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Spotlight on the vertical migration of aged microplastics in coastal waters
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This study examined how aging and weathering processes change the physical and chemical properties of microplastics, which in turn affects whether they sink or float in coastal waters. Researchers found that different aging pathways, such as UV exposure and biofouling, alter particle density and surface characteristics in ways that drive vertical movement, helping explain why microplastics distribute throughout the water column rather than staying at the surface.
Coastal waters are complex and dynamic areas with unique environmental attributes that complicate the vertical migration of microplastics (MPs). The MPs that enter coastal waters from diverse sources, including terrestrial, riverine, oceanic, and shoreline inputs undergo various aging pathways. In this study, the variations in the physiochemical characteristics of MPs undergoing various aging pathways and their vertical migration under dynamic conditions subjected to the effects of different MP characteristics and coastal environmental features were comprehensively explored. Opposite effects of aging on the vertical migration of hydrophobic and hydrophilic MPs were observed, with aging appearing to promote the dispersion of hydrophobic MPs but enhance the vertical migration of hydrophilic ones. The positive role of salinity and the negative role of humic acid (HA) concentrations on MP vertical migration were identified, and the mechanisms driving these effects were analyzed. Notably, intense turbulence not only promoted the floating of positively buoyant MPs but also reversed the migration direction of negatively buoyant MPs from downward to upward. Aging-induced changes in MP characteristics had a limited effect on MP vertical migration. The inherent characteristics of MPs and the surrounding environmental features, however, played major roles in their vertical migration dynamics. ENVIRONMENTAL IMPLICATION: Microplastics (MPs) have emerged as a significant global environmental concern and the coastal zones are the hotspots for MP pollution due to their high population density. This study comprehensively investigated the variations in the physiochemical characteristics of MPs undergoing various aging pathways. Their vertical migration patterns under dynamic conditions subjected to the effects of different MP characteristics and coastal environmental features were revealed. The roles of turbulence and MP density in their migration were identified. The findings of this study have important implications for understanding the transport and determining the ecological risks of MPs in coastal waters.
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Researchers studied how weathering changes the physical properties of microplastics and affects where they end up in the water column. They found that exposure to sunlight and environmental conditions altered the density and surface chemistry of plastic particles, causing them to settle or float differently than new plastics. The study suggests that current water sampling methods may miss a significant portion of weathered microplastics, since these altered particles distribute more widely across different water depths.
Sinking rates of microplastics and potential implications of their alteration by physical, biological, and chemical factors
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Researchers conducted sinking experiments with diverse microplastic particles and found that sinking velocity depends not only on density and size but also on particle shape, and that biofouling and weathering can substantially alter sinking rates with implications for how microplastics distribute through the water column.
Sinking characteristics of microplastics in the marine environment
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This study investigated the sinking behavior of microplastics in the marine environment, finding that particle properties such as density, shape, and biofouling strongly influence whether particles float or sink, helping explain why much of the expected floating plastic is unaccounted for.
Comprehensive Understanding on the Aging Process and Mechanism of Microplastics in the Sediment–Water Interface: Untangling the Role of Photoaging and Biodegradation
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Researchers examined how microplastics break down at the boundary between water and sediment in coastal wetlands, comparing the roles of sunlight-driven aging and biological degradation. They found that photoaging was the dominant process, accounting for over 55% of surface changes, and that biodegradable plastics aged faster than conventional ones. The study provides important insights into how microplastics transform in real-world coastal environments.
Transport of aged microplastics in river confluence zones: Settling behavior and influencing factors
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Scientists studying how tiny plastic bits move where rivers meet found that weathering (aging) and water turbulence change whether these particles float along or sink to the riverbed, with plastic type and density mattering too. This matters because it helps predict where microplastics build up in waterways, which can affect drinking water sources and the aquatic food chain that eventually reaches our plates.
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