Wastewater discharges from publicly owned treatment works are a significant source of endocrine disruptors and other contaminants to the aquatic environment in the US. Although remaining pollutants in wastewater pose environmental risks, treated wastewater is also a primary source of stream flow, which in turn is critical in maintaining many aquatic and riparian wildlife habitats. Here we calculate the dilution factor—the ratio of flow in the stream receiving discharge to the flow of wastewater discharge—for over 14,000 receiving streams in the continental US using streamflow observations and a spatially explicit watershed-scale hydraulic model. We found that wastewater discharges make up more than 50% of in-stream flow for over 900 streams. However, in 1,049 streams that experienced exceptional low-flow conditions, the dilution factors in 635 of those streams fell so low during those conditions that the safety threshold for concentrations of one endocrine disrupting compound was exceeded, and in roughly a third of those streams, the threshold was exceeded for two compounds. We suggest that streams are vulnerable to public wastewater discharge of contaminants under low-flow conditions, at a time when wastewater discharges are likely to be most important for maintaining stream flow for smaller sized river systems.

中文翻译：

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由于废水稀释不充分，在低流量期间，美国河流中的内分泌污染物含量很高

公有处理厂的废水排放是美国水生环境中内分泌干扰物和其他污染物的重要来源。尽管废水中残留的污染物构成环境风险，但经过处理的废水也是溪流的主要来源，这反过来对于维持许多水生和河岸野生生物栖息地至关重要。在这里，我们使用流量观测和空间明确的分水岭规模水力模型，计算了美国大陆上14,000多个接收流的稀释系数（接收流中的流量与废水排放量之比）。我们发现，废水排放量占900条以上溪流的50％以上。但是，在1049条遇到异常低流量条件的流中，在这些条件下，其中635种物流的稀释因子下降得如此之低，以至于超过了一种内分泌干扰化合物浓度的安全阈值，而在大约三分之一的物流中，两种化合物均超过了该阈值。我们建议，在低流量条件下，当废水排放对于保持较小规模河流系统的水流最重要时，在低流量条件下，河流很容易受到污染物排放的污染。