The residue levels of thiram during potato cultivation in open field were evaluated. Thiram residues were determined by methylation derivation method with high performance liquid chromatography (HPLC). Wettable powder (WP) formulation containing 25% thiram was applied at 2320 g active gradient hm−2 (a.i. hm−2) dosage for the dissipation study. The decline rate in potato leave and soil followed first-order kinetics equation, and the half-life ranged from 2.8 to 5.4 days and 2.6 to 9.9 days, respectively. In terminal residue, the thiram was sprayed at 580 g a.i. hm−2 (low concentration, recommended dosage) and 1160 g a.i. hm−2 (high concentration, double of recommended dosage). The residues of thiram in potato and soil samples collected in the field at preharvest interval of 21 days and 30 days were all below 0.02 mg kg−1. The results show that thiram possesses low dietary risk in potato at harvest according to supervised residue field trial. It may be safe when used at recommended rate of application.
Pesticides rank as one of the most important agrochemicals to ensure agricultural production yield and quality. However, they may remain in soil, water, or plants [
In this work, an analytical method based on the methylation derivation and further determined by HPLC-UV was applied to evaluate the decline rate and terminal residues of thiram in potato and soil. In this experiment, 25% thiram WP was applied to control potato late blight (
Thiram standard was provided by Institute for the Control of Agrochemicals, Ministry of Agriculture (ICAMA), China, with a certified purity of 98.5%. 25% of thiram WP was supplied from China Agricultural University. Acetonitrile was HPLC grade, obtained from DIMA Technology Inc. (Richmond Hill, USA). Deionizated water was obtained from the Milli-Q SP Reagent Water system (Millipore, Bedford, MA, USA). Other reagents (L-cysteine, Na2EDTA, sodium hydroxide, tetrabutylammonium hydrogen sulfate, hydrochloric acid, hexane, chloroform, 1,2-propanediol, methyl iodide, and anhydrous Na2SO4) were analytical grade, purchased from Beijing Chemical Reagents Co. (Beijing, China). Anhydrous Na2SO4 was baked at 500°C for 5 h before use.
Thiram standard stock solution 500 mg
The open field trial was carried out in Beijing, Hunan, and Jiangsu Province in China from 2011 to 2012. Every site was composed of 24 plots for eight experiment treatments, one of which consisted of three replicate plots. The treatments were designed for decline study for potato leave and soil at high dose, controls for potato leave and soil without thiram spray, terminal residue study at the recommended dose and high dose. Every plot was separated by irrigation channel.
Thiram was sprayed in the experiment at the dosage of 2320 g a.i. hm−2. Triplicate potato leaf samples were picked from every treated plot and untreated controls randomly before spraying and 0 (2 h), 1, 3, 5, 7, 14, 28, and 36 days after foliar application. Soil samples were collected on the top of 10 cm depth from the experimental plots at the same time as potato leaf, and pebbles and other unwanted materials in soil were removed manually.
580 g a.i. hm−2 and 1160 g a.i. hm−2 were sprayed two and three times with interval of 7 days. Potatoes were selected randomly and the soil on the potato surface was removed. Soil samples on the top of 10 cm depth were collected at 21 and 30 days after the last spray.
Potato leaf was cut into small segments and mixed in a blender. Potatoes were quartered, and subsamples from the opposite quarters were collected and chopped and then homogenized in a blender. Soil sample was air-dried and sieved through 0.45 mm sieve. All prepared samples were stored at −20°C until analysis.
The weather condition and soil properties of experimental sites during the test period were listed in Tables
The weather condition of experimental sites during the test period.
Year | Site | Temperature (°C) | Relative humidity (%) | Precipitation | ||||||
---|---|---|---|---|---|---|---|---|---|---|
Max | Min | Av | Max | Min | Av | Mam (mm) | Av (mm) | Total days | ||
2011 | Hunan | 29.1 | 10.5 | 20.7 | 82.1 | 43.1 | 60.9 | 34.0 | 6.1 | 20 |
Beijing | 36.3 | 18.0 | 28.6 | 88.1 | 48.5 | 56.3 | 59.2 | 4.6 | 14 | |
Jiangsu | 27.4 | 10.0 | 21.7 | 85.2 | 57.7 | 67.6 | 41 | 4.3 | 19 | |
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2012 | Hunan | 29.6 | 17.6 | 22.3 | 80.1 | 55.6 | 64.5 | 34.0 | 2.5 | 15 |
Beijing | 36.8 | 15.2 | 20.8 | 79.9 | 30.1 | 47.5 | 35.3 | 4.2 | 23 | |
Jiangsu | 37.2 | 16.4 | 31.3 | 96.2 | 58.3 | 76.9 | 118 | 7.8 | 27 |
Note: the test period of Hunan is from May to June in both 2011 and 2012; the test period of Beijing is from July to August in 2011 and in 2012 it is from August to September; the test period of Jiangsu is from May to June in 2011 and in 2012 it is from July to August; Max: abbreviation of maximum; Min: abbreviation of minimum; Av: abbreviation of average.
The soil properties of different experimental sites.
