Using chemical desorption of PAHs from sediment to model biodegradation during bioavailability assessment

Unveiling the long-term dynamic effects: Biochar mediates bacterial communities to modulate the petroleum hydrocarbon degradation in oil-contaminated sediments

Sediment, as the destination of marine pollutants, often bears much more serious petroleum pollution than water. Biochar is increasingly utilized for remediating organic pollutant-laden sediments, yet its long-term impacts on oil-contaminated sediment remain poorly understood. In this study, simulation experiments adding 2.5 wt% biochars (corn straw and wood chips biochar at different pyrolysis temperatures) were conducted. The effects on petroleum hydrocarbon attenuation, enzyme activities, and microbial community structure were systematically investigated. Results showed enhanced degradation of long-chain alkanes in certain biochar-treated groups. Biochar species and PAH characteristics together lead to the PAHs' attenuation, with low-temperature corn straw biochar facilitating the degradation of phenanthrene, fluorene, and chrysene. Initially, biochars reduced polyphenol oxidase activity but increased urease and dehydrogenase activities. However, there was a noticeable rise in polyphenol oxidase activity for a long time. Biochars influenced bacterial community succession and abundance, likely due to nutrient release stimulating microbial activity. The structural equations model (SEM) reveals that DON affected the enzyme activity by changing the microbial community and thus regulated the degradation of PAHs. These findings shed light on biochar's role in bacterial communities and petroleum hydrocarbon degradation over extended periods, potentially enhancing biochar-based remediation for petroleum-contaminated sediments.

Effects of electron acceptors and donors on anaerobic biodegradation of PAHs in marine sediments

Polycyclic aromatic hydrocarbons (PAHs) are typical organic pollutants accumulated in the environment. PAHs' bioremediation in sediments can be promoted by adding electron acceptor (EA) and electron donor (ED). Bicarbonate and sulfate were chosen as two EAs, and acetate and lactate were selected as two EDs. Six groups of amendments were added into the sediments to access their role in the anaerobic biodegradation of five PAHs, containing phenanthrene, anthracene, fluoranthene, pyrene, and benzo[a]pyrene. The concentrations of PAHs, EAs and EDs, electron transport system activity, and microbial diversity were analyzed during 126-day biodegradation in serum bottles. The HA group (bicarbonate and acetate) achieved the maximum PAH degradation efficiency of 89.67 %, followed by the SL group (sulfate and lactate) with 87.10 %. As the main PAHs degrading bacteria, the abundance of Marinobacter in H group was 8.62 %, and the addition of acetate significantly increased the abundance of Marinobacter in the HA group by 75.65 %.

Prediction of adsorption capacity and biodegradability of polybrominated diphenyl ethers in soil

Polybrominated diphenyl ethers (PBDEs) are widely used brominated flame retardants with strong toxicity concerns. Understanding the behaviors of PBDEs in soil is essential to evaluate their environmental impact. However, the limited, incoherent, and inaccurate data has challenged predicting the adsorption capacity and biodegradability of all 209 PBDE congeners in the soil. Moreover, there are minimal studies regarding the interactions between adsorption and biodegradation behaviors of PBDEs in the soil. Herein, in this study, we adopted quantitative structure-property relationship (QSAR) modeling to predict the adsorption behavior of 209 PBDE congeners by estimating their organic carbon-water partition coefficient (K_OC) values. In addition, the biodegradability of commonly occurring PBDE congeners was evaluated by analyzing their affinity to extracellular enzymes responsible for biodegradation using molecular docking. The results highlight that the degree of bromination plays a significant role in both the absorption and biodegradation of PBDEs in the soil due to compound stability and molecular geometry. Our findings help to advance the knowledge on PBDE behaviors in the soil and facilitate PBDE remediation associated with a soil environment.

Mn oxides enhanced pyrene removal with both rhizosphere and non-rhizosphere microorganisms in subsurface flow constructed wetlands

The polycyclic aromatic hydrocarbons (PAHs) are substantial wastewater pollutants emitted mostly by petroleum refineries and petrochemical industries, and their environmental fate has been of increasing concern among the public. Consequently, subsurface flow constructed wetlands (SFCWs) filled with Mn oxides (W-CW) or without Mn oxides (K-CW) were established to investigate the performance and mechanisms of pyrene (PYR) removal. The average removal rates of PYR in W-CW and K-CW were 96.00% and 92.33%, respectively. The PYR removal via other pathways (microbial degradation, photolysis, volatilisation, etc.) occupied a sizeable proportion, while the total PYR content in K-CW plant roots was significantly higher than that of W-CW. The microorganisms on the root surface and rhizosphere played an important role in PYR degradation in W-CW and K-CW and were higher in W-CW than that in K-CW in all matrix zones. The microorganisms between the 10-16 cm zone from the bottom of W-CW filled with Mn oxides (W-16) were positively correlated with PYR-degrading microorganisms, aerobic bacteria and facultative anaerobes, whereas K-16 without birnessite-coated sand was negatively correlated with these microorganisms.

