Ultrasonic extraction of arsenic and selenium from rocks associated with mountaintop removal/valley fills coal mining: Estimation of bioaccessible concentrations

Supercritical carbon dioxide extraction of plant phytochemicals for biological and environmental applications - A review

Recently, supercritical fluid CO₂ extraction (SFE) has emerged as a promising and pervasive technology over conventional extraction techniques for various applications, especially for bioactive compounds extraction and environmental pollutants removal. In this context, temperature and pressure regulate the solvent density and thereby effects the yield, selectivity, and biological/therapeutic properties of the extracted components. However, the nature of plant matrices primarily determines the extraction mechanism based on either density or vapor pressure. The present review aims to cover the recent research and developments of SFE technique in the extraction of bioactive plant phytochemicals with high antioxidant, antibacterial, antimalarial, and anti-inflammatory activities, influencing parameters, process conditions, the investigations for improving the yield and selectivity. In another portion of this review focuses on the ecotoxicology and toxic metal recovery applications. Nonpolar properties of Sc-CO₂ create strong solvent strength via distinct intermolecular interaction forces with micro-pollutants and toxic metal complexes. This results in efficient removal of these contaminants and makes SFE technology as a superior alternative for conventional solvent-based treatment methods. Moreover, a compelling assessment on the therapeutic, functional, and solvent properties of SFE is rarely focused, and hence this review would add significant value to the SFE based research studies. Furthermore, we mention the limitations and potential of future perspectives related to SFE applications.

Fractions of arsenic and selenium in fly ash by ultrasound-assisted sequential extraction

Sequential extraction has been validated as an effective method to assess the fractions of elements in fly ash. However, the time consumption and high labor costs limit the application of the conventional sequential extraction (CSE) for fast screening of elemental fractions in fly ash. In this study, two ultrasound-assisted sequential extraction (UASE) methods were developed for fast analysis of arsenic (As) and selenium (Se) fractions in fly ash (FA). The parameters of UASE were optimized by comparing the results of As and Se obtained from UASE with those values observed via CSE. The operation time of sequential extraction procedures for As and Se were shortened from 24.5 h to less than 90 min. A certified reference material (CRM, GBW08401) and real fly ash samples were applied to validate the developed UASE. The recoveries of As and Se were found in the range of 82.3% to 114%. For all fractions, the performance of UASE was faster than CSE with the acceptable uncertainties. The analytical results demonstrated that the concentration of As in F3 was found to be higher than other fractions, while the main forms of Se were found to be in F1 and F3 in the fly ash samples. Based on the advantages of high efficiency and easy operation, the developed UASE procedures can be applied for fast screening of the mobility and bioavailability of As and Se in FA from coal fired power plants.

Atmospheric particulate matter in proximity to mountaintop coal mines: sources and potential environmental and human health impacts

Mountaintop removal mining (MTM) is a widely used approach to surface coal mining in the US Appalachian region whereby large volumes of coal overburden are excavated using explosives, removed, and transferred to nearby drainages below MTM operations. To investigate the air quality impact of MTM, the geochemical characteristics of atmospheric particulate matter (PM) from five surface mining sites in south central West Virginia, USA, and five in-state study control sites having only underground coal mining or no coal mining whatsoever were determined and compared. Epidemiologic studies show increased rates of cancer, respiratory disease, cardiovascular disease, and overall mortality in Appalachian surface mining areas compared to Appalachian non-mining areas. In the present study, 24-h coarse (>2.5 µm) and fine (≤2.5 µm) PM samples were collected from two surface mining sites in June 2011 showed pronounced enrichment in elements having a crustal affinity (Ga, Al, Ge, Rb, La, Ce) contributed by local sources, relative to controls. Follow-up sampling in August 2011 lacked this enrichment, suggesting that PM input from local sources is intermittent. Using passive samplers, dry deposition total PM elemental fluxes calculated for three surface mining sites over multi-day intervals between May and August 2012 were 5.8 ± 1.5 times higher for crustal elements than at controls. Scanning microscopy of 2,249 particles showed that primary aluminosilicate PM was prevalent at surface mining sites compared to secondary PM at controls. Additional testing is needed to establish any link between input of lithogenic PM and disease rates in the study area.

