Extractability and Subsequent Biodegradation of PAHs from Contaminated Soil

The biodegradation of polyaromatic hydrocarbons (PAHs) has been well documented; however, the biodegradation of PAHs in contaminated soil has proved to be problematic. Sorption of PAHs to soil over time can significantly decrease their availability for extraction much less than for biodegradation. In this study the ability of various organic solvents to extract PAHs from coal tar-contaminated soil obtained from former manufactured gas plant (MGP) sites was investigated. Solvents investigated included acetone/hexane, dichloromethane, ethanol, methanol, toluene, and water. The extraction of MGP soils with solvents was investigated using soxhlet extraction, multiple soxhlet extractions, sonication, and brief agitation at ambient temperature with a range of solvent concentrations. Of particular interest was the documentation of the recalcitrance of PAHs in weathered MGP soils to extraction and to bioremediation, as well as to demonstrate the ease with which PAHs extracted from these soils can be biodegraded. The efficiency of extraction of PAHs from MGP soils was found to be more dependent upon the choice of solvent. The environmentally-benign solvent ethanol, was shown to be equal to if not better than acetone/hexane (the EPA recommended solvent) for the extraction of PAHs from MGP soils, brief contact/agitation times (minutes) using small quantities of ethanol (2 volumes or less) can achieve nearly quantitative extraction of PAHs from MGP soils. Moreover aqueous slurries of an MGP soils experienced less than 10% biodegradation of PAHs in 14 days while in the same period about 95% biodegradation was acieved using PAHs extracted from this soil by ethanol and subsequently added to aqueous bacterial suspensions.     

Organic compounds of different extractability in total solvent extracts from soils of contrasting water repellency

Previous studies examining organic compounds that may cause water‐repellent behaviour of soils have typically focussed on analysing only the lipophilic fraction of extracted material. This study aimed to provide a more comprehensive examination by applying single‐ and sequential‐accelerated solvent extraction (ASE), separation and analysis by GC/MS of the total solvent extracts of three soils taken from under eucalypt vegetation with different degrees of water repellency. Water repellency increased in all the soils after extraction with DCM/MeOH (95:5), but was eliminated with iso‐propanol/ammonia (95:5). Quantities of major lipid compound classes varied between solvents and soils. Iso‐propanol/ammonia (95:5) solvent released saccharides, glycerol, aromatic acids and other polar organic compounds, which were more abundant in fractionated extracts from the single extraction and the third step sequential ASE extraction, than in the extracts from the DCM/MeOH ASE solvent. Dominant compounds extracted from all soils were long‐chain alkanols (>C₂₂), palmitic acid, C₂₉ alkane, β‐sitosterol, terpenes, terpenoids and other polar compounds. The soil with the lowest repellency lacked >C₁₈ fatty acids and had the lowest concentrations of alkanols (C_26,C₂₈ and C₃₀) and alkanes (C₂₉, C₃₁), but a greater abundance of more complex polar compounds than the more repellent soils. We therefore speculate that the above compounds play an important role in determining the water repellency of the soils tested. The results suggest that one‐stage and sequential ASE extractions with iso‐propanol/ammonia and subsequent fractionation of extracts are a useful approach in providing a comprehensive assessment of the potential compounds involved in causing soil water repellency.     

An Improved Gravimetric Method to Determine Total Petroleum Hydrocarbons in Contaminated Soils

A gravimetric method to determine heavy fractions of total petroleum hydrocarbons (TPH) in soils is reported. The method was adapted and calibrated by modifying previous standard methods published, incorporating energy and cost savings where possible. Artificially contaminated soils with different organic matter content, and aged in stationary mode for a period of 8 months were used for calibration. Insufficient solvent evaporation was identified as the most prevalent and largest positive interference in the gravimetric detection. To overcome this, while minimizing the need for heating, a combination of three 10-min rotary evaporator steps and 30 min of vacuum in a desiccator were applied, for a total solvent volume of 60 ml. Hexane was chosen as the extraction solvent and a 40–60 min treatment in an ultrasound bath of 260 W was found suitable to extract 80–95% of TPH extracted by the Soxhlet method. Finally, the use of silica gel for cleanup of co-extracted natural organic matter was found unnecessary, because of the low amounts co-extracted for soils with up to 5% organic carbon, and because the chemical nature of the co-extracted organic matter prevents its selective adsorption to silica.     

