Distribution of chlorpyrifos residue in maize (Zea mays)

Chlorpyrifos is an organophosphate insecticide. It has low aqueous solubility, is volatile and non-mobile, moderately persistent in soil, highly toxic to mammals, and is an acetylcholinesterase inhibitor. The main use of chlorpyrifos is to control various types of agricultural pests. This study aims to determine the absorption of chlorpyrifos residues in maize plants. The study was conducted in July-December 2019. Experimental research was conducted at Jakenan experimental field on land contaminated with chlorpyrifos residue. The maize used was a hybrid maize variety NK 6172 Perkasa. Pesticide residue analysis was carried out at the Laboratory of the Agricultural Environmental Research Institute (IAERI). The results showed that the highest chlorpyrifos residue was in the stalks and leaf with a value of 0.0318-0.5682 mg kg−1 but still below the maximum residue limit (MRL) of 10 mg kg−1 recommended by The National Standardization Agency of Indonesia. The concentration of chlorpyriphos residue in maize grain is 0.0014-0.2203 mg kg−1 (MRL=0.05 mg kg−1). Chlorpyriphos residue in the soil is 0.0148-0.0786 mg kg−1 (MRL=3.2 mg kg−1), and the lowest was root (<0.0014 mg kg−1). Information on residue distribution on maize and soils can be helpful as an early warning about the use of insecticides and food safety measures.


Introduction
Pesticides have been used globally to control pests and diseases in cultivated plants [1][2][3][4].More broadly, pesticides are also used in the health sector to eradicate disease vectors and other pests [5][6].The increasing usage of pesticides has led to their transformation into an environmentally hazardous contaminants.Some pesticides are persistent in the environment, and chlorpyrifos is one of the compounds that are quite persistent in soil, bioaccumulates, and can potentially be toxic to non-target organisms [7][8].
Soil contaminated with heavy metals or pesticides will cause the plants that grow on the soil to become contaminated.Plants can absorb and transfer pesticide residual chemicals from the soil, which can contaminate food crops [1,[9][10][11][12].Samples of maize grown on farms in Ejura, Ghana, contained between 0.001 and 0.103 mg kg -1 of organochlorine pesticides, between 0.002 and 0.019 mg kg -1 ) of organophosphorus pesticides, and between 0.002 and 0.028 mg kg -1 of pyrethroid pesticides [2].Additionally, 1.45 mg kg -1 to 3.3 mg kg -1 of chlorpyrifos residue was discovered in Pakistani rice [13].
Different soil pesticide concentrations, pesticide physicochemical qualities, plant species, soil type, and plant-supporting soil biology and chemistry all play a role in determining pesticide accumulation in 1230 (2023) 012075 IOP Publishing doi:10.1088/1755-1315/1230/1/012075 2 plants [14].People who eat foods tainted with pesticide residues run the risk of experiencing long-term health problems [2].The purpose of this research is to determine the absorption of chlorpyrifos residues in maize plants.

Material and method
The research was conducted from July to December 2019 at the Jakenan experimental field, Pati Regency, located at coordinates 6°46'33" SL and 111°11'48" E, with an altitude of ± 11 meters above sea level.The study was conducted using a lysimeter on contaminated soil in 9 blocks.Analysis of pesticide residues on soil and plants was carried out at the Integrated Laboratory, Indonesian Agricultural Research Institute, Pati.The maize seed used was the NK 6172 Perkasa variety.Urea, SP36, and KCl fertilization are carried out based on recommendations from the soil analysis results using the dry soil test kit (PUTK).The variables observed included the content of chlorpyrifos in soil and plants (roots, stalks and leaves, and maize grain).Soil and plant samples were taken at harvest time.

Pesticide residue analysis
Analysis of chlorpyrifos in soil and plants using the QuEChERS technique [15][16].The analytical process is weighing the sample (up to 10 grams of soil/plant material), placing it in a 50 ml Teflon or glass bottle, adding 10 ml of acetone p.a., and shaking the solution for a minute until it is homogenous.After that, you can either add 4 grams of anhydrous magnesium sulfate (MgSO 4) powder or 1 gram of anhydrous sodium sulfate and 1 gram of sodium chloride (NaCl).After that, the solution was centrifuged for 2 minutes at 3000 rpm.Then, we collect the extractant in a 10 ml test tube after filtering it through filter paper impregnated with anhydrous NaSO4 powder.To prepare the extractant for injection into the GC instrument, rinse the filter paper with acetone p.a. until the volume reaches 5 ml.The peak chromatogram of the chlorpyrifos pesticide component can be read and compared to the peak chromatogram of a reference solution.
The bioaccumulation factor (BAF) is the ratio of the concentration of a pollutant in the grain to its concentration in the corresponding soil (Equation 1).BAF was calculated for each maize seed sample to measure the effect of maize seed bioaccumulation on the uptake of chlorpyrifos from soil [17][18].
Cg represents the concentration of chlorpyrifos in maize grain, and Cs represents the concentration of chlorpyrifos in the soil.Soil-root translocation factors (TFs-r) or mobilization ratios are calculated to determine the relative translocation of pesticide residues from the soil to the plant roots (Equation 2) [18].The root-stalks and leaf translocation factors (TFr-cl) were calculated to determine the relative translocation of chlorpyrifos from the roots to the stalks and leaves of the maize plant (Equation 3).Similarly, the stalks and leaf-grain translocation factor (TFcl-g) were evaluated as the ratio of the pollutant concentration in maize grain to the corresponding concentrations in maize stalks and leaves (Equation 4).
Cr represents the concentration of chlorpyrifos in roots; Cs is the concentration of chlorpyrifos detected in the soil; Ccl is the concentration of chlorpyrifos detected in maize stalks and leaves; and Cg represents the concentration of chlorpyrifos in maize grain.

