【作者】 沈燕；

【导师】 封超年；

【作者基本信息】 扬州大学 ， 农产品安全与环境， 2007， 博士

【摘要】 本研究于2003~2006年,在对江苏省小麦生产区农药残留调查分析的基础上,于扬州大学江苏省作物遗传生理重点实验室试验场进行了小麦开花灌浆期使用多菌灵、乐果、毒死蜱和吡虫啉防治小麦赤霉病、麦蚜、灰飞虱等病虫害的试验。较系统地研究了上述农药在植株不同部位及土壤中的残留特性;探明了不同杀虫剂在小麦上的降解机制;研究了大田可操作的栽培农艺降解措施;结合农药残留特性提出了麦田防治病虫兼治灰飞虱的综合防治策略及其理论依据。研究主要结论如下:(1)江苏省中弱筋小麦生产区农药残留的调查分析表明,小麦籽粒和土壤有机磷农药检出率分别为95.2%和100%,农药残留状况比较普遍;中等毒性有机磷农药毒死蜱和乐果在苏中地区普遍存在,里下河优质中筋小麦区个别点毒死蜱超出国标(GB16333-1996),沿海南部和丘陵饼干糕点小麦亚区个别点乐果超出国标(GB5127-1998),此现状有待缓解,但建立无公害优质专用小麦生产体系有一定基础;高沙土优质酥性饼干、糕点小麦亚区均未检出是优质专用型弱筋小麦的安全生产区。(2)较系统地明确了常用杀虫剂乐果、毒死蜱和吡虫啉在小麦不同部位的残留特性及其差异。杀虫剂乐果、毒死蜱和吡虫啉喷施后,随时间的推移在穗部、叶片和茎鞘上的农药残留均呈下降趋势。乐果和毒死蜱喷施初期,残留下降的幅度不受植株部位不同的限制,在不同部位的降解具有同步性;吡虫啉残留与乐果和毒死蜱有所不同,在穗部和叶片上的下降幅度大于茎鞘,在不同部位的降解属异步性。说明吡虫啉降解的主要影响因子与乐果和毒死蜱不同。小麦地上部不同部位乐果、毒死蜱和吡虫啉的残留降解趋势采用一级反应动力学方程Ct=C0e-KT( T为施药后天数/d;Ct为时间T时的农药残留量/mg·kg-1;K为消解速率常数)来拟合,拟合度均达到显著或极显著水平。乐果的降解半衰期范围在1.23~4.75d,毒死蜱的降解半衰期范围在1.17~3.36d,吡虫啉的降解半衰期范围在1.33~5.78d,半衰期与农药剂量相关性不显著。乐果、毒死蜱和吡虫啉在小麦植株上降解的快慢主要由喷药后3天内的降解速率决定,且与喷药期有一定关系。喷药时期较早的处理药后3d的降解速率小于药后1d,但花后35天处理的乐果、毒死蜱和吡虫啉降解速率药后3d略大于药后1d,可能此时植株已比较老化,该时期喷施的乐果、毒死蜱和吡虫啉更长时间的分布于植株外部,极少被株体吸收,受环境影响更大。小麦成熟期乐果、毒死蜱的残留主要分布在籽粒中的麸皮、以及颖壳和土壤里。在只喷施一次的情况下,小麦收获10天之前大田喷施推荐剂量和加倍剂量的乐果和毒死蜱,收获籽粒符合国家标准(GB5127-1998;GB16333-1996)。且籽粒中乐果、毒死蜱经过磨粉加工过程,麸皮被分离还会去除大量的残留乐果,提高了面粉食用的安全性。但乐果喷施时间越早,进入面粉内部的可能性越大。在本试验范围内,收获期小麦植株的各部位均未检出吡虫啉。小麦开花后喷施乐果、毒死蜱和吡虫啉行间土的残留均呈下降趋势,残留降解趋势亦可用一级反应动力学方程Ct=C0e-KT来拟合,达到显著或极显著水平。乐果和毒死蜱在小麦根际土中的残留呈先上升后下降的趋势,下降速度大于行间土。毒死蜱喷药后1天根际土中的残留浓度占行间土的百分比与乐果喷药后3天的残留浓度占行间土的百分比相当,说明毒死蜱在土壤中的渗透性要比乐果强。农药残留特性进行比较,乐果和毒死蜱的降解半衰期长短顺序为土壤>穗>茎鞘≥叶片,穗、茎鞘和叶片的差异前期大于后期;吡虫啉的降解半衰期长短顺序为土壤>茎鞘>叶片≈穗。(3)较系统地明确了小麦常用杀菌剂多菌灵在植株不同部位的残留特性及其差异。小麦收获期多菌灵在籽粒、穗、叶片和茎鞘上的残留浓度基本规律是用药剂量高,最终残留量也相对较高。多菌灵的残留主要在叶片、颖壳和穗轴,籽粒和茎鞘中均未检出。多菌灵在小麦穗部、叶片和茎鞘上的降解符合一级化学反应动力学方程Ct=C0e-kt。不同器官在喷药初期的初始沉积量不同,表现为穗>叶片>茎鞘;各部位的降解动态表现为随生育进程,残留量逐渐下降,至成熟期降至最低,各器官趋势一致,且前期降解速率较快,后期速率减缓。不同器官中多菌灵降解的半衰期不同,表现为穗部的半衰期短于叶片和茎鞘,穗部的降解较快,可能与穗部位处植株最上层受光性好于叶片和茎鞘有关,且多菌灵在小麦上主要是光解和雨水淋溶。两年的降解方程系数及半衰期不一致,这主要与生长条件不同有关。吡虫啉、毒死蜱分别与多菌灵混合施用后对多菌灵残留产生影响:吡虫啉使多菌灵的降解半衰期延长,毒死蜱使多菌灵的降解半衰期缩短。在植株的不同部位结果一致,且在穗部的影响更大,可能进一步说明光解是多菌灵在小麦植株中降解的主要方式。按本试验的处理方法,成熟期籽粒中的多菌灵残留量均低于0.5mg/kg的国家标准(GB 14870-1994)。(4)探索了参试农药在小麦上可能的降解途径。喷施不同农药后,穗部乐果和毒死蜱初始沉积量的主要影响因子是气温和穗鲜重,吡虫啉的主要影响因子是穗鲜重,气温对吡虫啉在穗部的初始沉积量没有影响;气温、叶片鲜重和风速是乐果在小麦叶片上初始沉积量的主要影响因子,毒死蜱在叶片上初始沉积量的影响因子主要是气温和叶片鲜重;吡虫啉的叶片上初始沉积量的影响因子是叶片鲜重,气象因子中气温、风速等没有影响。而茎鞘各农药的初始沉积量的主要影响因子均为茎鞘鲜重。乐果和毒死蜱降解初期的主要影响因子是气温,因气温主要对农药的挥发速率起作用,说明乐果和毒死蜱在降解初期,可能主要是挥发作用使植株上残留减少,但气温对土壤中的残留降解影响不显著。由于小麦地上部不同器官的温度相同,挥发作用是乐果和毒死蜱在各部位初期的降解具有同步性的主要原因。小麦穗和叶片中的吡虫啉降解主要影响因子是日照时数,但日照时数对茎鞘中的吡虫啉降解影响不显著,可能茎鞘的受光性不如穗和叶片是吡虫啉在小麦不同部位降解异步性的主要原因,同时说明光解是吡虫啉在小麦植株上初期的主要降解方式。(5)研究了可实际操作的大田栽培农艺降解措施。叶面喷施化学物质对农药的降解以喷洒碱性的NaOH和Na2CO3对乐果、毒死蜱和吡虫啉的降解效果达到显著水平,微酸性的KH2PO4和中性的NaCl溶液对乐果、毒死蜱和吡虫啉的降解几乎没有效果,说明碱性溶液可加速这三种农药的降解,但应注意在碱性土壤上不宜使用。丙酮和NaOH对麸皮中的多菌灵有显著降解效果,核黄素和氯化铁对颖壳中的多菌灵有显著降解效果,但丙酮属于有机溶剂,易燃易爆不安全,对多菌灵虽有较好的降解效果,但多菌灵属于低毒低残留药剂,因此不建议丙酮作降解剂使用。施用氮肥和钾肥对农药的降解效果为,有机肥好于尿素和碳铵,草木灰好于KCl和K2CO3处理。可能由于有机肥改善了微生物生长环境,促进了农药的降解。(6)提出了麦田防治病虫兼治灰飞虱的综合防治策略及其理论依据。小麦开花期喷施多菌灵、花后7天喷施毒死蜱和乐果均能导致花后27天灰飞虱虫口密度显著增加。经相关分析,麦田灰飞虱虫口密度与小麦叶片、穗中游离氨基酸含量、还原糖含量和蔗糖转化酶(Invertase, Inv)活性呈正相关,与小麦叶片中酚含量和多酚氧化酶(Polyphenol oxidase, PPO)活性呈负相关。与对照相比,除吡虫啉和咪鲜胺外的农药处理均使小麦叶片、穗中的游离氨基酸、还原糖含量和Inv活性增加,酚含量和PPO活性降低,以多菌灵加毒死蜱处理的调控效应最大。说明农药对灰飞虱虫量的影响,可能是由于农药使小麦植株生理生化发生变化而引起。把灰飞虱虫量作为重要考虑因素,建议防治小麦赤霉病时宜轮换使用多菌灵与咪鲜胺,防治麦蚜时宜选用吡虫啉。且根据吡虫啉的残留特性,即使花后35天使用吡虫啉加倍剂量仍不会使收获的小麦籽粒残留超标,防治麦田蚜虫和灰飞虱使用吡虫啉是安全的。更多还原

