The Residues Of Pendimethalin In Soil And Its Safety Evaluation For Several Crops

Pendimethalin is an efficient dinitroaniline herbicides combining lowtoxicity, which is widely applied to controlling annual gramineoues weeds in dryland. However, there are currently a limited number of literature reports about the safety studies pertaining to the pendimethalin impacts on crops of Pendimethalin residues in soil. This paper studied the digestion law of Pendimethalin residues in soil and the safety of its residues, where the results provided ascientific basis for the safe use of Pendimethalin in dryland. The results were summarized as follows:1. Developed a method for determining the residue of Pendimethalin in corn, pepper, cowpea, peanut, tomato and soil.The plant samples were extracted with acetonitrile, while the soil samples were extracted with methanol. The residues of Pendimethalin were detected by GC-μECD. The result indicated that the minimum detectable amount of Pendimethalin was 1.1×10-9 g, the minimum detectable concentration of Pendimethalin was 0.0005 mg/kg. At three spiking levels from 0.005 mg/kg to 0.1 mg/kg, average recoveries of Pendimethalin in corn, pepper, cowpea, peanut and tomato samples respectively were at the range of 82.3 to 91.3%,83.7 to 96.8%,93.5 to 98.1%,88.3 to 100.3%,96.1 to 100.4% respectively, with the relative standard deviations of 3.27 to 4.75%,2.52 to 4.26%,2.64 to 5.38%,3.14 to 4.99%,2.36 to 3.94%; Recoveries and RSD of the method at spiked concentrations between 0.002 mg/kg to 0.2 mg/kg were 88.6 to 95.1% and 4.83 to 4.69% for soil samples. These results suggested that the sensitivity and precision of methods was sufficient to satisfy the requirements for the residue analysis of pesticide.2. Pendimethalin in soil degradation was in line with the first-order kinetics. The temperature and the rainfall had great effect on the degradation of Pendimethalin. After 45 days the residue of Pendimethalin in soil was 0.047 mg/kg, which was safe to the crops.3. The study of crop selectivity index of Pendimethalin on five kinds.Laboratory tests studied the Pendimethalin selectivity index for the five kinds of crops with good control effect annual gramineous weeds of barnyard grass. The results showed that the virulence of Pendimethalin on five kinds of crops order from high to low was cowpea, peanut, pepper, corn and tomato. The selective indexes of Pendimethalin on corn, pepper, bean, peanut and tomato were 0.33,0.33,0.31,0.36,1.36, respectively, which suggested that the use of Pendimethalin was safe on tomato, but risky on cowpea.4. Evaluate the effects on seeding rate、height and yield of Pendimethalin in corn, pepper, cowpea, peanut and tomato.Pendimethalin did not demonstrate influence on the height, yield of five crops in harvest period at recommended dose.The inhibition rate of emergence rate on corn, cowpea, peanut in harvest period was less than 5% under the condition that two times of the recommended dose of Pendimethalin being used. For corn, the inhibition of height was 10.7%, the inhibition of hundred-grain weight was 5.6% in harvest period, while the inhibitions of hundred-grain weight of cowpea and peanut were 13% and 11.1% in harvest period, respectively. There was no effect of the seeding rate on pepper and tomato at two times recommended dose of Pendimethalin. In harvest period, the inhibition of height on pepper was 14.6, the inhibition of fruit number on pepper and tomato were 13.9% and 16%. The inhibition rate of emergence rate on corn in harvest period was 19%, on cowpea and peanut is less than 5% at four times recommended dose of Pendimethalin. For corn, the inhibition of height was 19.7%. The inhibitions of hundred-grain weight of corn, cowpea and peanut were 20.5%,18.9% and 19.1% in harvest period. The inhibition rate of seeding rate on pepper and tomato in harvest period was less than 5% at four times. In harvest period, the inhibition of height on pepper was 27.4% and the inhibition of fruit number on pepper and tomato were 50% and 48%. According to the field of five crops injury diagnosis and data statistical analysis provided ascientific basis for the safe use of Pendimethalin on corn, pepper, cowpea, peanut and tomato.5. Developed the dose-response model and residues-reaction model of Pendimethalin in corn, pepper, cowpea, peanut and tomato.By comparing the regression analysis of the linear, exponential and logarithmic approaches, the dose-response model and residues-reaction model of y= alnx+b were established. The correlation confficients of the dose-response model was above 0.87. This experiment result indicated that either different types of crops or diffent parts of same crop diaplayed varieties of sensitivity levels against Pendimethalin. The correlation coefficient of residues-reaction model was above 0.71. The residues-reaction model illustrated the relationship between residue doses in crops and the degree of phytotoxicity.