Hongbin WANG,Lei LI,Yang ZHANG

1.College of Resource and Environmental Science,Jilin Agricultural University,Changchun 130118,China;2.Gongzhuling Station of Quarantine and Plant Protection,Gongzhuling 136100,China

Chlorothalonil is a broad-spectrum protective fungicide that can inhibit glyceraldehyde-3-phosphate dehydrogenase(GAPDH)in fungal cells and bind to cysteinecontaining proteins in GAPDH,thereby destroying the activity of GAPDH,leading to metabolic damage and loss of vitality in fungal cells.Chlorothalonil is incapable of uptake and translocation,but it has good adhesion ability to the surface after being sprayed to plants and can not be easily washed away by rain,resulting in the long-term efficacy.

Currently,a large numberof studies have been carried out at home and abroad on the degradation and residual dynamics of chlorothalonil in soil.Chenet al.[1]investigated the residual quantity and degradation and residualdynamics ofchlorothalonil and metalaxyl in cucumber and soil.Zhouet al.[2]changed ozone input quantity and access frequency in soil and found that the input quantity and access frequency of ozone exhibited a significant positive correlation with the degradation rate of chlorothalonil in soil. Studies have shown that chlorothalonil has a stable structure and can not be easily degraded in soil.However,so far,little information is available on the residual dynamics of chlorothalonil in acidified soil under different conditions of soil moisture content and pH.In this study,the effects of soil moisture content and pH on residual quantity of chlorothalonil in acidified soil were analyzed,which was conducive to the remediation of soil environment and maintenance of a health cultivation system.

Materials and Methods

Materials

Collection and pretreatment of soil samplesExperimental soil belonged to black soil type,which was collected from Xinlicheng Town,Jingyue Dis-trict,Changchun City,Jilin Province.The land was suitable for protected cultivation.Surface soil(0-20 cm)was collected,brought back to the laboratory and air-dried.After removal of gravels,roots and other debris,soil samples were sifted through a 2 mm sieve before use.According to the determination results,experimental soil contained 30.5 g/kg organic matter,pH 5.20,belonging to acidified soil type.

Instruments6890N gas chromatograph(equipped with μ-ECD detector),produced by AgilentTechnologies,Inc.;TDL-40B desktop high-speed centrifuge,produced by Shanghai Lishen Scientific Equipment Co.,Ltd.;RE-5285A rotary evaporator,produced by Shanghai Yarong Biochemical Instrument Factory;HG75-3 electric heating/constant temperature dual purpose drying oven,produced by Shanghai Laboratory Instrument Works Co.,Ltd.

ReagentsChlorothalonil standard(purity:99.2%),provided by Anyang Wuxing Pesticide Factory;chlorothalonil raw material(purity:97%),provided by Zhejiang Baoling Pesticide Factory.

Methods

Effects of soil moisture content and pH on chlorothalonil residues

Effects of soil moisture content on chlorothalonil residuesSimulation tests were conducted using bonsai pots with sealed bottom.Specifically,5 kg of experimental soil was loaded in each pot,added with 10,20 and 50 mg/kg chlorothalonil raw material.By adding distilled water,soil moisture content was adjusted to 5%,10%,20%and 30%,respectively.Each treatment was repeated three times.Soil samples were incubated continuously at 20℃for 35 d with regular water supplement.At 0,3,7,14,21,28 and 35 d,soil samples were transferred to the flask,extracted,purified and added with distilled water to a final volume.Quantitative analysis was performed using gas chromatography.

Effects of soil pH on chlorothalonil residuesSimulation tests were conducted using bonsai pots with sealed bottom.Specifically,5 kg of experimental soil was loaded in each pot,added with 10,20 and 50 mg/kg chlorothalonil raw material.By adding buffer solution,soil pH was adjusted to 4,5 (control),6 and 7,respectively.Soil moisture content was maintained at 10% (insufficient buffer was supplemented with distilled water).Each treatment was repeated three times.Soil samples were incubated continuously at 20℃for 35 d with regular water supplement.At 0,3,7,14,21,28 and 35 d,soil samples were transferred to the flask,extracted,purified and added with distilled water to a final volume.Quantitative analysis was performed using gas chromatography.

Sample determination

Pretreatment of samplesAfter incubation,an appropriate amount of soil sample was weighed and transferred to a 250 ml erlenmeyer flask with a stopper,added with 25.0 ml of acetone,and shaken at 160 r/min for 2 h at 25℃.The extract was transferred to a centrifuge tube;the flask was rinsed with 10-20 ml of acetone,and the eluent was also added into the centrifuge tube.Subsequently,the mixture was centrifuged at 4 000 r/min for 15 min;the supernatant was transferred to a separatory funnel,added with 20 ml of saturated sodium chloride solution,extracted three times with 20,15 and 10 ml of petroleum ether, respectively; the extracted chlorothalonil was transferred to a organic phase,dehydrated by anhydrous sodium sulfate and filtered into a beaker;the filtrate was concentrated using a rotary evaporator and added with distilled water to a final volume of 2 ml for GC analysis.

Gas chromatographic conditions

Chromatographic column:DB1701 quartz capillary column(30.0 m×250 μm × 1 μm);detector:μ-ECD detector;carrier gas:N2;purity:99.999%;inlet temperature:220℃;oven temperature:178℃;ECD temperature:300℃;carrier gas flow rate:2 ml/min;injection mode:splitless injection;injection volume:1 μl;make-up gas flow rate:35 ml/min.