Development of New Method for Extraction of α‐Zein from Corn Gluten Meal Using Different Solvents

A modified procedure for the extraction of α‐zein from corn gluten meal was developed and compared against a commercial extraction method. The modification involved raising the concentration of alcohol in solvent and removing the precipitate by centrifugation. Five organic solvent mixtures were compared using the modified extraction procedure developed along with the reductant sodium bisulfite and NaOH. The modified procedure precipitated most of the non‐α‐zein protein solids by increasing the concentration of alcohol. The supernatant had α‐zein‐rich fraction, resulting in higher yield of α‐zein than the commercial method when cold precipitated. The commercial extraction procedure had a zein yield of 23% and protein purity of 28% using 88% 2‐propanol solvent. The three best solvents, 70% 2‐propanol, 55% 2‐propanol, and 70% ethanol, yielded ≈35% of zein at protein purity of 44% using the modified extraction procedure. Zeins extracted using the novel method were lighter in color than the commercial method. Densitometry scans of SDS‐PAGE of α‐zein‐rich solids showed relatively large quantities of α‐zein with apparent molecular weights of 19,000 and 22,000 Da. The α‐zein‐rich solids also had small amounts of δ‐zein (10,000 Da) because it shares similar solubility properties to α‐zein. A solvent mixture with 70% 2‐propanol, 22.5% glycerol, and 7.5% water extracted significantly less zein (≈33%) compared to all other solvents and had α‐zein bands that differed in appearance and contained little to no δ‐zein.     

Solvent-based washing removes lipophilic contaminant interference with phospholipid fatty acid analysis of soil communities

Phospholipid fatty acid (PLFA) analysis is an informative method for characterising and quantifying changes in the phenotypic profile of the soil microbial community when soils are exposed to chemical toxicants and other xenobiotics. However, where such materials are lipophilic, a range of non-polar compounds can be co-extracted with PLFAs and can consequently mask PLFA chromatograms. We found this to be the case with the lipophilic anti-microbial compound triclosan, which can enter the soil via the addition of sewage sludge. A simple method of washing soil in solvent prior to extraction was developed in order to remove triclosan without altering the relative abundance of PLFAs. Three contrasting soils were spiked with 500 mg kg⁻¹ of triclosan before being washed with methanol (MeOH), dichloromethane (DCM), hexane or aqueous solutions of these solvents. PLFAs were then extracted and analysed. All treatments were found to remove triclosan effectively, allowing all peaks to be identifiable. Whilst the polar solvents MeOH and DCM significantly altered the relative abundance of extracted fatty acids in most of the soils tested, soil washing with a small quantity of hexane was able to remove triclosan whilst best preserving the fidelity of the PLFA profiles.     

Sequential extraction of low concentrations of pyrene and formation of non-extractable residues in sterile and non-sterile soils

In this study, temporal changes in the extractability of ¹⁴C-pyrene, at native concentrations, were followed in two soils with differing organic matter contents, under sterile and non-sterile conditions over 24 weeks by a sequential solvent extraction scheme. No significant loss of the added ¹⁴C-pyrene was observed during the incubation. Significant decreases in methanol:water and n-butanol extractability were observed with increasing soil-pyrene contact time. Significant non-extractable residues were formed in all soils, with the largest increases found in the non-sterile soils. After 8 weeks soil-pyrene contact time, there was a significant increase in the rate and extent of sequestration of pyrene in the biologically active soils. This indicated that the aging of pyrene was initially a physical process, with active microbial communities increasing the rate and extent of residue formation after 8 weeks soil-pyrene contact time. These findings suggest that there is a need for longer term ageing experiments following the role of microbial communities on the formation of solvent non-extractable residues. The humin fraction of the soil organic matter contained the majority of the ¹⁴C-pyrene associated activity which was not extractable using the scheme of sequential solvents. Saponification of the soil humin resulted in the release of similar amounts of ¹⁴C-pyrene associated activity from sterile and non-sterile soils. Solvent extraction with methanol:water was found to significantly underestimate the bioavailable fraction, whereas n-butanol overestimated the bioavailability of the ¹⁴C-pyrene-associated activity when assessed by bacterial mineralization after 24 weeks soil-pyrene contact time.     

