Studies On Residues And Dissipation Of Pyrethriods In Auricularia

A multiresidue analytical method of bifenthrin, fenpropathrin, lambda-cyhalothrin,beta-cypermethrin, fenvalerate and deltamethrin in Auricularia and its substrate wasdeveloped in this study, and the residues of selected pyrethroid pesticides in twenty driedhair wood ear samples and thirty black wood ear samples collected randomly from marketswere determined. The dissipation dynamics of pyrethroids in substrate and the transferfrom substrate to fruiting body were evaluated, and the effect of substrate sterilization onpyrethroid residues was analyzed. The dissipation dynamics and the terminal residues ofpyrethroids in Auricularia polytricha were studied.1. The multiresidue analytical method for pyrethroids in Auricularia polytricha andits substrateThe sample was extracted by acetonitrile, cleaned up by florisil column and detected byGC-ECD. The correlation coefficients were more than0.9993in the concentration rangesfrom0.005to0.5mg·kg^-1.When three pesticides were spiked at the levels of0.005,0.05and0.5mg·kg^-1, respectively, the average recoveries of pyrethroid pesticides ranged from76.04%to103.09%with RSD of0.49-4.26%in dried hairy wood ear; and it is in the rangeof73.08%^-103.38%with RSD of0.75-5.68%in dried black wood ear. The averagerecoveries were found to be from81.68%to96.39%in fresh hairy wood ear with a relativestandard deviation（RSD） from1.87%to5.36%, from82.66%to102.83%in substrate withRSD from1.11%to4.99%, respectively. These results indicated that the method isaccurate and sensitive, and could meet the requirement of pesticide residue analysis.2. Determination of pyrethroid pesticides residues in Auricularia from marketsTwenty dried hair wood ear samples and thirty black wood ear samples were collectedrandomly at large supermarkets and farmers’ markets from different regions in AnhuiProvince （Tongling, Hefei and Anqing）and Jilin Province （Liaoyuan）.Results show that thepositive rate of bifenthrin and fenpropathrin were relatively low, i.e.2%. However,fenyalerate and deltamethrin were not detectable. On the other hand, the positive rate oflambda-cyhalothrin and beta-cypermethrin were higher than others, i.e.16%,12%respectively. There are totally15pyrethroid pesticides samples and the positive rate is30.0%. Dried hairy wood ear have been detected7, the positive rate is35.0%，themaximum is860.0g·kg^-1;dried black wood ear have been detected8, the positive rate is26.7%and the maximum is73.1g·kg^-1. 3. Influences of substrate sterilization on pyrethroids residuesThe degradation rates of pyrethroids pesticides in the substrate after sterilization werestudied, from the results, it can be seen that the sterilization has greatly influence on theresidues of selected pyrethroids pesticides in substrate, and the degradation rates was37.59-57.65%,the highest degradation rates of pyrethroids pesticides waslambda-cyhalothrin and the lowest was bifenthrin and fenpropathrin. The differentdegradation rates of those pyrethroids could easily associate with their diffe rentphysicochemical properties and the amount of the initial deposition.4. Dynamics of pyrethroid residues in substrateThe results showed that the dissipation of selected pyrethroids in substrate wascorresponded to the mathematic pattern. The dissipation half-lives of bifenthrin,fenpropathrin, lambda-cyhalothrin, beta-cypermethrin and deltamethrin were40.06d、24.57d、25.57d、22.57d、25.2d and14.76d respectively. The substrate of hairy wood earswas cultivated in dark moist conditions at around15℃for three months, that may be themain reason for slow dissipation rate.5. Transfer of pyrethroid residues from s ubstrate to Auricularia polytrichaResult showed that the pyrethroid pesticide residues quantity with two differentconcentration treatments were found in substrate when picking hairy wood ear in its firststubble （95days after treatment）, the second stubble （110days after treatment） and thethird stubble （125days after treatment），and the residues was0.09¹.45mg·kg^-1、0.03⁰.88mg·kg^-1and0.01⁰.81mg·kg^-1, respectively. However no pesticide residues were found infruiting bodies of hairy wood ear. Therefore, in growth process, pyrethroid pesticides donot transfer to hairy wood ear’s fruiting body from substrate, and have little harm to thesafety of hairy wood ear’s quality6. Dynamics and terminal residue of pyrethroid residues in Auricularia polytrichaThe half-lives of bifenthrin, fenpropathrin, lambda-cyhalothrin, beta-cypermethrin anddeltamethrin were5.26d、3.10d、4.22d、3.71d and4.02d, respectively. Except bifenthrin,the dissipation rates were more than90%in fruiting bodies on the14th day