Source apportionment of heavy metal(loid)s in sediments of a typical karst mountain drinking water reservoir and the associated risk assessment based on chemical speciation

Abstract

Abstract As important place for water storage and supply, karst reservoirs play a key role in ensuring human well-being, and its water quality safety has attracted much attention. Source apportionment and ecological risks of heavy metal(loid)s in sediments of drinking-water reservoir are of great significance to ensure the safety of water quality and public health, especially in karst mountain areas where water resources are scarce. To expound the accumulation, potential ecological risks and sources of heavy metal(loid)s in a drinking-water reservoir from Northwest Guizhou, China, the surface sediments were collected and analyzed based on the combined use of the geo-accumulation index (Igeo), sequential extraction (BCR), ratios of secondary phase and primary phase (RSP), risk assessment code (RAC), modified potential ecological risk index (MRI), as well as the Positive Matrix Factorization (PMF) methods. Results showed that the concentrations of Cd, As, Pb, Cr, Cu, Ni, and Zn in sediments exceeded the corresponding background values of soils in Guizhou Province. The Igeo indicated that the accumulation of Cd was high, approximately 61.9% of the samples were at moderate and above accumulation levels, followed by Pb, Cu, Ni, and Zn, whereas the As and Cr were at low level. Based on the sum of toxic units (STU), the surface sediments in the reservoir showed a moderate level of toxicity. A large proportion of BCR-extracted acid extractable and reducible fraction was found in Cd (72.5%) and Pb (40.3%), suggesting high bioavailability. Combined RSP, RAC and MRI results showed that Cd was the major pollutants, which had a higher potential risk, while the other elements were at a lower risk level. Source apportionment of heavy metal(loid)s in the drinking-water reservoir indicated that Cd (75.76%) and Zn (23.1%) mainly originated from agricultural activities; As(69.82%), Cr(50.05%), Cu(33.47%), and Ni(31.87%) were associated with domestic sources related to residents' lives; Cu (52.36%), Ni (44.57%), Cr (34.33%), As (26.51%), Pb (24.77%), and Zn (23.80%) were primarily from natural geological sources; and Pb (47.56%), Zn (22.46%) and Cr (13.92%) might be introduced by mixed sources of traffic and domestic. The contribution ratios of the four sources were 18.41%, 36.67%, 29.48% and 15.44%, respectively.