Sampling and Quality Assurance and Quality Control: A Guide for Scientists Investigating the Occurrence of Microplastics Across Matrices

Microplastics in sea surface waters around Scotland

This is the first regional, multi-annual assessment of floating microplastics in Scotland's seas. Sea surface samples were collected from 2014 to 2020, using a catamaran swimmer body/neuston net trawl and evaluated for the presence of microplastics. Microplastics were present in the surface waters of all Scottish Marine Regions (SMR) and Offshore Marine Regions (OMR) though almost 35% of sample sites contained no microplastics. Concentrations ranged from 0 to 91,128 microplastics km^-2 sea surface. Potential hotspots were identified in the Clyde (0-77,168 microplastics km^-2), Forth & Tay (0-83,729 microplastics km^-2) and the Solway (607-91,128 microplastics km^-2). Fragmented plastics accounted for almost 50% of the microplastics recovered and this may suggest that the microplastics in Scotland's seas are predominantly from the breakdown of larger items. Due to the variable geographic and temporal extents of the data it was not possible to carry out a trend assessment.

Plastic microfibre pollution: how important is clothes' laundering?

Plastic microfibre pollution produced by domestic and commercial laundering of synthetic textiles has recently been incriminated in the press and the scientific literature as the main source (up to 90%) of primary microplastics in the oceans. Polyethylene terephthalate (PET) is the most common microfibre encountered. This review aims to provide updated information on worldwide plastic microfibre pollution caused by textile laundering and some possibilities for its control. Release of microfibres during domestic washing and tumble drying, their fate in wastewater treatment plants (WWTPs) and the oceans, and their environmental effects on the aquatic biota are discussed, as well as potential control methods at the levels of textile modification and laundry procedures. Environmental effects on aquatic biota are important; as a result of their small size and length-to-diameter ratio, microfibers are more effectively incorporated by organisms than other plastic particle groups. Simulation laundering studies may be useful in the development of a Standard Test Method and modification of WWTPs may reduce microfibre release into aquatic systems. However, improvements will be necessary in textile design and appliance design, and recommendations should be made to consumers about reducing their personal impact on the environment through their laundering choices, which can include appliances, fabric care products and washing conditions. Official regulation, such as that introduced recently by the French government, may be necessary to reduce plastic microfibre release from clothes' laundering.

Interlaboratory comparison of microplastic extraction methods from marine biota tissues: A harmonization exercise of the Plastic Busters MPAs project

In the framework of the Plastic Busters MPAs project, a harmonization exercise on two methods of microplastic extraction from biological samples i.e. 15% H₂O₂ digestion and 10% KOH digestion was carried out. The two methods were tested in four laboratories on fish gastrointestinal tracts and mussel tissues spiked with polyethylene, polypropylene and polyethylene terephthalate. The recovery percentage of microplastics for each method, species and polymer tested were overall similar among laboratories, and interlaboratory coefficient of variation was less than 11% for the majority of samples. Microplastic recovery rates for the two methods were similar for each sample tested, but overall mean interlaboratory recovery rate using KOH (96.67%) was higher than H₂O₂ (88.75%)_. Results validate the use of both methods for extracting microplastics from biota tissues. However, when comparing the two methods in terms of microplastic recovery rate, time consumed, technical difficulties and cost, digestion with 10% KOH is considered optimal.

Sampling and processing methods of microplastics in river sediments - A review

Microplastics (MP) in marine environments attract widespread attention due to their small particle size and potential hazardous impacts on aquatic and terrestrial ecosystems. Compared to marine sediments, knowledge about the occurrence of MP in freshwater sediments, especially in river sediments, is limited. Although MP concentrations in sediments and soils have been reported in a considerable number of studies, no standardized method is available for sampling and sample processing. Thus, a comparison of results is hardly possible. The present study reviews over 47 articles to evaluate reports of MP in river sediments and current sampling and processing techniques by highlighting various techniques, equipment and approaches for implementing quality assurance and quality control procedures. The authors emphasize that MP quantification techniques could lead to overestimation or underestimation depending on how sampling and sample processing is conducted. Standardization and harmonization of these techniques are crucial to underpin monitoring decisions aimed at safeguarding the ecological integrity of freshwater environments.

