Finding phytoremediators: the search for metal(loid) extracting or excluding Australian native plants

This study helps to develop and promote the use of southeastern Australian native flora for phytoremediation of selected base metals manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), lead (Pb) and the metalloid arsenic (As).

A phytoremediating plant dataset was created and analysed for these elements. In flora across the globe, the plant families Asteraceae, Fabaceae and Poaceae were more likely to be suitable for phytoremediation as hyperaccumulators, extractors, indicators and stabilizers, and a significant association was observed between the plant family Asteraceae and phytoextractors. The families Fabaceae, Myrtaceae and Poaceae had the largest number of extractors and excluders in Australian native flora.

A methodological study showed that handheld X-ray fluorescence spectrometry is suitable as a screening tool to use in the field to determine plant elemental composition, although sample moisture lowers the apparent elemental concentrations. For more accurate compositional data, plant samples should be cleaned, dried, milled, and analysed with a matrix-matched calibration or digested for other forms of analysis.

Plants growing naturally at legacy base metal mines in southeastern Australia were used to prospect for potentially new phytoremediator species. Hibbertia obtusifolia (Hoary guinea-flower), Leptospermum polygalifolium (Jelly bush), and Leucopogon melaleucoides (Snow bush) are Mn phytoextractors. Angophora floribunda (Rough-barked apple), Cassinia longifolia (Cauliflower bush), Ozothamnus diosmifolius (Rice flower) and Ozothamnus obcordatus (Grey everlasting) are Zn phytoextractors, and H. obtusifolia is a Pb phytoextractor. Elemental analyses of H. obtusifolia stems showed that Pb was confined to the stem cortex, and Stypandra glauca (Nodding blue lily) accumulated Zn in its leaves, mesophyll cells and vascular bundles.

Vegetation indices calculated using leaf reflectance spectra of Eucalyptus rossii (White gum) and Eucalyptus goniocalyx (Long-leaved box) showed no significant stress caused by metal, so remote sensing could not be used to identify these plants as metal extractors remotely.