Detecting Micro- and Nanoplastics Released from Food Packaging: Challenges and Analytical Strategies

Nanoplastics Detected in Commercial Sea Salt

People of all ages consume salt every day, but is it really just salt? Plastic nanoparticles [nanoplastics (NPs)] pose an increasing environmental threat and have begun to contaminate everyday salt in consumer goods. Herein, we developed a combined surface enhanced Raman scattering (SERS) and stimulated Raman scattering (SRS) approach that can realize the filtration, enrichment, and detection of NPs in commercial salt. The Au-loaded (50 nm) anodic alumina oxide substrate was used as the SERS substrate to explore the potential types of NP contaminants in salts. SRS was used to conduct imaging and quantify the presence of the NPs. SRS detection was successfully established through standard plastics, and NPs were identified through the match of the hydrocarbon group of the nanoparticles. Simultaneously, the NPs were quantified based on the high spatial resolution and rapid imaging of the SRS imaging platform. NPs in sea salts produced in Asia, Australasia, Europe, and the Atlantic were studied. We estimate that, depending on the location, an average person could be ingesting as many as 6 million NPs per year through the consumption of sea salt alone. The potential health hazards associated with NP ingestion should not be underestimated.

Everything falls apart: How solids degrade and release nanomaterials, composite fragments, and microplastics

To ensure the safe use of materials, one must assess the identity and quantity of exposure. Solid materials, such as plastics, metals, coatings and cements, degrade to some extent during their life cycle, and releases can occur during manufacturing, use and end-of-life. Releases (e.g., what is released, how does release happen, and how much material is released) depend on the composition and internal (nano)structures of the material as well as the applied stresses during the lifecycle. We consider, in some depth, releases from mechanical, weathering and thermal stresses and specifically address the use cases of fused-filament 3D printing, dermal contact, food contact and textile washing. Solid materials can release embedded nanomaterials, composite fragments, or micro- and nanoplastics, as well as volatile organics, ions and dissolved organics. The identity of the release is often a heterogenous mixture and requires adapted strategies for sampling and analysis, with suitable quality control measures. Control materials enhance robustness by enabling comparative testing, but reference materials are not always available as yet. The quantity of releases is typically described by time-dependent rates that are modulated by the nature and intensity of the applied stress, the chemical identity of the polymer or other solid matrix, and the chemical identity and compatibility of embedded engineered nanomaterials (ENMs) or other additives. Standardization of methods and the documentation of metadata, including all the above descriptors of the tested material, applied stresses, sampling and analytics, are identified as important needs to advance the field and to generate robust, comparable assessments. In this regard, there are strong methodological synergies between the study of all solid materials, including the study of micro- and nanoplastics. From an outlook perspective, we review the hazard of the released entities, and show how this informs risk assessment. We also address the transfer of methods to related issues such as tyre wear, advanced materials and advanced manufacturing, biodegradable polymers, and non-solid matrices. As the consideration of released entities will become more routine in industry via lifecycle assessment in Safe-and-Sustainable-by-Design practices, release assessments will require careful design of the study with quality controls, the use of agreed-on test materials and standardized methods where these exist and the adoption of clearly defined data reporting practices that enable data reuse, meta-analyses, and comparative studies.

Regulatory Science Perspective on the Analysis of Microplastics and Nanoplastics in Human Food

