Assessment of phenanthrene bioavailability in aged and unaged soils by mild extraction

Adsorption of sulfamethoxazole and ethofumesate in biochar- and organoclay-amended soil: Changes with adsorbent aging in the laboratory and in the field

Biochars and organoclays have been proposed as efficient adsorbents to reduce the mobility of agrochemicals in soils. However, following their application to soils, these adsorbents undergo changes in their physicochemical properties over time due to their interaction with soil components. In this study, the adsorption capacity of a commercial biochar and a commercial organoclay for the antibiotic sulfamethoxazole (SFMX) and the pesticide ethofumesate (ETFM) was evaluated over aging periods of 3 months in the laboratory and 1 year in the field, subsequent to their application to a Mediterranean soil. The results showed that the adsorption of SFMX and ETFM in the soil amended with the adsorbents was greater than in the unamended soil, but for both chemicals, adsorption decreased with aging of the adsorbents in the soil. Characterization of the adsorbents before and after aging revealed physical blocking of adsorption sites by soil components. The loss of adsorption capacity of the adsorbents upon aging led to higher leaching of SFMX and ETFM in the soil containing field-aged adsorbents, although leaching remained lower than in unamended soil. Our findings reveal that, under the Mediterranean environment studied, the efficacy of the studied materials as adsorbents is maintained to a considerable extent for at least one year after their field application, which would have positive implications in their use for attenuating the dispersion of agricultural contaminants in the environment.

Degradation of crude oil-associated polycyclic aromatic hydrocarbons by marine-derived fungi

One of the major environmental concerns today is hydrocarbon contamination resulting from the activities related to the petrochemical industry. Crude oil is a complex mixture of hydrocarbons like alkanes, naphthene and polycyclic aromatic hydrocarbons (PAHs). PAHs are known to be highly toxic to humans and animals due to their carcinogenic and mutagenic effects. PAHs are environmentally recalcitrant due to their hydrophobicity which makes them difficult to degrade, thus making them persistent environmental contaminants. The mechanical and chemical methods in practice currently to remove hydrocarbon contaminants have limited effectiveness and are expensive. Bioremediation is a cost-effective technology for treating hydrocarbon-contaminated sites as it results in the complete mineralisation of the pollutant. This study demonstrates the degradation of crude oil and associated PAHs using ten fungal cultures isolated from the aquatic environment. The current study reported a 98.6% and 92.9% reduction in total PAHs in crude oil by Fusarium species, i.e. isolate NIOSN-T4 and NIOSN-T5, respectively. The fungal isolate, NIOSN-T4, identified as Fusarium equiseti, showed maximum PAH degradation efficiency of LMW PAHs 97.8%. NIOSN-M126, identified as Penicillium citrinum, exhibited a 100% removal of HMW PAHs. Microorganisms possess an untapped potential for various applications in biotechnology, and the current study demonstrated the potential of marine fungi for use in the bioremediation of xenobiotic hydrocarbons in the environment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03753-2.

The Role of Nanoengineered Biochar Activated with Fe for Sulfanilamide Removal from Soils and Water

Biochar is a nanoengineered sorbent proposed to control the contamination derived from the presence of residual concentrations of sulfonamides in soil. In this work, we evaluated the sorption of sulfanilamide (SFA) in commercial biochar (BC) produced at 500 °C from oak hardwood (Quercus ilex) and its analog activated with 2% (w/w) Fe (BC-Fe). Subsequently, the effect on dissipation and transport of SFA in untreated soil and soil treated with BC and BC-Fe was also assessed. Laboratory batch studies revealed that BC-Fe increased the sorption of SFA as compared to the pristine BC with Kd of 278 and 98 L/kg, respectively. The dissipation of SFA in either untreated soil or soil treated with BC or BC-Fe was similar, displaying half-lives ranging between 4 and 6.4 days. Conversely, the concurrent determination of sorption during the incubation experiment showed that lower amounts of SFA in solution at the beginning of the experiments were bioavailable in BC-Fe-treated soil when compared to the rest of the treatments shortly after application. Leaching column studies confirmed the amendment’s capability to bind the SFA compound. Therefore, the decrease in bioavailability and movement of SFA in treated soils suggest that biochar soil application can reduce SFA soil and water contamination. According to our results, BC surface modification after Fe activation may be more appropriate for water decontamination than for soil since there were no significant differences between the two types of biochar when added to the soil. Therefore, these outcomes should be considered to optimize the SFA mitigation potential of biochar.

