Co-contaminated Soil Research Articles

Implication of exogenous abscisic acid (ABA) application on phytoremediation: plants grown in co-contaminated soil.

Abscisic acid (ABA) may play an important role in alleviating negative effects of heavy metal stress on growth performance of plants. A pot experiment was conducted to investigate differential effects of exogenous ABA with different concentrations (0, 20, 40, and 60 μmol/L) on heavy metal accumulation and physiological response of Cd/Zn hyperaccumulator Sedum alfredii Hance and non-hyperaccumulator Hylotelephium spectabile (Boreau) H. Ohba grown in co-contaminated soil. In the experiment, Cd, Zn, or Pb concentration in stem and leaf of H. spectabile was significantly increased by exogenous ABA application than control. However, the opposite pattern was observed for S. alfredii. With decrease of Cd concentration, Zn or Pb concentration in root of H. spectabile grown in co-contaminated soil was significantly increased by exogenous ABA application than control. Cd, Zn, or Pb concentration in root of S. alfredii was significantly increased by exogenous ABA application than control. Compared with S. alfredii, BCF and TF of Cd, Zn, or Pb for H. spectabile were significantly increased by exogenous ABA application. With negative effect on root growth, total biomass of the two species, especially H. spectabile, was significantly increased by exogenous ABA application than control. With increase of their total chlorophyll content, antioxidant capacity of the two species subjected to heavy metal stress was improved by exogenous ABA application than control. Heavy metal-induced growth inhibition was significantly alleviated by exogenous ABA application when the two species were grown in co-contaminated soil. We tentatively concluded that differential effects of exogenous ABA application on transport pathway of ions incurred different patterns of heavy metal accumulation between Cd/Zn hyperaccumulator S. alfredii and non-hyperaccumulator H. spectabile. It is suggested that compared with Cd/Zn hyperaccumulator S. alfredii, exogenous ABA application may improve heavy metal uptake in root and transport of heavy metal ions between different organs for non-hyperaccumulator H. spectabile grown in co-contaminated soil. Our results provide insight into effects of exogenous ABA application on phytoremediation of Cd-, Pb-, and Zn-co-contaminated soil.

Performance of biochar-supported nanoscale zero-valent iron for cadmium and arsenic co-contaminated soil remediation: Insights on availability, bioaccumulation and health risk

Simultaneous stabilization of cadmium (Cd) and arsenic (As) in co-contaminated soil is challenging in environmental remediation because of their opposite properties. In this study, biochar-supported nanoscale zero-valent iron (nZVI-BC) was designed for simultaneously decreasing the soil availability of Cd and As and their bioaccumulation in vegetables. It was found that nZVI-BC exhibited remarkable performance for the stabilization of Cd and As in soil, and their availability decreased by 34.93% and 32.64% compared to the control sample, respectively, under 1.00% nZVI-BC treatment. The increase of soil pH and complexation dominated the Cd remediation process, while the formation of precipitation together and surface complexes transformed labile As into stable forms. Pot experiments showed that nZVI-BC application inhibited the bioaccumulation of Cd and As in vegetables by 23.63–36.48% and 43.09–45.10%, respectively, and hence effectively decreased the cancer risks by 38.19–42.93% related with vegetable consumption (P < 0.05). This study revealed that nZVI-BC is a promising amendment for achieving the simultaneous remediation of Cd and As co-contaminated farmland soil.

Physiological and biochemical characteristic of Miscanthus × giganteus grown in heavy metal – oil sludge co-contaminated soil

