Optima 8000

Inductively coupled plasma optical emission spectrometry (ICP-OES, Optima 8000, PerkinElmer, Waltham, MA, USA) was utilized to determine Sb concentrations following the USEPA SW-846 Test Method 6010D (USEPA, 2018). For the detection of Ag concentrations, inductively coupled plasma mass spectrometry (ICP-MS) (7700×; Agilent Corp., Santa Clara, CA, USA) was used in accordance with USEPA Method 6020B (USEPA, 2014).

Twenty four (24) tilapia and crustaceans, sixty-two (62) and thirty-five (35) samples of SW and GW, respectively, were collected in 2019 at various locations described in Figure 1. Crustaceans and tilapia were collected in 11 and 13 different places in Marinduque, respectively. The samples were cut into about 0.5 cm pieces and dried at MSC-Mapua joint research laboratory at Boac, Marinduque using a dehydrator at 68 °C for 7–8 h. A total of 121 samples were analyzed in triplicates for the presence of eight transition and post-transition metals such as cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni), and zinc (Zn) using Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) Perkin Elmer Optima 8000 with minimum R² = 0.9995 per metal. The digestion and analysis were in accordance with U.S. EPA Method 200.3/200.11 and U.S. EPA Method 3005A/200.7 for tilapia and crustaceans’ tissues and inland water samples, respectively. The analysis was carried out at the Wet Laboratory of Yuchengco Innovation Center of Mapua University in Manila, Philippines.

The XRD patterns of the samples were analyzed using a D8-Advance X-ray diffractometer (Bruker). The morphological structures and chemical compositions of the samples were observed using SEM (Hitachi Regulus 8100, Tokyo, Japan). The composition and chemical state of the elements were determined by XPS (Thermo Scientific K-Alpha, Waltham, MA, USA). The surface charge of the catalysts was determined by measuring the ζ potential in Milli-Q ultrapure water using a Zetasizer (Nano ZS90, Malvern, UK). The Cu content in CuC was detected using an inductively coupled plasma optical emission spectrometer (ICP-OES, Perkin Elmer Optima 8000, Waltham, MA, USA).

For the measurement of Na⁺ and K⁺ levels, the seedlings were transferred to basal medium supplemented with 0 or 150 mM NaCl after growing for 7 days in beakers. Ninety-six hours later, the aerial parts of the plants were excised, washed twice with ultrapure water, and subsequently vacuum dried overnight. The dried samples were digested using nitric and hydrochloric acids at a 4:1 ratio, boiled at 200 °C for 2 h, and subsequently filtered after 1 h of equilibration at room temperature. The levels of Na⁺ and K⁺ in the resulting filtrates were determined using an inductively coupled plasma optical emission spectrometer (ICP-OES, PerkinElmer Optima 8000).

The organic elements were tested by a Vario EL cube analyzer (Hanau, Germany). The O content was calculated by subtracting a hundred percentage with contents of ash, C, H and N. The alkali and alkaline earth metals (AAEMs) were tested by an Optima 8000 Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES, PerkinElmer, Waltham, MA, USA). For a typical ICP-OES analysis, 0.3 g corncobs were digested by 1 mL HClO₄ and 3 mL HNO₃ in a test tube. The digested biomass was diluted to 10 mL using deionized water. The main analysis conditions included nebulizer flow of 1.5 L/min, flush time of 10 s, delay time of 40 s and wash time of 40 s. The normalized valencies of total AAEMs were calculated as the following equation: $\mathrm{The}\mathrm{normalized}\mathrm{total}\mathrm{AAEMs}\mathrm{valencies}=\frac{(\mathrm{K}+\mathrm{Na}+2\mathrm{Ca}+2\mathrm{Mg})\mathrm{in}\mathrm{pretreated}\mathrm{corncobs}}{(\mathrm{K}+\mathrm{Na}+2\mathrm{Ca}+2\mathrm{Mg})\mathrm{in}\mathrm{untreated}\mathrm{corncobs}}$