Study of factors affecting on the extraction efficiency of polycyclic aromatic hydrocarbons from soils using open-vessel focused microwave-assisted extraction

As part of an evaluation of focused microwave-assisted extraction (FMAE) using an open-vessel system, the effects of matrix, moisture content, ageing, and solvent have been studied on the extraction efficiency of polycyclic aromatic hydrocarbons (PAHs) from spiked soils. PAHs were spiked onto three different uncontaminated air dried and originally wet soil matrices with 1- and 20-day ageing periods. Solvents used were hexane–acetone (1:1), cyclohexane–acetone (1:1) and dichloromethane. FMAE only required a small amount of solvent (20 ml) and short extraction time (10 min) in the open cell under 90 W of microwave power. The results revealed that the extraction efficiency strongly depends on the nature of soil matrix; moisture content may enhance the recoveries of PAHs for many cases; and, the influence of the type of solvent is not significant. A comparison between microwave extraction and 16-h Soxhlet extraction has been made on spiked soils. It evidenced that the microwave method under ambient pressure is a suitable alternative to Soxhlet method for the analysis of PAHs in soils. For the evaluation of the developed FMAE method, three reference materials were used. The PAHs recovered from three reference materials were in a good agreement with reference values.     

Optimization of selective pressurized liquid extraction for extraction and in-cell clean-up of PCDD/Fs in soils and sediments

This paper describes the development of methods for selective extraction of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from soils and sediments, using pressurized liquid extraction with in-cell clean-up (SPLE). Two binary solvent mixtures, viz. dichloromethane/n-heptane (DCM/Hp), and diethylether/n-heptane (DEE/Hp), were evaluated. The SPLE extraction conditions were optimized using central composite face (CCF) design. Three factors were investigated: extraction temperature (60–160 °C), number of extraction cycles (1–3) and time per cycle (2–18 min). The results showed that DCM/Hp (1/1, v/v) and DEE/Hp (1/2, v/v) were the best extraction solvent compositions and that the extraction temperature was a critical factor that needed careful optimization to achieve high extraction efficiency without co-extraction of sulfuric acid. Under the optimal conditions, the SPLE methods provided results with good accuracy and precision. For the sandy soil certified reference material (CRM-529) the quantification results ended up in the range 82–110% as compared to the concentrations obtained by a reference method based on Soxhlet extraction and external column clean-up. Furthermore, for a clay soil (CRM-530) and a sediment reference material (WMS-01), the accuracy (trueness) of the TEQ values were +11% (DCM/Hp) and +8% (DEE/Hp) for CRM-530, +8% and ?7% for WMS-01, respectively. The individual congener concentrations also agreed well with the certified values. These findings show that SPLE is a promising method for combined extraction and clean-up of PCDD/Fs in soil/sediment samples.     

Characterization of polycyclic aromatic hydrocarbons (PAHs) on lime spray dryer (LSD) ash using different extraction methods

In this study, traditional Soxhlet, automatic Soxhlet and ultrasonic extraction techniques were employed to determine the speciation and concentration of polycyclic aromatic hydrocarbons (PAHs) on lime spray dryer (LSD) ash samples collected from the baghouse of a spreader stoker boiler. To test the efficiencies of different extraction methods, LSD ash samples were doped with a mixture of 16 US EPA specified PAHs to measure the matrix spike recoveries. The results showed that the spike recoveries of PAHs were different using these three extraction methods with dichloromethane (DCM) as the solvent. Traditional Soxhlet extraction achieved slightly higher recoveries than automatic Soxhlet and ultrasonic extraction. Different solvents including toluene, DCM:acetone (1:1 V/V) and hexane:acetone (1:1 V/V) were further examined to optimize the recovery using ultrasonic extraction. Toluene achieved the highest spike recoveries of PAHs at a spike level of 10 microg kg(-1). When the spike level was increased to 50 microg kg(-1), the spike recoveries of PAHs also correspondingly increased. Although the type and concentration of PAHs detected on LSD ash samples by different extraction methods varied, the concentration of each detected PAH was consistently low, at microg kg(-1) levels.     