The effect of oil sludge and zinc, present in soil both separately and as a mixture on the physiological and biochemical parameters of Miscanthus × giganteus plant was examined in a pot experiment. The opposite effect of pollutants on the accumulation of plant biomass was established: in comparison with uncontaminated control the oil sludge increased, and Zn reduced the root and shoot biomass. Oil sludge had an inhibitory effect on the plant photosynthetic apparatus, which intensified in the presence of Zn. The specific antioxidant response of M. × giganteus to the presence of both pollutants was a marked increase in the activity of superoxide dismutase (mostly owing to oil sludge) and glutathione-S-transferase (mostly owing to zinc) in the shoots. The participation of glutathione-S-transferase in the detoxification of both the organic and the inorganic pollutants was assumed. Zn inhibited the activity of laccase-like oxidase, whereas oil sludge promoted laccase and ascorbate oxidase activities. This finding suggests that these enzymes play a part in the oxidative detoxification of the organic pollutаnt. With both pollutants used jointly, Zn accumulation in the roots increased 6-fold, leading to increase in the efficiency of soil clean-up from the metal. In turn, Zn did not significantly affect the soil clean-up from oil sludge. This study shows for the first time the effect of co-contamination of soil with oil sludge and Zn on the physiological and biochemical characteristics of the bioenergetic plant M. × giganteus. The data obtained are important for understanding the mechanisms of phytoremediation with this plant.

Interactive effects of biochar type and pH on the bioavailability of As and Cd and microbial activities in co-contaminated soils

The differing chemical properties of arsenic (As) and cadmium (Cd) make co-remediation in soil systems a major challenge. This study aimed to gain a mechanistic understanding of how two contrasting biochars (poultry litter and sugar-gum wood) impacted the potential bioavailability of As and Cd in soil matrix varying in initial pH (4.6, 5.7, 6.4, 7.1 and 7.4). The application of poultry-litter biochar significantly increased potential bioavailability of As from 11 to 58 mg kg−1 across all soil pH while the potential bioavailability of Cd was decreased from 15 to 2 mg kg−1 at pH ≤ 6.4. Biochar derived from sugar-gum wood decreased bioavailable As from 11 to 8 mg kg−1 and 14 to 12 mg kg−1 in soils with pH 4.6 and 5.7, respectively, while increased it from 14 to 31 mg kg−1 at pH ≥ 6.4. Biochars transformed the residual fraction of As into the exchangeable fraction but the reverse was true for Cd. Biochar application changed the microbial respiration with contrasting dynamic patterns throughout the 30-d incubation. Soil respiration and microbial biomass C responded more quickly in low-pH than high-pH soils due to low As bioavailability at low pH. These new findings provide strong evidence regarding how contrasting biochars control the mobility of As and Cd over a wide range of soil pH within the same soil matrix.

A novel mechanism study of microplastic and As co-contamination on indica rice (Oryza sativa L.)

Although the compound pollution of microplastics and arsenic (As) in paddy soil can affect the growth and quality of rice, relevant research on this phenomenon was limited. Therefore, we combined a pot experiment with computational chemistry to explore the effects and mechanism of polystyrene (PSMP) and polytetrafluoroethylene (PTFE) microplastics on As bioavailability. PSMP and PTFE interacted with rice root exudates through van der Waals forces, approached the rice root system, inhibited root activity, reduced the relative abundance of Geobacteria and Anaeromyxobacter, and consequently reduced the iron plaques on the root surfaces. Consequently, As uptake by the rice was inhibited. PSMP and PTFE reduced the hemoglobin content by directly destroying its tertiary structure, thereby retarding rice growth. In contrast, As increased the hemoglobin content by inducing reactive oxygen species in rice. Under the influence of PSMP, PTFE, and As, the activities of soluble starch synthase and pyrophosphorylase in rice grains were inhibited, and starch accumulation decreased. Thus, PSMP, PTFE, and As reduced rice biomass and yield owing to their physiological toxicity and adverse impacts on root activity. Grain yields in soil with an As content of 86.3 mg·kg–1, 0.5% small particle-sized PSMP, and 0.5% small particle-sized PTFE decreased by 30.7%, 20.6%, and 19.4%, respectively, compared to the control. This study determined the comprehensive mechanism through which PSMP and PTFE affect As bioavailability, which is critical for managing rice biomass and low yields in As and microplastic co-contaminated soil.

