# Residual Level of Chlorpyrifos in Lettuces Grown on Chlorpyrifos-Treated Soils
## 3 Results and Discussion
The residue was proportional to the amount of chemical applied. The average residue in the plot treated with an application of 10.0 mg/kg was the highest at 1.47 mg/kg, followed by 1.11 mg/kg in the plot treated with 20.0 mg/kg, and 0.12 mg/kg in the plot treated with 2.0 mg/kg. \begin{table}
\begin{tabular}{c c c c c} \hline
**Pesticide** & **Fortification Level (mg/kg)** & **Recovery \(\pm\) CV * (\%)** & **MLOQ ** (mg/kg)** \\ \hline \multirow{4}{*}{Chlorpyrifos} & 0.2 & \multirow{2}{*}{Field 1 Soil} & 109.1 \(\pm\) 3.6 & \multirow{4}{*}{0.02} \\  & 1.0 & & 102.7 \(\pm\) 0.4 & \\ \cline{1-1} \cline{2-5}  & 0.2 & \multirow{2}{*}{Field 2 Soil} & 106.3 \(\pm\) 3.0 & \\ \cline{1-1}  & 1.0 & & 102.3 \(\pm\) 1.5 & \\ \cline{1-1} \cline{2-5}  & 0.2 & \multirow{2}{*}{Lettuce} & 90.2 \(\pm\) 2.1 & \multirow{2}{*}{0.02} \\  & 1.0 & & 92.3 \(\pm\) 4.6 & \\ \hline \multicolumn{4}{l}{* Coefficient of variation: (Standard deviation/average) \(\times\) 100. ** Method limit of quantitation: (mg/kg) = (LOQ \(\times\) final solution volume)/(injection volume \(\times\) sample weight).} \\ \end{tabular}
\end{table} 
Table 2: Recovery of chlorpyrifos from the tested soil and lettuce. Figure 1: Dissipation of chlorpyrifos in the treated soils. (**A**) Soil samples from field 1; (**B**) Soil samples from field 2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample (Field 1)**} & \multicolumn{2}{c}{**1.0 mg/kg Treatment**} & \multicolumn{2}{c}{**2.0 mg/kg Treatment**} \\ \cline{2-5}  & **Resolute (mg/kg)** & **CBR * (\%)** & **Resolute (mg/kg)** & **CBR (\%)** \\ \hline
22 DAT **\({}^{*}\)** & 0.04 \(\pm\) 0.01 & 4.50 \(\pm\) 0.50 & 0.02 \(\pm\) 0.01 & 0.66 \(\pm\) 0.28 \\
25 DAT & 0.04 \(\pm\) 0.01 & 4.33 \(\pm\) 0.37 & 0.06 \(\pm\) 0.01 & 2.64 \(\pm\) 0.12 \\
28 DAT & 0.05 \(\pm\) 0.01 & 5.98 \(\pm\) 0.58 & 0.12 \(\pm\) 0.01 & 5.21 \(\pm\) 0.25 \\
32 DAT & 0.02 \(\pm\) 0.00 & 2.44 \(\pm\) 0.37 & 0.05 \(\pm\) 0.01 & 2.24 \(\pm\) 0.21 \\
36 DAT & N.D. & - & N.D. & - \\ \hline \multirow{2}{*}{**Sample (Field 2)**} & \multicolumn{2}{c}{**10.0 mg/kg Treatment**} & \multicolumn{2}{c}{**20.0 mg/kg Treatment**} \\ \cline{2-5}  & **Resolute (mg/kg)** & **CBR (\%)** & **Resolute (mg/kg)** & **CBR (\%)** \\ \hline
35 DAT & 1.47 \(\pm\) 0.20 & 13.26 \(\pm\) 1.83 & 1.03 \(\pm\) 0.10 & 4.56 \(\pm\) 0.43 \\
37 DAT & 1.07 \(\pm\) 0.15 & 9.65 \(\pm\) 1.33 & 1.11 \(\pm\) 0.08 & 4.92 \(\pm\) 0.37 \\
39 DAT & 1.10 \(\pm\) 0.16 & 9.89 \(\pm\) 1.46 & 0.86 \(\pm\) 0.06 & 3.81 \(\pm\) 0.28 \\
41 DAT & 0.92 \(\pm\) 0.20 & 8.26 \(\pm\) 1.82 & 0.61 \(\pm\) 0.15 & 2.71 \(\pm\) 0.66 \\
43 DAT & 0.76 \(\pm\) 0.03 & 6.84 \(\pm\) 0.29 & 0.66 \(\pm\) 0.07 & 2.92 \(\pm\) 0.31 \\ \hline \hline \end{tabular} \({}^{*}\)CBR: crop bioconcentration ratio. **\({}^{*}\)**DAT: Days after treatment.  
\end{table} 
Table 3: Residue levels of chlorpyrifos in lettuce grown in treated soil. Crop bioconcentration ratio of chlorpyrrifos. The CBR was obtained after calculation by comparing the concentration in the crop to the initial concentration in the soil. The initial concentrations of chlorpyrrifos in soil were 0.86, 2.31, 11.10, and 22.59 mg/kg. The calculated CBRs are shown in Table 3. The highest average residue was 1.47 mg/kg at 35 DAT in field 2. This meant that 13.26% of the chlorpyrrifos concentration compared to the initial soil concentration was observed in the lettuce. Although the MRL of chlorpyrrifos for lettuce is not set, in order for concentrations in lettuce to remain under the non-detection criteria of 0.01 mg/kg required by the Positive List System, it could be suggested that the MRL be 0.75 mg/kg using the highest CBR (0.13) in soils used for the cultivation of lettuce. The residual pesticides in soil could be absorbed by lettuce depending on the physicochemical properties of the target pesticide, especially its water solubility. Lettuce took 2.2% and 2.4% of boscalid residue, when it was grown in the soil spiked with boscalid. The uptake rates of chlorfenapyr by cabbage were 1.3% to 1.5% of the soil concentration of chlorfenapyr.