Chemical contaminants in rice, spice and vegetable samples

Abstract

The amount of food produced is very important as the human population increases. Over the last 40 years, food production has been increased 20-50 % where pesticides were played an important role. Proper use of pesticides can protect storage food and vegetable from damage without causing any obvious toxic effects, and final residues of pesticides in edible parts are under recommended maximum residue levels (MRLs). In developing countries, including Bangladesh, the cultivation of crops is mainly carried out by small farmers. To get more products, they use pesticides in overdose than needed in many cases. These are creating serious health problems in Bangladesh. As a part of PhD work, some survey about the present pesticides used in field and storage level have done. A total of 94 pesticides, with 299 trade names, of different groups and formulations, have been registered for use in agriculture. From the observation of the most recent government figures available, the total pesticides imported in Bangladesh are increases gradually. However, our field survey revealed that a large number of unregistered pesticides are being used for storage food and vegetable samples in the country. Therefore, the present research project has been undertaken to determine the residual pesticides/natural toxins in stored food and vegetable samples. In all the analyses certified standard reference samples (91-99 % purity) were used. Rice is cultivated in three seasons in Bangladesh. As Bangladesh is a hot and humid country moisture content is increased even the crops dried properly. For this climate of Bangladesh, aflatoxins (natural mycotoxins that are produced by certain molds) can be grown in rice. The aim of the study was to assess the level of aflatoxins (if any) in some rice samples. Rice samples were collected from three districts of Bangladesh (Dhaka, Noakhali and Kurigram). The samples were extracted with aqueous methanol and the extract was purified by immunoaffinity column. The analytes were identified and quantified by reverse-phase high performance liquid chromatography where KOBRA Cell was attached after column for post-column bromo derivatisation (PCD) which gave fluorescence. Calibration curves were linear with coefficient of determinant r2 ≥ 0.9998, 09997, 0.9956 and 0.9969 for B1, B2, G1 and G2, respectively. The limit of detection (LOD) and quantification (LOQ) were 0.009 and 0.025 μg kg-1 for B1, 0.006 and 0.018 μg kg-1 for B2, 0.039 and 0.116 μg kg-1 for G1 and 0.025 and 0.075 μg kg-1 for G2, respectively. The total aflatoxins (B1, B2, G1 and G2) in the rice samples were found to be in the range of trace to 3.54 µg kgµg kgµg kgµg kg -1. Aflatoxin B1, B2, G1 and G2 were present in 70, 60, 40 and 10 % of rice samples, respectively. The results revealed that 18 out of 20 samples contained detectable amount of aflatoxins. Aflatoxin B1 (in the range of 0.04 to 0.70 µg kgµg kgµg kgµg kgµg kg-1), B2 (in the range of trace to 0.20 µg kgµg kg µg kgµg kg-1), G1 (in the range of 0.22 to 1.82 µg kgµg kgµg kgµg kgµg kg-1) and G2 (in the range of 0.12 to 1.56 µg µg kg -1) were quantified in 17, 16, 6 and 4 samples, respectively. Recoveries (n = 4) were carried out at two different spiking concentrations (1.39 and 2.77 μg kg-1 for B1, 0.49 and 0.98 μg kg-1 for B2, 1.56 and 3.12 μg kg-1 for G1 and 0.51 and 1.01 μg kg-1 for G2) and were ranged from 56.71 ± 1.60 to 70.37 ± 5.59 % for B1, 57.71 ± 0.58 to 75.36 ± 6.77 % for B2, 65.53 ± 0.73 to 72.85 ± 5.93 % for G1 and 65.83 ± 2.92 to 99.20 ± 3.16 % for G2, respectively. Commercial grade turmeric powder samples were analyzed for the presence of carbofuran residues by high performance liquid