An audit of microplastic abundance throughout three Australian wastewater treatment plants

Wastewater treatment plants (WWTPs) have been identified as an important pathway of microplastics to the environment. Most studies have focused on wastewater effluent, but generally only a small fraction of microplastics entering WWTPs are present in treated effluent. Instead, the majority of microplastics are expected to be retained in the sludge. To our knowledge, there is limited information on microplastics in sludge/biosolids from Australian WWTPs, despite 75% of biosolids produced in Australia being used for agriculture. This study evaluated the abundance of microplastics throughout the treatment trains of three WWTPs in Australia. The fate of microplastics >25 μm during treatment and their release to the environment was evaluated using an audit approach. The highest microplastic concentrations were detected in the influent, with fibres the dominant form of microplastic found. The screening and grit removal process preceding primary treatment removed 69-79% of microplastics, with these microplastics transported to landfill. Only 0.2-1.8% of the total microplastics in the influent were present in the final effluent, while 8-16% were retained in biosolids. This equates to between 22.1 × 10⁶ to 133 × 10⁶ microplastic particles per day released in effluent, between 864 × 10⁶ to 1020 × 10⁶ microplastic particles per day in biosolids, and between 4100 × 10⁶ to 9100 × 10⁶ microplastic particles per day transported to landfill. This study shows for the first time that most microplastics are retained during the initial screening and grit removal process with the load of microplastics going to landfill an order of magnitude greater than that in biosolids. Landfills may thus be an important sink (and potential future source) of microplastics from wastewater.

Plackett Burman design for microplastics quantification in marine sediments

Microplastics are gaining worldwide attention due to their omnipresence. The marine environment is one of the most affected systems; especially the sediment compartment. Microplastic separation from the sediment matrix is the first step to evaluate its abundance and availability. Nevertheless, a lack of consistency in extraction protocols is a fact. This paper describes the optimization of the microplastic extraction procedure from marine sediments. The Plackett-Burman saturated factorial design was used to identify the significant factors and to select optimum working conditions. With this purpose, the following variables were studied: the number of extractions; the amount of sediment; the settling time; the density separation solution volume; the agitation time and the suitability of using wet or freeze-dried sediment. The Plackett-Burman design has revealed that the most statistically significant variables were sediment mass and agitation time. The optimized method was applied for two marine sediments collected in the Mar Menor Lagoon.

Toward a unified framework for investigating micro(nano)plastics in packaged beverages intended for human consumption

The continuously increasing presence of micro- and nanoplastics contamination in numerous food products for human consumption is threatening and their potential health effects towards humans remain uncertain. At present, investigations on packaged beverages (e.g. bottled drinking water, beer, milk and refreshments) have received scientific attention and represent an important part of microplastic research as humans are orally exposed to these anthropogenic contaminants every day. Rapid and effective detection methods are important to quantify micro- and nanoplastic particles with a great accuracy as well as to identify their sources and characteristics. A number of methods are currently in use to assess microplastics in packaged beverages; however, the great variations in methods and data acquisition render difficulties when comparing the results and developing the protocols. Based on the challenges, this paper aims to provide a comprehensive understanding of emerging technological approaches, points out the current limitations from sample preparation to quantification and present recommendations. From the results of our analysis, we postulate an example framework that can be applied to different types of drinking products for investigating micro- and nanoplastics. Overall, this review will serve as a first step towards harmonization of micro- and nanoplastic monitoring efforts and a point of reference to help direct future researches focusing on drinking products intended for human consumption.