Co-application of indole-3-acetic acid/gibberellin and oxalic acid for phytoextraction of cadmium and lead with Sedum alfredii Hance from contaminated soil

Exogenous application of plant-growth promoting substances in combination with chelators is a common way to enhance the phytoextraction of heavy metals. A pot experiment was used to explore the influences of indole-3-acetic acid (IAA)/gibberellin (GA3) alone or together with oxalic acid (OA) on the growth, physiological response, and nutrient contents of hyperaccumulator Sedum alfredii Hance, and cadmium (Cd) and lead (Pb) phytoextraction efficiency. The results showed that a foliar spray of IAA/GA3 alone or together with OA increased plant growth. The largest shoot biomass with increase by 29.7% was produced by the 50 μmol L−1 IAA combined with 2.5 mmol kg−1 OA (50I+2.5OA) treatment as compared with the control treatment (CK). The presence of IAA and GA3 enhanced the chlorophyll a, carotenoid, and potassium contents in leaves and decreased the malondialdehyde content. The Cd content in leaf and the translocation factor (TFshoot) value from 50I+2.5OA treatment was increased by 4.29% and 21.4%, and the Pb content in stem and shoot, and the TFshoot of Pb after applying 50 μmol L-1 GA3 combined with 2.5 mmol kg−1 OA was enhanced by 32.5%, 13.4%, and 57.6%, compared with CK, respectively. The optimal Cd and Pb phytoextraction efficiency occurred from 50I+2.5OA treatment with increase by 82.4% and 79.3% as compared with CK, respectively. Therefore, the results showed that a combined application of 50 μmol L−1 IAA and 2.5 mmol kg−1 OA could effectively enhance S. alfredii Hance phytoremediation of Cd and Pb co-contaminated soil.

Rhizosphere interactions between PAH-degrading bacteria and Pteris vittata L. on arsenic and phenanthrene dynamics and transformation

The pot experiment was conducted to monitor the dynamics in soil solution chemistry in order to determine the main rhizosphere processes determining As and PAH bioavailability when utilizing P. vittata and PAH-degrading bacteria to remediate co-contaminated soils. The result showed that P. vittata was capable of depleting soil solution As and increasing phenanthrene solubilization, and thus facilitating plant As uptake and phenanthrene dissipation. Bacterial inoculation enhanced soil phenanthrene dissipation and concurrently modified As bioavailability though increasing soil pH, facilitating Fe and Ca minerals solubilization, and accelerating organic matter decomposition. However, the main factors that determine As bioavailability in the rhizosphere considerably varied with plant genotypes. Upon bacterial inoculation, P and Fe strongly influenced As(V) availability and its uptake by the Guangxi accession, and DOC, Fe, and pH were the main parameters correlated with As(V) availability in the rhizosphere of the Hunan accession. Bacterial inoculation tended to stimulate As(V) reduction in the rhizosphere of P. vittata. Microbial-induced changes in Ca, S, and C cycling and pH were indicators of As(V) reduction. Although bacterial inoculation increased soil As and phenanthrene availability, striking differences in As and nutrients uptake and phenanthrene dissipation were observed between P. vittata genotypes. It is suggested that apart from the microbial transformation, plant genotypes and bacterial mediated plant nutrition are also the critical factors in controlling the fates of As and phenanthrene. Our results uncovered the interactions between P. vittata and PAH-degrading bacteria on rhizosphere properties and nutrients cycling regulating As and PAH availability and remediation efficiency.

Selenium improved the combined remediation efficiency of Pseudomonas aeruginosa and ryegrass on cadmium-nonylphenol co-contaminated soil

Most chemical plant wastewater contains both organic and inorganic pollutants, which are easy to diffuse along with surface runoff. The combined pollution of nonylphenol (NP) and cadmium (Cd) in soil is a serious problem that has not attracted enough attention. Based on the effects of selenium (Se) and Pseudomonas aeruginosa (P. aeruginosa) on plant and soil microbial communities, we speculated that the application of Se and P. aeruginosa in soil could improve the phytoremediation efficiency of ryegrass on contaminated soil. In this study, pot experiments with Cd and NP co-contaminated soil were conducted, and the results showed that application of P. aeruinosa alone could improve the removal rates of NP and Cd by ryegrass, and the supplementary of Se further enhanced the effect of micro-phyto remediation, with the highest removal rates of NP and Cd were 79.6% and 49.4%, respectively. The application of P. aeruginosa plus Se reduced the adsorption of Cd and NP through C–O and Si–O–Fe of the soil, changed the enzyme activity, and also affected the changing trend of the microbial community in soil. Pseudomonas, Sphingomonadales, Nitrospira, and other beneficial bacteria were enriched after a 60-day period with P. aeruginosa and Se treatment, thus promoting the removal of NP and Cd. In light of the above results, we suggest that P. aeruginosa application can efficiently facilitate the phytoremediation of ryegrass on Cd-NP co-contaminated soil, and Se supplementation in soil showed the synergistic effect on the remediation.