Comparing biochar and hydrochar for reducing the risk of organic contaminants in polluted river sediments used for growing energy crops

In Europe alone, >200 million m³ of river sediments are dredged each year, part of which are contaminated to such an extent that they have to be landfilled. This study compares the use of biochar and hydrochar for the remediation of sediment contaminated with pentachlorobenzene, hexachlorobenzene, lindane, trifluralin, alachlor, simazine, and atrazine with the motivation to make sediments contaminated by such priority substances usable as arable land for growing energy crops. Biochar and hydrochar originating from Miscanthus giganteus and Beta vulgaris shreds were compared for their potential to reduce contaminant associated risk in sediments. Specifically, by investigating the effects of sorbent amendment rate (1, 5, and 10 %) and incubation time (14, 30, and 180 d) on contaminant bioaccessibility, toxicity to the bacteria Vibrio fischeri, as well as toxicity and plant uptake in Zea mays. Biochar reduced contaminant bioaccessibility up to five times more than hydrochar. The bioaccessibility of contaminants decreased up to sevenfold with increasing incubation time, indicating that the performance of carbonaceous sorbents may be underestimated in short-term lab experiments. Biochar reduced contaminants toxicity to Vibrio fischeri, whereas hydrochar was itself toxic to the bacteria. Toxicity to Zea mays was determined by contaminant bioaccessibility but also sorbent feedstock with cellulose rich Beta vulgaris based sorbents exhibiting toxic effects. The plant uptake of all contaminants decreased after sorbent amendment.

Effect of terminal electron acceptors on the anaerobic biodegradation of PAHs in marine sediments

The existing polycyclic aromatic hydrocarbons (PAHs) in marine sediment has become a critical threat to biological security. Terminal electron acceptor (TEA) amendment has been applied as a potential strategy to accelerate bioremediation in sediment. HCO₃^-, NO₃^-, and SO₄^2- were separately added to anaerobic sediment system containing five kinds of PAH, namely, phenanthrene, anthracene, fluoranthene, pyrene and benzo(a)pyrene. PAH concentration, PAH metabolites, TEA concentration, and electron transport system (ETS) activity were investigated. The HCO₃^- amendment group achieved the max PAH degradation efficiency of 84.98 %. SO₄^2- group led to the highest benzo(a)pyrene removal rate of 69.26 %. NO₃^- had the lowest PAH degradation rate of 76.16 %. ETS activity test showed that NO₃^- significantly inhibited electron transport activity in the sediment. The identified PAH metabolites were the same in each group, including 4,5-dimethylphenanthrene, 3-acetylphenanthrene, 9,10-anthracenedione, pyrene-7-hydroxy-8-carboxylic acid, anthrone, and dibenzothiophene. After 126 d's anaerobic degradation at 25 °C, the utilization of HCO₃^- and SO₄^2- as selected TEAs promoted the PAH biodegradation performance better than the utilization of NO₃^-.

Biodegradation Potential of Bacillus sp. PAH-2 on PAHs for Oil-Contaminated Seawater

Microbial degradation is a useful tool for inhibiting or preventing polycyclic aromatic hydrocarbons (PAHs) widely distributed in marine environment after oil spill accidents. This study aimed to evaluate the potential and diversity of bacteria Bacillus sp. PAH-2 on Benzo (a) anthracene (BaA), Pyrene (Pyr), and Benzo (a) pyrene (BaP), their composite system, aromatic components system, and crude oil. The seven-day degradation rates against BaA, Pyr, and BaP were 20.6%, 12.83%, and 17.49%, respectively. Further degradation study of aromatic components demonstrated PAH-2 had a high degradation rate of substances with poor stability of molecular structure. In addition, the degradation of PAHs in crude oil suggested PAH-2 not only made good use of PAHs in such a more complex structure of pollutants but the saturated hydrocarbons in the crude oil also showed a good application potential.

Century-long record of polycyclic aromatic hydrocarbons from tree rings in the southeastern Tibetan Plateau

Limited studies have been carried out on the historical variations of atmospheric polycyclic aromatic hydrocarbons (PAHs), especially in remote regions of the world. In this study, century-long record of PAHs (1916-2018) were reconstructed from tree rings in the remote southeastern Tibetan Plateau (TP). The total concentrations of 15 PAHs varied from 27.5 to 6.05 × 10² ng/g dry weight (dw), with a mean value of 1.40 × 10² ng/g dw. Higher levels of PAHs were observed during World War Ⅱ and the Peaceful Liberation of Tibet, and increasing trends were observed starting from rapid industrialization in India. Both the isomer ratios and the positive matrix factorization model results indicated biomass and coal combustion were the dominant sources of PAHs. The carcinogenic risk of PAHs to local residents was assessed, which might have been negligible in most past periods and lower than in other regions of the world. Nevertheless, since the beginning of the 21st century, the cancer risk has been increasing year by year, indicating more actions are needed to reduce emissions of PAHs. This study provides an idea for reconstructing the pollution history of PAHs at the global scale.

Intensive removal of PAHs in constructed wetland filled with copper biochar

In this study, biochar-loading copper ions (Cu-BC), a novel composite for removing phenanthrene very efficiently from water, was prepared using the impregnation method. The performance of constructed wetlands (CWs) with these modified and original biochar as substrates was analyzed. CW with Cu-BC removed a large amount of phenanthrene (94.09 ± 3.02%). According to the surface characteristics analysis, Cu-BC can promote the removal of pollutants via complex absorption, hydrophobic adsorption, increasing the Lewis Pair and electrostatic attraction. Furthermore the higher nitrate removal rate in the treated system (91.11 ± 1.17%) was observed to have higher levels of bacterial metabolic diversity and denitrifier types. The phenanthrene accumulated in plants with this treatment system was enhanced by the role of copper in photosynthesis. It is able to boost the plant extraction of organic matter.

