Effect of Light on the Degradation of Two Neonicotinoids viz Acetamiprid and Thiacloprid in Soil Suman Gupta Æ V. T. Gajbhiye Æ R. K. Gupta Received: 9 October 2007 / Accepted: 17 March 2008 / Published online: 4 April 2008 Ó Springer Science+Business Media, LLC 2008 Abstract Persistence of two neonicotinoids viz thiaclo- prid and acetamiprid in soil as affected by UV and sunlight exposure was studied. Treated soil was placed in petri- plates, brought to field capacity moisture and then exposed to UV and sunlight. Dissipation for both the pesticides followed monophasic first order kinetics under sunlight, however under UV-light biphasic dissipation was recorded. Residues of acetamiprid and thiacloprid in soil dissipated with half-lives of 11.1 and 12.8 days under UV light and 25.1 and 19.1 days under sunlight, respectively. Residues of both the neonicotinoids dissipated quickly under UV light as compared to sunlight. Exposure of thin film of acetamiprid and thiacloprid to UV and sunlight revealed that acetamiprid is more photo labile than thiacloprid. More than 95% acetamiprid dissipated within 24 h as compared to *70% dissipation observed for thiacloprid. Keywords Thiacloprid Á Acetamiprid Á Dissipation Á Soil Á Ultra violet light Á Sunlight Pesticides, used in agriculture or in public health control, reach the soil either by direct application or by spray drift. Once in the soil, pesticides undergo various dissipation processes like microbial degradation, chemical hydrolysis, photolysis, volatilization, leaching and surface runoff. The contribution made by each of these dissipation processes towards the overall dissipation depends upon the nature of soil, pesticides and other environmental factor. It has been reported in literature that among various biotic and abiotic transformation processes, photodegradation is an impor- tant factor influencing the fate of pesticides in the field (Konstantinou et al. 2001). In practice also it has been observed that pesticides persist longer under laboratory studies as compared to field studies (Sanyal et al. 2000; Ganier et al. 1996; Fernandez et al. 2001). Also surface residues following foliar spray degrade faster than the translocated residues inside plant matrix even though physiological activity is more inside the plant matrix. Faster degradation of highly persistent DDT under sunlight as compared to samples kept under dark has already been reported (Miller and Zepp 1983). All these observations emphasise on the important role played by light in pesticide degradation. Thiacloprid (N-(3-(6-chloro-pyridin-3-ylmethyl)-thiaz- olidin-2-ylidene)-cyanamide) and acetamiprid ((E)-N-[(6- chloro-3-pyridyl) methyl]-N 0 -cyano-N-methyl-acetamidine) (Fig. 1) belong to neonicotinoid group of insecticides. They have been found effective for the control of sucking insect pests such as aphids, whiteflies, jassids, thrips, leafminer, beetles etc. in various crops like okra, gram, mustard, cot- ton, citrus, etc. (Albuquerque et al. 1999; Li et al. 2000; Branco and Pontes 2001; Boselli and Vergnani 2001; Singh and Kulshrestha 2005; Gupta et al. 2005; Pramanik et al. 2006). The effect of light on persistence of thiacloprid and acetamiprid has not been reported in literature so far. Therefore, the present experiments were conducted to study the effect of light (sunlight and UV light) on persistence of these two neonicotinoids in soil. Materials and Methods Soil required for the study was collected from the plough layer (0–15 cm depth) of the research farm of Indian S. Gupta (&) Á V. T. Gajbhiye Á R. K. Gupta Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi 110 012, India e-mail: drsumangupta2002@yahoo.com 123 Bull Environ Contam Toxicol (2008) 81:185–189 DOI 10.1007/s00128-008-9405-x