Critical Assessment of Analytical Methods for the Harmonized and Cost-Efficient Analysis of Microplastics

Coverage of microplastic data underreporting and progress toward standardization

The analysis of microplastics in various environmental matrices is becoming more prevalent in almost every region of the world. Microplastics are underreported depending on how they are extracted and analyzed, and their magnitude and impacts are unknown or unstudied. This paper aims to synthesize a concrete assessment of the important factors that underpin microplastics data underreporting. Our analysis revealed that there is considerable evidence to highlight data underreporting on microplastic abundance and characteristics, which stems from a combination of partial evaluation, economic constraints, recovery efficiency of microplastic extraction, filter pore size used for microplastic separation, and the detection limit of the quantification and characterization method. The majority of unreported data fell into the category of significantly smaller-sized microplastic particles (1-300 μm), which are known to be more harmful to the environment and human health. Recommendations toward the improvement of methodologies for improving microplastic data, as well as the critical areas that will drive standardization ahead, are addressed.

Monitoring microplastics in drinking water: An interlaboratory study to inform effective methods for quantifying and characterizing microplastics

California Senate Bill 1422 requires the development of State-approved standardized methods for quantifying and characterizing microplastics in drinking water. Accordingly, we led an interlaboratory microplastic method evaluation study, with 22 participating laboratories from six countries, to evaluate the performance of widely used methods: sample extraction via filtering/sieving, optical microscopy, FTIR spectroscopy, and Raman spectroscopy. Three spiked samples of simulated clean water and a laboratory blank were sent to each laboratory with a prescribed standard operating procedure for particle extraction, quantification, and characterization. The samples contained known amounts of microparticles within four size fractions (1-20 μm, 20-212 μm, 212-500 μm, >500 μm), four polymer types (PE, PS, PVC, and PET), and six colors (clear, white, green, blue, red, and orange). They also included false positives (natural hair, fibers, and shells) that may be mistaken for microplastics. Among laboratories, mean particle recovery using stereomicroscopy was 76% ± 10% (SE). For particles in the three largest size fractions, mean recovery was 92% ± 12% SD. On average, laboratory contamination from blank samples was 91 particles (± 141 SD). FTIR and Raman spectroscopy accurately identified microplastics by polymer type for 95% and 91% of particles analyzed, respectively. Per particle, FTIR spectroscopy required the longest time for analysis (12 min ± 9 SD). Participants demonstrated excellent recovery and chemical identification for particles greater than 50 μm in size, with opportunity for increased accuracy and precision through training and further method refinement. This work has informed methods and QA/QC for microplastics monitoring in drinking water in the State of California.

A Simple Sample Preparation Method to Significantly Improve Fourier Transform Infrared (FT-IR) Spectra of Microplastics

Spectroscopic analysis has become an essential part of the rapidly growing field of microplastic (MP) research. Here, we introduce a simple sample preparation method that dramatically improves results from Fourier transform infrared (FT-IR) analysis of MP and other environmental fibers. Our method provides cost-effective, reliable, high-quality spectra that achieve high-matching scores to polymer libraries. The efficacy of this method is demonstrated with two environmental datasets from Singapore and Phnom Penh that were collected while sampling for atmospheric MPs. The method developed and applied in this study is a simplification of the KBr method, where the analyzed fiber is pressed to a thickness of <10 μm; however, no KBr powder is required. For the combined dataset, 379 non-pressed fibers were analyzed with 193 (51%) returning a search score of ≥80% (chosen minimum search score threshold) and 259 pressed fibers, with 254 (98%) returning a search score of ≥80%. Direct comparisons of fibers before and after pressing show that the highest individual search score, and average search score from multiple single-point measurements, is overwhelmingly higher following our method. Our method immobilizes and improves the surface of the fiber, by creating a wider and uniform area for measurements. For FT-IR operators, this saves considerable time, improves reliability of the analysis, and, importantly, provides reproducibility of the spectra generated.

Microplastic detection and identification by Nile red staining: Towards a semi-automated, cost- and time-effective technique

Microplastic pollution is an issue of concern due to the accumulation rates in the marine environment combined with the limited knowledge about their abundance, distribution and associated environmental impacts. However, surveying and monitoring microplastics in the environment can be time consuming and costly. The development of cost- and time-effective methods is imperative to overcome some of the current critical bottlenecks in microplastic detection and identification, and to advance microplastics research. Here, an innovative approach for microplastic analysis is presented that combines the advantages of high-throughput screening with those of automation. The proposed approach used Red Green Blue (RGB) data extracted from photos of Nile red-fluorescently stained microplastics (50-1200 μm) to train and validate a 'Plastic Detection Model' (PDM) and a 'Polymer Identification Model' (PIM). These two supervised machine learning models predicted with high accuracy the plastic or natural origin of particles (95.8%), and the polymer types of the microplastics (88.1%). The applicability of the PDM and the PIM was demonstrated by successfully using the models to detect (92.7%) and identify (80%) plastic particles in spiked environmental samples that underwent laboratorial processing. The classification models represent a semi-automated, high-throughput and reproducible method to characterize microplastics in a straightforward, cost- and time-effective yet reliable way.

Isolation and Quantification of Polystyrene Nanoplastics in Tissues by Low Pressure Size Exclusion Chromatography

Ecotoxicity investigations of plastic nanoparticles (NPs) should pay more attention to their ability to pass barriers, accumulate, and initiate toxicity in cells. The purpose of this study was to develop a simple size exclusion chromatography (SEC) methodology to measure plastic NPs in biological tissues. A SEC column was prepared using a high-resolution gel for large macromolecules to separate plastic NPs from the protein/lipid pools in tissues. It was necessary to prepare the samples in high salt and non-ionic detergent (0.5 M NaCl and 0.2% Tween-20) and apply 0.2% Tween-20 containing 14 mM NaCl for the elution buffer to limit proteins adsorption to NPs. This methodology was able to resolve 50 and 100 nm polystyrene NPs from the protein/lipid pools in tissue homogenates. The fluorescent dye neutral red (NR) was also used for transparent NPs. Moreover, a sample fractionation step was also proposed for plastic NPs concentration using a salting-out methodology with saturated NaCl (5 M) and acetonitrile. Polystyrene NPs partition in acetonitrile, which were further analyzed by SEC. This methodology was tested in two case studies with clams collected in a high boat traffic (harbor) area and with caged freshwater mussels downstream of a large urban area. Although the present methodology was developed with polystyrene NPs it should be amenable to other plastic polymers that react with the NR fluorescent probe.

A reliable method for the isolation and characterization of microplastics in fish gastrointestinal tracts using an infrared tunable quantum cascade laser system

Societal and environmental concern due to frequent reports of microplastics in fish stomachs raised as they may accumulate along the trophic chain. The request for analysing microplastics in fish stresses two major analytical issues: sample treatment and final characterization. The, so far, workhorse for chemical characterization is infrared spectroscopy which is time-consuming. Here, a quantum cascade laser-based device is used to accelerate the characterization stage. Its novelty poses new challenges for sample processing and particle handling because the unknown particles must be transferred to a reflective slide. In this study, three sample digestion protocols (alkaline-oxidative with H₂O₂, and alkaline-oxidative with NaClO and enzymatic-oxidative) and three different procedures to transfer the filter cake to reflective slides are compared. A simplified enzymatic-oxidative digestion (validated through an interlaboratory exercise) combined with a Syncore® automatic evaporation system and a Laser Direct Infrared Imaging (LDIR) device is proposed first time as a reliable and relatively fast method to treat gastrointestinal tracts of fish. Analytical recoveries were studied using samples of Scomber scombrus and they were ca. 100% for big -i.e., >500 μm- and ca. 90% for medium -i.e., 200-300 μm- particles and ca. 75% for 10 μm thick fibres.