不同萃取方法对长江口边滩多环芳烃萃取效果的影响

选取索氏提取法和加速溶剂萃取仪(ASE)提取法,对长江口边滩样品进行多环芳烃萃取实验,并利用气相色谱/质谱仪对萃取出来的多环芳烃进行定量分析,研究了不同萃取方法以及不同溶剂条件下多环芳烃的总量、分布特征.结果表明,长江口边滩多环芳烃最高值出现在吴淞口;索氏提取法在多环芳烃萃取效果上优于加速溶剂萃取仪提取法;混合溶剂萃取...     

Comparative study of extraction methods for the determination of PAHs from contaminated soils and sediments

The following four methods were compared on the extraction efficiency of 16 EPA (US Environmental Protection Agency) polycyclic aromatic hydrocarbons (PAHs): German method of the Verband Deutscher Landwirtschaftlicher Untersuchungs und Forschungsanstalten (VDLUFA), two methods of the International Organization for Standardization using shaking (ISO A) and Soxhlet extraction (ISO B) and an ultrasonic method. Recovery rates of 16 PAHs were determined in two soils. Extraction efficiency was evaluated in five soils and three sediments. Effect of drying soils and sediments on extraction efficiency was tested using the VDLUFA and the ultrasonic methods. Our study shows that the number of aromatic rings, rather than extraction procedures, significantly influenced recovery rates of individual PAHs. No significant differences in extraction efficiency of the four methods were observed for less polluted samples. For highly polluted soils, extraction efficiency decreased in the following order: VDLUFA method > ISO A > ultrasonic method > ISO B. Influence of soil moisture on extraction efficiency depended to some extent on both solvent used and content of PAHs in samples. A mixture of dichloromethane/acetone (5:1) is recommended for PAH extraction from moist samples when the ultrasonic method is used.     

Determination of PAHs in wastewater irrigated agricultural soil using accelerated solvent extraction

A procedure was developed for determination of 16 polycyclic aromatic hydrocarbons (PAHs) in heavily contaminated paddy soil from wastewater irrigated farmland near Tianjin. The sample was distilled with accelerated solvent extraction (ASE), purified by a silica gel column, and measured with GC/MS. The optimal conditions for the distillation were at 140 degrees C (1500 psi) with a 1:1 mixture of dichloromethane and acetone for 5 min. Application of cyclohexane for extract transfer improved the recovery when the ASE extraction was followed by a silica gel cleanup procedure. Recoveries from the method for 16 PAHs ranged from 57-140% with the coefficients of variation of the results ranging from 0.35% to 5.75%. The total 16 PAHs in a composite sample collected from a wastewater irrigated paddy field near Tianjin was 3.90 mg/kg.     

Screening of compost for PAHs and pesticides using static subcritical water extraction.

Static subcritical water extraction (SubWE) along with solid phase extraction (SPE) was used for the analysis of PAHs and pesticides in municipal solid waste compost. Yields obtained for PAHs in certified reference sediment (CRM 104) were acceptable. The extraction method was simple, rapid, used small sample sizes, and no sample drying was required. Analysis of samples was performed by GC/MS and HPLC. Recovery of spiked pesticides was greatest at 110 degrees C for 20 min extraction time. The optimum extraction for PAH analysis was achieved at 150 degrees C for 20 min. Addition of C-18 resin as an "alternate sorbent" upon cooling increased recovery of PAHs but not of pesticides, however, it increased the stability of atrazine and propazine at higher temperatures. Analysis of three municipal compost samples from the Dayton, OH (USA) area showed no pesticides above the detection limit, however, PAH totals for 11 PAHs were 15.97, 14.42, and 20.79 microg g(-1). The totals of six of the seven carcinogenic PAHs, for which remediation goals in the United States is 4.6 microg g(-1), were determined to be 9.89, 6.77, and 13.06 microg g(-1) dry weight. The highest PAH totals were obtained from compost containing sewage sludge.     