Assessment of the Streptomyces-plant system to mitigate the impact of Cr(VI) and lindane in experimental soils.

Phytoremediation techniques have been proposed as ecological methods to clean up contaminated sites. This study is aimed to evaluate the effect of the Streptomyces sp. Waksman & Henrici and Zea mays L. plant system on the dissipation of Cr(VI) and/or lindane from a co-contaminated soil, being 2mgkg-1 of lindane and 150mgkg-1 of chromium used. Lindane dissipation was improved in the presence of plant-microorganism association; however, Cr(VI) removal was higher when plants or the microorganism were separately. In co-contaminated systems, chromium content in plant tissues was lower than metal content in plants grown only with Cr(VI), suggesting that lindane could interfere with metal accumulation in the plant. The high malondialdehyde (MDA) concentration detected in non-inoculated plants grown with chromium could be consequence of high metal concentration in plant tissues. Interestingly, plants inoculated with Streptomyces sp. Z38 growing with Cr(VI) showed decrease in MDA concentration, indicating that the bacterium could activate defense mechanisms in the plant. Also, inoculated plants showed the highest value of superoxide dismutase activity. Lettuce plants used as bioindicators grew better in biologically treated soils compared with lettuce grown on non-treated soil. The results presented in this work provide the basis that will allow the optimization of future trials on a larger scale.

Influence of electrical fields enhanced phytoremediation of multi-metal contaminated soil on soil parameters and plants uptake in different soil sections

The influence of electrical fields on phytoremediation of multi-metal (Cd, Cu, and Zn) naturally contaminated soils has been investigated based on different soil sections. After ryegrass and hybrid penisetum were sowed for 30 d, electrical fields were applied during 30 days with the switching polarity every 30 min and continuing for 16 h d−1. After electrokinetic (EK) assisted phytoremediation process, soil electrical conductivity (EC) in anode section and available soil potassium (K) in cathode section were obviously elevated. Plants biomass in middle and cathode sections were increased in both plants, especially in middle section the overall biomass of hybrid penisetum increased by 68.8%. The influence of electrical field on the contents of heavy metals in plants was different depending on the species of plants, kind of heavy metals and soil section. For Cd, Cu, and Zn co-contaminated soils, shoot metals accumulation in middle section in both plants were improved at least about 20% (with the exception of Zn in ryegrass). Electrical fields had the most significant effect on copper absorption by ryegrass and shoot Cu accumulation were elevated 32.5% in all the section. The soil EC maybe an important factor that affected electrical fields enhanced plants growth, plant metals concentrations and remediation efficiency.

Comparison of the effects of large-grained and nano-sized biochar, ferrihydrite, and complexes thereof on Cd and As in a contaminated soil–plant system

Cd and As are difficult to co-remediate in co-contaminated soils. In this study, remediation materials comprising large-grained and nano-sized biochar (BC), ferrihydrite (FH), and complexes thereof were added to Cd- and As-contaminated soil. The uptake of Cd and As by pak choi (Brassica chinensis L.) was then evaluated using a pot experiment and the Cd and As concentrations of the soil pore water and leaching water were measured. The Cd and As concentrations of the pore and leaching water were slightly increased with the addition of BC, and decreased with addition of FH and the biochar–ferrihydrite complex (BC-FH). However, nano-sized BC (BCN), FH (FHN), and BC-FH (BC–FHN) had little influence on the decreases in Cd and As of the two monitored water types. Large-grained remediation materials, rather than nanomaterials, decreased the Cd and As concentrations of the two monitored water types. Nonetheless, nanomaterial treatments more effectively decreased the Cd and As concentrations in plants by an average of >10% relative to the large-grained treatments. The DLVO theory analysis suggested that BCN, FHN, and BC-FHN, immobilized in the topsoil, adsorbed heavy metals in the rhizosphere soil. The remainder of the nano-sized materials was dispersed in the rhizosphere soil pores, shielding the uptake of Cd and As by the roots. Although the doses of nanomaterials used in this study were less than one-fortieth of those of the large-grained materials, changes in the plant rhizosphere microenvironment caused by the nanomaterials decreased the risk of toxicity transfer from the soil to the plants.