Soil physical and chemical properties
The experiment's soil's physicochemical characteristics are listed in Table 1.Pesticide contamination ranged from 0.0148 mg kg -1 to 0.0786 mg kg -1 in the soil used in this investigation.Soil Chlorpyrifos levels continue to remain well below Alberta Environment's Maximum Residue Level (MRL) of 3.2 mg kg -1 [19].A considerable influence in the fate of xenobiotic chemicals, including pesticides, is played by increasing the c-organic content of the soil by adding organic matter through organic amendments [20].Soil organic matter (SOM) and dissolved organic matter (DOM) from organic amendments might alter the physicochemical behavior of pesticides (such as adsorption-desorption, persistence, bioavailability, degradation, and mobility) [21][22].Due to the low C-organic concentration, pesticide residues in the soil are less efficiently adsorbed, allowing plants to more readily take them up.A lesser percentage of pesticides are immobilized in soils with a low C-organic concentration [22].To lower a pesticide's half-life [21], organic matter in the soil acts as an efficient adsorbent [23].[26].
Although chlorpyrifos adsorption to the soil was measured, the CEC value of the soil utilized in the experiment was low, suggesting that soil adsorption of pollutants was also low.Soil organic matter amendments can boost CEC levels.By lowering pesticide concentrations in the soil, organic matter application can help cut down on their non-biological impact [27][28].The kind and amount of clay and the type of soil minerals also play an essential role in determining the behavior of pesticides in the soil and impacting the uptake of pesticides by plants [27], in addition to organic matter content, soil pH, and soil temperature.
A clay loam soil type can be identified by its texture.Metal ion concentrations and pesticide concentrations in the soil are both directly related to the soil's texture.Soil types with the highest pesticide availability were loams and sand, while fine-textured loams had the lowest [27,29].The internal reactive surface area of clay soils is significantly higher than that of other soils, making them ideal for pesticide adsorption [18].(30).

Distribution of Chlorpyrifos in roots, stalks-leaves, and grain
The amount of chlorpyrifos in roots, stalks-leaves, and grains was calculated based on the concentrations detected.The concentrations of chlorpyrifos in three parts are presented in Table 2.The chlorpyrifos pesticide residues studied were contained in plant parts, including roots, stalks and leaves, and grain.One sample of maize grain was found to exceed the MRL (> 0.05 mg kg -1 ) recommended by The National Standardization Agency of Indonesia.In the stalks and leave, the chlorpyrifos content was still below the MRL (<10 mg kg -1 ) [30].In the roots, chlorpyrifos concentration was found to be the lowest among other parts of the maize.The highest accumulation of chlorpyrifos was found in the stalksleaf part.The same phenomenon was also found in several previous studies where most of the pesticide residues were absorbed by maize plants and accumulated in the stalks and leaves [31][32][33][34].One of the reasons for the high absorption of pesticide residues in the leaf segments of maize plants is the high polarity of the leaf cuticle [31].

Bioaccumulation Factor (BAF) and Translocation Factor (TF)
The bioaccumulation factor (BAF) of chlorpyrifos from soil to maize grain ranged from 0.018 to 3.913.BAF allows quantification of the capacity to accumulate chlorpyrifos in the upper parts of plants (stalks, leaves, and grains).Table 3 shows chlorpyrifos' translocation rate (TF) from soil to roots, from roots to stalks-leaves, and from stalks-leaves to grains.The TF of chlorpyrifos ranged from 0.018 to 0.095, from 22.714 to 405.857, and from 0.002 to 0.044 sera, respectively.TF from roots to stalks-leaves has a value above 1.Chlorpyrifos is more transferred from roots to stalks-leaves, and less is accumulated in the roots.On the other hand, the TF value from stalks-leaf to grain has a value of less than 1, which means that more chlorpyrifos accumulates in the stalks-leaf than is passed on to the grain.This indicates that in maize plants, chlorpyrifos is strongly absorbed by roots and accumulates mainly in stalks and leaves.Similar results were also found for imidacloprid pesticide residues which were absorbed by the roots and accumulated in the leaves [33].Maize stalks act as high-efficiency chromatographic columns that can accumulate chemicals in the leaves [33].

Conclusion
Chlorpyrifos concentrations in the studied soils were under the MRL (< 3.2 mg kg -1 ) recommended by Alberta Environment for soil remediation.The low content of CEC and C-organic increases the potential for absorption of chlorpyrifos by plants.The concentration of chlorpyrifos in maize grain that exceeds the MRL requires caution regarding its effect on consumer health.Chlorpyrifos accumulates more in stalks and leave.It should also be aware of the risks of using plant parts for compost or animal feed.

Table 2 .
The concentration of chlorpyrifos in parts of the maize plant variety NK 6172 Perkasa.

Table 3 .
Bioaccumulation factor and translocation factor on maize.