Detection of plastic particles in marine sponges by a combined infrared micro-spectroscopy and pyrolysis-gas chromatography-mass spectrometry approach

Plastic pollution threatens the marine environment, especially due to the adverse effects caused by micro and nano particles interacting with the marine biota. In order to provide reliable data regarding micro and nanoplastic contamination and the related impacts, efficient analytical solutions are needed. We developed a new analysis workflow that uses marine sponges to monitor plastic pollution by characterizing the plastic particles accumulated in their tissue. Specimens of cf. Haliclona (Haplosclerida) were sampled in the Maldivian archipelago. The aim was to optimize the method and to carry out a pilot study of the contamination of the related reef habitat. Particles were isolated, size fractioned, counted and submitted to morphological and chemical characterization. The constituting polymer was identified by infrared microspectroscopy for particles >25 μm, and by pyrolysis coupled with gas chromatography mass spectrometry for those <25 μm. Method recoveries were between 87 and 83% and limits of quantitation (LOQs) were between 6.6 and 30.2 ng/g. Analyses showed that 70% of the sponges presented plastic contamination, with an average of 1.2 particles/g tissue for the 25-150 μm size range, and a total plastic concentration of up to 4.8 μg/g in the 0.2-25 μm size range, with polyolefin being the most represented polymer in both size ranges. Overall, the study demonstrated the reliability of the proposed analytical workflow and of the use of sponges as biosamplers for plastic particles.

Microplastics in Latin America and the Caribbean: A review on current status and perspectives

A literature review was carried out to analyze the current status of microplastic research in Latin America and the Caribbean (LAC). Specifically, this work focused on publications pertaining to (1) occurrence and distribution of microplastics in the environment, including water, sediments, and soil and (2) the environmental impact of MPs, particularly their presence and effects on aquatic and terrestrial organisms. The review included peer-reviewed articles from Scopus, Science Direct, Web of Science, Google Scholar and two iberoamerican open access databases (Redalyc and SciELO). It was found that LAC has only contributed to 5% of the global scientific output on microplastics, and overall the highest contributor within the region was Brazil (52%), followed by Chile (16%) and Mexico (13%). An additional section analyzing the barriers to conducting microplastic research in LAC and their exacerbation by the current COVID-19 pandemic was included to provide additional context behind the relatively low scientific production and improve recommendations encouraging research in this region.

Microplastics in two German wastewater treatment plants: Year-long effluent analysis with FTIR and Py-GC/MS

Microplastics (MP) have been recorded in various environments around the globe. For a better understanding of distribution patterns and for providing a basis for risk assessments, detailed data on MP concentrations and polymer compositions are required. This study investigated the effluents of two German wastewater treatment plants (WWTP) monthly over one year, in order to better understand their temporal input of MP into the receiving river systems. MP item data down to 11 μm were obtained by means of Fourier Transform Infrared (FTIR) spectroscopy under the application of an improved polymer database. Complementary mass data were obtained by pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) (for one WWTP). Both FTIR and Py-GC/MS analysis revealed a homogeneous polymer composition over the year, with a general dominance of polyolefins. Elevated MP item and mass concentrations (maximum: 3 × 10⁴ items m^-3 and 3.8 × 10³ μg m^-3) were observed during winter months and were accompanied by either heavy rainfall (increased discharge and total organic carbon) or elevated turbidity values. These observations emphasize the need for the assessment of background parameters in future MP monitoring studies. By providing monthly data over one year on MP items and masses in WWTP effluents, this study helps enhancing the understanding of temporal MP dynamics and can act as a valuable reference point for future assessments.

The micro-, submicron-, and nanoplastic hunt: A review of detection methods for plastic particles

Plastic particle pollution has been shown to be almost completely ubiquitous within our surrounding environment. This ubiquity in combination with a variety of unique properties (e.g. density, hydrophobicity, surface functionalization, particle shape and size, transition temperatures, and mechanical properties) and the ever-increasing levels of plastic production and use has begun to garner heightened levels of interest within the scientific community. However, as a result of these properties, plastic particles are often reported to be challenging to study in complex (i.e. real) environments. Therefore, this review aims to summarize research generated on multiple facets of the micro- and nanoplastics field; ranging from size and shape definitions to detection and characterization techniques to generating reference particles; in order to provide a more complete understanding of the current strategies for the analysis of plastic particles. This information is then used to provide generalized recommendations for researchers to consider as they attempt to study plastics in analytically complex environments; including method validation using reference particles obtained via the presented creation methods, encouraging efforts towards method standardization through the reporting of all technical details utilized in a study, and providing analytical pathway recommendations depending upon the exact knowledge desired and samples being studied.

A Simple Method for Quantification of Polyhydroxybutyrate and Polylactic Acid Micro-Bioplastics in Soils by Evolved Gas Analysis

Conventional plastics are being slowly replaced by biodegradable ones to prevent plastic pollution. However, in the natural environment, the biodegradation of plastics is usually slow or incomplete due to unfavorable conditions and leads to faster micro-bioplastic formation. Many analytical methods were developed to determine microplastics, but micro-bioplastics are still overlooked. This work presents a simple method for determining poly-3-hydroxybutyrate and polylactic acid micro-bioplastics in soil based on the thermogravimetry–mass spectrometry analysis of low molecular gases evolved during pyrolysis. For the method development, model soils containing different soil organic carbon contents were spiked with micro-bioplastics. Specific gaseous pyrolysis products of the analytes were identified, while the ratio of their amounts appeared to be constant above the level of detection of the suggested method. The constant ratio was explained as a lower soil influence on the evolution of the gaseous product, and it was suggested as an additional identification parameter. The advantages of the presented method are no sample pretreatment, presumably no need for an internal standard, low temperature needed for the transfer of gaseous products and the possibility of using its principles with other, cheaper detectors. The method can find application in the verification of biodegradation tests and in the monitoring of soils after the application of biodegradable products.

Does size matter? Quantification of plastics associated with size fractionated biosolids

This study investigated the occurrence and contribution of plastic particles associated with size fractionated biosolids to the total concentration in biosolids (treated sewage sludge) samples collected from 20 wastewater treatment plants (WWTP) across Australia. This was achieved through sequential size fractionation of biosolids samples to quantify the mass concentration of 7 common plastics across a range of biosolids size fractions, including below 25 μm which has not been assessed in many previous studies. Quantitative analysis was performed by pressurized liquid extraction followed by pyrolysis coupled to gas chromatography - mass spectrometry. Of the total quantified plastics (Σ₇plastics), the greatest proportion (27%) of the total mass were identified in the nominal <25 μm sized biosolids fraction. Polyethylene dominated the polymer mass in every size fraction, even though profiles varied between WWTPs. When comparing the sum of all sites for each sized biosolids fraction, the plurality of the polyethylene, polyvinyl-chloride, polystyrene, polypropylene, polycarbonate, and polyethylene-terephthalate concentrations were associated with the smallest size fraction (<25 μm). We confirm for the first time the presence of plastic particles in biosolids below a size fraction that is not captured by many methods. This is important, because of the potential greater significance of plastics in the low sizes to environmental and human health.

