Geochemical speciation, anthropogenic contamination, risk assessment and source identification of selected metals in freshwater sediments—A case study from Mangla Lake, Pakistan

Geochemical speciation of selected metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr and Zn) using modified BCR sequential extraction procedure was performed in the sediments collected from Mangla Lake, Pakistan. The extraction method was optimized using certified reference material (BCR-701) which showed significant recoveries (95–106%). Among the metals, Cd, Co, Ni, Pb and Sr exhibited relatively higher mobility and bioavailability, while Cu, Fe, Mn and Zn were found mainly in the residual fractions. Principal component analysis (PCA) revealed four groups of the metals in the sediments; I (Cd–Cr–Ni–Sr), II (Co–Pb), III (Fe–Zn), and IV (Mn–Cu); first two groups were mostly contributed by anthropogenic sources. The pollution indicators (individual contamination factor, enrichment factor and geoaccumulation index) revealed significant anthropogenic contamination of Cd, Co, Ni, Pb, Sr and Zn in the sediments. Risk assessment code (RAC) indicated medium risk for Co and Ni; high risk for Cd and Pb; and very high risk for Sr in the sediments. Cluster analysis (CA) and global contamination factor (GCF) were used to identify the pollution hotspots, which indicated more severe metal contamination at sites near to Mirpur city and other urban/semi-urban areas (S3–S5), especially for Cd, Co, Ni, Pb and Sr.