A comparative study on the recovery of polycyclic aromatic hydrocarbons from fly ash and lignite coal

The recovery of polycyclic aromatic hydrocarbons (PAHs) from lignite coal burnt in Greek power stations and the fly ash produced is examined comparatively using Soxhlet, ultrasonic and accelerated solvent extraction procedures with various organic solvents. Soxhlet using toluene/methanol mixture and accelerated solvent extraction/toluene were found to be the most efficient methods for fly ash PAHs, yielding average recoveries of about 80%. The accelerated solvent extraction/toluene procedure was superior for lignite PAHs, yielding 96% average recovery, whereas ultrasonic and Soxhlet extraction yielded relatively lower recoveries (75% and 67%, respectively).     

Persistent chlorinated pesticides and polychlorinated biphenyls in selected fish species from Lake Tanganyika, Burundi, Africa

Concentrations of selected organochlorine pesticides and PCBs in seven fish species (cichlids) from the north end of the Lake Tanganyika, Burundi, Africa were determined. Results were compared to previous work on the Lake Tanganyika and other water bodies and to the European Community maximum residue levels (MRLs) in edible fat. The analytical method included a hot Soxhlet extraction with a mixture of acetone: hexane (1:3, v/v), gravimetrically lipid determination, and a single step clean-up. For PCBs and stable pesticides, the clean-up was done on activated silica gel impregnated with concentrated sulfuric acid, while for non acid-stable pesticides superposed layers of alumina, silica and florisil impregnated with 15% methanolic solution of KOH were successively used. Recoveries of organochlorine pesticides from certified reference material (CRM 430) were ranging from 86% for p,p'-DDT to 107% for endrin, while recoveries from blank fat spiked fortified at three different levels were between 65% for alachlor at the lowest fortification level and 107% for mirex at the highest fortification level. The limits of detection for each analyte were ranging from 0.1 ng/g to 0.5 ng/g fat. All chlorinated pesticides were found in the analyzed species but at low concentrations. Boulengerochromis microlepis contained the highest concentrations of HCHs (288.2 +/- 15.5 ng/g fat) and DDTs (909.1 +/- 42.5 ng/g fat), while the highest PCB levels (166.7 +/- 37.4 ng/g fat for the sum of 12 congeners) were found in Oreochromis niloticus. However, there is no evidence that Lake Tanganyika is more contaminated with pesticides than other African water bodies.     

Sonolytic reactions of phenanthrene in organic extraction solutions

Ultrasonic extraction is a common method used to extract semi-volatile and nonvolatile organic compounds such as polycyclic aromatic hydrocarbons (PAHs) from solid matrices. However, ultrasonic energy has been suspected to lead to undesired reactions of the solute and thus affect qualitative and quantitative results. In this paper, sonolytic reactions of phenanthrene in common organic extraction solutions were examined using a 20 kHz ultrasonic probe under conditions commonly used for ultrasonic extraction. Extraction parameters including phenanthrene concentration, solvent type, pulse length, and sonication time were investigated. Hexane:acetone (1:1 V/V) resulted in less phenanthrene degradation than dichloromethane (DCM):acetone (1:1 V/V). Initial solute concentration, length of sonication time, and solvent type affected the degradation of phenanthrene. Reaction byproducts including methylphenanthrene and methylnaphthalene detected after sonication indicate that phenanthrene reacts by both direct pyrolysis and reaction with methyl or ethyl radicals formed from solvent pyrolysis.     