【Abstract】 Pesticide residue was one of the most important factors affecting wheat hygienic quality. Wheat plant was enriched in nutriment during flowering and grain-filling period, which might result in high incidence of diseases and pests. So many kinds of fungicides and insecticides were applied to control wheat diseases and pests. While these pesticides would inevitably deposit in wheat grains, plants and soil, causing potential harm to grain hygienic quality and field environment. So it was necessary to investigate the residue characteristics and degradation mechanisms of common pesticides in wheat so as to control residues in wheat. From 2003 to 2006, based on the results of systematic investigation and analysis of pesticide residue in seven counties in Jiangsu Province, the experiments on controlling measures of carbendazim, dimethoate, chlorpyrifos and imidacloprid against wheat pests were conducted on the Experimental Farm of Jiangsu Provincial Key Lab of Crop Genetics and Physiology of Yangzhou University to investigate residue characteristics, degradation mechanism and to find some cultivation measures to degrade residue, and integrated control approach of deseases, pests and small brown planthoppers in wheat. The main results were as follows.1 The residue detection rates of seven organophosphorus pesticides in grains and soil in wheat fields in seven counties of the middle region of Jiangsu Province were 95.2% and 100%, respectively, indicating that organophosphorus pesticide residues were very common in Jiangsu Province. Chlorpyrifos and dimethoate, which were middle-poisonous organophosphorus pesticides, were common in the middle region of Jiangsu. The average concentrations of seven kinds of organophosphorus pesticides in wheat grains were lower than National Residue Standard(GB16333-1996; GB5127-1998), indicating that there was a certain foundation for establishing a good quality, special-end-use and nuisance less wheat production system in Jiangsu Province.2 The residue characteristics and their differences of dimethoate, chlorpyrifos and imidacloprid in different parts of wheat were systematicly found. Dimethoate, chlorpyrifos and imidacloprid were sprayed on wheat plants after anthesis. The detection results indicated that the residues of these three pesticides decreased in ears, leaf blades, stems and leaf sheaths of wheat. The degradation rate of dimethoate and chlorpyrifos was synchronous in different up-ground parts of wheat plants during the early period of degradation, but the degradation of imidacloprid was not synchronous, which indicated that the dominant factors of imidacloprid degradation were different from dimethoate and chlorpyrifos. Degradation of dimethoate, chlorpyrifos and imidacloprid in ears, leaf blades, stems and leaf sheaths of wheat could be expressed by first-order kinetic equation. The half-life of dimethoate, chlorpyrifos and imidacloprid in wheat were within the ranges of 1.23~4.75d, 1.17~3.36d, and 1.33~5.78d, respectively and the effect of the pesticide dosages on the half-lives of the pesticides was insignificant. The half-life had significantly positive correlation with the degradation percentage of pesticides on the 3rd day after spraying. The residues of dimethoate and chlorpyrifos were mainly in bran, glumes and soil