Groundwater contamination sources and health risk assessment in the Kula–Selendi region, western Anatolia

Groundwater contamination in western Türkiye's basins remains poorly understood because geogenic and anthropogenic influences overlap. This study assesses sources and human health risks associated with groundwater contamination in the Kula-Selendi region (Manisa), where geothermal, cold mineral-rich, and cold fresh groundwater types coexist. Thirty water samples (27 groundwater and 3 surface water) were analyzed for major ions, trace metal(loid)s (TMs), and physicochemical parameters. Principal component analysis (PCA) identified four dominant hydrogeochemical processes: silicate weathering, carbonate dissolution, anthropogenic contamination, and arsenic mobilization. Geothermal waters in the Vezirler mélange contained low arsenic (≤2 µg L^-1), whereas cold groundwater in sedimentary aquifers reached 3050 µg L^-1, indicating that arsenic enrichment is decoupled from the Kula Geothermal System. Elevated nitrate (up to 454.7 mg L^-1) in shallow aquifers reflects inputs from agricultural and livestock activities. Health risk assessment (HRA) showed that arsenic in sedimentary aquifers posed high carcinogenic risk and dominated non-carcinogenic risk via drinking water, followed by lithium, nitrate, and boron. Dermal exposure generally posed low risk, although boron and lithium made relatively greater contributions. The combined PCA-HRA approach links hydrogeochemical processes to human health risks and supports targeted monitoring of naturally enriched TMs (As, B, Li) and mitigation of nitrate pollution.