A Rapid Method for Detecting Microplastics Based on Fluorescence Lifetime Imaging Technology (FLIM)

With the increasing use and release of plastic products, microplastics have rapidly accumulated in ecological environments. When microplastics enter the food chain, they cause serious harm to organisms and humans. Microplastics pollution has become a growing concern worldwide; however, there is still no standardized method for rapidly and accurately detecting microplastics. In this work, we used fluorescence lifetime imaging technology to detect four kinds of Nile red-stained and unstained microplastics, and the unique phasor fingerprints of different microplastics were obtained by phasor analysis. Tracing the corresponding pixels of the “fingerprint” in the fluorescence lifetime image allowed for the quick and intuitive identification of different microplastics and their location distributions in a mixed sample. In our work, compared with staining the four microplastics with a fluorescent dye, using the phasor “fingerprint library” formed by the autofluorescence lifetimes of the microplastics was more easily distinguished than microplastics in the mixed samples. The feasibility of this method was further tested by adding three single substances—SiO₂, chitin and decabromodiphenyl ethane (DBDPE), and surface sediments to simulate interferent in the environment, and the results providing potential applications for the identification and analysis of microplastics in complex environments.

Automated analysis of microplastics based on vibrational spectroscopy: are we measuring the same metrics?

The traditional manual analysis of microplastics has been criticized for its labor-intensive, inaccurate identification of small microplastics, and the lack of uniformity. There are already three automated analysis strategies for microplastics based on vibrational spectroscopy: laser direct infrared (LDIR)-based particle analysis, Raman-based particle analysis, and focal plane array-Fourier transform infrared (FPA-FTIR) imaging. We compared their performances in terms of quantification, detection limit, size measurement, and material identification accuracy and speed by analyzing the same standard and environmental samples. LDIR-based particle analysis provides the fastest analysis speed, but potentially questionable material identification and quantification results. The number of particles smaller than 60 μm recognized by LDIR-based particle analysis is much less than that recognized by Raman-based particle analysis. Misidentification could occur due to the narrow tuning range from 1800 to 975 cm^-1 and dispersive artifact distortion of infrared spectra collected in reflection mode. Raman-based particle analysis has a submicrometer detection limit but should be cautiously used in the automated analysis of microplastics in environmental samples because of the strong fluorescence interference. FPA-FTIR imaging provides relatively reliable quantification and material identification for microplastics in environmental samples greater than 20 μm but might provide an imprecise description of the particle shapes. Optical photothermal infrared (O-PTIR) spectroscopy can detect submicron-sized environmental microplastics (0.5-5 μm) intermingled with a substantial amount of biological matrix; the resulting spectra are searchable in infrared databases without the influence of fluorescence interference, but the process would need to be fully automated.

The impact of nano/micro-plastics toxicity on seafood quality and human health: facts and gaps

Contamination of the food and especially marine environment with nano/micro-plastic particles has raised serious concern in recent years. Environmental pollution and the resulting seafood contamination with microplastic (MP) pose a potential threat to consumers. The absorption rate of the MP by fish is generally considered low, although the bioavailability depends on the physical and chemical properties of the consumed MP. The available safety studies are inconclusive, although there is an indication that prolonged exposure to high levels of orally administered MP can be hazardous for consumers. This review details novel findings about the occurrence of MP, along with its physical and chemical properties, in the marine environment and seafood. The effect of processing on the content of MP in the final product is also reviewed. Additionally, recent findings regarding the impact of exposure of MP on human health are discussed. Finally, gaps in current knowledge are underlined, and the possibilities for future research are indicated in the review. There is an urgent need for further research on the absorption and bioavailability of consumed MP and in vivo studies on chronic exposure. Policymakers should also consider the implementation of novel legislation related to MP presence in food.

Evidence of underestimation in microplastic research: A meta-analysis of recovery rate studies

Research on microplastics in the environment is of high interest to many scientists and industries globally. Key to the success of this research is the accuracy, efficiency, reliability, robustness and repeatability of the method(s) used to isolate the microplastics from environmental media. However, with microplastics now being found in new complex media, many multifaceted methods have been developed to research the quantities of these pollutants. To validate new methods, recovery studies can be undertaken by spiking the test medium with known quantities of plastics. The method is typically run as normal, and the recovered plastics counted to give a recovery rate. A current issue in this field is that methods are rarely or poorly validated in this way. Here, we conducted a meta-analysis on 71 recovery rate studies. We found sediment was the most studied medium and saline solutions were the most used reagents. Polyethylene and polystyrene were the most used spiking polymers, which is relevant to the most common polymers in the environment. We found that recovery rates were highest from plant material, whole organisms and excrement (>88%), and lowest from fishmeal, water and soil (58-71%). Moreover, all reagents but water were able to recover more than 80% of the spiked plastics. We believe we are the first (to our knowledge) to provide an overarching indication for the underestimation of microplastics in the environment of approximately 14% across the studies we reviewed, varying with the methods used. Furthermore, we recommend that the quality, use and reporting of recovery rate studies should be improved to aid the standardisation and replication of microplastic research.

Computer-Assisted Analysis of Microplastics in Environmental Samples Based on μFTIR Imaging in Combination with Machine Learning

The problem of automating the data analysis of microplastics following a spectroscopic measurement such as focal plane array (FPA)-based micro-Fourier transform infrared (FTIR), Raman, or QCL is gaining ever more attention. Ease of use of the analysis software, reduction of expert time, analysis speed, and accuracy of the result are key for making the overall process scalable and thus allowing nonresearch laboratories to offer microplastics analysis as a service. Over the recent years, the prevailing approach has been to use spectral library search to automatically identify spectra of the sample. Recent studies, however, showed that this approach is rather limited in certain contexts, which led to developments for making library searches more robust but on the other hand also paved the way for introducing more advanced machine learning approaches. This study describes a model-based machine learning approach based on random decision forests for the analysis of large FPA-μFTIR data sets of environmental samples. The model can distinguish between more than 20 different polymer types and is applicable to complex matrices. The performance of the model under these demanding circumstances is shown based on eight different data sets. Further, a Monte Carlo cross validation has been performed to compute error rates such as sensitivity, specificity, and precision.

Novel methodology for identification and quantification of microplastics in biological samples

Currently, the evidence of the ingestion of microplastics (MPs) by organisms or the accumulation in different environmental compartments has been achieved using several methodological procedures. However, its uses have not been standardized across studies. In this study, we aim to assess and validate a protocol that can be useful for optimizing the identification and quantification procedures of polyethylene microplastics (PE MPs) in biological samples. Initially, considering that numerous studies filter samples previously digested in cellulosic membranes for isolation and analysis of MPs, we evaluated whether washing these membranes with different reagents could contribute to the complete detachment of particles, as well as to their dispersion in the obtained solutions. However, none of the tested reagents (dimethyl sulfoxide, acetone, ethyl alcohol and chloroform), including purified water, was able to completely remove the MPs adhered to the membranes or facilitate their dispersion in the solutions. On the other hand, we observed that the digestion of the membranes by acetonitrile constituted a procedure that prevents the loss of particles due to adherence, in addition to promoting good dispersion of MPs. Subsequently, we evaluated the use of Neubauer chambers for the quantification of MPs, having observed a good recovery rate (>92%) and results with insignificant variation, in PE MPs solutions with different concentrations (0.15; 0.075 and 0.0375 mg/mL). Ultimately, the validation of the proposed procedures took place from the evaluation of the accumulation of PE MPs in Astyanax spp. juveniles, having demonstrated the efficiency and sensitivity of the method proposed for this purpose. Subsequently, our study provides a methodological alternative that can optimize MPs quantifications in biological samples and reduce the generation of biased or unreliable results.