Pressurized fluid extraction for quantitative recovery of chloroacetanilide and nitrogen heterocyclic herbicides in soil

Pressurized fluid extraction (PFE) is a new sample extraction method operated at elevated temperatures and pressures with liquid solvents. The use of PFE was investigated for the extraction of four Hawaiian clayey soils fortified with the selected chloroacetanilide and nitrogen heterocyclic herbicides Alachlor, Bromacil, Hexazinone, Metribuzin, and Tebuthiuron. The effects of operation temperature, pressure, flush volume, and static cycles on PFE performance were studied. Water was the most effective modifier of PFE for quantitative recoveries of the five herbicides in soils. The simple extraction method required pretreatment of the soil with 37.6% water and subsequent two-static-cycle extraction with a total of 32 mL of acetone at 1500 psi and 100 degrees C. Average recoveries of Alachlor, Bromacil, Hexazinone, Metribuzin, and Tebuthiuron ranged from 93 to 103% by the water-assisted PFE, compared with only 68-83% recoveries of the corresponding chemicals when no water was used. The extraction time and total organic solvent consumption were reduced from 18 h and 300 mL by Soxhlet to 22 min or less and 80 mL or less of organic solvent by PFE.     

银杏黄酮苷提纯工艺研究

根据黄酮苷的物性选择丙酮，正丁醇，正丙醇，乙酸乙酯为萃取剂。单因素实验优选出正丙醇为萃取黄酮苷的主萃取剂。对其进行改性，通过单因素实验和正交实验优化出：水∶正丙醇=1∶25为萃取黄酮苷的较佳萃取剂。T=25℃，t=10 min，固液比=15∶1(g/100 mL)为其最佳萃取工艺参数。最后得到纯度＞50%，得率＞80%的总黄酮苷产品。为后续提纯分离打下较好的基础。     

Analysis and Sorption Behavior of Fluoroquinolones in Solid Matrices

A simple analytical method for the quantitative analysis of fluoroquinolone group antibiotics, enrofloxacin (ENR) and ciprofloxacin (CIP) in soil was developed based on the mechanical extraction with vortex and ultrasonication and solid phase extraction followed by high pressure liquid chromatography-fluorescence detection (HPLC-FLD). Type of extraction solvents and number of extraction cycles were optimized during the method development. The most efficient extraction solvent was found as phosphate buffer at pH 3 in combination with 50% of organic modifier acetonitrile with the extraction cycle of four. Overall method was applied on three different types of soils, namely, sandy, loamy sand and sandy loam and recovery rates ranged between 71–100% for ENR and 61–89% for CIP depending on the portion of organic and clay content in soils. The analytical method was also used for the estimation of fluoroquinolone concentrations in manure amended agricultural soils sampled from the different parts of Turkey and enrofloxacin was detected in the concentration range of 0.013–0.204 mg/kg. In addition, sorption of fluoroquinolone antibiotics on all types of soils was investigated and the highest distribution coefficients (K_d and K_f) of fluoroquinolone compounds were obtained for loamy sand (K_d?=?1.29 l/g and K_f?=?0.66 for CIP; K_d?=?0.97 l/g and K_f?=?0.56 for ENR) with the highest organic carbon.     

IRON AND ALUMINIUM AS CEMENTING SUBSTANCES OF SOIL AGGREGATES

A method is described for extracting fractions of soil iron and aluminium without removing organic matter. The extraction is by acetylacetone in a non–polar solvent and is virtually complete in zoo h. Similar amounts of iron and aluminium are extracted by acetylacetone in either benzene or water, but organic matter is extracted in detectable amounts only by acetylacetone in water. Extraction in aqueous solution after acetylacetone in benzene removes only organic matter, with no appreciable release of iron and aluminium. Metals extracted by acetylacetone in benzene are therefore considered to be bonded to that part of the organic matter which is extracted by acetylacetone. Water alone does not extract significant amounts of organic matter after removal of iron and aluminium by acetylacetone in benzene. The refolding of the hydrophilic surface units of the organic matter, caused by non–polar solvents, may hinder the extraction by water.     

