Bioaccumulation of metals by edible bivalve Saccostrea cucullata and its application as a bioindicator of metal pollution, tropical (Zuari) estuary, Goa, India

Abstract

The distribution and abundance of iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) was assessed in sediment (total and labile), water, total suspended matter (TSM), and edible bivalve (shell and soft tissue) Saccostrea cucullata for October and November months in the Zuari Estuary, Goa, India. Variation in total metal levels with time (October and November; surface and bottom) and space in sediments was attributed to changes in the source of metals and diagenetic processes. The concentration of Mn was considerably higher in a labile fraction in sediments, which suggested its mobilization potential as a function of change in ionic composition and pH. Saccostrea cucullata showed variation in metals during October and November and so as along the lower to the upper region of the estuary. This was attributed to the variation in the source of the metal, labile concentration, affinities towards metallothionein, and function of size, sex types, age, habitat, etc. The content of Mn, Zn, and Cu was accumulated more in the soft tissue than the hard shell which was attributed to the availability of metal-binding metallothionein proteins in soft tissue. Further, the presence of essential metals (Fe, Mn, and Zn) in hard shells of bivalve above the recommended value in addition to soft tissue suggested their anthropogenic source and pollution in the Zuari Estuary. Pollution was also construed through the metal pollution index (MPI) and supported the application of Saccostrea cucullata as a metal pollution bio-indicator. The study revealed the bioaccumulation of metals in bivalves was not entirely restricted to their availability in water and adsorption on TSM but indeed influenced by biological and geochemical factors.