Bioavailability Of Phenanthrene Research Articles

Effects of biodegradable microplastics coexistence with biochars produced at low and high temperatures on bacterial community structure and phenanthrene degradation in soil

The increasing use of biodegradable plastics may result in more serious pollution of microplastics which often coexist with biochar in soil, this will affect how organic pollutants move and transform in the soil. This work investigated the effect of biodegradable polybutylene adipate-co-terephthalate (PBAT) coexistence with biochars produced at temperatures of 400 and 700 °C (W4 and W7) on soil bacterial communities and phenanthrene degradation. The results showed that coexistence of PBAT and biochar paticles greatly boosted the relative abundance of Nocardioides while decreased the relative abundance of Sphingomonas as compared to soils with a single addition of PBAT or biochar. Changes in soil Eh values were the most influential factor in bacterial communities (more than 40% contribution). The degradation ratio of phenanthrene when PBAT coexisted with W7 (39.6 ± 3.6%) was not significantly different from the treatment with a single W7 addition (35.0 ± 2.3%, P＞0.05), and was related to phenanthrene degradation in the adsorbed state of W7 in soil. In contrast, the degradation ratio of phenanthrene in PBAT coexisting with W4 (35.1 ± 3.5%) was intermediate between that of single PBAT (49.8 ± 0.9%) and W4 (13.7 ± 5.8%) treatments. This was primarily due to changes in the experiment's initial bioavailable phenanthrene content. Furthermore, after the introduction of earthworms, phenanthrene degradation ratio in coexistence treatments were very similar to that described above in the absence of earthworms. Except for two treatments that contain W7, phenanthrene degradation ratio in the other treatments was increased by the presence of earthworms (up to 23%), which is related to the enhanced relative abundance of polycyclic aromatic hydrocarbon-degraders. Our findings indicated that PBAT coexistence with high-temperature or low-temperature biochar had a completely different impact on bacterial communities and phenanthrene degradation in soil.

Impact mechanisms of various surfactants on the biodegradation of phenanthrene in soil: Bioavailability and microbial community responses

The present study was conducted to systematically explore the mechanisms underlying the impact of various surfactants (CTAB, SDBS, Tween 80 and rhamnolipid) at different doses (10, 100 and 1000 mg/kg) on the biodegradation of a model polycyclic aromatic hydrocarbon (PAH) by indigenous soil microorganisms, focusing on bioavailability and community responses. The cationic surfactant CTAB inhibited the biodegradation of phenanthrene within the whole tested dosage range by decreasing its bioavailability and adversely affecting soil microbial communities. Appropriate doses of SDBS (1000 mg/kg), Tween 80 (100, 1000 mg/kg) and rhamnolipid at all amendment levels promoted the transformation of phenanthrene from the very slow desorption fraction (Fvslow) to bioavailable fractions (rapid and slow desorption fractions, Frapid and Fslow), assessed via Tenax extraction. However, only Tween 80 and rhamnolipid at these doses significantly improved both the rates and extents of phenanthrene biodegradation by 22.1–204.3 and 38.4–76.7 %, respectively, while 1000 mg/kg SDBS had little effect on phenanthrene removal. This was because the inhibitory effects of anionic surfactant SDBS, especially at high doses, on the abundance, diversity and activity of soil microbial communities surpassed the bioavailability enhancement in dominating biodegradation. In contrast, the nonionic surfactant Tween 80 and biosurfactant rhamnolipid enhanced the bioavailability of phenanthrene for degradation and also that to specific degrading bacterial genera, which stimulated their growth and increased the abundance of the related nidA degradation gene. Moreover, they promoted the total microbial/bacterial biomass, community diversity and polyphenol oxidase activity by providing available substrates and nutrients. These findings contribute to the design of suitable surfactant types and dosages for mitigating the environmental risk of PAHs and simultaneously benefiting microbial ecology in soil through bioremediation.

Adsorption of Phenanthrene on Multi-Walled Carbon Nanotubes in the Presence of Nonionic Surfactants.