Results and Analysis

Residual dynamics of chlorothalonil under different conditions of soil moisture content

The residual dynamics of chlorothalonil in experimental soil were observed for 35 d to draw the curves of residualdynamics ofchlorothalonil with different initial concentrations(10,20 and 50 mg/kg)under different conditions of soil moisture content(5%,10%,20%and 30%)with residual quantity of chlorothalonil in soil as the ordinate,incubation time as the abscissa(Fig.1).According to the residual dynamics of chlorothalonil under different conditions of soil moisture content, the residualquantity of chlorothalonil was reduced gradually with the extension of incubation time.To be specific,among different treatments,in the initial period(3 d),the reduction rate of chlorothalonil residues in soil was extremely high;at 3-7 d,the reduction rate of chlorothalonil residues declined slightly;after 7 d,the residual quantity of chlorothalonil in soil was reduced slowly and steadily[3].

When the initial concentration of chlorothalonil in soil was 10 mg/kg,the average residual quantity of chlorothalonil in 5%moisture treatment,10%moisture treatment,20%moisture treatment and 30%moisture treatment was 6.31,3.92,2.12 and 4.32 mg/kg respectively after 35 d;when the initialconcentration of chlorothalonil in soil was 20 mg/kg,the average residual quantity of chlorothalonil in 5%moisture treatment,10%moisture treatment,20%moisture treatment and 30%moisture treatment was 12.76,8.52,4.94 and 8.90 mg/kg respectively after 35 d;when the initialconcentration of chlorothalonil in soil was 50 mg/kg,the average residual quantity of chlorothalonil in 5%moisture treatment,10%moisture treatment,20%moisture treatment and 30%moisture treatment was 34.86,24.95,18.53 and 25.96 mg/kg respectively after 35 d.Under the same initial concentration,the residual quantity of chlorothalonil among different treatments exhibited a descendingorderof5% moisture treatment＞ 30%moisture treatment＞10%moisture treatment＞20%moisture treatment.

In different soil samples,when the initial concentration of chlorothalonil was 10,20 and 50 mg/kg,the residual quantity of chlorothalonil in 5%moisture treatment,10%moisture treatment and 20%moisture treatment was reduced with the increase of soil moisture content.Specifically,the residual quantity of chlorothalonil reached the maximum in 5%moisture treatment and reached the minimum in 20%moisture treatment.Moreover,the residual quantity of chlorothalonil in 30%moisture treatment was lower than the residual quantity in 5%moisture treatment but higher than that in 20%moisture treatment;the residual quantity of chlorothalonil in 10%moisture treatmentand 30% moisture treatment was similar.However,as shown in Fig.1,among different experimental treatments with three initial concentrations of chlorothalonil,the residual quantity of chlorothalonil in 10%moisture treatment was lower than that in 30%moisture treatment.

Residual dynamics of chlorothalonil under different conditions of soil pH

The residual dynamics of chlorothalonil in experimental soil were observed for 35 d to draw the curves of residual dynamics of chlorothalonil with different initial concentrations(10,20 and 50 mg/kg)under different conditions of soil pH (4,5,6 and 7)with residual quantity of chlorothalonil in soil as the ordinate,incubation time as the abscissa (Fig.2).According to the residual dynamics of chlorothalonil under different conditions of soil pH,the residual quantity of chlorothalonil was reduced gradually with the extension of incubation time.To be specific,among different treatments,the reduction rate of chlorothalonil residues in soil was extremely high in the initial period (3 d)and declined slightly at 3-7 d;after 7 d,the residual quantity of chlorothalonilin soilwas reduced slowly and steadily[4].

When the initial concentration of chlorothalonil in soil was 10 mg/kg,the average residual quantity of chlorothalonil in pH 4 treatment,pH 5 treatment,pH 6 treatment and pH 7 treatment was 4.61,3.92,3.65 and 3.19 mg/kg respectively after 35 d;when the initialconcentration of chlorothalonil in soil was 20 mg/kg,the average residual quantity of chlorothalonil in pH 4 treatment,pH 5 treatment,pH 6 treatment and pH 7 treatment was 9.19,8.52,8.35 and 7.38 mg/kg respectively after 35 d;when the initialconcentration of chlorothalonil in soil was 50 mg/kg,the average residual quantity of chlorothalonil in pH 4 treatment,pH 5 treatment,pH 6 treatment and pH 7 treatment was 26.17 mg/kg,24.95,23.73,21.45 mg/kg respectively after 35 d.Under the same initial concentration, the residual quantity of chlorothalonilamong different pH treatments exhibited a descending order of pH 4 treatment＞pH 5 treatment＞pH 6 treatment＞pH 7 treatment.

In different soil samples,when the initial concentration of chlorothalonil was 10,20 and 50 mg/kg,residual dynamics of chlorothalonil were basically the same.Overall,the residual quantity of chlorothalonil in pH 4 treatment,pH 5 treatment,pH 6 treatment and pH 7 treatment was reduced with the increase of pH.

Conclusions

Soil moisture content poses a significant impact on the degradation rate of chlorothalonil.Under the same initial concentration,the degradation rate of chlorothalonil in different soil samples exhibited a descending order of 20%moisture treatment＞10%moisture treatment＞ 30%moisture treatment＞5%moisture treatment.

Within the experimental range of soilpH,the degradation rate of chlorothalonil in soil was positively correlated with pH.Under the same initial concentration,the degradation rate of chlorothalonil in different soil samples exhibited a descending order of pH 7 treatment＞ pH 6 treatment＞pH 5 treatment＞pH 4 treatment.

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