Recent Advances in Spectroscopic Techniques for the Analysis of Microplastics in Food

Reducing microplastics in tea infusions released from filter bags by pre-washing method: Quantitative evidences based on Raman imaging and Py-GC/MS

Microplastics released from plastic-based filter bags during tea brewing have attracted widespread attention. Laser confocal micro-Raman and direct classical least squares were used to identify and estimate micron-sized microplastics. Characteristic peaks from pyrolysis-gas chromatography/mass spectrometry of polyethylene terephthalate, polypropylene, and nylon 6 were selected to construct curves for quantification submicron-sized microplastics. The results showed that microplastics released from tea bags in the tea infusions ranged from 80 to 1288 pieces (micron-sized) and 0 to 63.755 μg (submicron-sized) per filter bag. Nylon 6 woven tea bags released far fewer microplastics than nonwoven filter bags. In particular, a simple strategy of three pre-washes with room temperature water significantly reduced microplastic residues with removal rates of 76 %-94 % (micron-sized) and 80 %-87 % (submicron-sized), respectively. The developed assay can be used for the quantitative evaluation of microplastics in tea infusions, and the pre-washing reduced the risk of human exposure to microplastics during tea consumption.

Ionic Liquid-Assisted Thermal Evaporation of Bimetallic Ag-Au Nanoparticle Films as a Highly Reproducible SERS Substrate for Sensitive Nanoplastic Detection in Complex Environments

Nanoplastic particles are emerging as an important class of environmental pollutants in the atmosphere that have adverse effects on our ecosystems and human health. While many methods have been developed to quantitatively detect nanoplastics; however, sensitive detection at low concentrations in a complex environment remains elusive. Herein, we demonstrate a greener method to fabricate a surface-enhanced Raman spectroscopy (SERS) substrate consisting of self-assembled plasmonic Ag-Au bimetallic nanoparticle (NP) films for quantitative SERS detection of nanoplastics in complex media. The self-assembly of Ag-Au bimetallic NPs was achieved through thermal evaporation onto a vapor-phase compatible ionic liquid based on deep eutectic solvent over the growth substrate. The finite-difference time-domain simulation revealed that the localized field enhancement is strong in the gaps, which generate uniform SERS "hotspots" in the obtained substrate. Benefiting from highly accessible SERS "hotspots" at the gaps, the SERS substrate exhibits excellent sensitivity for detecting crystal violet with a limit of detection (LOD) as low as 10-14 M and excellent reproducibility (RSD of 5.8%). The SERS substrate is capable of detecting PET nanoplastics with LOD as low as 1 μg/mL and about 100 μg/mL in real samples such as tap water, lake water, diluted milk, and wine. Moreover, we also validated the feasibility of the designed SERS substrate for the practical detection of PET nanoplastics collected from commercial drinking water bottles, and it showed great potential applications for sensitive detection in actual environments.

Characterization of microplastics in skim-milk powders

The diffusion of microplastics in the food supply chain is prompting public concern as their impact on human health is still largely unknown. The aim of this study was to qualitatively and quantitatively characterize microplastics in skim-milk powder samples (n = 16) from different European countries (n = 8) through Fourier-transform infrared micro-spectroscopy in attenuated total reflectance mode analysis. The present study highlights that the use of hot alkaline digestion has enabled the efficacious identification of microplastics in skim-milk powders used for cheese-making across European countries. The adopted protocol allowed detection of 29 different types of polymeric matrices for a total of 536 plastic particles. The most abundant microplastics were polypropylene, polyethylene, polystyrene, and polyethylene terephthalate. Microplastics were found in skim-milk powders in 3 different shapes (fiber, sphere, and irregular fragments) and 6 different colors (black, blue, brown, fuchsia, green, and gray). Results demonstrate the presence of microplastics in all skim-milk powder samples, suggesting a general contamination. Results of the present study will help to evaluate the impact of microplastics intake on human health.

