Using Chromatography to Detect Rare Pesticides in Water

Some pesticides and biocides are tricky to test for because of their unusual chemical properties, so they often get left out of routine drinking water (DW) testing. This means we do not have a clear picture of how much of these chemicals are present in tap water or how they could affect human health. To help close this gap, a team at the Nancy Laboratory for Hydrology (part of the French Agency for Food, Environmental and Occupational Health & Safety) developed and tested new methods for detecting 21 of these harder-to-test chemicals in drinking water. Twenty of them were measured using solid-phase extraction coupled to high-performance liquid chromatography-tandem mass spectrometry (SPE-HPLC-MS/MS), while the last one required direct injection ion chromatography-tandem mass spectrometry (DI-IC-MS/MS). The findings were published in the journal Talanta.¹

Why Do Certain Pesticides and Biocides Remain Poorly Documented?

“Although the occurrence of many conventional pesticides, TPs, and several biocides has been extensively investigated in environmental and DW matrices,” the authors of the paper write,¹ “this is not the case for all active substances. Several compounds remain insufficiently documented because their determination is analytically challenging owing to their diverse physicochemical properties, including high polarity, low water solubility, strong sorption potential, instability, or unfavorable chromatographic behavior. Such characteristics frequently limit their inclusion in routine multiresidue methods and contribute to the scarcity of occurrence data.”

Biocides are a good example of this problem, though how well-studied they are really depends on the specific chemical and what it is used for. Unlike typical farm pesticides, many biocides come from everyday sources (cities, factories, homes, and healthcare settings) and can wash into rivers and streams through wastewater, urban runoff, or by leaching out of treated materials like paints or plastics.^2,3

What Evidence Suggests These Pesticides and Biocides Might Be Present in Drinking Water Sources?

In France, researchers recently ran the country's first large-scale study looking for 49 emerging contaminants (including 32 biocides and 17 surfactants) in surface water, sediment, wastewater, and sludge. They found roughly a third to half of these substances at least once, depending on what they were testing. A few biocides showed up especially often, and some were found at levels high enough to potentially harm aquatic life, confirming that several under-the-radar biocides are out in the environment in France. The study, however, mainly examined rivers and wastewater, not the treated tap water people drink.⁴

At the same time, scientists have become increasingly interested in a group of chemicals nicknamed "persistent and mobile" pollutants—basically, substances that do not break down easily and move around a lot, making them prone to ending up in the groundwater and rivers that get turned into drinking water. One study focused specifically on pesticides with these traits and found several of them present in water sources used to supply tap water.^5,6

Together, these findings send a clear message: chemicals that don't get much attention in routine testing can still be lurking in the water we eventually drink. That's exactly why, in the minds of the research team, it's so important to keep developing better testing methods and monitoring programs that can catch them.¹

How Well Did the New Testing Methods Work, and What Did They Find When Applied to Real Drinking Water Samples?

To make sure the new testing methods were reliable, the researchers checked them against official standards using six different types of tap water. The methods performed well overall: they could detect even very tiny amounts of these chemicals, the results were consistent and accurate, and repeat testing gave similar results most of the time. There was some built-in uncertainty in the measurements, as is normal with this kind of testing, though a bit higher for a few of the chemicals.¹

Once confirmed to work well, these methods were used to test 313 drinking water samples collected as part of a nationwide French monitoring effort, covering water systems that serve roughly a fifth to a quarter of the country's population. Out of the 21 chemicals being tested for, only one—fluopyram—turned up, and only in a single sample, at a very low level. None of the other chemicals were found in any of the samples with valid results.¹

“These findings,” write the authors of the paper,¹ “are consistent with national occurrence databases, which indicate extremely low quantification frequencies (QFs) for most investigated substances. The developed methods provide robust tools for routine monitoring of the investigated parent compounds and establish a framework for future studies incorporating relevant transformation products in DW.”

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References

1. Khoury, D.; Pallez, C.; Lardy-Fontan, S. et al. Analytical Method Development for Twenty-one Analytically Challenging and Under-investigated Pesticides in Drinking Water. Talanta 2026, 312 (Pt C), 130561. DOI: 10.1016/j.talanta.2026.130561
2. Margot, J.; Rossi, L.; Barry, D.A. et al. A Review of the Fate of Micropollutants in Wastewater Treatment Plants. Wiley Interdiscip. Rev.: Water2015, 2 (5), 457-487. DOI: 10.1002/wat2.1090
3. Paijens, C.; Bressy, A.; Frère, B. et al. Biocide Emissions from Building Materials During Wet Weather: Identification of Substances, Mechanism of Release and Transfer to the Aquatic Environment. Environ. Sci. Pollut. Control Ser.2020, 27 (4), 3768-3791. DOI: 10.1007/s11356-019-06608-7
4. Assoumani, A.; Lestremau, F.; Ferret, C. et al. Nation-wide Monitoring Campaign of 49 Biocides and Surfactants in Surface Waters and Wastewaters. Sci. Total Environ. 2024, 954, 176624. DOI: 10.1016/j.scitotenv.2024.176624
5. Reemtsma, T.; Berger, U.; Arp H. P. et al. Mind the Gap: Persistent and Mobile Organic Compounds-Water Contaminants That Slip Through. Environ Sci Technol. 2016, 50 (19), 10308-10315. DOI: 10.1021/acs.est.6b03338
6. Sjerps, R. M.; Kooij, P. J.; van Loon, A. et al. Occurrence of Pesticides in Dutch Drinking Water Sources. Chemosphere2019, 235, 510-518. DOI; 10.1016/j.chemosphere.2019.06.207