at maturity in wheat. According to National Standard (GB 5127-1998; GB 16333-1996), grains after harvest were safe in quality if dimethoate and chlorpyrifos were spayed with a dosage less than double recommend dosage before 10th day prior to harvest. But the earlier the spray was conducted, the more the dimethoate could be detected in the flour. The residue of imidacloprid at maturity was not detected, which indicated that imidacloprid was safer than dimethoate and chlorpyrifos. Degradation of dimethoate, chlorpyrifos and imidacloprid in the soil of wheat could be described by the first-order kinetic equation, and it decreased after pesticides spay. But the residue of dimethoate and chlorpyrifos elevated first and then dropped in the rhizosphere soil. The half-lives of dimethoate and chlorpyrifos in different parts of wheat followed the order of soil>ear>stem and leaf sheath≥leaf blade, and the half-lives of imidacloprid were in the order of soil>stem and leaf sheath >leaf blade≈ear.3 Studies on the degradation and residue characteristics of carbendazim in wheat plants above ground and the effects of insecticide imidacloprid and chlorpyrifos on the residue of carbendazim showed that when more carbendazim was used, greater residue could be detected in wheat grains, ears, leaf blades, stems and leaf sheaths. The residue of carbendazim was mainly in leaf blades and ears; while in grains, stems and leaf sheaths, the residue was too low to be detected. The degradation of carbendazim in wheat ears, leaf blades, stems and leaf sheaths followed one-level dynamic equation Ct=C0e-KT. Different organs had different deposits in the early time after carbendazim was used, indicating that the deposit in ears and leaf blades was higher than in stems and leaf sheaths. The degradation dynamic of each part showed that the residue decreased along with the growing process. The lowest level was detected at the ripen stage. At the earlier stage, the degradation rate was faster, but in the latter, it became slower. The half-life of carbendazim in ears was shorter than in leaf blades, stems & sheaths. Differences in degradation equation and the half-life existed because different growth and environmental conditions between two growing seasons. When imidacloprid or chlorpyrifos was blended with carbendazim separately, both produced great effects on the residue of carbendazim. Imidacloprid lengthened the half life of carbendazim, while the chlorpyrifos made it shorter. The result in different parts of wheat plants was similar. The effects on ears were more significant. According to the treatment of this experiment, the residue of carbendazim in grains was lower than National Standard, 0.5mg.kg-1 (GB 14870-1994 in China), so grains were hygienically edible.4 Possible pathway of pesticide degradation in wheat was found. During the grain filling period after pesticides were spayed, air temperature and ear fresh weight were the two main factors influencing the initial deposition content of dimethoate and chlorpyrifos in ears. Ear fresh weight was the main factor affecting the initial deposition content of imidacloprid in ears; Air temperature, blade fresh weight and wind speed were the three main factors influencing the initial deposition content of dimethoate in leaf blades. Air