Characterisation of microplastics is key for reliable data interpretation

Microplastic research has gained attention due to the increased detection of microplastics (<5 mm size) in the aquatic environment. Most laboratory-based research of microplastics is performed using microparticles from specific suppliers with either superficial or no characterisation performed to confirm the physico-chemical in-formation detailed by the supplier. The current study has selected 21 published adsorption studies to evaluate how the microplastics were characterised by the authors prior experimentation. Additionally, six microplastic types described as 'small' (10-25 mu m) and 'large' (100 mu m) were commercially acquired from a single supplier. A detailed characterisation was performed using Fourier transform infrared spectroscopy (FT-IR), x-ray diffraction, differential scanning calorimetry, scanning electron microscopy, particle size analysis, and N2-Brunauer, Emmett and Teller adsorption-desorption surface area analysis. The size and the polymer composition of some of the material provided by the supplier was inconsistent with the analytical data obtained. FT-IR spectra of small polypropylene particles indicated either oxidation of the particles or the presence of a grafting agent which was absent in the large particles. A wide range of sizes for the small particles was observed: polyethylene (0.2-549 mu m), polyethylene terephthalate (7-91 mu m) and polystyrene (1-79 mu m). Small polyamide (D50 75 mu m) showed a greater median particle size and similar size distribution when compared to large polyamide (D50 65 mu m). Moreover, small polyamide was found to be semi-crystalline, while the large polyamide displayed an amorphous form. The type of microplastic and the size of the particles are a key factor in determining the adsorption of pollutants and subsequent ingestion by aquatic organisms. Acquiring uniform particle sizes is challenging, however based on this study, characterisation of any materials used in microplastic-related experiments is critical to ensure reliable interpretation of results, thereby providing a better understanding of the potential environ-mental consequences of the presence of microplastics in aquatic ecosystems.

Automated summary

Microplastic research is important due to the detection of microplastics in aquatic environments. Most laboratory-based research fails to characterize the microplastics used in experiments. This study evaluated the characterization of microplastics in 21 published adsorption studies and found inconsistencies between the supplied material and analytical data. The study highlights the importance of characterizing materials used in microplastic-related experiments to ensure reliable interpretation of results and better understand the environmental consequences of microplastics in aquatic ecosystems.