Critical evaluation of the performance of rhamnolipids as surfactants for (phyto)extraction of Cd, Cu, Fe, Pb and Zn from copper smelter-affected soil.

Rhamnolipids are biosurfactants produced by bacteria belonging to the Pseudomonas genus. They are discussed to complex heavy metal cations stronger than cations of Fe, Ca, Mg. It is therefore suggested to employ rhamnolipids in phytoextraction where their addition to soil should result in preferential complexation of heavy metals that can be taken up by plants, thus enabling rapid and ecological clean-up of contaminated soil. In order to test this concept, we evaluated the rhamnolipid-mediated phytoextraction of heavy metal from soil collected from the vicinity of a copper smelter. The following aspects were investigated: i) selectivity of rhamnolipids towards Cu, Zn, Pb, Cd and Fe during soil washing; ii) phytoextraction efficiency of each ion with respect to the effective concentration of rhamnolipids; iii) possible phytotoxic effects; iv) effect of micro-sized polystyrene amendment. The experiments evaluated soil washing efficiency, BCR (Community Bureau of Reference) sequential extraction to determine the impact of rhamnolipids on the mobility of metal ions, phytoextraction with maize (Zea mays L.) and phytotoxic effects based on dry matter, chlorophyll fluorescence and content. The obtained results indicated that rhamnolipids lack desired selectivity towards heavy metal ions as Fe was complexed more efficiently by 80 % of the available rhamnolipids compared to priority pollutants like Zn, Cu, Pb, which were complexed by only 20 % of the tested rhamnolipids. With increased concentration of rhamnolipids, the soil washing efficiency increased and shifted in favour of Fe, reaching values of approx. 469 mg for Fe and only 118 mg in total of all tested heavy metals. Phytoextraction also favoured the accumulation of Fe, while Cd was not removed from the soil even at the highest applied rhamnolipid concentrations. Considering the selectivity of rhamnolipids and the costs associated with their production, our results suggest the need to search for other alternative (bio)surfactants with better selectivity and lower price.

Teeth and bones micro-slurries introduction to MIP OES for elements simultaneous quantification.

This study aims development of new, rapid and direct method for simultaneous multi-elemental determination in micro-volume slurried samples of teeth and bones. The method proposed allow for direct, without prior sample decomposition, injection of 15 µL of slurries (Bone Meal NIST 1486, deciduous human and dog teeth) into microwave induced plasma optical emission spectrometer (MIP OES) and determination of Ca, Cu, Fe, K, Mg, Mn, Na, Pb, Sr and Zn. The optimization procedures were undertaken (univariate and simplex methods) to achieve the best values of parameters influencing the analytical signals. Minimum dead volume, high nebulization and slurry transport efficiency were obtained by using on-axis low-volume spray chamber/v-groove pneumatic nebulizer interface for 15 µL slurry injection in discontinues mode (at 1.2 mL min-1 pump speed). Analytical parameters of the proposed method were assessed by determination of the limits of detection (LODs), absolute detection limit and precision (RSDs). The obtained LODs were appropriate (in the range of mg/kg) for the determination of the elements in the standard reference material (Bone Meal NIST 1486) for validation procedure and successful application in two real samples (deciduous human and dog teeth).