Diffuse reflectance spectroscopy study of heavy metals in agricultural soils of the Changjiang River Delta, China.

Heavy metal contamination of soil is becoming an increasingly serious problem in the Changjiang River Delta (China) as a result of rapid economic development. Conventional methods for investigating the contamination based on raster sampling and laboratory analysis are time-consuming and relatively expensive. Diffuse reflectance spectroscopy (DRS) within the visible-near-infrared (VNIR) region (400-2500 nm) has been widely used to identify spectrally active constituents in soils. Correlations between heavy metals (Cd, Cr, Pb, Cu, Zn, Hg and As) and DRS spectra of agricultural soils from Changjiang River Delta were studied to assess their binding forms. The results show that Cr, Cu, Zn and As have stronger negative correlation coefficients with the spectral bands attributed to the absorption features of iron oxides, clays and organic matter, suggesting they are strongly bound to these soil constituents. However, Cd, Pb and Hg only display a significant correlation with the spectral region related to organic carbon, indicating that binding with organic matter is important for these metals. This finding is consistent with the fact that Cr, Cu, Zn and As have significant correlations with Fe2O3, Al2O3 and TOC, but Cd, Pb and Hg only display a significant correlation with TOC.