Research article Residues of endosulfan in surface and subsurface agricultural soil and its bioremediation Greeshma Odukkathil * , Namasivayam Vasudevan Centre for Environmental Studies, Anna University, Chennai, Tamilnadu 600025, India article info Article history: Received 15 April 2015 Received in revised form 20 July 2015 Accepted 14 September 2015 Available online xxx Keywords: Bioaugumentation Bioavailability Bioremediation Persistent organic pollutants Biosurfactant abstract The persistence of many hydrophobic pesticides has been reported by various workers in various soil environments and its bioremediation is a major concern due to less bioavailability. In the present study, the pesticide residues in the surface and subsurface soil in an area of intense agricultural activity in Pakkam Village of Thiruvallur District, Tamilnadu, India, and its bioremediation using a novel bacterial consortium was investigated. Surface (0e15 cm) and subsurface soils (15e30 cm and 30e40 cm) were sampled, and pesticides in different layers of the soil were analyzed. Alpha endosulfan and beta endo- sulfan concentrations ranged from 1.42 to 3.4 mg/g and 1.28e3.1 mg/g in the surface soil, 0.6e1.4 mg/g and 0.3e0.6 mg/g in the subsurface soil (15e30 cm), and 0.9e1.5 mg/g and 0.34e1.3 mg/g in the sub- surface soil (30e40 cm) respectively. Residues of other persistent pesticides were also detected in minor concentrations. These soil layers were subjected to bioremediation using a novel bacterial consortium under a simulated soil profile condition in a soil reactor. The complete removal of alpha and beta endosulfan was observed over 25 days. Residues of endosulfate were also detected during bioremedia- tion, which was subsequently degraded on the 30th day. This study revealed the existence of endosulfan in the surface and subsurface soils and also proved that the removal of such a ubiquitous pesticide in the surface and subsurface environment can be achieved in the field by bioaugumenting a biosurfactant- producing bacterial consortium that degrades pesticides. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction The occurrence of pesticide residues in various environments is primarily the result of the intensive use of pesticides in agriculture, pesticide industries (point source), atmospheric fall out, agricul- tural runoff, and industrial discharges. Among these pesticides, endosulfan is a new chemical on the Stockholm Convention on Persistent Organic Pollutants list. Endosulfan is an organochlorine pesticide under the Cyclodiene subgroup and belongs to the class of organochlorine insecticides. It was one of the leading chemicals used against a broad spectrum of insects and mites in agriculture and allied sectors (Harikrishnan and Usha, 2012). Commercial formulation of endosulfan (1,2,3,4,7,7-hexachlorobicyclo-2,2,1- heptene-2,3-bishydroxy methane-5,6-sulfite) is a mixture of ste- reo isomers of a and b endosulfan in the ratio 7:3 (Kataoka and Takagi, 2013). Its water solubility is 0.33 mg/L, and its half-life is more than a hundred years. Residues of persistent organic pollutants such as endosulfan, DDT and HCH were detected in industrial, urban and agricultural soils of many countries (Eun et al., 2014; Ssebugere et al., 2010; Wang et al., 2007). Studies of major water resources in India report the occurrence of Endosulfan residues, which proves its persistence (Puneeta et al., 2011; Bhattacharya et al., 2003; Rao, 2006). Endosulfan and its metabolites varied from 0.8 mg/kg to 6.39 mg/kg and 2 mg/kg to 11.2 mg/kg in the soil of Thiruvallur District of Tamilnadu, India (Jayashree and Vasudevan, 2007a). Major reason for the persistence of endosulfan in the environment is its less water solubility and is not bioavailable for microbial degradation. Biodegradation of such less water soluble compounds in soil can be enhanced by amending synthetic or biological sur- factants (Laha et al., 2009), but the usage of the former is restricted due to its toxicity and the later due to its cost. This study explores a method for bioremediation of pesticide contaminated soil to overcome this limitation of biosurfactant. Many studies were conducted on the biodegradation of endo- sulfan and its biochemical pathway in an aqueous system, but there are fewer studies on endosulfan and endosulfate degradation in * Corresponding author. E-mail address: greeshma.o@gmail.com (G. Odukkathil). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2015.09.020 0301-4797/© 2015 Elsevier Ltd. All rights reserved. Journal of Environmental Management 165 (2016) 72e80