A major cross-border study has found micropollutants in 96% of groundwater monitoring sites across the Upper Rhine region, raising urgent questions about the long-term quality of one of western Europe's most important drinking water reserves, which supplies more than five million people across France, Germany and Switzerland. Stretching 300 kilometres from Basel to Frankfurt across a densely populated and intensively farmed plain, the aquifer is the subject of the most comprehensive cross-border assessment ever conducted in the region: the findings of the ERMES-ii-Rhein project paint a picture of widespread, persistent and growing chemical contamination.
What the data shows
Across 1,497 monitoring sites and 181 parameters analysed, the results are unambiguous. Micropollutants were detected at 96% of sites, and at 59% of sites at least one European or national drinking water threshold was exceeded. On average, nine different trace substances were found per monitoring point. Of the 144 organic micropollutants investigated, 131 were detected at least once across the network. The dominant contaminants were pesticide metabolites and PFAS, followed by food additives and pharmaceutical residues. Around Basel and in southern Alsace, up to forty different substances from multiple source categories were identified at a single monitoring point, illustrating what the report calls the "cocktail effect": the potential for toxic impacts to compound even at individually low concentrations, with effects on health and ecosystems that remain poorly understood.
The report calls for action on three interconnected fronts: reducing pollutants at source, upgrading wastewater treatment plants to quaternary treatment, and improved monitoring
A particularly vulnerable aquifer
The Upper Rhine Graben aquifer is largely shallow and highly permeable, meaning surface water, rainfall and river flows can infiltrate rapidly, carrying contaminants with them. The study found that wastewater treatment plants play a significant and underappreciated role in this contamination pathway. Most plants were not designed to eliminate micropollutants, and substances such as carbamazepine, sulfamethoxazole and tramadol were found at markedly higher concentrations downstream of discharge points, both in surface water and in groundwater. Rivers in the region effectively act as a transport medium for household-derived pollutants into the aquifer. The study also highlighted trifluoroacetic acid (TFA), the smallest and most mobile PFAS compound, as a particular concern: detected at 96% of monitoring sites, it is extremely persistent, accumulates in the water cycle, and currently has no unified European regulatory standard.
Recommendations and the road ahead
The report identifies three interconnected priorities. Source reduction comes first: limiting the use of the most mobile and persistent substances in agriculture, industry and households, while closely monitoring replacement compounds that too often reproduce the same problems under different names. Second, wastewater treatment infrastructure needs upgrading. Quaternary treatment, already operational in Switzerland since 2016, can remove the majority of micropollutants. The 2024 EU directive on urban wastewater now requires France and Germany to implement this progressively by 2045. Third, monitoring must improve. The project deployed non-target screening for the first time at a trinational scale, a methodology capable of capturing the full chemical fingerprint of a water sample rather than searching only for pre-selected substances. Between 61 and 194 compounds were identified per sample in the six pilot areas, including many not covered by conventional analysis. The authors argue this approach should become standard practice.
The broader message of ERMES-ii-Rhein is institutional as much as scientific. A resource shared across three countries, multiple federal states and two river basins cannot be protected by unilateral action. The project itself, coordinated by APRONA and co-financed by the Interreg Upper Rhine programme, demonstrates what coordinated cross-border monitoring can achieve. Translating that scientific foundation into aligned policy and investment is now the central challenge.