Development of an online μ-matrix cartridge extraction method for fipronil extraction in contaminated soils

Nowadays, environment fate and behavior of pesticides in soil is still not fully understood due to the lack of standardized soil extraction method. In this work, a soil-filled micro-matrix cartridge was online combined with high performance liquid chromatography-mass spectrometry (HPLC-MS) through a six-way valve for the simultaneous extraction and determination of residual fipronil in soil. Compared with conventional extraction methods, such as hydroxypropyl-β-cyclodextrin (HPCD) extraction, shaking extraction, ultrasonic-assisted extraction (UAE), three-step extraction and matrix solid phase dispersion (MSPD), the novel, miniaturized, and integrated online micro-matrix cartridge extraction (online μ-MCE) method exhibited better performance in terms of desorption efficiency (99.4%), analysis time, solvent consumption, sensitivity, and automation. In sequential extraction, online μ-MCE could further desorb fipronil from the extracted soil with the percentage of 1.05%-58.55%. High recovery of 92.69% obtained for the ISO certificated test-soil verified the satisfactory accuracy of the method. Besides, its wide universality was also validated in three variables: 1) various pesticides-soil interactions, 2) four types of compounds (aromatic hydrocarbons, carboxylic acids, alcohols and aldehydes), and 3) three types of soils (sandy soil, silty loam and silty clay). The superior desorption capacity might be attributed to the instantaneously increased high-pressure, continuous flow dynamic desorption and short residence time. The present encouraging findings might shed light on new ways to develop a mild, highly efficient, reliable and one-fit-all extraction method toward pesticide contaminated soil.

Vermiremediation of engine oil contaminated soil employing indigenous earthworms, Drawida modesta and Lampito mauritii

Engine oil consists of hazardous substances that adversely affect the environment and soil quality. Bioremediation (employing organisms) is an appropriate technique to mitigate engine oil pollution. In the present study, the earthworm species, Drawida modesta (epigeic) and Lampito mauritii (anecic) were used to restore the soil polluted with polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbons (TPHs) from used engine oil. Four treatments were set up in addition to positive and negative controls. A maximum of 68.6% PAHs and 34.3% TPHs removal in the treatment with soil (1 kg), cow dung (50 g), used engine oil (7.5 mL) and earthworms was recorded after 60 days. Undoubtedly, earthworms effectively removed PAHs and TPHs from the oil-contaminated soil. PAHs were more strongly accumulated in D. modesta (16.25 mg kg^-1) than in L. mauritii (13.25 mg kg^-1). Further, histological analysis revealed the epidermal surface irregularity, cellular disintegration, and cellular debris in earthworms. The pH (6.3%), electrical conductivity (12.7%), and total organic carbon (35.4%) were significantly (at P < 0.05) decreased after 60 days; while, total nitrogen (62%), total potassium (76.2%), and total phosphorus (19.2%) were substantially increased at the end of the experiment. The seed germination assay with fenugreek indicates that germination percentage (95%), and germination index (179), were dramatically increased in earthworm inoculated treatments when compared to the negative control (without earthworms). The results reveal that there is a great scope for utilizing the earthworms, D. modesta and L. mauritii for the bioremediation of soils contaminated with PAHs and TPHs.

Effects of crude oil and aromatic compounds on growth and bioluminescence of Vibrio campbellii FS5

Fifteen native luminescent bacteria were isolated from the Gulf of Thailand, and their sensitivity for the detection of toxicity of crude oil and its aromatic components was investigated. Of these isolates, Vibrio campbellii strain FS5 was one of the two most highly inhibited bacteria at all crude oil concentrations. This bacterium showed a decrease in luminescence intensity of between 10.7 and 80.2% after a 15-min exposure to 0.0001-10 mg/L of crude oil. The degree of bioluminescence inhibition increased with increasing concentrations of crude oil. The presence of crude oil at all concentrations had negative effects on the log bioluminescence per log number of viable cells after 15- to 105-min exposure. About 10 to 100 times, lower half maximal effective concentration (EC₅₀) values were observed for polycyclic aromatic hydrocarbons (PAHs) than those for benzene, toluene, ethylbenzene, and xylene (BTEX). In the presence of each individual BTEX and PAH, the bioluminescence inhibition increased with increasing exposure time (1-32 h). This indigenous bacterium can be used as a simple and general indicator of oil contamination and its impact on coastal waters as well as for assessing potential toxicity during oil bioremediation.

