Complex and organic-rich solid substrates such as sludge and soil have been shown to be contaminated by microplastics; however, methods for extracting plastic particles have not yet been systemically ...tested or standardized. This study investigated four main protocols for the removal of organic material during analysis of microplastics from complex solid matrices: oxidation using H2O2, Fenton’s reagent, and alkaline digestion with NaOH and KOH. Eight common polymer types were used to assess the influence of reagent exposure on particle integrity. Organic matter removal efficiencies were established for test sludge and soil samples. Fenton’s reagent was identified as the optimum protocol. All other methods showed signs of particle degradation or resulted in an insufficient reduction in organic matter content. A further validation procedure revealed high microplastic extraction efficiencies for particles with different morphologies. This confirmed the suitability of Fenton’s reagent for use in conjunction with density separation for extracting microplastics. This approach affords greater comparability with existing studies that utilize a density-based technique. Recommendations for further method optimization were also identified to improve the recovery of microplastic from complex, organic-rich environmental samples.
Lithium in spodumene is tightly bound by coulombic forces inside the silicon-oxide and aluminum-oxide polyhedron structure. Therefore, the key to the extraction of lithium from spodumene is ...destroying the aluminosilicate structure. Traditionally, the naturally occurring α-spodumene needs to be roasted at 1000 °C to be converted to β-spodumene, and is then decomposed with acid. This method greatly increases energy consumption and environmental pollution. Therefore, developing a new technology to extract lithium from α-spodumene is an urgent matter. Aluminosilicates are common gangue minerals that coexist with bauxite. Diaspore is a type of refractory bauxite, and its decomposition requires a high temperature and alkalinity during the Bayer process. However, under such conditions, aluminosilicate gangues, such as kaolinite and illite, are preferentially decomposed, which leads to a heavy burden caused by the desilication products. The main structures of spodumene and illite contain both tetrahedral SiO4 and octahedral AlO6 geometries, in which the Si4+ in SiO4 is partially replaced by Al3+, which causes the cation Li+ or K+ to enter the mineral structure and maintain the overall charge neutrality. Based on the similarities between spodumene and illite, it is speculated that the Bayer method may be used to treat α-spodumene. Experiments were carried out to verify this possibility. The results indicate that α-spodumene can indeed be directly decomposed by alkali. The addition of CaO, and a higher temperature and alkalinity, had a significant influence on the decomposition reaction. Under optimized conditions, the lithium leaching efficiency was 93%. Sodium phosphate was used to precipitate lithium from an alkaline leach solution considering the low solubility of Li3PO4, and the alkali-containing mother liquor was reused. During ten consecutive cycles in the proposed flowsheet, the α-spodumene decomposition was stable, and resulted in about 90% leaching efficiency of lithium. The closed loop extraction process can significantly reduce energy consumption, and provides a new process for the sustainable development of lithium resources.
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•A green cyclic and efficient method is proposed for recovering Li from α-spodumene.•The process eliminates the traditional high temperature roasting step (α to β).•α-spodumene can be directly decomposed by alkaline leaching with addition of CaO.•Lithium is precipitated from alkaline solution as Li3PO4.•Cyclic leaching of α-spodumene has a stable high decomposition ratio.
