Identification and remediation-related monitoring of potential toxic elements (PTE) in the hyperaccumulator plant Brassica juncea with hyperspectral imaging.

Across Europe there are 2.5 million potentially contaminated sites due to natural and anthropogenic activities. In this regard, phytoremediation approaches are need as a cost-effective and ecosystem-friendly technique to rehabilitate soil compared to conventional methods. Hyperspectral imaging provides an ideal method to improve and monitor existing bioremediation methods, using hyperaccumulator plants. In our study, the hyperaccumulator plant Brassica juncea showed a high tolerance to the accumulation of Cu, Zn and Ni. Hyperspectral measurements were conducted with a HySpex VNIR-SWIR hyperspectral sensor (408-2500 nm) in-situ and in the laboratory. To monitor and optimize the process of accumulation with hyperspectral imaging, we calculated different vegetation indices, related to metal-induced plant stress, such as TCARI/OSAVI, Chlorophyll Vegetation Index (CVI), Red-Edge Stress Vegetation Index (RSVI), Normalized Pigments Chlorophyll Index (NPCI), Red-Edge Inflection Point (REIP) and Disease Water Stress Index (DWSI), using various pre-processing steps (raw, smoothed and brightness corrected data). In addition, the relation between the different indices and the measured heavy metal content in the samples were tested with a multivariate technique using Partial Least Squares Regression (PLSR). Our results revealed, even with no pre-processed image data, changes in chlorophyll- and red-egde-related indices with increasing PTE concentration. With hyperspectral imaging we are already able to monitor differences of the PTE accumulation within the hyperaccumulator plant Brassica juncea.