Simultaneous removal of copper and biodegradation of BDE-209 with soil microbial fuel cells

The microbial fuel cells (MFCs) were developed in the present study to remove copper (Cu) and decabromodiphenyl ether (BDE-209) from an artificially contaminated soil. The performance of electricity generation, BDE-209 degradation and Cu removal were investigated. Soil enzyme activity, BDE-209 mineralization and microbial community structures were analyzed. Experimental results showed that the removal of BDE-209 and Cu was effectively enhanced by the application of soil MFCs. After 60-day MFC operation, total Cu was removed by 69.2%, 66.4% and 62.5% for an initial Cu content of 250, 500 and 1000 mg/kg, respectively. More than 80% Cu removed was transformed to pure copper and deposited on the cathode plates. Soil enzyme activity and BDE-209 removal (85.5%) were both highest in the case of 500 mg/kg Cu. Genomic sequencing results indicates that electrogenic and debromination bacteria survived together in the soil MFCs. The MFC operation promoted the growth and reproduction of electrogenic bacteria. These results demonstrate that the soil MFCs can be employed as a durable and effective approach for detoxicating organic-metal co-contaminated soil.

Remediation of As/Cr co-contaminated soil by electrokinetic coupled with permeable reactive barrier

In this study, the permeable-reactive-barrier (PRB) assisted electrokinetic (EK) was used to remediate As/Cr Co-contaminated soil, aiming to explore the optimal remediation conditions and the migration of As/Cr. The effects of PRB active substance, PRB location, voltage gradient and running time on the migration and transformation of Cr and As in simulated As/Cr contaminated kaolin were studied. The optimal parameters were as follows: PRB position was located near the anode (PRB A, the medium of PRB was hydrocalumite (CaAl-LDH)), initial voltage gradient was 1 V/cm, running time was 96 h. Under the optimal conditions, the removal efficiency of total arsenic (TAs) and total chromium (TCr) were 40.1% and 81.0%, respectively. This indicated that EK can effectively migrate As and Cr, and PRB can effectively adsorb As and Cr. The migration of As tends to both anode and cathode, while Cr tends to migrate towards the anode. The XRD patterns and FTIR spectra confirmed that the As immobilized by CaAl-LDH was mainly adsorbed on the surface, while Cr existed in CaAl-LDH by surface adsorption and intercalation.

Immobilization of Cd and Pb in a contaminated acidic soil amended with hydroxyapatite, bentonite, and biochar

This study aims to investigate the dynamic changes over time in the immobilization efficiency of hydroxyapatite, bentonite, and biochar for Cd and Pb co-contaminated soil given the potential remobilization of immobilized heavy metals for long-term stabilized soils. Hydroxyapatite, bentonite, and biochar were applied only once at 2.5% (w/w) of soil during a 5-year pot experiment with pepper-cabbage (Capsicum annuum L.-Brassica pekinensis) rotation. The dynamic changes of soil pH, soil organic carbon (SOC), TCLP (toxicity characteristic leaching procedure)-, DTPA-, and PBET (simulated human gastric solution extraction)-Cd and Pb in soil, fractionation of Cd and Pb in soil, as well as the dynamic variations of bioaccessible Cd and Pb in vegetables were determined. The results indicated the application of hydroxyapatite, bentonite, and biochar significantly increased the proportion of residual fraction of Cd and Pb, and reduced the mobility, bioavailability, and bioaccessibility of Cd and Pb analyzed by TCLP, DTPA, and PBET, respectively. Moreover, the concentrations of TCLP-, DTPA-, and PBET-Cd and Pb gradually increased over time. The proportions of acid-extractable Cd and Pb in amended treatments in 2019 were higher than those in 2016. The increment for acid-extractable Cd fraction was 4.69%, 5.53%, and 4.19% in hydroxyapatite, bentonite, and biochar, respectively. While the increment for acid-extractable Pb fraction was 1.48%, 2.08%, and 1.91%, respectively. The bioaccessible Cd and Pb in pepper and cabbage significantly decreased after remediation while no remarkable changes were observed for Pb from 2017 to 2019. The three amendments were effective ameliorants for Cd and Pb co-contaminated acidic soil, but the immobilization efficiency decreased over time. Moreover, hydroxyapatite showed the highest efficiency on metal stabilization and vegetable safety.