Standardisation and validation of methods for microplastics research is essential. A major methodological challenge is the removal of planktonic organisms from marine water samples allowing for the ...identification of microplastics associated to planktonic communities. To improve the reproducibility and accuracy of digestion methods for the removal of planktonic biomass, we compared and modified existing chemical digestion methods. These digestion methods included an acidic digestion using nitric acid, alkaline digestions with potassium hydroxide (alkaline 1 digestion) and sodium hydroxide from drain cleaner (alkaline 2 digestion), an oxidative digestion using sodium dodecyl sulfate with hydrogen peroxide, and an enzymatic digestion using enzyme drain clean pellets. Chemical digestion of three densities of zooplankton communities (high, medium, and low) in the presence of five commonly found environmental microplastic pollutants (polyamide, polyethylene, polyethylene terephthalate, polypropylene, and polystyrene) were performed for each treatment. The chemical treatments were assessed for (i) their digestion efficiency of zooplankton communities by different biomass densities, and (ii) their impact on microplastic particles through the comparison of both chemical (Raman spectroscopy) and physical (length, width, and visual) changes, between the pre-treatment and post-treatment microplastic particles. The alkaline 1, alkaline 2 and oxidative methods demonstrated significantly better digestion efficiency (p < 0.05) than the modified enzymatic and acidic treatments. The acidic, alkaline 1, and alkaline 2, treatments caused the most damages to the microplastic particles. We suggest future studies to implement the oxidative digestion method with sodium dodecyl sulfate and hydrogen peroxide because of its high digestion efficiency, and low damage to microplastic particles. This method is similar to the wet peroxide oxidation digestion method used throughout the literature but can be implemented at a lower cost.
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•Five chemical digestion methods compared for microplastic research standardisation and validation.•Two alkaline methods and one oxidative method had the highest digestion efficiency.•Modified enzymatic treatment was the least effective digestion method.•Acidic digestion resulted in the most damage to microplastic particles.
Accurate analysis of microplastic particles (MPs) in environmental samples requires removal of interferences during sample preparation. Wastewater samples are interference-rich and thus particularly ...challenging, with concentrated sulfuric acid currently deemed impractical as a reagent. Therefore, this study aimed to establish a straightforward, effective, and safe method employing concentrated sulfuric acid and potassium hydroxide to eliminate interferents from effluent samples obtained from wastewater treatment plants (WWTPs). We found that 80 % sulfuric acid at room temperature with a brief contact time of 5 min was viable through a qualitative spot test involving 37 plastics categorized into three types (I, II, and III) based on their polymer structure's oxygen position. A quantitative assessment revealed that treatments involving H2SO4 and KOH (20 %, 24 h, 48 °C), either separately or in combination, had no discernible physical impact on the overall plastics, except for a subtle one for Type III plastics (e.g., nylon and PMMA) known to be labile under harsh pH conditions. This acid/alkaline digestion (AAD) method, incorporating such conditions for H2SO4 and KOH treatments, yielded a high mass removal efficacy (97.8 ± 2.4 %, n = 13) for eliminating natural particle interferents for primary, secondary, and tertiary effluent samples. Furthermore, the AAD method allowed for the determination of MPs in effluents with high surrogate particle recoveries (e.g., 95.1 % for larger than 500 μm size fraction). This method is readily adaptable to create appropriate protocols for different types of environmental matrices.
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•Plastics were categorized into three types by polymer structure's oxygen position.•No visible change for most plastic particles treated with 80 % H2SO4 for 5 min•Plastics barely had no effect on mass, size and FTIR identification by AAD method.•The AAD method possessed very high mass removal efficacy for effluent samples.•Established the H2SO4 (80 %, 5 min, RT) and the KOH (20 %, 24 h, 48 °C) unit processes
The reliable quantification of microplastic contamination in chitinous organisms requires validated methods to remove interfering complex organic and inorganic material. This study trialled KOH, H2O2 ...and HNO3 digestion methods on the digestive tracts of two large decapods (Panulirus cygnus and Portunus armatus) to validate a protocol that facilitates reliable microplastic extraction. KOH digestion provided the best recovery (>95 %) of all polymers (e.g. polyamide, polyethylene, polyethylene terephthalate, polypropylene, polystyrene and polyvinyl chloride), with the lowest impact to their physical morphology and chemical spectra. While HNO3, and HNO3 + H2O2 treatments were more effective at digesting chitin, they destroyed polyamide, and altered several other polymers. High digestion efficiency did not result in high matrix clarification or high microplastic recovery for large decapods. This study emphasises the importance of validating species-specific microplastic extraction methods, whilst proposing additional post-digestion protocols, such as density separation, for complex samples, that can be applied in future research investigating plastic contamination in large decapods.
