A total of four cereal crops (corn, rice, common millet and sorghum) were investigated for the presence of seventeen pesticide residues. The investigated pesticide compounds were p,p’-DDT, p,p’-DDE, Chlordane, Hexachlor benzene, β-Lindane, Lindane, α-Lindane, Aldrin, hexachlorepoxide, α-Endosulfan, β-Endosulfan, Endosulfan Sulfate, Methoxychlor, Heptachlor, Dimethoate, Chlorpyrifos and Profenofos.
Validation result
As presented in Table 1, the percentage recoveries of the pesticides standard were found to be acceptable ranging from 71.2% for β- endosulfan to 112.3% for lindane, which indicates that the reproducibility of the method was satisfactory. The limits of detection pesticides standard were ranged between 0.008-0.902 mgkg-1 and limits of quantification varied from 0.027 to 3.022 mgkg-1.
Table 1: Percentage recoveries and validation information of pesticides standards used for this study.
Pesticides standard
|
Percentage Recovery (%)
|
Limits of Detection (mgkg-1)
|
Limits of Quantification (mgkg-1)
|
|
|
|
|
p,p’-DDE
|
90.5
|
0.010
|
0.033
|
p,p’-DDT
|
85.7
|
0.016
|
0.054
|
Chlordane
|
101.6
|
0.108
|
0.362
|
endosulfan salfate
|
72.4
|
0.008
|
0.027
|
α-endosulfan
|
98.1
|
0.078
|
0.261
|
Hexachlor benzene
|
81.3
|
0.241
|
0.807
|
β-Lindane
|
73.9
|
0.512
|
2.705
|
Lindane
|
112.3
|
0.016
|
0.054
|
α-Lindane
|
82.3
|
0.193
|
0.647
|
Aldrin
|
89.4
|
0.020
|
0.067
|
Hexachlorepoxide
|
78.8
|
0.902
|
3.022
|
Methoxychlor
|
91.2
|
0.038
|
0.127
|
Heptachlor
|
81.4
|
0.193
|
0.647
|
Dimethoate
|
94.8
|
0.018
|
0.060
|
Chlorpyrifos
|
88.0
|
0.310
|
1.039
|
Profenofos
|
71.5
|
0.032
|
0.107
|
β- endosulfan
|
71.2
|
0.205
|
0.687
|
Calibration curvatures have been created for quantification. Linearity has been detected entirely alongside the region of concentration considered subject on the target pesticide substances. The calibration curvatures were gotten by inoculating eight diverse concentrations of the pesticide standards in a variety of 4-300ng/ml. The regression coefficient (r2) was > 0.997 for all the pesticides the under investigation. Calibration curves of the analyzed pesticides revealed acceptable linearity over designated concentration variety with regression correlation coefficients (r2) ranging from 0.997 for p,p'- DDE, to 0.999 for Endosulfan sulfate.
Analysis of pesticide residues
Four organo-chlorine pesticide residues namely, p,p’-DDT and its metabolite (p,p’-DDE), Endosulfan salfate, and Aldrin and one organophosphate pesticide residue (i.e. Dimethoate) were detected from food samples collected from the sample sites. p,p’-DDT and p,p’-DDE were the most frequently detected contaminants in all food items obtained from Gurafarda site as shown in Table 2. Pesticide residues varied from 0.011±0.003 to 0.018±0.005 mgkg-1 in corn, 0.035±0.013 to 0.076±0.025 mgkg-1 in rice, 0.037±0.005 to 0.068±0.042 mgkg-1 in sorghum and common millet were 0.039±0.030 to 0.087±0.006 mgkg-1. Highest concentration of Endosulfan sulfate (0.076 mgkg-1) was detected in rice, followed by Dimethoate (0.068 mgkg-1) and p,p’-DDE (0.087 mgkg-1) in sorghum and common millet, respectively.
Table 2: Concentration (mgkg-1) of pesticide residues in assessed food items from Gurafarda site.
Pesticide residues
|
Food items
|
Corn
|
Rice
|
Sorghum
|
Common millet
|
p,p’-DDT
|
0.018±0.005
|
0.046±0.020
|
0.048±0.007
|
0.062±0.027
|
p,p’-DDE
|
0.011±0.003
|
0.035±0.013
|
0.054±0.009
|
0.087±0.006
|
Endosulfan salfate
|
ND
|
0.076±0.025
|
0.047±0.013
|
0.039±0.030
|
Aldrin
|
ND
|
0.06±0.033
|
0.037±0.005
|
0.042±0.008
|
Dimethoate
|
ND
|
0.065±0.023
|
0.068±0.042
|
0.080±0.018
|
Table 3 illustrated that, the crop samples analyzed in North-Bench site, Dimethoate was less frequently detected in corn. Highest concentration of p,p’-DDT (0.133 mgkg-1) was detected in common millet, which indicates the recent use of the pesticide DDT in the study area.
