| Job's-tears (Coix lachryma-jobi) is a common drug-diet annual herb, with the seeds strengthening spleen, clearing away heat and diuresis, draining purulence, detoxification, supporting anti-cancer effects, and so on. Unfortunately, the medicinal herbs are susceptible to corn borer, armyworm and other pests attack in the field, so pesticides are widely used for their protection.The present study has examined the dissipation dynamics and residual behavior of chlorpyrifos and fipronil in Job's-tears(Coix lachryma-jobi) seeds and soils, and would help to formulate safe application standard of chlorpyrifos and fipronil in Job's-tears(Coix lachryma-jobi) production.A simple, rapid residue analysis method of chlorpyrifos and fipronil in Job's-tears (Coix lachryma-jobi) seeds and soils was developed. The residues of chlorpyrifos and fipronil were extracted from samples with a methanol and distilled water mixture (V:V=90:10), concentrated extracts, cleaned up by alumina neutral column and determined by GC using capillary column equipped with a electron capture detector. The detectable limit of GC-ECD estimated for chlorpyrifos and fipronil is 0.001 and 0.002ng respectively, and the minimum detectable concentration is 0.0001 and 0.0002mg/kg correspondingly. The fortified recoveries of these two pesticides in analytical samples were in range of 86.92%-101.50%, with relative standard deviations of 1.31 %-8.04%.According to the result of residue tests under the control condition of 30, 20, 10℃, degrading speed of chlorpyrifos and fipronil in soil are related with the temperature. The higher the temperature is, the highter degrading speed is. The half life of chlorpyrifos in Taishun soil were 8.8(30℃), 10.7(20℃), 16.9(10℃) days separately. Under the same test condition, the half life of fipronil in Taishun soil were 16.7 (30℃), 23.7(20℃), 29.5(10℃) days respectively. The hydrolysis test of chlorpyrifos showed that the half life of chlorpyrifos in buffer solution were 13.6(pH=5), 9.7(pH=7), 8.8(pH=9) days at different pH and 25℃temperature; the chlorpyrifos in buffer solution were 2.2(35℃),9.7(25℃),27.1(15℃) days at different temperature and pH=7.Results of field test showed that the half life of chlorpyrifos in soil and Job's-tears (Coix lachryma-jobi) seeds were 6.5-12.6 days and 12.9-16.0 days, and one of fipronil in soil and Job's-tears (Coix lachryma-jobi) seeds were 6.8- 18.2 days and 9.2-10.5 days respectively. It is 30 days that the chlorpyrifos residue was degraded below 0.1 mg/kg in 600 g·ai/hm~2 treated trials. Under the condition of 720 g·a.i/hm~2 treatment, the residues of chlorpyrifos in Taishun and Jinyun Job's-tears seeds were 0.1134 mg/kg and 0.0885 mg/kg from the preharvest 30 days. It is 21 days (30 g·a.i/hm~2) and 30 days (45g·a.i/hm~2) that the residues of fipronil were degraded below 0.01 mg/kg in Job's-tears (Coix lachryma-jobi) seeds of Taishun and Jinyun. Therefore it is recommended that the pre-harvest interval (PHI) of chlorpyrifos in job's-tears is 30 days for the 600 g·a.i/hm~2 treatment, and PHI of Fipronil are 21 days for the 30 g·ai/hm~2 treatment and 30 days for the 45g·a.i/hm~2 treatment, respectively.
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