Environmental Safety Of Fluopicolide And Its Residue Analysis In Cucumber And Soil

Fluopicolide, one kind of benzamide fungicide, is receiving extensive attention in China because of its special chemical structure, novel mechanism and outstanding control effect. In order to study the environmental risk of this pesticide, five aspects had been investigated, including the acute toxicity, chronic toxicity, environmental behavior, residue degradation dynamics in cucumber plant and soil, the final residues in cucumber. We expected to provide the basic information for its rational use and management in China. Besides, we would like to provide a guideline for the safety assessment of other amide fungicides.Acute toxicity results showed that fluopicolide had low toxicity to Apis mellifera(Oral toxicity and contact toxicity, with LD50(48h) over 100μg each bee, Coturnix japonica(with LD50(168h) over 1000mg·kg-1, earthworms and silkworms. It exhibited low risk to trichogramma with safety factor over 264.1. But acute toxicity results also indicated that fluopicolide was moderate toxicity to zebrafish, algae and daphnia magna; high toxicity to amphibians with LC50(96h) equals 0.943mg·L-1.Fluopicolide had lethal capabilities to the three stages of zebrafish, of which the LC50(48h) to larvae, LC50(96h) to adult fish and juvenile was 0.204 mg·L-1, 0.286 mg·L-1 and1.489 mg·L-1, respectively. Studies shown that fluopicolide with the dosage of 0.0596 mg·L-1 or higher concentrations exhibited certain lethal effect to zebrafish embryos, and the embryos which were treated with high concentrations displayed various symptoms, such as pericardial cyst, yolk sac non-absorbing, less melanin deposition and fish bending. After exposing to fluopicolide for 14 days, unfavorable symptoms were observed for the adult zebrafishs, including weight loss, fecundity reduction and the reduction of effective egg amount. After treated with 0.0298 mg·L-1 fluopicolide, the residual fluopicolide in water had the potential toxicity to the growth and development of zebrafish, whatever the life stage.Hydrolysis and photolysis of fluopicolide were accorded with the first-order kinetics equation. Fluopicolide was a little more difficult to hydrolysis. When the light intensity was 40000 lx, 110000 lx and the UV intensity was 9000-11000uw·cm-2 with 500 W mercury lamp, the photolysis half-life were 3.76 hours, 0.867 hours and 2.30 hours, respectively, which ranked as easy photolysis. When the light intensity was 8000 lx, the UV intensity was 64.5 uw·cm-2 with 300 W xenon lamp, the photolysis half-life was 130.75 hours(difficult to photolysis).The degradation of fluopicolide in Shandong brown soil, Northeast China black soil and the Jiangxi red soil were investigated under aerobic conditions. The half-life were 19.47 d, 38.29 d and 45.00 d, ranked as easy degradation, moderate degradation and moderate degradation, respectively. When it comes to anaerobic conditions, the degradation of fluopicolide in Shandong brown soil, Jiangxi red soil and North east China black exhibited a half-life of 40.53 d, 72.19 d and 203.82 d, ranked as moderate degradation, moderate degradation and difficult level, respectively. Anaerobic conditions were unfavorable for the degradation of fluopicolide in soils.The adsorption equilibrium time in Jiangxi red soil, black soil in Northeast China and Shandong brown soil of fluopicolide were 9h, 18 h and 21 h while the soil adsorption coefficient of three kinds of soil were 246.51, 813.03 and 217.85, which were ranked as difficult, easy and medium adsorption level. The adsorption of fluopicolide in above soils all belong to physical adsorption. The Rf value of fluopicolide in thin layer chromatography of Northeast China black soil, Shandong brown soil and Jiangxi red soil were 0.099, 0.303 and 0.400, respectively. The movement speed of fluopicolide was ranked as: Jiangxi red soil > Shandong brown soil > northeast China black soil. The leaching of fluopicolide in three kinds of soil was also investigated. The residual percentage of added fluopicolide in the leaching liquid of Jiangxi red soil, northeast China black soil and Shandong brown soil was 30%, 1% and none, respectively. More than 50% of the added fluopicolide can be detected for the soil picked from 10 cm below the surface of northeast china black soil, and 50% of the total amount could be detected for Shandong brown soil with the soil picked from 20 cm below the surface. The leaching speed of fluopicolide in above three kinds of soil ranked as: Jiangxi red soil > Shandong brown soil > northeast china black soil.Fluopicolide can be accumulated in fish body. When Zebrafish was exposed to fluopicolide with the concentration of 0.745, 0.149 and 0.0149 mg·L-1 for 192 h, BCF was 33.65, 26.39 and 193.25, respectively. According to the experimental criterion for environmental safety evaluation of chemical pesticide evaluation standard, fluopicolide belongs to the medium bioaccumulation pesticide(10<BCF≤1000).Fluopicolide was sprayed at the dosage of 140.625 g·ha-1, and then the residue was measured 2h later. The residue in cucumber plants was 99.40 mg·kg-1, while its residue in the surface soil layer(5cm) was 2.52mg·kg-1; the residue in plant is far greater than that in the soil. In the dynamic degradation test, the half-life of fluopicolide in cucumber and soil was 7.64 d and 14.59 d respectively; in other words, the decayed speed of fluopicolide in cucumber was faster than that in the soil. Fluopicolide was detected at the concentration of 0.397 mg·kg-1 in cucumber 13 days after treatment and 0.040 mg·kg-1 25 days after treatment.In 2014, national standard GB 2763-2014 of China suggested that the maximum residue limit(MRL) of fluopicolide in cucumber is 0.5 mg·kg-1. In this study, fluopicolide was sprayed at the dosage 70.3125 g·ha-1 every 3days for 4 times. The amount of fluopicolide residue was detected 3d after fungicide treatment, the results showed that it was lower than MRL. When the dosage was 140.625 g·ha-1, the residue was also lower than MRL according to the results of 10 d after the final treatment. We suggested that the dosage of fluopicolide applied on should be 70.3125 g·ha-1 and its application should not exceed 4 times. We shall harvest three days after final treatment, namely a safety interval of 3 days.In summary, fluopicolide was relatively safe to bees, birds, Bombyx mori, earthworms, trichogramma and other environmental organisms except for a certain toxicity to aquatic organisms. Fluopicolide exhibited favorable chemical stability, specially, it could hardly degrade nor photolyze. Unfortunately, fluopicolide could be accumulated in fish, which ranked as moderate accumulation. Fluopicolide was also difficult to degrade in soil. The adsorption of fluopicolide in three kinds of soil varied a lot, ranking as difficult to move or moderate to move. It was difficult to leach in Northeast black soil, and the leaching speed ranked as: Jiangxi red soil > Shandong brown soil > Northeast China black soil. Given its high toxicity to aquatic organisms and the bio-concentration in vertebrates, fluopicolide was suggested to be applied far away from water source and fishpond to avoid polluting water. The suggested dosage of fluopicolide for field application was 70.3125 g·ha-1 and its application should not exceed 4 times, besides, the safety interval was 3days.