A rapid experimental protocol to determine the desorption resistant fraction of sediment-sorbed hydrophobic organic contaminants

Desorption of hydrophobic organic contaminants (HOCs) from sedimentary materials plays a vital role in dictating the fate and transport of HOCs in the environment. Desorption irreversibility is a commonly observed phenomenon in laboratory sorption/desorption studies of HOCs. A desorption-resistant fraction (DRF) typically exists during the desorption process. To correctly evaluate the DRF of HOCs can considerably contribute to the understanding of availability and bioavailability of HOCs. This can substantially benefit contaminant remediation and cleanup operations. Conventional batch method to measure the DRF replies on repetitive washing of the sediments, which is time-consuming and can be impractical. This study presents an experimental protocol to quantify the DRF of the sediment-sorbed organic contaminants in a rapid manner. This protocol utilizes cosolvent to expedite desorption kinetics and adopts an ultrafiltration/centrifugation combined method to achieve a complete separation of sediment and solution phases. This proposed experimental protocol can facilitate the quantification of the DRF of sorbed contaminants to understand and minimize the uncertainties associated with risk-based pollution remediation approach. This protocol has the potential to be widely used in environmental studies to characterize sorption and desorption properties of HOCs with soil and sedimentary materials.

Effects of aeration on the suspended matter from a tropical and eutrophic estuary

A comprehensive understanding of the complex biogeochemical interactions between organic matter and persistent contaminants in the suspended matter is vital for eco-efficient estuary recovery. However, little is known regarding aeration effects in suspended particulate aggregates. Therefore, this study aimed to investigate the effects of aeration on the suspended matter from a Tropical and Eutrophic estuarine environment. Anoxic water with 60 g/L of suspended particulate matter (SPM) was collected from Guanabara Bay, Rio de Janeiro, Brazil, transferred to experimental boxes and aerated for 61 days. SPM aggregates monitoring included abiotic variables measurements and, determination of total organic matter (TOM), biopolymers composition, bacterial activity, trace metals, and polycyclic aromatic hydrocarbons (PAHs) concentrations. The aeration enhanced dissolved oxygen (DO) concentration and the redox potential (Eh). However, from days 0 to 61 the predominant bacterial activities were denitrification and fermentation. Electron transport system activity increased after day 10, and aerobic activity was detected after day 19. In summary, aeration increased aerobic bacterial activity, lipids (LIP) and trace metal concentrations, although diminished protein/carbohydrate ratio and PAH concentration. Trace metals concentration (Ni, Pb, Cu, Cr, Mn, and Fe) were the highest on day 19 when the pH was 5.9. Copper presented toxic values (Cu > 20.0 μg/g). The pH showed a strong negative correlation with Eh (r = -0.94; p < 0.001). Acidic environment (pH ≤ 5.9) in marine ecosystems with high loads of toxic trace metals is unsafe for biota. Therefore, managers must be aware of the environmental and biological risks of introducing the aeration technique into a eutrophic marine environment.

Lindane and hexachlorobenzene sequestration and detoxification in contaminated sediment amended with carbon-rich sorbents

Sediment represents a sink for toxic and persistent chemicals such as hexachlorobenzene (HCB) and lindane (γ-HCH). This paper investigates the possibility of reducing the risks associated with the presence of these pollutants in sediments by amending the sediment with carbon-rich materials (activated carbon (AC) and humus (HC)) to sequester the contaminants and render them biologically unavailable. The effects of the dose and contact time between the sediment and the carbon-rich amendments on the effectiveness of the detoxification are estimated. Four doses of carbon-rich amendments (0.5-10%) and four equilibration contact times (14-180 days) were investigated. Results have shown that the bioavailable fraction of γ-HCH and HCB decreased significantly in comparison to the unamended sediment. Regarding the AC amendments, almost 100% for both compounds; and for HC amendments around 95% for γ-HCH, and 75% for HCB. Aging caused further reductions in the bioavailable fraction, compared to the untreated sediment. Phytotoxicity tests showed that Zea mays accumulated significantly higher amount of γ-HCH and HCB from unamended sediment, comparing to Cucurbita pepo and Lactuca sativa. Toxicity of HC and AC amended sediment assessed by Vibrio fischeri luminescence inhibition test and by measuring Zea mays germination and biomass yield was significantly reduced in the amended sediment samples. γ-HCH and HCB accumulation in the Zea mays biomass in the unamended sediment were a significantly higher than in the all HC and AC amended sediment. Both sorbents show potential to be used as remediation agents for organically contaminated sediment, but AC exhibited the better performance.