Applicable and cost-efficient microplastic analysis by quantitative 1 H-NMR spectroscopy using benchtop NMR and NoD methods

In continuation of our work on the proof-of-concept that quantitative NMR spectroscopy may be a valuable tool in microplastic (MP) analysis and quantification, we present here investigations using low-field NMR spectrometers and nondeuterated solvents for the analysis of solutions of MP particles in suitable solvents. The use of low-field NMR spectrometers (benchtop NMR) that are considerably more cost-effective in terms of purchase and operating costs compared with high-field NMR spectrometers and the use of nondeuterated solvents (NoD method) leads to an applicable and cost-efficient method for mass-based MP analysis. For benchtop 80-MHz NMR, limits of detection for polyvinylchloride (PVC), polyethylene terephthalate (PET), and polystyrene (PS) are in the same range as if a high-field 500-MHz NMR spectrometer was used for quantification (500 MHz: PET 1 μg/ml, PVC 42 μg/ml, and PS 9 μg/ml; 80 MHz: PET 4 μg/ml, PVC 19 μg/ml, and PS 21 μg/ml) for polymers being dissolved in deuterated solvents. The same is true for the corresponding limits of quantification. Moreover, it is shown for the first time that quantitative determination of the mass concentration of PET, PVC, and PS is also possible using NoD methods by evaluating the integrals of polymer-specific signals relative to an internal or external standard. Detection limits for NoD methods are in a similar range as if deuterated solvents were used (PET 2 μg/ml, PVC 39 μg/ml, and PS 8 μg/ml) using a high-field 500-MHz spectrometer or the 80-MHz spectrometer (PET 5 μg/ml).

Are research methods shaping our understanding of microplastic pollution? A literature review on the seawater and sediment bodies of the Mediterranean Sea

The lack of standardization on the definition and methods in microplastic (MP) research has limited the overall interpretation and intercomparison of published data. This has presented different solutions to assess the presence of these pollutants in the natural environment, bringing the science forward. Microplastics have been reported worldwide across different biological levels and environmental compartments. In the Mediterranean Sea, numerous research efforts have been dedicated to defining the MP pollution levels. The reported MP concentrations are comparable to those found in the convergence zone of ocean gyres, pointing to this basin as one of the world's greatest plastic accumulation areas. However, to what extent are the data produced limited by the methods? Here, we present the results of a systematic review of MP research methods and occurrence targeting the seawater and sediment bodies of the Mediterranean Sea. Based on this dataset, we 1) assess the discrepancies and similarities in the methods, 2) analyze how these differences affect the reported concentrations, and 3) identify the limitations of the data produced for the Mediterranean Sea. Moreover, we reaffirm the pressing need of developing a common reporting terminology, and call for international collaboration between Mediterranean countries, especially with North African countries, to provide a complete picture of the MP pollution status in this basin.

Development and application of a health-based framework for informing regulatory action in relation to exposure of microplastic particles in California drinking water

Microplastics have been documented in drinking water, but their effects on human health from ingestion, or the concentrations at which those effects begin to manifest, are not established. Here, we report on the outcome of a virtual expert workshop conducted between October 2020 and October 2021 in which a comprehensive review of mammalian hazard studies was conducted. A key objective of this assessment was to evaluate the feasibility and confidence in deriving a human health-based threshold value to inform development of the State of California's monitoring and management strategy for microplastics in drinking water. A tiered approach was adopted to evaluate the quality and reliability of studies identified from a review of the peer-reviewed scientific literature. A total of 41 in vitro and 31 in vivo studies using mammals were identified and subjected to a Tier 1 screening and prioritization exercise, which was based on an evaluation of how each of the studies addressed various quality criteria. Prioritized studies were identified largely based on their application and reporting of dose-response relationships. Given that methods for extrapolating between in vitro and in vivo systems are currently lacking, only oral exposure in vivo studies were identified as fit-for-purpose within the context of this workshop. Twelve mammalian toxicity studies were prioritized and subjected to a Tier 2 qualitative evaluation by external experts. Of the 12 studies, 7 report adverse effects on male and female reproductive systems, while 5 reported effects on various other physiological endpoints. It is notable that the majority of studies (83%) subjected to Tier 2 evaluation report results from exposure to a single polymer type (polystyrene spheres), representing a size range of 0.040 to 20 µm. No single study met all desired quality criteria, but collectively toxicological effects with respect to biomarkers of inflammation and oxidative stress represented a consistent trend. While it was possible to derive a conservative screening level to inform monitoring activities, it was not possible to extrapolate a human-health-based threshold value for microplastics, which is largely due to concerns regarding the relative quality and reliability of current data, but also due to the inability to extrapolate data from studies using monodisperse plastic particles, such as polystyrene spheres to an environmentally relevant exposure of microplastics. Nevertheless, a conservative screening level value was used to estimate a volume of drinking water (1000 L) that could be used to support monitoring activities and improve our overall understanding of exposure in California's drinking water. In order to increase confidence in our ability to derive a human-health-based threshold value in the future, several research recommendations are provided, with an emphasis towards strengthening how toxicity studies should be conducted in the future and an improved understanding of human exposure to microplastics, insights critically important to better inform future risk assessments.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s43591-022-00030-6.

Detection and characterization of small-sized microplastics (≥ 5 µm) in milk products

Microplastics (MPs) have gained a high degree of public interest since they are associated with the global release of plastics into the environment. Various studies have confirmed the presence of MPs throughout the food chain. However, information on the ingestion of MPs via the consumption of many commonly consumed foods like dairy products are scarce due to the lack of studies investigating the "contamination" of this food group by MPs. This lack of occurrence data is mainly due to the absence of robust analytical methods capable of reliably quantifying MPs with size < 20 µm in foods. In this work, a new methodology was developed to accurately determine and characterize MPs in milk-based products using micro-Raman (μRaman) technology, entailing combined enzymatic and chemical digestion steps. This is the first time that the presence of relatively low amounts of small-sized MP (≥ 5 µm) have been reported in raw milk collected at farm just after the milking machine and in some processed commercial liquid and powdered cow's milk products.

Deep Learning for Reconstructing Low-Quality FTIR and Raman Spectra─A Case Study in Microplastic Analyses

Herein we report on a deep-learning method for the removal of instrumental noise and unwanted spectral artifacts in Fourier transform infrared (FTIR) or Raman spectra, especially in automated applications in which a large number of spectra have to be acquired within limited time. Automated batch workflows allowing only a few seconds per measurement, without the possibility of manually optimizing measurement parameters, often result in challenging and heterogeneous datasets. A prominent example of this problem is the automated spectroscopic measurement of particles in environmental samples regarding their content of microplastic (MP) particles. Effective spectral identification is hampered by low signal-to-noise ratios and baseline artifacts as, again, spectral post-processing and analysis must be performed in automated measurements, without adjusting specific parameters for each spectrum. We demonstrate the application of a simple autoencoding neural net for reconstruction of complex spectral distortions, such as high levels of noise, baseline bending, interferences, or distorted bands. Once trained on appropriate data, the network is able to remove all unwanted artifacts in a single pass without the need for tuning spectra-specific parameters and with high computational efficiency. Thus, it offers great potential for monitoring applications with a large number of spectra and limited analysis time with availability of representative data from already completed experiments.

