Aanalyst 200

The samples of sediments from the Santiago River (SRS) were characterized by measuring the following parameters in situ using a YSI 1725 water quality meter: pH, oxidation–reduction potential (ORP), electric conductivity (EC), salinity, and total dissolved solids (TDS). Chemical oxygen demand (COD), total organic carbon (TOC), total solids (TS), and volatile solids (VS) were determined in laboratory facilities using colorimetric Hach probes for the first two (2125915 LM, 2815945, respectively) in DR900, and the gravimetric technique for the last two. Dissolved oxygen was measured using an electrode.
For heavy metal determination, atomic absorption spectrophotometry equipment PerkinElmer AAnalyst 200 was used. The sediment sample was ground and preserved by adding nitric acid until it reached a pH of less than 2 and kept at 4 °C until analysis. Three sample replicates were filtered, and residues were vacuum-dried and sieved to a particle size of 2 mm. A mixture of HCl:HNO₃ at a 1:3 ratio was used for digestion using an autoclave. Concentrations were interpolated using high-purity NIST-traceable standards. For the determination of arsenic, a hydride generator included in the PerkinElmer AAnalyst 200 flame atomic absorption spectrophotometry equipment was used.

Crucibles were rinsed with deionized water and then heated at 105 °C and put into the ashing furnace at 600 °C for 2 to 4 h. The sludge samples were ashed in triplicates by placing them into the ashing furnace at 600 °C for 6 to 8 h. The samples were mixed and heated with 5 mL of 3N HCl (Fisher Scientific, UK) until the solid samples were completely dissolved in an HCl solution. When the mixture of samples and HCl was cooled down to room temperature, the mixture was filtered with filter paper (Advantec No.1 125 mm, Toyo Roshi Kaisha, Ltd., Tokyo, Japan) and prepared in a 100 mL volumetric flask for further analysis of heavy metals using a flame atomic absorption spectrometer (AAnalyst 200, PerkinElmer, Inc., Waltham, MA, USA).