State of the art and future challenges for polycyclic aromatic hydrocarbons is sediments: sources, fate, bioavailability and remediation techniques

Polycyclic aromatic hydrocarbons (PAHs) are amongst the most abundant contaminants found in the aquatic environment. Due to their toxicity and carcinogenicity, their sources, fate, behaviour, and cleanup techniques have been widely investigated in the last several decades. When entering the sediment-water system, PAH fate is determined by particular PAH and sediment physico-chemical properties. Most of the PAHs will be associated with fine-grained, organic-rich, sediment material. This makes sediment an ultimate sink for these pollutants. This association results in sediment contamination, and in this manner, sediments represent a permanent source of water pollution from which benthic organisms may accumulate toxic compounds, predominantly in lipid-rich tissues. A tendency for biomagnification can result in critical body burdens in higher trophic species. In recent years, researchers have developed numerous methods for measuring bioavailable fractions (chemical methods, non-exhaustive extraction, and biomimetic methods), as valuable tools in a risk-based approach for remediation or management of contaminated sites. Contaminated sediments pose challenging cleanup and management problems, as conventional environmental dredging techniques are invasive, expensive, and sometimes ineffective or hard to apply to large and diverse sediment sites. Recent studies have shown that a combination of strategies including in situ approaches is likely to provide the most effective long-term solution for dealing with contaminated sediments. Such in situ approaches include, but are not limited to: bioaugmentation, biostimulation, phytoremediation, electrokinetic remediation, surfactant addition and application of different sorbent amendments (carbon-rich such as activated carbon and biochar) that can reduce exposure and limit the redistribution of contaminants in the environment.

Effect of Tenax addition amount and desorption time on desorption behaviour for bioavailability prediction of polycyclic aromatic hydrocarbons

In this work, Tenax consecutive extractions of polycyclic aromatic hydrocarbons (PAHs) were conducted in two spiked sediments to investigate the influence of different Tenax addition amounts and desorption times on the rapidly desorbing fraction of PAHs, and to determine a reliable method for estimating PAHs bioavailability. The results indicated that a large Tenax addition amount has a positive effect on the desorption of PAHs from sediments. The desorption amounts of target PAHs compounds (3-ring phenanthrene and 4-ring fluoranthene) increased as the Tenax: sediment ratios increased from 0.25 to 2 in two spiked sediments. The highest desorption percentages of phenanthrene and fluoranthene were 48.91% and 34.70% for Jialing industrial park sediment, and 43.36% and 33.24% for Huanghuayuan bridge sediment, respectively. The results of desorption kinetics were suitably fitted with first order three-compartment model to estimate the rapidly desorbing fraction, Moreover, the Tenax: sediment ratio of 1 and desorption time of 24 h were found to be suitable for the desorption of phenanthrene and fluoranthene from sediments. The PAHs in sediments were biodegraded well by the bacterial strain J1-q. Comparing the maximum biodegraded amount of target PAHs in 30 days and the desorbed fraction over 400 h, the results showed that Tenax had better correlation with the high molecular weight fluoranthene than with the low molecular weight phenanthrene.

Sorption and desorption characteristics of anionic surfactants to soil sediments

Surfactants are important environmental chemicals due to their extensive domestic and industrial applications, such as subsurface organic pollution remediation and enhanced oil recovery. However, the interaction of surfactants with subsurface material particularly the desorption behavior of surfactants is less understood. Surfactant desorption is essential to control the fate and transport of surfactants as well as organic pollutants. In this study, the sorption and desorption of linear sodium dodecylbenzene sulfonate (SDBS) and sodium hexadecyl diphenyl oxide disulfonate (DPDS) with two types of soil sediment samples are compared. Sorption of surfactants can be modeled by hydrophobic sorption. Less DPDS sorption is observed at a higher aqueous concentration, which is attributed to the competition between surfactant micelles and sediment organic matter for DPDS sorption. A significant fraction of the sorbed surfactants resists desorption, and this is not a result of surfactant precipitation or desorption kinetics. Surfactant desorption behavior is similar to the irreversible desorption of hydrocarbons from soil with only half of the resistant phase surfactant being readily extracted by heated solvent extraction. The sorption/desorption data are interpreted with a molecular topology and irreversible sorption model. The knowledge of this study can be useful in understanding the environmental fate and transport of these common anionic surfactants. The methodology developed in this study can be expanded to study the sorptive nature of a wider range of surfactants in the environment.

Influence of soil γ-irradiation and spiking on sorption of p,p'-DDE and soil organic matter chemistry

The fate of organic chemicals and their metabolites in soils is often investigated in model matrices having undergone various pre-treatment steps that may qualitatively or quantitatively interfere with the results. Presently, effects associated with soil sterilization by γ-irradiation and soil spiking using an organic solvent were studied in one freshly spiked soil (sterilization prior to contamination) and its field-contaminated (sterilization after contamination) counterpart for the model organic compound 1,1-Dichloro-2,2-bis(4-chlorophenyl)ethene (p,p'-DDE). Changes in the sorption and potential bioavailability of spiked and native p,p'-DDE were measured by supercritical fluid extraction (SFE), XAD-assisted extraction (XAD), and solid-phase microextraction (SPME) and linked to qualitative changes in soil organic matter (SOM) chemistry measured by diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy. Reduced sorption of p,p´-DDE detected with XAD and SPME was associated more clearly with spiking than with sterilization, but SFE showed a negligible impact. Spiking resulted in an increase of the DRIFT-derived hydrophobicity index, but irradiation did not. Spectral peak height ratio descriptors indicated increasing hydrophobicity and hydrophilicity in pristine soil following sterilization, and a greater reduction of hydrophobic over hydrophilic groups as a consequence of spiking. In parallel, reduced sorption of p,p´-DDE upon spiking was observed. Based on the present samples, γ-irradiation appears to alter soil sorptive properties to a lesser extent when compared to common laboratory processes such as spiking with organic solvents.

