Protocol for the production of micro- and nanoplastic test materials

Abstract

Micro- and nanoplastics (MNP) are ubiquitous, but little is known about the risks they pose to human health. Currently available data are of limited use for developing relevant risk assessments due to poor quality control, the lack of a standardised approach to particle characterisation and environmental analysis, and the use of test materials that do not reflect those found in the environment. A set of well-characterised MNP test materials would greatly alleviate this. Here, we present a robust method to produce, fractionate and characterise such test materials of PP and PVC. Initial size reduction of commercial powders to 500 µm was performed using a centrifugal mill under cryogenic conditions. Further ball-milling between room temperature and − 50°C in 1-propanol was then performed to reach the final particle sizes. Fractionation into size ranges of < 1, 1–5, 5–10, 10–90, 90–180 and 180–300 µm was performed by sedimentation and filtration. Characterisation of the reference materials through SLS, SEM-EDX, XRF and TGA demonstrated that the fractions were of the desired size and levels of contamination from the procedure were < 1 wt%. Stability testing in both 1-propanol and 0.05 wt% BSA solution showed that whilst some agglomeration occurred during storage in 1-propanol the suspensions were stable in BSA over 9 months and some of the previous agglomeration was reversed.

Preparation of block copolymer-stabilised microspheres of common polymers and their use as microplastics proxies in degradation studies

“…(15) More environmentally relevant microplastics have been achieved through top-down fragmentation of environmental plastic litter as well as through aging and weathering of commercially available plastics. (14,16,17) However, in order to link environmental fate and behaviour to well-controlled modi cations of physico-chemical properties, in-house synthesis of model microplastics is considered an advantage. Varying the type of primary polymer of the microplastic particles, enables evaluation of polymer-speci c effects from for example swelling, diffusivity, sensitivity to oxidation, exposure to salts, moisture, UV-light and weathering on the behaviour of the microplastic mimics.…”