Heavy metal contamination in surface sediment and seafood from the Pra Estuary (Ghana): an ecological and human health risk assessment

Estuaries influenced by artisanal and small-scale gold mining (ASGM) are highly susceptible to contamination by heavy metals and excessive sediment inputs. These disturbances can disrupt benthic communities, alter biogeochemical processes, and elevate human exposure risks through seafood consumption. This study assessed benthic macroinvertebrates and ecological and human health risks from Cu, Zn, Ni, and Hg in sediments, fish, and oysters (Crassostrea tulipa) from the Pra Estuary. Surface sediments, five fish species, and Crassostrea tulipa were sampled at six locations within the estuary. Metal concentrations were measured using atomic absorption spectroscopy (Cu, Zn, Ni, Fe) and direct mercury analysis (Hg). Sediment contamination was evaluated with enrichment factors and geo-accumulation indices. Ecological risks were assessed through benthic sampling, Sediment Quality Guidelines, and biota–sediment accumulation factors. Human health risks were estimated using target hazard quotients (THQs) and total THQs (TTHQs). Zn and Hg levels posed minimal ecological risks, while Cu and Ni showed moderate risks. No benthic macroinvertebrates were found, indicating severe habitat degradation linked to factors such as turbidity, sedimentation, and contaminants. Crassostrea tulipa accumulated higher metal levels than fish, with Hg nearly double sediment concentrations. Fish posed no significant health risks (TTHQs < 1), but Crassostrea tulipa exceeded safety thresholds (TTHQ = 2.36), raising food safety concerns. In conclusion, the Pra Estuary exhibits ecological stress, with moderate heavy-metal contamination and the absence of benthic macroinvertebrates indicating degraded ecosystem health. The findings underscore the need for sustainable mining practices to protect ecosystem integrity and public health.