Imidacloprid in processed tea and tea liquor

Imidacloprid in processed tea and tea liquor 1 first-author 1 2 3 4 corresp ‡Corresponding Author ‡Corresponding Author †E-mail:agchemical@rediffmail.com †E-mail:agchemical@rediffmail.com agchemical@rediffmail.com Department of Agricultural Chemicals, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur 741 252, India Department of Agricultural Chemicals, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur 741 252, India Institute of Environmental Studies and Wetland Management, Salt Lake City, Kolkata 700 098, India Institute of Environmental Studies and Wetland Management, Salt Lake City, Kolkata 700 098, India Department of Entomology, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur 741 252, India Department of Entomology, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur 741 252, India Department of Agricultural Chemistry and Soil Science, Calcutta University, Kolkata 700 019, India Department of Agricultural Chemistry and Soil Science, Calcutta University, Kolkata 700 019, India Imidacloprid is a newly introduced broad-spectrum chloronicotinyl insecticide and will find its way in agricultural production, particularly in Asia. However, information on the fate of imidacloprid in crop plants is lacking. The degradation of imidacloprid in processed CTC tea and tea liquor was investigated in the present study in which imidacloprid was applied at recommended application rate (30.0 g a.i./ha) and twice the recommended application rate (60.0 g a.i./ha) for three consecutive seasons. Imidacloprid was rapidly dissipated in processed tea following first order reaction kinetics at all application rates and had half-lives of 0.91~1.16 d with the residue in tea liquor found to be below detectable limit on 3rd day samples. The study revealed that imidacloprid is safe for human consumption and will not pose any residual toxicity problem. Imidacloprid Processed tea Tea liquor Residue Dissipation INTRODUCTION 1 Tea ( Camellia sinensis ) is known as queen of beverages. India is the biggest producer of tea in the world and is being cultivated mainly in northeast and south India where it is the most important cash crop due to its export potentialities. Tea production levels in India were about 1000 kg/ha during the 1950’s and increased up to about 1800 kg/ha in the mid 1980’s due to the introduction of green revolution technologies such as external chemical inputs (Senapati et al., 1994 1994 ). In northeast India tea is the main commercial crop receiving wide range of pesticides to boost production. Pests, pathogens and weeds are important factors limiting the productivity and quality of tea in almost all the tea growing countries of the world. During the last few decades the use of synthetic chemicals achieved control of pests, diseases and weeds in tea fields. Though broad-spectrum chemicals offer powerful incentives in the form of good control, increased yield and high economic returns, they have serious drawbacks such as resistance to pesticides, pest resurgence, outbreak of secondary pests, harmful effects on human health and environment and presence of undesirable residues. Imidacloprid, 1-[(6-chloro-3-pyridyl)-methyl]-2-nitroimidazolidin (Fig. 1 1 ), represents a modern potent insecticide group, chloronicotinyl that interacts like nicotine, epibatidine and nereis toxin analogues with the postsynaptic nicotinic acetylcholine receptor (Bai et al., 1991 1991 ; Tomizawa and Yamamoto, 1993 1993 ). It is effective for controlling aphids, plant bugs, leafhoppers, plant hoppers, thrips, scales, whiteflies and various other harmful pest species including resistant strains (Ishii et al., 1994 1994 ). Imidacloprid was found most effective against tea mealy bug (Ignacimuthu and Jayaraj, 2003 2003 ) and also has excellent systemic properties, which makes it suitable for seed, soil and foliar treatment (Wamhoff and Schneider, 1999 1999 ). Imidacloprid undergoes rapid photochemical degradation with 1-(6-chloro-3-piridinyl)-methyl-2-imidazolidinone being identified as the major photo metabolite (Wamhoff and Schneider, 1999 1999 ). Roy et al.