10 - Monitoring the process of phytoremediation of heavy metals using spectral reflectance and remote sensing

Abstract

Heavy metal contamination of soils became a major global problem in recent years due to increase in geological and anthropogenic activities. Phytoremediation is a relatively low-cost and environmentally friendly method of cleaning up of environmental pollutants by using green plants. However, the plants must be carefully screened and selected to optimize the process of phytroremediation for selected heavy metals. Excess metal exposure negatively affects photosynthetic processes and typically induces plant stress. Ultrastructural changes in the chloroplast of leaves, xylem, and phloem vessels of shoot and root will typically increase with metal exposure, which has obvious consequences on photosynthesis and plant growth. Spectral reflectance and remote sensing of large metal contaminated areas can be efficiently used to monitor the progress of phytoremediation. Specific applications of spectral reflectance and remote sensing include early recognition of contaminated areas through plant stress monitoring, assessment of phytoremediation and restoration efforts, spatial, and temporal variation of metal contamination, and assessment of risk to human and environmental health. This chapter summarizes the studies to investigate the feasibility of using spectral reflectance to monitor As and Cr accumulation in Chinese Brake Fern (Pteris Vittata) and Indian mustard (Brassica juncea) plants, and to search for spectral indices sensitive to structural changes caused by metal accumulation during the process of phytoremediation. These studies reflect that the infrared reflectance spectrum of plant canopy and the derived spectral indices may provide a nonintrusive monitoring method to assess the physiological status of plants grown in heavy metal-contaminated soil. These results also systematically illustrate the physiological implications of ultrastructural alterations caused by As and Cr at higher concentrations in mustard and brake fern plants.