Bioswales as potential sinks for tyre wear particle pollution

Microplastics are known to be ubiquitous throughout the Earths ecosystems, with plastics found everywhere from terrestrial soils to deep ocean trenches. Much of the research to date has focussed on microplastics typically found in, for example, plastics bags, disposable utensils and food containers, with a large focus on marine microplastics. Recently, tyres have been identified as major sources of microplastics to the environment, due to the synthetic rubber they contain. Currently, estimates of the tyre microplastic burden in the environment suggest up to a third of marine microplastics and a third of terrestrial microplastics are tyre wear particles. Despite an increase in tyre wear research we still lack knowledge and understanding of the fate, transport and dynamics of tyre wear particles in the environment. Here, we investigate the role of green infrastructure, specifically bioswales, on the fate of tyre wear from road runoff. We present data from bioswales constructed in 2010, which were subsequently sampled in 2011, 2015 and 2023, providing a temporal record of tyre wear in the bioswales. We analysed samples from two bioswales (wet versus dry) to determine if there is an advantage of different bioswale designs to act as a sink of tyre wear particles. Samples were taken within the bioswale from upstream of the culvert inflow pipe, at various points down the bioswale and upstream of the bioswale outflow. These sampling sites were selected to provide information on potential transport through the bioswale, including whether bioswales are acting as sinks for tyre wear particles and if areas of preferential settling upstream of check dams produce increased rates of settling and trapping of tyre wear particles compared to other areas. The total mass of styrene-butadiene rubber and natural rubber in the samples was analysed using pyrolysis-gas chromatography-mass spectrometry, particle count, size and morphology were determined using optical microscopy. This study aims to determine whether bioswales can be used to effectively remediate tyre wear pollution from road runoff and the best design for this potential storage.