Toxicity evaluation and biodegradation of phenanthrene by laccase from Trametes polyzona PBURU 12

The newly isolated Trametes polyzona PBURU 12 demonstrated a high tolerance and potential for the degradation of phenanthrene. The fungal isolate was able to tolerate 100 ppm of phenanthrene with 45% relative growth. The crude laccase produced by Trametes polyzona PBURU 12 was able to degrade phenanthrene by up to 98% within 24 h. The degradation metabolites showed the absence of toxic compounds. Microbial viability tests using E. coli and B. subtilis revealed that the treated phenanthrene was less toxic than untreated phenanthrene. Phytotoxicity and genotoxicity tests, using Vigna radiata and Allium cepa, indicated that the treated phenanthrene was less toxic to the plants. No mutagenic activity was found in the Ames test. The crude laccase from Trametes polyzona PBURU 12 was demonstrated as a potential tool for the biodegradation of PAHs (phenanthrene), with low toxic effects after the degradation.

Alternative Evaluation to Earthworm Toxicity Test in Polychlorinated Biphenyls Spiked and Remediated Soils

Polychlorinated biphenyls (PCBs) are a class of persistent organic pollutants that pose a threat to environment and human health. Aiming at predicting PCBs risk in actual soil ecosystem, this study was conducted by chemical and biological methods to assess the bioavailability of PCBs in spiked soil, and in field-contaminated soils before or after remediation. The three chemical methods were Soxhlet, n-butanol and hydroxypropyl-β-cyclodextrin (HPCD). Results were compared to actual PCB bioaccumulation in earthworms (Eisenia fetida). HPCD extraction was the best to predict the actual PCB bioaccumulation in all soils. The results suggest that HPCD could be an effective alternative method to earthworm toxicity test. This study provides strategy to understand the toxicity assessment in contaminated soil and soil after remediation.

A new approach to estimate bioavailability of pyrethroids in soil by compound-specific stable isotope analysis

In this study, the microbial degradation of six pyrethroids (bifenthrin, fenpropathrin, permethrin, α-cypermethrin, fenvalerate and deltamethrin) was investigated in soil to develop a new approach to estimate bioavailability of pyrethoids by compound-specific stable isotope analysis (CSIA). After 56-day incubation, the residual concentrations of pyrethroids in unsterilized soil were much lower than those in sterilized soil, indicating that microbial degradation was dominant for the elimination of pyrethroids. Meanwhile, the stable carbon isotope ratios of the six pyrethroids were determined during the degradation. Significant stable carbon isotope fractionation was observed during the microbial degradation of fenpropathrin, α-cypermethrin and deltamethrinhe. The enrichment factor ε was determined as -1.88‰, -1.82‰ and -2.00‰, respectively. A new approach was then developed to estimate the bioavailability of the three pyrethroids by determining stable carbon isotope ratios. The approach established in the study provides an alternative method to dynamically and quantitatively estimate bioavailability of compounds in soil based on CSIA.

Released fraction of polychlorinated biphenyls from soil-biosolid system using a leaching procedure and its comparison with bioavailable fraction determined by wheat plant uptake

The bioavailability of polychlorinated biphenyls (PCBs) in soils amended with biosolids was estimated using an aqueous leaching process of the compounds combined with rotating disk sorptive extraction (RDSE), and compared with bioavailability determined through of PCB absorption in wheat plants growing in the same soil-biosolid matrix. The matrices consisted of soil amended with biosolids at doses of 30, 90, and 200 Mg/ha, which increase concomitantly the organic matter content of the matrix. Considering that PCBs were natively absent in both the biosolids and soil used, the compounds were spiked in the biosolids and aged for 10 days. For each biosolid dose, the aqueous leaching profile was studied and equilibrium time was calculated to be 33 h. The leaching fractions determined by RDSE, considering total PCBs studied, were 12, 7, and 6% and the bioavailable fractions absorbed by the wheat root were found to be 0.5, 0.3, and 0.2% for 30, 90, and 200 Mg/ha doses, respectively. Both fractions leachable and bioavailable decrease with both increasing hydrophobicity of the compound (Kow) and increasing in the biosolid dose. It was found that both fractions (leaching and bioavailable) correlated according to the bivariate least squares regression, represented by a coefficient of correlation of 0.86. Therefore, the application of the chemical method involving a leaching procedure is an alternative to estimate the bioavailable fraction of PCBs in wheat plants in a simpler and in a shorter time.

