Changes in Concentration of Poly Aromatic Hydrocarbons (PAHs) at the surface sediments of the Iranian coast Caspian Sea up to 30 m depth (2018-2019)

The purpose of this research was to determine the concentration of poly aromatic hydrocarbons (PAHs) in the surface sediments during four seasons at different transects of the southern basin of the Caspian Sea and to investigate the causes of their temporal and spatial changes, to compare with the standard limits, and to find the origin of these compounds. The samples from the surface sediments were collected using a grab (van Veen grab) from depths of 10 and 30 m in the coasts of Guilan, Mazandaran, and Golestan provinces at eight transects (Astara, Anzali, Sefidroud, Ramsar, Nowshahr, Babolsar, Amirabad, and Torkaman) during the autumn and winter seasons of 2018, spring and summer of 2019. The sediment samples were prepared in order to investigate PAHs using a standard method (extraction with organic compounds by the Soxhlet apparatus). The results showed that the mean (±SE) annual concentration of PAHs in the four seasons of autumn, winter, spring, and summer was 29.6±11.5, 2125±611, 4.2±3.0, and 5.3±3.1 µg/kg dry weight, respectively, and the maximum concentration of PAHs was recorded in the Nowshahr transect in the winter season. The results of the current research showed that 2 and 6 rings compounds had a low percentage of abundance in the sediments and the mean concentrations of PAHs and BaP in most of the samples were lower than the international threshold standards. The origin of PAHs compound in the sediment was recorded in more pyrogenic sources based on the diagnostic ratio (LMW/HMW=0.3).