Studies On Residual Determination And Degradation Of Xiaochongliulin On Orange And In Soil

Xiaochongliulin, invented by Sichuan Academy of Chemical Industry Research and Design, is an organophosphorous insecticide and acaricide, which is effectively against a wide range of insects, especially the citrus arrowhead scale. At present, the pesticide has been temporarily registered to control citrus arrowhead scale in China. However, the residual determination methods for this pesticide and the data of residues on orange and in soil after application have not yet been reported. Therefore, the studies are of great significance on its residual determination and degradation on orange and in soil.A method was developed for determination xiaochongliulin residues on orange and in soil by capillary gas chromatography. The samples were extracted with acetone and the extracts were partitioned with dichloromethane. After cleanup on a mixture column of aluminum oxide (neutral) and activated charcoal, the residues were analyzed using gas chromatography equipped with FTD. The DB-17 column,15m 0.540mm i.d., was used for chromatographic separation of this pesticide. The Limit of detection of this method was 1.4 10-10g. Average recoveries of xiaochongliulin from fortified orange pulp, peel and soil samples at levels of 0.05~0.5mg kg-1 were in the range from 88.37% to 93.17%, from 87.07% to 94.07% and from 86.47% to 93.30% respectively, with coefficient of variation hi the range from 1.65% to 4.14%.Residue trials of 30% xiaochongliulin EC were conducted in Guangxi and Hunan Province during 2002-2003. The results indicated that with application dose of 1000mg(a.i.)/kg the degradation of xiaochongliulin was moderate in soil and on orange peel with the decline half-lives of ranging from 10.33 to 15.20 days and from 13.58 to 14.69 days, respectively. The degradation kinetics of this pesticide in soil andon orange followed the first-degree reaction pattern.The results also indicated that the residues of this pesticide on orange pulp, on orange peel, on orange and in soil ranged from LOD to 0.0109mg/kg, from 0.7418 to 2.0861mg/kg, from 0.0777 to 0.4602mg/kg and from 0.2350 to 1.2103mg/kg respectively in Guangxi Province, and ranged from LOD to 0.0307mg/kg, from 0.2080 to 1.3698mg/kg, from 0.0429 to 0.2959mg/kg, and from 0.0627 to 0.7307mg/kg respectively in Hunan Province, when 30% xiaochongliulin was sprayed two or three tunes with the dosage of 500mg(a.i.)/kg and 1000mg(a.i.)/kg and an interval of IS days during the growing season of orange trees, and the last application was carried out 14,21 and 28d before the harvest. Under field trial conditions, there were positive relation between residue and amount as well as tunes sprayed for, and negative relation between residue and the days from last application to harvest.Xiaochongliulin was a new pesticide invented in our country and there was no reference MRL at present in FAO/WHO and other countries. The resulting residue data then were necessary for government to establish MRL and guideline for safety application of this pesticide on orange, and to conduct risk assessment of this pesticide.