μATR-FTIR Spectral Libraries of Plastic Particles (FLOPP and FLOPP-e) for the Analysis of Microplastics

Raman spectral libraries specific to microplastics demonstrated improved spectral matching results when weathered plastics and a variety of particle colors and morphologies were included. Here, we explore if this is true for Fourier transform infrared (FTIR) spectroscopy as well. We present two novel databases specific to microplastics using attenuated total reflection (μATR-FTIR): (1) an FTIR library of plastic particles (FLOPP), containing 186 spectra from common plastic items, across 14 polymer types and (2) an FTIR library of plastic particles sourced from the environment (FLOPP-e), containing 195 spectra across 15 polymer types. Both libraries include particles from a variety of sources, morphologies, and colors. We demonstrate the applicability of these libraries for microplastics research by comparing spectral match results from two microplastic datasets. For this, we use different combinations of libraries including: commercially available reference libraries, an open-access polymer library, and FLOPP and FLOPP-e. Among tests, the greatest mean HQI result was achieved when the greatest number of libraries was included. This work demonstrates that spectral libraries specific to plastic particles found in the environment improve the accuracy of spectral matching and are best used in combination with commercial libraries containing chemical components that are commonly found within plastics and other anthropogenic particles. Multivariate principal component analyses of FLOPP and FLOPP-e spectra confirmed differences among polymer types and higher variation in principal component scores among weathered particles, but no patterns were observed among particle colors or morphologies. These results demonstrate that ATR-FTIR analyses are sensitive to weathering of plastics but not to particle color and morphology.

The occurrence and fate of microplastics in a mesophilic anaerobic digester receiving sewage sludge, grease, and fatty slurries

The mesophilic digester of a wastewater treatment plant serving 790,000 inhabitants was analyzed for incoming and outgoing microplastics (MPs). The annual MP load on the digester was 7326 kg y^-1 and 1.20 × 10¹⁴ N y^-1, while the digested sludge contained 4885 kg y^-1 and 0.85 × 10¹⁴ N y^-1. The corresponding mean reduction of approximately 30% was though within the variability of the analyzed samples, and size distributions and polymer composition before and after the digester could similarly neither confirm nor deny if MPs were lost in the digester. The load on the digester corresponded to a per capita load of 0.025 g capita^-1 day^-1 or 4.14 × 10⁵ N capita^-1 day^-1. In terms of MP numbers, the values were high compared to most previous studies, which most likely was due to differences in analytical methods, where the present study applied FPA-μFTIR hyperspectral imaging with automatized MP recognition in the size range 10-500 μm and ATR-FTIR on all particles in the range 500-5000 μm. The polymer composition was quite diverse, with 15 identified polymer types, of which polyethylene and polyester were the most common in the sludge, while the variation in composition was larger in the grease that came from the plant's grease trap and the fatty slurries which came from grease traps in the drainage area. The load on the digester was finally used to demonstrate how especially the determined mass loads can be used to set upper boundaries for specific sources, for example human excretion.

Moving forward in microplastic research: A Norwegian perspective

Given the increasing attention on the occurrence of microplastics in the environment, and the potential environmental threats they pose, there is a need for researchers to move quickly from basic understanding to applied science that supports decision makers in finding feasible mitigation measures and solutions. At the same time, they must provide sufficient, accurate and clear information to the media, public and other relevant groups (e.g., NGOs). Key requirements include systematic and coordinated research efforts to enable evidence-based decision making and to develop efficient policy measures on all scales (national, regional and global). To achieve this, collaboration between key actors is essential and should include researchers from multiple disciplines, policymakers, authorities, civil and industry organizations, and the public. This further requires clear and informative communication processes, and open and continuous dialogues between all actors. Cross-discipline dialogues between researchers should focus on scientific quality and harmonization, defining and accurately communicating the state of knowledge, and prioritization of topics that are critical for both research and policy, with the common goal to establish and update action plans for holistic benefit. In Norway, cross-sectoral collaboration has been fundamental in supporting the national strategy to address plastic pollution. Researchers, stakeholders and the environmental authorities have come together to exchange knowledge, identify knowledge gaps, and set targeted and feasible measures to tackle one of the most challenging aspects of plastic pollution: microplastic. In this article, we present a Norwegian perspective on the state of knowledge on microplastic research efforts. Norway's involvement in international efforts to combat plastic pollution aims at serving as an example of how key actors can collaborate synergistically to share knowledge, address shortcomings, and outline ways forward to address environmental challenges.

Generation of nanoplastics during the photoageing of low-density polyethylene

In this work, we studied the hydrolytic and photochemical degradation of three low-density polyethylene (LDPE) materials, within the size range of microplastics (MP). The MPs were exposed to mechanical agitation and UV irradiation equivalent to one year of solar UVB + UVA in a stirred photoreactor. Flow cytometry was used to track the formation of small (1-25 μm) MPs by applying Mie's theory to derive the size of MP particles from scattering intensity readings. The calculation was based on a calibration with polystyrene (PS) beads. The results showed that the generation of 1-5 μm MP reached 10⁴-10⁵ MPs in the 1-25 μm range per gram of LDPE. ATR-FTIR and micro-FTIR measurements evidenced the formation of oxygenated moieties, namely hydroxyl, carbonyl, and carbon-oxygen bonds, which increased with irradiation time. We also found evidence of the production of a high number of nanoplastics (<1 μm, NPs). The Dynamic Light Scattering size of secondary NPs was in the hundreds of nm range and might represent up to 10¹⁰ NPs per gram of LDPE. Our results allowed the unambiguous spectroscopic assessment of the generation of NPs from LDPE under conditions simulating environmental exposure to UV irradiation and used flow cytometry for the first-time to track the formation of secondary MPs.

Can the presence of additives result in false positive errors for microplastics in infant feeding bottles?

In recent years, it has been shown that food contact materials can be a potential source of microplastics (MP). Recently, it was reported that more than 16 million polypropylene (PP) particles L^-1 may be released from infant feeding bottles (IFBs) made of PP. In the present study seven different IFBs were investigated by the same method used in the aforementioned publication. In our tests, however, only one IFB showed a level of MP above the limit of detection. More importantly, the MP detected were not of the same material as the bottle and are more likely the result of contamination. In addition, there was a notable difference in released MP particles when the water simulant was filtered for µ-Raman spectroscopy at hot temperature (70°C) instead of filtering it after cooling down to room temperature. Thermal desorption gas chromatography mass spectrometry showed that these differences may be the result of migration and precipitation of additives such as fatty acid esters, often used as release agents in bottle production. These observations, that migrating additives could result in false positive errors for MP, indicate the need for critical consideration when polymers have been subjected to heat.