( 2005 2005 ) reported the photodegradation pathway of a commercial formulation of imidacloprid in irrigated water. The photo metabolites obtained were 1-[(6-chloro-3-pyridinyl)-methyl] imidazolidin-2-one, 1-[(6-chloro-3-pyridyl)-methyl] -N-nitro-4-imidazolidene-2-ylideneamine, 6-hydroxy nicotinic acid and 6-chloronicotinic acid. The photolytic process affected the imidazolidine moiety while the 6-chloropyridine moieties remained unchanged. The proposed phototransformation pathway involved hydrolysis, oxidation and dehydration. In the Indian market, the active ingredient (imidacloprid) is embodied in the trade products Gaucho for seed treatment and Confidor for leaf and soil treatment. Its use as a replacement for other insecticides is increasing. Based on the above information, a three-season field study of imidacloprid was conducted in northeast India for determination of the dissipation pattern and the residue level in processed tea and tea liquor. MATERIALS AND METHODS 1 A three seasons (1st season, March 2003; 2nd season, September 2003; 3rd season, March 2004), field experiment on tea (variety TV1) was conducted at Kamalpur Tea Estate, Darjeeling, West Bengal, India. Confidor 200SL was applied thrice on tea bushes at an interval of 7 d as high volume spray (400 L/ha) by a knapsack sprayer. It was applied at 30.0 g a.i./ha (recommended application rate, i.e., T 1 ) and 60.0 g a.i./ha (twice the recommended application rate, i.e., T 2 ). Untreated control (T 3 ) was simultaneously maintained. Each treatment including control was replicated thrice in a randomized block design (RBD). The number of bushes per treatment was 100 and spacing between the bushes was regular double hedge type. Green tea leaves (two leaves and a bud, 1 kg) were plucked randomly from each treatment replication at different time intervals [0 (2 h after last spraying), 1, 2, 3 and 5 d] and the green leafs were into processed CTC tea (100 g) at Kamalpur Tea Estate factory following standard manufacturing methods. Imidacloprid was quantified using high performance liquid chromatography (JASCO UV 1575 UV-Vis detector equipped with 3392A integrator). For recovery studies, processed tea samples (1:2, w/v) were fortified with acetonitrile solution of imidacloprid to obtain concentrations corresponding to different doses. The samples were immediately extracted three times with 100 ml of acetonitrile on an electric shaker (1 h), each time followed by ultrasonic vibration for 5 min. After centrifugation at 3000 r/min for 10 min, the extracts were combined and imidacloprid was partitioned into CHCl 3 (100 ml+50 ml+50 ml). The combined organic extract was put into a 250 ml round bottomed flask and evaporated to dryness with rotary vacuum evaporator with the water bath temperature adjusted to 40 °C. The concentrated extract was then subjected to adsorption chromatography over florisil (60~120 mesh) with 10 cm layer of anhydrous sodium sulphate on the top. The column was eluted with 200 ml of acetonitrile:methanol (95:5, v/v). The organic fraction was evaporated to dryness, rinsed with HPLC grade methanol and filtered (0.2 μm) for direct HPLC analysis. Imidacloprid