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Spatiotemporal patterns, loads, and risks of microplastics in the stormwater system of a subtropical coastal city
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Researchers found that stormwater drains in a coastal city (Macao) are packed with tiny plastic particles—sometimes thousands per liter—that get washed off streets during rain and flow straight into the ocean, where marine life can ingest them. This matters because these microplastics eventually make their way up the food chain into the seafood we eat, and the study found the plastic types detected pose a notably high risk to ecosystems, highlighting the need for better stormwater filtering systems in cities.
Urban stormwater runoff is a critical pathway for microplastics (MPs) to enter marine ecosystems, posing a significant threat. However, systematic studies on spatiotemporal patterns, loads, and risks of MPs in stormwater systems, particularly in subtropical coastal cities, remain limited. This study characterized MPs in Macao's stormwater drains across seasons, using density separation, H 2 O 2 digestion, stereomicroscopy, and μ-FTIR analysis to investigate their abundance and distribution. MPs were ubiquitous across all sample sites, with abundance ranging from 0.86 to 53.03 n/L. Irregular shaped fragments (56.78 ±.13.80%) and the colour black (38.44 ± 7.47%) were dominant, and the most common polymers were Polyethylene terephthalate (39.55 ± 16.63%), polypropylene (23.05 ± 18.15%), and polyethylene (9.52 ± 8.87%). While abundance of MPs was higher in the wet season, no significant seasonal variation was found. MP characteristics varied significantly with land use. The concentration range of MPs was estimated to be from 2.86 ± 0.38 to 3145.94 ± 766.74 μg/L, with an overall mean of 454.68 ± 572.20 μg/L through the mass concentration models. The daily MP emission load into the receiving water was estimated to range from 8.29 × 10 3 to 3.09 × 10 8 particles per day or 2.66 to 10,365.23 g/day. MP risk was high (Polymer Hazard Index/Potential Ecological Risk Index: III/V) due to hazardous polymers, with spatiotemporal variations further observed from fluctuating water flow erosion. Correlation analysis revealed that MP abundance showed a significant negative correlation with dissolved oxygen and a positive correlation with antecedent rainfall. These findings identify stormwater drains as a key MP conduit, influenced by rainfall and land use, calling for targeted management in urban coastal areas.
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Scientists studying beaches near Adelaide, Australia found that concrete stormwater drains dump nearly twice as many microplastics (tiny plastic bits, mostly from clothing fibers and tires) into coastal waters compared to natural river mouths. This matters because these microplastics can work their way into seafood and the broader food chain, and it suggests that upgrading how cities manage stormwater runoff could be a meaningful way to cut down on plastic pollution before it reaches our oceans and, eventually, our plates.
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Researchers found that stormwater runoff from densely populated, residential neighborhoods in a Brazilian coastal city carried far more microplastic particles, mostly tiny fibers from fabrics and rubber bits, likely from tires, than runoff from industrial or empty lots. This matters because rain washes these plastics straight into rivers and oceans, where they enter the marine food chain and, eventually, the seafood we eat, meaning where and how we build our cities directly affects plastic pollution reaching our plates.
Microplastics discharged from urban drainage system: Prominent contribution of sewer overflow pollution
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Researchers evaluated the abundance and distribution of microplastics in urban drainage systems in coastal Chinese cities, with a focus on sewer overflow events during storms. The study found that overflow pollution during wet weather is a prominent contributor to microplastic discharge into urban water bodies, with meteorological conditions and land use patterns significantly influencing microplastic transport and release.
A plastic storm: The role of stormwater in the microplastic load of an urban river system
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A study of an urban river system found that stormwater runoff is a major source of microplastic pollution, transporting particles from roads, buildings, and other urban surfaces directly into waterways during rain events. Stormwater contributed a significant fraction of the total microplastic load reaching the ocean, comparable to inputs from wastewater treatment plants. Better management of urban stormwater could meaningfully reduce microplastic pollution in rivers and coastal waters.
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