Innovative reference materials for method validation in microplastic analysis including interlaboratory comparison exercises

Abstract

Reference materials (RMs) are vital tools in the validation of methods used to detect environmental pollutants. Microplastics, a relatively new environmental pollutant, require a variety of complex approaches to address their presence in environmental samples. Both interlaboratory comparison (ILC) studies and RMs are essential to support the validation of methods used in microplastic analysis. Presented here are results of quality assurance and quality control (QA/QC) performed on two types of candidate microplastic RMs: dissolvable gelatin capsules and soda tablets. These RMs have been used to support numerous international ILC studies in recent years (2019–2022). Dissolvable capsules containing polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyethylene (PE), and polystyrene (PS), in different size fractions from 50 to 1000 µm, were produced for one ILC study, obtaining relative standard deviation (RSD) from 0 to 24%. The larger size fraction allowed for manual addition of particles to the capsules, yielding 0% error and 100% recovery during QA/QC. Dissolvable capsules were replaced by soda tablets in subsequent ILC studies and recovery test exercises because they were found to be a more reliable carrier for microplastic RMs. Batches of soda tablets were produced containing different single and multiple polymer mixtures, i.e., PE, PET, PS, PVC, polypropylene (PP), and polycarbonate (PC), with RSD ranging from 8 to 21%. Lastly, soda tablets consisting of a mixture of PE, PVC, and PS (125–355 µm) were produced and used for recovery testing during pretreatment of environmental samples. These had an RSD of 9%. Results showed that soda tablets and capsules containing microplastics >50 µm could be produced with sufficient precision for internal recovery tests and external ILC studies. Further work is required to optimize this method for smaller microplastics (< 50 µm) because variation was found to be too large during QA/QC. Nevertheless, this approach represents a valuable solution addressing many of the challenges associated with validating microplastic analytical methods.

Nile red staining for rapid screening of plastic-suspect particles in edible seafood tissues

“…However, the homogeneity of MP in the solid salt tablets was lower compared to the reconstituted salt tablets (RSD = 8%), as the solid carrier matrix immobilised MP during handling and transport [ 41 ]. The same was observed comparing spiking reproducibility with soda tablets instead of soluble capsules (RSD = 9% for mixed MP in soda tablets) [ 42 ]. Consequently, spiking food matrices with solid MP carriers like salt tablets as opposed to particle dispersions should be considered in the future.…”

“…Current studies on developing MP reference material for interlaboratory comparison tests indicated that high heterogeneity between samples can occur. The RSD of particle numbers of MP-loaded capsules or reconstituted salt tablets (dissolved in water) ranged between 12 and 24% [ 41 , 42 ]. Martínez-Francés et al [ 42 ] observed higher deviations for particles below 50 µm, which was also indicated in this study for example when comparing PA6 (Ø 10–50 µm, RSD = 30%) with PVC (Ø 20–350 µm, RSD = 17%).…”

“…The RSD of particle numbers of MP-loaded capsules or reconstituted salt tablets (dissolved in water) ranged between 12 and 24% [ 41 , 42 ]. Martínez-Francés et al [ 42 ] observed higher deviations for particles below 50 µm, which was also indicated in this study for example when comparing PA6 (Ø 10–50 µm, RSD = 30%) with PVC (Ø 20–350 µm, RSD = 17%). This highlighted the difficulty of reproducible sample spiking for seafood method validation and standardisation.…”

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

“…Additionally, the academic publishing establishment, particularly editors and technical reviewers, should enforce these guidelines when making decisions about whether to accept peer-reviewed manuscripts that make broad claims about the prevalence of MPs and NPs in foods or their potential to impact human health, and professional societies should establish criteria by which the reliability of data on MPs and NPs can be determined, much as has been done in the toxicological sciences . Academic laboratories, government agencies, and/or industry should especially prioritize development of reliable reference materials; although some activity in this area exists, − broadly available MP and NP standards are currently inadequate to support regulatory science. Setting a common methodological denominator would increase comparability of research studies so that the potential of global plastics debris to affect human health can be considered by policymakers from a broad perspective rather than as a series of isolated data points, many of which may have limited value.…”

Small micro- and nanoplastic test and reference materials for research: Current status and future needs

“…It is evident that a lack of available sMP and NP test and reference materials, representative of those that may be expected to be released into or formed through plastic degradation in the environment, is limiting progress in understanding the fate, effects and ultimately, the environmental and human health risks of this ubiquitous form of pollution. The current situation is primarily explained by the significant challenges in developing effective and reproducible methods for producing well-characterised reference sMP and NP particles in sufficient qualities (Huber et al, 2023;Martínez-Francés et al, 2023). This is further compounded by the development of suitable analytical tools representing a major bottleneck with respect to understanding the fate and effects of sMP and NP (Nguyen et al, 2019).…”