The potential impact on the biodegradation of organic pollutants from composting technology for soil remediation

Large numbers of organic pollutants (OPs), such as polycyclic aromatic hydrocarbons, pesticides and petroleum, are discharged into soil, posing a huge threat to natural environment. Traditional chemical and physical remediation technologies are either incompetent or expensive, and may cause secondary pollution. The technology of soil composting or use of compost as soil amendment can utilize quantities of active microbes to degrade OPs with the help of available nutrients in the compost matrix. It is highly cost-effective for soil remediation. On the one hand, compost incorporated into contaminated soil is capable of increasing the organic matter content, which improves the soil environment and stimulates the metabolically activity of microbial community. On the other hand, the organic matter in composts would increase the adsorption of OPs and affect their bioavailability, leading to decreased fraction available for microorganism-mediated degradation. Some advanced instrumental analytical approaches developed in recent years may be adopted to expound this process. Therefore, the study on bioavailability of OPs in soil is extremely important for the application of composting technology. This work will discuss the changes of physical and chemical properties of contaminated soils and the bioavailability of OPs by the adsorption of composting matrix. The characteristics of OPs, types and compositions of compost amendments, soil/compost ratio and compost distribution influence the bioavailability of OPs. In addition, the impact of composting factors (composting temperature, co-substrates and exogenous microorganisms) on the removal and bioavailability of OPs is also studied.

Remediation and cytotoxicity study of polycyclic aromatic hydrocarbon-contaminated marine sediments using synthesized iron oxide-carbon composite

The study developed a new and cost-effective method for the remediation of marine sediments contaminated with polycyclic aromatic hydrocarbons (PAHs). Iron oxide (Fe₃O₄) nanoparticles were synthesized as the active component, supported on carbon black (CB), to form a composite catalyst (Fe₃O₄-CB) by using a wet chemical method. The oxidation of 16 PAH contaminants present in marine sediments significantly activated sodium persulfate (Na₂S₂O₈) to form sulfate free radicals (SO₄^-·); this was investigated in a slurry system. In addition, in vitro cytotoxic activity and oxidative stress studies were performed. The synthesized composite catalysts (Fe₃O₄-CB) were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, a superconducting quantum interference device magnetometry, and environmental scanning electron microscopy. The efficiency of PAH removal was 39-63% for unactivated persulfate (PS) from an initial dose of 1.7 × 10^-7-1.7 × 10^-2 M. The removal of PAHs was evaluated using Fe₃O₄/PS, CB/PS, and Fe₃O₄/PS and found to be 75, 64, and 86%, respectively, at a temperature of 303 K, PS concentration of 1.7 × 10^-5 M, and pH of 6.0. An MTT assay was used to assess the cytotoxicity of the composite catalyst at five concentrations (25, 50, 100, 200, and 400 μg/mL) on human hepatoma carcinoma (HepG2) cells for 24 h. This revealed a dose-dependent decrease in cell viability. A dichlorofluorescein diacetate assay was performed to evaluate the generation of reactive oxygen species, which principally originated from the ferrous ions of the composite catalyst.

The role of organic matter and clay content in sediments for bioavailability of pyrene

Evaluation of the bioavailable fractions of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) is extremely important for assessing their risk to the environment. This available fraction, which can be solubilised and/or easily extracted, is believed to be the most accessible for bioaccumulation, biosorption and/or transformation. Sediment organic matter (OM) and clay play an important role in the biodegradation and bioavailability of PAHs. The strong association of PAHs with OM and clay in sediments has a great influence not only on their distribution but also on their long-term environmental impact. This paper investigates correlations between bioavailability and the clay and OM contents in sediments. The results show that OM is a better sorbent for pyrene (chosen as a model PAH) and that increasing the OM content reduces the bioavailable fraction. A mathematical model was used to predict the kinetic desorption, and these results showed that the sediment with the lowest content of OM had an F_fast value of 24%, whereas sediment with 20% OM gave a value of 9%. In the experiments with sediments with different clay contents, no clear dependence between clay and rate constants of the fast desorbing fractions was observed, which can be explained by the numerous possible interactions at the molecular level.

Synthesis of magnetic biochar from bamboo biomass to activate persulfate for the removal of polycyclic aromatic hydrocarbons in marine sediments

This study developed a new and cost-effective method for the remediation of marine sediments contaminated with PAHs. Fe₃O₄ particles were synthesized as the active component, supported on bamboo biochar (BB) to form a composite catalyst (Fe₃O₄-BB). The effects of critical parameters, including the initial pH, sodium persulfate (PS) concentration, and dose of catalyst were investigated. The concentration of high-molecular-weight PAHs in sediments was much higher than that of low-molecular-weight PAHs; pyrene was an especially prominent marker of PAH contamination in sediments. Fe₃O₄-BB/PS exhibited a substantial improvement in PAH degradation efficiency (degradation rate: Fe₃O₄-BB/PS, 86%; PS, 14%) at a PS concentration of 1.7×10^-5M, catalyst concentration of 3.33g/L, and pH of 3.0. The results of this study demonstrate that possible activation mechanisms include Fe²⁺-Fe³⁺ redox coupling and electron shuttling that mediates electron transfer of the BB oxygen functional groups, promoting the generation of SO₄^- in the Fe₃O₄-BB/PS system.

