Bioretention cells remove increasingly small microplastics from stormwater
Résumé
Microplastics are a suite of pollutants of increasing concern within the aquatic, atmospheric and terrestrial environments. In particular, stormwater runoff is a significant entry pathway of microplastics into the downstream environment. In our previous study, we showed that microplastics greater than 106 μm in size can be efficiently removed and retained from stormwater using a bioretention cell, a type of green infrastructure. Over time microplastics, plastic particles in the range of 1 μm to 5 mm, fragment into increasingly small particles due to mechanical and/or biological stresses and sunlight exposure. With increasingly small size, microplastics pose increasing threats to humans and other organisms. As
microplastic size gets smaller, there is a higher risk of transfer via bioretention soil pores toward surface water, groundwater, or the hydraulically connected municipal systems. A bioretention cell, located in Vaughan, Ontario, was monitored over 2 years in 2018 and 2019. Stormwater samples were collected from its inlet and outlet where the drainage area consisted of a parking lot made of recycled rubber tire pavers. Previous results for microplastics > 106 μm, showed an 84 % concentration decrease from 186 to 31 microparticles/ L at the bioretention inlet
and outlet respectively. In this work, we will present new results on the fate of the > 25 μm size range that highlighted an average 67 % concentration decrease between the inlet and outlet of the bioretention cell. These new results demonstrate that this conventionally designed bioretention cell continues to effectively remove microplastics down to 25 μm.