Characterisation of potentially genotoxic compounds in sediments collected from United Kingdom estuaries

The mutagenic activity bioassay Mutatox was used to assess the mutagenic activity associated with sediments collected from five UK estuaries. Assays were performed on extracts of sediment pore water and residual particulate material isolated from sediment samples collected from the rivers Tyne, Tees, Mersey, and Thames as well as Southampton Water. No mutagenic activity was associated with the pore water extracts, however, 7 of the 28 organic solvent extracts of sediment particulate material contained potential genotoxins. By using Mutatox in association with bioassay-directed fractionation, attempts were made to identify the mutagenic compounds present in the extracts. The fractionation procedure used normal phase solid phase extraction, C18 reverse phase HPLC and cyano/amino bonded silica normal phase HPLC. GC-MS (EI and NICI) analysis was used to identify polycyclic aromatic hydrocarbons (PAH), alkyl substituted PAH, nitro-polycyclic aromatic compounds (nitro-PACs), polycyclic aromatic ketones, oxygenated-PACs, and other known mutagens contributing to the genotoxicity measured in the samples. Some potentially genotoxic compounds remain unidentified.     

Fatty acid profile and elemental content of avocado (Persea americana Mill.) oil –effect of extraction methods

Interest in vegetable oil extracted from idioblast cells of avocado fruit is growing. In this study, five extraction methods to produce avocado oil have been compared: traditional solvent extraction using a Soxhlet or ultrasound, Soxhlet extraction combined with microwave or ultra-turrax treatment and supercritical fluid extraction (SFE). Traditional Soxhlet extraction produced the most reproducible results, 64.76 ± 0.24 g oil/100 g dry weight (DW) and 63.67 ± 0.20 g oil/100 g DW for Hass and Fuerte varieties, respectively. Microwave extraction gave the highest yield of oil (69.94%) from the Hass variety. Oils from microwave extraction had the highest fatty acid content; oils from SFE had wider range of fatty acids. Oils from Fuerte variety had a higher monounsaturated: saturated FA ratio (3.45–3.70). SFE and microwave extraction produced the best quality oil, better than traditional Soxhlet extraction, with the least amount of oxidizing metals present.     

Removal of indigenous compounds to determine maximum capacities for adsorption of phenanthrene by sediments

The maximum amounts of phenanthrene that can be adsorbed in both the slowly desorbing domain and the very slowly desorbing domain of two sediments were determined. To this end, native compounds were removed by mild solvent extraction, heating, or extraction by Tenax. Maximum capacities for adsorption of phenanthrene in the very slowly desorbing domain after removal of native compounds by heating the sediments at 300 degrees C for 24 h were comparable to those after extraction with Tenax at 60 degrees C for 13 days. Mild solvent extraction resulted in lower capacities due to incomplete removal of native compounds. For the slowly desorbing domain, heating the sediment or performing mild solvent resulted in maximum capacities for adsorption exceeding those obtained after non-invasive extraction with Tenax. That was taken to indicate alterations of the sorbent by the solvent or high temperature resulting in an overestimation of the maximum capacities for adsorption. It is concluded that for the determination of maximum capacities of adsorption in the very slowly desorbing domain, removal of native compounds by heating at 300 degrees C for 24 h is reliable and practical. However, for the determination of maximum adsorption capacities of the slowly desorbing domain, native compounds have to be removed by a non-invasive technique such as extraction by Tenax.     

Extraction of organic contaminants from marine sediments and tissues using microwave energy.

In this study, we compared microwave solvent extraction (MSE) to conventional methods for extracting organic contaminants from marine sediments and tissues with high and varying moisture content. The organic contaminants measured were polychlorinated biphenyl (PCB) congeners, chlorinated pesticides, and polycyclic aromatic hydrocarbons (PAHs). Initial experiments were conducted on dry standard reference materials (SRMs) and field collected marine sediments. Moisture content in samples greatly influenced the recovery of the analytes of interest. When wet sediments were included in a sample batch, low recoveries were often encountered in other samples in the batch, including the dry SRM. Experiments were conducted to test the effect of standardizing the moisture content in all samples in a batch prior to extraction. SRM1941a (marine sediment). SRM1974a (mussel tissue), as well as QA96SED6 (marine sediment), and QA96TIS7 (marine tissue), both from 1996 NIST Intercalibration Exercise were extracted using microwave and conventional methods. Moisture levels were adjusted in SRMs to match those of marine sediment and tissue samples before microwave extraction. The results demonstrated that it is crucial to standardize the moisture content in all samples, including dry reference material to ensure good recovery of organic contaminants. MSE yielded equivalent or superior recoveries compared to conventional methods for the majority of the compounds evaluated. The advantages of MSE over conventional methods are reduced solvent usage, higher sample throughput and the elimination of halogenated solvent usage.     

