# Simultaneous Analysis of Heavy Metal Concentration in Soil Samples
## 1 Introduction  
The assessment of the degree of soil pollution with heavy metals is still a serious challenge for scientific departments dealing with this problem. The recognition of areas potentially contaminated with heavy metals is legally sanctioned in many countries. An exemplary document that is in force in the European Union is Directive No. 2010/75/EU [1] and the resulting Regulation (Dz.U. 2016 poz. 1395 (2016) in Polish law) [2]. A typical procedure for determining the degree of contamination of soil is based on sampling in accordance with the designated grid, an analysis of the contamination levels in the laboratory, and the interpretation of test results based on geostatistical methods. Commonly used methods for determining heavy metal content, such as inductively coupled plasma optical emission spectrometry [3], are time-consuming and expensive. In the case of the need to recognize the scale of pollution of a large area, the cost and time needed to perform the necessary research increases significantly. In connection with the above, potential use of infrared spectroscopy as a new, less time-consuming, and less expensive method for determining the physicochemical parameters of soils has been studied for several years. Infrared spectroscopy is a useful tool for investigating soil parameters such as total carbon, total nitrogen, the C/N ratio, lignin, dissolved OC, carbonyl-C, aromatic-C, O-alkyl-C, and alkyl-C contents. A review of the applications of Fourier-transform infrared (FT-IR) spectroscopy for the analysis of soil samples was presented by [PERSON] et al. [4]. [PERSON] et al. [5] presented the state of the art in the field of the application of infrared spectroscopy in soil analyses as an alternative to traditional so-called \"wet\" methods. The authors considered both the advantages and limits of this technique. [PERSON] and [PERSON] [6] presented a review of the application of infrared spectroscopy to agricultural and environmental management. Previous studies have shown various possible applications of infrared spectroscopy for soil analysis. [PERSON] et al. [7] examined different soil properties, including pH, organic carbon, slag, silt, sand, cation exchange capacity, exchangeable calcium, exchangeable aluminum, nitrate nitrogen, available phosphorus, exchangeable potassium, and electrical conductivity. The authors compared PLS calibration models based on spectra obtained using the technique of diffuse reflectance (DRIFT) both separately and jointly in different infrared regions. [PERSON] et al. [8] evaluated the use of field portable and laboratory benchtop infrared spectrometers in the range of near infrared (NIR) and mid infrared (MIR) for the rapid nondestructive assessment of petroleum-contaminated soils. FT-IR has also been used for the analysis of the heavy metal concentration in soils. [PERSON] et al. [9] studied the ability of near-infrared spectroscopy to detect the effects of heavy metals on the chemical composition of forest soil. The authors underlined that some concentrations (especially high concentrations) of heavy metals obtained using NIR spectroscopy were lower than in reality due to the fact that heavy metals in industrial samples are partially present in the inorganic form. Similar results were obtained by [PERSON] et al. [10] for soil metal content in highly contaminated soil samples obtained from industrial regions. The authors concluded that using mid-infrared lead to more accurate models compared to NIR. [PERSON] et al. [11] assessed the usefulness of the VIS-NIR method in the monitoring of toxic elements in soil samples from reclaimed dumpsites. [PERSON] et al. [12] applied visible and near infrared for fast analysis of cadmium pollution of soils. [PERSON] et al. [13] used the DRIFT mode in the MIR range combined with PLS to estimate the contamination of soil with arsenic. [PERSON] et al.