Environmental and health risks of metal-contaminated soil in the former tannery area of Hazaribagh, Dhaka

Abstract

Soil and plant samples collected from Hazaribagh, the former tannery area in Dhaka, Bangladesh, were analyzed for heavy metals (Cr, Pb, Ni, Zn, Cd, and Cu). The pollution and health risks of the metals were assessed with commonly used indicators. The mean soil Cr concentration was 4321 mg/kg (range 294–23,148 mg/kg). Most sites had a moderate to high degree of contamination and were classified as extremely polluted (Pollution Load Index > 1). The non-carcinogenic hazard index was greater than 1 for Pb and Cr for both children and adults, which indicates considerable non-cancer health risk. The combined cancer risks for Pb and Cr exceeded the allowable range of 1 × 10−6–1 × 10−4 for most sites (8 out of 11 sites in the case of adults, all sites in the case of children) with Cr being the dominant contributor and oral ingestion the primary pathway. The cancer and non-cancer risks for children were 26- and 3-fold higher, respectively, than for adults. Among all heavy metals, Pb and Zn were the most susceptible to leaching and becoming mobilized in groundwater. Concentrations of Pb, Cr, and Zn in edible parts of vine spinach (Basella alba) exceeded safe limits. However, Pb and Cu showed significant accumulation in plants (Mean Transfer Factor of 1.064 and 0.94, respectively, for Pb and Cu), while Cr exhibited relatively lower bioavailability. The spatial distribution of heavy metal contamination and associated risks presented in this study will allow policymakers to pinpoint areas of intervention for remediation.