Microplastics are increasingly reported, not only in the environment but also in a wide range of food commodities. While studies on microplastics in food abound, the current state of science is limited in its application to regulatory risk assessment by a continued lack of standardized definitions, reference materials, sample collection and preparation procedures, fit-for purpose analytical methods for real-world and environmentally relevant plastic mixtures, and appropriate quality controls. This is particularly the case for nanoplastics. These methodological challenges hinder robust, quantitative exposure assessments of microplastic and nanoplastic mixtures from food consumption. Furthermore, limited toxicological studies on whether microplastics and nanoplastics adversely impact human health are also impeded by methodology challenges. Food safety regulatory agencies must consider both the exposure and the risk of contaminants of emerging concern to ascertain potential harm. Foundational to this effort is access to and application of analytical methods with the capability to quantify and characterize micro- and nanoscale sized polymers in complex food matrices. However, the early stages of method development and application of early stage methods to study the distribution and potential health effects of microplastics and nanoplastics in food have largely been done without consideration of the stringent requirements of methods to inform regulatory activities. We provide regulatory science perspectives on the state of knowledge regarding the occurrence of microplastics and nanoplastics in food and present our general approach for developing, validating, and implementing analytical methods for regulatory purposes.

Unraveling the micro- and nanoplastic predicament: A human-centric insight

Micro- and nanoplastics are vast anthropogenic pollutants in our direct surroundings with a robust environmental stability and a potential for a long-lasting and increasing global circulation. This has raised concerns among the public and policy makers for human health upon exposure to these particles. The micro- and nanoplastic burden on humans is currently under debate, along with criticism on the experimental approaches used in hazard assessment. The present review presents an overview of the human-relevant aspects associated with the current micro-and nanoplastic burden. We focus on environmental circulation and the estimation of exposure quantities to humans, along with a state-of-the-art overview of particle accumulation in over 15 human organs and other specimen. Additionally, data regarding particle characteristics used in toxicity testing was extracted from 91 studies and discussed considering their environmental and human relevance.

Machine learning driven methodology for enhanced nylon microplastic detection and characterization

In recent years, the field of microplastic (MP) research has evolved significantly; however, the lack of a standardized detection methodology has led to incomparability across studies. Addressing this gap, our current study innovates a reliable MP detection system that synergizes sample processing, machine learning, and optical photothermal infrared (O-PTIR) spectroscopy. This approach includes examining high-temperature filtration and alcohol treatment for reducing non-MP particles and utilizing a support vector machine (SVM) classifier focused on key wavenumbers that could discriminate between nylon MPs and non-nylon MPs (1077, 1541, 1635, 1711 cm-1 were selected based on the feature importance of SVM-Full wavenumber model) for enhanced MP identification. The SVM model built from key wavenumbers demonstrates a high accuracy rate of 91.33%. Results show that alcohol treatment is effective in minimizing non-MP particles, while filtration at 70 °C has limited impact. Additionally, this method was applied to assess MPs released from commercial nylon teabags, revealing an average release of 106 particles per teabag. This research integrates machine learning with O-PTIR spectroscopy, paving the way for potential standardization in MP detection methodologies and providing vital insights into their environmental and health implications.

Single-Particle Analysis of the Photodegradation of Submicron Polystyrene Particles Using Infrared Photothermal Heterodyne Imaging

Sunlight irradiation is the predominant process for degrading plastics in the environment, but our current understanding of the degradation of smaller, submicron (<1000 nm) particles is limited due to prior analytical constraints. We used infrared photothermal heterodyne imaging (IR-PHI) to simultaneously analyze the chemical and morphological changes of single polystyrene (PS) particles (∼1000 nm) when exposed to ultraviolet (UV) irradiation (λ = 250-400 nm). Within 6 h of irradiation, infrared bands associated with the backbone of PS decreased, accompanied by a reduction in the particle size. Concurrently, the formation of several spectral features due to photooxidation was attributed to ketones, carboxylic acids, aldehydes, esters, and lactones. Spectral outcomes were used to present an updated reaction scheme for the photodegradation of PS. After 36 h, the average particle size was reduced to 478 ± 158 nm. The rates of size decrease and carbonyl band area increase were -24 ± 3.0 nm h-1 and 2.1 ± 0.6 cm-1 h-1, respectively. Using the size-related rate, we estimated that under peak terrestrial sunlight conditions, it would take less than 500 h for a 1000 nm PS particle to degrade to 1 nm.