chromatography (HPLC) coupled with photodiode array (PDA) detector. A total 46 turmeric powder samples (37 were packet and 9 were loose samples) were extracted with ethyl acetate by following QuEChERS (quick, easy, cheap, effective, rugged and safe) method. The extract was cleaned up using an open column packed with mixture of florisil, alumina and charcoal (5:5:1 ratio). Calibration curves were linear with coefficient of determinant r2 ≥ 0.9996, 09973 and 0.9958. The limit of detection (LOD) and quantification (LOQ) were 0.01 and 0.03 mg kg-1 carbofuran, respectively. No residue was found when the sample was heated in a water bath for 30 min. The amount of carbofuran residues were found to be in the range of 2.5 ± 0.07 to 23.1 ± 0.30 and 2.06 ± 0.14 to 7.8 ± 0.32 mg kg--1 in the packet and loose samples, respectively. Recoveries (n = 7) were carried out at three different spiking concentrations (0.4, 0.8, 1.0 and 20 mg kg-1) and were ranged from 92.52 ± 0.01 92.52 ± 0.01 to 103.14 ± 2.41 103.14 ± 2.41 %. For the study of post-harvest intervals of diazinon and carbosulfan in cauliflower, bean, eggplant and tomato samples, the samples were collected from BARI (Bangladesh Agricultural Research Institute) experimental field. Three replicate treated samples of cauliflower, bean, eggplant and tomato and one control sample were collected from BARI at 0 (2 hours after spraying), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 and 15 days after application of diazinon(2 mL L-1) and carbosulfan (1.5 mL L-1). Quantification of residue of diazinon was done on a gas chromatograph (GC) with an electron capture detector (ECD). Nitrogen was used as carrier and make up gas. Separations were performed on Non-polar (HP-5 MS) capillary column of 30 m long x 250 μm i.d. x 0.25 μm film thicknesses from Agilent, USA. A QuEChERS method was used for extraction using ethyl acetate as an extraction solvent, and clean up was carried out using primary secondary amine. The linearity was excellent (r2 ˃ 0.9976, 0.9967, 0.9922 and 0.9905) in calibrations. The recoveries at three spiking levels were 99 to 105 % for tomato, 97 to 104 % for cauliflower, 89 to 108 % for bean and 93 to 104 % for eggplant with relative standard deviations in the range of 1.68 to10.64 %. The limit of quantification (LOQ) of this method was found to be 0.003 mg kg−1 whereas limit of detection (LOD) being 0.001 mg kg−1. The results revealed that the dissipation pattern of diazinon was followed first-order kinetic. The residues of diazinon in tomato, bean, cauliflower and eggplant were found to be in the range of 0.02 ± 0.01 to 1.66 ± 0.24, 0.005 ± 0.001 to 0.152 ± 0.007, 0.03 ± 0.01 to 4.02 ± 0.37, and 0.02 ± 0.01 to 1.29 ± 0.09 mg kg-1, respectively. The maximum residue limit (MRL) of diazinon on cauliflower, tomato, eggplant and bean has been fixed by CODEX is 0.5 mg kg-1. The diazinon residues declined to a level below the maximum residue limits within 3, 3 and 10 days for eggplant, tomato and cauliflower, respectively. The residue of diazinon was below the maximum residue limit even at 0 day (two hours after spraying) for bean. The estimated dissipation half-life (t1/2) of diazinon was found to be 2.63, 2.23, 1.12 and 0.90 days in cauliflower, tomato, bean and eggplant, respectively. The analysis of residue of carbofuran in tomato was done by using gas chromatography (GC) equipped with a flame ionization detector (FID). Nitrogen was used as carrier and makeup gas. Hydrogen and air were used for flame. Separations were performed on HP-5 (30 m long & 0.25 inner diameter) capillary WCOT quartz column. The tomato samples were extracted and cleaned up by QuEChERS method. The limit of detection (LOD) and limit of quantification (LOQ) were 0.1 and 0.3 