Laboratory versus field soil aging: Impact on DDE bioavailability and sorption

Solid-phase microextraction (SPME), XAD, and the sequential supercritical fluid extraction (SFE) were used to assess the influence of aging of p,p'-DDE in a laboratory contaminated soil for up to 730 days. The end points determined were the freely dissolved concentration (C_free) using SPME, the potentially bioaccessible fraction (F_XAD, %) and the distribution of p,p'-DDE among fast, moderate, and slow desorbing soil sites determined by three sequentially stronger SFE conditions. C_free and F_XAD decreased during the first 35 days of aging by up to 40%. After this, no significant changes were observed up to the end of the aging experiment. The relative percentage of fast desorbing sites tended to exponentially decrease with aging, while the percentage of moderate and slow desorbing sites increased over time. These changes were most apparent within the first 90 days of aging, after which the relative distribution of p,p'-DDE among desorbing sites remained relatively constant. Significant correlations between SFE and XAD results demonstrated that the XAD method preferentially desorbed p,p'-DDE from fast and moderate desorbing sites and is capable of extracting the bioaccessible fraction. The distribution among desorbing sites, C_free and F_XAD values determined after different periods of laboratory aging were then compared to those measured for a field-contaminated soil where p,p'-DDE had resided for more than 40 years. C_free, F_XAD and SFE profiles measured for the field-aged p,p'-DDE were similar to those observed for p,p'-DDE aged in laboratory for between 35 and 90 days. These results suggest that aging in the laboratory must be carried out for periods of months if it is to approximate field aging.

Bacterial community shift and hydrocarbon transformation during bioremediation of short-term petroleum-contaminated soil

A laboratory study was conducted to evaluate the impact of bioaugmentation plus biostimulation (BR, added both nutrients and bacterial consortia), and natural attenuation (NA) on hydrocarbon degradation efficiency and microflora characterization during remediation of a freshly contaminated soil. After 112 days of remediation, the initial level of total petroleum hydrocarbon (TPH) (61,000 mg/kg soil) was reduced by 4.5% and 5.0% in the NA and BR treatments, respectively. Bioremediation did not significantly enhance TPH biodegradation compared to natural attenuation. The degradation of the aliphatic fraction was the most active with the degradation rate of 30.3 and 28.7 mg/kg/day by the NA and BR treatments, respectively. Soil microbial activities and counts in soil were generally greater for bioremediation than for natural attenuation. MiSeq sequencing indicated that the diversity and structure of microbial communities were affected greatly by bioremediation. In response to bioremediation treatment, Promicromonospora, Pseudomonas, Microcella, Mycobacterium, Alkanibacter, and Altererythrobacter became dominant genera in the soil. The result indicated that combining bioaugmentation with biostimulation did not improve TPH degradation, but soil microbial activities and structure of microbial communities are sensitive to bioremediation in short-term and heavily oil-contaminated soil.

Removal of phenanthrene in contaminated soil by combination of alfalfa, white-rot fungus, and earthworms

The aim of this study was to investigate the removal of phenanthrene by combination of alfalfa, white-rot fungus, and earthworms in soil. A 60-day experiment was conducted. Inoculation with earthworms and/or white-rot fungus increased alfalfa biomass and phenanthrene accumulation in alfalfa. However, inoculations of alfalfa and white-rot fungus can significantly decrease the accumulation of phenanthrene in earthworms. The removal rates for phenanthrene in soil were 33, 48, 66, 74, 85, and 93% under treatments control, only earthworms, only alfalfa, earthworms + alfalfa, alfalfa + white-rot fungus, and alfalfa + earthworms + white-rot fungus, respectively. The present study demonstrated that the combination of alfalfa, earthworms, and white-rot fungus is an effective way to remove phenanthrene in the soil. The removal is mainly via stimulating both microbial development and soil enzyme activity.