Effect of microplastics used in agronomic practices on agricultural soil properties and plant functions: Potential contribution to the circular economy of rural areas

The extensive use of plastic materials and their improper disposal results in high amounts of plastic waste in the environment. Aging of plastics leads to their breakdown into smaller particles, such as microplastics (MPs) and nanoplastics. This research investigates plastics used in agricultural practices as they contribute to MP pollution in agricultural soils. The distribution and characteristics of MPs in agricultural soils were evaluated. In addition, the effect of MPs on soil properties, the relationship between MPs and metals in soil, the effect of MPs on the fate of pesticides in agricultural soils and the influence of MPs on plant growth were analysed, discussing legume, cereal and vegetable crops. Finally, a brief description of the main methods of chemical analysis and identification of MPs is presented. This study will contribute to a better understanding of MPs in agricultural soils and their effect on the soil-plant system. The changes induced by MPs in soil parameters can lead to potential benefits as it is possible to increase the availability of micronutrients and reduce plant uptake of toxic elements. Furthermore, although plastic pollution remains an emerging threat to soil ecosystems, their presence may result in benefits to agricultural soils, highlighting the principles of the circular economy.

Quantitative Determination of Poly(methyl Methacrylate) Micro/Nanoplastics by Cooling-Assisted Solid-Phase Microextraction Coupled to Gas Chromatography-Mass Spectrometry: Theoretical and Experimental Insights

Determinations of micro/nanoplastics (MNPs) in environmental samples are essential to assess the extent of their presence in the environment and their potential impact on ecosystems and human health. With the aim to provide a sensitive method with simplified pretreatment steps, cooling-assisted solid-phase microextraction (CA-SPME) coupled to gas chromatography-mass spectrometry (GC-MS) is proposed as a new approach to quantify mass concentrations of MNPs in water and soil samples. The herein proposed CA-SPME method offers the unique advantage of integrating the thermal decomposition of MNPs and enrichment of signature compounds into one step. Poly(methyl methacrylate) (PMMA) was used as a model substance to verify the method performance in this work. Theoretical insights demonstrated that pyrolysis is the rate-determining step during the extraction process and that PMMA is effectively decomposed at 350 °C with an estimated incubation time of 13 min. Eight compounds were identified in the pyrolysis products by CA-SPME-GC-MS with the use of a DVB/CAR/PDMS coating, wherein methyl methacrylate was considered as the best indicator and dimethyl 2-methylenesuccinate was selected as the confirmation compound. Under the optimized conditions, the proposed method exhibited wide linearity (0.5-2000 μg for water and 5-1000 μg for soil) and high sensitivity, with limits of detection of 0.014 and 0.28 μg for water and soil, respectively. Finally, the proposed method was successfully applied for determinations of PMMA MNPs in real water and soil samples with satisfactory recoveries attained. The method only required the employment of a filter membrane for water analysis, while soil samples were analyzed directly without any pretreatment. The solvent-free approach, straightforward operation, and high sensitivity of the proposed method show great potential for the analysis of MNPs in different environmental samples.

Migration testing of microplastics from selected water and food containers by Raman microscopy

The migration of microplastics (MPs) from plastic food packaging has received increasing attention. Despite numerous studies quantifying MPs released from food packaging, there is lack of systematic investigation on migration of MPs from food packages under US Food and Drug Administration (FDA)'s guidance for food contact substances. Herein, we aimed to determine the quantity and size distribution of MPs migrating from water and food plastic containers following US Food and Drug Administration (FDA)'s guidance using Raman microscopy. Six commonly used water and food containers made of polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS) were treated using distilled water and food stimulants (10% and 50% ethanol) under various conditions. A range of 23,702 to 490,330 particles per liter MPs with 77%- 92% smaller than 5 µm were detected, in which the PP food container exhibited the highest release of MPs when incubated with 50% ethanol at 130 °C for 15 min (equivalent to heating fatty food in a microwave). The temperature and food types were key attributes for elevating MP migration in general. Further comparison observed direct microwave (534,109 particles per liter) heating led to a significantly higher release of MPs compared to the FDA-suggested method (155,572 particles per liter). Part of MPs (12-63%) failed to be identified by Raman microscopy due to small particle size. Our estimation suggests that individuals might inhale up to 4511 MPs per kg per day. This research offers vital insights into MP migration from food and water containers, aiding in the development of relevant guidelines and facilitating MPs' risk assessment and management.

