ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY https://doi.org/10.14233/ajchem.2017.20229 INTRODUCTION Endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a- hexahydro-6,9-methano-2,4,3-benzodioxathiepin-3-oxide) belongs to organochlorine cyclodiene (OCPs) group of insec- ticides used globally, mainly in developing countries against a wide range of sucking, chewing and boring agriculture insect pests, like lepidoptera, coleoptera, heteroptera, homoptera, thysanoptera and diptera. It is reported to be used widely on a variety of food crops such as vegetables, fruits, corn, cereals, oilseeds, tea and coffee and in non-food crops like cotton and tobacco [1]. Endosulfan is considered as one of the highly persistent insecticides after DDT and though has been banned in some states of India but is being applied in other states on several crops like vegetables, cereals etc. at various places in the country. Endosulfan is a mixture of two stereoisomers alpha (α) 70 % and beta (β) 30 % and both are equally toxic to aquifers [2]. Low temperatures at increasing depths of soil results in persistence of endosulfan and its metabolites for long periods of time in aquatic environment. Degradation of any pesticide is affected by several environmental conditions like tempera- ture, humidity and microbial population in soil. Endosulfan sulfate is the main oxidative metabolite formed due to degra- dation in aerobic soils while another metabolite, endosulfan diol is mainly formed by chemical or biological hydrolysis of this compound in anaerobic soils by bacteria [3,4]. Influence of Soil Amendments and their Conjoint Application with Microbial Consortium in Enhancing Endosulfan Degradation and Reducing its Leaching to Groundwater ARCHANA SUYAL 1 , ANJANA SRIVASTAVA 1,* , ANITA SHARMA 2 and P.C. SRIVASTAVA 3 1 Department of Chemistry, College of Basic Sciences and Humanities, G.B. Pant University of Agriculture and Technology, Pantnagar-263 145, India 2 Department of Microbiology, College of Basic Sciences and Humanities, G.B. Pant University of Agriculture and Technology, Pantnagar-263 145, India 3 Department of Soil Science, College of Agriculture, G.B. Pant University of Agriculture and Technology, Pantnagar-263 145, India *Corresponding author: E-mail: anj612003@yahoo.com Received: 6 August 2016; Accepted: 10 October 2016; Published online: 30 December 2016; AJC-18196 A laboratory experiment using soil columns was conducted to study the effect of soil amendments (e.g., farmyard manure, press mud compost, cereal straw, gypsum and fresh cow dung) and their conjoint use with microbial consortium (Bacillus sp. GS20 plus other bacterial isolates) in degradation of α- and β-endosulfan and reducing its leaching to underground water. Among all the five soil amendments used in the study, application of cereal straw and gypsum @ 5 t ha -1 separately decreased the maximum leaching of endosulfan, whereas in conjoint application with microbial consortium, cereal straw @ 5 t ha -1 was more effective in reducing leaching of endosulfan. Keywords: Soil columns, Endosulfan, Amendments, Leaching, Microbial consortium. The WHO listed endosulfan in Category II as moderately hazardous, while the US EPA categorized it under highly hazardous pesticide [1]. Residues of endosulfan affect the fertility of agricultural soil and are toxic to soil inhabitants like earth worms and soil microbes. The compound is also known to inhibit soil microflora and essential activity like nitrogen fixation [5] in soils. The rate of percolation, sorption and breakdown of a pesticide within the soil profile determines the risk of ground- water contamination [6] and the presence of endosulfan in ground waters, confirms significant mobility of this agrochemical through the soil system [7]. The movement of pesticides from soil system to underground water strongly depends on the extent to which they are retained on the soil which in turn depends on the sorption properties of different soil [8]. Currently in Asia, India is the largest producer of dynamic pesticides and ranks 12th in world for their consumption [9]. Injudicious and indiscriminate use of pesticides in agriculture sector to enhance food production for continuously rising population has led to diffusion of pesticide residues into groundwater, which has raised a serious concern regarding lives existing in ecosystem [10]. Ground water is the main source of drinking and intake of water contaminated with pesticide residues may cause long term negative health issues in humans and other living beings. Some studies show that the application of organic amend- ments on soil increases its organic matter/carbon content. The Asian Journal of Chemistry; Vol. 29, No. 3 (2017), 547-550