Determination of ethylenethiourea in grapes and wine

Residues of ethylenethiourea (ETU) in grapes and wine were determined by capillary gas chromatography and paper chromatography, without a cleanup step, and after derivatization to S-benzyl-ETU. The detection limit was 0.0002 mg/kg for flame ionization detection, 0.008 mg/kg for paper chromatography with photodensitometric evaluation of the detected spot. Results were compared with a generally used GC method specifying electron capture detection of trifluoroacetylated S-benzyl-ETU. The recoveries of ETU in grapes and wine at different concentration levels were determined. ETU residues were determined in treated grapes but no residues were detected in wine.     

氰霜唑的光降解研究

采用高效液相色谱法研究了10％氰霜唑悬浮剂在自然光照和黑暗条件下,在水溶液中和黄瓜植株叶片上的消解动态。结果表明,在自然光照下氰霜唑在黄瓜植株叶片上消解的半衰期为63．6h,而黑暗处理下消解不明显。在室内试验条件下,研究了不同pH值、温度、光源和光强等因子对氰霜唑光降解的影响：在pH值分别为4．96、7．02、9．56缓冲溶液中,其半衰期分别为167．7、102．4和64．0min,光解速率随着pH值升高而加快;在pH值为4．96的缓冲溶液中,在15℃、25℃和35℃时,其光解半衰期为368．7、167．7和112．5min。在3700、7600和12300 lx的模拟自然光（氙灯）光强下,其半衰期分别为962．7、167．7和120．1min,说明氰霜唑的降解速率与光强和温度呈正相关关系。氰霜唑在pH值为4．96的缓冲溶液在紫外光（254nm）下的半衰期为53．5min。     

苹果中乙撑硫脲膳食摄入风险的非参数概率评估

为明确国产苹果中乙撑硫脲残留水平及量化中国居民乙撑硫脲膳食摄入风险。基于渤海湾(辽宁、山东、河北)和西北黄土高原(陕西、山西、河南)两大苹果优势主产区采集的282份苹果样品,运用专业风险评估软件@Risk,尝试构建非参数概率评估模型,对中国居民乙撑硫脲膳食摄入风险进行概率评估。结果表明:参试的282份苹果样品,乙撑硫脲检出率为80.9%,残留量均值为6.1μg/kg,最高残留量为74.1μg/kg,绝大多数苹果样品(占90.4%)乙撑硫脲残留量10.0μg/kg。282份苹果样品中乙撑硫脲残留量的离散程度较大(变异系数达134.6%),不同省份变异系数排序,陕西(150.7%)辽宁(146.8%)河北(91.2%)山东(88.1%)河南(54.9%)山西(51.8%)。不同年龄组人群膳食摄入风险存在明显差异,幼儿(2~6岁)和儿童(7~13岁)乙撑硫脲膳食摄入风险均明显高于青少年(14~17岁)和成年(18~59岁),为重点监控对象。总体而言,不同年龄组人群乙撑硫脲膳食摄入风险均很低,其中慢性膳食摄入风险介于0.35%~13.12%,急性膳食摄入风险介于0.22%~3.94%,均远低于100%;不同省份和不同主产区苹果乙撑硫脲膳食摄入风险虽存在明显差异,但均远低于100%,不同省份和不同主产区苹果乙撑硫脲膳食摄入风险也是可以接受的。基于最大残留限量估计值(estimate maximum residue limit,e MRL),建议中国苹果中乙撑硫脲最大残留限量值设为0.2 mg/kg。本研究可为苹果质量安全监管和今后系统开展果品质量安全风险评估提供有益借鉴和参考。     

Liquid chromatographic-electrochemical determination of ethylenethiourea in foods by revised official method

AOAC official method 29.119-29.125 was revised to determine ethylenethiourea (ETU) directly by a liquid chromatographic-electrochemical (LC-EC) determinative technique and to improve ETU recovery. ETU is extracted from food products with a methanol-aqueous sodium acetate solution. A portion of the concentrated filtrate is added to a column of diatomaceous earth, and ETU is eluted with 2% methanol in methylene chloride to separate it from food coextractives, which are retained on the column. The eluate is collected in a siliconized flask and evaporated, the residue is dissolved in water, and 20 microL of solution is injected onto an LC graphitized carbon column. ETU is eluted from the LC column with a mobile phase of acetonitrile-aqueous 0.1M phosphoric acid-water (5 + 25 + 70), and the eluted ETU is detected by using an amperometric electrochemical detector equipped with a gold/mercury working electrode. Recovery data were obtained by fortifying 13 food products with ETU: baked potatoes; canned applesauce, mushrooms, creamed spinach, green beans, spinach, and tomatoes; cooked fresh cabbage and frozen collards; fresh celery and lettuce; grape jelly; and powdered sugar cake donuts. Raw celery was found to cause low ETU recoveries. Average percent recoveries of ETU from the other 12 food products were 92 with a standard deviation of 12 for the low (0.05 and 0.1 ppm) fortification levels and 90 with a standard deviation of 6 for the higher (0.5 and 1 ppm) fortification levels. The limits of quantitation were 0.01 and 0.02 ppm for food products with low and high sugar content, respectively.     

