Towards a more appropriate water based extraction for the assessment of organic contaminant availability

This study correlated extractabilities of 37 d aged phenanthrene residues in four dissimilar soils with the fraction that was available for earthworm (Lumbricus rubellus) accumulation and microorganism (Pseudomonas sp.) mineralisation. Extractability was determined using two established techniques, namely, (1) a water based extraction using CO(2) equilibrated water and (2) an aqueous based hydroxypropyl-beta-cyclodextrin (HPCD) extraction. Results showed no relationship between earthworm accumulation and phenanthrene extractability using either HPCD (r(2)=0.07; slope=-4.76; n=5) or the water based extraction (r(2)=0.31; slope=-5.34; n=5). Earthworm accumulation was overestimated by both techniques. In contrast, the fraction of phenanthrene extractable using both the HPCD technique and the water based extraction correlated strongly with microbial mineralisation. However, the slopes of these linear relationships were 0.48 (r(2)=0.96; n=10), and 0.99 (r(2)=0.88; n=10) for the water based extraction and HPCD, respectively. Thus, the HPCD extraction provided values that were numerically close to the mineralisation values, whilst the water based extraction values were approximately half the mineralisation values. It is submitted that HPCD extraction provided an appropriate method of assessing the fraction of contaminant available for microbial mineralisation in these dissimilar soils.     

Further validation of the HPCD-technique for the evaluation of PAH microbial availability in soil

There is currently considerable scientific interest in finding a chemical technique capable of predicting bioavailability; non-exhaustive extraction techniques (NEETs) offer such potential. Hydroxypropyl-beta-cyclodextrin (HPCD), a NEET, is further validated through the investigation of concentration ranges, differing soil types, and the presence of co-contaminants. This is the first study to demonstrate the utility of the HPCD-extraction technique to predict the microbial availability to phenanthrene across a wide concentration range and independent of soil-contaminant contact time (123 d). The efficacy of the HPCD-extraction technique for the estimation of PAH microbial availability in soil is demonstrated in the presence of co-contaminants that have been aged for the duration of the experiment together in the soil. Desorption dynamics are compared in co-contaminant and single-PAH contaminated spiked soils to demonstrate the occurrence of competitive displacement. Overall, a single HPCD-extraction technique proved accurate and reproducible for the estimation of PAH bioavailability from soil.     

Rapid quantification of polycyclic aromatic hydrocarbons in hydroxypropyl-beta-cyclodextrin (HPCD) soil extracts by synchronous fluorescence spectroscopy (SFS)

Synchronous fluorescence spectroscopy (SFS) was directly applied to rapidly quantify selected polycyclic aromatic hydrocarbons (PAHs: benzo[a]pyrene and pyrene) in aqueous hydroxypropyl-beta-cyclodextrin (HPCD) soil extract solutions from a variety of aged contaminated soils containing four different PAHs. The method was optimized and validated. The results show that SFS can be used to analyse benzo[a]pyrene and pyrene in HPCD based soil extracts with high sensitivity and selectivity. The linear calibration ranges were 4.0x10(-6)-1.0x10(-3)mM for benzo[a]pyrene and 6.0x10(-6)-1.2x10(-3)mM for pyrene in 10mM HPCD aqueous solution alone. The detection limits according to the error propagation theory for benzo[a]pyrene and pyrene were 3.9x10(-6) and 5.4x10(-6)mM, respectively. A good agreement between SFS and HPLC was reached for both determinations of PAHs in HPCD alone and in soil HPCD extracts. Hence, SFS is a potential means to simplify the present non-exhaustive hydroxypropyl-beta-cyclodextrin (HPCD)-based extraction technique for the evaluation of PAH bioavailability in soil.     

