Wastewater discharge to rivers is a controversial practice that compromises water quality, aquatic habitats and human health worldwide. Here we show how untreated wastewater laced with microplastics and raw sewage is routinely discharged into UK river flows that are too low to disperse the microplastics downstream. These ‘dry weather’ spills lead to acute microplastic contamination of river bed habitats. Many aquatic fauna feed in the benthic zone, the quality of which affects the entire riverine ecosystem. All microplastic types accumulate to high concentrations on the channel bed until flushed downstream by floods. These findings pose fundamental questions about the sustainable management of urban wastewater. Treating the wastewater would shut down the major source of microplastic fragments and microbeads in such rivers and prevent their transport to the ocean. Riverine microplastic transport is primarily partitioned between: (1) continuous transport at low concentrations of synthetic fibres from treated wastewater effluent; and (2) episodic flood-driven transport of the full microplastic assemblage entrained from contaminated channel beds. Focusing only on the buoyant non-flood microplastic load can produce highly unrepresentative assessments of riverine microplastic contamination. Climate warming and urban population growth will intensify the microplastic burden on many river ecosystems as summer baseflows decline and wastewater fluxes increase.

向河流排放废水是一种有争议的做法，它损害了全球的水质，水生生境和人类健康。在这里，我们展示了如何将未经处理的废水与微塑料和原污水绑在一起，这些废水如何按常规排放到英国河水中，而这太低了，无法将微塑料分散到下游。这些“干燥天气”的溢出导致河床栖息地的急性塑料污染。底栖地带有许多水生动物，其质量会影响整个河流生态系统。所有微塑性类型都在河床上堆积高浓度，直到被洪水冲入下游。这些发现提出了有关城市废水可持续管理的基本问题。处理废水将关闭此类河流中的微塑料碎片和微珠的主要来源，并阻止其向海洋的运输。河流微塑料的运输主要分为以下两个部分：（1）来自处理过的废水中低浓度的合成纤维的连续运输；（2）由受污染的河床带走的完整的微塑性组合的爆发式洪水驱动运输。仅关注浮力的非洪水微塑料负荷会产生对河流微塑料污染的极不具代表性的评估。随着夏季基流减少和废水通量增加，气候变暖和城市人口增长将加剧许多河流生态系统的微塑负担。（1）从处理后的废水中以低浓度连续运输合成纤维；（2）由受污染的河床带走的完整的微塑性组合的爆发式洪水驱动运输。仅关注漂浮的非洪水微塑料负荷会产生对河流微塑料污染的极不具代表性的评估。随着夏季基流减少和废水通量增加，气候变暖和城市人口增长将加剧许多河流生态系统的微塑负担。（1）从处理后的废水中以低浓度连续运输合成纤维；（2）由受污染的河床带走的完整的微塑性组合的爆发式洪水驱动运输。仅关注漂浮的非洪水微塑料负荷会产生对河流微塑料污染的极不具代表性的评估。随着夏季基流减少和废水通量增加，气候变暖和城市人口增长将加剧许多河流生态系统的微塑负担。仅关注漂浮的非洪水微塑料负荷会产生对河流微塑料污染的极不具代表性的评估。随着夏季基流减少和废水通量增加，气候变暖和城市人口增长将加剧许多河流生态系统的微塑负担。仅关注漂浮的非洪水微塑料负荷会产生对河流微塑料污染的极不具代表性的评估。随着夏季基流减少和废水通量增加，气候变暖和城市人口增长将加剧许多河流生态系统的微塑负担。