Ultrasonic Enhanced Desorption of DDT from Contaminated Soils

In this study, using high-power low-frequency ultrasound, heated slurries with anionic surfactant sodium dodecyl sulfate (SDS) were treated to enhance desorption of DDT from soils with high clay, silt, and organic matter content and different pH (5.6?C8.4). The results were compared with DDT extracted using a strong solvent combination as reference. Slurry ranges from 5 to 20 wt.% were studied. For a soil slurry (10 wt.%) at pH 6.9 with 0.1% v/v SDS surfactant heated to 40°C for 30 min, desorption was above 80% in 30 s using 20 kHz, 932 W/L ultrasonic intensity without solvent extraction. Other soils gave lower desorption efficiency in the range 40?C60% after 30 s ultrasonic treatment. The percentage of organic matter, dissolved organic carbon, soil surface area, clay and silt percentage, and soil pH level were the key parameters influencing variations in desorption of DDT in the three soils in similar experimental conditions. DDT dissolution in SDS and soil organic matter removal employing the ultrasonic-enhanced organic matter roll-up mechanism emerged as the two best possible methods of DDT desorption. The method offers a practical, potentially low-cost alternative to high volume, costly, hazardous solvent extraction of DDT.     

Extraction of chili,black pepper,and ginger with near-critical CO2, propane,and dimethyl ether: analysis of the extracts by quantitative nuclear magnetic resonance

Ginger, black pepper, and chili powder were extracted using near-critical carbon dioxide, propane, and dimethyl ether on a laboratory scale to determine the overall yield and extraction efficiency for selected pungent components. The temperature dependency of extraction yield and efficiency was also determined for black pepper and chili using propane and dimethyl ether. The pungency of the extracts was determined by using an NMR technique developed for this work. The volatiles contents of ginger and black pepper extracts were also determined. Extraction of all spice types was carried out with acetone to compare overall yields. Subcritical dimethyl ether was as effective at extracting the pungent principles from the spices as supercritical carbon dioxide, although a substantial amount of water was also extracted. Subcritical propane was the least effective solvent. All solvents quantitatively extracted the gingerols from ginger. The yields of capsaicins obtained by supercritical CO(2) and dimethyl ether were similar and approximately double that extracted by propane. The yield of piperines obtained by propane extraction of black pepper was low at approximately 10% of that achieved with dimethyl ether and CO(2), but improved with increasing extraction temperature.     

Changes in microstructure of soils following extraction of organically bonded metals and organic matter

The influence of selective removal of organically bonded metals and organic matter on soil microstructure was investigated. Two samples of soils with different mineralogical, chemical and mechanical composition were treated with acetylacetone in both polar and non-polar solvents to dissolve amorphous organic iron and aluminium, and with hydrogen peroxide to destroy organic matter. Transmission electron micrographs of ultrathin sections and scanning electron micrographs of <5?μm fractions of the extracted soils showed distinct changes of microstructure of clays after successive removal of cementing agents. Although untreated soils showed flocculent or honeycomb structure, soils with organic matter and organically bonded metals removed showed turbostratic domain structure with stepped clusters. The changes in microstructure of soils following extraction were confirmed by determination of pore-size distribution and total cumulative volume of pores using the mercury porosimetry method. In addition, the surface area of the extracted soils was determined by water adsorption. The results showed that organically bonded iron and aluminium and organic matter distinctly influence the fabric of microstructure as flocculating agents.     

Ein neues Verfahren zur Extraktion von organischen Stoffen aus Böden mit überkritischen Gasen

A new procedure for the extraction of organic matter from soils by supercritical gases Organic solvents beyond critical temperature and pressure have excellent properties for solving polymere organic substances. For soil samples yields of organic material with low ash content are much higher than those obtained by the common NaOH/HCl-extraction. Fractionation of the samples is easily achieved by a simple change of solvent bottles. In comparison to the original material oxygen contents are lower, due to a thermal or solvolytical split off of methanol or water. Extraction with supercritical gases – in addition to oxidative degradation –may be regarded as a useful method to enlighten the structure of humic acids. The effective extraction of firmly bound pesticides in soil is another point of interest.     

