Lessons learned from an intercalibration exercise on the quantification and characterisation of microplastic particles in sediment and water samples

Abstract

An intercalibration exercise on the characterisation of microplastics in marine sediment and water samples was carried out among five laboratories involved in the implementation of the Marine Strategy Framework Directive (MSFD) in their country. The samples were prepared by mixing cleaned natural sediment and sea water with microplastics sets made of particles of various polymers, shapes and colours. Overall, the errors on total counts were under 25% in absolute value. The risk of non-detection and loss of particles is greater than the risk of contamination during sample analysis. Significant differences are observed among particle types. It appears difficult to obtain reliable and comparable data on the colour of microplastics. A comparison of the errors with regards to the protocols used led to recommend NaCl [1.2 g/cm3] density separation for sediment and one filtering step (200 μm). The operators' experience appears as a key factor for the quality of the results. Highlights► Underestimation is the most frequent cause of error on the total counts ► Recommended protocol: NaCl density separation for sediment, filtering 200 µm. Operators' experience is a key quality factor ► Data on colour is not reliable and comparable ► Obtaining clean natural sediment reference material is an issue ► FT-IR analysis is useful to remove ambiguities on mineral and biological particles

Microplastics in freshwater fishes: Occurrence, impacts and future perspectives

“…Microplastic visual screening varies with individual experience and the particular shapes, sizes and colours of MP particles (Cadiou et al, 2020). MP screenings under microscopy should aim to be conservative and carried out blind, in a randomized order, with a pre-determined and standardized search time and search criteria to reduce bias and variation in counts.…”

Microplastics Pollution and Regulation

“…The implementation of the MSFD in the EU countries was an important driver for increasing the number of studies in European waters on this issue. Although the methods used for sampling and analysis have already been reviewed (see e.g., Hidalgo-Ruz et al 2012;GESAMP 2019), differences between the studies highlighted the need to improve standardization by defining simple, effective, and reproducible methods (Cadiou et al 2020;Prata et al 2019;Maes et al 2019;Cowger et al 2020). Related to the establishment of a monitoring program for MPs in the marine environment, the environmental indicators should have the following characteristics (see e.g., UNEP 2016);…”

“…While particle counting, estimation, and identification technology has advanced considerably in recent years, the manual work of analysts remains essential for the foreseeable future, but represents a critical source of analytical deviation and error. A recent critical review focused on quality criteria for the analysis of MPs in biota samples (Hermsen et al 2018), while an intercalibration exercise on MP characterization and quantification in sediment and water samples has also been published recently (Cadiou et al 2020). In this last study, the authors reported a 25% deviation in the interlaboratory exercise, mainly due to underestimation of the methodological processes, the risk of losing MP with the applied extraction methods, and human error in particle counting.…”

“…Considering variance in the MP extraction step and the level of human error observed in the intercalibration exercise between five different laboratories at European level, it was concluded that the results were not comparable, demonstrating the difficulty of obtaining comparable results in similar samples. This is a weakness that makes it difficult to make a sound assessment of the contamination of plastics (especially MPs) on a regional scale and emphasizes once again the need for harmonized MP monitoring methods across all environmental compartments (including biota) and the introduction of standard reference materials to ensure accuracy of analysis and robustness of results (Cadiou et al 2020).…”

Steps Scientists Can Take to Inform Aquatic Microplastics Management: A Perspective Informed by the California Experience

“…20,21 A few studies have been conducted to compare results among measurement methods. [22][23][24][25][26] In addition, several groups, including the Japanese Ministry of the Environment on behalf of an international consortium, have published standardized methods. 27,28 However, those efforts have been focused on single or limited media, such as seafood or the water column, or have focused on only a subset of required standardization activities, such as field collection methods, microplastics extraction, or measurement technology.…”