【作者】 逯忠斌；

【导师】 袁星；

【作者基本信息】 东北师范大学 ， 环境科学， 2011， 博士

【摘要】 HW-02是华中师范大学农药化学研究所开发的有机磷类除草剂,可用于玉米田和草坪防除阔叶杂草。本文对HW-02的环境行为进行较为系统的研究,包括HW-02的土壤吸附规律,光解、水解速率和降解机理,HW-02对土壤中4种酶活性的影响,建立了玉米籽粒中HW-02的残留分析方法,进行了最终残留量测定,并对MRL进行了安全风险评估。具体研究结果如下:1.不同类型土壤对HW-02的吸附规律选取草甸黑土、盐化潮土、黄棕壤、白浆土和黑钙土5种不同类型的土壤,采用经典的振荡平衡法进行吸附性研究,结果表明,HW-02在5种土壤中的吸附速率较快,3-5 h后基本达到吸附平衡,其吸附特性均可用Freundlich方程描述;5种土壤的吸附能力为草甸黑土>盐化潮土>黑钙土>黄棕壤>白浆土,吸附自由能为-22.25--28.57 (kJ/mol),说明HW-02在土壤中的吸附以物理吸附为主。HW-02在土壤上的吸附能力与土壤有机质含量具有明显的相关性,而与土壤pH和阳离子交换量(CEC)相关性不显著,但二因子组合与KF的相关性较好。实验结果总体表明,HW-02在5种不同类型土壤中的吸附能力为中等至较强,反之其在土壤中的淋溶性为较弱至中等。2. HW-02在不同有机溶剂中的光解进行了HW-02在4种有机溶剂中的光降解实验,用GC-MS对HW-02母体化合物的光解速率进行测定,并对其光解产物进行分离和鉴定,结果表明,HW-02在4种有机溶剂中的光解反应均符合一级动力学规律,在强度为1.641×105 lux紫外光下照射40 min,HW-02在4种溶剂中的降解顺序为正己烷>甲醇>二甲苯>丙酮,降解速率分别为99.3%、72.72%、54.4%和42.9%,光解半衰期分别为11.72,21.74,30.27和39.40 min,说明HW-02在4种溶剂中的光解速度具有较大差异,原因是4种有机溶剂对紫外光的吸收强度差异所致,综合比较,HW-02在4种有机溶剂中的光解速率均较快。利用GC-MS技术鉴定了紫外光照射下HW-02在有机溶剂中的光降解产物,鉴定出主要8种光解产物,根据HW-02母体及其光降解产物的结构特征,可以看出在光解过程中发生了三种不同的反应:一是酯键断裂,二是脱氯反应,三是酯化反应。其光降解机理包括了光水解、光还原和酯化作用三种反应机制。研究中还发现HW-02的中间光解产物还可以进一步光解,并不产生积累,最终可能矿化成磷酸和碳氧化物。3. HW-02在不同条件下的水解用GC-MS测定了HW-02在不同缓冲溶液、不同温度、不同来源水体条件下的降解速率,研究结果表明,HW-02在上述条件下的水解反应均符合一级动力学规律,水解半衰期分别为0.40-167.99 h、0.81-4.08 h和5.09-6.50 h。HW-02在缓冲溶液中的水解速率随pH增加和温度的升高而加快,表现出明显的正相关,其提高幅度为5-400倍,在正常气候条件下,可推测HW-02在地表水中不会造成积累。利用GC-MS分离鉴定了不同pH的缓冲溶液中HW-02的水解产物,结果发现,在不同的缓冲溶液中,均发现了两种不同的水解产物,其浓度随着水解时间的延长而增大。与质谱库对比,确认两种产物为2,4-二氯苯氧基乙酸甲酯和2,4-二氯苯氧基乙酸。根据HW-02母体结构特点和所鉴定出的水解产物分子结构,对HW-02的水解机理进行推测,HW-02的水解是典型的双原子亲核取代反应,导致O-C键断裂,生成2,4-二氯苯氧基乙酸,再与有机磷母体结构上脱下的甲醇发生酯化反应,生成2,4-二氯苯氧基乙酸甲酯。根据HW-02水解活化能计算结果,可以判断出HW-02属于较易水解农药,不易在水域环境中长期残留,对环境影响较小。4. HW-02对土壤酶活性的影响测定了HW-02对土壤磷酸酶、脲酶、转化酶和过氧化氢酶活性的影响,结果表明, HW-02在使用后1天内,对脲酶和过氧化氢酶有激活作用,之后则表现为抑制作用; HW-02使用后1天内,对转化酶有较强的抑制作用,之后则表现为激活作用;磷酸酶则始终表现为激活作用。HW-02对土壤中4种主要酶的总体抑制率影响幅度为-33.41-43.95%,大部分都在20%以内。由此得出,HW-02对土壤中主要酶活性的影响较小。5. HW-02在玉米籽粒中最终残留量测定与安全风险评估本文建立了HW-02在玉米籽粒中最终残留量的气相色谱分析方法,该方法具有准确度高,重现性好,提取与净化简单等特点。用此方法测定了经两年田间试验所采集的玉米籽粒样本,提出了HW-02在玉米籽粒中MRL为0.25 mg/kg的建议,并对此建议值进行了安全风险评估。评估结果表明,HW-02在450-900 g a.i/hm2用量下所制定的MRL是安全的。更多还原