was separated on an Intersil 150 mm×4.6 mm ODS 2, 5 μm (RP C 18 ) using a mobile phase of methanol and water (60:40, v/v) at a flow rate of 1 ml/min and column temperature at 40 °C. Quantification was performed against imidacloprid standard at a wavelength of 270 nm. Under this condition the retention time of imidacloprid was 3.9 min, the limit of detection was 0.01 mg and the sensitivity of the method was 0.005 mg/kg. The average imidacloprid recovery was 91.2%. Determination of imidacloprid residues in the treated samples was carried out as per the recovery study. The liquor was prepared by adding 10 g of processed CTC tea in 200 ml of boiling water and was stirred for 5 min with spoon and then filtered. The same procedure was followed for the tea liquor after extraction of the compound by liquid-liquid partition with dichloromethane. RESULTS AND DISCUSSION 1 Initial deposits, dissipation percent, half-life values and regression equation of imidacloprid in processed CTC tea and residues remaining in tea liquor are presented in Tables 1 1 ~ 3 3 . The results showed that the residues of imidacloprid in processed tea decreased progressively with time irrespective of application rates and seasons. The initial deposits of imidacloprid on day 0 (2 h after last spraying) were found to be 0.2163×10 −6 ~0.2314×10 −6 and 0.4190×10 −6 ~0.4520×10 −6 for the treatments T 1 and T 2 respectively among the seasons. The dissipation rate was found to be rapid and the initial deposit dissipated upto 26.16%~33.10% after the 1st day followed by 78.18%~85.40% on the 3rd day irrespective of application rates and seasons. The residue level decreased to below detectable limit on the 5th day for T 1 and 7th day for T 2 . In the untreated control (T 3 ), no imidacloprid residues were detected. The half-life values calculated from the best-fit lines of the logarithm of residual concentrations versus incubation period, suggested first order reaction kinetics in the dissipation of imidacloprid residue. The study revealed that the dissipation rate was independent of initial deposit and the that half-life ( t ½ ) values of imidacloprid in processed tea ranged from 0.91 to 1.16 d according to the seasons and application rate. BDL: Below detectable limit Season Period (d) Mean residue± SD (×10 −6 ) Dissipation (%) Regression equation [half-life (d)] 4 1st 0 0.2208±0.0078 4 y =−0.3296 x +1.8137 [0.91] 1 0.1525±0.0054 30.95 2 0.1085±0.0082 50.84 3 0.0400±0.0004 81.86 5 BDL 4 2nd 0 0.2163±0.0003 4 y =−0.2096 x +1.5780 [1.14] 1 0.1447±0.0043 33.10 2 0.1116±0.0029 48.41 3 0.0472±0.0037 78.18 5 BDL 5 3rd 0 0.2314±0.0002 5 y =−0.2709 x +1.7060 [1.11] 1 0.1633±0.0016 29.43 2 0.1020±0.0073 55.92 3 0.0338±0.0048 85.40 5 BDL BDL: Below detectable limit Season Period (d) Mean residue± SD (×10 −6 ) Dissipation (%) Regression equation [half-life (d)] 5 1st 0 0.4520±0.0005 5 y =−0.2633 x +1.9994 [1.14] 1 0.3159±0.0027 30.10 2 0.2287±0.0019 49.40 3 0.0776±0.0002 82.82 5 0.0440±0.0034 90.26 7 BDL 5 2nd 0 0.4190±0.0053 5 y =−0.2586 x +1.9634 [1.16] 1 0.2853±0.0007 31.91 2 0.2316±0.0083 44.73 3 0.0758±0.0061 81.91 5 0.0414±0.0003 90.12 7 BDL 6 3rd 0 0.4430±0.0069 6 y =−0.2610 x +1.9932 [1.15] 1 0.3271±0.0018 26.16 2 0.2150±0.0008 51.47 3 0.0831±0.0001 81.24 5 0.0436±0.0040 90.16 7 BDL BDL: Below detectable limit 2 Season 2 Period (d) 2 Mean residue± SD (×10 −6 ) T 1 T 2 3 1st 0 0.0160±0.0013 0.0230±0.0021 1 0.0083±0.0006 0.0121±0.0017 2 BDL 0.0076±0.0011 3 BDL 3 2nd 0 0.0139±0.0003 0.0228±0.0053 1 0.0071±0.0029 0.0137±0.0077 2 BDL 0.0081±0.0043 3 BDL 4 3rd 0 0.0145±0.0020 0.0251±0.009 1 0.0086±0.0027 0.0128±0.0037 2 BDL 0.0079±0.0004 3 BDL