Contamination fingerprinting and tracing techniques in karst aquifer systems: insights from Ireland

Karst springs are globally important for drinking water supply but are often exceptionally vulnerable to contamination and may be impacted by multiple pollution sources. In rural and suburban areas, human wastewater effluent (from on-site domestic wastewater treatment systems - DWTSs) and agricultural sources are generally considered among the most significant threats to groundwater quality. This is particularly concerning in Ireland, where more than one third of the population (>500,000 homes) relies on DWTSs. However, significant knowledge gaps exist with respect to linking contaminants with the origins of pollution and quantifying different pollution impacts on groundwater quality in karst environments.To address some of these knowledge gaps, it was necessary to evaluate a range of contamination fingerprinting and tracing techniques. The techniques included flow cytometric (FCM) fingerprinting of bacterial cells, faecal indicator bacteria (FIB) analysis, and turbidity measurements to assess their potential to provide fast and descriptive information on microbial pollution and karst aquifer dynamics. Additionally, yeast was re-examined as a microbial artificial tracer using modern detection methods at two sites. The study also tested several chemical fingerprinting techniques, including fluorescent whitening compounds, microplastic particles, and faecal sterols and stanols, to evaluate their effectiveness in identifying DWTSs pollution impacts on karst aquifers. The results of this study demonstrate the potential of combining a range of fingerprinting techniques to improve the detection and understanding of pollution impacts on karst aquifer systems.