Phytoavailability and mechanism of bound PAH residues in filed contaminated soils

Understanding the phytoavailability of bound residues of polycyclic aromatic hydrocarbons (PAHs) in soils is essential to assessing their environmental fate and risks. This study investigated the release and plant uptake of bound PAH residues (reference to parent compounds) in field contaminated soils after the removal of extractable PAH fractions. Plant pot experiments were performed in a greenhouse using ryegrass (Lolium multiflorum Lam.) to examine the phytoavailablility of bound PAH residues, and microcosm incubation experiments with and without the addition of artificial root exudates (AREs) or oxalic acid were conducted to examine the effect of root exudates on the release of bound PAH residues. PAH accumulation in the ryegrass after a 50-day growth period indicated that bound PAH residues were significantly phytoavailable. The extractable fractions, including the desorbing and non-desorbing fractions, dominated the total PAH concentrations in vegetated soils after 50 days, indicating the transfer of bound PAH residues to the extractable fractions. This transfer was facilitated by root exudates. The addition of AREs and oxalic acid to test soils enhanced the release of bound PAH residues into their extractable fractions, resulting in enhanced phytoavailability of bound PAH residues in soils. This study provided important information regarding environmental fate and risks of bound PAH residues in 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.

The variability of standard artificial soils: cadmium and phenanthrene sorption measured by a batch equilibrium method

Artificial soil (AS) is used in soil ecotoxicology as a test medium or reference matrix. AS is prepared according to standard OECD/ISO protocols and components of local sources are usually used by laboratories. This may result in significant inter-laboratory variations in AS properties and, consequently, in the fate and bioavailability of tested chemicals. In order to reveal the extent and sources of variations, the batch equilibrium method was applied to measure the sorption of 2 model compounds (phenanthrene and cadmium) to 21 artificial soils from different laboratories. The distribution coefficients (K_d) of phenanthrene and cadmium varied over one order of magnitude: from 5.3 to 61.5L/kg for phenanthrene and from 17.9 to 190L/kg for cadmium. Variations in phenanthrene sorption could not be reliably explained by measured soil properties; not even by the total organic carbon (TOC) content which was expected. Cadmium logK_d values significantly correlated with cation exchange capacity (CEC), pH_H2O and pH_KCl, with Pearson correlation coefficients of 0.62, 0.80, and 0.79, respectively. CEC and pH_H2O together were able to explain 72% of cadmium logK_d variability in the following model: logK_d=0.29pH_H2O+0.0032 CEC -0.53. Similarly, 66% of cadmium logK_d variability could be explained by CEC and pH_KCl in the model: logKd=0.27pH_KCl+0.0028 CEC -0.23. Variable cadmium sorption in differing ASs could be partially treated with these models. However, considering the unpredictable variability of phenanthrene sorption, a more reliable solution for reducing the variability of ASs from different laboratories would be better harmonization of AS preparation and composition.

Comparing different methods for assessing contaminant bioavailability during sediment remediation

Sediment contamination by persistent organic pollutants from historical episodes is widespread and remediation is often needed to clean up severely contaminated sites. Measuring contaminant bioavailability in a before-and-after manner lends to improved assessment of remediation effectiveness. However, a number of bioavailability measurement methods have been developed, posing a challenge in method selection for practitioners. In this study, three different bioavailability measurement methods, i.e., solid phase microextraction (SPME), Tenax desorption, and isotope dilution method (IDM), were compared in evaluating changes in bioavailability of DDT and its degradates in sediment following simulated remediation treatments. When compared to the unamended sediments, all three methods predicted essentially the same degrees of changes in bioavailability after amendment with activated carbon, charcoal or sand. After normalizing over the unamended control, measurements by different methods were linearly correlated with each other, with slopes close to 1. The same observation was further made with a Superfund site marine sediment. This finding suggests that different methods may be used in evaluating remediation efficiency. However, Tenax desorption or IDM consistently offered better sensitivity than SPME in detecting bioavailability changes. Results from this study highlight the value of considering bioavailability when evaluating remediation effectiveness and provide guidance on the selection of bioavailability measurement methods in such assessments.

Surfactant enhanced pyrene degradation in the rhizosphere of tall fescue (Festuca arundinacea)

The present study was conducted to evaluate the effect of two non ionic surfactants (Tween 80 and Triton X-100), a biosurfactant (Lecithin), and randomly methylated-β-cyclodextrins (RAMEB) on the remediation of pyrene from soil planted with tall fescue (Festuca arundinacea). Soils with pyrene concentration of about 243 mg kg(-1) was grown with tall fescue and were individually amended with 0, 200, 600, 1000, and 1500 mg kg(-1) of Tween 80, Triton X-100, biosurfactant, and RAMEB. The results show that all surfactants significantly increased plant biomass compared to unamended soil. Dehydrogenase activity was also stimulated as a result of surfactant addition. Only 3.9 and 3.2 % of pyrene was decreased in the uncovered and covered abiotic sterile control, suggesting that microbial degradation was the main removal mechanism of pyrene from soil. In the planted treatment receiving no surfactant, the remediation of pyrene was 45 % which is significantly higher than that of corresponding unplanted control soil, suggesting that the cultivation of tall fescue alone could enhance the overall remediation of pyrene in soil. All surfactants had significantly higher rates of pyrene remediation compared to the unamended planted soil. Generally, RAMEB displayed the highest remediation rates, i.e., 64.4-79.1 % followed by the Triton X-100, i.e., 60.1-74.8 %. The positive impact of surfactants on pyrene remediation could possibly be because of their capacities to increase its bioavailability in soil. The evidence from this study suggests that the addition of surfactants could enhance phytoremediation of PAHs polluted soil.

