Identifying Heavy Metals in Vegetation with an NIR Spectroradiometer


Modernizing our world has resulted in unfortunate environmental consequences. Increased industrialization and modern agricultural practices, have resulted in heightened heavy metal contamination of soil and vegetation. The post-mining era has also led to a staggering concentration of heavy metal elements, such as copper, cobalt, molybdenum, and nickel. Vegetation plays a significant role in element migration, which can adsorb and transport ore-forming elements to the surface and result in a near-surface anomaly.

Heavy metal exposure interferes with plant metabolism and enzyme activity, causing effects in photosynthetic processes and generally induces stress in plants. Plants uptake excessive concentrations of heavy metals in soil, causing potentially harmful changes in their growth. Elevated levels of heavy metals decrease chlorophyll content and cause changes in the internal structure of the leaf. Additionally, heavy metal contamination can cause lower biomass, altered water uptake and nutrient assimilation, senescence, and plant death. In some cases, the absorbed metal ion replaces the central magnesium atom in the chlorophyll molecule. This substitution reduces or prevents light harvesting and results in a photosynthetic breakdown affecting both growth and photosynthesis. These changes, directly and indirectly, influence the reflectance spectral feature of the plant leaves.

Currently, heavy metal pollution monitoring depends on traditional geochemical methods, which are time-consuming, inefficient, and unsuitable for large-scale monitoring. A more suitable approach to identifying heavy metal contamination in vegetation is using a field-portable NIR spectroradiometer. Spectral Evolution’s line of field-portable instruments present researchers with rapid data collection in-the-field, allowing for more scans in less time. High spectral resolution and high sensitivity deliver improved data and reflectance values leading to higher quality leaf data.
Spectral response of the plant leaves by metal-induced stress is vital for monitoring environmentally damaged areas such as metal mine-polluted land.

A typical indicator of heavy metal stress in vegetation involves the red edge measurement in spectra. As heavy metal negatively affects the production of chlorophyll, the red edge moves toward shorter wavelengths, and reflectance increases at 680nm. The plot shows an example of the red edge shift and increased reflectance in leaf spectra.

Spectral Evolution’s field spectroradiometers are a convenient solution for quickly understanding the effects of heavy metal contamination. All Spectral Evolution spectroradiometers come equipped with DARWin™ SP Data Acquisition software. This software includes 20 vegetation indices, including REP (Red Edge Position) and NDVI (Normalized Difference Vegetation Index), for analysis of heavy metal concentration in vegetation and soil.

As technology and industrialization progress, it is more important than ever to quickly identify destructive processes that cause heavy metal contamination in vegetation. By using a Spectral Evolution field spectroradiometer, paired with convenient vegetation indices, researchers can help identify the impact of contamination on our environment and ever-evolving climate.

The red edge shift and increased reflectance spectra in DARWin™ SP Data Acquisition software.