Pesticide residues varied from 0.045 to 0.066 mgkg-1 in corn, 0.040 to 0.077mgkg-1 in rice, 0.031-0.082 mgkg-1 in sorghum and 0.018-0.133 mgkg-1 was detected in common millet. Highest concentration of p,p’-DDT (0.133 mgkg-1) was detected in common millet, followed by Aldrin (0.082mgkg-1) and Dimethoate (0.077mgkg-1) in Sorghum and common millet, respectively.
Table 3: Concentration (mgkg-1) of pesticide residues in assessed food items from North-Bench site
Pesticide residues
|
Food items
|
Corn
|
Rice
|
Sorghum
|
Common millet
|
p,p’-DDT
|
0.064±0.023
|
0.059±0.26
|
0.031±0.011
|
0.133±0.069
|
p,p’-DDE
|
0.066±0.039
|
0.058±0.027
|
0.044±0
|
0.057±0.007
|
Endosulfan salfate
|
0.045±0.003
|
0.061±0.034
|
0.049±0.018
|
0.018±0.002
|
Aldrin
|
0.065±0.028
|
0.040±0.02
|
0.082±0.007
|
0.027±0.002
|
Dimethoate
|
ND
|
0.077±0.028
|
0.04±0.013
|
0.039±0.006
|
As illustrated in Table 4, Dimethoate was detected in about 50% samples of the food items obtained from South- Bench site. It was only detected in rice (0.060 mgkg-1) and sorghum (0.051 mgkg-1). The average residues concentration were varied from 0.056 to 0.059 mgkg-1in corn, 0.035 to 0.057 mgkg-1 in rice, 0.051 to 0.130 mgkg-1 in sorghum and 0.038 to 0.074 mgkg-1 in common millet. Highest concentration of Aldrin residue (0.130 mgkg-1) was detected in sorghum.
Table 4: Concentration (mg/kg-1) of pesticide residues in assessed food items from South- Bench site
Pesticide residues
|
Food items
|
Corn
|
Rice
|
Sorghum
|
Common millet
|
p,p’-DDT
|
0.056±0.042
|
0.035±0.013
|
0.075±0.022
|
0.038±0.016
|
p,p’-DDE
|
0.059±0.023
|
0.057±0.023
|
0.078±0.018
|
0.074±0.022
|
Endosulfan salfate
|
0.081±0.004
|
0.065±0.023
|
0.059±0.036
|
0.044±0.020
|
Aldrin
|
0.074±0.025
|
0.069±0.027
|
0.130±0.146
|
0.045±0.017
|
Dimethoate
|
ND
|
0.060±0.030
|
0.051±0.021
|
ND
|
Comparison of pesticide residue with the maximum residue limit (MRL)
Table 5, 6 and 7 are summarizes the comparisons of average mean concentration of detected residues with MRLs established by the European Union (EU) and the Co-dex Alimentarius regulations. As indicated in the Table 5, the comparisons of residue concentration in food samples obtained from Gurafarda site, aldrin detected in rice, sorghum and common millet were a residue of above the MRLs set by Codex Alimentarius regulations [37] and European Union (EU) [41], while the Dimethoate residue detected in rice, sorghum and common millet were contained a residue of above the MRLs set by European Union (EU). In addition, p,p’-DDT in common millet and Endosulfan sulfate in rice exceeded corresponding MRLs set by European Union.
Table 5: Comparisons of average mean concentration of pesticide residues with European Union and Codex Alimentareous standards from Gurafarda site.