The bioavailability and mobility of phenanthrene (Phe) adsorbed by multi-walled carbon nanotubes (MWCNTs) may be substantially influenced by nonionic surfactants used both in the synthesis and dispersion of MWCNTs. The adsorption mechanisms of Phe adsorbed onto MWCNTs under the different nonionic surfactants Tween 80 (TW-80) and Triton X-100 (TX-100) in the aqueous phase were investigated in terms of changes in the MWCNTs' compositions and structures. The results showed that TW-80 and TX-100 were easily adsorbed onto MWCNTs. Phe adsorption data onto MWCNTs were better suited to the Langmuir equation than the Freundlich equation. Both TW-80 and TX-100 reduced the adsorption capacity of Phe onto MWCNTs. When TW-80 and TX-100 were added in the adsorption system, the saturated adsorption mass of Phe decreased from 35.97 mg/g to 27.10 and 29.79 mg/g, respectively, which can be attributed to the following three reasons. Firstly, the hydrophobic interactions between MWCNTs and Phe became weakened in the presence of nonionic surfactants. Secondly, the nonionic surfactants covered the adsorption sites of MWCNTs, which caused Phe adsorption to be reduced. Finally, nonionic surfactants can also promote the desorption of Phe from MWCNTs.

Inhibition of polycyclic aromatic hydrocarbon (PAHs) release from sediments in an integrated rice and crab coculture system by rice straw biochar

As persistent organic pollutants that are widely present in the environment and that pose substantial threats to human health, polycyclic aromatic hydrocarbons (PAHs) have received much attention from researchers around the world, but few studies have investigated the PAHs contamination of sediments in rice and crab coculture farming systems. In this study, rice straw biochar was prepared from rice straw, an abundant agricultural waste product, under oxygen-limited conditions at 500 °C. The rice straw biochar was characterized by scanning electron microscopy (SEM), specific surface and pore size analysis (BET), Fourier transform infrared spectroscopy (FTIR), and Raman Spectroscopy. The effect of using rice stalk biochar as a sorbent on the inhibition of the release and migration of PAHs from sediments in a rice and crab coculture system and the biological effects of PAHs within the system were studied for the first time. The results showed that rice straw biochar has a rich pore structure and high specific surface area, and the high-temperature charring method utilized in this study improved the charring and aromaticity of rice straw. The addition of rice straw biochar increased the immobilization of PAHs in sediments by 40.41%–119.62% and inhibited the migration of PAHs from the sediments to the overlying water, which reduced the PAHs content of the pore water at the sediment-water interface by 11.41%–58.73% and reduced the PAHs content of the overlying water in the dissolved and particulate forms by 54.67%–81.03% and 5.08%–55.20%, respectively. The addition of rice straw biochar reduced the biological effectiveness of PAHs in the system, and the enrichment of PAHs in crabs and rice decreased by 38.17–69.53% and 32.12%–97.63%, respectively. In addition, rice straw biochar changed the distribution of PAHs in rice, increasing the PAHs content of the stalks and leaves of rice by 2%–15% and 4%–17%, respectively, while the PAHs content of the roots was reduced by 8%–20%. These results confirm that rice straw biochar can effectively inhibit the migration and release of PAHs from sediments and reduce the bioavailability of phenanthrene (PHE) in integrated farming systems. The results provide theoretical and technical support for the study of straw waste utilization and remediation of PAHs pollution.

Microplastics lag the leaching of phenanthrene in soil and reduce its bioavailability to wheat

Microplastics wildly occur in soil and they can become the carriers of persistent contaminants. However, the influence of microplastics on polycyclic aromatic hydrocarbons vertical translocation in the soil system after rainfall is limitedly understood. Here, experiments were conducted to study the influence of polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC) microplastics on the leaching behavior and bioavailability of phenanthrene (Phe). The adsorption capacity of phenanthrene on the microplastics followed the order of PS > PE > PVC. The Phe concentrations in the top soil layer after 15 days of leaching with water were 30.25, 28.32 and 27.25 mg kg−1 for the treatments of Phe-PS, Phe-PE and Phe-PVC respectively, which is consistent with the adsorption capacities of microplastics. The concentrations of Phe were correlated with the microplastic adsorption capacities at soil depths of 5–45 cm. Under long-term leaching, Phe could reach the deeper soil layer. Phe concentrations significantly decreased in the leachate over time. Phe concentrations in wheat had a positive correlation with that in leachate/leached top soil layer. Our findings are beneficial to accurately evaluate the ecological risk of the combined contamination of PAHs and microplastics, and improve the understanding of the environmental behaviors of different microplastics.