•KOH provided best recovery of microplastics from digestive tracts of large decapods.•High digestion efficiency (HNO3/H2O2) did not result in high polymer recovery.•Specific method protocols depend on sample composition.•Density separation is needed when digestive tracts contain sediment.
PHAs are a form of cellular storage polymers with diverse structural and material properties, and their biodegradable and renewable nature makes them a potential green alternative to fossil ...fuel-based plastics. PHAs are obtained through extraction via various mechanical, physical and chemical processes after their intracellular synthesis. Most studies have until now focused on pure cultures, while information on mixed microbial cultures (MMC) remains limited. In this study, ultrasonic (US) disruption and alkaline digestion by NaOH were applied individually and in combination to obtain PHAs products from an acclimated MMC using phenol as the carbon source. Various parameters were tested, including ultrasonic sound energy density, NaOH concentration, treatment time and temperature, and biomass density. US alone caused limited cell lysis and resulted in high energy consumption and low efficiency. NaOH of 0.05–0.2 M was more efficient in cell disruption, but led to PHAs degradation under elevated temperature and prolonged treatment. Combining US and NaOH significantly improved the overall process efficiency, which could reduce energy consumption by 2/3rds with only minimal PHAs degradation. The most significant factor was identified to be NaOH dosage and treatment time, with US sound energy density playing a minor role. Under the semi-optimized condition (0.2 M NaOH, 1300 W L-1, 10 min), over 70% recovery and 80% purity were achieved from a 3 g L−1 MMC slurry of approximately 50% PHAs fraction. The material and thermal properties of the products were analyzed, and the polymers obtained from US + NaOH treatments showed comparable or higher molecular weight to previously reported results. The products also exhibited good thermal stability and rheological properties, compared to the commercial standard. In conclusion, the combined US and NaOH method has the potential in real application as an efficient process to obtain high quality PHAs from MMC, and cost-effectiveness can be further optimized.
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•Ultrasonic (US) and alkaline digestion used to recover PHB from a mixed culture.•US disruption had limited effect of cell lysis and high energy consumption.•NaOH digestion was more efficient but led to PHA degradation under high temperature.•US + NaOH showed synergetic effect, reduced treatment time and energy consumption.•US + NaOH can be cost-effective after optimization, showing potential of scaling-up.
The recovery of rare earth elements (REEs) from coal combustion fly ash has recently gained attention as a possible beneficial reuse application that could provide an alternative, low-grade source of ...REEs in an unstable global supply market. To economically recover REEs, an efficient process needs to be developed to remove them from the ash. This study investigated different methods of leaching REEs from fly ash and other coal combustion ashes. Aqueous acid and alkaline leaching were employed on multiple types of coal fly ash samples (representing coals from three major U.S. coal basin sources) with variable leaching parameters that include extractant type (HCl, NaOH), extractant concentration, leachate-to-ash ratio, and addition of CaO during the leaching process. Acid leaching of high calcium-containing fly ashes such as samples derived from Powder River Basin coals had the highest recoveries of REEs (near 100% of total REE contents), while leaching efficiencies were much lower (<40%) for low calcium fly ashes from Appalachian and Illinois Basin coals. If the fly ashes were subjected to aqueous NaOH (to decompose alumunosilicates) and followed with dilute acid to maintain solubility of metal cations, recoveries of the REEs was up to 85% for Appalachian ashes. Overall, these results demonstrate that REEs in the Powder River Basin-based coal fly ashes are more easily leached into acidic solution than the other ashes tested. While the Appalachian Basin-based coal ashes contained the highest total REEs concentrations out of all regional coal ash sources, these ashes required more complex leaching methods that first decompose the aluminosilicate glassy matrix of the ash (e.g. alkaline digestion) prior to acid leaching.
•REEs were efficiently leached by heated HCl in Powder River Basin coal fly ashes.•Acid leaching was not effective for ashes from Appalachian and Illinois Basin coals.•Aqueous NaOH digestion of the coal ashes improved the acid leachability of REEs.
