Dissolved and particulate-adsorbed hydrocarbons in the waters of shatt al-Arab River, Iraq

Abstract

N-alkanes were measured both in dissolved and particulate-adsorbed phases of water samples collected from five stations located along Shatt al-Arab River in Iraq. The aim of this study was to provide a background information on the presence, origin, and distribution of n-alkanes in the waters of Shatt al-Arab River. Total concentrations of n-alkanes were lower in the dissolved phase (29.37 (μg L⁻¹) than in the particulate-adsorbed fraction (17.62 μg g⁻¹ dw). Distribution of n-alkanes in both fractions is characterized by two distinct patterns. First, for C compounds numbered C₁₄ to C₂₂, the ‘odd’ numbered hydrocarbons were slightly more abundant with C₁₇ being the most concentrated. The second is shown within n-alkanes greater than C₂₂. In these the ‘odd’ numbered hydrocarbons show even greater predominance indicating that much of the n-alkanes in the waters of Shatt al-Arab, may have originated from aquatic biogenic sources; i.e., diatoms, algal forms, bacterial activities, and higher plants. The CPI values were found to be from 0.99 to 1.98 in the dissolved fraction and from 0.70 to 2.10 in the particulate fraction. Petroleum hydrocarbon inputs and urban related oil discharges (anthropogenic pollution) may also have contributed to the input of n-alkanes in Shatt al-Arab, particularly near the city of Basrah (St. IV). Total concentrations at station IV were much higher (8.40 μg L⁻¹ and 5.80 μg g⁻¹) than that for the most upstream station, # I, (3.20 μg L⁻¹ and 1.48 μg g⁻¹) and decreased again further downstream at station V (7.10 μg L⁻¹ and 4.32 μg g⁻¹). The CPI values were around 1.0 in station IV. In a conclusion, results obtained in this study indicate that the n-alkanes in the waters of Shatt al-Arab River are of aquatic biogenic and anthropogenic (petroleum related) origins.