**Abstract**

The aim of this work is to verify the quality, robustness, and accuracy of a standard analytical protocol for the determination of microplastics in aqueous textile matrices. In order to reach this objective, a round robin scale identification and quantification test program was conducted. In particular, this chapter describes the round robin test, an interlaboratory comparison test on standard microfilament suspensions initiated in November 2021 by an expression of interest open call. In total, 18 laboratories expressed their interest, and 13 participants sent their results. Each of these laboratories received a set of 10 samples, accompanied by a protocol. The 10 samples consisted of three replicates per type of three different synthetic yarns and a control sample**.** The data required were the number of microplastics per sample recognized as fibers or particles, microplastic fiber lengths and diameters, and identification of the polymer using vibrational spectroscopy (μ-FTIR and/or μ-Raman). The data collected were statistically elaborated. The results highlighted that the laboratories had different recovery rates directly related to their specific procedures and equipment. Although there were issues related to the correct use of the standard method and to the behavior of operators, the method proved to be valid for the determination of microplastics in aqueous matrices.

**Keywords:** standard microplastic suspensions, interlaboratory test, quantification of microplastics, vibrational spectroscopy, microplastic counting

### **1. Introduction**

Microplastics are considered to be emerging pollutants in aquatic and terrestrial environments. Microplastics are generally defined as particles with dimensions in the range of 5 mm, and this term denotes microscopic plastic particles such as fragments, beads, or fibers [1]. They have been detected worldwide and are currently present even in remote areas such as Antarctica [2].

In recent years, a particular kind of microplastic has gained the attention of researchers and scientists after its problematic occurrence in the water environment. Indeed, among the different microplastic forms, studies have demonstrated that the

predominant shape is the fibrous or the filament form in marine and freshwater ecosystems [3, 4]. Microplastic fibers, also called microfilaments, can be produced by the fragmentation of large plastics, in particular from textile garments [5]. Many synthetic and natural microplastics are released from textiles during domestic or industrial washing processes [6]. Out of all the released microfilaments found in the environment, the synthetic ones play a crucial role as pollutants of the environment. Polyesters (PET), acrylics (PAN), and polyamides (PA) are the major contributors [7]. Thus, all the source of microplastic in water are summarized in **Figure 1**. Synthetic microplastics are released from different sources, such as personal care products, city dust, and textiles [8]. Specifically, textiles can be a source of microfilaments during their production, use, and disposal stages. The mechanical abrasion and the physical stress applied to garments in any life stages are responsible for the shedding of microplastics with a fibrous shape [9].

Furthermore, domestic filters and wastewater treatment plants (WWTPs) are sometimes unable to trap them totally. It has been estimated that significant numbers of microfilaments escape from the traps and up to 40% can enter rivers, lakes, and oceans downstream [10]. Moreover, the sludge removed from treatment plants is usually stored or landfilled, allowing microfilaments to reach the environment again.

Despite the concerns about microplastics, the consumption of synthetic textiles is constantly growing, mainly due to fast-fashion trends. For instance, more than 45 million tons of polyester garments are produced every year [10]. Consequently, the world-released microplastic keeps rising, especially in marine and freshwater ecosystems [11]. Fortunately, several scientists worldwide have been moving in this direction in recent years to identify and limit microplastic pollution.

In particular, the occurrence of microfilaments in the aqueous environment is causing increasingly colossal concern. For this reason, in order to have a clearer view of microfilament pollution, a brief overview of the potential identification method is proposed.
