Plastic litter is accumulating in ecosystems worldwide. Rivers are a major source of plastic litter to oceans. However, rivers also retain and transform plastic pollution. While methods for calculating particle transport dynamics in rivers are well established, they are infrequently used to quantify the transport and retention of microplastics (i.e., particles < 5 mm) in flowing waters. Measurements of microplastic movement in rivers are needed for a greater understanding of the fate of plastic litter at watershed and global scales, and to inform pollution prevention strategies. Our objectives were to (1) quantify the abundance of microplastics within different river habitats and (2) adapt organic matter “spiraling” metrics to measure microplastic transport concurrent with fine particulate organic matter (FPOM). We quantified microplastic and FPOM abundance across urban river habitats (i.e., surface water, water column, benthos), and calculated downstream particle velocity, index of retention, turnover rate, and spiraling length for both particle types. Microplastic standing stock was assessed using a habitat-specific approach, and estimates were scaled up to encompass the study reach. Spatial distribution of particles demonstrated that microplastics and FPOM were retained together, likely by hydrodynamic forces that facilitate particle sinking or resuspension. Microplastic particles had a higher downstream particle velocity and lower index of retention relative to FPOM, suggesting that microplastics were retained to a lesser degree than FPOM in the study reaches. Microplastics also showed lower turnover rates and longer spiraling lengths relative to FPOM, attributed to the slow rates of plastic degradation. Thus, rivers are less retentive of microplastics than FPOM, although both particles are retained in similar locations. Because microplastics are resistant to degradation, individual particles can be transported longer distances prior to mineralization than FPOM, making it likely that microplastic particles will encounter larger bodies of water and interact with various aquatic biota in the process. These empirical assessments of particle transport will be valuable for understanding the fate and transformation of microplastic particles in freshwater resources and ultimately contribute to the refinement of global plastic budgets.

中文翻译：

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城市溪流中微塑料和细颗粒有机物的分布和运输

塑料垃圾正在全球生态系统中积累。河流是海洋塑料垃圾的主要来源。然而，河流也保留并转化塑料污染。虽然计算河流中颗粒迁移动力学的方法已经很成熟，但它们很少用于量化流动水中的微塑料（即小于 5 毫米的颗粒）的迁移和滞留。需要测量河流中的微塑料运动，以更好地了解流域和全球范围内塑料垃圾的命运，并为污染预防策略提供信息。我们的目标是 (1) 量化不同河流栖息地中微塑料的丰度，(2) 采用有机物“螺旋”指标来测量微塑料与细颗粒有机物 (FPOM) 的同时运输。我们量化了城市河流栖息地（即地表水、水柱、底栖生物）中的微塑料和 FPOM 丰度，并计算了两种粒子类型的下游粒子速度、滞留指数、周转率和螺旋长度。使用特定栖息地的方法评估微塑料常备存量，并扩大估计值以涵盖研究范围。颗粒的空间分布表明微塑料和 FPOM 保持在一起，可能是通过促进颗粒下沉或再悬浮的流体动力。与 FPOM 相比，微塑料颗粒具有更高的下游颗粒速度和更低的保留指数，这表明微塑料在研究中的保留程度低于 FPOM。与 FPOM 相比，微塑料还显示出较低的周转率和较长的螺旋长度，这归因于塑料降解速度较慢。因此，与 FPOM 相比，河流对微塑料的保留较少，尽管两种颗粒都保留在相似的位置。由于微塑料不易降解，因此单个颗粒在矿化之前可以比 FPOM 传输更长的距离，这使得微塑料颗粒很可能会遇到更大的水体并在此过程中与各种水生生物群相互作用。这些对颗粒运输的经验评估对于了解微塑料颗粒在淡水资源中的命运和转化具有重要意义，并最终有助于完善全球塑料预算。与 FPOM 相比，河流对微塑料的保留较少，尽管这两种颗粒都保留在相似的位置。由于微塑料不易降解，因此单个颗粒在矿化之前可以比 FPOM 传输更长的距离，这使得微塑料颗粒很可能会遇到更大的水体并在此过程中与各种水生生物群相互作用。这些对颗粒运输的经验评估对于了解微塑料颗粒在淡水资源中的命运和转化具有重要意义，并最终有助于完善全球塑料预算。与 FPOM 相比，河流对微塑料的保留较少，尽管这两种颗粒都保留在相似的位置。由于微塑料不易降解，因此单个颗粒在矿化之前可以比 FPOM 传输更长的距离，这使得微塑料颗粒很可能会遇到更大的水体并在此过程中与各种水生生物群相互作用。这些对颗粒运输的经验评估对于了解微塑料颗粒在淡水资源中的命运和转化具有重要意义，并最终有助于完善全球塑料预算。与 FPOM 相比，单个颗粒在矿化之前可以运输更长的距离，这使得微塑料颗粒很可能会遇到更大的水体并在此过程中与各种水生生物群相互作用。这些对颗粒运输的经验评估对于了解微塑料颗粒在淡水资源中的命运和转化具有重要意义，并最终有助于完善全球塑料预算。与 FPOM 相比，单个颗粒在矿化之前可以运输更长的距离，这使得微塑料颗粒很可能会遇到更大的水体并在此过程中与各种水生生物群相互作用。这些对颗粒运输的经验评估对于了解微塑料颗粒在淡水资源中的命运和转化具有重要意义，并最终有助于完善全球塑料预算。