temperature and leaf blade fresh weight were the two main factors influencing the initial deposition content of chlorpyrifos in leaf blades. Leaf blade fresh weight was the main factor affectingthe initial deposition content of imidacloprid in leaf blades. For these three pesticides, stem and leaf sheath fresh weight was the main factor influencing the initial deposition content in stems and sheaths. During the early degradation period, air temperature was the main factor influencing the degradation speed of dimethoate and chlorpyrifos, and air temperature mainly impacted the volatilization rate of pesticides. Probably the decreased concentration of dimethoate and chlorpyrifos at the earlier stage was mainly caused by volatilization rather than degradation. Sunshine duration was the main factor influencing imidacloprid degradation, but it was not a significant impact on the imidacloprid degradation in stems and sheathes. Perhaps it was related to light distribution. Photodegradation might be a pathway of imidacloprid degradation at the earlier stage after spraying.5 Spraying NaOH and Na2CO3 (alkaline) in wheat field could significantly degrade the residue of dimethoate, chlorpyrifos and imidacloprid, but spraying KH2PO4 (acid) and NaCl (neutral) solution did not have significant impacts on the degradation of the three pesticides. Acetone and NaOH could significantly degrade the residue of carbendazim in wheat bran. Riboflavin and FeCl3 could significantly degradethe residue of carbendazim in wheat glumes. Compared with urea and ammonium, organic fertilizer was better in degrading pesticide. In contrast to KCl and K2CO3, plant ash was more efficient in the degradation.6 Carbendazim, chlorpyrifos and dimethoate were observed to have boosted the population of samll brown planthopper (Laodelphax striatellus Fallén) on the 20th day after sparying. The population density of small brown planthoppers in plots treated with chlorpyrifos or chlorpyrifos and carbendazim were 255.2% or 425.6% higher than the control, respectively. Free amino acid, deoxidized sugar, total phenolic content, invertase (Inv.), polyphenol oxidase (PPO) activity in leaf blades and ears of wheat were investigated on the 27th day after anthesis. The results showed that compared with the control, all pesticide treatments except imidacloprid and prochloraz caused increment of free amino acid, deoxidized sugar content and Inv activity, and decrement of total phenolic content and PPO activity in leaf blades and ears in wheat. Of all the treatments, chlorpyrifos plus carbendazim treatment was the most serious. Results from correlation analysis showed that the population density of small brown planthoppers were positively correlated to free amino acid, deoxidized sugar content and Inv activity in leaf blades and ears in wheat, and negatively correlated to total phenolic content and PPO activity in leaf blades in wheat, suggesting that the influence of pesticides on the small brown planthoppers might be the results of physiological and biochemical changes in wheat plants. Given the population density of small brown planthoppers, it was suggested that carbendazim and prochloraz were applied alternately to control wheat scab, and that imidacloprid were applied to control wheat aphids.更多还原