Assessment of Heavy Metal Pollution Indices in the Atrak River Water Flow Due to the Discharge of Bojnord Municipal Wastewater Treatment Plant Effluent

This study investigates variations in heavy metal concentrations to assess potential pollutant transport and effective transport distances in the Atrak River, influenced by urban wastewater treatment plant discharge and downstream agricultural activities. The methodology comprises field surveys, in-situ measurements, sample collection, and index analysis. Water and sediment samples were collected from five and one selected stations, respectively, during summer 2024, using duplicate sampling to ensure Quality Assurance (QA) and Quality Control (QC). Heavy metals were quantified via ICP-OES. The Contamination Degree (Cd) index indicated moderate contamination at all stations except S2 (downstream of WWTP discharge). The Heavy Metal Evaluation Index (HEI) and Heavy Metal Pollution Index (HPI) confirmed peak contamination at Station S2. Spatial distribution patterns varied: arsenic (As) and lead (Pb) showed consistent concentrations along the river, while chromium (Cr) and iron (Fe) exhibited an increasing trend downstream, attributed to their strong correlation. The Geoaccumulation Index (Igeo) revealed no sediment contamination for any of the metals. The Contamination Factor (CF) indicated moderate pollution for Cd. The Hazard Index (HI) for children was approximately 0.5, signifying non-carcinogenic risk. Consequently, under prevailing hydraulic conditions, the river’s capacity to transport wastewater-derived pollutants is limited to a 50–100 meters range from the discharge point. These findings underscore the critical importance of wastewater management and continuous water quality monitoring in similar watersheds.