Approach to an answer to "How dangerous microplastics are to the human body": A systematic review of the quantification of MPs and simultaneously exposed chemicals

This review aims to facilitate future research on microplastics (MPs) in the environment using systematic and analytical protocols, ultimately contributing to assessment of the risk to human health due to continuous daily exposure to MPs. Despite extensive studies on MP abundance in environment, identification, and treatment, their negative effects on human health remain unknown due to the lack of proof from clinical studies and limited technology on the MP identification. To assess the risk of MPs to human health, the first step is to estimate MP intake via ingestion, inhalation, and dermal contact under standardized exposure conditions in daily life. Furthermore, rather than focusing on the sole MPs, migrating chemicals from plastic products should be quantified and their health risk be assessed concurrently with MP release. The critical factors influencing MP release and simultaneously exposed chemicals (SECs) must be investigated using a standardized identification method. This review summarises release sources, factors, and possible routes of MPs from the environment to the human body, and the quantification methods used in risk assessment. We also discussed the issues encountered in MP release and SEC migration. Consequently, this review provides directions for future MP studies that can answer questions about MP toxicity to human health.

A Hidden Pathway for Human Exposure to Micro- and Nanoplastics-The Mechanical Fragmentation of Plastic Products during Daily Use

In numerous environmental compartments around the world, the existence of micro- and nanoplastics (MNPs) in the environment has been verified. A growing number of studies have looked at the interaction between MNPs and human activities due to the risks they may pose to humans. Exposure pathways are key factors in measuring MNPs risks. However, current research largely ignores the contribution of mechanical fragmentation pathways to MNPs exposure during the daily use of plastic products. Our critical review demonstrated the research gap between MNP fragmentation and risk assessments via a network analysis. The release of fragmented MNPs and their properties were also described at various scales, with emphasis on environmental stressors and mechanical fragmentation. In the scenarios of daily use, plastic products such as food packaging and clothing provide acute pathways of MNPs exposure. The release tendency of those products (up to 102 mg MNPs) are several orders of magnitude higher than MNPs abundances in natural compartments. Despite the limited evidence available, waste recycling, landfill and municipal activities represented long-term pathways for MNPs fragmentation and point sources of MNPs pollution in environmental media. Assessing the health effects of the fragmentation process, unfortunately, is further hampered by the current absence of human exposure impact assessments for secondary MNPs. We proposed that future studies should integrate aging evaluation into risk assessment frameworks and establish early warning signs of MNPs released from plastic products.

Microplastics in food - a critical approach to definition, sample preparation, and characterisation

The ubiquity of microplastics (MPs) is a more and more frequently brought up topic. The fact that such particles are present in food raises particular concern. Information regarding the described contamination is incoherent and difficult to interpret. Problems appear already at the level of the definition of MPs. This paper will discuss ways of explaining the concept of MPs and methods used for its analysis. Isolation of characterised particles is usually performed using filtration, etching and/or density separation. Spectroscopic techniques are commonly applied for analysis, whereas visual evaluation of the particles is possible thanks to microscopic analysis. Basic information about the sample can be obtained by the combination of Fourier Transform Infrared spectroscopy or Raman spectroscopy and microscopy or using the thermal method combined with spectroscopy or chromatography. The unification of the research methodology will allow a credible assessment of the influence of this pollution coming from food on health.

Interaction of Microbes with Microplastics and Nanoplastics in the Agroecosystems-Impact on Antimicrobial Resistance

