Dissipation rates of some selected pesticides from the soil of tea agroecosystem in Assam, India

An experiment was carried out in Rosekandy Tea Estate, Barak Valley, Assam to investigate the persistence of some selected pesticides (i.e Endosulfan, Fipronil, Paraquat and 2,4-D) on the soil. These pesticides were applied in the soil as per the application rate, where one year old tea plants were growing and the residue were analysed for a period of 50 days. Their degradation kinetics in soil was also studied and described. Soil samples were collected with the help of soil corer. The samples were brought to the laboratory, air dried in room temperature and extracted for analysis with high performance liquid chromatography (HPLC). Among the pesticides 2,4-D was highly persistent with half life of 57.75 days followed by Endosulfan which lost 42.64% of its initial concentration by the last sampling period (i.e 50 days) after the spraying. Fipronil and paraquat lost 65% and 70.32% of initial residue in soil making them the least persistent amongst these pesticides in the studied soil. Considering the impact of pesticide residues on human health, the less persistent pesticides may be used in tea plantations to minimize the potential negative impact of pesticides in the environment. The cost benefit ratios of the use of the pesticides should be also worked out.