Exploration of biodegradation mechanisms of black carbon-bound nonylphenol in black carbon-amended sediment

The present study aimed to investigate biodegradation mechanisms of black carbon (BC)-bound contaminants in BC-amended sediment when BC was applied to control organic pollution. The single-point Tenax desorption technique was applied to track the species changes of nonylphenol (NP) during biodegradation process in the rice straw carbon (RC)-amended sediment. And the correlation between the biodegradation and desorption of NP was analyzed. Results showed that microorganisms firstly degraded the rapid-desorbing NP (6 h Tenax desorption) in RC-amended sediment. The biodegradation facilitated the desorption of slow-desorbing NP, which was subsequently degraded as well (192 h Tenax desorption). Notably, the final amount of NP degradation was greater than that of NP desorption, indicating that absorbed NP by RC amendment can be degraded by microorganisms. Finally, the residual NP amount in RC-amended sediment was decided by RC content and its physicochemical property. Moreover, the presence of the biofilm was observed by the confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) so that microorganisms were able to overcome the mass transfer resistance and directly utilized the absorbed NP. Therefore, single-point Tenax desorption alone may not be an adequate basis for the prediction of the bioaccessibility of contaminants to microorganisms or bioremediation potential in BC-amended sediment.

Importance of the structure and nanoporosity of organic matter on the desorption kinetics of benzo[a]pyrene in sediments

The desorption kinetics and mechanism were investigated using a Tenax extraction technique on different sediments spiked with radiocarbon-labeled benzo[a]pyrene (BaP). Five sedimentary fractions were sequentially fractionated, and the only nonhydrolyzable organic carbon fractions (NHC) were characterized using advanced solid-state ¹³C nuclear magnetic resonance spectroscopy (NMR), improved six end-member model, and a CO₂ gas adsorption technique. The sediments contained high percentages of algaenan and/or sporopollenin but low percentages of black carbon and lignin. A first-order, two-compartment kinetics model described the desorption process very well (R² > 0.990). Although some of the organic carbon fractions were significantly related to the desorption kinetics parameters, the NHC fractions showed the highly significant correlation. Moreover, the nanoporosity or specific surface area (SSA) of the NHC fractions was highly related to their OC contents and aliphatic C (R² = 0.960, p < 0.01). The multiple regression equations among the desorption kinetics parameters, structural parameters, and nanoporosity were well established (R²=>0.999). Nanoporosity and aromatic C were the dominant contributors. Furthermore, the enhanced percentages of desorbed BaP at elevated temperatures significantly showed a linear regression with the structure and nanoporosity. To our knowledge, the above evidence demonstrates for the first time that the transfer (or diffusion) of BaP in the nanopores of condensed aromatic components is the dominant mechanism of the desorption kinetics of BaP at organic matter particle scale.

Polycyclic aromatic hydrocarbons bioavailability in industrial and agricultural soils: Linking SPME and Tenax extraction with bioassays

The aims of this study were to evaluate the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in industrial and agricultural soils using chemical methods and a bioassay, and to study the relationships between the methods. This was conducted by comparing the quantities of PAHs extracted from two manufactured gas plant (MGP) soils and an agricultural soil with low level contamination by solid-phase micro-extraction (SPME) and Tenax-TA extraction with the quantities taken up by the earthworm (Eisenia fetida). In addition, a biodegradation experiment was conducted on one MGP soil (MGP-A) to clarify the relationship between PAH removal by biodegradation and the variation in PAH concentrations in soil pore water. Results demonstrated that the earthworm bioassay could not be used to examine PAH bioavailability in the tested MGP soils; which was the case even in the diluted MGP-A soils after biodegradation. However, the bioassay was successfully applied to the agricultural soil. These results suggest that earthworms can only be used for bioassays in soils with low toxicity. In general, rapidly desorbing concentrations extracted by Tenax-TA could predict PAH concentrations accumulated in earthworms (R²=0.66), while SPME underestimated earthworm concentrations by a factor of 2.5. Both SPME and Tenax extraction can provide a useful tool to predict PAH bioavailability for earthworms, but Tenax-TA extraction was proven to be a more sensitive and precise method than SPME for the prediction of earthworm exposure in the agricultural soil.

