Application of rhamnolipid surfactant for remediation of toxic metals of long- and short-term contamination sites

A rhamnolipid extract from Pseudomonas aeruginosa was tested on soils from short- and long-term contamination sites. Mass spectrometry analysis revealed a predominance of di-rhamnolipid congeners (85%), of which hydroxydecanoyl-hydroxydecanoate was the most abundant. Artificial contamination of a sandy soil resulted in final concentrations of arsenic, cadmium and zinc of 182, 20 and 983 mg kg −1 , respectively. The rhamnolipid showed a high extractive capacity for transition metals and metalloids, removing 53% of the arsenic, 90% of the cadmium and 80% of the zinc from the artificially contaminated soil. When tested against soil samples from a deactivated mining site, the rhamnolipid removed 59% of the arsenic, 57% of cadmium and 9% of zinc. The biosurfactant showed excellent biocompatibility with Artemia salina . Well diffusion tests demonstrated that the rhamnolipid was innocuous for commensally soil bacteria and yeast. A method for precipitation of As, Cd and Zn was tested to allow eco-friendly disposal of these metal(loid) contaminants. The precipitation method was able to remove all the arsenic and cadmium, while removing 84.5% of zinc in the biosurfactant solution. The possibility of applying this biosurfactant to soil remediation processes without purification steps and the development of new and rapid methods for metal precipitation are strategically important for the mining industry, to properly dispose or recycle metal contaminants and thus reduce the demand for new raw materials.