PROJECT HIGHLIGHT
This project examines how infrastructures meant to control stormwater runoff — in particular “infiltration” structures, like rain gardens and permeable pavement — retains and releases microplastics. The researchers examine both design elements and factors in the surrounding catchment area, and aim to inform both the design and operation of infrastructure and the development of management strategies that effectively reduce microplastic pollution, thereby improving community health.
PROJECT SUMMARY
Stormwater best management practices (BMPs) include physical infrastructure meant to control the quantity and quality of stormwater runoff. Low Impact Development (LID) BMPs like rain gardens and permeable pavements mimic natural systems and encourage rainwater to soak into the ground rather than flow quickly into waterways.
Past studies have shown that more than 90% of microplastics carried into LID BMPs accumulate in the top few centimeters of their "filter layers." Because microplastics degrade slowly, they can be later washed out of the BMP via storm events and sent into waterways. To better understand these dynamics, the researchers have collected deposited road dust samples from over 50 locations in the Los Angeles area and are conducting extensive soil core sampling. They are using both innovative smartphone-enabled methods and vibration microscopy (FTIR) to analyze microplastic content in these samples.
The researchers are examining how both land use and trash management practices in the surrounding catchment impact microplastic accumulation in structural BMPs, utilizing NASA Earth observation products including MODIS data to analyze factors such as plant density and proximity to highways, waste sites and wastewater treatment plants. They are also assessing the impacts of various design elements.
Initial findings from this work have revealed three key insights. First, analysis of road dust and sediment shows that microplastics are uniformly distributed across different areas, suggesting that factors like income level or location do not affect exposure risk since these particles spread widely through the air. Second, while previous studies assumed microplastics stayed trapped in stormwater BMPs, new laboratory results show that up to 40% can be washed out during storms, significantly reducing these systems' effectiveness at controlling plastic pollution. Third, the team has found that adding a gravel layer on top of BMP filters can greatly reduce this wash-out effect, offering a practical way to improve how well these systems retain microplastics. This simple design modification could significantly increase the effectiveness of stormwater BMPs in reducing plastic pollution in our waterways.