Two-liquid-phase system: A promising technique for predicting bioavailability of polycyclic aromatic hydrocarbons in long-term contaminated soils

A two-liquid-phase system (TLPS), which consisted of soil slurry and silicone oil, was employed to extract polycyclic aromatic hydrocarbons (PAHs) in four long-term contaminated soils in order to assess the bioavailability of PAHs. Extraction kinetics of six PAHs viz. phenanthrene, fluoranthene, pyrene, benzo(a)anthracene, benzo(a)pyrene, dibenzo(a,h)anthrancene were selected to investigate as they covered the susceptible and recalcitrant PAHs in soil. A parallel experiments were also carried out on the microbial degradation of these PAHs in soil with and without biostimulation (by adding (NH₄)₂HPO₄). The rapidly desorbed fraction of fluoranthene, as indicated by the two-fraction model, was found the highest, ranging from 21.4% to 37.4%, whereas dibenzo(a,h)anthrancene was the lowest, ranging from 8.9% to 20.5%. The rapid desorption of selected PAHs was found to be finished within 24 h. The rapidly desorbed fraction of PAHs investigated using TLPS, was significantly correlated (R² = 0.95) with that degraded by microorganisms in biostimulation treatment. This suggested that the TLPS-assisted extraction could be a promising technique in determining the bioavailability of aged PAHs in contaminated soils. It also suggested that applying sufficient nutrients in bioremediation of field contaminated soils is crucial. Further work is required to test its application to more hydrophobic organic pollutants in long-term contaminated soils.

Extraction techniques using isopropanol and Tenax to characterize polycyclic aromatic hydrocarbons bioavailability in sediment

Polycyclic aromatic hydrocarbon (PAH)-degrading bacterium strain J1-q (Sphingomonas pseudosanguinis strain J1-q) was isolated from Yangtze River surface sediment in the downtown area of Chongqing in a previous study. Isopropanol and Tenax extraction techniques were used to characterize the bioavailability of target PAH compounds. Phenanthrene (Phe) and fluoranthene (Fluo) were the target PAHs due to their significant background concentrations in surface sediment samples. Isopropanol solutions at concentrations of 50-100% and residual Phe and Fluo concentrations in sediment were correlated, with R² values of 0.9846 and 0.9649, respectively. The quantities of the Phe and Fluo fractions extracted for 3days with isopropanol from sediment were closely related with the corresponding quantities of PAHs degraded by bacterial strain J1-q when the extracting concentrations were 55% and 80%, respectively. The quantity of Phe extracted by Tenax agreed with the total quantity biodegraded when the Tenax: sediment mass ratio was 0.25 and the target PAHs were degraded for 30d, whereas the extracted quantity of Fluo accounted for 93.30% of the total quantity biodegraded by the bacterium. The triphasic model was appropriate to simulate the consecutive Phe and Fluo extraction process using Tenax at various Tenax: sediment ratios, and all simulated correlation coefficients were >0.9151. A 24-h extraction period was adequate to estimate the rapidly desorbing fractions when they were extracted with Tenax. Isopropanol extraction was preferable to characterize Phe and Fluo bioavailability under the experimental conditions, whereas Tenax extraction was useful to predict bioavailability of the two target PAHs with particular selectivity.

Risk assessment and uncertainty analysis of PAHs in the sediments of the Yangtze River Estuary, China

To better explore the concentration of polycyclic aromatic hydrocarbons (PAHs) in the sediments of the Yangtze River Estuary (YRE), 16 priority PAHs were analyzed based on sampling data obtained in February 2011. The results showed that the total concentrations of PAHs in sediments of the YRE varied from 65.07 to 668.98ng·g^-1. The results of toxic equivalent quantities of benzo[a]pyrene and the sediment quality guideline quotient suggested that PAHs had little or no adverse effects on the environment. The cancer risk results showed that the cancer risk at all sites exceeded 10^-6, with 73% of sites exceeding 10^-4, suggesting that people remain at risk of cancer as a result of their exposure to carcinogenic PAHs. However, the result of hazard index results showed that the non-cancer risks were substantially lower than one, indicating that PAHs in these sediments likely pose little or no adverse health threats to local inhabitants.

Effects of carbonaceous materials on microbial bioavailability of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in sediments

In this study, we investigated the influence of various types of carbonaceous materials (CMs) on the bioavailability of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) to polybrominated diphenyl ether (PBDE)-degrading microorganisms in CM-amended sediments. The microbial debromination ratio of BDE-47 was reduced by 92.8%-98.2% in the 5.0% CM-amended sediment compared with in sediment without CM amendment after 100 d of anaerobic incubation. The concentrations of lower brominated products also decreased when the content of CMs increased from 0.2% to 5.0%. The inhibitory effects of CMs on BDE-47 debromination were CM content- and characteristic-specific. The reciprocals of BDE-47 debromination ratios and lower brominated product concentrations showed positive linear correlations with CM contents in sediments (p<0.01), and the slopes of linear regression fitting generally correlated with specific surface areas (SSAs) of CMs. Desorption of BDE-47 from CMs indicated the declined desorbing fraction of BDE-47 was responsible for the reduction in BDE-47 bioavailability to microorganisms, thus decreasing its debromination in sediments amended with CMs. This study revealed that CM amendment could reduce the PBDE bioavailability to PBDE-degrading microorganisms in sediments, and it is expected to help deepen our understanding of the environmental behaviors and risks of PBDEs.

Selection of oxidant doses for in situ chemical oxidation of soils contaminated by polycyclic aromatic hydrocarbons (PAHs): A review

In situ chemical oxidation (ISCO) is a promising alternative to thermal desorption for the remediation of soils contaminated with organic compounds such as polycyclic aromatic hydrocarbons (PAHs). For field application, one major issue is the selection of the optimal doses of the oxidizing solution, i.e. the oxidant and appropriate catalysts and/or additives. Despite an extensive scientific literature on ISCO, this choice is very difficult because many parameters differ from one study to another. The present review identifies the critical factors that must be taken into account to enable comparison of these various contributions. For example, spiked soils and aged, polluted soils cannot be compared; PAHs freshly spiked into a soil are fully available for degradation unlike a complex mixture of pollutants trapped in a soil for many years. Another notable example is the high diversity of oxidation conditions employed during batch experiments, although these affect the representativeness of the system. Finally, in this review a methodology is also proposed based on a combination of the stoichiometric oxidant demand of the organic pollutants and the design of experiments (DOE) in order to allow a better comparison of the various studies so far reported.