Fatty acid profile and elemental content of avocado (Persea americana Mill.) oil--effect of extraction methods

Interest in vegetable oil extracted from idioblast cells of avocado fruit is growing. In this study, five extraction methods to produce avocado oil have been compared: traditional solvent extraction using a Soxhlet or ultrasound, Soxhlet extraction combined with microwave or ultra-turrax treatment and supercritical fluid extraction (SFE). Traditional Soxhlet extraction produced the most reproducible results, 64.76 ± 0.24 g oil/100 g dry weight (DW) and 63.67 ± 0.20 g oil/100 g DW for Hass and Fuerte varieties, respectively. Microwave extraction gave the highest yield of oil (69.94%) from the Hass variety. Oils from microwave extraction had the highest fatty acid content; oils from SFE had wider range of fatty acids. Oils from Fuerte variety had a higher monounsaturated: saturated FA ratio (3.45-3.70). SFE and microwave extraction produced the best quality oil, better than traditional Soxhlet extraction, with the least amount of oxidizing metals present.     

Optimisation of pressurised liquid extraction for elimination of sulphur interferences during determination of organotin compounds in sulphur-rich sediments by gas chromatography with flame photometric detection

A simple method for species-selective analysis of organotin compounds (OTCs) (butyl and phenyl) in sediments was developed. The sample preparation procedure was specifically optimised for sulphur-rich sediments to eliminate interferences from elemental sulphur and organosulphur compounds. Tin species were extracted from sediment samples using pressurised liquid extraction technique (PLE), ethylated - with simultaneous extraction to isooctane - in aqueous phase with sodium tetraethylborate (NaBEt(4)) and separated/detected by gas chromatography with flame photometric detection (GC-FPD). PLE operational variables (extraction temperature and pressure, solvent composition and number of static extraction steps) and extract handling routine were fine-tuned to minimise the amount of extracted interferents while keeping OTCs recovery at an acceptable level. Best results were obtained after extraction of sediment samples with methanol/water (75% v/v methanol) solution of acetic acid/sodium acetate with tropolone addition (0.6 g l(-1)). Derivatisation of low temperature, high-pressure (50 degrees C, 13.8 MPa) extracts gives isooctane extracts which are clean enough to be directly analysed by GC-FPD without any further cleanup. Interferences from elemental sulphur were completely eliminated while concentrations of other interferents were reduced to the level not impairing quantitation of OTCs under the study. No negative effects in terms of chromatographic column deterioration were observed after repeated injections of such extracts. Two certified reference materials, BCR646 and PACS-2, were analysed to assess performance of the method. Recoveries of all OTCs under the study, except MBT, were in the range of 91-114%. MBT extraction efficiency was low (34-47%) therefore the method is unsuitable for precise determinations of this compound.     

Extraction of polychlorinated dibenzo-p-dioxins and dibenzofurans from solid samples using the Randall technique

This study deals with a new sample extraction technique which minimizes pollution in analytical laboratories whilst reducing sample preparation time and cost. The device uses the Randall technique for solid sample extraction, performed by immersion of the sample in boiling solvent. The fast solubilization operated by the hot solvent leads to a sharp reduction in extraction time. This method was tested for the extraction of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) from different solid matrices using toluene as extractant, and compared with the conventional Soxhlet. The reduction in the extraction times (from 48 to 2 h) with an efficiency similar to or higher than that afforded by the conventional Soxhlet technique indicates the suitability of this method.     