Effects of different order spiking on bioavailability and ecological risk of phenanthrene in mangrove sediment-biochar system

Biochar shows unique advantage in decreasing the bioavailability of phenanthrene and has huge potential into the in-situ remediation of contaminated sediment. The different order spiking influences the bioavailability and ecological risk of phenanthrene, this study provides a comprehensive investigation of biochar (derived from mangrove Kandelia obovata -sediment system under three conditions: I) co-addition of biochar and sediment; II) biochar and subsequently sediment addition (after biochar adsorption reached equilibrium); III) sediment and subsequently biochar addition (after sediment adsorption reached equilibrium). It was observed that the adsorption capability under model I and III was much smaller than that under model II (p < 0.05). Regardless of time, K. obovate - biochar significantly (p < 0.05) increase the sorption of phenanthrene in sediment -water system. The results provide valuable studies for further in-situ remediation of phenanthrene and engineering applications.

Responses of bioavailability and degradation of phenanthrene in soils with or without earthworms to the addition of mixed particles of biochar and polyethylene

Responses of bioavailability and degradation of phenanthrene in soils with or without earthworms to the addition of mixed particles of biochar and polyethylene

Bioaugmentation treatment of polycyclic aromatic hydrocarbon-polluted soil in a slurry bioreactor with a bacterial consortium and hydroxypropyl-β-cyclodextrin

ABSTRACT The aim of the study was to verify the effect of bioaugmentation by the bacterial consortium YS with hydroxypropyl-β-cyclodextrin (HPCD) in a soil slurry. The bacterial consortium YS was enriched from a petroleum-polluted soil using pyrene as sole carbon resource. After 3 weeks, the degradation rate of phenanthrene in CK increased from 22.58% to 55.23 and 78.21% in bioaugmentation (B) and HPCD + bioaugmentation (MB) respectively. The degradation rate of pyrene in CK increased from 17.33% to 51.10% and 60.32% in B and MB respectively in the slurry. The augmented YS persisted in the slurry as monitored by 16S rRNA gene high-throughput sequencing and outcompeted some indigenous bacteria. Enhanced polycyclic aromatic hydrocarbon (PAH) degradation was observed in the addition of HPCD due to the enhanced bioavailability of phenanthrene and pyrene. Additionally, the amount of PAH-degrading bacteria and enzymatic activity in bioaugmentation with HPCD were higher than that in the CK group. The results indicated that bioaugmentation with a bacterial consortium and HPCD is an environmentally friendly method for the bioremediation of PAH-polluted soil.

Adsorption of phenanthrene onto magnetic multi-walled carbon nanotubes (MMWCNTs) influenced by various fractions of humic acid from a single soil

In the present study, two magnetic multi-walled carbon nanotubes (MMWCNTs) with different ratios of Fe2+/Fe3+ were prepared, and the effects of different fractions of dissolved humic acid (DHA) on the adsorption of phenanthrene by multi-walled carbon nanotubes (MWCNTs) and MMWCNTs from the aqueous solution were investigated. The adsorption kinetics of DHA1 and DHA4 were best fitted with pseudo-second order model. The adsorption of DHAs on MMWCNTs was weaker than that on MWCNTs, and DHA1 was easier to adsorb to MWCNTs and MMWCNTs than DHA4. The phenanthrene adsorption capacities by 1:2:1MMWCNTs and 4:2:1MMWCNTs with higher polar groups and magnetic gradient were less than that of MWCNTs. The pH value had no obvious effect on the adsorption of phenanthrene to MWCNTs loaded with different iron. Additionally, the DHAs could form soluble complexes of DHAs–Fe (II) in solution to reduce the phenanthrene adsorption on MMWCNTs, DHA1 inhibit more obviously phenanthrene adsorbed onto MWCNTs and MMWCNTs than DHA4. As for MMWCNTs, the main mechanisms of phenanthrene adsorbed onto it included new adsorption sites formed by π−π interaction and magnetic gradient. In this study, MMWCNTs after adsorbed DHAs had a weaker inhibitory effect on phenanthrene adsorption than MWCNTs, implying that when phenanthrene is adsorbed by DHAs-coated MMWCNTs, the bioavailability and mobility of phenanthrene will be reduced, and it is easy to be removed by the magnet for further processing.

