Urbanization, the expansion of impervious surfaces have intensified the stormwater pollution. In this study, six rainfall events were monitored in the Tehran’s District 22 to quantify the event mean concentrations (EMCs) of the total suspended solids (TSS) an‎d heavy metals, including Pb, Zn, Cu, Cd, Cr, Hg, Fe, an‎d as across four lan‎d uses (residential, commercial, industrial an‎d traffic). The results indicated that the average TSS concentrations ranged from 185 mg/L in the residential areas to 360 mg/L in the traffic zones. Among heavy metals, Zn (≈270 µg/L) an‎d Pb (≈220 µg/L) recorded the highest levels in industrial lan‎d traffic lan‎d uses, while Cd an‎d Hg were recorded at the relatively lower levels but still exceeded World Health Organization (WHO) thresholds. SWAT simulations estimated an annual sediment yield of approximately 1,650 tons, with heavy metal loads ranging from 35 to 210 kg per year depending on lan‎d use. The ecological risk index (RI) revealed very high risk in traffic (RI ≈ 520) an‎d industrial areas (RI ≈ 480), while residential zones were categorized as the moderate risk. Model calibration demonstrated strong reliability (NSE = 0.94, R² = 0.96, low RMSE), confirming the accuracy of SWAT in reproducing the observed EMC values. Overall, the findings highlight that urban runoff in District 22 is a major source of heavy metal pollution, posing the severe threats to aquatic ecosystems an‎d food safety in downstream agricultural lan‎ds. These results underscore the urgent need for the continuous monitoring, green infrastructure adoption, an‎d integrated stormwater management policies to mitigate the pollutant loads

سعيد اسلاميان

عليرضا گوهري , شاهرخ سلطاني نيا

منوچهر حيدرپوراسفرجاني , محمدحسين گل محمدي