Paired Assessment of Potentially Toxic Elements, Hydrochemistry, and Screening-Level Human Health Risks in Groundwater of the Southern Harran Plain, Türkiye

Groundwater contamination by potentially toxic elements (PTEs) presents potential health concerns in intensively irrigated agricultural regions. This study assessed paired changes in groundwater chemistry, dissolved PTE concentrations, and screening-level human health risk indicators in the southern Harran Plain, Türkiye, using the same 16 boreholes sampled in 2019 and 2025. Physicochemical parameters, major ions, and nine PTEs were analyzed; oral ingestion risks for adults and children, the entropy-weighted water quality index (EWQI), irrigation suitability, and PHREEQC mineral saturation indices were assessed. Mean As concentrations increased from 18.61 to 20.54 µg L−1, while mean Cd concentrations increased from 53.88 to 58.57 µg L−1. Both elements exceeded the applied drinking-water guideline values at all 16 boreholes in both sampling years. Paired statistical comparisons revealed significant increases in As and Cd concentrations (p < 0.001). Mean hazard indices increased from 11.45 to 12.59 in adults and from 26.72 to 29.37 in children; As and Cd dominated these estimates. Arsenic-related incremental lifetime cancer risk estimates also increased, but represent screening-level indicators based on assumed exposure rather than observed health outcomes. Mean electrical conductivity rose from 1.86 to 2.55 mS cm−1, and EWQI deteriorated at all boreholes. These findings highlight As and Cd as priority contaminants for analytical verification, exposure assessment, and continued groundwater monitoring, while acknowledging that two-period comparisons cannot establish continuous temporal trends or contaminant sources.