Hydroxypropyl-β-cyclodextrin as non-exhaustive extractant for organochlorine pesticides and polychlorinated biphenyls in muck soil

Hydroxypropyl-β-cyclodextrin (HPCD) was used as a non-exhaustive extractant for organochlorine pesticides (OCs) and polychlorinated biphenyls (PCBs) in muck soil. An optimized extraction method was developed which involved using a HPCD to soil mass ratio of 5.8 with a single extraction period of 20 h. An aging experiment was performed by spiking a muck soil with ¹³C-labeled OCs and non-labeled PCBs. The soil was extracted with the optimized HPCD method and Soxhlet apparatus with dichloromethane over 550 d periodically. The HPCD extractability of the spiked OCs was greater than of the native OCs. A decreased in HPCD extractability was observed for the spiked OCs after 550 d of aging and their extractability approached those of the natives. The partition coefficient between HPCD and soil (log K_CD-Soil) was negatively correlated with the octanol-water partition coefficient (log K_OW) with r² = 0.67 and p < 0.05.     

H NMR metabolomics of earthworm exposure to sub-lethal concentrations of phenanthrene in soil

¹H NMR metabolomics was used to monitor earthworm responses to sub-lethal (50-1500 mg/kg) phenanthrene exposure in soil. Total phenanthrene was analyzed via soxhlet extraction, bioavailable phenanthrene was estimated by hydroxypropyl-β-cyclodextrin (HPCD) and 1-butanol extractions and sorption to soil was assessed by batch equilibration. Bioavailable phenanthrene (HPCD-extracted) comprised ∼65-97% of total phenanthrene added to the soil. Principal component analysis (PCA) showed differences in responses between exposed earthworms and controls after 48 h exposure. The metabolites that varied with exposure included amino acids (isoleucine, alanine and glutamine) and maltose. PLS models indicated that earthworm response is positively correlated to both total phenanthrene concentration and bioavailable (HPCD-extracted) phenanthrene in a freshly spiked, unaged soil. These results show that metabolomics is a powerful, direct technique that may be used to monitor contaminant bioavailability and toxicity of sub-lethal concentrations of contaminants in the environment. These initial findings warrant further metabolomic studies with aged contaminated soils.     

Hydroxypropyl-β-cyclodextrin extractability and bioavailability of phenanthrene in humin and humic acid fractions from different soils and sediments

Organic matter (OM) plays a vital role in controlling polycyclic aromatic hydrocarbon (PAH) bioavailability in soils and sediments. In this study, both a hydroxypropyl-β-cyclodextrin (HPCD) extraction test and a biodegradation test were performed to evaluate the bioavailability of phenanthrene in seven different bulk soil/sediment samples and two OM components (humin fractions and humic acid (HA) fractions) separated from these soils/sediments. Results showed that both the extent of HPCD-extractable phenanthrene and the extent of biodegradable phenanthrene in humin fraction were lower than those in the respective HA fraction and source soil/sediment, demonstrating the limited bioavailability of phenanthrene in the humin fraction. For the source soils/sediments and the humin fractions, significant inverse relationships were observed between the sorption capacities for phenanthrene and the amounts of HPCD-extractable or biodegradable phenanthrene (p?<?0.05), suggesting the importance of the sorption capacity in affecting desorption and biodegradation of phenanthrene. Strong linear relationships were observed between the amount of HPCD-extractable phenanthrene and the amount degraded in both the bulk soils/sediments and the humin fractions, with both slopes close to 1. On the other hand, in the case of phenanthrene contained in HA, a poor relationship was observed between the amount of phenanthrene extracted by HPCD and the amount degraded, with the former being much less than the latter. The results revealed the importance of humin fraction in affecting the bioavailability of phenanthrene in the bulk soils/sediments, which would deepen our understanding of the organic matter fractions in affecting desorption and biodegradation of organic pollutants and provide theoretical support for remediation and risk assessment of contaminated soils and sediments.     

