Beheshtimaal Arghavan, Xu Ruichen, Wang Binbin, Salehi Maryam
Department of Civil and Environmental Engineering, University of Missouri, Columbia, MO, USA.
Department of Civil and Environmental Engineering, University of Missouri, Columbia, MO, USA; Missouri Water Center, Columbia, MO, USA.
Water Res. 2025 Aug 22;287(Pt B):124456. doi: 10.1016/j.watres.2025.124456.
Microplastics (MPs) exposure to environmental conditions results in weathering, alters their physicochemical properties, and subsequently influences their mobility in aquatic systems. This study aims to investigate the interrelated roles of MP type and weathering conditions on their terminal settling/rise velocities and subsequently distribution in the water column under turbulent flow to further inform sampling methodologies. Low density polyethylene (LDPE), polyvinyl chloride (PVC), and ground tire rubber (GTR) were subjected to accelerated photodegradation and sedimentation processes, and biofilm was grown on LDPE and GTR MPs. The variations in their density, surface chemistry, morphology, and hydrophobicity following weathering were studied. The analyses revealed an increasing density for photodegraded and sedimented PVC MPs. Moreover, photodegradation enhanced the hydrophilicity of LDPE and GTR MPs. Weathering decreased the terminal rise velocity for LDPE, while it increased the settling velocities for PVC and GTR MPs due to the variations in their density and hydrophilicity. Weathering-induced changes in MP physicochemical properties, such as increased hydrophilicity and density, alter their settling and suspension behavior within the water column. These behavioral changes lead to a more dispersed vertical distribution, affecting the efficiency of grab sampling methods that rely on sampling at limited depths. The MP's total recovery through grab sampling from the top, middle, and bottom of the water tank revealed the order of new LDPE (16.40%)>new PVC (7.93%)>new GTR (6.7%). MP weathering mostly reduced their total recovery. The reduced recovery of weathered MP may be attributed to increased hydrophilicity and density, which promoted their settling and suspension within the water column and decreased their likelihood of being captured during sampling. This study underscores the urgent need to account for MP type and weathering when designing sampling protocols. Moreover, their non-uniform distribution suggests that a single-point or single-type grab sample may underestimate the MPs content in the aquatic system.
微塑料（MPs）暴露于环境条件下会导致老化，改变其物理化学性质，进而影响它们在水生系统中的迁移性。本研究旨在调查MP类型和老化条件对其最终沉降/上升速度的相互关联作用，以及随后在湍流条件下在水柱中的分布情况，以便为采样方法提供更多信息。低密度聚乙烯（LDPE）、聚氯乙烯（PVC）和废轮胎橡胶（GTR）经历了加速光降解和沉降过程，并且在LDPE和GTR MPs上生长了生物膜。研究了老化后它们在密度、表面化学、形态和疏水性方面的变化。分析表明，光降解和沉降后的PVC MPs密度增加。此外，光降解增强了LDPE和GTR MPs的亲水性。老化降低了LDPE的最终上升速度，而由于其密度和亲水性的变化，老化增加了PVC和GTR MPs的沉降速度。老化引起的MP物理化学性质变化，如亲水性和密度增加，改变了它们在水柱中的沉降和悬浮行为。这些行为变化导致更分散的垂直分布，影响了依赖于在有限深度采样的抓取采样方法的效率。通过从水箱顶部、中部和底部进行抓取采样对MP的总回收率显示，新LDPE（16.40%）>新PVC（7.93%）>新GTR（6.7%）。MP老化大多降低了它们的总回收率。老化MP回收率降低可能归因于亲水性和密度增加，这促进了它们在水柱中的沉降和悬浮，并降低了它们在采样过程中被捕获的可能性。本研究强调在设计采样方案时迫切需要考虑MP类型和老化情况。此外，它们的不均匀分布表明单点或单类型抓取样本可能低估了水生系统中MP的含量。