It matters how we measure - Quantification of microplastics in drinking water by μFTIR and μRaman

The water treatment for microplastics (MP) at a Danish groundwater-based waterworks was assessed by Fourier-Transform IR micro-spectroscopy (μFTIR) (nominal size limit 6.6 μm) and compared to results from Raman micro-spectroscopy (μRaman) (nominal size limit 1.0 μm) on the same sample set. The MP abundance at the waterworks' inlet and outlet was quantified as MP counts per cubic metre (N/m3) and estimated MP mass per cubic metre (μg/m3). The waterworks' MP removal efficiency was found to be higher when analysing by μFTIR (counts: 78.14 ± 49.70%, mass: 98.73 ± 11.10%) and less fluctuating than when using μRaman (counts: 43.2%, mass: 75.1%). However, both techniques pointed to a value of ∼80% for the counts' removal efficiency of MPs >6.6 μm. Contrarily to what was shown by μRaman, no systematic leaking of MPs from the plastic elements of the facility could be identified for the μFTIR dataset, either from the counts (inlet 31.86 ± 17.17 N/m3, outlet 4.98 ± 2.09 N/m3) or mass estimate (inlet 76.30 ± 106.30 μg/m3, outlet 2.81 ± 2.78 μg/m3). The estimation of human MP intake from drinking water calculated from the μFTIR data (5 N/(year·capita)) proved to be approximately 332 times lower than that calculated from the μRaman dataset, although in line with previous studies employing μFTIR. By merging the MP length datasets from the two techniques, it could be shown that false negatives became prevalent in the μFTIR dataset already below 50 μm. Further, by fitting the overall frequency of the MP length ranges with a power function, it could be shown that μFTIR missed approximately 95.7% of the extrapolated MP population (1-1865.9 μm). Consequently, relying on only μFTIR may have led to underestimating the MP content of the investigated drinking water, as most of the 1-50 μm MP would have been missed.

Simulation and Characterization of Nanoplastic Dissolution under Different Food Consumption Scenarios

Understanding of the potential leaching of plastic particles, particularly nanoplastics (NPs), from food packaging is crucial in assessing the safety of the packaging materials. Therefore, the objective of this study was to investigate potential exposure risks by simulating the release of NPs from various plastic packaging materials, including polypropylene (PP), general casting polypropylene (GCPP) or metalized casting polypropylene (MCPP), polyethylene (PE), polyethylene terephthalate (PET), and polyphenylene sulfone (PPSU), under corresponding food consumption scenarios. Surface-enhanced Raman scattering (SERS) and scanning electron microscopy (SEM) were utilized to identify and characterize the NPs leached from plastic packaging. The presence of separated NPs was observed in PP groups subjected to 100 °C hot water, GCPP plastic sterilized at a high temperature (121 °C), and PE plastic soaked in 100 °C hot water, exhibited a distorted morphology and susceptibility to aggregation. The findings suggest that the frequent consumption of takeaway food, hot beverages served in disposable paper cups, and foods packaged with GCPP materials may elevate the risk of ingestion of NPs. This reminds us that food packaging can serve as an important avenue for human exposure to NPs, and the results can offer valuable insights for food safety management and the development of food packaging materials.

Prevalence of microplastics in commercially sold soft drinks and human risk assessment

