**2.3 Water sample preparation**

Water and sediment samples collected were filtered using the Johnson test paper filter paper with a diameter of 125 mm. In total, 10 ml of each filtrate was drawn into a 250 ml beaker, to which a 25 ml mixture was made up of 15 ml conc. HNO3 and 10 ml conc. HCL was added and digested in a fume chamber for about 20 minutes. For efficient digestion of the water samples, an additional 10 ml of conc. HCL was added and heated in the fume chamber for about 15 minutes. Upon cooling, further filtration was carried out. Distilled water was added to the filtrate and made up to the 100 ml mark.

### **2.4 Determination of heavy metal concentrations**

For each soil/water sample, calibration curves were prepared using heavy metal standards: 0.50, 1.00, 2.00, and 4.00 mg L−1 standards were each prepared in the spectrophotometric quantification of Cr, Cu, and Pb while calibration curves of concentrations 0.10, 0.20, 0.40, and 0.80 mg L−1 were ready in the case of Cd. For each soil/water sample, duplicate analyses were performed using Perkin Elmer 400 atomic absorption spectrophotometer with air-acetylene gas serving as fuel for the flame. Serial dilutions were performed on the samples where concentrations were very high, and after that, their dilution factors were factored in determining their concentrations.
