Cochin estuary high on insecticides, says study

Endosulfan detected in 2011; residues exceed norms

January 19, 2014 11:16 am | Updated May 13, 2016 10:49 am IST - THIRUVANANTHAPURAM

Map of Cochin Estuary

Map of Cochin Estuary

A study by researchers of Department of Chemical Oceanography of Cochin University of Science and Technology shows that Cochin estuary has one of the highest concentrations of organochlorine insecticides in the World.

Residual levels of organochlorine insecticides in the Cochin estuary sediment are of higher toxicity than those reported from more than 20 world wide locations, researchers P.S. Akhil and C.H. Sujatha said in a paper published in Marine Pollution Bulletin recently.

They had analysed samples from 17 locations in the southern, middle and northern areas of the estuary and total contamination in sediment was 1170 nanograms per gram (parts per billion) in 2009 and 1087 nanograms per gram in 2011 in the entire study region. Maximum concentration of Organochlorine insecticide was found in the northern part of the estuary. The results indicated health risks to the habitat in both southern and northern area.

Most of the pesticide residues detected from the study area were above sediment quality guidelines drawn up in United States and Canada (India has not issued such guidelines). The highest concentrations were detected at stations near the discharge points close to industries.

Among the contaminants, cyclodienes followed by hexachlorocyclohexanes (associated with pesticide lindane, erroneously known as BHC) and dichlorodiphenyltrichloroethane (DDT). A high concentration of endosulfan was detected in one of the stations in 2011. The presence of elevated concentration of alpha isomer of the chemical over 2009 indicated recent input of the pesticide in the study area. These are chemicals listed for elimination from the World or restricted use under Stockholm convention on Persistent Organic Pollutants.

The study indicated excessive and indiscriminate use of Aldrin in the study area in 2009 while presence of heptachlor epoxide went down beyond detectable levels by 2011. Total concentration of hexachlorocyclohexanes in the entire study area decreased from 423 nanograms per gram of sediment in 2009 to 23.7 nanograms per gram in 2011. Its levels were generally higher than that for DDT. DDT residues came from mainly aged and weathered agriculture soils.

Meanwhile, the World Health Organisation recently listed hazardous pesticides as one of the 10 chemicals or groups of chemicals that are of major public health concern. The others are air pollution, arsenic, asbestos, benzene, cadmium, dioxin and dioxin-like substances, inadequate or excess fluoride, lead and mercury.

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