Raman Spectroscopy for the Analysis of Microplastics in Aquatic Systems

Raman spectroscopy is gaining ground in the analysis of microplastics, especially due to its high spatial resolution that allows the investigation of small plastic particles, whose numeric abundance is argued to be particularly relevant in aquatic systems. Here, we aimed at outlining the status of Raman analysis of microplastics from aquatic systems, highlighting the advantages and the drawbacks of this technique and critically presenting tools and ways to effectively employ this instrument and to improve the spectra obtained and their interpretation. In particular, we summarized procedural information for the use of Raman spectroscopy, and we discussed issues linked to fluorescence interference and the analysis of weathered polymers, which may complicate the interpretation of Raman signatures. In this context, a deep understanding of the different plastic polymers and their Raman peaks and chemical fingerprints is fundamental to avoid misidentification. Therefore, we provided a catalog with detailed information about peaks of most common plastic polymers, and this represents, to the best of our knowledge, the first comprehensive resource that systematically synthesized plastic Raman peaks. Additionally, we focused on plastic additives, which are contained in the majority of plastics. These compounds are often intense in Raman scattering and may partly or completely overlie the actual material types, resulting in the identification of additives alone or misidentification issue. For these reasons, we also presented a new R package "RamanMP" that includes a database of 356 spectra (325 of which are additives). This will help to foster the use of this technique, which is becoming especially relevant in microplastic analysis.

Microplastic analysis in drinking water based on fractionated filtration sampling and Raman microspectroscopy

Microplastics (MP) as emerging persistent pollutants were found in raw and drinking water worldwide. Since different methods were used, there is an urgent need for harmonized protocols for sampling, sample preparation, and analysis. In this study, a holistic and validated analytical workflow for MP analysis in aqueous matrices down to 5 μm is presented. For sampling of several cubic meters of water, an easily portable filter cascade unit with different pore sizes (100-20-5 μm) was developed and successfully applied for the sampling of three processed drinking waters, two tap waters and one groundwater. The size distribution and polymer types of MP were determined using a two-step semi-automated Raman microspectroscopy analysis. For quality control, comprehensive process blanks were considered at all times and a recovery test yielded an overall recovery of 81%. The average concentration of identified MP was 66 ± 76 MP/m³ ranging from 1 MP/m³ to 197 MP/m³. All found concentrations were below the limit of quantitation (LOQ) of 1880 MP/m³. The majority consisted of PE (86% ± 111%) while comparatively low numbers of PET (10% ± 25%), PP (3% ± 6%), and PA (1% ± 4%) were found. 79% of all particles were smaller than 20 μm. In summary, this study presents the application of a workflow for sampling and analysis of MP down to 5 μm with first results of no significant contamination in drinking water and groundwater.

Chemical Analysis of Microplastics and Nanoplastics: Challenges, Advanced Methods, and Perspectives

Microplastics and nanoplastics have become emerging particulate anthropogenic pollutants and rapidly turned into a field of growing scientific and public interest. These tiny plastic particles are found in the environment all around the globe as well as in drinking water and food, raising concerns about their impacts on the environment and human health. To adequately address these issues, reliable information on the ambient concentrations of microplastics and nanoplastics is needed. However, micro- and nanoplastic particles are extremely complex and diverse in terms of their size, shape, density, polymer type, surface properties, etc. While the particle concentrations in different media can vary by up to 10 orders of magnitude, analysis of such complex samples may resemble searching for a needle in a haystack. This highlights the critical importance of appropriate methods for the chemical identification, quantification, and characterization of microplastics and nanoplastics. The present article reviews advanced methods for the representative mass-based and particle-based analysis of microplastics, with a focus on the sensitivity and lower-size limit for detection. The advantages and limitations of the methods, and their complementarity for the comprehensive characterization of microplastics are discussed. A special attention is paid to the approaches for reliable analysis of nanoplastics. Finally, an outlook for establishing harmonized and standardized methods to analyze these challenging contaminants is presented, and perspectives within and beyond this research field are discussed.

Environment and food safety: a novel integrative review

Environment protection and food safety are two critical issues in the world. In this review, a novel approach which integrates statistical study and subjective discussion was adopted to review recent advances on environment and food safety. Firstly, a scientometric-based statistical study was conducted based on 4904 publications collected from the Web of Science Core Collection database. It was found that the research on environment and food safety was growing steadily from 2001 to 2020. Interestingly, the statistical analysis of most-cited papers, titles, abstracts, keywords, and research areas revealed that the research on environment and food safety was diverse and multidisciplinary. In addition to the scientometric study, strategies to protect environment and ensure food safety were critically discussed, followed by a discussion on the emerging research topics, including emerging contaminates (e.g., microplastics), rapid detection of contaminants (e.g., biosensors), and environment friendly food packaging materials (e.g., biodegradable polymers). Finally, current challenges and future research directions were proposed.

Insight into the Interaction Between Microplastics and Microorganisms Based on a Bibliometric and Visualized Analysis

Microplastics are abundant in the environment and have been proven to affect ecosystems and human health. Microorganisms play essential roles in the ecological fate of microplastics pollution, potentially yielding positive and negative effects. This study reviews the research progress of interaction between microplastics and microorganisms based on a bibliometric and visualized analysis. Publication numbers, subjects, countries, institutions, highly cited papers, and keywords were investigated by statistical analysis. VOSviewer software was applied to visualize the co-occurrence and aggregation of national collaboration, subjects, and keywords. Results revealed trends of rapidly increasing publication output that involved multiple disciplines. Contributing countries and their institutions were also identified in this study. Keywords, co-occurrence network visualization, highly cited papers analysis, and knowledge-based mining were all used to give insight into microorganisms or microbiota related to microplastics pollution, and the potential impacts that microplastics biodegradation may cause. In the future, research efforts need to focus on the following areas: microbial degradation processes and mechanisms, assessment of ecological microplastics risks, and potential effects of microplastics bioaccumulation and human exposure. This study provides a holistic view of ongoing microplastics and related microbial research, which may be useful for future microplastics biodegradation studies.

Analysis of microplastics in drinking water and other clean water samples with micro-Raman and micro-infrared spectroscopy: minimum requirements and best practice guidelines

Microplastics are a widespread contaminant found not only in various natural habitats but also in drinking waters. With spectroscopic methods, the polymer type, number, size, and size distribution as well as the shape of microplastic particles in waters can be determined, which is of great relevance to toxicological studies. Methods used in studies so far show a huge diversity regarding experimental setups and often a lack of certain quality assurance aspects. To overcome these problems, this critical review and consensus paper of 12 European analytical laboratories and institutions, dealing with microplastic particle identification and quantification with spectroscopic methods, gives guidance toward harmonized microplastic particle analysis in clean waters. The aims of this paper are to (i) improve the reliability of microplastic analysis, (ii) facilitate and improve the planning of sample preparation and microplastic detection, and (iii) provide a better understanding regarding the evaluation of already existing studies. With these aims, we hope to make an important step toward harmonization of microplastic particle analysis in clean water samples and, thus, allow the comparability of results obtained in different studies by using similar or harmonized methods. Clean water samples, for the purpose of this paper, are considered to comprise all water samples with low matrix content, in particular drinking, tap, and bottled water, but also other water types such as clean freshwater.

Comparison and uncertainty evaluation of two centrifugal separators for microplastic sampling

For commonly applied microplastic sampling approaches based on filtration, high throughput and no size-discrimination are conflicting goals. Therefore, we propose two efficient centrifugal separators for small microplastic sampling, namely the utilization of a hydrocyclone as well as a continuous flow centrifuge. Thorough method optimization was followed by application in an extensive sampling study to investigate the separators' retention behavior for particulate plastics from estuarine waters. Microplastic concentrations ranged from 193 to 2072 particles m^-3. The most dominant identified polymer types were polypropylene, acrylates, polyvinyl chloride and polyethylene. More than 95% of particles were < 100 µm. For the first time in microplastic research, an expanded uncertainty was calculated according to the "Guide to the expression of Uncertainty in Measurement" (JCGM 100:2008). Bottom-up uncertainty evaluation revealed the different sampling methods (~ 44%), sample replicates (~ 26%) and the different detection techniques (~ 16%) as the major sources of uncertainty. Depending on the number of particles detected in the samples, the relative expanded uncertainty (U_rel (k = 2)) ranged from 24% up to > 200% underpinning tremendous importance of sound uncertainty evaluation. Our results indicate that scientist should rethink many "observed patterns" in the literature due to being insignificant and herewith not real.

