Explorative Quantitative Nontarget Analysis Reveals Micropollutants in Danish Groundwater

Groundwater is the only source of drinking water in Denmark and is vulnerable to chemical contaminant infiltration from various origins such as agriculture, hospitals, and industrial activities. Since targeted analysis is not sufficient for profiling unknown contaminants, untargeted analysis is vital to detect pollutants that are potentially overlooked. In this study, 81 groundwater sites across Denmark were investigated using a sensitive untargeted platform with nanoflow liquid chromatography hyphenated to a tandem high-resolution Orbitrap mass spectrometer (HRMS/MS). Following solid-phase extraction of groundwater samples, 121 micropollutants reflecting mixed contributions from multiple sectors relating to agrochemical, industrial, medical/veterinary, and natural compounds were identified across the sites. Micropollutant concentration levels ranged from 2 pg/L to 9.7 μg/L, and pesticide degradation products were found at the highest concentrations. About 29% of the identified micropollutants were present at concentrations above 100 ng/L in 78% of the sites. The nontargeted data set still contains another 230,913 unidentified features. Our study reveals the occurrence of micropollutants from multiple sectors, which are not included in the regular targeted groundwater monitoring program in Denmark, and such findings may challenge drinking water producers. The study demonstrates that nontarget analysis can play an important role in future groundwater monitoring