Surfactants in the sea-surface microlayer and sub-surface water at estuarine locations: Their concentration, distribution, enrichment, and relation to physicochemical characteristics

- Comparisons of surfactants in the SML and SSW at two different locations.
- Anionic surfactants were more dominant than cationic surfactants in this study.
- Surfactants showed significant correlations with dissolved organic carbon.
- Cationic surfactants were negatively correlated with salinity in Kaohsiung.
- Higher surfactant levels in Kaohsiung pose higher potential chronic toxicity.

Samples of sea-surface microlayer (SML) and sub-surface water (SSW) were collected from two areas-Kaohsiung City (Taiwan) and the southwest coast of Peninsular Malaysia to study the influence of SML on enrichment and distribution and to compare SML with the SSW. Anionic surfactants (MBAS) predominated in this study and were significantly higher in Kaohsiung than in Malaysia. Industrial areas in Kaohsiung were enriched with high loads of anthropogenic sources, accounted for higher surfactant amounts, and pose higher environmental disadvantages than in Malaysia, where pollutants were associated with agricultural activities.The dissolved organic carbon (DOC), MBAS, and cationic surfactant (DBAS) concentrations in the SML correlated to the SSW, reflecting exchanges between the SML and SSW in Kaohsiung. The relationships between surfactants and the physiochemical parameters indicated that DOC and saltwater dilution might affect the distributions of MBAS and DBAS in Kaohsiung. In Malaysia, DOC might be the important factor controlling DBAS.