Effect of metals on the adsorption and extractability of 14C-phenanthrene in soils

The fate of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils may be affected by several environmental factors including the presence of co-contaminants. This study was conducted in order to assess the effect of metals on (i) the adsorption of 14C-phenanthrene in soils and (ii) its extractability and ability to form non-extractable residues. The first objective was accomplished using batch adsorption experiments with an uncontaminated agricultural soil spiked with the metals Cd, Cu, Pb, and Zn. Adsorption of phenanthrene was significantly higher after the addition of the metals (Kf = 21.48 vs. 8.55) and the desorption less readily reversible when compared to the unspiked soil. The extractability of phenanthrene was assessed with incubation (4 months, laboratory conditions) and microlysimeter experiments (6 months, natural climatic conditions) on three soils spiked with metals. All the soils were labelled with 14C-phenanthrene. The amount of extractable phenanthrene residues was significantly higher when the metals had been added to the soils. Nevertheless, the quantity of non-extractable residues was non-significantly different between the spiked and unspiked soils. The mechanism leading to increased adsorption and extractability of phenanthrene in the presence of metals is still unknown. In perspective, it would be interesting to assess the bioavailability of PAHs in the presence of metals in further experiments.     

Enhanced desorption of phenanthrene from soils using hydroxypropyl-beta-cyclodextrin: experimental results and model predictions

Objective of this study was to evaluate the effects of hydroxypropyl-beta-cyclodextrin (HPCD) on the removal of phenanthrene from solid phase. Batch tests for the phenanthrene distribution between aqueous and solid phase were conducted in the presence of HPCD. Column tests and numerical simulations were conducted to evaluate the roles of HPCD cavities and interaction rates between water, HPCD, and solid phase in the enhanced removal of phenanthrene. Experimental results showed that HPCD was effective in removing sorbed phenanthrene from subsurface environment, primarily due to its negligible sorption to the solid phase and the partitioning of phenanthrene into HPCD cavities. From the numerical simulations, it was found that rate-limited partitioning of phenanthrene into HPCD cavities was most influential factor in the enhanced elution of phenanthrene. Sorption and desorption rate of phenanthrene between aqueous and solid phase was very fast or near equilibrium state. Interaction rates of contaminant between water, HPCD, and solid phase could be affected by other factors such as soil types and organic matter contents. Results from this study implied that HPCD flushing could be effectively applied for the removal of hydrophobic organic pollutants existing in the soils as sorbed or NAPL state.     

Enhanced Desorption of Phenanthrene from Soils Using Hydroxypropyl‐β‐cyclodextrin: Experimental Results and Model Predictions

Objective of this study was to evaluate the effects of hydroxypropyl‐β‐cyclodextrin (HPCD) on the removal of phenanthrene from solid phase. Batch tests for the phenanthrene distribution between aqueous and solid phase were conducted in the presence of HPCD. Column tests and numerical simulations were conducted to evaluate the roles of HPCD cavities and interaction rates between water, HPCD, and solid phase in the enhanced removal of phenanthrene. Experimental results showed that HPCD was effective in removing sorbed phenanthrene from subsurface environment, primarily due to its negligible sorption to the solid phase and the partitioning of phenanthrene into HPCD cavities. From the numerical simulations, it was found that rate‐limited partitioning of phenanthrene into HPCD cavities was most influential factor in the enhanced elution of phenanthrene. Sorption and desorption rate of phenanthrene between aqueous and solid phase was very fast or near equilibrium state. Interaction rates of contaminant between water, HPCD, and solid phase could be affected by other factors such as soil types and organic matter contents. Results from this study implied that HPCD flushing could be effectively applied for the removal of hydrophobic organic pollutants existing in the soils as sorbed or NAPL state.     

The estimation of PAH bioavailability in contaminated sediments using hydroxypropyl-beta-cyclodextrin and Triton X-100 extraction techniques

A study was conducted to investigate whether cyclodextrins and surfactants can be used to predict polycyclic aromatic hydrocarbon (PAH) bioavailability in contaminated sediments. Two sediment samples were extracted with aqueous solutions of hydroxypropyl-beta-cyclodextrin (HPCD) and Triton X-100. PAH removal during extraction was compared with PAH removal during biodegradation and solid-phase extraction. The latter two methods were used as reference methods to establish which part of the PAHs could be biodegraded and to what extent biodegradation was governed by bioavailability limitations. It was demonstrated that HPCD extraction followed solid-phase extraction and removed primarily readily bioavailable PAHs, while Triton X-100 extracted both readily and poorly bioavailable PAHs. Moreover, HPCD did not affect the degradation of PAHs in biodegradation experiments, while Triton X-100 enhanced the degradation of low molecular weight PAHs. It was concluded that HPCD extraction may provide a good method for the prediction of PAH bioavailability. Triton X-100 extraction is unfit for the prediction of PAH bioavailability.     