Kinetic modelling of a diesel-polluted clayey soil bioremediation process

A mathematical model is proposed to describe a diesel-polluted clayey soil bioremediation process. The reaction system under study was considered a completely mixed closed batch reactor, which initially contacted a soil matrix polluted with diesel hydrocarbons, an aqueous liquid-specific culture medium and a microbial inoculation. The model coupled the mass transfer phenomena and the distribution of hydrocarbons among four phases (solid, S; water, A; non-aqueous liquid, NAPL; and air, V) with Monod kinetics. In the first step, the model simulating abiotic conditions was used to estimate only the mass transfer coefficients. In the second step, the model including both mass transfer and biodegradation phenomena was used to estimate the biological kinetic and stoichiometric parameters. In both situations, the model predictions were validated with experimental data that corresponded to previous research by the same authors. A correct fit between the model predictions and the experimental data was observed because the modelling curves captured the major trends for the diesel distribution in each phase. The model parameters were compared to different previously reported values found in the literature. Pearson correlation coefficients were used to show the reproducibility level of the model.

Variations in the bioavailability of polycyclic aromatic hydrocarbons in industrial and agricultural soils after bioremediation

The aim of this study was to demonstrate the variations in bioavailability remaining in industrial and agricultural soils contaminated by polycyclic aromatic hydrocarbons (PAHs) after bioremediation. After inoculation of Mycobacterium sp. and Mucor sp., PAH biodegradation was tested on a manufactured gas plant (MGP) soil and an agricultural soil. PAH bioavailability was assessed before and after biodegradation using solid-phase extraction (Tenax-TA extraction) and solid-phase micro-extraction (SPME) to represent bioaccessibility and chemical activity of PAHs, respectively. Only 3- and 4-ring PAHs were noticeably biodegradable in the MGP soil. PAH biodegradation in the agricultural soil was different from that in the MGP soil. The rapidly desorbing fractions (F(rap)) extracted by Tenax-TA and the freely dissolved concentrations of 3- and 4-ring PAHs determined by SPME from the MGP soil decreased after 30 days biodegradation; those values of the 5- and 6-ring PAHs changed to a lesser degree. For the agricultural soil, the F(rap) values of the 3- and 4-ring PAHs also decreased after the biodegradation experiment. The Tenax-TA extraction and the SPME have the potential to assess variations in the bioavailability of PAHs and the degree of biodegradation in contaminated MGP soils. In addition, Tenax-TA extraction is more sensitive than SPME when used in the agricultural soil.

Assessment of the bioavailability and phytotoxicity of sediment spiked with polycyclic aromatic hydrocarbons

Large amounts of sediment are dredged globally every year. This sediment is often contaminated with low concentrations of metals, polycyclic aromatic hydrocarbons, pesticides and other organic pollutants. Some of this sediment is disposed of on land, creating a need for risk assessment of the sediment disposal method, to minimize the degradation of environmental quality and prevent risks to human health. Evaluating the available fractions of certain polycyclic aromatic hydrocarbons is very important, as in the presence of various organisms, they are believed to be easily subject to the processes of bioaccumulation, biosorption and transformation. In order to determine the applicability of applying these methods for the evaluation of pollutant bioavailability in sediments, the desorption kinetics from the sediment of various polycyclic aromatic hydrocarbons in the presence of Tenax and XAD4 were examined over the course of 216 h. Changes in the PAH concentrations in dredged sediments using five different seed plants during a short time of period (10 days) were also followed. Using chemical extraction techniques with Tenax and XAD4, a time of around 24 h is enough to achieve equilibrium for all four PAHs. Results showed good agreement between the seed accumulation and PAH extraction methods with both agents. If we compare the two extraction techniques, XAD4 gave better results for phenanthrene, pyrene and benzo(a)pyrene, and Tenax gave better results for chrysene.

Environmental risk assessments and spatial variations of polycyclic aromatic hydrocarbons in surface sediments in Yangtze River Estuary, China

In this study, based on sampling data from 30 sites in August 2010, the environmental risks associated with 16 priority PAHs were estimated in surface sediments from the Yangtze River Estuary (YRE). The results indicated that the toxic equivalent quantities of the benzo[a]pyrene (TEQBap) from 30 sites were in the range of 1.93-75.88ngg(-1), and the low-molecular-weight PAHs were the dominated species with higher potential toxicity. The results of the Incremental Lifetime Cancer Risk (ILCR) model indicated that the ILCR values of dermal contact were higher than 10(-6) in the northeast region, suggesting that there were significant potential carcinogenic health risks for fishermen exposure to sedimentary PAHs via dermal contact in these areas. RQ values of PAHs indicated the various distributions of ecological risk levels in the study area. These variations might be caused by the natural and anthropogenic inputs and currents in the YRE.