Distribution of linear alkylbenzenes as a domestic sewage molecular marker in surface sediments of International Anzali Wetland in the southwest of the Caspian Sea, Iran

Abstract

Due to directly receiving high volume of untreated urban and industrial sewage and in turn transferring the pollutants to fish and back to humans, the International Anzali Wetland has been considered to be urgently registered in the Montreux Record. Hence, the present study was aimed to determine the spatial distribution of the linear alkylbenzenes (LABs) in surface sediments of the wetland and its sewage contamination situation. The surface sediments (sampling stations = 167) were collected from the western, eastern, southwest, and central regions of the wetland. The samples were extracted, fractioned, and then analyzed using gas chromatography–mass spectrometry (GC-MS). The concentration of LABs in the sediment samples revealed a range from 394.12 to 109,305.26 ng g⁻¹ dw. The concentrations of ΣLABs in the eastern region were significantly higher than that in the other regions. The occurrence of low ratio of internal to external isomers (I/E ratio) of LABs (from 0.65 to 1.30) and D% (from − 0.07 to 24.13) implied effluent row or poorly untreated sewage into the wetland. No correlation was observed between the detected LAB concentrations with total organic carbon (TOC) and grain size. Taken together, regional anthropogenic inputs are the controlling factors for the observed spatial distributions of ∑LABs in the International Anzali Wetland. The findings suggested that LABs are powerful indicators to trace anthropogenic sewage contamination and also highlighted the necessity of sewage treatment plants to be founded around the International Anzali Wetland, especially in the vicinity of the eastern and central regions.