Spectroscopic Differentiation of Ash Containing Technology Critical Elements (TCEs): Toward Remote Monitoring of Informal Electronic Waste (E-Waste) Processing Sites

E-waste is a fast growing global waste stream that is both an economic opportunity and a complex disposal problem. There is an estimated $61 billion-worth of raw materials contained within the world's e-waste. These valuable materials are often extracted informally, without regulation or monitoring, in low-income settings. This 'recycling' is characterized by dangerous practices such as, open-pit burning and acid leaching that release contaminants, especially trace metals (e.g., TCEs), directly to surface soils. In tropical and sub-tropical environments, research has found that TCEs released by informal e-waste processing are very labile, infiltrating nearby water sources, food supplies, and the soil column. In contrast, work in a semi-arid environment found that the highest concentrations of trace metals are associated with ash from within the tested e-waste burn site and released trace metals are not especially labile. As a result, burn site ash spectral signatures from similar locations have been used to remotely detect e-waste burn sites from satellite imagery. This study addresses whether e-waste ash can be spectrally distinguished from other ash and is therefore an accurate proxy for soil contamination by TCEs released by informal e-waste processing in semi-arid environments. Our preliminary results show that spectral signatures of high-Pb ash from an arid e-waste burn site have local reflectance minima at 2240 nm. Wildfire ash spectra collected by the Airborne Visual Imaging Infrared Spectrometer (AVIRIS) over the 2014 King wildfire in southern California have SWIR band centers at 2300 nm. The spectrum of ash from a brush fire nearby the tested e-waste burn site has a sharper SWIR band than either the e-waste or the King fire spectra, with a band center at 2290 nm. Ash detections by imaging spectrometers such as, AVIRIS often rely on bands in the short-wave infrared (SWIR) region (e.g., 2370 nm). Bands in the SWIR region (1726 nm - 2426 nm) have been previously associated with soil organic matter, to which ash is spectrally similar. SWIR band centers may also be affected by adsorbed TCEs. Spectral differentiation of e-waste ash is an important step in the development of universally applicable remote sensing methods to monitor pollution from informal e-waste processing in semi-arid environments.