Ultrasound-assisted single extraction tests for rapid assessment of metal extractability from soils by total reflection X-ray fluorescence

In this work, ultrasound-assisted extraction (UAE) was employed for acceleration of metal extraction from soil samples. After extraction, multielemental analysis (Cr, Mn, Fe, Ni, Cu, Zn and Pb) of EDTA and acetic acid extracts was performed by total reflection X-ray fluorescence spectrometry (TXRF). High-intensity ultrasonic processors, i.e. the ultrasonic probe (50W) and the cup-horn sonoreactor (200W) were applied. Both ultrasonic procedures were compared with a miniaturized version of the single extraction scheme proposed by the Standards, Measurements and Testing program (SM&T). The extraction time with EDTA was reduced from 1h (conventional procedure) to 2 min (ultrasonic probe) or to 10 min (cup-horn sonoreactor). The time required for acetic acid extraction was also reduced from 16 h (conventional procedure) to 6 min (ultrasonic probe) or to 30 min (cup-horn sonoreactor). In addition, the amount of sample and extractants was drastically reduced as a result of the miniaturization implemented in the developed approaches. The combination of UAE and TXRF allows assessing the potential metal mobility and bioavailability in a simple way.

Selenium Adsorption onto Iron Oxide Layers beneath Coal-Mine Overburden Spoil

A field experimental study to determine the feasibility of sequestering dissolved selenium (Se) leached from coal-mine waste rock used an iron (Fe)-oxide amendment obtained from a mine-drainage treatment wetland. Thirty lysimeters (4.9 × 7.3 m), each containing 57.7 t (1.2-1.8 m thickness) of mine-run carbonaceous shale overburden, were installed at the Hobet mine in southeastern West Virginia. The fine-grained Fe-oxide was determined to be primarily metal oxides (91.5% ferric and 4.37% aluminous), with minor (<3%) SO and Ca, perhaps as gypsum. The mineralogy of the Fe was goethite, although residual ferrihydrite may have been present. Various thicknesses of this amendment (0.0064, 0.057, 0.229, and 0.457 m, plus a zero-amendment control) were used, ranging from 0 to 2.2% weight percent of the spoil. The control and each treatment were replicated six times to estimate uncertainty due to compositional and hydrological variation. Infiltration of rainfall created leachate that drained to individual batch-collection tanks that were sampled 46 times at approximately 2-wk intervals from 2010 to 2012. Basal Fe-oxide layers in the three highest amendment categories removed up to 76.1% selenium (in comparison to unamended piles) from leachate by adsorption. Only lysimeters with very thin Fe-oxide layers showed no significant reduction compared with unamended piles. Reproducibility of replicates was within acceptable limits for amended and unamended lysimeters. Results indicate that in situ amendment using Fe-oxide obtained from treatment of mine water can sequester Se by adsorption on surfaces of goethite and possibly also ferrihydrite. This process is demonstrated to substantially reduce dissolved Se in leachate and improve compliance with regulatory discharge limits.

Selenium fractions in organic matter from Se-rich soils and weathered stone coal in selenosis areas of China

A high degree of association between Selenium (Se) and organic matter has been demonstrated in natural environments, but Se fractions and speciation in organic matter is unclear. In this study, a method for quantifying organic matter associated with Se (OM-Se) was developed to investigate Se fractions in organic matter in Se-rich soils and weathered stone coal from Enshi, China, where Se poisoning of humans and livestock has been documented. Initially, Se was extracted using water and a phosphate buffer. Subsequently, OM-Se was extracted using NaOH, and then speciated into Se associated with fulvic acids (FA-Se) and humic acids (HA-Se). Both FA-Se and HA-Se were further speciated into the weakly bound and strongly bound fractions using a customized hydride generation reactor. The results show that FA-Se (1.91-479 mg kg(-1)) is the predominant form of Se in all Se-rich soils and the weathered stone coal samples, accounting for more than 62% of OM-Se (3.07-484 mg kg(-1)). Weakly bound FA-Se (1.33-450 mg kg(-1)) was prevalent in the total FA-Se, while weakly bound HA-Se (0.62-26.2 mg kg(-1)) was variable in the total HA-Se (1.15-32.5 mg kg(-1)). These data indicate that OM-Se could play a significant source and sink role in the biogeochemical cycling of Se in the supergene environment. Weakly bound FA-Se seems to act as a potential source for bioavailable Se, whereas strongly bound HA-Se is a possible OM-Se sink which is not readily transformed into bioavailable Se.

