Variation in The Concentrations of Polycyclic Aromatic Hydrocarbons in Water of The Northern Part of Shatt Al-Arab River ,Basrah-Iraq

Abstract

Abstract: Investigated the seasonal variation of polycyclic aromatic hydrocarbon (PAH) c in water of Shatt al-Arab River, Basrah- Iraq. Water samples from five stations (Al-Qurna, Al-Shafi, Al-Dair, Karma Ali, and Al-Zuraiji) were collected during summer and winter seasons. Total PAH concentrations ranged between 2.24 and 11.28 ŋg/L, with higher concentrations in summer (mean 9.46 ŋg/L) than in winter (mean 7.20 ŋg/L). The most significant effect was the radical seasonal shift in PAH composition, with HMW PAHs (4+ rings) dominating summer samples (78.4% total PAHs) and LMW PAHs (2-3 rings) dominating during winter samples (82.7%). This resulted in a 17-fold seasonal difference in the LMW/HMW ratio (summer: 0.28; winter: 4.81). Diagnostic ratios indicated predominantly petrogenic sources in winter and mixed sources in summer. Statistical analysis indicated a strong negative correlation between water temperature and the LMW/HMW ratio (r = -0.88, p < 0.001), implicating temperature as a primary driver of seasonal PAH compositional patterns. Spatial distribu-tion indicated hotspots of contamination at Karma Ali and Al-Shafi stations, in proximity to industrial activities and oil installations. Concentrations of carcinogenic PAHs, particularly during summer, exceeded global guide-lines for unpolluted freshwater, with potential risks to aquatic life and human health. This study provides nec-essary baseline data on seasonal PAH composition variation and highlights the need for season-specific moni-toring and pollution control strategies for this vital water body.