Effect of ageing on benzo[a]pyrene extractability in contrasting soils

Changes in benzo[a]pyrene (B[a]P) extractability over 160 days ageing in four contrasting soils varying in organic matter content and clay mineralogy were investigated using dichloromethane: acetone 1:1 (DCM/Ace), 60 mM hydroxypropyl-β-cyclodextrin (HPCD) solution, 1-butanol (BuOH) and Milli-Q water. The B[a]P extractability by the four methods decreased with ageing and a first-order exponential model could be used to describe the kinetics of release. Correlation of the kinetic rate constant with major soil properties showed a significant effect of clay and sand contents and pore volume fraction (<6 nm) on sequestration of the desorbable fraction (by HPCD) and the water-extractable fraction. Analysis of (14)C-B[a]P in soils after ageing showed a limited loss of B[a]P via degradation. Fractionation of B[a]P pools associated with the soil matrix was analysed according to extractability of B[a]P by the different extraction methods. A summary of the different fractions is proposed for the illustration of the effect of ageing on different B[a]P-bound fractions in soils. This study provides a better understanding of the B[a]P ageing process associated with different fractions and also emphasises the extraction capacity of the different methods employed.

Earthworm responses to different reclamation processes in post opencast mining lands during succession

This study provides earthworm population data obtained from localities with a substantial anthropogenic impact spoils. The spoil heaps were reclaimed at the end of an opencast brown coal mining period. We studied spoils reclaimed by the two most commonly used reclamation processes: forestry and agricultural. The results show the significance of the locality age and the utilized reclamation process and treatment and their effect on earthworm communities. Our data indicate that apart from soil physical and chemical properties, the reclamation process itself may also induce viability and distribution of earthworm communities. Under standardized soil properties, the changes in earthworm populations during the succession were larger within the agricultural reclamation process as opposed to the forestry reclamation process for earthworm ecological groups and individual species.

Use of isotope dilution method to predict bioavailability of organic pollutants in historically contaminated sediments

Many cases of severe environmental contamination arise from historical episodes, where recalcitrant contaminants have resided in the environment for a prolonged time, leading to potentially decreased bioavailability. Use of bioavailable concentrations over bulk chemical levels improves risk assessment and may play a critical role in determining the need for remediation or assessing the effectiveness of risk mitigation operations. In this study, we applied the principle of isotope dilution to quantify bioaccessibility of legacy contaminants DDT and PCBs in marine sediments from a Superfund site. After addition of 13C or deuterated analogues to a sediment sample, the isotope dilution reached a steady state within 24 h of mixing. At the steady state, the accessible fraction (E) derived by the isotope dilution method (IDM) ranged from 0.28 to 0.89 and was substantially smaller than 1 for most compounds, indicating reduced availability of the extensively aged residues. A strong linear relationship (R2=0.86) was found between E and the sum of rapid (Fr) and slow (Fs) desorption fractions determined by sequential Tenax desorption. The IDM-derived accessible concentration (Ce) was further shown to correlate closely with tissue residue in the marine benthic polychaete Neanthes arenaceodentata exposed in the same sediments. As shown in this study, the IDM approach involves only a few simple steps and may be readily adopted in laboratories equipped with mass spectrometers. This novel method is expected to be especially useful for historically contaminated sediments or soils, for which contaminant bioavailability may have changed significantly due to aging and other sequestration processes.