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

Microplastics are of major concerns for society and is currently in the focus of legislators and administrations. A small number of measures to reduce or remove primary sources of microplastics to the environment are currently coming into effect. At the moment, they have not yet tackled important topics such as food safety. However, recent developments such as the 2018 bill in California are requesting the analysis of microplastics in drinking water by standardized operational protocols. Administrations and analytical labs are facing an emerging field of methods for sampling, extraction, and analysis of microplastics, which complicate the establishment of standardized operational protocols. In this review, the state of the currently applied identification and quantification tools for microplastics are evaluated providing a harmonized guideline for future standardized operational protocols to cover these types of bills. The main focus is on the naked eye detection, general optical microscopy, the application of dye staining, flow cytometry, Fourier transform infrared spectroscopy (FT-Ir) and microscopy, Raman spectroscopy and microscopy, thermal degradation by pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) as well as thermo-extraction and desorption gas chromatography-mass spectrometry (TED-GC-MS). Additional techniques are highlighted as well as the combined application of the analytical techniques suggested. An outlook is given on the emerging aspect of nanoplastic analysis. In all cases, the methods were screened for limitations, field work abilities and, if possible, estimated costs and summarized into a recommendation for a workflow covering the demands of society, legislation, and administration in cost efficient but still detailed manner.

Toward the Systematic Identification of Microplastics in the Environment: Evaluation of a New Independent Software Tool (siMPle) for Spectroscopic Analysis

Microplastics (MP) are ubiquitous within the environment, but the approaches to analysis of this contaminant are currently quite diverse, with a number of analytical methods available. The comparability of results is hindered as even for a single analytical method such as Fourier transform infrared spectroscopy (FT-IR) the different instruments currently available do not allow a harmonized analysis. To overcome this limitation, a new free of charge software tool, allowing the systematic identification of MP in the environment (siMPle) was developed. This software tool allows a rapid and harmonized analysis of MP across FT-IR systems from different manufacturers (Bruker Hyperion 3000, Agilent Cary 620/670, PerkinElmer Spotlight 400, and Thermo Fischer Scientific Nicolet iN10). Using the same database and the automated analysis pipeline in siMPle, MP were identified in samples that were analyzed with instruments with different detector systems as well as optical resolutions and the results discussed.

Critical Review of Processing and Classification Techniques for Images and Spectra in Microplastic Research

Microplastic research is a rapidly developing field, with urgent needs for high throughput and automated analysis techniques. We conducted a review covering image analysis from optical microscopy, scanning electron microscopy, fluorescence microscopy, and spectral analysis from Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, pyrolysis gas-chromatography mass-spectrometry, and energy dispersive X-ray spectroscopy. These techniques were commonly used to collect, process, and interpret data from microplastic samples. This review outlined and critiques current approaches for analysis steps in image processing (color, thresholding, particle quantification), spectral processing (background and baseline subtraction, smoothing and noise reduction, data transformation), image classification (reference libraries, morphology, color, and fluorescence intensity), and spectral classification (reference libraries, matching procedures, and best practices for developing in-house reference tools). We highlighted opportunities to advance microplastic data analysis and interpretation by (i) quantifying colors, shapes, sizes, and surface topologies with image analysis software, (ii) identifying threshold values of particle characteristics in images that distinguish plastic particles from other particles, (iii) advancing spectral processing and classification routines, (iv) creating and sharing robust spectral libraries, (v) conducting double blind and negative controls, (vi) sharing raw data and analysis code, and (vii) leveraging readily available data to develop machine learning classification models. We identified analytical needs that we could fill and developed supplementary information for a reference library of plastic images and spectra, a tutorial for basic image analysis, and a code to download images from peer reviewed literature. Our major findings were that research on microplastics was progressing toward the use of multiple analytical methods and increasingly incorporating chemical classification. We suggest that new and repurposed methods need to be developed for high throughput screening using a diversity of approaches and highlight machine learning as one potential avenue toward this capability.