Per- und polyfluorierte Alkylsubstanzen (PFAS) stellen auf-grund ihrer Persistenz und Toxizität ein wachsendes Risiko für Wasser-ressourcen dar. In einer achtmonatigen Messkampagne wurde Regen-wasserabfluss eines Berliner Industriegebiets auf 26 PFAS und andere Industriechemikalien untersucht. Zusätzlich wurde ein urbaner See beprobt, der ausschließlich durch Regenwasserabfluss und Grundwasser gespeist wird. PFAS-Konzentrationen im Regenwasserabfluss lagen zwischen 5 und 35 ng/L, PFOA und PFHxA waren am häufigsten nachweisbar. Die Konzen-trationen lagen im Bereich vorgeschlagener Umweltqualitätsnormen für Oberflächengewässer mit Maximalwerten deutlich darüber. Im See wurden deutlich höhere Konzentrationen (bis 99 ng/L) gemessen, die vermutlich durch Altlasten des benachbarten Flughafens und nicht primär durch Regenwasserabfluss verursacht werden. Im Vergleich zu Kläranlagenab-läufen waren die gemessenen PFAS-4-Konzentrationen im Regenwasser-abfluss in dieser Studie um den Faktor 3-10 niedriger. Für Gewässer sind Kläranlagenabläufe auch durch die größeren Volumina als Eintragspfad von PFAS wahrscheinlich von größerer Relevanz als Regenwasserabflüsse. Dennoch ist Regenwasserabfluss insbesondere in Schwammstadt-konzepten mit Versickerungssystemen als potentiell relevanter Eintrags-pfad für PFAS zu betrachten. Die Ergebnisse zeigen die Notwendigkeit eines besseren Verständnisses urbaner PFAS-Quellen für ein effektives Wasserschutzmanagement.

Agricultural water reuse is one approach to mitigate water stress. In addition to the minimum requirements, the European water-reuse regulation 2020/741 mandates a risk management approach for agricultural water reuse. In contrast to the microbiological monitoring, the extent of the chemical risk assessment and monitoring is not clearly defined. The resulting complexity of a typical agricultural water-reuse scheme was analyzed. Potentially relevant parameters were identified based on European and German regulatory frameworks, concerning key subjects of protection. An interdisciplinary assessment of efforts and challenges, regarding required analyses, was accomplished, using expertise from recent research investigating agricultural water reuse in Germany. Suggestions were provided for disinfection validation, microbiological monitoring parameters and analytical methods. Additionally, chemical indicator parameters were suggested to address relevant processes during monitoring. Both microbiological and chemical parameters presented analytical challenges, which were described with future needs to support water-reuse implementation. Costs for analyses were estimated using available price information, highlighting the high costs of certain analyses, especially for organic micropollutants. Therefore, analyses need to be further facilitated by the application of process indicators and the implementation of cost-effective, multi-target methods tailored to the requirements of risk management for agricultural water reuse.

In 2020, the European Union published ordinance EU 2020/741, establishing minimum requirements for water reuse in agriculture. The ordinance differentiates between several water quality classes. For the highest water quality class (Class A), the ordinance mandates analytical validation of the treatment performance of new water reuse treatment plants (WRTP) related to the removal of microbial indicators for viral, bacterial, and parasitic pathogens. While the ordinance clearly defines the numeric target values for the required log10-reduction values (LRV), it provides limited to no guidance on the necessary sample sizes and statistical evaluation approaches. The main requirement is that at least 90 % of the validation samples should meet the requirements. However, the interpretation of this 90 % validation target can significantly impact the required sample size, efforts necessary, and the risk of misclassifying WRTPs in practice. The present study compares different statistical evaluation approaches that might be considered applicable for LRV validation monitoring. Special emphasis is placed on the use of tolerance intervals, which combine percentile estimations with sample size-based uncertainty and confidence regions. Tolerance interval-based approaches are compared with alternative methods, including a) a binomial evaluation and b) the calculation of empirical percentiles. The latter are already used in existing European and U.S. regulations for bathing water and irrigation water quality. Our study demonstrates that using tolerance intervals allows for the reliable validation of WRTPs that achieve high LRVs relative to regulatory targets with comparatively smaller sample sizes compared to the other two approaches, while reducing the risk of misclassification. Additionally, we show that simplified approaches, such as a “9 out of 10” approach, pose a substantial risk of misclassification and should not be applied. We illustrate the behavior of these different approaches through simulation experiments and application to real data collected in 2022 and 2023 at a large WRTP in Germany.