Correlations between PAH bioavailability, degrading bacteria, and soil characteristics during PAH biodegradation in five diffusely contaminated dissimilar soils

The natural biodegradation of seven polycyclic aromatic hydrocarbons (PAHs) by native microorganisms was studied in five soils from Normandy (France) from diffusely polluted areas, which can also pose a problem in terms of surfaces and amounts of contaminated soils. Bioavailability tests using cyclodextrin-based extractions were performed. The natural degradation of low molecular weight (LMW) PAHs was not strongly correlated to their bioavailability due to their sorption to geosorbents. Conversely, the very low degradation of high molecular weight (HMW) PAHs was partly correlated to their poor availability, due to their sorption on complexes of organic matter and kaolinites or smectites. A principal component analysis allowed us to distinguish between the respective degradation behaviors of LMW and HMW PAHs. LMW PAHs were degraded in less than 2-3 months and were strongly influenced by the relative percentage of phenanthrene-degrading bacteria over total bacteria in soils. HMW PAHs were not significantly degraded, not only because they were less bioavailable but also because of a lack of degrading microorganisms. Benzo[a]pyrene stood apart since it was partly degraded in acidic soils, probably because of a catabolic cooperation between bacteria and fungi.

Tenax extraction for exploring rate-limiting factors in methyl-β-cyclodextrin enhanced anaerobic biodegradation of PAHs under denitrifying conditions in a red paddy soil

The effectiveness of anaerobic bioremediation systems for PAH-contaminated soil may be constrained by low contaminants bioaccessibility due to limited aqueous solubility and lack of suitable electron acceptors. Information on what is the rate-limiting factor in bioremediation process is of vital importance in the decision in what measures can be taken to assist the biodegradation efficacy. In the present study, four different microcosms were set to study the effect of methyl-β-cyclodextrin (MCD) and nitrate addition (N) on PAHs biodegradation under anaerobic conditions in a red paddy soil. Meanwhile, sequential Tenax extraction combined with a first-three-compartment model was employed to evaluate the rate-limiting factors in MCD enhanced anaerobic biodegradation of PAHs. Microcosms with both 1% (w/w) MCD and 20mM N addition produced maximum biodegradation of total PAHs of up to 61.7%. It appears rate-limiting factors vary with microcosms: low activity of degrading microorganisms is the vital rate-limiting factor for control and MCD addition treatments (CK and M treatments); and lack of bioaccessible PAHs is the main rate-limiting factor for nitrate addition treatments (N and MN treatments). These results have practical implications for site risk assessment and cleanup strategies.

PAH phytoremediation: rhizodegradation or rhizoattenuation?

Dealing with soil contaminated with persistent organic pollutants (POP) is an increasing concern amplified by both regulatory constraints and the dramatic impact of human activities on the soil resource. The most used management options are treatments which totally eradicate the toxic compounds targeted. When possible, environmental-friendly processes should be used, and recent years have seen the emergence of green technologies using biological energies involving microorganisms (bioremediation) and plants (phytoremediation). Research has focused on phytoremediation and many have presented this technology as the process ideally combining efficiency, low cost and environmental acceptance. However, the applicability of phytoremediation on soils contaminated by bio-recalcitrant organic compounds, such as polycyclic aromatic hydrocarbons (PAH), has not yet proved as successful as expected. We propose here a review and discussion of the overall question of PAH status in soil and their potential for treatment. The limits and applicability of bioremediation technologies are discussed, and the specific beneficial effect of plants is objectively evaluated with a special interest to processes which lead to rhizoattenuation. Given the PAH high affinity to soil organic matter, availability is the main limitation to phytoremediation. In this context, bioavailability quantification remains an issue as well as the characterization of the recalcitrant fraction.

Pseudo-basal levels of and distribution of anti-oxidant enzyme biomarkers in Eisenia fetida and effect of exposure to phenanthrene

In the paper, the pseudo-basal levels of anti-oxidant system in different earthworm life stages (juvenile and adult) and the pseudo-basal distribution in different regions of adult earthworms (pre-clitellum, clitellum and post-clitellum) were studied using filter contact tests. The effects of phenanthrene (PHE) at different exposure levels on anti-oxidant enzymes along the earthworm body were also investigated after 24 and 48h of exposure. The pseudo-basal levels of the anti-oxidant enzymes varied during the different growth phase, and results indicated that earthworm has a low oxidative risk and SOD plays important roles during the development whereas CAT and POD are more important in maintain the low ROS level in adult earthworm. The pseudo-basal distribution of the anti-oxidant enzymes along the earthworms was heterogeneous and MDA mainly located in clitellum. POD in pre-clitellum, SOD in clitellum and CAT in post-clitellum were important to eliminate excess total ROS. Time of exposure impacted the anti-oxidant enzyme activities and their distribution patterns along earthworms, from the viewpoint of which supported that exposure time was an environment stress factors. In a short exposure time (24 h), CAT and SOD in the three regions, POD in pre-clitellum and clitellum might be good indicator to a low PHE stress level (0.0629 μg cm(-2) treatments). In a long exposure time (48 h), only SOD in clitellum is a good indicator to both low and high PHE stress (0.629 μg cm(-2) treatments). Earthworm biomembrane system inflicted no oxidative damage until the stress magnitude reached or exceeds the level of exposure in low PHE concentration condition for 48 h.