Influence of Triton X-100 and β-cyclodextrin on the bioavailability and biodegradation of crystalline phenanthrene covered with biofilms

PAH biodegradation aided by surfactants and cyclodextrins has been widely studied because the former's micelles and the latter's hydrophobic cavities can increase the apparent solubility of PAHs. In this work, the effects of Triton X-100 (TX-100) and β-cyclodextrin (β-CD) on the bioavailability and biodegradation of phenanthrene (PHE) were investigated. The degrading microorganism used was Moraxella osloensis CFP312, a new strain screened from polluted soil and could form biofilms on crystalline PHE. At the same concentrations, β-CD solubilized less PHE than TX-100 but promoted PHE biodegradation. The two solubilizers had almost no different effects on CFP312 hydrophobicity; however, β-CD significantly eluted fewer cells from biofilms on crystalline PHE than TX-100. Microscopy observation revealed that the residual structure of the biofilm treated with β-CD was more complete than that of the biofilm treated with TX-100. This effect is beneficial to the function of biofilms and conducive to mass transfer from the exposed area in the crystalline PHE to the aqueous phase. Although TX-100 and β-CD could enhance the mass transfer of PHE to the aqueous phase, the latter significantly improved the bioavailability and biodegradation of PHE mainly because its solubilization was accompanied by easy desorption and retention of the biofilm functional integrity.

Influence of Triton X-100 and β-cyclodextrin on the bioavailability and biodegradation of crystalline phenanthrene covered with biofilms

PAH biodegradation aided by surfactants and cyclodextrins has been widely studied because the former's micelles and the latter's hydrophobic cavities can increase the apparent solubility of PAHs. In this work, the effects of Triton X-100 (TX-100) and β-cyclodextrin (β-CD) on the bioavailability and biodegradation of phenanthrene (PHE) were investigated. The degrading microorganism used was Moraxella osloensis CFP312, a new strain screened from polluted soil and could form biofilms on crystalline PHE. At the same concentrations, β-CD solubilized less PHE than TX-100 but promoted PHE biodegradation. The two solubilizers had almost no different effects on CFP312 hydrophobicity; however, β-CD significantly eluted fewer cells from biofilms on crystalline PHE than TX-100. Microscopy observation revealed that the residual structure of the biofilm treated with β-CD was more complete than that of the biofilm treated with TX-100. This effect is beneficial to the function of biofilms and conducive to mass transfer from the exposed area in the crystalline PHE to the aqueous phase. Although TX-100 and β-CD could enhance the mass transfer of PHE to the aqueous phase, the latter significantly improved the bioavailability and biodegradation of PHE mainly because its solubilization was accompanied by easy desorption and retention of the biofilm functional integrity.

Responses of phenanthrene degradation to the changes in bioavailability and microbial community structure in soils amended with biochars pyrolyzed at low and high temperatures

This study investigated the impact of wheat straw biochars pyrolyzed at temperatures of 100–700 ℃ (BC100-BC700) on biodegradation of phenanthrene in soils. During a 42-day experiment, biochar amendment reduced the biodegradation ratio of phenanthrene in soils by no change-77.0%. The biodegradation ratio decreased with the increase of pyrolysis temperature from 100 to 400 ℃ and then increased with the increase of pyrolysis temperature from 400 to 700 ℃, exhibiting a U-shape. Meanwhile, desorbing fraction of phenanthrene extracted by n-butanol declined with increasing pyrolysis temperature. Biochar-derived dissolved organic carbon (DOC) obviously influenced the soil DOC contents which were negatively correlated with the total relative abundances of dominant polycyclic aromatic hydrocarbon (PAH)-degraders. These results indicated that in soils amended with biochars pyrolyzed at low temperatures (i.e. 100–400 ℃), both the reduced bioavailability of phenanthrene and the reduced PAH-degrader abundance resulted in decreasing phenanthrene degradation with pyrolysis temperature. In soils amended with biochars pyrolyzed at high temperatures (i.e. 500–700 ℃; HT-biochars), two possible reasons contribute to increasing phenanthrene degradation with pyrolysis temperature: (1) high sorbed-phenanthrene concentration due to large specific surface area and high aromaticity of the biochars, and (2) the increased dominant PAH-degrader abundance for the removal of sorbed-phenanthrene due to the impact of HT-biochars on soil properties (mainly on DOC content).