Effects of microbial spatial distribution on organic biodegradation and immobilization of trace metals in co-contaminated soils

Predicting the transport and fate of organic and inorganic contaminants in co-contaminated soils is challenging, since various complex, inter-related processes are involved. In the presence of soil microbes that metabolise organic compounds (e.g., phenol), the chemical and the physical properties of the soil may alter and consequently affect the transport of inorganic trace metals e.g., Cu, Cd, Ni, Pb. However, the impact of their spatial distributions on the co-transport processes are still poorly understood and rarely available in literature. Here, we distribute the microbial colonies spatially in uniform and various non-uniform configurations and observe that the transport of weakly-sorbed Cd and Ni is greatly influenced by the distance of the colonies from the contaminant source rather than the size of the colonies. Whereas, for strongly-sorbed Pb and Cu, both the distance and the size are important. The spread of phenol in the model domain was substantially restricted by distributing the colonies more towards the transverse direction than in the longitudinal direction of the groundwater flow. In the context of co-contaminated soil remediation, this study demonstrates that optimum and efficient spatial distribution patterns can be obtained to restrict the spread of both organic and inorganic contaminants, with subsequent reduced environmental impacts.

Small structures with big impact: Multi-walled carbon nanotubes enhanced remediation efficiency in hyperaccumulator Solanum nigrum L. under cadmium and arsenic stress

With the fast development of nanotechnology, nanomaterials are being increasingly applied for the remediation of contaminated soils. However, few researches have been reported on the complex interactions of carbon nanotubes with heavy metal (loid)s in phytoremediation. Here, we conduct a pot experiment to investigate the effects of multi-walled carbon nanotubes (MWCNTs) on the plant growth and behavior of heavy metal (loid)s in hyperaccumulator-soil system. Cd hyperaccumulator Solanum nigrum L. (S. nigrum) were cultivated in Cadmium (Cd) and Arsenic (As) contaminated soils amended with MWCNTs at 100, 500, and 1000 mg kg−1 for 60 days, respectively. The application of MWCNTs increased the shoot length and plant dry biomass by 5.56%∼25.13% and 5.23%∼27.97%. Whereas, root and leaf growth were inhibited in 1000 mg kg−1 MWCNTs treatments. Meanwhile, MWCNTs at 500 mg kg−1 significantly enhanced the accumulation of heavy metal (loid)s in S. nigrum（18.29% for Cd and 32.47% for As）and alleviated co-contamination induced toxicity, by motivating plant growth, stimulating antioxidant enzymatic activities, and increasing micronutrient content (p < 0.05). The bio-concentration factor of As was decreased (15.31–28.08%) under MWCNTs application, which plays an important role in the alleviation of phytotoxicity. Besides, bioavailable Cd and As were reduced in rhizosphere soils, and the most significant reduction (16.29% for Cd and 8.19% for As) were shown in 500 mg kg−1 MWCNTs treatment. These findings demonstrate that suitable concentration of MWCNTs can enhance remediation efficiency. Our study gives a strong evidence to promote the phytoremediation for co-contaminated soils by using nanomaterials.

Effective remediation of organic-metal co-contaminated soil by enhanced electrokinetic-bioremediation process

Effective remediation of organic-metal co-contaminated soil by enhanced electrokinetic-bioremediation process

Spatial Distribution of As and Cd in Co-contaminated Soils Within the Rice Root Microzone.