Experimental evidence for in situ natural attenuation of 2,4- and 2,6-dinitrotoluene in marine sediment

Dinitrotoluenes (DNTs) are widely used in the manufacturing of explosives and propellants hence causing contamination of several terrestrial and aquatic environments. The present study describes biotransformation of 2,4-DNT and 2,6-DNT in marine sediment sampled from a shipwreck site near Halifax Harbour. Incubation of either 2,4-DNT or 2,6-DNT in anaerobic sediment slurries (10% w/v) at 10 degrees C led to the reduction of both DNTs to their corresponding diaminotoluene (2,4-DAT and 2,6-DAT) via the intermediary formation of their monoamine derivatives (ANTs). The production of diaminotoluene was enhanced in the presence of lactate for both DNT isomers. Using [(14)C]-2,4-DNT less than 1% mineralization was observed as determined by liberated (14)CO(2). Sorption of DNTs, ANTs, and DATs was thus investigated to learn of their fate in marine sediments. Under anaerobic conditions, sorption followed the order: DNTs (K(d)=8.3-11.7lkg(-1))>ANTs (K(d)=4.5-7.0lkg(-1))>DATs (K(d)=3.8-4.5lkg(-1)). Incubation of 2,4-DAT in aerobic sediment led to rapid disappearance from the aqueous phase. LC/MS analysis of the aqueous phase and the acetone sediment extract showed the formation of azo- and hydrazo-dimers and trimers, as well as unidentified polymers. Experiments with radiolabelled 2,4-DAT showed a mass balance distributed as follows: 22% in the aqueous phase, 24% in acetone extracts, and 50% irreversibly bound to sediment. We concluded that DNT in anoxic marine sediment can undergo in situ natural attenuation by reduction to DAT followed by oxidative coupling to hydrazo-oligomers or irreversible binding to sediment.     

Solvent extraction for heavy crude oil removal from contaminated soils

A new strategy of heavy crude oil removal from contaminated soils was studied. The hexane-acetone solvent mixture was used to investigate the ability of solvent extraction technique for cleaning up soils under various extraction conditions. The mixtures of hexane and acetone (25 vol%) were demonstrated to be the most effective in removing petroleum hydrocarbons from contaminated soils and approx 90% of saturates, naphthene aromatics, polar aromatics, and 60% of nC₇-asphaltenes were removed. Kinetic experiments demonstrated that the equilibrium was reached in 5 min and the majority of the oil pollutants were removed within 0.5 min. The effect of the ratio between solvent and soil on the extraction efficiency was also studied and results showed that the efficiency would increase following the higher solvent soil ratio. Then the multistage continuous extraction was considered to enhance the removal efficiency of oil pollutants. Three stages crosscurrent and countercurrent solvent extraction with the solvent soil ratio 6:1 removed 97% oil contaminants from soil. Clearly the results showed that the mixed-solvent of hexane and acetone (25 vol%) with character of low-toxic, acceptable cost and high efficiency was promising in solvent extraction to remove heavy oil fractions as well as petroleum hydrocarbons from contaminated soils.     

Treatment system for solid matrix contaminated with fluoranthene. I--Modified extraction technique.

A laboratory-scale ultrasonication technique was developed for fluoranthene extraction from soils and sediments where the utilized organic solvent would be recovered after the extraction process. Therefore, the remedied soils and sediments would be free from toxicant and trace of added chemicals. The developed ultrasonication technique outlined here is an integrated part of a complete remediation system consisting of extraction and solar detoxification reactors. This paper investigates extraction efficiencies under different conditions, outlines solvent recovery technique and compares extraction efficiency of the developed ultrasonication technique with a commercially available laboratory-scale sonication bath. The spiked soil sample with fluoranthene (19.4 microg g(-1)) and organic solvent was ultrasonicated at 40 degrees C for 20 min. The sonicated mixture was allowed to settle for 10 min before the extract gravitated into the modified solar reactor for fluoranthene detoxification. The added solvents were removed from the remedied soil before it was released to site. The mixture of cyclohexane and ethanol (CH:ETOH) (3:1) was the favorable solvent from among 10 organic solvents because of its high extraction efficiency, safety and low cost. Preliminary results indicated that the developed extraction technique recovered more than 93% of fluoranthene from soil samples.