Heavy metal contamination and health risk assessment in surface water of the Karnaphuli estuary, Bangladesh

The Karnaphuli estuary (KE) is a highly dynamic coastal system in southeastern Bangladesh, functioning as a critical trade gateway and supporting rich biodiversity. It is an ecologically and commercially vital location with distinct tidal dynamics; however, intense shipping, land reclamation, industrial effluents, urban sewage, and agricultural runoff have negatively impacted water quality, endangering both aquatic ecosystems and human health. To estimate health risk and pollution sources of heavy metal (HM) contamination, ten surface water (SW) samples were collected from the KE during the dry season of 2023. Concentrations of eleven HMs were measured using an Inductively Coupled Plasma Mass Spectrometer, with a notably high load of HMs, where average concentrations followed the descending order of Zn > Pb > Cu > Mn > Cr > Ni > Se > As > Cd > Hg > Co in µg/L. Notably, Zn (43,037 µg/L), Pb (253 µg/L), and As (52.5 µg/L) exceeded the respective WHO and DoE guideline values by approximately 21.5 and 8.6 fold for Zn, while Pb and As concentrations were 253 and 17.5 fold higher than the respective guidelines, respectively. Multiple indices were used to assess HM contamination status, showing severe contamination. Human health risk assessment revealed that children consistently experienced higher chronic daily intake than adults across all HMs, where Pb, As, and Zn posed non-carcinogenic risks to both age groups, and Cr additionally affected children . Total carcinogenic risks exceeded the acceptable limit for As (2.49 × 10 − 3 and 5.27 × 10 − 3 ), Cr (1.20 × 10 − 3 and 2.54 × 10 − 3 ), and Cd (1.01 × 10 − 3 and 2.14 × 10 − 3 ) for adults and children , respectively. Thus, SW of the KE requires appropriate treatment before being used for domestic purposes, as the water was found to be unsuitable for direct consumption, emphasizing the urgent need for effective pollution control and management measures to protect the estuary’s ecological health and preserve its socio-economic value.