Microplastics (MPs) and nanoplastics (NPs) are hotspots for the exchange of antimicrobial resistance genes (ARGs) between different bacterial taxa in the environment. Propagation of antimicrobial resistance (AMR) is a global public health issue that needs special attention concerning horizontal gene transfer (HGT) under micro-nano plastics (MNPs) pressure. Interactions between MNPs and microbes, or mere persistence of MNPs in the environment (either water or soil), influence microbial gene expressions, affecting autochthonous microbiomes, their resistomes, and the overall ecosystem. The adsorption of a range of co-contaminants on MNPs leads to the increased interaction of pollutants with microbes resulting in changes in AMR, virulence, toxin production, etc. However, accurately estimating the extent of MNP infestation in agroecosystems remains challenging. The main limitation in estimating the level of MNPs contamination in agroecosystems, surface and subsurface waters, or sediments is the lack of standardized protocols for extraction of MPs and analytical detection methods from complex high organic content matrices. Nonetheless, recent advances in MPs detection from complex matrices with high organic matter content are highly promising. This review aims to provide an overview of relevant information available to date and summarize the already existing knowledge about the mechanisms of MNP-microbe interactions including the different factors with influence on HGT and AMR. In-depth knowledge of the enhanced ARGs propagation in the environment under the influence of MNPs could raise the needed awareness, about future consequences and emergence of multidrug-resistant bacteria.

The release of polylactic acid nanoplastics (PLA-NPLs) from commercial teabags. Obtention, characterization, and hazard effects of true-to-life PLA-NPLs

This study investigates MNPLs release from commercially available teabags and their effects on both undifferentiated monocultures of Caco-2 and HT29 and in the in vitro model of the intestinal Caco-2/HT29 barrier. Teabags were subjected to mechanical and thermodynamic forces simulating the preparation of a cup of tea. The obtained dispersions were characterized using TEM, SEM, DLS, LDV, NTA, and FTIR. Results confirmed that particles were in the nano-range, constituted by polylactic acid (PLA-NPLs), and about one million of PLA-NPLs per teabag were quantified. PLA-NPLs internalization, cytotoxicity, intracellular reactive oxygen species induction, as well as structural and functional changes in the barrier were assessed. Results show that PLA-NPLs present high uptake rates, especially in mucus-secretor cells, and bio-persisted in the tissue after 72 h of exposure. Although no significant cytotoxicity was observed after the exposure to 100 µg/mL PLA-NPLs during 48 h, a slight barrier disruption could be detected at short-time periods. The present work reveals new insights into the safety of polymer-based teabags, the behavior of true-to-life MNPLs in the human body, as well as new questions on how repeated and prolonged exposures could affect the structure and function of the human intestinal epithelium.

Insights into Anthropogenic Micro- and Nanoplastic Accumulation in Drinking Water Sources and Their Potential Effects on Human Health

Anthropogenic microplastics (MPs) and nanoplastics (NPs) are ubiquitous pollutants found in aquatic, food, soil and air environments. Recently, drinking water for human consumption has been considered a significant pathway for ingestion of such plastic pollutants. Most of the analytical methods developed for detection and identification of MPs have been established for particles with sizes > 10 μm, but new analytical approaches are required to identify NPs below 1 μm. This review aims to evaluate the most recent information on the release of MPs and NPs in water sources intended for human consumption, specifically tap water and commercial bottled water. The potential effects on human health of dermal exposure, inhalation, and ingestion of these particles were examined. Emerging technologies used to remove MPs and/or NPs from drinking water sources and their advantages and limitations were also assessed. The main findings showed that the MPs with sizes > 10 μm were completely removed from drinking water treatment plants (DWTPs). The smallest NP identified using pyrolysis-gas chromatography-mass spectrometry (Pyr-GC/MS) had a diameter of 58 nm. Contamination with MPs/NPs can occur during the distribution of tap water to consumers, as well as when opening and closing screw caps of bottled water or when using recycled plastic or glass bottles for drinking water. In conclusion, this comprehensive study emphasizes the importance of a unified approach to detect MPs and NPs in drinking water, as well as raising the awareness of regulators, policymakers and the public about the impact of these pollutants, which pose a human health risk.

