Residue decreasing in water samples, finds fourth phase of CWRDM study

Though its concentration is slowly decreasing, residues of endosulfan, the controversial chemical pesticide, are still present in the soil samples collected from different panchayats of Kasaragod district, says a scientific study.

The fourth and latest phase of a continuing study undertaken by a team of scientists led by P.S. Harikumar, principal investigator and head of the water quality division of the Centre for Water Resources Development and Management (CWRDM), Kozhikode, pointed to a greater persistence of endosulfan in soil and sediment samples than in water samples.

Interestingly the latest study, the report of which was submitted to the Kerala State Council for Science, Technology and Environment (KSCSTE), was conducted in the surrounding panchayats of the Plantation Corporation of Kerala’s estates about 11 years after the company put an end to the aerial spraying of the pesticide in its plantations.

According to Dr. Harikumar, the residues found in the samples need not be necessarily of the pesticide aerially sprayed in the region over 10 years ago.

“It can also be of some recent use by other means since a complete ban on the pesticide came only a couple of years ago in the State,” he said.

Study since 2010

The CWRDM has been conducting a study on the persistence of endosulfan in water, soil, and sediment samples of Kasaragod in different phases since 2010. The latest is the fourth phase of that study. Though the residues of the pesticide were found to be waning more quickly from the water samples, it didn’t happen so with the sediment and soil samples. “Its decrease was found particularly slow with the soil samples,” said Dr. Harikumar.

According to him, the degradation rates of both endosulfan isomers were greatly affected by environmental conditions.

The study proved that combined toxic residues of endosulfan in the sediment and soil samples of selected areas of Kasaragod district were found to be persistent for a period of 1.5 to 2 years, but the persistence showed variations depending upon the climatic conditions and physico-chemical characteristics like pH, organic matter content, and particle size of the soil in the area.

Out of 13 soil samples, the pesticide was detected in five samples during the second phase and during the third phase, endosulfan was detected in three samples. Sampling was again continued in the fourth phase to find out the persistence of endosulfan. Out of the three soil samples in which endosulfan was detected during the third phase, it was found to be persistent in two soil samples from Panathadi and Muliyar panchayats during the fourth phase.

Need to enforce ban

A relatively high concentration of endosulfan was detected in the soil, according to scientists, because of the fact that it is fairly immobile in soil and is highly persistent. “We need to keep tabs on the time the pesticide takes for natural degradation in the soil. In the meanwhile, we have to also check whether the ban on endosulfan is being strictly followed by all,” said Dr. Harikumar.

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