The global threat from plastic pollution

Plastic pollution accumulating in an area of the environment is considered "poorly reversible" if natural mineralization processes occurring there are slow and engineered remediation solutions are improbable. Should negative outcomes in these areas arise as a consequence of plastic pollution, they will be practically irreversible. Potential impacts from poorly reversible plastic pollution include changes to carbon and nutrient cycles; habitat changes within soils, sediments, and aquatic ecosystems; co-occurring biological impacts on endangered or keystone species; ecotoxicity; and related societal impacts. The rational response to the global threat posed by accumulating and poorly reversible plastic pollution is to rapidly reduce plastic emissions through reductions in consumption of virgin plastic materials, along with internationally coordinated strategies for waste management.

Microplastic fibers - Underestimated threat to aquatic organisms?

Awareness of microplastic pollution in aquatic environments increased strongly during the last decade. Environmental monitoring studies detected microplastic items in every tested water body and found them in various aquatic organisms. Yet, many studies conducted so far, refer to microplastic particles and spheres but not fibers. Microplastic fibers are often not considered due to methodological issues and high contamination risk during sampling and analysis. Only a few of the microplastic exposure studies with aquatic organisms were conducted with microplastic fibers. Recent effect studies demonstrated several negative impacts of microplastic fibers on aquatic organisms, which include tissue damage, reduced growth, and body condition and even mortality. Such negative effects were predominantly observed in taxa at the basis of the food chain. Higher taxa were less heavily affected in direct exposure experiments, but they presumably suffer from negative effects on organisms at lower food chain levels in the wild. Consequently, ongoing and future pollution with microplastic fibers may disturb the functioning of aquatic ecosystems. The present review outlines the current state of knowledge on microplastic fiber abundance in nature, bioavailability, and impacts on aquatic animals. Based on these findings, we recommend inclusion of microplastic fibers in prospective monitoring studies, discuss appropriate methods, and propose to conduct exposure studies with - as well as risk assessments of - these underestimated pollutants.

Car and truck tire wear particles in complex environmental samples - A quantitative comparison with "traditional" microplastic polymer mass loads

Tire wear particles (TWP) are assumed to be the most dominant source of environmental microplastics (MP). Besides rubber components around 60% of tires are additives such as filling material and various chemicals added for vulcanization. The inevitably released TWP in daily traffic are therefore considered a threat to the ecosystem. Nevertheless, published studies on MP mass loads often exclude elastomers. Data concerning composition and concentrations of TWP compared to prominent "traditional" MP polymers, such as polyethylene, polypropylene, poly(ethylene terephthalate) and poly(vinyl chloride), are missing. Identification and quantification of TWP was implemented in an existing pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) method for MP determination. An approach to differentiate between car and truck tire wear and to quantify their respective mass loads is presented. Complex environmental samples such as road dust, fresh water and marine sediments, blue mussels, and marine salts were partly retrospectively analyzed using Py-GC/MS. The results showed ratios of car to truck tire wear up to 16 to 1 and underline the dominance of car compared to truck tire wear mass loads in all analyzed samples. Even though some retrospective data sets might be affected by suboptimal density separation conditions (NaBr, ρ = 1.5 g/cm³), TWP concentrations in road dust clearly exceeded those of "traditional" MP (Ø 5 g TWP vs 0.3 g MP per kg road dust (dry weight). Samples included in this study, which were archived further away from TWP sources such as roads, reflected decreasing TWP concentrations (Ø 24 μg TWP vs. 107 μg MP per kg sediment (dry weight); Ø 126 μg TWP vs. 378 μg MP per kg marine salt) or were no longer present (blue mussels), while "traditional" polymers were still ubiquitously distributed.

Results of WEPAL-QUASIMEME/NORMANs first global interlaboratory study on microplastics reveal urgent need for harmonization

To survey the conformity and quality of results among laboratories for microplastics determination worldwide, an international laboratory intercomparison and development exercise was organized. The 34 participants were requested to determine the polymer type and number or mass of polymer particles in 12 samples, i.e. six samples containing of pre-production pellets, five dissolvable soda tablets containing different (smaller) polymer particles and one blank soda tablet. A novel method for providing the test materials in aluminium strips was used. Thirty laboratories (88%) submitted data using their own method of choice, resulting in a variety of identification and quantification methods (n = 7). The majority of the labs (53-100%) correctly identified the type of polymer in all samples but one. The performance of the laboratories in quantifying and weighing the pellets was very good. The analysis of the number of the particles in the soda tablets varied considerably between laboratories (29-91%). The results of this study highlight the complexity of microplastics analysis and the need for harmonization of both reporting format and methods. Continued development and assessment of the comparability among analytical methods and laboratories are urgently needed to support monitoring programmes, research and decision-making.

Optimising sample preparation for FTIR-based microplastic analysis in wastewater and sludge samples: multiple digestions

The lack of standardised methodologies in microplastic research has been addressed in recent years as it hampers the comparison of results across studies. The quantification of microplastics in the environment is key to the assessment of the potential eco-toxicological impacts that this new category of emerging pollutants could have on terrestrial and aquatic species. Therefore, the need for protocols that are robust, simple and reliable together with their standardisation are of crucial importance. This study has focused on removal of organic matter with Fenton reagent from wastewater and sludge samples. This step of analysis was optimised by implementing a multi-digestion treatment on these samples that have high concentration of complex mixtures of organic matter, which interfere with microplastic enumeration. Moreover, this study targeted the detection of microplastics in the sub-hundred-micron size range due to the potential higher risks associated with smaller-sized particles and the limited data available from previous wastewater research. To show the validity of the method, triplicate samples of raw sewage, final effluent and sludge were independently spiked with two different sizes and types of microplastic polymers. Due to the various analytical stages required for the isolation of microplastics, time is a limiting factor in sample processing. The sequential digestion with Fenton reagent represents an inexpensive and time-efficient procedure for wastewater research providing effective degradation of organic material. These advantages over other currently available methods mean the method is suitable for analysis of large numbers of samples allowing robust monitoring data sets to be generated.

Which particles to select, and if yes, how many? : Subsampling methods for Raman microspectroscopic analysis of very small microplastic

Micro- and nanoplastic contamination is becoming a growing concern for environmental protection and food safety. Therefore, analytical techniques need to produce reliable quantification to ensure proper risk assessment. Raman microspectroscopy (RM) offers identification of single particles, but to ensure that the results are reliable, a certain number of particles has to be analyzed. For larger MP, all particles on the Raman filter can be detected, errors can be quantified, and the minimal sample size can be calculated easily by random sampling. In contrast, very small particles might not all be detected, demanding a window-based analysis of the filter. A bootstrap method is presented to provide an error quantification with confidence intervals from the available window data. In this context, different window selection schemes are evaluated and there is a clear recommendation to employ random (rather than systematically placed) window locations with many small rather than few larger windows. Ultimately, these results are united in a proposed RM measurement algorithm that computes confidence intervals on-the-fly during the analysis and, by checking whether given precision requirements are already met, automatically stops if an appropriate number of particles are identified, thus improving efficiency. To provide quality control in the MP quantification by Raman microspectroscopy, a window subsampling and bootstrap protocol is presented, which can provide confidence intervals that enable the assessment of the reliability of the data. This is brought together with a proposed on-the-fly algorithm that assesses the precision during the measurement and stops at the optimal point.

