Karst aquifers provide drinking water for a quarter of the world’s population. That’s a lot of people! But because of their unique geology, chemicals from the surface can quickly get into the groundwater, potentially contaminating drinking water. We’ve seen nitrate, chloride, and bacteria contaminate karst aquifers before, but we don’t know much about “contaminants of emerging concern” (CECs), like pharmaceuticals. Researchers looked at 58 water samples from 13 sites in the Salem Plateau, a karst area in southwestern Illinois, USA, over 17 months. They tested for 12 pharmaceutical and personal care products (PPCPs), 7 natural and synthetic hormones, and 49 typical water quality factors like nutrients and bacteria. Hormones showed up in only 23% of samples, with concentrations between 2.2 and 9.1 nanograms per liter. PPCPs, though, were in 89% of groundwater samples. The most common PPCPs were triclocarban, an antimicrobial, found in 81% of samples, and gemfibrozil, a heart medication, in 57%. The team combined these results with local stream flow, weather, and land use data to do a few things: 1) figure out how much CECs contaminated the aquifer, 2) group sites with similar PPCP contamination, and 3) create models to explain the contamination. On average, they found 3 PPCPs in karst groundwater, totaling 4.6 nanograms per liter. The sites fell into 3 groups, each with its own contamination patterns. In Cluster I sites, PPCP contamination linked to stream height, manganese, boron, and heterotrophic bacteria. Cluster II sites connected to groundwater temperature, specific conductivity, sodium, and calcium. Cluster III sites showed ties to dissolved oxygen and barium. Overall, no single factor or small group of factors strongly predicted PPCP contamination, but gemfibrozil levels were closely related to the total amount of PPCPs in the karst groundwater.

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