Occurrence of microplastics in tap and bottled water, and food packaging: A narrative review on current knowledge

Nowadays, microplastic has been detected in many environmental samples, including aquatic and terrestrial environments. However, few studies recently have addressed their attention to microplastic contamination in different drinking sources and food packages. This review paper has narrated those few findings in brief. Literature showed that different pieces of microplastic fragments, e.g., polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc. are detected in plastic drinking bottle, tap water, and food packaging containers. Microplastic fragmentation may be associated with mechanical stress, UV radiation, low plastic material quality, aging factor, and atmospheric deposition. Besides these, microplastic is a hub of different chemical compounds and can also retain other complex materials from the surroundings. This makes the microplastic contamination even more complicated and difficult to detect them accurately in a single method. Additionally, one of the common practices at the community level is the long-time repeated usage of plastic drinking bottles and food boxes that subsequently cause microplastic leaching and potential health threats to consumers. This narrative study summarizes the current scenario of microplastic contamination from drinking bottles and food containers and emphasizes doing more quality research in this subtle but highly imposed field to understand potential exposure better.

Microplastics in human food chains: Food becoming a threat to health safety

While versatile application of plastics has generated huge benefits in our life, the 'plastic end-of-life' comes with downsides of emerging concern is plastic particles within all parts of environments. Plastics are highly resistant to degradation and sustain in the environment for a prolonged period resulting in easy access of microplastics into human food chain. Microplastic exposure to humans is caused by foods of both animal and plant origin, food additives, drinks, and plastic food packaging. Living organisms can accumulate microplastics in cells and tissues which results in threats of chronic biological effects and potential health hazards for humans including body gastrointestinal disorders, immunity, respiratory problem, cancer, infertility, and alteration in chromosomes. Because of the threat of microplastics on human health, it is essential to ensure food safety as well as control plastic use with strict regulation of proper management. This study aims to enlighten future research into the core component of microplastics, their exposure to human food, prevention to human food chain, and biological reactions in human body. Finally, it is recommended to consider the presence of microplastics in different foods, as most of the existing research mainly focused on sea foods. And it is important to study the mechanism of toxicity with pathways in the human body based on the different types, shapes, and sizes of plastic particles.

Strategies and Challenges of Identifying Nanoplastics in Environment by Surface-Enhanced Raman Spectroscopy

Nanoplastics (<1000 nm) have been evidenced to be universal in a variety of environmental media. They pose a potential cytotoxicity and health risk due to their tiny size, which allows them to easily penetrate biological barriers and enter cells. Here, we briefly review the various prevalent analytical techniques or tools for identifying nanoplastics, and further move to focus on their advantages and disadvantages. Surface-enhanced Raman spectroscopy (SERS) has been implemented for the identification of individual nanoparticles because of its high sensitivity to molecules and ease of rapid characterization. Therefore, we introduce the SERS technique in the following aspects, (1) principles of SERS; (2) strategies and advances in SERS detection of nanoplastics; and (3) applying SERS to real environmental samples. We put our effort into the summarization of efficient SERS substrates that essentially enable the better detection of nanoplastics, and extend to discuss how the reported nanoplastics pretreatment methodologies can bring SERS analysis to practical applications. A further step moving forward is to investigate the problems and challenges of currently applied SERS detection methods and to look at future research needs in nanoplastics detection employing SERS analysis.

Microplastic Contamination of Chicken Meat and Fish through Plastic Cutting Boards

Microplastic contamination was found in fish and chicken bought on the market, in food stores and in chain supermarkets in the Middle East with the contamination ranging from 0.03 ± 0.04 to 1.19 ± 0.72 particles per gram of meat in chicken and from 0.014 ± 0.024 to 2.6 ± 2.8 particles per gram in fish. Only one fish was found to be free of microplastic. The source of the microplastic was established to be the polythene-based plastic cutting board the food was cut on. More microplastic contamination was found in food cut from the bone than in cut fillets when the fillets themselves were prepared on surfaces other than plastic. Washing the fish and chicken before food preparation decreased but did not completely remove the microplastic contamination. The fate of the microplastic in grilled fish was studied. The mechanical properties of typical plastic cutting boards commercially used in the markets were investigated in the form of tensile, hardness, and wear tests. Overall, the plastic cutting boards showed similar wear rates.

