Abstract：
Riverbed sediments have been identified as temporary and long-term accumulation sites for microplastic particles (MPs), but the relocation and retention mechanisms in riverbeds still need to be better understood. In this study, we investigated the depth-specific occurrence and distribution (abundance, type, and size) of MPs in river sediments down to a depth of 100 cm, which had not been previously investigated in riverbeds. In four sediment freeze cores taken for the Main River (Germany), MPs (≥ 100 µm) were detected using two complementary analytical approaches (spectroscopy and thermoanalytical) over the entire depth with an average of 21.7 ± 21.4 MP/kg or 31.5 ± 28.0 mg/kg. Three vertical trends for MP abundance could be derived, fairly constant in top layers (0-30 cm), a decrease in middle layers (30-60 cm), and a strong increase in deep layers (60-100 cm). The dominant polymer types were polyethylene (PE), polypropylene (PP), and polystyrene (PS). Polyethylene terephthalate (PET) and PP were also found in deep layers, albeit with the youngest age of earliest possible occurrence (EPO age of 1973 and 1954). The fraction of smaller-sized MPs (100-500 µm) increased with depth in shallow layers, but the largest MPs (> 1 mm) were detected in deep layers. Based on these findings, we elucidate the relationship between the depth-specific MP distribution and the prevailing processes of MP retention and sediment dynamics in the riverbed. We propose some implications and offer an initial conceptual approach, suggesting the use of microplastics as a potential environmental process tracer for driving riverbed sediment dynamics.
摘要：
河床沉积物已被确定为微塑料颗粒（MPs）的临时和长期积累场所，但是河床中的搬迁和保留机制仍然需要更好地理解。在这项研究中,我们调查了特定深度的发生和分布(丰度，type,和大小)河流沉积物中的MP，深度为100厘米，以前没有在河床中进行过调查。在为Main河（德国）采取的四个沉积物冻结岩心中，使用两种互补的分析方法（光谱学和热分析）在整个深度上检测到MPs（≥100µm），平均为21.7±21.4MP/kg或31.5±28.0mg/kg。可以得出MP丰度的三个垂直趋势，在顶层相当恒定（0-30厘米），减少中间层（30-60厘米），和深层的强烈增加（60-100厘米）。主要的聚合物类型是聚乙烯（PE），聚丙烯（PP），和聚苯乙烯（PS）。聚对苯二甲酸乙二醇酯（PET）和PP也被发现在深层，尽管最早可能发生的年龄最小（EPO年龄为1973年和1954年）。较小尺寸的MPs（100-500µm）的分数随浅层深度的增加而增加，但在深层检测到最大的MPs(>1mm)。基于这些发现,我们阐明了特定深度的MP分布与河床中MP保留和沉积物动力学的主要过程之间的关系。我们提出了一些含义，并提供了一个初步的概念方法，建议使用微塑料作为驱动河床沉积物动力学的潜在环境过程示踪剂。
