محمد فروهر

The Sefidrud River, a vital ecosystem near the Caspian Sea, is heavily contaminated with potentially toxic elements (PTEs), threatening ecological and public health. This study assesses seven PTEs—arsenic (As), chromium (Cr), nickel (Ni), copper (Cu), cobalt (Co), antimony (Sb), and zinc (Zn)—in water and sediment samples from five stations. We usedtheenrichment factor(EF), geoaccumulation index(Igeo),potential ecological risk index(PERI), hazard quotient (HQ), hazard index (HI), and carcinogenic risk (CR) to evaluate risks. Results show severe ecological risks, with water risk indices (5598.9–6252.9) exceeding sediment risks (962.29–6252.9). Cu and As dominate water risks, while As, Co, and Sbdrivesediment risks. Station 2 (sediments) and Station 4 (water) are critical hotspots, influenced by volca nic geology and local human activities like mining and agriculture. Health risks are significant, with water HI (16.79–18.42) and CR (3.75–4.65 × 10-3) indicating serious non-carcinogenic and carcinogenic threats, primarily from As ingestion. Sediments act as PTE sinks, but water's higher bioavailability increases exposure risks. Compared to global rivers, the Sefidrud's contamination is severe, necessitating urgent water treatment, sediment cleanup, and continuous monitoring to protect ecosystems and ensure sustainable river management.