M.Todorova, S. Atanassova , B. Sitaula, D. Apturachim, P. Valkova, D. Dermendgieva

Abstract. Determination of heavy metals content in soil by acid or microwave mineralization and spectrophotometer measurement via AAS or ICP are sufficiently accurate, but they are time consuming and labour intensive. These methods are not flexible enough for environmental research. Application of near infrared spectroscopy (NIRS) as a tool for ecological assessment and monitoring of soil quality have been investigated recently. The reported results for determination of trace elements in soil by NIRS are controversial. The objective of this study was to investigate the application of NIRS as a rapid and nonexpensive method for determination of heavy metals content in soil. A total of 121 soil samples from the 0–20 and 20–40 cm layer were collected from Stara Zagora, Chirpan, Kazanlak and Gurkovo regions. Total Zn, Cu, Pb, Ni and Cd content in the investigated soil samples were determined by AAS using AAnalyst 800 Atomic Absorption Spectrometer, Perkin Elmer. Near-infrared spectra of all soil samples were measured using spectrophotometer NIRQuest 512, within the range from 900 to 1700 nm. PLS regression was used for developinged models related tested parameters to the spectra. According to the statistical parameters of a regression procedure the best accuracy of determination was obtained for total Cu content with correlation coefficient R=0.92 and RPD=3.9 for the calibration set of data and r=0.77 and RPD=2.3 for the test data. Models for determination of Cd, Pb, Zn and Ni content via near-infrared spectroscopy could be classified as with good to low accuracy of determination, according to the obtained ratio SD/SEC and SD/SEP.