【Abstract】 HW-02 is an organic phosphorus herbicide invented by Institute of Pesticide Chemistry, Central China Normal University, can be used to control broad-leaved weeds in corn field and lawn. The environmental behavior of HW-02 was systemically investigated in this dissertation, including the soil adsorption of HW-02, photolysis, hydrolysis, the degradation mechanism and the effect of HW-02 on four enzymes. In addition, the analysis method for HW-02 residue in maize grain was established, and the determination of the final residue and the risk assessment of MRL were conducted. The detailed results can be seen as follows:1. Absorption of HW-02 on different types of soilThe absorption of HW-02 on five types of soil (i.e. meadow black, sandy loam, clay loam, baijiang soil and chernozem) was investigated by the method of the classical oscillation balance. The results indicated that the absorption of HW-02 on all five types of soil followed Freundlich equation. The absorption velocity was rapid. The absorption balance could be reached in 3-5 h. The absorption capability of these five soils was meadow black>sandy loam> chernozem>clay loam>baijiang soil. The absorption free energy was -22.25--28.57 (kJ/mol). This indicated that the absorption of HW-02 in soil was mainly physical adsorption. The absorption capability of HW-02 on soil was significant correlative with the content of soil organic matter, but little correlation with soil pH and cation exchange capacity was observed. All the results above showed that the absorption capability of HW-02 on these five soils was from medium to relatively strong. Contrarily, the eluviation of HW-02 in soil was from relatively weak to medium.2. Photolysis of HW-02 in different organic solventsThe photolysis of HW-02 in four organic solvents was conducted, and the photolysis velocity of HW-02 matrix compound was determined by using GC-MS. The photolytic products were separated and analyzed, too. The results indicated that the photolysis of HW-02 in all four organic solvents followed the first order kinetics. After 40 min UV illumination (1.641×10~5 lux), the photolysis velocity was n-hexane > methanol > xylene>acetone in these four organic solvents, the photolysis rate were 99.3%,72.72%, 54.4% and 42.9%,the half life were 11.72,21.74,30.27 and 39.40 min, respectively. This indicated that the photolysis velocity of HW-02 in these four organic solvents varied greatly, which was due to the different UV light adsorption in these four organic solvents. Anyhow, the photolysis of HW-02 in these four organic solvents could be conducted rapidly. Under UV light, HW-02 could be photolyzed in organic solvents and eight photolytic products were identified by GC-MS. According to the HW-02 matrix and the photolytic products, it could be seen that three different reactions occurred in the photolytic processes: (i) ester bond cleavage, (ii) dechlorination and (iii) esterification reaction. The photolysis mechanism included photo-hydrolysis, photoreduction and esterification. Additionally, the Intermediate product of photolysis could photolyze further and did not accumulate. Phosphate and carbon oxides might be the final products.3. The hydrolysis of HW-02The hydrolysis rate of HW-02 was tested by GC-MS under the condition of different buffer, temperature and water. The result indicated that the hydrolysis of HW-02 followed the first order kinetics. The half lifes were 0.40-167.99 h、0.81-4.08 h和5.09-6.50 h, respectively. The hydrolysis rate in buffer was enhanced with the increasing of pH value. The range was 5-400 times than control. In general conditions, HW-02 will not accumulated in water. The products of HW-02 hydrolysis indicated in different buffer were also different. The result indicated that the products were different in different buffers. The concentrations were increased with the extending of hydrolysis time. The two products were 2,4 -dichlorophenoxyacetic acid methyl ester and 2,4-dichlorophenoxy acetic acid. The hydrolysis reaction mechanism was the typical nucleophilic substitution, dued to the C-O bond cleavage and formed 2,4-dichlorophenoxy acetic acid. Since the composition of HW-02 were bridged by organophosphates and phenoxyacetate, the C-O bond cleavage could also formed 2,4-dichlorophenoxy acetic acid. The 2,4 -dichlorophenoxyacetic acid methyl ester was formed by esterification with methanol. The result also indicated that HW-02 was easier to hydrolysis and will not residue for long in aquatic environment. The influence of HW-02 to the environment was small.4. The influence of HW-02 on the enzyme activityThese studies test the enzyme activity of phosphatase, urease, catalase and invertase. After the usage of HW-02, the soil urease and catalase activity were stimulated at first and were inhibited in the end. The invertase was inhibited after useage and was stimulated after that. The phosphatase was stimulated. The inhibition rate of HW-02 on the soil enzyme was -33.41-43.95%, most of them were under 20%. The result indicated that the influence of HW-02 on soil enzyme was low.5. The residue levels and risk assessment of HW-02 in cornThe study established the analytical method of HW-02 in maize kernel. This method has the characteristics of high accuracy, good reproducibility and easier to extraction and purification. This method was tested maize kernels for two years field experiment. The result suggested that the MRL of HW-02 in maize kernel was 0.25mg/kg and the risk assessment were also done. The result was that the MRL was safe when the usage of HW-02 under the dosage of 450-900 g a.i/hm ~2.更多还原