Abstract
A modeling method based on discrete wavelet transform (DWT) was introduced to analyze the concentration of chromium, copper, zinc, arsenic and lead in soil with a portable X-ray fluorescence (XRF) spectrometer. A total of 111 soil samples were collected and observed. Denoising and baseline correction were performed on each spectrum before modeling. The optimum conditions for pre-processing were denoising with Coiflet 3 on the 3rd level and baseline correction with Coiflet 3 on the 9th level. Calibration curves were established for the five heavy metals (HMs). The detection limits were compared before and after the application of DWT, the qualitative detection limits and the quantitative detection limits were calculated to be three and ten times as high as the standard deviation with silicon dioxide (blank), respectively. The results showed that the detection limits of the instrument using DWT were lower, and that they were below national soil standards; the determination coefficients (R2) based on DWT-processed spectra were higher, and ranged from 0.990 to 0.996, indicating a high degree of linearity between the contents of the HMs in soil and the XRF spectral characteristic peak intensity with the instrument measurement.
Highlights
Rapid population growth and urbanization, together with expansion of industrial production, have resulted in serious soil contamination issues globally
The results showed that the detection limits of the instrument using discrete wavelet transform (DWT) were lower, and that they were below national soil standards; the determination coefficients (R2 ) based on DWT-processed spectra were higher, and ranged from 0.990 to 0.996, indicating a high degree of linearity between the contents of the heavy metals (HMs) in soil and the X-ray fluorescence (XRF)
HMs in soil involve the use of strong acid to digest soil samples, which are tested by methods such as atomic absorption spectroscopy (AAS) [4], inductively coupled plasma atomic emission spectrometry (ICP-AES) [5], and inductively coupled plasma mass spectrometry (ICP-MS) (ICP-MS) [6]
Summary
Rapid population growth and urbanization, together with expansion of industrial production, have resulted in serious soil contamination issues globally. Heavy metal (HM) pollution is a major type of soil pollution. HMs in soil mainly derive from atmospheric dust, sewage irrigation, mining and smelting, and the application of pesticides and fertilizers [1]. Heavy metal pollution in soil deteriorates air and water quality, causes a decline in the yield and quality of crops, and threatens human health through the food chain [2]. HM pollution is difficult to identify because of the range of different contaminants and attempts to conceal pollution events, and difficult to remediate owing to the complex chemical behavior of HMs and their ecological effects [3]. The main detection methods of HMs in soil involve the use of strong acid to digest soil samples, which are tested by methods such as atomic absorption spectroscopy (AAS) [4], inductively coupled plasma atomic emission spectrometry (ICP-AES) [5], and inductively coupled plasma mass spectrometry (ICP-MS) (ICP-MS) [6]
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