Study finds mercury, lead in fish from Ennore creek

Chennai

The seafood you eat could have toxic elements like mercury , arsenic, lead and cadmium, a study has found. Such heavy metals pose health threats that include cancer, lung infection and failure of kidneys and other organs.

A study by Aquaculture Foundation of India and three institutions including Anna University have found concentration of heavy metals in the water and marine organisms in and around Ennore creek due to pollution from industries and domestic sources.

The study , published last year, examined the level of eight metals in the water and in five species that are eaten.The concentration was compared to that of permissible limits prescribed by the Food and Agriculture Organisation (FAO), an agency of the United Nations and the World Health Organisation.

After finding the levels to be high, the consortium initiated another round of investigation to take a closer look at nickel content in seafood.

Species like green mussel and tiger bass were found to have high concentration of mercury . Asian tiger shrimp was found to have up to 0.9 units of mercury as against the safe limit of 0.5 units.While the vastly consumed flathead grey mullet (`mada vai' or `kayal meen') and Indian oyster had levels close to the prescribed limits. The study points out that the liver and kidney of fish and shellfish tend to concentrate environmental mercury .

“Marine organisms possess a capacity to turn inorganic mercury into organic compounds, thus rendering mercury more easily transferable throughout the aquatic food chain,“ the study says. Earlier studies have also shown that fish consumption may constitute an important sources of mer cury exposure for health.

All the five species of Asian tiger shrimp, green mussel, Indian oyster, mullet and tiger bass had high cadmium concentration; shrimp had the highest level of 19.25 units (microgram per gram) against the permissible limit of 0.05 to 5.5. The study shows that bivalves accumulated higher proportions of copper, chromium, nick el and arsenic in Ennore creek than shrimp, grey mullet and tiger bass.

Aquaculture Foundation of India scientist M Jaikumar said the concentration of heavy metal deposits are high around the railway bridge at Ennore creek. “Heavy metals get deposited in the river because of lack of proper dredging. The mouth of the estuary is dredged to about five metres, while the depth near the railway bridge is only about 1.5m,“ he said. “Dredging has to be done up to 5m, and to a length of about 5km.“

Jaikumar said they are now studying nickel bioaccumulation in tissues of four marine species: Mullet, crab, oyster and polychetae, a worm used as a feed in shrimp hatcheries.

National Institute of Ocean Technology has also conducted studies at Ennore creek that showed the biochemical oxygen demand and fecal coliform levels are beyond the assimilative capacity of the water body . “It was found during the comprehensive field study that the biggest contributor was untreated municipal sewage from Buckingham Canal,“ said an NIOT scientist.