Extraction of polycyclic aromatic hydrocarbons (PAHs) from surface soils of East Kolkata wetland, India, and its distribution, sources, and risk assessment.

Abstract

The East Kolkata wetland (EKW) in West Bengal, India is a Ramsar site and has ecological importance to the city. The booming urbanization history of Kolkata city causes increase in concentration of persistent air pollutants like polycyclic aromatic hydrocarbons (PAHs) which got adsorbed eventually in the wetland soil due to their hydrophobicity and lipophilicity. Therefore, current study aims to investigate PAHs pollution level along with associated ecological health risk and optimization of PAHs extraction to develop standard analysis protocol. Three different extraction methods including Soxhlet extraction (SE), Ultrasound-assisted extraction (UAE) and Mechanical stirring extraction (MSE), four different organic solvents with different polarity (acetone, n-Hexane, DCM and Toluene) and varying extraction time between 6 and 24 h are used in the optimization study. The SE method outperformed among them with toluene as most effective solvent with maximum yield at 12 h of time. Concerning risk assessment study, total PAHs concentration (288.47 ± 14.52 μg g-1) exceeded the effect range median (ERM, 44.79 μg g-1) and probable effect levels (PEL, 16.77 μg g-1) based on sediment quality guidelines (SQGs) indicating adverse biological effects on the ecosystems. The values of Benzo[a]Pyrene-toxicity equivalent quotient (BaP-TEQcar = 70.54 ± 4.83 μg g-1; BaP-MEQ = 64.51 ± 6.30 μg g-1) suggest high level of risk. On the contrary, the total carcinogenic PAHs concentration suggests very low risk via the ingestion. The source apportionment study using different diagnostic ratios (DRs) reveal pyrogenic and petrogenic origins along with biomass. Hence, the findings of the present investigation could aid in enhancing the sustainable management of EKW area.