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Dissipation Pattern and Residue of Fenvalerate in Tea of Bangladesh

Nilufar Nahar
Department of Chemistry, Dhaka University, Dhaka-1000, Bangladesh

Mihir Lal Sarker
Bangladesh Tea Research Institute (BTRI), Srimongal, Sylhet, Bangladesh

M Iqbal Rouf Mamun
Department of Chemistry, Dhaka University, Dhaka-1000, Bangladesh

Hiron Moy Sharma
Department of Chemistry, Dhaka University, Dhaka-1000, Bangladesh

Mohammad Shoeb
Department of Chemistry, Dhaka University, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

Fenvalerate, a non-systematic insecticide is extensively used for protection of tea leaves in Bangladesh. Excessive use of insecticides with improper pre-harvest intervals may cause the tea unsuitable for consumption and trade. The study was designed to determine the safe perharvest interval after the application of fenvalerate on tea trees at two different doses. Fenvalerate was applied on tea plants in experimental plots at the full and half of the recommended doses (0.1 kg a.i /ha and 0.05 kg a.i /ha, respectively). Tea leaves were collected at 0 (2 h after application), 1, 3, 5, 7, 10 and 14 days after application of the insecticide and made into black tea which was infused with hot water. Both brew and brew free residue were extracted, cleaned up and analyzed by GC-ECD. The residue levels in the brew were 0.189, 0.033 and 0.007 mg/kg at zero, 7 and 10 days, respectively, when it was applied at half of the recommended dose. In case of the recommended dose, residue levels were 0.644 and 0.010 mg/kg at 0 and 10 day, respectively. Residues were below the maximum residue level (MRL: 0.1 mg/kg) on 5 day at half of the recommended dose and on 7 day at recommended dose. Dissipation of fenvalerate followed first order kinetics at both doses with half lives of 2.6 days in brew part and 4.6 days in brew free part. Recoveries were 6.56±0.003% and 90.6±0.033% in brew part and brew free residue part, respectively, giving a total recovery of 96.6±0.036%. LOD and LOQ were 0.002 and 0.006 mg/kg, respectively.

Keywords: Bangladesh, dissipation, GC-MS, fenvalerate, pesticide, tea,

Location: Experimental field (open field) of Bangladesh Tea Research Institute (BTRI), Srimongal, Moulvibazar

Start Date:

End Date:

Program Area: Pest Management

Commodity: Insecticide

Objectives:

The present study was made to find out how fenvalerate dissipates from tea after applying the recommended and half of the recommend dose under agro climate condition of Bangladesh.

Methodology:

Field experiment and sampling Tea was grown in an experimental field (open field) of Bangladesh Tea Research Institute (BTRI), Srimongal, Moulvibazar. Three treated and one control plots were chosen for the studies. Commercial grade of fenvalerate (active ingredient 20EC i.e 20% emulsifiable concentrate) were applied at full and half of recommended doses (0.1 kg a.i /ha and 0.05 kg a.i /ha, respectively) and tea leaves were collected at 2 h and 1, 3, 5, 7, 10 and 14 days after application during June 2009. Both of the batches of collected tea sample were made into black tea at the tea production plant of the BTRI. Sample were packed, labeled and transferred to the laboratory and stored at -20 ºC until analysis was carried out. Reagents and materials Florisil was purchased from Sigma-Aldrich, USA. Anhydrous sodium sulfate and extra pure analytical grade ethyl acetate (EtOAc), dichloromethane (DCM), n-hexane and acetone were purchased from E. Merck, Germany. Anhydrous sodium sulfate was purified by heating at 3000 C for 10 h in a furnace and alumina & florisil were activated by heating for 12 h at 130 ºC in an oven and were allowed to cool at room temperature before use. The analytical standard fenvalerate (purity 98.5%) was purchased from Dr. Ehrenstrofer GmbH, Augsberg-Germany. Standards were stored at -20 ºC in a freezer and away from the experimental samples. Instruments Quantifications were performed using a Shimadzu-2010 gas chromatograph (GC) equipped with an AOC-20i auto sampler and an electron capture detector (ECD). Injector and detector temperatures were set at 280ºC and 290ºC, respectively. The injection (1 µL) was made in the split-less mode opening after 2 min. Separations were performed on a HP-5 capillary column (30 m x 0.25 i.d. and film thickness, 0.25 µm) where nitrogen was used as carrier and make-up gas, and flow rate was 1.78 mL/min. Oven temperature was programmed at initial temperature 120ºC (2 min hold) and raised at 10ºC/min up to 280ºC (hold 10 min). Gas Chromatography-Mass Spectrometry (GC-MS) analyses were carried out using an Agilent 6890 series GC coupled with a 5973 mass selective detector (MSD) (Agilent Technologies, Wilmington, DE) having auto-injector and auto-sampler. Separations were accomplished using a capillary column HP-5MS (30 m x 0.25 i.d. and film thickness, 0.25 µm) connected with a Quadrupole Mass analyzer with Electron Ionization at 70 eV in scan mode. Helium was used as the carrier gas with average linear velocity of 36 cm/s. The injector was maintained constant at 250ºC and the oven temperature was programmed at initially 120ºC up to 1 min, 10 ºC/min till 200ºC and hold for 5 min, 5ºC/min till 280 ºC and hold for 5 min. Extraction Extraction of tea by hot water and clean up Tea sample (5 g) was infused with 100 mL hot water at 80 ºC for 5 min in a thermostated water bath. Brew was filtered by vacuum filtration through a filter paper into a conical flask and transferred into a separatory funnel (250 mL). Then NaCl (5 g) was added and the mixture was partitioned twice with ethyl acetate (100 & 50 mL). The organic layer was separated, dried completely by evaporation and reconstitued in 1 mL DCM. The samples were cleaned up using florisil–alumina column, the column first packed with florisil (12 g) followed by neutral alumina (5 g). DCM (60 mL) was used for packing and equilibration the column. The extract (1 mL) was applied to the column and eluted with DCM (100 mL) and was collected in a round bottomed flask, dried completely by rotary evaporator and reconstituted in 1.0 mL n-hexane. Extraction of brew free tea by ethyl acetate and clean up 3 After brewing, the residue was extracted twice with ethyl acetate (100 and 50 mL) and filtered through anhydrous sodium sulfate on porcelain Buchner funnel, dried completely and re-dissolved in 1 mL DCM. Sample extracts were cleaned up using same procedure described in brew part. Standard calibration curves The calibration curve of fenvalerate was made by injecting solutions at concentration 0.025, 0.05, 0.25, 0.5, 1.0 and 2.0 mg/kg of the standard fenvalerate into the GC-ECD, plotted integrated areas of the peaks against the standard concentration using MS Excel software. Correlation coefficient (r²) was 0.997. LOD and LOQ were found to be 0.002 (Signal to noise ration 3:1) and 0.006 mg/kg (S/N:: 10:1), respectively. Recovery Control tea sample (5.0 g) was spiked with 2.5 mg/kg of standard fenvalerate solution and were extracted and cleaned up following the same procedure as described above for brew and brew free tea. The recoveries were found to be 6.56±0.003% and 90.04±0.033% in brew part and brew free residue part, respectively. The total recovery was 96.6%.

Source of Information: Dhaka Univ. J. Sci. 63(2): 73-76, 2015 (July)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

From the present study, it can be concluded that at or after the 7th day of harvest, there was no detectable residue transfer to infusion at the half of the recommended and the recommended dose. Thus, infusion consumption is safe in samples harvested 7 days after fenvalerate treatment.

Knowledge Management: Journal