**2.3. Fluorescence spectroscopy and X-ray diffraction**

The 3D fluorescence analysis was performed [15–17]. A Perkin Elmer fluorescence spectrophotometer LS55 was used, with 150 watts xenon lamp as excitation source. In the characterization of the samples, 45 individual emission spectra were obtained at emission wavelengths (λem) between 250 and 600 nm with intervals of 5 nm and, collected at excitation wavelengths (λexc) between 200 and 450 nm. The samples were analyzed at a concentration < 2 mg/L COD [15, 17]. A 290 nm filter was used in all analyses to eliminate Raleigh peak light interference. The excitation-emission matrix (EEM) of distilled water was subtracted from the EEM of the industrial wastewater samples to eliminate interference caused by Raman peaks. In order to verify the presence of chromium retained in the soil, the X-ray diffraction analysis was performed.
