We can't find the internet
Attempting to reconnect
Something went wrong!
Hang in there while we get back on track
Transport of microplastics in stormwater treatment systems under freeze-thaw cycles: Critical role of plastic density
Summary
Researchers found that freeze-thaw cycles transport microplastics downward through stormwater treatment system substrates, with plastic density being a critical factor determining how far MPs migrate. Dense PET microplastics penetrated deepest, raising concern that treatment systems in cold climates may inadvertently channel MPs toward groundwater during winter thaw cycles.
Stormwater treatment systems remove and accumulate microplastics from surface runoff, but some of them can be moved downward to groundwater by natural freeze-thaw cycles. Yet, it is unclear whether or how microplastic properties such as density could affect the extent to which freeze-thaw cycles would move microplastics in the subsurface. To examine the transport and redistribution of microplastics in the subsurface by freeze-thaw cycles, three types of microplastics, with density smaller than (polypropylene or PP), similar to (polystyrene or PS), or greater than (polyethylene terephthalate or PET) water, were first deposited on the top of packed sand-the most common filter media used in infiltration-based stormwater treatment systems. Then the columns were subjected to either 23 h of drying at 22 ⁰C (control) or freeze-thaw treatment (freezing at -20 ⁰C for 6 h and thawing at 22 ⁰C for 17 h) followed by a wetting event. The cycle was repeated 36 times, and the effluents were analyzed for microplastics. Microplastics were observed in effluents from the columns that were contaminated with PET and subjected to freeze-thaw cycles. Comparison of the distribution of microplastics in sand columns at the end of 36 cycles confirmed that freeze-thaw cycles could disproportionally accelerate the downward mobility of denser microplastics. Using a force balance model, we show that smaller microplastics (<50 µm) can be pushed at higher velocity by the ice-water interface, irrespective of the density of microplastics. However, plastic density becomes critical when the size of microplastics is larger than 50 µm. The coupled experimental studies and theoretical framework improved the understanding of why denser microplastics such as PET and PVC may move deeper into the subsurface in the stormwater treatment systems and consequently elevate groundwater pollution risk.
Sign in to start a discussion.
More Papers Like This
Mobility of polypropylene microplastics in stormwater biofilters under freeze-thaw cycles
Researchers discovered that freeze-thaw cycles move deposited microplastics deeper into stormwater biofilter soil than simple drying-and-wetting cycles, because expanding ice crystals break up the soil and release trapped particles. This finding suggests that in cold climates, microplastics filtered from stormwater could migrate further underground than previously estimated.
UV exposure to PET microplastics increases their downward mobility in stormwater biofilters undergoing freeze–thaw cycles
Researchers found that UV weathering of PET microplastics increases their downward mobility in stormwater biofilters undergoing freeze-thaw cycles, as UV exposure creates polar surface groups that decrease hydrophilicity and enhance particle transport.
Subsurface transport of microplastic particles in gravel columns: Impacts of different rain events and particle characteristics
Researchers conducted column experiments using pre-stained microplastic particles of two density types in gravel sediment to investigate how different rainfall intensities and land-use scenarios influence the vertical transport and retention of microplastics in subsurface environments. The study found that both particle density and rainfall event characteristics significantly affected microplastic mobility through subsurface sediments, informing models of microplastic fate in soil-water systems.
Impact of particle density on the mobility of microplastics in sediments
This study investigates how the density of microplastic particles affects their mobility through soil and potential to reach groundwater, using column experiments with polyethylene particles of different densities. Particle density was found to influence transport behavior, with implications for understanding how microplastics migrate through terrestrial environments.
Revealing the Freezing-Induced Alteration in Microplastic Behavior and Its Implication for the Microplastics Released from Seasonal Ice
Researchers revealed how freeze-thaw cycling alters microplastic behavior in environmental matrices, finding that freezing changes particle aggregation, surface properties, and transport dynamics with implications for polar and seasonally frozen environments.