Microplastic Spectral Classification Needs an Open Source Community: Open Specy to the Rescue!

Microplastic pollution research has suffered from inadequate data and tools for spectral (Raman and infrared) classification. Spectral matching tools often are not accurate for microplastics identification and are cost-prohibitive. Lack of accuracy stems from the diversity of microplastic pollutants, which are not represented in spectral libraries. Here, we propose a viable software solution: Open Specy. Open Specy is on the web (www.openspecy.org) and in an R package. Open Specy is free and allows users to view, process, identify, and share their spectra to a community library. Users can upload and process their spectra using smoothing (Savitzky-Golay filter) and polynomial baseline correction techniques (IModPolyFit). The processed spectrum can be downloaded to be used in other applications or identified using an onboard reference library and correlation-based matching criteria. Open Specy's data sharing and session log features ensure reproducible results. Open Specy houses a growing library of reference spectra, which increasingly represents the diversity of microplastics as a contaminant suite. We compared the functionality and accuracy of Open Specy for microplastic identification to commonly used spectral analysis software. We found that Open Specy was the only open source software and the only software with a community library, and Open Specy had comparable accuracy to popular software (OMNIC Picta and KnowItAll). Future developments will enhance spectral identification accuracy as the reference library and functionality grows through community-contributed spectra and community-developed code. Open Specy can also be used for applications beyond microplastic analysis. Open Specy's source code is open source (CC-BY-4.0, attribution only) (https://github.com/wincowgerDEV/OpenSpecy).

Recommended best practices for collecting, analyzing, and reporting microplastics in environmental media: Lessons learned from comprehensive monitoring of San Francisco Bay

Microplastics are ubiquitous and persistent contaminants in the ocean and a pervasive and preventable threat to the health of marine ecosystems. Microplastics come in a wide variety of shapes, sizes, and plastic types, each with unique physical and chemical properties and toxicological impacts. Understanding the magnitude of the microplastic problem and determining the highest priorities for mitigation require accurate measures of microplastic occurrence in the environment and identification of likely sources. The field of microplastic pollution is in its infancy, and there are not yet widely accepted standards for sample collection, laboratory analyses, quality assurance/quality control (QA/QC), or reporting of microplastics in environmental samples. Based on a comprehensive assessment of microplastics in San Francisco Bay water, sediment, fish, bivalves, stormwater, and wastewater effluent, we developed recommended best practices for collecting, analyzing, and reporting microplastics in environmental media. We recommend factors to consider in microplastic study design, particularly in regard to site selection and sampling methods. We also highlight the need for standard QA/QC practices such as collection of field and laboratory blanks, use of methods beyond microscopy to identify particle composition, and standardized reporting practices, including suggested vocabulary for particle classification.

A novel approach based on multiple fish species and water column compartments in assessing vertical microlitter distribution and composition

The assessment of the distribution and composition of microlitter in the sea is a great challenge. Biological indicators can be an irreplaceable tool since they measure microlitter levels in their environments in a way that is virtually impossible to replicate by direct physical measurements. Furthermore, trends can provide policymakers with statistically robust analysis. We looked into the capacity of multiple fish species to describe the distribution and composition of microlitter vertically across different compartments of the water column. A total of 502 individuals from six selected species (Scomber scombrus, Oblada melanura, Spicara smaris, Boops boops, Merluccius merluccius and Mullus barbatus) were collected on the western side of Sardinia island and allocated to three compartments: surface, mid-water and bottom. The species of the surface exhibited a higher frequency of occurrence (41.89%) of microlitter ingestion, compared to those of the mid-water and bottom (19.60%; 22.58%). A significant difference in the average number of ingested microlitter was found between the surface and the bottom compartment. All the microlitter fragments found were analysed through Fourier Transform Infrared Spectroscopy (FTIR). The comparison of the expected buoyancies of the polymers identified puth faith in the allocation of the species to the respective compartments. Therefore, considering the Marine Strategy Framework Directive objective, this approach could be useful in assessing microlitter distribution and composition vertically across the water column.

Addressing the environmental and health impacts of microplastics requires open collaboration between diverse sectors

Public concern over the environmental and public health impacts of the emerging contaminant class "microplastics" has recently prompted government agencies to consider mitigation efforts. Microplastics do not easily fit within traditional risk-based regulatory frameworks because their persistence and extreme diversity (of size, shape, and chemical properties associated with sorbed chemicals) result in high levels of uncertainty in hazard and exposure estimates. Due to these serious complexities, addressing microplastics' impacts requires open collaboration between scientists, regulators, and policymakers. Here we describe ongoing international mitigation efforts, with California as a case study, and draw lessons from a similarly diverse and environmentally persistent class of emerging contaminants (per- and polyfluoroalkyl substances) that is already disrupting traditional regulatory paradigms, discuss strategies to address challenges associated with developing health-protective regulations and policies related to microplastics, and suggest ways to maximize impacts of research.

Towards the Development of Portable and In Situ Optical Devices for Detection of Micro and Nanoplastics in Water: A Review on the Current Status

The prevalent nature of micro and nanoplastics (MP/NPs) on environmental pollution and health-related issues has led to the development of various methods, usually based on Fourier-transform infrared (FTIR) and Raman spectroscopies, for their detection. Unfortunately, most of the developed techniques are laboratory-based with little focus on in situ detection of MPs. In this review, we aim to give an up-to-date report on the different optical measurement methods that have been exploited in the screening of MPs isolated from their natural environments, such as water. The progress and the potential of portable optical sensors for field studies of MPs are described, including remote sensing methods. We also propose other optical methods to be considered for the development of potential in situ integrated optical devices for continuous detection of MPs and NPs. Integrated optical solutions are especially necessary for the development of robust portable and in situ optical sensors for the quantitative detection and classification of water-based MPs.

Dark-field hyperspectral microscopy for label-free microplastics and nanoplastics detection and identification in vivo: A Caenorhabditis elegans study

Microplastics pollution is a serious ecological threat, severely affecting environments and human health. Tackling microplastics pollution requires an effective methodology to detect minute polymer particles in environmental samples and organisms. Here were report a novel methodology to visualise and identify nanoscale (down to 100 nm) and microscale synthetic commercially-available uniform spherical polymer particles using dark-field hyperspectral microscopy in visible-near infrared (400-1000 nm) wavelength range. Polystyrene particles with diameters between 100 nm-1 μm, polymethacrylate 1 μm and melamine formaldehyde 2 μm microspheres suspended in pure water samples were effectively imaged and chemically identified based on spectral signatures and image-assisted analysis. We succeeded in visualisation and spectral identification of pure and mixed nano- and microplastics in vivo employing optically-transparent Caenorhabditis elegans nematodes as a model to demonstrate the ingestion and tissue distribution of microplastics. As we demonstrate here, dark-field hyperspectral microscopy is capable for differentiating between chemically-different microplastics confined within live invertebrate intestines. Moreover, this optical technology allows for quantitative identification of microplastics ingested by nematodes. We believe that this label-free non-destructive methodology will find numerous applications in environmental nano- and microplastics detection and quantification, investigation of their biodistribution in tissues and organs and nanotoxicology.