Microplastics in road dust: A practical guide for identification and characterisation.

The contamination of the environment by microplastics (MPs) in road dust poses a serious ecological and health concern. MPs have been detected in road dust worldwide and their presence has been mainly attributed to plastic litter fragmentation and vehicle tyre abrasion. Although current technologies such as Raman and Fourier Transform InfraRed spectroscopy as well as Scanning Electron Microscopy are capable of detecting MPs in road dust, the analysis of MPs shape and MPs smaller than 20 µm is limited and often labour demanding. More accurate, cost-effective and rapid techniques have now become necessary to analyse MPs in road dust, particularly since the development of large infrastructure projects that incorporate recycled plastic into road assets and roadside furniture. Nile red (NR) staining is a promising technique to identify MPs in environmental samples; however, it has not yet been applied to road dust. This study investigates the use of NR fluorescence microscopy to detect MPs in road dust and provides information about MP amount, shape and size distribution. The staining duration and temperature, solvent selection and NR concentration were optimised considering 33 different road dust materials, including 13 types of plastic. The NR staining procedure developed in this work is capable of successfully differentiating between MPs down to 1 µm and other non-plastic road dust materials. Future applications include assessing the contribution of plastic-modified roads to MP pollution, comparing the level of MP pollution in urban and rural areas and providing a rapid, simple, inexpensive and reliable monitoring approach for further studies to compare MP using a singular optimised methodology.

Paving roads with recycled plastics: Microplastic pollution or eco-friendly solution?

Although plastic-modified roads are a promising approach to reducing the amount of landfilled and incinerated plastic and improving asphalt pavement performance, the contribution of plastic-modified roads to microplastic pollution is unknown. This study aimed to develop a new abrasion procedure to quantify the release of microplastics from recycled plastic-modified asphalt depending on environmental factors, the type and content of plastic used, and the incorporation method in bitumen/asphalt. A Wet Track Abrasion machine was used to simulate road traffic abrasion on a plastic-modified asphalt sample, and a novel microplastic extraction procedure was designed to extract the generated microplastics. Incorporating recycled plastic as a polymer modifier in the bitumen matrix resulted in an early release of microplastics compared to its addition as a synthetic aggregate substitute in the asphalt mix. Cold temperatures and low pH values favoured the generation of microplastics from plastic-modified asphalt. Due to the lack of universal thresholds for the release of microplastics into the environment, environmental agencies and local authorities could benefit from this novel laboratory-based microplastic assessment procedure to foster the sustainable use of recycled plastic in roads.