Mechanism of the biodemulsifier-enhanced biodegradation of phenanthrene by Achromobacter sp. LH-1

Biodemulsifiers are widely applied in petroleum processing, mining and petroleum pollution treatment. Polycyclic aromatic hydrocarbons (PAHs) are a common component in petroleum-polluted environments; however, little is known about the mechanism behind the effect of biodemulsifiers on promoting PAH biodegradation. To obtain clear mechanistic insights, the facilitating effects of biodemulsifiers on the bioavailability of phenanthrene (PHE), which is used as a model PAH, and the cell membrane properties of PHE-degrading bacteria Achromobacter sp. LH-1 were researched. The results showed that LH-1 achieved a 96.1 % degradation rate and a 60 % adsorption rate. Biodemulsifiers could encapsulate PHE within micelles to solubilize PHE and increase the cell surface hydrophobicity (CSH) of LH-1 to improve the association of LH-1 with PHE. Furthermore, biodemulsifier molecules can be embedded in the phospholipid bilayer of the LH-1 membrane to increase the permeability and the area of the LH-1 membrane, and they can increase the unsaturated fatty acid contents of the LH-1 membrane to loosen the arrangement of carbon chains, thus further facilitating the uptake of PHE by LH-1 for biodegradation. These results suggest that biodemulsifiers are powerful biological products for increasing the degradation potential of PHE-degrading bacteria in ecosystems, and their application will be important for the economical and efficient bioremediation of PHE-contaminated environments.

Different bioavailability of phenanthrene to two bacterial species and effects of trehalose lipids on the bioavailability

Effects of trehalose lipids produced from Rhodococcus erythropolis ATCC 4277 on phenanthrene (PHE) mineralization by two soil microorganisms were investigated. Biodegradation experiments were conducted, with and without the biosurfactant, in three batch systems: water, soil, and soil–water slurry. PHE sorption to the soil did not limit the mineralization by the test microorganisms, Pseudomonas strain R (PR) and Sphingomonas sp. strain P5-2 (SP5-2). Both microorganisms, however, demonstrated significant difference in the PHE mineralization capability in the systems. While SP5-2 mineralized PHE faster than PR in liquid culture, PR having more hydrophobic surface greatly exceeded SP5-2 in ability to access soil-sorbed PHE. While the addition of the biosurfactant little affected the apparent cell hydrophobicity of SP5-2, it substantially improved PHE mineralization by this strain in all systems tested. Contrary to SP5-2, the apparent cell hydrophobicity was significantly stimulated with increasing concentration of the biosurfactant for PR. However, the biosurfactant had no significant effect on PHE mineralization by this microorganism. The results demonstrated that the addition of the biosurfactant may have great potential for remediation of sites contaminated with polycyclic aromatic hydrocarbons but its effects and benefits may be dependent on characteristics of microorganisms involved and environmental conditions.

Carbon nanomaterials differentially impact mineralization kinetics of phenanthrene and indigenous microbial communities in a natural soil

