Development of new microplastic reference particles for usage in pre-defined numbers

Abstract

For almost two decades now, scientists have increasingly focused on the occurrence of microplastics in the environment and their impact on environmental and human health. Currently, the variety of analytical methods used in microplastic research result in data of different quality and resolution. This largely hampers comparability between data sets and consequently prevents a reliable risk assessment. In this context, the lack of suitable reference microplastic particles that can be added as internal standard in an exactly known number further prevents quality assessment of, and harmonization in terms of comparability between different analytical methods. Although this lack has widely been recognized, currently only reference microplastic particles in form of micro-beads or -fragments (powders) are commercially available. Manual addition of such reference microplastic particles to samples in a precisely defined number as an internal standard is inefficient and the alternative use of microplastic particle suspensions does not allow for the addition of an exactly defined particle number. The optimum solution to solve this issue would be reference microplastic particles embedded in an easy-to-use soluble matrix in exact numbers. This would allow for evaluating analytical quality during microplastic analysis as well as establishing harmonization in terms of comparability between different methods. In the present study we focused on the development of such reference microplastic particles. We used CNC milling for the production of small diameter plastic columns followed by gelatine embedment and subsequent cryosectioning. This results in gelatin slices containing an exactly defined number of reference microplastic particles with well-defined size, shape and polymer type / chemical composition that can be added to a sample easily with the dissolution of the gelatine. We successfully produced square shaped reference microplastic particles in a size range of 125–1000 µm of five different polymers. The overall size-deviation of the reference microplastic particles never exceeded ± 11.2% from the mean value of a set of particles. The highest percentage weight-deviation was 25.5% from the mean value of a set of 125 x 125 x 20 µm PS reference microplastic particles. Our approach allows for the production of reference microplastic particles tailored to specific needs of all different analytical methods used in current microplastic research. Beyond analytical method validation, these reference microplastic particles furthermore open possibilities for experiments on microplastics ranging from organismic uptake to environmental distribution.

Plastic Quantification and Polyethylene Overestimation in Agricultural Soil Using Large-Volume Pyrolysis and TD-GC-MS/MS

“…25 We solved the problem of weighing by using precisely cut, volume-defined particles out of our plastic standard materials and used these for lower limit calibration. 26 The lower limit of calibration was linear for PE (R 2 = 0.98), PET (R 2 = 0.93), and PS (R 2 = 0.92) and stayed in accordance with Dierkes et al who reported an R 2 of 0.98 for PE and 0.99 for PS using a calibration range from 0.005 to 10 mg in a Py-GC-MS system. 23 Method Development�Comparison of Plastic Specific Signals to Organic Materials.…”

“…For production of standard plastic particles, a protocol from Oster et al was used. 26 Injection-molded polymer blocks made of LD-PE, PET, and PS were cut into rectangular pieces (10 × 10 × 4 mm 3 ). These were then processed using a CNC mill (CMX 600 V; DMG MORI Inc., Bielefeld, Germany) to create columns on a baseplate with the intended diameter of the particles.…”