Institute for Environmental Sciences, University Koblenz-Landau, Fortstraße 7, D-76829 Landau in der Pfalz, Germany.
Federal Environment Agency, Wörlitzer Platz 1, D-06844 Dessau-Roßlau, Germany.
Sci Total Environ. 2017 Nov 15;598:805-813. doi: 10.1016/j.scitotenv.2017.04.180. Epub 2017 Apr 27.
Incomplete removal during wastewater treatment leads to frequent detection of compounds such as pharmaceuticals and personal care products in municipal effluents. A fixed standard dilution factor of 10 for effluents entering receiving water bodies is used during the exposure assessment of several chemical risk assessments. However, the dilution potential of German receiving waters under low flow conditions is largely unknown and information is sparse for other European countries. We calculated dilution factors for two datasets differing in spatial extent and wastewater treatment plant (WWTP) size: a national dataset comprising 1225 large WWTPs in Central and Northern Germany and a federal dataset for 678 WWTPs of a single state in Southwest Germany. We found that the fixed factor approach overestimates the dilution potential of 60% and 40% of receiving waters in the national and the federal dataset, with median dilution factors of 5 and 14.5, respectively. Under mean flow conditions, 8% of calculated dilution factors were below 10, with a median dilution factor of 106. We also calculated regional dilution factors that accounted for effluent inputs from upstream WWTPs. For the national and the federal dataset, 70% and 60% of calculated regional dilution factors fell below 10 under mean low flow conditions, respectively. Decrease of regional dilution potential in small receiving streams was mainly driven by the next WWTP upstream with a 2.5 fold drop of median regional dilution factors. Our results show that using the standard dilution factor of 10 would result in the underestimation of environmental concentrations for authorised chemicals by a factor of 3-5 for about 10% of WWTPs, especially during low flow conditions. Consequently, measured environmental concentrations might exceed predicted environmental concentrations and ecological risks posed by effluents could be much higher, suggesting that a revision of current risk assessment practices may be required.
在废水处理过程中不完全去除会导致药物和个人护理产品等化合物在城市废水中频繁检出。在进行多次化学风险评估时，对于进入受纳水体的废水，采用固定的标准稀释因子 10。然而，德国低流量条件下受纳水体的稀释潜力在很大程度上是未知的，其他欧洲国家的相关信息也很匮乏。我们针对两个数据集计算了稀释因子，这两个数据集在空间范围和污水处理厂（WWTP）规模上存在差异：一个数据集包含德国中北部 1225 个大型 WWTP，另一个数据集包含德国西南部一个州的 678 个 WWTP。我们发现，固定因子方法高估了全国数据集和联邦数据集 60%和 40%的受纳水体的稀释潜力，其中位数稀释因子分别为 5 和 14.5。在平均流量条件下，计算出的稀释因子有 8%低于 10，中位数稀释因子为 106。我们还计算了考虑上游 WWTP 废水输入的区域稀释因子。对于全国数据集和联邦数据集，在平均低流量条件下，分别有 70%和 60%的计算区域稀释因子低于 10。小型受纳溪流区域稀释潜力的下降主要是由上游的下一个 WWTP 驱动的，其区域稀释因子中位数下降了 2.5 倍。我们的研究结果表明，对于约 10%的 WWTP，在低流量条件下，使用标准的 10 稀释因子会导致授权化学品的环境浓度低估 3-5 倍，因此，实际的环境浓度可能会超过预测的环境浓度，废水造成的生态风险可能会更高，这表明可能需要修订当前的风险评估实践。
