Studies of chemical contaminants in different food stuff

Abstract

Imidacloprid, a neonicotinoid pesticide is allowed to use in food storage. A total of 30 rice samples and 15 wheat flour samples were analyzed to determine the residaul amount of imidacloprid. Among 30 rice samples, 9 (fragrant) packed samples were found to contain imidacloprid residues in the range 1.59 – 4.51 µg g -1 which was greater than the MRL value (1.5 µg g -1 in rice, EPA 2010) and 9 (fragrant) unpacked samples were found to contain imidaclopridresidues in the range 0.06 – 1.10 µg g -1 which was lower than the MRL value. The imidacloprid residue in non-fragrant rice samples were found below detection limit. In cooked rice samples, no trace of imidacloprid was observed. Among 15 wheat flour samples, imidacloprid residues were observed only in 8 samples, ranging from 0.03 – 0.44 µg g which were lower than the MRL value (1.5 µg g -1 in wheat, EPA 2010). The toxic effect of imidacloprid in rice was evaluated against adults Sitophylus oryzae. The average mortality of adult weevils was 57% at 72 hours while spiking the control rice with a concentration level 1.25 µg g -1 , therefore, a concentration lower than this value would be enough to control the growth of weevils during storage. Therefore, the results of residual analysis in rice indicate indiscriminate use of imidacloprid in the market samples during storage. The dissipation pattern of quinalphos was studied in tomato, bean and cauliflower which were grown in the experimental field of Bangladesh Agricultural Research Institute (BARI). Quinalphos treated samples were collected from 0 (2 hours after application) to 15 successive days, transferred to the laboratory rezeerf ni derots dna ( ta- 20 0 C ). sohplaniuq fo tnuoma ehT otamot ni eudiser, fo egnar eht ni eb ot dnuof erew rewolfiluac dna naeb0.05 – 6.31 ,0.05 – 3.10 dna0 . 06 – 6.5µg g -1 and dissipated below MRL (0.20, 0.20 and 0.50 µg g in cauliflower, tomato and bean, EPA 2011) value within 6, 4 and 7 days after application, respectively. The safe period of consumption and the dissipation pattern of five different pesticides; Vitaban 48 EC (chlorpyrifos), Double 50 EC (mix formulation of imidacloprid and cypermethrin), Nitro 505 EC (mix formulation of chlorpyrifos and cypermethrin), Asataf 75 SP (acephate) and Reeva 2.5 EC (lambda-cyhalothrin) in eight different vegetables (cabbage, cucumber, bottle gourd, sweet gourd, sponce gourd, green chili, cauliflower and tomato) were studied. The pesticides were applied in the agricultural field of Nuritola, Comilla, Bangladesh, collected, brought to the laboratory and analysed for successive 10 days keeping them at ambient temperature. The residual amount of chlorpyrifos, in tomato, bottle gourd, sweet gourd and green chili, went below the MRL after 5 days and in cabbage, cauliflower, sponce gourd and cucumber, after 8 days of application. The average half life of chlorpyrifos in the vegetables was found to be 1.14 days. Pesticides of Nitro 505 EC; chlorpyrifos residues, in bottle gourd, tomato and sweet gourd, went below the MRL value after 3 days, in sponce gourd, green chili and cucumber,it was after 5 days and in cabbage and cauliflower, it was after 8 days of application whereas cypermethrin residues, in tomato, cauliflower, sweet gourd, sponce gourd, green chili and cucumber went below MRL value after 1 day, in case of cabbage and sponce gourd, it was after 3days of application. The average half-lives of chlorpyrifos and cyperethrin in Nitro 505 EC were found to be 0.92 and 0.58 days, respectively. Pesticides of Double 50 EC; imidacloprid residues went below the MRL value after 1day of application for tomato and green chili, after 3 days of application for cabbage, cauliflower, sweet gourd, bottle gourd and cucumber and after 5days of application for sponce gourdwhereas cypermethrin residues went below the MRL values after 1 day of application for tomato, cauliflower, green chili and after 3 day of application for cabbage, bottle gourd, sweet gourd and sponce gourd. The average half-lives were found to be 0.62 and 0.54 day for imidacloprid and cymermethrin, respectively in Double 50 EC. The initial concentration of lambda-cyhalothrin residue declined very sharply and went below the MRL value after 1 day of application. The residual amount of acephate went below the MRL value after 5 days of application for cabbage and cauliflower and after 3 days of application for the rest of the samples. The average half life of acephate was 1.1 days. Storage stability of the five pesticides in freezer (-20 0 C) were done by fortifying the control vegetable samples with the five pesticides and the samples were then stored in a freezer (-20 C) for about 30 days. The average recoveries of the pesticides were found in the range of 84% 93% which indicates that the pesticides were quiet persistent at freezing condition and not degraded during storage.