Microplastics are increasingly recognised as posing a significant environmental threat across systems. Their pervasive presence in freshwater poses a serious concern, given the heavy reliance of both humans and biodiversity on healthy, functioning freshwater ecosystems. Acknowledgment of the potential risks led the transboundary Orange-Senqu River Commission (ORASECOM) to include sampling for microlitter (primarily microplastics) in riverine sediment, surface water, and fishes, across Southern Africa as part of the third Joint Basin Survey (JBS3) in 2021. The aim was to establish a first, basin-wide estimate of microlitter contamination across compartments, setting a baseline for further monitoring. The survey showed that the abundance of microlitter in riverine sediment (0 – 4000 particles.kg-1 dry weight (dw)) and riverine water (1.00 ± 0.71 – 69.75 ± 68.55 SD items.L-1) varied considerably between sample sites, with no correlation between the two. The abundance of microlitter in fishes was low (average of 0.7 ± 0.4 items.individual-1). Course resolution analyses suggested that microlitter concentrations in riverine sediment and riverine water at each site did not correlate with land use directly upstream, though variation in microlitter abundance did isolate some hotspots of contamination. Discharge data collected from nine gauging stations near sampling sites confirmed that low flows prevailed in the system during the study, with high flows occurring approximately 5 months prior during the summer months. There is some variation in river flow across the catchment which is a likely driver of microlitter transport. This was evident in the polymer composition for sediment and water samples. Based on the average discharge at each gauging station and microlitter concentrations measured in riverine water, the estimated microlitter load ranged from ∼889 particles.s-1 to ∼17.9 million particles.s-1, with a substantial amount ending likely up in the mudbelt adjacent to the Orange River mouth. This assessment provides a first insight into the characterisation and distribution of microlitter in multiple compartments across the Orange-Senqu River basin. Overall, the findings highlight the need for continued monitoring across compartments at catchment scales to improve our understanding of microplastic pathways into and within riverine systems.

中文翻译：

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测定 Orange-Senqu 河流域沉积物、水和鱼类中的塑料微粒


人们越来越认识到微塑料对各个系统构成重大环境威胁。鉴于人类和生物多样性严重依赖健康、功能正常的淡水生态系统，它们在淡水中的广泛存在令人严重担忧。认识到潜在风险后，跨界奥兰治-森渠河委员会 （ORASECOM） 在 2021 年第三次联合流域调查 （JBS3） 中对南部非洲的河流沉积物、地表水和鱼类中的微垃圾（主要是微塑料）进行了采样。目的是建立第一个全流域范围的跨隔间微垃圾污染估计，为进一步监测设定基线。调查显示，河流沉积物（0 – 4000 颗粒.kg-1 干重 （dw））和河流水（1.00 ± 0.71 – 69.75 ± 68.55 SD 项目）中微垃圾的丰度。L-1） 在样本点之间差异很大，两者之间没有相关性。鱼类中微垃圾的丰度较低（平均 0.7 ± 0.4 项。航向分辨率分析表明，每个地点的河流沉积物和河流水中微垃圾浓度与直接上游的土地利用无关，尽管微垃圾丰度的变化确实隔离了一些污染热点。从采样点附近的 9 个测量站收集的排放数据证实，在研究期间，系统中普遍存在低流量，高流量发生在大约 5 个月前的夏季。流经集水区的河流流量存在一些变化，这可能是微垃圾运输的一个驱动因素。这在沉积物和水样的聚合物成分中很明显。 根据每个测量站的平均排放量和在河流水中测量的微垃圾浓度，估计的微垃圾负荷范围为 ∼889 个颗粒.s-1 到大约 1790 万个颗粒.s-1，其中大量可能最终进入奥兰治河河口附近的泥带。该评估为了解 Orange-Senqu 河流域多个隔间中微垃圾的特征和分布提供了初步见解。总体而言，这些发现强调了在集水区规模上持续监测隔间的必要性，以提高我们对进入河流系统和内部的微塑料途径的理解。