Pesticide residues
|
Food items
|
Corn
|
MRLs
|
Rice
|
MRLs
|
Sorghum
|
MRLs
|
Common millet
|
MRLs
|
CA
|
EU
|
CA
|
EU
|
CA
|
EU
|
CA
|
EU
|
p,p’-DDT
|
0.018
|
0.1
|
0.05
|
0.046
|
0.1
|
0.05
|
0.048
|
0.1
|
0.05
|
0.062
|
0.1
|
0.05
|
p,p’-DDE
|
0.011
|
0.1
|
0.05
|
0.035
|
0.1
|
0.05
|
0.054
|
0.1
|
0.05
|
0.087
|
0.1
|
0.05
|
Endosulfan sulfate
|
ND
|
NA
|
0.05
|
0.076
|
NA
|
0.05
|
0.047
|
NA
|
0.05
|
0.039
|
NA
|
0.05
|
Aldrin
|
ND
|
0.02
|
0.01
|
0.06
|
0.02
|
0.01
|
0.037
|
0.02
|
0.01
|
0.042
|
0.02
|
0.01
|
Dimethoate
|
ND
|
NA
|
0.01
|
0.065
|
NA
|
0.01
|
0.068
|
NA
|
0.01
|
0.080
|
NA
|
0.01
|
MRLs = maximum residue limits; NA = not available; ND = not detected; CA= Codex Alimentarius; EU= European Union
The average concentration of p,p’-DDT and p,p’-DDE residues detected in all food samples obtained from North-Bench site were above the MRLs established by European Union and p,p’-DDT and Endosulfan sulfate residue detected in common millet and rice were also above the MRLs established Codex Alimentarius standards and European Union, respectively as shown in Table. The average concentration of Aldrin residue detected in all food samples obtained from this site was above the MRLs established by Codex Alimentarius standards and European Union. The only organophosphate (Dimethoate) detected in three food samples (i.e. rice, sorghum and common millet) obtained from North-Bench site was also above the MRLs established by European Union.
Table 6: Comparisons of average mean concentration of pesticide residues with European Union and Codex Alimentareous standards from North-Bench site.
Pesticide residues
|
Food items
|
Corn
|
MRLs
|
Rice
|
MRLs
|
Sorghum
|
MRLs
|
Commonmillet
|
MRLs
|
CA
|
EU
|
CA
|
EU
|
CA
|
EU
|
CA
|
EU
|
p,p’-DDT
|
0.064
|
0.1
|
0.05
|
0.059
|
0.1
|
0.05
|
0.031
|
0.1
|
0.05
|
0.133
|
0.1
|
0.05
|
p,p’-DDE
|
0.066
|
0.1
|
0.05
|
0.058
|
0.1
|
0.05
|
0.044
|
0.1
|
0.05
|
0.057
|
0.1
|
0.05
|
Endosulfan sulfate
|
0.045
|
NA
|
0.05
|
0.061
|
NA
|
0.05
|
0.049
|
NA
|
0.05
|
0.018
|
NA
|
0.05
|
Aldrin
|
0.065
|
0.02
|
0.01
|
0.040
|
0.02
|
0.01
|
0.082
|
0.02
|
0.01
|
0.027
|
0.02
|
0.01
|
Dimethoate
|
ND
|
NA
|
0.01
|
0.077
|
NA
|
0.01
|
0.04
|
NA
|
0.01
|
0.039
|
NA
|
0.01
|
MRLs = maximum residue limits; NA = not available; ND = not detected; CA= Codex Alimentarius; EU= European Union
The average concentration of p,p’-DDT and p,p’-DDE residues detected in all food samples obtained from South- Bench site were above the MRLs established by European Union as indicated in Table 7. Moreover, Endosulfan salfate residue was detected in three food items namely; corn, rice and sorghum. It was above the MRLs established by European Union. The average concentration of Aldrin residue detected in all food samples obtained from this site was above the MRLs established by Codex Alimentarius standards and European Union. Dimethoate residue detected in 50% if the food sample was above the MRLs established by European Union.
Table 7: Comparisons of average mean concentration of pesticide residues with European Union and Codex Alimentareous standards from South- Bench site.
Pesticide residues
|
Food items
|
Corn
|
MRLs
|
Rice
|
MRLs
|
Sorghum
|
MRLs
|
Commonmillet
|
MRLs
|
CA
|
EU
|
CA
|
EU
|
CA
|
EU
|
CA
|
EU
|
|
|
|
|
|
|
|
|
|
|
|
|
|
p,p’-DDT
|
0.056
|
0.1
|
0.05
|
0.035
|
0.1
|
0.05
|
0.075
|
0.1
|
0.05
|
0.038
|
0.1
|
0.05
|
p,p’-DDE
|
0.059
|
0.1
|
0.05
|
0.057
|
0.1
|
0.05
|
0.078
|
0.1
|
0.05
|
0.074
|
0.1
|
0.05
|
Endosulfan sulfate
|
0.081
|
NA
|
0.05
|
0.065
|
NA
|
0.05
|
0.059
|
NA
|
0.05
|
0.044
|
NA
|
0.05
|
Aldrin
|
0.074
|
0.02
|
0.01
|
0.069
|
0.02
|
0.01
|
0.130
|
0.02
|
0.01
|
0.045
|
0.02
|
0.01
|
Dimethoate
|
ND
|
NA
|
0.01
|
0.060
|
NA
|
0.01
|
0.051
|
NA
|
0.01
|
ND
|
NA
|
0.01
|
MRLs = maximum residue limits; NA = not available; ND = not detected; CA= Codex Alimentarius; EU= European Union.