This study determines the levels of surfactants at 12 stations located in the Melaka River Estuary. This river estuary is located within a tourism area of Melaka Historical City. The concentrations of anionic and cationic surfactants in the sea surface microlayer (SML) and sub-surface water (SSW) were determined by using two colorimetric methods, methylene blue active substances (MBASs) and disulphine blue active substances (DBASs), respectively. The results showed that cationic surfactants as DBAS (ranging between 0.19 and 0.25 μmol L-1) dominated the concentrations of surfactants in SML. The enrichment factor (Ef) between MBAS and DBAS in the SML and SSW ranged between 1.0 and 2.0, and 1.0 to 1.4, respectively. There was no significant correlation (p > 0.05) between MBAS and DBAS for both SML and SSW. Nevertheless, there were strong correlations (p < 0.05) between both MBAS and DBAS in the SML and SSW. The results showed the potential contribution of degradation processes of organic substances microorganisms in SSW towards the concentrations of surfactants in SML. Compared to previous studies, tourism-related activities may influence the concentrations of surfactants, especially DBAS, in this river estuary.
Keywords: Anionic; Cationic; DBAS; Estuary; MBAS; SML; SSW.