Comparison of extraction buffers for the detection of fumonisin B(1) in corn by immunoassay and high-performance liquid chromatography

The Associatian of Official Analytical Chemists approved method for quantification of fumonisin B(1) (FB(1)) in corn meal or corn-based food products includes extraction into methanol (MeOH)/water (3:1, v/v). Disposal of the extraction medium can pose safety and environmental problems. To secure a rapid and inexpensive screen for FB(1) contamination, a sensitive competitive ELISA using a rabbit polyclonal antibody was developed. This assay was used in a comparative study measuring the extraction efficiency of FB(1) in aqueous or organic solvent buffers using 16 field corn samples. An aqueous phosphate buffer was found to be suitable for extracting FB(1), thus eliminating the need for organic solvents. HPLC and ELISA determinations compared well in fortified samples at known concentrations between 1 and 50 microg/mL of extract. Overestimation at levels >50 microg/mL were common. The characteristics and application of the ELISA for screening purposes are discussed.     

THE EFFECT OF SOIL FACTORS ON THE EXTRACTION OF SOIL ORGANIC MATTER BY ANHYDROUS FORMIC ACID

Twenty-five soils, having a wide range of organic matter contents, were extracted with anhydrous formic acid containing 10 per cent acetylacetone, and the extracted material precipitated in two fractions with diisopropyl ether. Precipitates comprised from 5.1 to 51.1 per cent of the original soil organic matter, the proportion extracted tending to be greatest from acid soils of fairly high organic matter content and least from neutral or slightly alkaline soils of low organic matter content. Soil clay content appeared to have no effect on the efficiency of organic matter extraction, but was the most important soil factor governing the proportion of the total soil-N extracted. Amounts of N extracted ranged from 10.2 to 57.8 per cent of the original soil N content, extraction efficiency being greatest with soils of low clay content and low pH. There was evidence to suggest that soil clay afforded some protection to N compounds against extraction. The results indicate that formic acid/acetylacetone is most effective with soils in which much of the organic matter is only partly humified.     

Extraction of tricyclazole from soil and sediment with subcritical water

The use of subcritical water to extract tricyclazole from soils and sediments was examined. Extraction efficiency and kinetics were determined as a function of temperature, sample age, sample matrix, sample size, and flow rate. Extraction temperature was the most influential experimental factor affecting extraction efficiency and kinetics, with increasing temperature (up to 150 degrees C) yielding faster and higher efficiency extractions. Higher extraction temperatures were also important for quantitative recovery of tricyclazole from aged samples. Extraction at 50 degrees C yielded 97% recoveries from samples aged 1 day but only 30% recoveries for samples aged 202 days, whereas extraction at 150 degrees C yielded recoveries of 85-100% that were independent of incubation time and sample matrix, with the exception of one sediment that contained a large amount of organic matter. Sample extracts from subcritical water extraction were generally a pale yellow color, contrasted with a dark brown color from organic solvent extractions of the same matrixes. Less sample cleanup was therefore required prior to analysis, with the total time for the extraction and analysis of a single sample being approximately 2 h. Subcritical water extraction is an effective technique for the rapid and quantitative extraction of tricyclazole from soils and sediments.     

Development of a solid-phase extraction method for phenoxy acids and bentazone in water and comparison to a liquid-liquid extraction method