2,4-D丁酯的水解与光解特性研究

通过室内模拟试验,研究2,4-D丁酯在不同pH值和温度下的水解动态和在有机溶剂中的光解特性。结果表明,2,4-D丁酯的水解与光解均符合一级动力学方程。在pH7以下的缓冲溶液中,2,4-D丁酯的水解反应十分缓慢,但在碱性溶液中其水解速率加快。25℃下2,4-D丁酯在pH5、7和9的缓冲溶液中的水解半衰期分别为23.5、5.8d和10.7min。2,4-D丁酯的水解速率随温度升高而增加,在温度为15、25℃和35℃的pH7缓冲溶液中的水解半衰期分别为21.5、5.8、3.9d,平均温度效应系数为2.57。2,4-D丁酯水解反应的活化能与温度之间无明显相关性,而活化熵与温度呈显著相关性。2,4-D丁酯的水解主要由活化熵所驱动。采用GC-MS技术对2,4-D丁酯水解产物进行鉴定,确定水解产物主要是2,4-二氯苯氧乙酸和2,4-二氯苯酚。2,4-D丁酯在正己烷中光解速率比在甲醇中快,在丙酮中几乎不发生光解,其光解速率随浓度的升高而减慢。     

Photolysis experiments on phosmet, an organophosphorus insecticide

The organophosphorus insecticide phosmet is used in plant protection as well as against parasites on animals. Phosmet showed numerous photoinduced reaction pathways, which first were studied in the presence of model environments for animal fur lipids (e.g., wool wax). The model solvents for saturated and unsaturated lipids were cyclohexane and cyclohexene, whereas methanol and 2-propanol were used as models for primary and secondary alcohol moieties of lipids. The measured degradation rates over an irradiation period of 7 h in all solvents used were very similar (49-55%). The obtained photoproducts generally included phthalimide, N-hydroxymethylphthalimide, and N-methoxymethylphthalimide. Furthermore, depending on the solvent used, additional degradation products were detectable as N-isopropoxy- and N-methylphthalimide in the presence of 2-propanol and cyclohexene, respectively. However, in the presence of cyclohexene, despite the similar turnover, distinctly lower concentrations of photoproducts were found, indicating further still unknown degradation pathways. Irradiations in methanol with increasing percentages of water led to higher degradation rates; however, the products were found to be the same. Irradiation experiments with pure phosmet on silica TLC plates and glass surfaces resulted in degradation rates of 19 and 32%, respectively, after 6 h. The results obtained clearly demonstrate for the first time that the photoinduced degradation of phosmet is strongly dependent on the chemical environment, affecting less the turnover than the photoproducts formed. The results additionally demonstrate the need to investigate the degradation behavior of phosmet on wool and in the presence of wool wax.     

Formation and decay of ethylenethiourea (ETU) in soil and water under tropical conditions

Mancozeb is a fungicide frequently used in tropical countries. It rapidly decomposes into ethylenethiourea (ETU), a more stable and toxic metabolite than mancozeb that is, therefore, regarded as a pollutant of concern. The objective was to study ETU formation and decay kinetics in soil and water under tropical conditions in order to assess its potential for accumulation. Batch experiments, spiked with either mancozeb or ETU, were carried out under natural (= active) as well as tyndallized conditions. In active soils, dissipation of ETU occurred significantly faster (half‐life 1.5 h) than in tyndallized soils (half‐life time 28 h). In water under natural and sterile conditions, decay was slower than in soils with an ETU half‐life time of 115 and 99 h, respectively. Microbial activity was seen to play an important role in ETU dissipation in soil. However, in water nonbiological processes seem to be more important in the breakdown of the molecule, with hydrolysis being the most probable decay mechanism. Decay of both mancozeb and ETU was found to occur more rapidly than previously reported. The high humidity and temperatures under the simulated humid tropical conditions, and higher microbial activity, lead to more rapid decay of these molecules than under other conditions. Nevertheless, a concentration of 1.29 mg ETU L^–1 was still observed 8 d after adding mancozeb (20.83 mg L^–1) to water under humid tropical conditions. These results suggest that, in comparable regions in the humid tropics, it is unlikely that ETU would accumulate in soil but it represents a potential risk for accumulation in water bodies.