after treatment.The hairy wood ear was cultivated in moist conditions at around25℃, requires a certaintime of light and spraying water once or twice in order to maintain the moisture，thesefactors may caused the faster dissipation of5pyrethroids. The terminal residue results after pre-harvest interval （PHI） of3,5and7days. When5pyrethroids were applied at the two dosages （1.5times of the recommended dosage andapproximate recommended dosage on vegetables） over one and two times application, theresidue levels of5pyrethroids in fruiting bodies were still higher than the MRL establishedby European Union and China in edible fungi. Most of the terminal residue concentrationlevels of lambda-cyhalothrin, beta-cypermethrin and deltamethrin are below0.5mg·kg^-1which established by Japan after PHI of5and7days. All of the samples after PHI of3days or applied bifenthrin were overtop MRL in China, EU and Japan. This resultsuggested that it was not safe to harvest3days after applying or applied bifenthrin at thetwo dosages. The dosage of application and harvest interval should be controlled in orderto make it safer.7. Influence on pyrethroid residues in Auricularia polytricha by different dryingtreatmentsThe drying process will break down most of the porphyrin, and can prevent freshAuricularia polytricha being mildewy and rotten, thus extend the storage time of theAuricularia. The influence on pyrethroid residues in Auricularia polytricha by differentdrying measures was studied. The results showed that the processing of dried withsunshine had a good effect on residues’ removing of selected pyrethroid pesticides inAuricularia polytricha, the degradation rate of low and high concentration of pyrethroidswas from26.02%to51.25%and from27.78%to46.76%, respectively; the processing ofoven dried had an inferior effect on residues’ removing of selected pyrethroid pesticides inAuricularia polytricha, the degradation rate of low and high concentration of pyrethroidswas from9.30%to23.76%, and from9.72%to24.82%., respectively. The residuesdigestion rate of different pyrethroid pesticides was different due to their physical andchemical properties （such as melting point, vapor pressure, light stability, solubility, etc.）and the residual location factors. This is obviously that the degradation of the sun-driedtreatment was higher than the oven drying process, this was due to the Illuminationaccelerates the rate of photolys and the higher surface temperature acceleratedtranspiration, and the processing time is longer （3d）; Oven drying was processing in a darkand sealed dry blast oven under50℃conditions for6h, therefore reduce the degradationrate. 8. Influence on pyrethroid residues in Auricularia polytricha with different storagemethodsThe impact on pyrethroid residues in Auricularia polytricha with different storagemethods was studied. It can be seen that the low-temperature preservation had a tiny effecton residues’ removing of selected pyrethroid pesticides in Auricularia polytricha, thedegradation rate of low and high concentration of pyrethroids was from13.8%to19.23%and from13.54%to18.52%, respectively; the conventional storage had a small effect onthe residues’ removing of selected pyrethroid pesticides in Auricularia polytricha, thedegradation rate was only25.19%⁴0.17%after150d. The low temperature, dark, dry andsealed conditions will slow down the degradation rate of the pyrethroid pesticides, a largenumber of studies have reported this phenomenon, too.9. The influence on pyrethroid residues in Auricularia polytricha with differentsoaking methodsThe influence on pyrethroid residues in Auricularia polytricha with different soakingmethods was studied. The results showed that soaking had a good effect on residues’removing of selected pyrethroid pesticides in Auricularia polytricha. While the soakingtime was60min and the temperature was17℃，the residues’ removing rate of selectedpyrethroid pesticides could basically reached50%and even more higher as temperatureswent up, times went on and water changed.Added salt （NaCl）, acetic acid （C₂H₄O₂） and baking soda （NaHCO₃） to formulate intodifferent concentrations （0.1%,0.2%,0.3%,0.4%,0.5%） of salt, acid and alkali aqueoussolutions, the removal rate of selected pyrethroids in Auricularia polytricha was high bytreating in these three solutions, the removal rates of three treatments were20.73%⁶2.58%,29.51%⁵0.65%,19.08%⁸2.98%. With concentrations increased, theremoval rates of NaCl group had a downward trend. However the removal rates of C₂H₄O₂and NaHCO₃groups had an upward trend. Wherein, the removal rates of NaHCO₃groupwas the best, due to pyrethroid was unstable under alkaline conditions.