Industrial activity, particularly coal fly ash pollution emanating from ash conveyance, storage and impounding structures have drastically altered the hydrology, ecology and topography of the Ennore creek, an expert study commissioned by the National Green Tribunal has said.
In its interim report, the expert committee constituted by the NGT, Southern Zone to review the environmental impacts of coal ash pollution on Ennore creek and areas surrounding North Chennai Thermal Power Station (NCTPS) at Ennore, recorded the findings of tests on water quality, fish and prawn samples.
The three-member panel, comprising Sultan Ahmad Ismail, director, Ecoscience Research Foundation, D. Narasimhan, associate professor (retd.), Department of Botany, Madras Christian College and Balaji Narasimhan, associate professor, Department of Civil Engineering, IIT–Madras, cautioned that any further degradation of the estuarine ecosystem would make several habitats inland vulnerable to the impacts of extreme weather and marine events. Salinity intrusion was a threat, as it is located in a transition zone buffering the inland freshwater areas from the coastal saline areas, the committee said.
Assessing Tangedco’s estimate of the total quantum of settled fly ash, of 2,18,257 m3, the panel said this appeared to be an underestimate.
“This appears to be only less than 2% of total fly ash volume that is in discrepancy. Still, 98% of fly ash has to be accounted for and recovered from the site,” said the study.
The extent of fly ash spill was visible over 344.39 hectares and the likely extent of fly ash in rivers, canals and water bodies was around 309 hectares.
The committee estimated the fly ash volume in the field to be above 9.8 million cubic metres (Mm3). It arrived at this approximate estimate after a field survey between September and December 2017 and recommended an intense field campaign and drone survey.
The study found all samples from Kosasthalai river, the backwaters and the secondary pond to contain elevated levels of several toxic metals.
Two borewell samples taken from Seppakkam, a village to the west of the ash pond, were severely contaminated with heavy metals like copper, manganese, cadmium, mercury, selenium, lead, chromium and nickel. One of the samples was additionally contaminated with molybdenum. The excessive presence of these metals indicated that toxic contamination had already resulted due to seepage from the fly ash pond, it was reported.
All five samples taken from the Kosasthalaiyar had lead, mercury, selenium and arsenic in excess of standards for discharge of environmental pollutants into inland water bodies. All five samples from backwaters had mercury levels in excess of standards for discharge of environmental pollutants.
Metals in fish samples
A total of 20 samples of fish, including fin fish, crab, prawn and oyster/mussels were taken. All samples contained detectable levels of copper which could cause deformity of gills and harm their ability to navigate and hunt for food, the study noted. The levels of cadmium and lead found in the fish taken from the creek were in excess of maximum concentration limits prescribed by European Union regulations.
Moreover, local fishermen confirmed that white prawns, black prawns, sand prawns, tiger prawns, green crab, grey eel catfish, mullet, silver biddy, perch, sea bass and other fish species had either disappeared or declined to insignificance.
Five samples of home-grown vegetables also had detectable and significant levels of chromium and lead, but this could not be linked solely to fly ash as the region itself was critically polluted, the report said. The experts also noticed degradation of mangroves.
The NGT has commissioned a separate study on the effects on human health, the report said, adding that fisherfolk in contact with contaminated water and fish consumers were at risk.