A pH-responsive phosphoprotein surface washing fluid for cleaning oiled shoreline: Performance evaluation, biotoxicity analysis, and molecular dynamic simulation

Abstract

Oil spill accidents can cause negative impacts on the shoreline ecosystem and endanger public health. In the present study, an innovative green surface washing method based on sodium caseinate (NaCas) was proposed for the cleanup of oiled sand that is removed from the shoreline and treated by washing ex-situ. The comprehensive performance evaluation, biotoxicity analysis, and molecular dynamic simulation were conducted to explore the washing process. The addition of NaCas was able to decrease both surface and interfacial tensions, thereby facilitating oil diffusion and leading to a higher oil removal performance. NaCas fluid displayed a comparable washing performance with some surfactants. The factorial analysis demonstrated that three individual factors (temperature, pH, and NaCas concentration) and three interactive effects (temperature/salinity, temperature/pH, and salinity/pH) had a significant impact on the washing performance of NaCas fluid. Notably, the washing effluent displayed good pH responsiveness, generating a super-clean supernatant with low turbidity and oil concentration. Moreover, biotoxicity tests proved that the presence of NaCas could relieve the toxicity caused by oil droplets by enhancing the chlorophyll concentration and decreasing the reactive oxygen species (ROSs) content, respectively. The molecular dynamic simulation further revealed that NaCas could break the oil layer on the sand surface and move the oil droplets away from the sand. NaCas fluid is a promising candidate for oiled shoreline cleanup due to its low cost, good biocompatibility, pH responsiveness, and high oil removal efficiency.