Vertical physicochemical parameter distributions and health risk assessment for trace metals in water columns in eastern Lake Tanganyika, Tanzania

The vertical distributions of trace metals and physicochemical parameters in water columns in Kigoma Bay and Kungwe Bay in eastern Lake Tanganyika, Tanzania, were studied. The Al, Ba, Ca, Co, K, Mg, Mn, Mo, Na, Sn, Sr, and V concentrations were low and varied very little with depth. The toxic heavy metal (As, Cr, Cu, Ni, Pb, and Zn) concentrations were relatively high in the surface water, and the Cu, Ni, Pb, and Zn concentrations decreased with depth. Principal component and cluster analyses indicated that the metals in the lake had three main sources. Al, Ba, Ca, Co, Cu, Cr, Mn, Sr, Sn, and V were found to be geogenic; As, Cr, Cu, Mo, Ni, Pb, Sn and Zn anthropogenic; and As, Ca, Co, Mg, and Na biogenic. Human health risk assessments were performed, and it was found that trace metals in the water at most of the sampling sites would cause no potential adverse effects or non-carcinogenic health risks through dermal contact or ingestion. However, trace metals in surface water in Kungwe Bay could have certain adverse effects on human health through the ingestion pathway (the total hazard quotient for ingestion (ΣHQ ) was 1.75 (a value >1 was defined as possibly indicating adverse effects). The Pb ΣHQ for surface water in Kungwe Bay was 1.50 and contributed >80% of the ΣHQ , implying that Pb pollution is a water quality and safety problem that needs to be carefully monitored and the potential sources identified.