**3.1. Physicochemical characteristics of the soil**

**Figure 1** shows the physico-chemical characteristics of the soil profile. The data obtained show a slight increase of pH as depth increases, with a value of 7.3 in the most superficial area and 7.5 at a depth of 50 cm. These pH values show that the soil is moderately alkaline, suggesting a medium availability of nutrients. The results of the electrical conductivity tests show a remarkable decrease along the soil column; the surface area has a value of 255.09 μS/cm and the deepest layer of 112.95 μS/cm. The lowest conductivity value (105.13 μS/cm) was observed at a depth of 30–40 cm (**Figure 1**). The cation exchange capacity remained constant throughout the soil column, with values of 30.20 Cmol/kg at a soil depth of 40–50 cm, and up to 38.21 Cmol/kg at 10–20 cm depth.

The content of organic carbon (OC) gradually decreased as the depth of the soil column increased: from 9.96 g/kg in the surface layer to 2.29 g/kg a depth of 40–50 cm. The percentage of organic matter (OM) also decreased with increasing depth; the highest value (17.17%) was observed in the surface layer, and the lowest value (3.95%) in the deepest layer. The percentage of humidity, like the OC content, decreased along the soil column by up to 29%, from 22.83% in the surface layer to 16.27% at a depth of 30–40 cm.

Regarding the texture of the different layers of the soil column, we obtained the following results: the most superficial layer (0–10 cm) had sandy loam soil; at depths of 10–20 and 30–40 cm, the soil had a loamy texture, and in the intermediate layers of the column (20– 30 cm) and in the lowest layer 40–50 cm, the soil had a loamy-clay texture (**Table 1**).

In general, all layers of the soil column had a loam texture. The literature on the subject states that a soil with medium alkaline pH is a sandy soil; this agrees with the texture data obtained in the present study, which showed a high sand content in all soil samples (**Table 2**). The results of this study also agree with the low amount of natural organic matter reported for these types of soils, as well as with deficiencies of B, Cu, Fe, Mn, Zn, and P [18].

> chromium VI, since the species distribution diagram for chromium indicates that the chromium species present in waters with pH values ranging from 1 to 5 is chromium VI. The

> **Figure 1.** Physical and chemical characteristics of the soil sample as a function of depth. EC = electric conductivity,

Chromium Species and 3D-Fluorescence Spectroscopy in a Soil Irrigated with Industrial…

http://dx.doi.org/10.5772/intechopen.77181

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The concentration of chromium in samples of the soil-saturated solution collected from the soil profile at depth intervals of 10 cm (**Table 4**); it also shows the amount of chromium accumulated in each section of the soil column. The initial concentration of Cr VI in the water used

wastewater studied here came from an electroplating plant in the city of Toluca.

OC = organic carbon, CEC = cation exchange capacity.

**3.3. Concentration of chromium VI in the soil solution throughout the soil column**
