Petrogenic and Biogenic Inputs of n-alkanes along Shoreline of the Caspian Sea in the Mazandaran Province, North of Iran

Abstract

The Caspian Sea is the largest lake in the world and is facing an increasing risk of contamination. Sea-based and land-based hydrocarbons inputs are the most critical pollutants of the Caspian Sea. In the present study, n-alkanes and related diagnostic ratios were used to identify the sources of hydrocarbon contaminants in surface sediments along the southern coastal area of the Caspian Sea in Mazandaran province. 27 surface sediment samples were collected from a depth of 5 meters under sea level. Contaminant’s compositions were extracted by Soxhlet apparatus and analyzed by Gas Chromatography-Mass Spectrometry. According to the results, the total concentration of n- alkanes (ΣHC) ranged from 5.2 µg g^-1 to 690.7 µg g^-1. The S20 (selected station in Noshahr port) had the highest concentration, and most of the stations have levels in a moderate range. Five diagnostic ratios are used to distinguish petrogenic and biogenic contaminants in shorelines of the Mazandaran province. In all stations, Carbon Preference Index (CPI), LMW/HMW, Pr/n-C₁₇, Phy/n-C₁₈, Pr/Phy, and U/R values indicated the petrogenic inputs. However, in some stations biogenic inputs were additionally detected. The petrogenic pollutants were almost from sea-based inputs such as oil spills from Turkmenistan and Azerbaijan. On the other hand, biogenic contaminants were almost from rivers and Hyrcania forests.