Iron Nanoparticles and Biopolymers for Plant Nutrient Fortification

Abstract

Novel iron (Fe) cross-linked alginate (FCA) beads were used for aqueous phosphate removal. Batch experiments were conducted with the beads using three different concentrations of phosphate (5, 50 and 100 mg PO43--P/L) as well as environmentally relevant (eutrophic lakes) concentration of 100 μg PO43--P/L. About 80-97% phosphate was removed within 3 h. for lower concentrations of phosphate. The maximum phosphate sorption capacity was found to be 78.7 mg PO43--P/g of beads. Phosphate removal was not affected because of the presence of Cl-, HCO3-, SO42-, NO3- and natural organic matter (NOM). FCA beads were also used with actual lake waters (11-69 μg PO43--P/L) and 81-100% phosphate removal was observed in 24 h. The FCA beads having a point of zero charge (PZC) of 9.2 make it an ideal candidate for phosphate removal in eutrophic lakes. Phosphate-laden spent iron cross-linked alginate (FCA) beads were used in hydroponics to evaluate the bioavailability of P and Fe using lettuce (Lactuca sativa) as a test plant. Phosphate-laden spent FCA beads were found to support the plants throughout the growth period. The bioavailability of P and Fe in the spent beads is promising considering the importance of phosphorus and iron in global nutrient security. Experiments were also conducted with lettuce and spinach (Spinacia oleracea) to evaluate the availability of iron from nanoscale zero-valent iron (NZVI). In both plants, bare NZVI enhanced the uptake of Fe as well as other essential elements. The results indicate that biofortification of spinach and lettuce with Fe is possible. The enhanced uptake of iron and other elements by lettuce and spinach is likely to have implications on global nutrient security. In another experiment, an iron-regulating gene (LsHA2) in lettuce was investigated to gain insights into the strategy taken by plants for acquisition of Fe from a readily unavailable source, e.g., NZVI. The gene of interest was found to be regulated by the presence or absence of available iron in the solution. This research is likely to give us insights into the mechanism of plant nutrient fortification with nanoparticles.