morph anatomy and development of the plant. Significant increases in the total area, cortical and central cylinder of the roots in the contamination presence. The plant provided the development of larger amounts of microorganisms in the rhizosphere zone, and higher petroleum compounds degradation, confirming their potential phytoremediation for soils contaminated by petroleum.

Spatial distribution and concentration assessment of total petroleum hydrocarbons in the intertidal zone surface sediment of Todos os Santos Bay, Brazil

The primary objective of this study was to investigate the concentrations and spatial distribution of the total petroleum hydrocarbons (TPHs) in the intertidal zone surface sediment of Todos os Santos Bay, Brazil, to assess the distribution and degree of contamination by TPHs, measure the level of TPH degradation in the surface sediment, and identify the organic matter sources. The surface sediment used in this study was collected in 50 stations, and TPHs, isoprenoid alkanes (pristane and phytane), and unresolved complex mixture (UCM) were analyzed by gas chromatography with a flame ionization detector. The total concentrations ranged from 0.22 to 40,101 μg g(-1) dry weight and showed a strong correlation with the total organic carbon (TOC) content. The highest TPH concentrations were observed in samples from the mangrove sediments of a river located near a petroleum refinery. Compared with other studies in the world, the TPH concentrations in the intertidal surface sediment of Todos os Santos Bay were below average in certain stations and above average in others. An analysis of the magnitude of UCM (0.11 to 17,323 μg g(-1) dry weight) and the ratios nC17/Pr and nC18/Ph suggest that an advanced state of oil weathering, which indicates previous contamination. The molar C/N ratios varied between 5 and 43, which indicate organic matter with a mixed origin comprising marine and continental contributions.

Effect of bioaugmentation to enhance phytoremediation for removal of phenanthrene and pyrene from soil with Sorghum and Onobrychis sativa

The use of plants to remove Poly-aromatic-hydrocarbons (PAHs) from soil (phytoremediation) is emerging as a cost-effective method. Phytoremediation of contaminated soils can be promoted by the use of adding microorganisms with the potential of pollution biodegradation (bioaugmentation). In the present work, the effect of bacterial consortium was studied on the capability of Sorghum and Onobrychis sativa for the phytoremediation of soils contaminated with phenanthrene and pyrene. 1.5 kg of the contaminated soil in the ratio of 100 and 300 mg phenanthrene and/or pyrene per kg of dry soil was then transferred into each pot (nine modes). The removal efficiency of natural, phytoremediation and bioaugmentation, separately and combined, were evaluated. The samples were kept under field conditions, and the remaining concentrations of pyrene and phenanthrene were determined after 120 days. The rhizosphere as well as the microbial population of the soil was also determined. Results indicated that both plants were able to significantly remove pyrene and phenanthrene from the contaminated soil samples. Phytoremediation alone had the removal efficiency of about 63% and 74.5% for pyrene and phenanthrene respectively. In the combined mode, the removal efficiency dramatically increased, leading to pyrene and phenanthrene removal efficiencies of 74.1% and 85.02% for Onobrychis sativa and 73.84% and 85.2% for sorghum, respectively. According to the results from the present work, it can be concluded that Onobrychis sativa and sorghum are both efficient in removing pyrene and phenanthrene from contamination and bioaugmentation can significantly enhance the phytoremediation of soils contaminated with pyrene and phenanthrene by 22% and 16% respectively.

Bioresources for control of environmental pollution

Environmental pollution is one of the biggest threats to human beings. For practical reasons it is not possible to stop most of the activities responsible for environmental pollution; rather we need to eliminate the pollutants. In addition to other existing means, biological processes can be utilized to get rid of toxic pollutants. Degradation, removal, or deactivation of pollutants by biological means is known as bioremediation. Nature itself has several weapons to deal with natural wastage and some of them are equally active for eliminating nonnatural pollutants. Several plants, microorganisms, and some lower eukaryotes utilize environmental pollutants as nutrients and some of them are very efficient for decontaminating specific types of pollutants. If exploited properly, these natural resources have enough potential to deal with most elements of environmental pollution. In addition, several artificial microbial consortia and genetically modified organisms with high bioremediation potential were developed by application of advanced scientific tools. On the other hand, natural equilibria of ecosystems are being affected by human intervention. Rapid population growth, urbanization, and industrialization are destroying ecological balances and the natural remediation ability of the Earth is being compromised. Several potential bioremediation tools are also being destroyed by biodiversity destruction of unexplored ecosystems. Pollution management by bioremediation is highly dependent on abundance, exploration, and exploitation of bioresources, and biodiversity is the key to success. Better pollution management needs the combined actions of biodiversity conservation, systematic exploration of natural resources, and their exploitation with sophisticated modern technologies.

Hydrocarbon biodegradation in intertidal wetland sediments

Intertidal wetlands, primarily salt marsh, mangrove and mudflats, which provide many essential ecosystem services, are under threat on numerous fronts; a situation that is made worse by crude-oil pollution. Microbes are the main vehicle for remediation of such sediments, and new discoveries, such as novel biodegradation pathways, means of accessing oil, multi-species interactions, and community-level responses to oil addition, are helping us to understand, predict and monitor the fate of oil. Despite this, there are many challenges, not least because of the heterogeneity of these ecosystems and the complexity of crude oil. For example, there is growing awareness about the toxicity of the oxygenated products that result from crude-oil weathering, which are difficult to degrade. This review highlights how developments in areas as diverse as systems biology, microbiology, ecology, biogeochemistry and analytical chemistry are enhancing our understanding of hydrocarbon biodegradation and thus bioremediation of oil-polluted intertidal wetlands.