Previous reports on how carbon nanomaterials (CNMs) affect the biodegradation and mineralization of organic contaminants are mainly limited to pure culture studies, but little is known about the mineralization process by more complex and environmentally-relevant microbial communities. This study investigated the impact of fullerenes C60 and two multi-walled carbon nanotubes (outer diameter < 8 nm: M8; >50 nm: M50) at 300 and 3000 mg/kg on the mineralization kinetics of 14C-phenanthrene (18.5 mg/kg) by indigenous microorganisms in a natural soil for 120 days. Phenanthrene mineralization kinetics fitted well with the logistic growth equation regardless of the CNMs present (R2 = 0.965–0.985). The maximum mineralization rates and the total mineralization fraction were positively correlated with the initial phenanthrene bioavailability, assessed via β-HPCD extraction. Phenanthrene exposure induced significant responses of the catabolic gene biomarker nidA, fungi and bacteria communities by 275, 30, and 5 times, respectively, indicating a non-neglectable role of the fungal communities in phenanthrene mineralization. CNMs exerted a sorption- and level-dependent suppression (7.4–47.2%) on the total phenanthrene mineralization fractions at 120 d. Carbon nanotubes (300, 3000 mg/kg) caused significant adverse effects on the biomass of bacterial (47.8–60.7%), fungal (31.4–71.6%) and nidA-carrying degraders (25.7–59.9%) in the absence or presence of phenanthrene, which contributed to the inhibition of the total mineralization fractions at 120 d. Bacterial community structure was not significantly impacted by CNMs alone or co-exposure of CNM-phenanthrene. However, the fungal community showed a significant shift upon exposure to carbon nanotubes, especially M8, with the relative abundance of potential PAH degraders repressed (8.5–40.3%) at both levels of M8 tested. This corroborates the higher sensitivity of fungal communities. The findings from this study are important to inform how the released CNMs affect soil microbial communities that play a key role in the fate and remediation of organic contaminants in soil.

Sorption of Phenanthrene to Soybean and Wheat Roots and the Bioavailability of Sorbed Phenanthrene

The study of PAHs sorption and bioavailability to different crop roots could help to reveal the environmental behavior of PAHs in the ecosystem and evaluate the ecological risk of PAHs. However, there is little information about the differences in PAHs sorption to different roots and the bioavailability of the sorbed PAHs. In this paper, the experiments were conducted on the sorption/desorption of phenanthrene to soybean and wheat roots under different sorption times and different phenanthrene concentrations. The results showed that the trend of phenanthrene sorption in vivo was first increased and then decreased and finally reached a balance, which was related to the transport delay in vivo; the trend in dead and dried roots was first increased and then reached a balance. The greater specific surface area and the higher fat content, the faster the balance was. Freundlich isotherm was fitted better than Henry isotherm for dead and dried roots, Langmuir isotherm was best fitted in wheat roots. All of the fitted isotherms indicated that the distribution and the surface adsorption could control the phenanthrene sorption. Because of the special binding between living roots and phenanthrene, the fit effect was poor. The phenanthrene sorption capacity of soybean roots was higher than that of wheat, which was related to the high water content, fat content and membrane permeability. The phenanthrene sorbed on the roots was hard to desorb, and the desorption trends were wheat roots> soybean roots; living roots> dried roots> dead roots. The bioavailability of root-sorbed phenanthrene was consistent with the desorption results. Our results could provide data for the assessment of environmental risks of PAHs sorbed onto crop roots.

Effects of dissolved organic matter derived from forest leaf litter on biodegradation of phenanthrene in aqueous phase

Dissolved organic matter (DOM) released from forest leaf litter is potentially effective for the degradation of polycyclic aromatic hydrocarbons (PAHs), yet the inherent mechanism remains insufficiently elucidated. In this study, we investigated the effects of DOM derived from Pinus elliottii and Schima superba leaf litter on the degradation of phenanthrene by the phenanthrene degrading bacterium Sphingobium sp. Phe-1. DOM from different origins and at a large range of concentrations enhanced the degradation rate of phenanthrene. DOM derived from P. elliottii leaf litter decomposed for 12 months used at a concentration of 100mg/L yielded the highest degradation rate (16.9% in 36h) and shortened the degradation time from 48h to 24h. Changes in the composition of DOM during degradation as measured by EEMs-FRI showed that proteins and tyrosine in the DOM supplied readily available nutrients that stimulated biological activity of Phe-1, increasing its growth rate and catechol 2,3-dioxygenase activity. Simultaneously, fulvic acid and humic acid in the DOM enhanced phenanthrene bioavailability by increasing the solubility and mass transfer of phenanthrene, enhancing the uptake kinetics of Phe-1, and increasing the bacteria’s direct access to DOM-associated phenanthrene. Humic acid was co-metabolized by Phe-1, resulting in further stimulation of phenanthrene degradation.