A battery of bioassays for the evaluation of phenanthrene biotoxicity in soil

A battery of bioassays was used to assess the ecotoxicological risk of soil spiked with a range of phenanthrene levels (0.95, 6.29, 38.5, 58.7, 122, and 303 μg g(-1) dry soil) and aged for 69 days. Multiple species (viz. Brassica rapa, Eisenia feotida, Vibrio fischeri), representing different trophic levels, were used as bioindicator organisms. Among acute toxicity assays tested, the V. fischeri luminescence inhibition assay was the most sensitive indicator of phenanthrene biotoxicity. More than 15 % light inhibition was found at the lowest phenanthrene level (0.95 μg g(-1)). Furthermore, comet assay using E. fetida was applied to assess genotoxicity of phenanthrene. The strong correlation (r (2) ≥ 0.94) between phenanthrene concentration and DNA damage indicated that comet assay is appropriate for testing the genotoxic effects of phenanthrene-contaminated soil. In the light of these results, we conclude that the Microtox test and comet assay are robust and sensitive bioassays to be employed for the risk evaluation of polycyclic aromatic hydrocarbon-contaminated soil.

Experimental increase in availability of a PAH complex organic contamination from an aged contaminated soil: consequences on biodegradation

Although high PAH content and detection of PAH-degraders, the PAH biodegradation is limited in aged-contaminated soils due to low PAH availability (i.e., 1%). Here, we tried to experimentally increase the soil PAH availability by keeping both soil properties and contamination composition. Organic extract was first removed and then re-incorporated in the raw soil as fresh contaminants. Though drastic, this procedure only allowed a 6-time increase in the PAH availability suggesting that the organic constituents more than ageing were responsible for low availability. In the re-contaminated soil, the mineralization rate was twice more important, the proportion of 5-6 cycles PAH was higher indicating a preferential degradation of lower molecular weight PAH. The extraction treatment induced bacterial and fungal community structures modifications, Pseudomonas and Fusarium solani species were favoured, and the relative quantity of fungi increased. In re-contaminated soil the percentage of PAH-dioxygenase gene increased, with 10 times more Gram negative representatives.

Biotoxicity assessment of pyrene in soil using a battery of biological assays

A test battery, composed of a range of biological assays, was applied to evaluate the ecological health of soil aged for 69 days and spiked with a range of pyrene levels (1.04, 8.99, 41.5, 72.6, 136, and 399 μg g(-1) dry soil; Soxhlet-extracted concentrations after 69 days of aging). Chinese cabbage (Brassica rapa), earthworm (Eisenia fetida), and bacteria (Vibrio fischeri) were used as test organisms to represent different trophic levels. Among the acute ecotoxicity bioassays used, the V. fischeri luminescence inhibition assay was the most sensitive indicator of pyrene toxicity. We observed >8 % light inhibition at the lowest concentration (1.04 μg g(-1)) pyrene, and this inhibition increased to 60 % at 72.6 μg g(-1). The sensitivity ranking for toxicity of the pyrene-contaminated soil in the present study was in the following decreasing order: root elongation of Chinese cabbage < earthworm mortality (14 days) < earthworm mortality (28 days) < luminescence inhibition (15 min) < luminescence inhibition (5 min). In addition, genotoxic effects of pyrene were also evaluated by using comet assay in E. fetida. The strong relationship between DNA damage and soil pyrene levels showed that comet assay is suitable for testing the genotoxicity of pyrene-polluted soil. In addition, tail moment was well correlated with soil pyrene levels (r (2) = 0.99). Thus, tail moment may be the most informative DNA-damage parameter representing the results of comet assay. Based on these results, the earthworm DNA damage assay and Microtox test are rapid and sensitive bioassays and can be used to assess the risk of soil with low to high levels of hydrocarbon pollution. Furthermore, an analysis of the toxic effects at several trophic levels is essential for a more comprehensive understanding of the damage caused by highly contaminated soil.