Pollution evaluation and health risks assessment of naturally occurring toxic metals in shallow groundwater: A study in southwestern tidal delta of Bangladesh

Abstract

Groundwater is the main source of potable water in rural regions of Bangladesh. Still, contamination with potentially harmful metals due to natural processes and anthropogenic activities leads to various health impacts. The focus of this research was to determine the extent of metal contamination in shallow groundwater from three southwestern districts of Bangladesh and the health hazards associated with it. A comprehensive analysis of metal, including metalloid, copper (Cu), aluminum (Al), chromium (Cr), Arsenic (As), Manganese (Mn), and boron (B) was performed on a set of 51 samples. Groundwater samples were analyzed for contamination using Atomic Absorption Spectroscopy and a UV–VIS Spectrophotometer, with pollution levels assessed via indices like the Metal Evaluation Index, Nemerow Pollution Index, and Contamination Index. Human health risks were evaluated through Chronic Daily Intake, Hazard Quotient, and Hazard Index calculations following USEPA guidelines. The results indicate that arsenic levels exceeded 25 samples and manganese levels exceeded 34 samples in accordance with WHO drinking water standards. Boron (B) concentrations exceeded the threshold in seven samples, whereas Al, Cu, and Cr exceeded limits in only two samples. The metal evaluation index (MEI), Nemerow pollution index (NI), and degree of contamination (C_d) revealed moderate to severe contamination in groundwater and unsuitability for drinking purposes. Out of the 51 analyzed samples, 48 samples exhibited potential non-carcinogenic health risks for adults, while all samples exceeded the hazard index (HI) threshold value (01) for children. Concentrations of As and Mn were identified as the main contributing factors to the higher HI values in both adults and children. However, the concentrations of Cu, Al, Cr, and B in groundwater were not individually found to be as risky. This study provided valuable insights to conduct a future comprehensive investigation of the designated region to delineate safe and hazardous zones for the installation of shallow tubewells. Furthermore, there's a need to enhance public awareness regarding the long-term ramifications of consuming contaminated water.