Site | Organic carbon content [ |
pH [ |
Sand [ |
Clay [ |
Silt [ |
---|---|---|---|---|---|
Hunan Province | 1.42 | 6.12 | 40.32 | 15.34 | 42.74 |
Beijing City | 1.56 | 7.28 | 61.95 | 10.15 | 26.88 |
Jiangsu Province | 1.14 | 5.97 | 52.60 | 12.78 | 37.97 |
20 g blended samples were weighed in a 150 mL beaker flask and extracted with 0.2 g of L-cysteine and 40 mL of 0.25 M EDTA in 0.45 M sodium hydroxide for 15 min in a shaking air bath at 20°C and 150 rpm. Spiking was carried out before EDTA solution was added. The extract was transferred to a 100 mL centrifuge tube and centrifuged for 5 min at 3800 rpm. The supernatant was poured into a 250 mL closed glass flask. The precipitation was extracted with another 40 mL solution again. pH of the combined supernatant was adjusted to ca. 7.0 with 2 M HCl aqueous solution after a solution of ammonium hydrogen sulfate (0.41 M, 5 mL) was added. The mixture was shaken vigorously for 10 min, together with 40 mL of methyl iodide (0.05 M) in chloroform-hexane (3/1; v/v) and stood for 20 min. The organic layer separated was centrifuged for 5 min at 3800 rpm, followed by addition of anhydrous sodium sulfate to remove residual water. The organic phase was evaporated to be nearly dry using rotatory evaporator at 30°C. The residue was constituted with 2 mL acetonitrile-water (1/1; v/v), followed by filtration with 0.45
The determination of thiram was carried out with Agilent 1100 series HPLC (Agilent Technologies, USA) coupled with diode array detector (DAD). A C18 column (Agilent ZORBAX SB-C18 250 × 4.6 mm 5
The concentration conversion formula between thiram and
The analytical method was performed on parameters of linearity, recovery, limit of detection (LOD), and limit of quantification (LOQ). The equation of linear working calibration of S-methylation derivative from thiram was
Recoveries and relative standard deviations (RSD) of fortified samples.
Sample | Fortified level (mg/kg) | Average recoveries (%) | RSD (%) | LODs (mg/kg) | LOQs (mg/kg) |
---|---|---|---|---|---|
Potato leave | 0.04 | 73.6 | 11.7 | 0.02 | 0.04 |
0.1 | 71.0 | 9.9 | |||
0.5 | 70.3 | 13.1 | |||
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Potato | 0.02 | 78.6 | 6.8 | 0.01 | 0.02 |
0.1 | 72.1 | 3.3 | |||
0.5 | 72.4 | 14.4 | |||
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Soil | 0.02 | 83.4 | 9.3 | 0.01 | 0.02 |
0.1 | 88.9 | 3.0 | |||
0.5 | 88.6 | 3.0 |
LOD: limit of detection; LOQ: limit of quantification.
Chromatograms of blank (a) and fortified level (0.02 mg kg−1 (b)) in soil samples.
Chromatograms of blank (a) and fortified level (0.02 mg/kg (b)) in potato samples.
Chromatograms of blank (a) and fortified level (0.04 mg/kg (b)) in potato leave samples.
The decline kinetics of thiram in potato leave and soil are presented in Figures
Dissipation in potato leave and soil.
Sample | Time | Sites | Regression equation | The square of correlation coefficient | Half-life (day) |
---|---|---|---|---|---|
Potato plant | 1st year | Beijing |
|
|
3.2 |
Hunan |
|
|
4.4 | ||
Jiangsu |
|
|
4.1 | ||
2nd year | Beijing |
|
|
3.9 | |
Hunan |
|
|
5.4 | ||
Jiangsu |
|
|
2.8 | ||
|
|||||
Soil | 1st year | Beijing |
|
|
2.6 |
Hunan |
|
|
6.9 | ||
Jiangsu |
|
|
9.9 | ||
2nd year | Beijing |
|
|
4.7 | |
Hunan |
|
|
8.7 | ||
Jiangsu |
|
|
3.2 |
The decline of thiram in potato leave of Beijing, Hunan, and Jiangsu.
The decline of thiram in soil of Beijing, Hunan, and Jiangsu.
Terminal residues of thiram in soil were lower than 0.02 mg/kg, while the residual thiram in all potato samples harvested in 21 days and 30 days after spray were not detectable, all of which revealed that the application of thiram during potato cultivation results in low residue in crops and soil.
In this work, the degradation of thiram under open field condition was studied in two consecutive years in Beijing, Hunan, and Jiangsu. Methylation derivation method to determine thiram with HPLC-UV was validated and applied for residues evaluation in potato leave, potato, and soil. The half-life of thiram in potato leave and soil was 2.8 to 5.4 days and 2.6 to 9.9 days. The final residues in soil were less than 0.08 mg kg−1 at 14 and 21 days after application. In the case of potato, the terminal residue is not detectable when sprayed at 580 and 1160 g a.i. hm−2 at interval of 7 days for two or three times. Therefore, the results demonstrated that thiram can be used in potato cultivation as a low toxicity pesticide for the environment and human beings.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This study was partially supported by Chinese National Natural Science Foundation (Project no. 31171872) and Guanxi Special Invited Scientist Fund.