Ecotoxicology Study of Various Homologues of Methyl Ester Sulfonates (MES) Derived from Palm Oil

Methyl ester sulfonate (MES) is an anionic surfactant derived from palm oil through sulfonation of fatty acid methyl esters. Due to limited ecotoxicological data on MES, this study was initiated to evaluate the ecotoxicological properties of MES and its impact to the environment. The respirometric method (OECD 301F) was used to monitor the biodegradation of various homologues of MES over 28 days. The algae growth inhibition test (OECD 201) was conducted to assess the effects of palm-based MES towards green algae by exposing exponentially-growing cultures of Pseudokirchneriella subcapitata (P. subcapitata) to five concentrations of MES with maximum concentrations of 100 mg/L. Results showed all MES samples were readily biodegradable, where the biodegradability of each homologue surpassed 60% within 28 days. It was also observed that the longer the carbon chain length of MES, the solubility and the biodegradability rate decreased. The ecotoxicity of C12 and C14 MES towards P. subcapitata after 72 h of experiment showed no inhibition of algae growth in C12 MES while, the growth of algae decreased as the concentration of C14 MES increases. The EC50 value for C14 MES and C16 MES towards green algae was > 100 and > 10 mg/L, respectively. It can be concluded that C12 and C14 MES were practically non-toxic towards P. subcapitata and the toxicity increased with an increase in chain length of the surfactant (EC50 value decreases). Therefore homologues of palm-based MES are not expected to cause environmental concern due to their biodegradability and low toxicity in the aquatic environment.