An effective water quality monitoring system must be easy to use, affordable, reliable, and – crucially – fast enough to trigger timely action. Over the past few decades, the Netherlands has built such a system: a harmonized early warning network based on online solid phase extraction (SPE) coupled to high-performance liquid chromatography with diode array detection (HPLC–DAD).
According to researchers at KWR Water Research Institute, this approach has become an indispensable link in the protection of Dutch surface waters and river ecosystems. In a recent paper, they describe how method harmonization, shared spectral libraries, and interlaboratory coordination transformed a relatively simple analytical technique into a national early warning platform.
We spoke with corresponding author Patrick S. Bäuerlein to find out how the system evolved – and what lessons other countries might draw from the Dutch experience.
When was the HPLC-DAD system first introduced in the Netherlands and how did the method evolve into its present form?
The current HPLC-DAD method has a long history. In the late 1990s, Dutch authorities, together with academic partners, developed the System for the Automated Monitoring of Organic Pollutants in Surface Water (SAMOS). This system combined online solid-phase extraction with GC-MS or LC-MS, enabling the automatic processing of large sample volumes. Demonstrations showed that 50–100 organic micropollutants, including polar pesticides, could be identified at concentrations of approximately 1 µg/L – representing a breakthrough for real-time water monitoring in European rivers.
Once installed at Lobith and Eijsden by RIZA (the National Institute for Integrated Freshwater Management and Wastewater Treatment, the former Dutch water management research institute that has been part of Rijkswaterstaat since 2007), the approach was further refined in collaboration with drinking water laboratories and drinking water utilities.
A harmonized platform emerged: a shared UV/Vis spectral library combined with a relatively simple linear retention time index based on the Kováts index. A retention time index is used to correct retention times for small differences that may occur between different HPLC–DAD systems. This enabled comparison of results between locations and helped water utilities identify and respond to contamination incidents.
Every two years an interlaboratory study is used to make sure that the methods of all participants are still harmonized. Recent developments, such as the open-source R Shiny tool HPLC-UV2R, have made the exchange of recorded UV/Vis spectra even easier. This application allows laboratories to normalize, store, and share UV/Vis spectra.
Thanks to these advances, HPLC-DAD has evolved into a cost-effective, resilient, and collaborative early warning system – an indispensable link in the protection of Dutch surface waters and river ecosystems.
What makes HPLC-DAD particularly well suited to water-quality monitoring – especially when compared with MS-based techniques?
HPLC-DAD stands out as a robust and affordable screening method that can be readily integrated into already existing alarm systems. It is also easy to understand and to maintain. One of its key strengths lies in its speed: within a few hours after analysis, results can be shared with others so decisions based on the results can be taken. Real-time monitoring and rapid communication are essential, because protecting drinking water supplies requires not only detection but also a swift response. The main weakness is obviously, that only UV-active compounds can be detected. For that reason, it is not a substitute for (HR)MS; it is complementary. However, MS-based techniques are much less robust, more costly, and require a much higher level of expertise from the operating staff and specific site requirements.
Is there a particular example that best demonstrates the value of this system?
I think the pyrazole incident was a very good example for showing the usefulness of the HPLC-DAD method. Thanks to the method, the compound was detected quickly and the harmonization made it possible to check other samples for the same compound. This happened in 2015: water abstraction from the Meuse by three water companies had to be suspended after the detection of an unknown polar compound. The mussel monitoring system raised the first alarm, after which HPLC-DAD revealed a strongly UV-active signal. Further analysis using HRMS showed that the compound was pyrazole, a by-product of acrylonitrile production. Concentrations reached 90–100 µg/L. The cause turned out to be a malfunctioning industrial wastewater treatment system. The discharge ultimately led to legal prosecution. HPLC-DAD was able to detect this compound easily, whereas it initially went unnoticed by HRMS.
Do you see comparable systems elsewhere, or is this network somewhat unique in its level of harmonization and coordination?
Some samples from Germany are measured using this method, but this is done in collaboration with our network. As far as we know there is no comparable initiative outside the Netherlands. And I doubt it is widely known in other countries/laboratories – which was one of the main reasons we wanted to publish the paper.
What key lessons do you think other countries could take from the Dutch experience of harmonizing methods, databases, and interlaboratory procedures?
Harmonization is immensely useful if different laboratories need to exchange data. The case involving pyrazole demonstrates the great importance of the harmonized HPLC-DAD platform. Robust, affordable, and user-friendly, the system is ideally suited as an early warning platform. It detects both known and unknown substances, generates rapid alerts, and enables authorities to intervene in a timely manner. HPLC-DAD has proven to be a reliable and powerful technique for quickly tracing contaminants, which is essential for ensuring the safety of drinking water supplies. When combined with complementary analytical techniques such as HRMS, non-UV-active substances can also be detected, further expanding the applicability of the method.
Looking ahead, how do you see water-quality monitoring evolving in the Netherlands?
Currently we are working on expanding the network of participants in the freshwater sector. For this reason, we published the article in ES&T including the software. The goal was to attract attention and to reduce the inhibition threshold to join. Other labs can now first test the software before committing. At the same time, we are hoping that laboratories or authorities from other areas of water research and monitoring have a look at our approach and decide if it might also be a useful approach for them.
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