A rapid solid-phase extraction (SPE) method was developed for the determination of bentazone and the phenoxy acids 2,4-D, dichlorprop, MCPA, and mecoprop in Norwegian environmental water samples. Cartridges with a high-capacity cross-linked polystyrene-based polymer were used for off-line preconcentration. The effects of elution solvent, elution volume, sample volume, sorbent mass, pH, and flow rate on the recoveries of the pesticides were investigated using HPLC. Average recovery of >90% was achieved with 500 mg sorbents using 2 mL of methanol with 5% NH3 as elution solvent. The recoveries were independent of sample pH in the tested range of pH 1-7. Using a sample volume of 200 mL, the limits of determination for the phenoxy acids and bentazone are 0.02 microg/L. Sample volumes up to 2000 mL at a flow rate of 60 mL/min could be handled without any loss of analytes, which makes it possible to lower the limits of determination. The SPE method was compared to a routinely used liquid-liquid extraction method. Three different water matrices spiked at 1.0 and 0.05 microg/L were extracted, and the quantification was performed by GC-MS. Both methods permitted the determination of phenoxy acids and bentazone in distilled water, creek water, and well water down to a level of 0.05 microg/L with recoveries >80% for 200 mL samples. Important advantages of the SPE method compared to the liquid-liquid extraction method were the short extraction times, lack of emulsions, use of disposable equipment, and reduced consumption of organic solvents.     

Evaluation of toxicity risk of polycyclic aromatic hydrocarbons (PAHs) in crops rhizosphere of contaminated field with sequential extraction

Purpose

The assessing bias of rhizosphere effect on polycyclic aromatic hydrocarbons (PAHs) degradation in soils would come out from formation of nonextractable PAHs and extractability difference of various solvents. The aim of this study was to evaluate the role of rhizosphere effect in long-term PAHs polluted soils by using sequential extraction approach.

Material and methods

The scheme of sequential extraction included methanol/water extractable PAHs, butanol extractable PAHs, DCM extractable PAHs, humic acid-bound PAHs, crude humin-bound PAHs, and organic-C enriched humin-bound PAHs. PAHs in plant tissues were extracted by dichloromethane after saponifying. The correlations between PAHs in plant tissues and sequentially extracted fractions were generated by partial least squares regression.

Results and discussion

The profiles of sequentially extracted PAHs varied with plant species. The discrepancy of toxicity equivalency concentrations between rhizosphere and bulk soils was much more significant than that of total PAHs concentrations. In partial least squares regression models, the concentration of PAHs in plant tissues was correlated with fractions strongly associated with soil.

Conclusions

The novelty of this study is the evaluation of concentration and toxicity equivalency concentration of PAHs in rhizosphere of crops sampled in a field polluted with PAHs for long term. This study has highlighted more significant role of rhizosphere in cleanup of cancerogenic toxicity of soil than amount of PAHs in polluted soils.     

Determination of total cadmium in calcareous soils by extraction using aliquat‐336 and 3‐heptan‐one after aqua regia digestion

Abstract

Measurement of total soil cadmium (Cd) is difficult due to calcium (Ca) and other chemicals which cause high background absorbance when trace levels of Cd are to be determined. When soil Cd is low, even use of deuterium background correction with flame atomic absorption spectroscopy (AAS) cannot provide accurate Cd results. Use of furnace atomic absorption with method of standard additions can circumvent these interferences, but the cost and time required are substantial. We desired a more rapid, convenient, and reliable alternative to extraction using dithizone and back‐extraction into acid, or to ammonium pyrollidinedithiocarbamate (APDC) which does not require close pH adjustment nor have many sources of potantial contamination. We evaluated analysis of these complex soil extracts with the method of Viets (1978) which extracts metals from 1N acid solutions using Aliquat‐336 in methylisobutyl‐ketone (MIBK). We tested the use of the less toxic and less water soluble 3‐heptanone as an organic solvent alternative to MIBK which can be directly analyzed by flame atomic absorption. A series of extraction experiments were conducted to determine if Cd was extracted from standard solutions and from total metal digests of calcareous soils into an Aliquat‐336/3‐heptanone solution, and under what conditions extraction was optimum. In the optimum method, Cd was extracted from aqua regia soil digests by 10% Aliquat‐336 in 3‐heptanone without addition of ascorbic acid or potassium iodide (KI) used by Viets. Excellent recovery of Cd was obtained for both standard reference soils and low Cd highly calcareous soils from North Dakota and Minnesota. Addition of ascorbic acid and KI did not increase the efficiency of extraction indicating that the extraction system used was free of ferric‐iron [Fe(III)] interference. The ion‐association complex of Cd remained stable for at least 24 hr after extraction, providing a very convenient method to analyze low levels of total Cd in soils and other geologic materials.