The iron ore mining activity in Goa has left an adverse impact on the sediment of two major rivers in the state, which has ultimately affected the bottom-dwelling organisms in them, a study has said.
The study, conducted by Marine Science Department of the Goa University, has revealed that while the Bicholim river is "strongly polluted" with iron and manganese, the Mandovi river is "moderately polluted" with manganese and lead.
Mandovi, which originates in Karnataka and empties into the Arabian Sea near Panaji, is the longest running river in Goa. Bicholim, which runs through the North Goa district, is one of the tributaries of the Mandovi river.
The research expressed concerns that the mining activity may also influence the concentration of metals in the Zuari estuary in South Goa.
The five-decade-old mining industry in the coastal state came to a standstill in March 2018, after the Supreme Court quashed the second renewal of 88 iron ore mining leases.
Researchers Cynthia Gaonkar and Vishnu Matta carried out detailed assessments of the impact of mining on the sediment cores of the rivers in Goa and also on the metal concentration in the Zuari estuary.
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The first study, published in the Research Journal of Environmental and Earth Sciences, says that in order to assess the long-term contamination history of pollutants due to intense mining activities in the adjoining areas of rivers of northern Goa, sediment core samples were collected from three rivers- Bicholim, Mandovi and Terekhol.
The sediments were analysed for texture, organic carbon, major elements and trace metals, it said.
"Environmental parameters such as contamination factor, geo accumulation, enrichment factor and pollution load index were used to assess the extent of pollution," it said.
The study revealed that the Bicholim river is strongly polluted with iron and manganese and moderately polluted with lead and chromium, while the Mandovi river is moderately polluted with manganese and lead.
On the other hand, Terekhol river (though unpolluted in the past) is getting polluted with copper and chromium in the recent years because of human interference, it added.
"The results indicate that mining has a considerable impact on the Bicholim and Mandovi river sediments, which in turn affected the ecology of bottom-dwelling organisms," the study concluded.
It said that concentrations of trace metals in waters of the Zuari estuary were significantly less as compared to the periods of rampant mining activities around Goa, indicating that mining can influence the concentration of metals in the Zuari estuary.