The interstitial location of selenium and arsenic in rocks associated with coal mining using ultrasound extractions and principal component analysis (PCA)

The release of selenium and arsenic from coal mine wastes into main waterways is an environmental cause for concern in the mining industry due to a myriad of subsequent ecotoxicological problems associated with the two metalloids. In a 2002 USEPA study undertaken in a mountaintop removal/valley fill (MTR/VF) mining area in southern West Virginia, measured Se concentrations were higher than the stipulated 5 ng/mL in 66 out of the 213 water samples collected. We studied the chemical composition of forty seven randomly selected pulverized core rock samples collected from depths of 25 ft to 881 ft from MTR/VF sites to determine the amounts of bioaccessible (ultrasound leachable) As and Se concentrations and their tentative locations within the rock matrix. The application of principal component analysis (PCA) to the chemical data, suggested that ultrasound leachable selenium concentrations were associated with 14 Å d-spacing phyllosilicate clays (chlorite, montmorillonite and vermiculite all 2:1 layered clays) whilst ultrasound leachable arsenic concentrations were closely related to the concentration of illite, another 2:1 phyllosilicate clay. Negative correlations between leachable arsenic and selenium with kaolinite a 1:1 layered clay, were also observed. We used the observed negative correlations to rule out the presence of selenium or arsenic in 1:1 kaolinite. Hence mining waste from MTR/VF sites containing substantial amounts of illite and 14 Å d-spacing clays may require to be placed in priority landfills or valley fills.

Removal of mercury from sediment by ultrasound combined with biomass (transgenic Chlamydomonas reinhardtii)

As one of the most pervasive environmental problems, Hg pollution in sediment is particularly difficult to remediate because it cannot be decomposed. The application of ultrasound combined with biomass (transgenic Chlamydomonas reinhardtii (C. reinhardtii), a green alga) for the removal of Hg from model and contaminated sediments (Al(2)O(3), α-HgS, and PACS-2 marine sediment) was investigated in this study. Ultrasound was found to enhance Hg release from Al(2)O(3), α-HgS, and PACS-2 marine sediment into the aqueous phase compared to mechanical shaking. A transgenic C. reinhardtii (2AMT-2) expressing a plasmamembrane-anchored metallothionein polymer effectively recovered Hg(II) released into the aqueous phase by sonication over a broad pH range from 2.0 to 9.0. The results showed that this combined technique of ultrasound and alga biomass (2AMT-2) engineered for enhanced metal recovery was effective to remove Hg from solids and sediments, especially from Al(2)O(3) and α-HgS with no natural organic matter. The results of this study are discussed with respect to the development of in situ remediation techniques for Hg-contaminated sediments.

Fractionation and bioavailability of arsenic in agricultural soils: solvent extraction tests and their relevance in risk assessment

Sequential extraction procedure (SEP) and a physiologically based extraction test (PBET) were performed with the aim to estimate the mobility, bioavailability (for plants and humans) and spatial variation of arsenic in agricultural soils in the Valleys of Arica and Parinacota Region (Northern Chile). For this purpose, 50 topsoil samples with different total arsenic contents in soil (36.2-729 mg kg(-1)) were collected from 10 selected sites in the Valley of Lluta, Azapa and Camarones. The SEP test results showed that arsenic was mainly associated to the least mobile fractions: bound to amorphous and poorly crystalline hydrous oxides of Fe and Al (11.6-44.2%) and well-crystallized hydrous oxides of Fe and Al (24.8-48.9%). Calculated values for arsenic Chronic Daily Intake (CDI), based on the information obtained in the tests of bioaccessibility using PBET (range 1.6-9.6 mg kg(-1)), were in the range of 0.021 to 0.128 μg As kg(-1) d(-1), not exceeding in any case the maximum Reference Dose for Chronic Oral Exposure, RfD = 0.3 μg kg(-1) d(-1), established by USEPA. In general, obtained results, allow us to establish that extraction processes using solvents can be utilized as a source of reliable and useful information for risk assessment of exposure to arsenic from soil, over the direct use of total arsenic contents, which can lead to an overestimation of the toxicity by direct ingestion.

Ultrasound-assisted emulsification-microextraction of fragrance allergens in water

A method based on ultrasound-assisted emulsification-microextraction (USAEME) and gas chromatography-mass spectrometry (GC-MS) has been developed for the analysis of regulated fragrance allergens in water. Extraction conditions such as the type of solvent, extraction temperature, irradiation time, and salting-out effect were optimized using a multivariate approach. Compounds were extracted during 2 min in an acoustically emulsified media formed by 100 μL chloroform and 10 mL sample. The USAEME process provided an efficient and exhaustive extraction (enrichment factor ∼100) and, after centrifugation, the extract was ready for GC analysis. Validation was performed using spiked ultrapure water as well as other most complex matrices such as sewage water. Recoveries between 75% and 110% were generally obtained, and precision was characterized by RSD values <10% in most cases. The limits of detection (LODs) were at the sub-nanogram per millilitre level. The proposed procedure was applied to the determination of allergens in several real samples including tap water, baby bathwater, recreational place water, public washing place water, and sewage water. The presence of some of the target compounds was confirmed in all the samples excluding tap water, demonstrating the ubiquity of this group of cosmetic and personal care products ingredients.