Metal fractionation in soils and assessment of environmental contamination in Vallecamonica, Italy

Metal contamination was investigated in soils of the Vallecamonica, an area in the northern part of the Brescia province (Italy), where ferroalloy industries were active for a century until 2001. The extent in which emissions from ferroalloy plants affected metal concentration in soils is not known in this area. In this study, the geogenic and/or anthropogenic origin of metals in soils were estimated. A modified Community Bureau of Reference sequential chemical extraction method followed by inductively coupled plasma optical emission spectroscopy (ICP-OES) analyses were employed to evaluate the potential bioavailability of Al, Cd, Mn, Fe, Cr, Zn, and Pb in soils. Principal component analysis (PCA) was used to assess the relationships among metal sources in soil samples from different locations. This approach allowed distinguishing of different loadings and mobility of metals in soils collected in different areas. Results showed high concentrations and readily extractability of Mn in the Vallecamonica soils, which may suggest potential bioavailability for organisms and may create an environmental risk and potential health risk of human exposure.     

Butanol extraction to predict bioavailability of PAHs in soil

The feasibility of a mild-solvent extraction procedure to predict the bioavailability of individual polycyclic aromatic hydrocarbons (PAHs) in soil was assessed. The quantities that were degraded during the course of biodegradation of phenanthrene and pyrene in soil with or without plants correlated with the amounts extracted by n-butanol, with R2 values of 0.971 and 0.994, respectively. Six consecutive groups of earthworms removed ca. 70% of the pyrene remaining after extensive biodegradation, a value similar to the quantity extracted by n-butanol. The amount of chrysene aged in sterilized soil that was extracted by n-butanol was not statistically different from the quantities assimilated by earth-worms (Eisenia fetida) introduced into the soil. Such a mild extraction procedure may be useful as a means of predicting PAH bioavailability.     

Application of a luminescence-based biosensor for assessing naphthalene biodegradation in soils from a manufactured gas plant

Despite numerous reviews suggesting that microbial biosensors could be used in many environmental applications, in reality they have failed to be used for which they were designed. In part this is because most of these sensors perform in an aqueous phase and a buffered medium, which is in contrast to the nature of genuine environmental systems. In this study, a range of non-exhaustive extraction techniques (NEETs) were assessed for (i) compatibility with a naphthalene responsive biosensor and (ii) correlation with naphthalene biodegradation. The NEETs removed a portion of the total soil naphthalene in the order of methanol > HPCD > βCD > water. To place the biosensor performance to NEETs in context, a biodegradation experiment was carried out using historically contaminated soils. By coupling the HPCD extraction with the biosensor, it was possible to assess the fraction of the naphthalene capable of undergoing microbial degradation in soil.     

均匀电场下多环芳烃在土壤中的迁移

当循环电解液流速为800 mL/h,电解液为无菌水时,电渗流流量、菲和芘在土壤中迁移量在电压梯度为1 V/cm作用下比电压梯度为0.5 V/cm时要多;电动注入表面活性剂Tween80和HPCD均可以提高菲和芘在土壤中的迁移,注入Tween80和HPCD浓度分别为500和1 000 mg/L时,相应地Phe提高5.8倍和11.7倍、芘提高2倍和3.4倍;而BaP在水中的溶解度太小,电场作用和电动注入表面活性剂对BaP在土壤中的迁移量影响很小。为建立电动修复有机污染物污染提供了技术基础。     

Influence of hydroxypropyl-beta-cyclodextrin (HPCD) on the bioavailability and biodegradation of pyrene

