Monitoring of sewage pollution in the surface sediments of coastal ecosystems using linear alkylbenzenes (LABs) as molecular markers

Abstract

Molecular organic markers are an effective tool to detect the adverse effects of anthropogenic inputs in the aquatic environment. Linear alkylbenzenes (LABs) are sewage molecular organic markers that are released into the environment as a consequence of the incomplete sulphonation step of industrial detergents. In the current work, the characterisation, sources and degradation of LABs in the surface sediments of Muar River and Johor Bahru Coast, Malaysia, were identified. The surface sediment samples were obtained from the Muar River and Johor Bahru Coast area using an Ekman dredge sampler. Both locations were selected to represent the current anthropogenic pollution situation. The sediment samples were subjected to Soxhlet extraction, first purification step, second fractionation step column chromatography and then gas chromatography-mass spectrometry (GC-MS) analysis. The results revealed that the LAB concentrations in the samples of the Muar River and Johor Bahru Coast ranged from 87.4 to 188.1 ng g−1 dry weight (dw) and from 87.6 to 188.7 ng g−1 dw, respectively. The ratios of internal isomer (the benzene ring is closed to the centre of the linear alkyl chain) to external isomer (the benzene ring nears the end of the linear alkyl chain) (I/E ratio) of LABs were between 1.7 and 2.2 in Muar River and between 1.8 and 2.7 in Johor Bahru Coast samples. These findings indicate that the concentrations of LABs in the sediments ranged from low to moderate contamination and the aquatic environment received both primary and secondary sewage effluents. This study emphasises that continuous monitoring of sewage pollution to minimise the environmental pollution in coastal areas is highly recommended.