Due to the increasing global plastic production and use in recent years, the amount of microplastic (MP) accumulating in the environment has also increased. This microplastic pollution potential has been documented mostly in studies of the sea or seafood. The presence of microplastics in terrestrial foods has therefore attracted less attention, despite the potential for future major environmental risks. Some of these researches are related to bottled water, tap water, honey, table salt, milk, and soft drinks. However, the presence of microplastics in soft drinks has not yet been evaluated in the European continent, including Türkiye. Hence, the current study focused on the presence and distribution of microplastics in ten soft drink brands in Türkiye since the water utilized in the bottling process of soft drinks originates from different water supply sources. Using FTIR stereoscopy and stereomicroscope examination, MPs were detected in all of these brands. According to the microplastic contamination factor (MPCF) classification, 80% of the soft drink samples indicated a high level of contamination with microplastics. The study's findings showed that each liter of consumed soft drinks exposes people to about nine microplastic particles, which is a moderate dose when compared to exposure levels in earlier research. It has been determined that bottle-production processes and the substrates used for food production may be the main sources of these microplastics. The chemical components of these microplastic polymers were polyamide (PA), polyethylene terephthalate (PET) and polyethylene (PE), and fibers were the dominant shape. Compared to adults, children were subjected to higher microplastic loads. The study's preliminary data on MP contamination of soft drinks may be useful for further evaluating the risks exposure to microplastics poses to human health.

Portable in situ temperature-dependent spectroscopy on a low-cost microfluidic platform integrated with a battery-powered thermofoil heater

A low-cost microfluidic platform integrated with a flexible heater was developed for in situ temperature-dependent spectroscopic measurement at the point of care. After verifying the system by comparing on-chip spectroscopic measurement of methylene blue with the conventional spectroscopy, we demonstrated its applications in temperature-dependent absorption spectroscopy of a model biomolecule, curcumin. The system is portable, battery-powered and requires ultra-low volumes of analytes, which is highly suitable for point-of-care characterization.

Microplastic distribution and migration in soil, water and sediments in Caohai Lake under the different hydrological periods, Southwest China

An increasing number of researchers have focused on microplastics (MPs) pollution in inland freshwater lakes due to its ecotoxicity, while little is known about the effects of hydrological periods on MPs distribution. Therefore, this study aims to investigate MPs distribution, morphological characteristics and physicochemical indices in various environments in dry and wet periods in Caohai Lake. The results exhibited that cultivated soil, water, and sediment in Caohai Lake have been polluted by MPs in dry and wet periods. There were pellets, fragments, film, and fibers of MPs in both dry and wet periods, and MP foam was additionally found in the wet period. MPs with 0 to 0.5 mm possessed the largest proportion in the five environments in dry and wet periods, followed by MPs with 0.5 to 1 mm and 1 to 5 mm. In Caohai Lake, the black, white, green, red, and transparent MPs in dry period, and black, colourful, grey, red and transparent MPs in wet period were found. The developed structural equation model confirmed that MPs in sediment were probably mainly from soil. There are negative effects of the relative abundance of MPs from cultivated soil to lake water in the dry period, whereas the opposite is true in the wet period. Interestingly, the complex and fast water velocity in the estuary in the wet period led to a lower relative abundance of MPs in its sediment in comparison with the dry period. The distribution model of MPs in estuary and lake water in dry and wet periods is not inconsistent. Our results suggest that the related government department should take measures to reduce the MPs pollution in Caohai Lake, especially from the source.

Feasibility of diffuser-incorporated near-infrared trans-reflectance measurement for quantitative detection of microplastics captured in perfluorocarbon

A diffuser-incorporated near-infrared (NIR) trans-reflectance measurement is demonstrated for quantitative detection of polyethylene (PE) particles captured in perfluorohexane (PFH, C₆F₁₄). PFH effectively captures PE particles through its hydrophobicity and absorbs little NIR radiation, recommending it for use in background-free NIR detection of captured PE particles. A reflective metal disk was used to push the captured PE particles in PFH toward the bottom of the vial that contained the sample, and the trans-reflectance measurement was performed by illuminating NIR radiation from the bottom of the vial at 45^o. Reproducibility is limited by the variation in the positions of small PE-particle aggregates at the water/PFH interface and the difficulty in ensuring full NIR sampling (coverage) of large aggregates. An effective way to secure improved reproducibility under these circumstances is illumination of broader and more uniform NIR radiation for measurement. For this purpose, a polytetrafluoroethylene (PTFE) disk was uniquely incorporated as a diffuser for the trans-reflectance measurement. Compared to the measurement with no diffuser, the diffuser-incorporated scheme produced more distinct PE peaks of low-quantity samples (0.1 and 0.2 mg) and enhanced the reproducibility in measurements of all the samples (0.1-4.0 mg of PE). As a result, the correlation between peak intensity and particle quantity was excellent (R²: 0.997), and a limit of detection of 0.07 mg was achieved.