It is well known that the limited aqueous solubilities of polycyclic aromatic hydrocarbons (PAH) often reduce their bioavailability to bacterial populations. The objective of this study was to test the impact of a solubility-enhancement reagent, hydroxypropyl-beta-cyclodextrin (HPCD), on the bioavailability and biodegradation of pyrene. No measurable loss of pyrene occurred for the control vials throughout the first 22 weeks of the experiment, indicating the absence of mass loss via abiotic transformation and volatilization. The vials containing pyrene and the degrader isolate (Burkholderia CRE 7), but no HPCD, also exhibited no measurable loss of pyrene throughout the experiment. Conversely, biodegradation of pyrene appears to have been initiated after approximately 15 weeks for the vials containing 10(4) mg l(-1) HPCD. By the end of the experiment, approximately 14% (w/w) of the pyrene was biodegraded in the presence of HPCD. These results indicate that HPCD may be useful for enhancing the bioavailability and biodegradation of pyrene and other PAHs.     

Simultaneous removal of organic compounds and heavy metals from soils by electrokinetic remediation with a modified cyclodextrin

Thousands of sites are contaminated with both heavy metals and organic compounds and these sites pose a major threat to public health and the environment. Previous studies have shown that electrokinetic remediation has potential to remove heavy metals and organic compounds when they exist individually in low permeability soils. This paper presents the feasibility of using cyclodextrins in electrokinetic remediation for the simultaneous removal of heavy metals and polycyclic aromatic hydrocarbons (PAHs) from low permeability soils. Kaolin was selected as a model low permeability soil and it was spiked with phenanthrene as well as nickel at concentrations of 500 mg kg-1 each to simulate typical mixed field contamination. Bench-scale electrokinetic experiments were conducted using hydroxypropyl beta-cyclodextrin (HPCD) at low (1%) and high (10%) concentrations and using deionized water in control test. A periodic voltage gradient of 2VDC cm-1 (with 5 d on and 2 d off) was applied to all the tests, and 0.01 M NaOH was added during the experiments to maintain neutral pH conditions at anode. In all tests, nickel migrated as Ni2+ ions towards the cathode and most of it was precipitated as Ni(OH)2 within the soil close to the cathode due to high pH condition generated by electrolysis reaction. The solubility of phenanthrene in the flushing solution and the amount of electroosmotic flow controlled the migration and removal of phenanthrene in all the tests. Even though high flow was generated in tests using deionized water and 1% HPCD, migration and removal of phenanthrene was low due to low solubility of phenanthrene in these solutions. The test with 10% HPCD solution showed higher solubility of phenanthrene which caused it migrate towards the cathode, but further migration and removal was retarded due to reduced electric current and electroosmotic flow. Approximately one pore volume of flushing resulted in approximately 50% removal of phenanthrene from the soil near the anode. Sustained higher electroosmotic flow with higher concentration cyclodextrin and maintaining low soil pH near cathode should be investigated to increase removal efficiency of both phenanthrene and nickel.     

Bioavailability of persistent organic pollutants in soils and sediments--a perspective on mechanisms, consequences and assessment

It has been observed that as soil-pollutant contact time increases, pollutant bioavailability and extractability decreases. This phenomenon has been termed 'ageing'. Decreased chemical extractability with increased soil-chemical contact time is evident where both 'harsh' techniques, e.g. dichloromethane Soxhlet extraction, and 'non-exhaustive' techniques, e.g. butanol shake extraction, have been used. It has also been observed that the amount of chemical extracted by these techniques varies considerably over time. Similarly, decreases in bioavailability with increased soil-pollutant contact time have been described in bacterial, earthworm and other organism studies. From these investigations, it has been shown that the fraction of pollutant determined to be bioavailable can vary between organisms. Thus, there is an immediate definition problem, what is bioavailability? Additionally, if bioavailability is to be assessed by a chemical means, which organisms should (or can) be mimicked by the extraction procedure? This review provides a background to the processes inherent to ageing, a discussion of its consequences on bioavailability and ends with some reflections on the appropriateness of chemical extraction techniques to mimic bioavailability     

