Major and trace metals in suspended and bottom sediments of the Mandovi and Zuari estuaries, western India: distribution, source, and pollution

Major elements and trace metals in suspended sediments along transect stations of the Mandovi and Zuari estuaries showed three types of distribution: (a) high concentrations of most metals (Al, Fe, Mn, Cr, Pb, Cu, Ni, Zn, Co, Sc, Mo, and U) in the upper estuary and their decreasing concentrations seaward in every season, (b) lower concentrations of some metals (Mg, Cr, Zr, V, Al, Th) in the upper estuary and bay and their increased concentrations in the lower estuary, and (c) higher concentrations of some metals (Cu, Ni, Zn, Pb, and Cr) in the upper estuary and bay and their decreased concentrations in the lower estuary. Mn was the most significant pollutant in both the estuaries. The Zn, Cr, Fe, and Mo in Mandovi during the monsoon and post-monsoon and, Pb, Ni, and Cr in Zuari during the post- and pre-monsoons were in the range "moderately to heavily polluted." The pollution load index of metals was high at upstream stations, with higher values in Mandovi during monsoon and Zuari during the post- and pre-monsoons. Most trace metals were correlated with Fe and Mn indicating their association primarily with Fe-Mn ore material. The principal component analysis indicated natural and anthropogenic inputs and the latter was predominantly related to ore material in both the estuaries. The distribution factor was high for Al, Mg, Zr, Th, and U in < 2-μm fraction and Cr, Cu, Ni, Zn, Co, V, Sc, and Zr in 2–4-μm size fraction sediments suggesting two sources of sediments. More than 60% concentrations of all trace metals were associated with < 2-μm fraction sediments. The distribution of trace metals along transect was affected by the physico-chemical conditions of the estuary, grain size of sediments, and anthropogenic contribution of metals.