Imidacloprid residues in tea liquor from zero (0) day samples were found to be 0.0139×10 −6 ~0.0160×10 −6 and 0.0228×10 −6 ~0.0251×10 −6 irrespective of the seasons for the treatments T 1 and T 2 respectively. Those from the 1st day sample were found to be 0.0071×10 −6 ~0.0086×10 −6 and 0.0121×10 −6 ~0.0137×10 −6 . The residue decreased to below detectable limit on the 2nd day for T 1 and 3rd day for T 2 . In the untreated control (T 3 ), no imidacloprid residues were detected irrespective of the seasons. The MRL (maximum residue limit) value of imidacloprid has not yet been established in tea. There is no recommended MRL value of imidacloprid in tea by WHO/FAO. But MRL value of imidacloprid in potato, tomato, apple, mango etc., has been fixed to 0.2×10 −6 ~0.5×10 −6 by FAO (FAOSTAT, 2005 2005 ). As no residue was detected in the 3rd day sample it might be stated that imidacloprid may not pose any residual toxicity problem in processed tea, which also fits the plucking schedule of India’s Tea Estates of the northeastern region of the country. References D Bai , SCR Lummis , W Leicht , H Beer , BD Sattelle . Action of imidacloprid and a related nitromethyl on cholinergic receptors of an identified insect motor neurone . Pest Sci , 1991 . 33 197 - 204 . . Action of imidacloprid and a related nitromethyl on cholinergic receptors of an identified insect motor neurone FAOSTAT 2005 . (Available from: Http://faostat.fao.org/faostat/collections?subset=FoodQuality Http://faostat.fao.org/faostat/collections?subset=FoodQuality . Last Updated on Apr. 12, 2005 and Accessed on Jan. 30, 2006) . S Ignacimuthu , S Jayaraj . Eco-friendly approaches for sustainable insect pest management . Current Sci , 2003 . 84 1292 - 1293 . . Eco-friendly approaches for sustainable insect pest management Y Ishii , I Kobori , Y Araki , S Kurogochi , K Iwaya , S Kagabu . HPLC determination of the new insecticide imidacloprid and its behaviour in rice and cucumber . J Agr Food Chem , 1994 . 42 ( 12 ): 2917 - 2921 . DOI: 10.1021/jf00048a051 http://doi.org/10.1021/jf00048a051 . HPLC determination of the new insecticide imidacloprid and its behaviour in rice and cucumber S Roy , RK Kole , MA Sarkar , 等 . Catalytic Photodegradation of the Insecticide Imidacloprid in Aqueous Media Exposed to Sunlight . 2005 . The BCPC International Congress and Exhibition—Crop Science & Technology . Glasgow, UK 821 - 826 . . Catalytic Photodegradation of the Insecticide Imidacloprid in Aqueous Media Exposed to Sunlight BK Senapati , PK Panigrahi , P Lavelle . Macrofaunal Status and Restoration Strategy in Degraded Soil under Intensive Tea Cultivation in India . Transactions of the 15th World Congress of Soil Science , 1994 . 4A Acapulco, Mexico 64 - 75 . . Macrofaunal Status and Restoration Strategy in Degraded Soil under Intensive Tea Cultivation in India M Tomizawa , I Yamamoto . Structure activity relationship of nicotinoids and imidacloprid analogues . J Pest Sci , 1993 . 18 91 - 98 . . Structure activity relationship of nicotinoids and imidacloprid analogues H Wamhoff , V Schneider . Photodegradation of imidacloprid . J Agr Food Chem , 1999 . 47 ( 4 ): 1730 - 1734 . DOI: 10.1021/jf980820j http://doi.org/10.1021/jf980820j . Photodegradation of imidacloprid The authors are thankful to the Department of Agricultural Chemicals, Bidhan Chandra Krishi Viswavidyalaya for providing all the necessary instrumental facilities. 10.1631/jzus.2006.B0619 Project supported by Bayer Crop. Science India Ltd. 2006-03-18 2006-05-17 2006-07-14 2022-01-05 Copyright © 2006, Journal of Zhejiang University Science 2006 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 08 07