Micro- and nanoplastics unavoidably enter into organisms and humans as a result of widespread exposures through drinking waters, foods, and even inhalation. However, owing to the limited availability ...of quantitative analytical methods, the effect of nanoplastics inside animal bodies is poorly understood. Herein, we report a sensitive and robust method to determine the chemical composition, mass concentration, and size distribution of nanoplastics in biological matrices. This breakthrough is based on a novel procedure including alkaline digestion and protein precipitation to extract nanoplastics from tissues of aquatic animals, followed by quantitative analysis with pyrolysis gas chromatography–mass spectrometry. The optimized procedure exhibited good reproducibility and high sensitivity with the respective detection limits of 0.03 μg/g for polystyrene (PS) nanoplastics and 0.09 μg/g poly(methyl methacrylate) (PMMA) nanoplastics. This method also preserved the original morphology and size of nanoplastics. Furthermore, to demonstrate the feasibility of the proposed method, 14 species of aquatic animals were collected, and PS nanoplastics in a concentration range of 0.093–0.785 μg/g were detected in three of these animals. Recovery rates of 73.0–89.1% were further obtained for PS and PMMA nanospheres when they were spiked into the tissues of Zebra snail and Corbicula fluminea at levels of 1.84–2.12 μg/g. Consequently, this method provides a powerful tool for tracking nanoplastics in animals.
Potassium hydroxide (KOH) digestion protocols are currently applied to separate microplastics from biological samples, allowing efficient digestion with minor degradation of polymers in a time- and ...cost-effective way. For biota samples with high-fat content, KOH reacts with triglycerides generating an overlying soap layer, making difficult the digestion and solubilization and subsequent microplastics extraction. Here we studied the addition of Tween-20 in different concentrations to evaluate the effect on the soap layer of post-digested samples. Addition of 10 % of Tween-20 presented higher flow rate during filtration, being set as optimal value. Incorporation of Tween-20 in the extraction procedure increased recovery rates of LDPE, PC and PET and appears to have a protective effect on PC and PET degradation. Tween-20 did not interfere in FTIR spectrum of polymers available in the marine environment. Being low-toxic, makes addition of Tween-20 a simple and economical way to optimize KOH digestion protocols for microplastics extraction.
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•KOH protocol was optimized to extract microplastics from GITs of fat fish species•Saponification of high-fat content samples was avoided, decreasing processing time•Recovery rates of LDPE, PC and PET polymers were increased•Tween-20 had a “protective effect” on the degradation of PC and PET polymers
Rapid industrialization has resulted in a progressive increase in human exposure to hazardous chemicals. The present work develops and validates a new method to determinate 18 endocrine disrupting ...chemicals (EDCs) in human nail samples. In contrast to other common biological samples, nail sampling is non-invasive and since they take several months to grow out, they are well suited for measuring and reflecting the cumulative exposure to harmful substances in the long term. A digestion of samples with a 0.04 M solution of sodium hydroxide is carried out followed by ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS), working in multiple-reaction-monitoring (MRM) mode. The compounds were separated in 8 min. Multivariate optimization strategies were used for the optimization of the parameters that affects the digestion procedure. The validation was developed using a matrix-matched calibration and a recovery assay with spiked samples. The limits of detection and quantification ranged from 0.3 to 1.2 ng g−1 and from 1 to 5 ng g−1, respectively. Recovery rates for spiked samples were between 88% and 113% and the relative standard deviation (% RSD) was lower than 12.7% for all studied EDCs. The method was applied for the analysis of these compounds in human nail samples from volunteers. All samples tested positive for several of the analyzed EDCs.
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•The determination of 18 endocrine disruptors (EDs) in human nail samples is proposed.•The method involves an alkaline digestion of nails prior to UHPLC-MS/MS analysis.•Sample treatment is optimized using a multivariate optimization strategy.•Most EDs have been found in human nail samples at important concentrations.•The method is an effective tool to determine general exposure to EDs of humans.
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