Soil samples were collected from the As and Cd co-contaminated demonstration area to analyze the spatial distributions of As and Cd in soils within the rice root microzone using the treatment of soil cubes (50mm × 50mm × 50mm). The results indicated that there was no significant difference in the spatial distributions of total As or Cd in the microzone with the percentage of root weight, horizontal distances (HD), and vertical depths (VD). Interestingly, available As or Cd increased with the increasing HD, and both of them showed a significant difference (p < 0.05) between < 75mm and ≥ 120mm. The availability of As or Cd increased from the center to the edge of the rice root microzone. Moreover, the risk assessment code (RAC) showed that the site with a high potential risk of As or Cd was located on the edge of the rice root microzone. This phenomenon implied that cultivating paddy rice in the low potential risk microzone might have a low accumulative risk.

The potential association of Echinochloa polystachya (Kunth) Hitchc. with bacterial consortium for petroleum degradation in contaminated soil

In recent years, environmental impacts related to the contamination of ecosystems by petroleum have become frequent. In contact with the environment, petroleum can cause toxic effects in the biodiversity and on human health and compromise both water and land resources. Among the strategies to overcome this issue, bioremediation stands out as viable and promising alternative for environmental decontamination. To bioremediate petroleum-contaminated sites, phytoremediation and bioaugmentation techniques can be used. Thus, this research aimed to evaluate through a pot experiment four bioremediation strategies: (1) natural attenuation, (2) phytoremediation with Echinochloa polystachya, (3) bioaugmentation with bacterial consortium and (4) bioaugmentation-assisted phytoremediation, for the treatment of a co-contaminated soil presenting 100 g kg−1 of petroleum. In addition, two control treatments were carried out with substrates not contaminated with petroleum: (5) control with E. polystachya and (6) control treatment with bacterial consortium and E. polystachya. The experiment lasted 60 days in a greenhouse. The survival rate of E. polystachya was 100% in the contaminant tolerance aspect, resulting in increased stomatal density and aerenchyma, affecting few parameters of the plant, which demonstrate its phytoremediation capacity. In all treatments, petroleum degradation occurred. The highest degree of total petroleum hydrocarbon removal was obtained for contaminated soil cultivated with E. polystachya (phytoremediation), followed by contaminated soil cultivated with E. polystachya and bacterial (bioaugmentation-assisted phytoremediation treatment) and contaminated soil treated with bacterial consortium (bioaugmentation). Natural attenuation was less effective, proving the efficiency of the phytoremediation by E. polystachya and bacterial consortium, that responded positively to the stresses generated by contamination. However, further studies should direct to aim understanding the metabolic processes involved in the degradation and that these approaches to assist in environmental decontamination.

Pristine and iron-engineered animal- and plant-derived biochars enhanced bacterial abundance and immobilized arsenic and lead in a contaminated soil

In this study, typical animal- and plant-derived biochars derived from pig carcass (PB) and green waste (GWB), and their iron-engineered products (Fe-PB and Fe-GWB) were added at the dose of 3% (w/w) to an acidic (pH = 5.8) soil, and incubated to test their efficacy in improving soil quality and immobilizing arsenic (As = 141.3 mg kg−1) and lead (Pb = 736.2 mg kg−1). Soil properties, microbial activities, and the geochemical fractions and potential availabilities of As and Pb were determined in the non-treated (control) and biochar-treated soil. Modification of PB (pH = 10.6) and GWB (pH = 9.3) with Fe caused a decrease in their pH to 4.4 and 3.4, respectively. The application of PB and GWB significantly increased soil pH, while Fe-PB and Fe-GWB decreased soil pH, as compared to the control. Application of Fe-GWB and Fe-PB decreased the NH4H2PO4-extractable As by 32.8 and 35.9%, which was more effective than addition of GWB and PB. However, PB and GWB were more effective than Fe-PB and Fe-GWB in Pb immobilization. Compared to the control, the DTPA-extractable Pb decreased by 20.6 and 21.7%, respectively, following PB and GWB application. Both biochars, particularly PB significantly increased the 16S rRNA bacterial gene copy numbers, indicating that biochar amendments enhanced the bacterial abundance, implying an alleviation of As and Pb bio-toxicity to soil bacteria. The results demonstrated that pristine pig carcass and green waste biochars were more effective in immobilizing Pb, while their Fe-engineered biochars were more effective in As immobilization in co-contaminated soils.