Impact of mining on metal concentration in waters of the Zuari estuary, India

The rationale of the current study was to establish that mining and associated activities are the chief sources of trace metal contamination in the Zuari estuary, Goa. Surface and bottom water samples were collected monthly, at 11 stations, starting from the mouth of the estuary, covering a stretch of 35 km towards the head during the period of ban on mining in Goa as per the directions of the Honourable Supreme Court of India. The water samples were analysed for physicochemical parameters and metals (Fe, Mn, Zn, Cr, Cu and Pb). Spatial variation of metals (Zn, Cr and Cu) indicated high concentrations at the mouth region, revealing that they are derived by resuspension of bottom sediments at higher salinities, while metals Fe, Mn and Pb showed higher concentrations at the head region, indicating that these are derived from freshwater discharge. Seasonal variation of metals revealing high concentrations during non-monsoonal months was attributed to a high rate of evaporation and intense anthropogenic activities except Pb. Contamination factors and enrichment factors of metals were calculated to assess the degree of metal contamination and relative abundance of pollutants, respectively. Sources of metals into the estuary were discussed by using principal component analysis. Correlation coefficients were calculated to find out the dynamics among the physicochemical factors and trace metals. The study exemplified that concentrations of trace metals in waters of the Zuari estuary were significantly less when compared to the periods of rampant mining activity around Goa, indicating that mining can influence the concentration of metals in the Zuari estuary.