Model aa 7000

The quantitative estimation of iron in the hematite ores collected from Pokhari, Nawalparasi District was carried out by Atomic Absorption Spectroscopy (AAS) method (SHIMADZU, Model AA-7000, Japan). In this method, 1 g of powder sample was taken and 10 mL of 1 : 1 HNO₃ was added and refluxed for 10 minutes, followed by the addition of 5 mL concentrated HNO₃ and refluxed till the total volume was reduced to 5 mL. In the reduced volume, 2 mL of water was added followed by the addition of 3% of H₂O₂ until the bubbling subsides. The solution was further refluxed to reduce volume up to 5 mL. Then, 10 mL of concentrated HCl was added and refluxed for 15 minutes. The whole sample was filtered through Whatmann no. 42. The filtrate was taken and diluted to 100 mL in a volumetric flask [29 ]. This was taken as an analyte sample.

Dyeing, composite (household plus different industrial wastewaters), garments, washing plant’s wastewaters were collected from Gazipur city areas of Bangladesh, while tannery wastewater was collected from Hazaribagh of Dhaka city, Bangladesh. The samples were collected in cleaned and sterilized screw cap bottles, and cold chain was maintained during transportation to the laboratory. Collected samples were stored at 4°C before analysis. Color and odor of the samples were noted. Total dissolve solid (TDS), salinity, and electrical conductivity (EC) were measured by Conductivity meter (Model: DDSJ-308A). Water pH was determined by the digital pH meter (model: HI 8424, HANNA). Water temperature and dissolved oxygen (DO) were measured during sample collection with the help of digital thermometer and digital DO meter (Model: HI 8424, HANNA), respectively. Copper (Cu), zinc (Zn), lead (Pb), chromium (Cr), and nickel (Ni) in different wastewater samples were determined by atomic absorption spectrophotometer (Model- AA-7000, Shimadzu, Japan) followed by procedures of American Public Health Association [APHA] (1998) . Physico-chemical characteristics of various wastewaters are presented in Supplementary Table S1.

Dietary Cr was analyzed by wet ashing the feed sample with Trace Metal Grade HNO₃ (Trace Metal Grade, Fisher Scientific, Raleigh, NC) using a hot plate digestion procedure (Brooks et al., 2016 (link)). Cr was measured using flameless atomic absorption spectrophotometry (Shimadzu, Model AA-7000, Kyoto, Japan).