Influence of ozonation on extractability of Pb and Zn from contaminated soils

The effect of soil ozonation on Pb and Zn extraction with EDTA, bioavailability (Ruby's Physiologically Based Extraction Test, PBET) and mobility (Toxicity Characteristic Leaching Procedure, TCLP) of Pb was studied on contaminated soils taken from 7 different locations in the Mezica Valley, Slovenia. EDTA extraction (40 mmol kg(-1)) removed from 27.4+/-1.5% to 64.8+/-1.5% of Pb, and from 1.9+/-0.2% to 22.4+/-2.0% of Zn from tested soils, and significantly reduced soil Pb bioavailability (PBET) and mobility (TCLP). Pretreatment of tested soils with ozone before EDTA extraction enhanced EDTA extractability of Pb for 11.0 to 28.9%, but had no effect on the extractability of Zn. In most of the soils, ozonation had no statistically significant effect on bioavailability and mobility of Pb, residual after EDTA extraction. Using linear regression analysis we found a significant increase (p<0.01) in EDTA extractability of Pb after soil ozonation in soils with a higher initial Pb content. EDTA extractability of Pb after soil ozonation was also significantly higher for soils with a lower Pb extractability when treated with EDTA alone. We found no correlation between soil organic matter content and the percentage of the Pb fraction bound to soil organic matter (where from 25.6+/-1.3% to 73.2+/-0.6% of Pb reside in tested soils) and Pb extractability with EDTA after soil ozonation.     

Correlations of Eisenia fetida metabolic responses to extractable phenanthrene concentrations through time

Eisenia fetida earthworms were exposed to phenanthrene for thirty days to compare hydroxypropyl-β-cyclodextrin (HPCD) extraction of soil and ¹H NMR earthworm metabolomics as indicators of bioavailability. The phenanthrene 28-d LC₅₀ value was 750 mg/kg (632-891, 95% confidence intervals) for the peat soil tested. The initial phenanthrene concentration was 319 mg/kg, which biodegraded to 16 mg/kg within 15 days, at which time HPCD extraction suggested that phenanthrene was no longer bioavailable. Multivariate statistical analysis of ¹H NMR spectra for E. fetida tissue extracts indicated that phenanthrene exposed and control earthworms differed throughout the 30 day experiment despite the low phenanthrene concentrations present after 15 days. This metabolic response was better correlated to total phenanthrene concentrations (Q² = 0.59) than HPCD-extractable phenanthrene concentrations (Q² = 0.46) suggesting that ¹H NMR metabolomics offers considerable promise as a novel, molecular-level method to directly monitor the bioavailability of contaminants to earthworms in the environment.     

The influence of a NAPL on the loss and biodegradation of 14C-phenanthrene residues in two dissimilar soils

This study was carried out to assess the influence of diesel, applied over a log concentration range, on the loss and extractability of phenanthrene (measured as putative 14C-phenanthrene residues) in two different soils. The influence of diesel on the ability of a cyclodextrin based extraction method to predict the microbial bioavailability of 14C-residues was also assessed. An increase in loss of 14C-residues with increasing diesel concentration from 0 to 2000 mg kg-1 was generally observed with time in both soils. It is suggested that this trend is attributable to competitive sorption for soil sorption sites and to a lesser extent to displacement of 14C-residues from soil sorption sites by diesel resulting in greater compound availability and therefore greater loss by degradation via the actions of indigenous microorganisms. However, in the 20000 mg kg-1 diesel treatments of both soils, results indicated a delayed loss. It is suggested that this retarded loss was due to the formation of a discrete NAPL-phase into which 14C-phenanthrene residues partitioned, thereby decreasing their availability and as a consequence their degradation. Furthermore, it is suggested that nutrient limitation may have slowed down degradation rates as diesel concentrations increased. Comparison between cyclodextrin-extractability and microbial mineralisation supported the use of cyclodextrin to assess microbial bioavailability of 14C-residues after 50 d or more ageing up to diesel concentrations of 2000 mg kg-1. However, results suggested that at high diesel concentrations (specifically 20000 mg kg-1) co-extraction of 14C-phenanthrene residues may have occurred as a result of the combined solvation powers of both the cyclodextrin and the diesel. Furthermore, mineralisation of 14C-phenanthrene residues may have been affected by extreme nutrient limitation in this treatment.