Estimation of contamination level in microplastic-exposed crayfish by laser confocal micro-Raman imaging

Crayfish is one of the most important freshwater aquaculture species in China. The potential risks of crayfish consumption caused by environmental microplastic pollution have attracted much attention. In this study, a total of 72 crayfish samples were exposed to the microplastic concentrations of 1 mg/L, 3 mg/L, and 9 mg/L for 7, 14, and 28 days, and microplastic contamination levels in crayfish were then explored by laser confocal micro-Raman (LCM-Raman) imaging and scanning electron microscope (SEM). LCM-Raman imaging showed better performance in microplastics identification. Besides, the average percentage of the contaminated area in visualized LCM-Raman images was used to quantitatively assess contamination levels. Following 28 days of exposure to 9 mg/L microplastics, microplastic accumulation reached about 13,000 particles per crayfish. The results confirmed that LCM-Raman imaging combined with image processing technology could be used to construct a high-performance analytical strategy for the assessment of microplastic contamination in crayfish.

Placental plastics in young women from general population correlate with reduced foetal growth in IUGR pregnancies

Constant exposure to plastics particulates has raised concerns against human health, particularly when it comes to birth outcomes. The present study explores the first appraisal of plastic particles in fresh human placenta and its association with foetal growth in neonates. Specifically, 43 pregnant women from general population were selected and their placentas were analyzed by digital microscopy and Raman microspectroscopy for microplastics (MPs <5 mm). We used regression analysis to estimate associations between MPs count in placenta and neonatal anthropometric measurements. MPs were found in all (13 out of 13) intrauterine growth restriction (IUGR) pregnancies and their average abundance ranged from 2 to 38 particles per placenta, but were less than limit of detection (LOD) in normal pregnancies except three out of 30 subjects. This study is one of very few that detected MPs in human placenta in which particles <10 μm were the most abundant in both IUGR and normal pregnancies, accounting for up to 64%. Fragments clearly prevailed at normal pregnancies and fragments together with fibers predominated at IUGR placentas. Despite four different polymers forming the MPs being identified, the majority of MPs comprised of PE (polyethylene) and PS (polystyrene). Inverse associations between MPs exposure and birth outcomes were observed in terms of birth weight (r = - 0.82, p < 0.001), length (r = - 0.56, p < 0.001), head circumference (r = - 0.50, p = 0.001), and 1-min Apgar score (r = - 0.75, p < 0.001) among those with IUGR, compared to those that were nominated as normal pregnancies. While it seems plastic particles may affect placental-foetal interrelationship, the pattern of associations between their content in placenta and birth outcomes, however, shows evidence of a nonlinear or nonmonotonic dose response possibly through perturbation of gas and nutrients exchange which is worth future investigation.

Identification and Evaluation of Microplastics from Tea Filter Bags Based on Raman Imaging

Microplastic (MP) contamination is a public issue for the environment and for human health. Plastic-based food filter bags, including polyethylene terephthalate, polypropylene, nylon 6 (NY6), and polyethylene, are widely used for soft drink sub-packaging, increasing the risk of MPs in foods and the environment. Three types of commercially available filter bags, including non-woven and woven bags, were collected, and MPs released after soaking were mapped using Raman imaging combined with chemometrics. Compared with peak area imaging at a single characteristic peak, Raman imaging combined with direct classical least squares calculation was more efficient and reliable for identifying MP features. Up to 94% of the bags released MPs after soaking, and there was no significant correlation with soaking conditions. Most MPs were tiny fragments and particles, and a few were fibrous MPs 620–840 μm in size. Woven NY6 filter bags had the lowest risk of releasing MPs. Source exploration revealed that most MPs originated from fragments and particles adsorbed on the surface of bags and strings. The results of this study are applicable to filter bag risk assessment and provide scientific guidance for regulating MPs in food.