Phenanthrene Bioavailability and Toxicity to Daphnia magna in the Presence of Carbon Nanotubes with Different Physicochemical Properties.

Studies investigating the effect of carbon nanotubes (CNTs) on the bioavailability and toxicity of hydrophobic organic compounds in aquatic environments have generated contradictory results, and the influence of different CNT properties remains unknown. Here, the adsorption of the polycyclic aromatic hydrocarbon phenanthrene (70-735 μg/L) to five types of CNTs exhibiting different physical and chemical properties was studied. The CNTs were dispersed in the presence of natural organic matter (nominally 20 mg/L) in order to increase the environmental relevance of the study. Furthermore, the bioavailability and toxicity of phenanthrene to Daphnia magna in the absence and presence of dispersed CNTs was investigated. Both CNT dispersion and adsorption of phenanthrene appeared to be influenced by CNT physical properties (diameter and specific surface area). However, dispersion and phenanthrene adsorption was not influenced by CNT surface chemical properties (surface oxygen content), under the conditions tested. Based on nominal phenanthrene concentrations, a reduction in toxicity to D. magna was observed during coexposure to phenanthrene and two types of CNTs, while for the others, no influence on phenanthrene toxicity was observed. Based on freely dissolved concentrations, however, an increased toxicity was observed in the presence of all CNTs, indicating bioavailability of CNT-adsorbed phenanthrene to D. magna.

Bioavailability of phenanthrene and nitrobenzene sorbed on carbonaceous materials

To better understand the mechanisms regarding effects of the interactions between organic contaminants (ORCs) and carbonaceous materials (CMs) on bioavailability of ORCs, 22 mg/kg of phenanthrene and nitrobenzene were spiked onto various CMs, and their microbial mineralization by the bacterium Mycobacterium vanbaalenii PYR-1 was investigated. The results showed that as sorption of phenanthrene and nitrobenzene to CMs increased 4.5 and 42.3 times, their freely dissolved concentrations (Cfree) decreased by 80.4% and 97.0%, respectively. Correspondingly, the maximum mineralization rate was reduced by 99.6% for phenanthrene and 98.2% for nitrobenzene. Functionalization of multiwalled carbon nanotubes (CNTs) with hydrophilic polar moieties greatly weakened sorption of phenanthrene and nitrobenzene. Correspondingly, the reduction in mineralization of them preloaded on CNTs was more modest. However, bioavailability of CM-sorbed phenanthrene and nitrobenzene was not solely controlled by Cfree. Model calculations of mineralization kinetics data and electron microscopy observations of CMs evidenced that bacteria access to sorbed phenanthrene and nitrobenzene through cell attachment to the particle surfaces, but this process was CM dependent. This work highlights the factors and underlying mechanisms governing microbial availability of ORCs sorbed on CMs, which is significant for risk assessment of ORCs and possible application of CMs for ORC pollution control through sequestration.

Specific adsorption of cadmium on surface-engineered biocompatible organoclay under metal-phenanthrene mixed-contamination

Bioremediation of polycyclic aromatic hydrocarbons (PAHs) is extremely challenging when they coexist with heavy metals. This constrain has led to adsorption-based techniques that help immobilize the metals and reduce toxicity. However, the adsorbents can also non-selectively bind the organic compounds, which reduces their bioavailability. In this study we developed a surface-engineered organoclay (Arquad® 2HT-75-bentonite-palmitic acid) which enhanced bacterial proliferation and adsorbed cadmium, but elevated phenanthrene bioavailability. Adsorption models of single and binary solutes revealed that the raw bentonite adsorbed cadmium and phenanthrene non-selectively at the same binding sites and sequestrated phenanthrene. In contrast, cadmium selectively bound to the deprotonated state of carboxyl groups in the organoclay and phenanthrene on the outer surface of the adsorbent led to a microbially congenial microenvironment with a higher phenanthrene bioavailability. This study provided valuable information which would be highly important for developing a novel clay-modulated bioremediation technology for cleaning up PAHs under mixed-contaminated situations.