mg kg-1, respectively. Calibration curves were linear over the calibration ranges with coefficient of determinants 0.9978 and 0.9967 for carbosulfan. The half-life (t1/2) of carbosulfan was found to be 5.25 days in tomato. According to Europion Union, the MRL value of carbosulfan in tomato is 0.05 mg kg-1. The residue of carbosulfan in tomato was found to be above the MRL value (0.05 mg kg-1 ) up to 14 days (9.43 ± 0.16 to 1.19 ± 0.06 mg kg-1). Forty five vegetable samples namely bean, eggplant, cauliflower and tomato were purchased from different markets of Dhaka city and Noakhali and Kurigram districts. Cypermethrin, chlorpyrifos, diazinon, fenvalerate and quinalphos were detected in some of them. Quantification of residues was done on a gas chromatograph (GC) with an electron capture detector (ECD). Calibration curves were linear with coefficient of determinant r2 ≥ 0.9912, 09962, 0.9929, 0.9947 and 0.9907 for chlorpyrifos, cypermethrin, diazinon, fenvalerate and quinalphos, respectively. The LOD was found to be determined 0.50 μg L-1 for chlorpyrifos, 2.50 μg L-1 for diazinon and quinalphos and 5.0 μg L-1 for cypermethrin and fenvalerate, respectively. LOQ was found to be determined 1.65 μg L-1 for chlorpyrifos, 8.25 μg L-1 for diazinon and quinalphos and 16.5 μg L-1 for cypermethrin and fenvalerate, respectively. Out of 10 bean samples, the residue of chlorpyriphos was detected in 3 samples (0.01 ± 0.01 mg kg-1; MRL 0.01 mg kg-1), cypermethrin was detected in 5 samples in the range of 0.05 ± 0.01 to 0.74 ± 0.09 mg kg-1 (MRL 0.05 mg kg-1) and fenvalerate was detected in 3 samples in the range of 0.39 ± 0.05 to 0.55 ± 0.04 mg kg-1 (MRL 1.0 mg kg-1). Among the 12 eggplant samples, the residue of chlorpyriphos was detected in 4 samples 0.02 ± 0.01 and 0.05 ± 0.01 mg kg-1 (MRL 0.5 mg kg-1) and cypermethrin was detected in 2 samples in the range of 0.04 ± 0.01 to 0.13 ± 0.01 mg kg-1 (MRL 0.2 mg kg-1). Out of 11 cauliflower samples, the residue of chlorpyriphos was detected in 10 samples in the range of 0.01 ± 0.01 to 0.79 ± 0.02 mg kg-1 (MRL 0.05 mg kg-1), cypermethrin was detected in 3 samples in the range of 0.09 ± 0.01 to 0.74 ± 0.16 mg kg-1 (MRL 1.0 mg kg-1) and quinalphos was detected in 4 samples in the range of 0.07 ± 0.01 to 0.49 ± 0.08 mg kg-1 (MRL 0.2 mg kg-1). Among the 12 tomato samples, the residue of chlorpyriphos was detected in 9 samples in the range of 0.01 ± 0.01 to 0.33 ± 0.02 mg kg-1 (MRL 0.2 mg kg-1) and cypermethrin was detected in 3 samples in the range of 0.05 ± 0.01 to ± 0.01 to ± 0.01 to 0.32 ± 0.04 mg kg-1 ( MRL 0.5 mg kg-1). The average recovery of chlorpyrifos in tomato (n = 5) was 98.48 ± 2.73% and in eggplant (n = 6) was 99.57 ± 6.98 % at spiking level of 0.05 mg kg-1. In bean (n = 3), the average recovery of chlorpyrifos was 88.51 ± 2.64 % at spiking level of 0.15 mg kg-1. The average recovery of cypermethrin in tomato (n = 5) was 79.65 ± 5.56 %, in eggplant (n = 6) was 86.29 ± 7.33 % and in bean (n = 3) was 97.43 ± 8.52 % at spiking level of 0.10 mg kg-1. The average recovery of diazinon in tomato (n = 5) was 109.92 ± 2.33 % and in eggplant (n = 6) was 101.41 ± 4.72 % at spiking level of 0.10 mg kg-1. In bean (n = 3), the average recovery of chlorpyrifos was 106.78 ± 3.55 % at spiking level of 0.15 mg kg-1. For fenvelarate, the average recovery in tomato (n = 5) was 90.88 ± 2.15 % and in eggplant (n = 6) was 84.10 ± 8.91 % at spiking level of 0.10 mg kg-1. In bean (n = 3), the average recovery of fenvelarate was 90.04 ± 9.29 % at spiking level of 0.15 mg kg-1. For quinalphos the average recovery in tomato (n = 5), eggplant (n = 6) and bean (n = 3) were 78.28 ± 4.85 , 85.15 ± 7.72 and 85.28 ± 2.32 % at the spiking level of 0.10,0.15 and 0.20 mg kg-1, respectively.