Detection and formation mechanisms of secondary nanoplastic released from drinking water bottles

Since nanoplastics are currently considered potentially hazardous to the environment and human health, reliability of studies on nanoplastic exposure becomes crucial. However, analytical challenges limit our understanding of their formation and detection, thus hampering their biological interactions assessment. Here we provide a combined approach to quantitatively and qualitatively detect the release of nanoplastics in water matrix and, in particular, to measure direct exposure of consumers by simulated use of drinking water plastic bottles. We measured that the polyethylene sealing of the bottles released particles with a size distribution ranging from few hundreds nanometers up to about one micron and estimated a mass release in the order of few tenths of nanograms per opening/closing cycle. We observe that mechanical stress alters the physical-chemical characteristics of the generated secondary nanoplastics and degrades the material properties compared to the original bulk source, thus complicating their spectroscopic chemical identification. Our findings demonstrate that understanding material degradation processes is therefore crucial for identifying and quantifying nanoplastics in real samples. Moreover, methods allowing quantitative studies on the release of nanoplastic as a source of exposure are considered essential for proper assessment of their potential health hazards and to promote improvements in consumer products plastic packaging design.

In Situ Fluorescent Illumination of Microplastics in Water Utilizing a Combination of Dye/Surfactant and Quenching Techniques

Although plastics have benefited our lives in terms of cost and convenience, the disposal of end-of-life plastics poses environmental problems, such as microplastics (MPs). Although the separation (e.g., filtration) and staining of MPs with fluorescent dye/solvent are generally accepted steps to observe MPs in an environmental matrix, in this study, an in situ selective fluorescent illumination of the MPs in water was attempted with the aid of surfactant. Nonpolar fluorescent dye in combination with surfactant affords nanometer-sized dye particles in water, which adsorb on MPs and penetrate the polymer matrix for effective staining and stable fluorescent behaviors. The effects of different staining parameters, including different dyes, surfactants, staining temperatures, staining times, dye/surfactant ratios, dye/MP ratios, and MP concentrations in aqueous solutions were investigated to better understand staining conditions. More interestingly, non-adsorbed free dye molecules in the staining solution were almost completely fluorescence-quenched by introducing the quenching agent, aniline, while the fluorescence intensity of the stained MP was maintained. By staining MPs with a dye/surfactant combination and subsequently quenching with aniline, in situ selective fluorescent illumination of the MPs in water was successfully achieved, which may eliminate the tedious separation/filtration procedure of MPs to accomplish the quick detection or monitoring of MPs.

Bioinspired Hydrogels as Platforms for Life-Science Applications: Challenges and Opportunities

Hydrogels, as interconnected networks (polymer mesh; physically, chemically, or dynamic crosslinked networks) incorporating a high amount of water, present structural characteristics similar to soft natural tissue. They enable the diffusion of different molecules (ions, drugs, and grow factors) and have the ability to take over the action of external factors. Their nature provides a wide variety of raw materials and inspiration for functional soft matter obtained by complex mechanisms and hierarchical self-assembly. Over the last decade, many studies focused on developing innovative and high-performance materials, with new or improved functions, by mimicking biological structures at different length scales. Hydrogels with natural or synthetic origin can be engineered as bulk materials, micro- or nanoparticles, patches, membranes, supramolecular pathways, bio-inks, etc. The specific features of hydrogels make them suitable for a wide variety of applications, including tissue engineering scaffolds (repair/regeneration), wound healing, drug delivery carriers, bio-inks, soft robotics, sensors, actuators, catalysis, food safety, and hygiene products. This review is focused on recent advances in the field of bioinspired hydrogels that can serve as platforms for life-science applications. A brief outlook on the actual trends and future directions is also presented.