Ecological risk assessment and source tracing of heavy metals in surface sediments of a hilly riverine reservoir in Chongqing, China

Abstract

Abstract Background This work conducted quantitative and qualitative analyses on the heavy metals in thirty-two surface sediment samples collected from eight sampling sites in Yutan reservoir, a typical mountainous hilly riverine reservoirin Southwest China across four seasons. Results Nine heavy metals were identified: (Cr, Cd, Pb, Cu, Zn, Hg, As, Ni and Co). The concentrations varied within the ranges of 23.16 ~ 34.62, 0.53 ~ 1.09, 31.88 ~ 59.04, 51.94 ~ 85.84, 106.76 ~ 227.69, 0.08 ~ 0.15, 12.57 ~ 25.60, 12.06 ~ 27.64, and 11.04 ~ 14.56 mg/kg respectively, following a decreased concentration order of Zn > Cu > Pb > Cr > Ni > As > Co > Cd > Hg. Except for the Cd, which accumulated in Winter, and Hg ,which reduced in Spring, the concentration of heavy metals showed no significant seasonal variation.The heavy metals generally had higher contents at the river mouth and lower concentrations in open water areas and branches. Igeo assessment indicated that the reservoir was uncomtamiated by Cr and Ni (Igeo<0), slightly polluted by Pb, Cu, Zn and Co(0 < Igeo<1), moderately polluted by Hg and As (1 < Igeo<2), and heavily polluted by Cd (1.44 < Igeo<2.48). The most polluted sites were at the river mouth, followed by the sediments in branches with slight pollution. Source tracing analysis revealed that Cr, Ni, Cd, Pb, Hg, As, OM, TN and TP were primarilyattributed to non-point sources, whereas Fe was linked to the hardware industry. Moreover, Al originated from sewage and drinking water treatment processes. The Cu and Zn were discharged from three components, indicating complex sources. Conclusions The findings underscored that non-point sources were the primary contributors to the increased risk of heavy metal contamination in the reserservior’s sediment. In addition, to effectively manage the risk and enhance the aquatic environment, greater focus should be placed on the inner load of heavy metals in the sediment of the mountainous hilly riverine reservoirs, particularly after controlling external pollution sources.