Degradation Dynamics And Terminal Residue Of Fluroxypyr In Rice Field

Fluroxypyr is an inner systemic herbicide developed by the United States Dow Agro-Sciences Company for control of the broad-leaved weeds, belonging to pyridine acid type. Fluroxypyr is widely used in cereal crop fields and some vegetable and fruit gardens to contrl the broad-leaved weeds. Based on the situation of application of fluroxypyr in field, rice was choosed as representative of crop. After applying fluroxypyr and sampling according to Field Trial Standard of Pesticide Residue, pre-treatment was followed referring to the cardinal principle and procedures of residue analysis of fluroxypyr, gas chromatography analysis method were adopted to detect the residue, and then the residue analysis methods of rice for fluroxypyr and dynamic equation were established, in order to provide scientific evidences for the reasonable and safe application of fluroxypyr in rice field. The study included fluroxypyr residue analysis methods, fluroxypyr degradation dynamics in rice plants, soil and water, and the final residue of fluroxypyr in brown rice, rice plants, soil and rice husk. The results were as follows.To establish the methods for fluroxypyr gas chromatography (GC) residue analysis, the soil, water, leaves and stems, rice and rice husk were used as tested to study the appending recovery experiments. The results showed that when the concentration of plants added was 0.02~1.0mg/kg. The average recovery was 88.91% ~ 100.50% with variation coefficient of 1.86% ~ 6.71%. When soil adding concentrations was 0.02~1.0mg/kg, the average recovery was 86.65% ~ 95.01%, with coefficient of variation being 4.26% ~6.52%. When the concentration of added water was 0.01~1.0mg/kg, the average recovery was 96.16% ~ 103.20%, and the coefficient of variation was 2.34% ~6.97%. When the concentration added rice husk was 0.02~1.0mg/kg, the average recovery was 89.04% ~ 93.02%, and the coefficient of variation was 6.32% ~ 9.94%. When the concentration of brown rice added was 0.02~1.0mg/kg, the average recovery was 85.51% ~ 92.28%, and the variation coefficient was 3.81% ~ 7.04%. Test results are to meet the requirements of residue analysis.Digestion dynamic test results show that under application of 675g.ai/h, fluroxypyr could be degraded quickly in rice plant with half-lives of 4.9 ~ 6.0 days. In paddy soil, fluroxypyr residues increased first and then gradually decreased, with the highest residue at about 3 d after application. The half-life was 5.5 ~ 8.6 d. But it was degraded slowly in water, with a half-life of 11.0 ~ 13.8 days. Fluroxypyr degradation in rice plant, field water and soil followed the first-degree reaction model. The eventually residues experiments were conducted in Qianshan, Anhui and Guangzhou, Guangdong respectively. The experiment results in Qianshan show that under application of 450 ~ 675 g.ai/h in paddy, one time of application and the sampling interval apart from last application being 60 days, fluroxypyr residue in brown rice, rice husk, rice plant and soil was 0.01 mg/kg ~ 0.0356 mg/kg, 0.0215 mg/kg ~ 0.0462 mg/kg, 0.0260 ~ 0.0683 mg/kg, and <0.002mg/kg respectively. The test results in Guangzhou show that under conditions of 450 ~ 675 g.ai/h application in paddy, one time of application and the sampling interval of 30 days, fluroxypyr residue in brown rice, rice husk rice plant and soil was 0.01 mg/kg ~ 0.1330 mg/kg, 0.0251 mg/kg ~ 0.0886 mg/kg, 0.0512 mg/kg ~ 0.0804 mg/kg, and < 0.002 mg/kg, respectively.The results of the final residue experiments for two years at two points in Anhui and Guangdong indicated that under conditions of 450 ~ 675 g.ai/h application in paddy, one time of application, sampling interval of 30d, fluroxypyr residue in brown rice was 0.01 mg/kg ~ 0.1330 mg/kg, and when the sampling interval apart from last application being 60 days, fluroxypyr residue in brown rice was 0.01 mg/kg ~ 0.0356 mg/kg. Fluroxypyr residue in brown rice, rice husk and rice plants was positively correlated with pesticide dose. The higher the dose of application was, the higher the residue. Simultaneously, the residues and the interval of the harvest and application were in a certain degree of negative correlation. The longer the interval of application and harvest was, the lower the residue. However, there was no obvious correlation between the residue in soil and application dose, and the residual volume was below 0.002 mg/kg.Based on our experiment results and the maximum residue limit (0.2mg/kg) of fluroxyyr in rice in China, under condition of 450 ~ 675 gai/h application in paddy, using one time, the sampling interval apart from last application being 60 days, the residue was lower than 0.2 mg/kg, but when the sampling interval apart from last application was 30 days, the residue would be possibly higher than 0.2 mg/kg. Therefore, the recommended criterion for considerable application of fluroxypyr was that 30% fluroxypyr WP was sprayed under application of 450 ~ 675 g.ai/h, using one time and the safe interval being 60 days.