Metabolism of niclosamide in sediment and water systems

A series of experiments analyzed the kinetics and mechanisms of [(14)C]niclosamide degradation. The aerobic aquatic metabolism of [(14)C]niclosamide was studied in nonsterile river water/sediment mixtures. Test systems, maintained under aerobic conditions, were treated with niclosamide and incubated in the dark at 25.0 +/- 1.0 degrees C for 30 days. Half-lives of 4.9 and 5.4 days were calculated for the chlorosalicylic acid- and chloronitroaniline-labeled test systems, respectively. From 0 to 21 days after treatment (DAT), the only metabolism product observed in either test system was aminoniclosamide. At the final sampling interval, five peaks were resolved from the chlorosalicylic acid label, and three peaks were resolved from the chloronitroaniline label test substance. By 30 DAT, sediment-bound residues represented approximately 70% of the observed radioactivity. For the anaerobic aquatic metabolism of [(14)C]niclosamide, test systems were incubated under anaerobic conditions for 365 days. Half-lives of 0.65 day for the chlorosalicylic acid label and 2.79 days for the chloronitroaniline label were calculated. From 0 to 3 DAT, niclosamide was first transformed into aminoniclosamide. Aminoniclosamide is readily formed, as it was observed in the chlorosalicylic acid label 0 DAT sampling. Several minor metabolites were observed in the water and sediment extracts. None of these metabolites were formed to a significant amount until the parent niclosamide dissipated below the detection limit. Two of the byproducts from these metabolism studies are polar unknowns eluting at 3 and 5 min by HPLC, similar to the unknowns observed in aqueous photolysis studies.     

Fate of 14C-carbofuran in soils

The degradation of¹⁴ C-Carbofuran was studied in sterilized, unsterilized and green manure amended clay soil under moist and flooded conditions overa period of 30 days. The¹⁴ C mass balance showed that carbofuran did not undergo any degradation in sterilized moist soil. In sterilized flooded soil bound residues were formed to the extent of about 47% of the applied radioactivity at the end of 30 days. Carbofuran underwent considerable degradation in unsterilized moist and flooded soils. In moist soil about 48% of the applied¹⁴ C activity was recovered as bound activity while in flooded soil, about 23% of the activity was bound. Green manure amendment resulted in formation of more bound residues under moist conditions while it enhanced the degradation of carbofuran under flooded conditions. In flooded amended soil about 44% of the applied^l4 C-activity was recovered as against about 54% in the unamended flooded soil. The notable degradation products formed under flooded soil conditions were 3-keto carbofuran and 3-hydroxy carbofuran.     

蒸发条件下粘土层对土壤水和溶质运移影响的模拟

以土壤水和溶质运移的动力学原理为基础 ,采用数值模拟方法 ,研究了在浅层地下水和蒸发条件下含有粘土层土壤的水和Cl-的运移状况 ,重点探讨了两种粘土的层位和层厚对水和Cl-运移影响的差别及原因。研究结果表明 ,粘土层对土壤的水和溶质运移影响的程度 ,与层状土壤中该粘土及其组合土壤的水力学性质有关。本文模拟的重粘土 (简称Y粘土 )与轻壤土所组成的层状土壤 ,其基本情况为 ,随粘土层层位的升高和层厚加大 ,土壤水分蒸发和地下水补给速率降低 ,Cl-积累减少。而轻粘土 (简称R粘土 )与轻壤土所组成的层状土壤 ,由于它们的导水率曲线在压力水头h约 - 10 0 0cm处相交 ,当h低于此值时 ,R粘土的导水率就大于轻壤土的。因此 ,蒸发、补给速率和Cl-积累强度出现以顶位最高 ,甚至高于均质轻壤土 ,其次为底位 ,最低为中部层位的现象。在蒸发条件下Cl-在剖面中的积聚部位主要是土表。粘土层的存在 ,起到了阻滞作用 ,而阻滞程度则与该粘土水力学性质、层位、厚度和地下水埋深有关     

Soil metabolism of a new herbicide, [14C]Pyribenzoxim, under flooded conditions

To elucidate the fate of a new pyrimidinyloxybenzoic herbicide, pyribenzoxim, a soil metabolism study was carried out with [14C]pyribenzoxim applied to a sandy loam soil under flooded conditions. The material balance of applied radioactivity ranged from 96.4 to 104.4% and from 96.1 to 101.9% for nonsterile and sterile soils, respectively. The half-life of [14C]pyribenzoxim was calculated to be approximately 1.3 and 9.4 days for nonsterile and sterile soils, respectively. The metabolites identified during the study were 2,6-bis(4,6-dimethoxypyrimidin-2-yloxy)benzoic acid (M1) and 2-hydroxy-6-(4,6-dimethoxypyrimidin-2-yloxy)benzoic acid (M2), resulting from the cleavage of the ester bond and subsequent hydrolysis. The nonextractable radioactivity levels increased to 37.8% for nonsterile conditions at 50 days after treatment and to 38.2% for sterile conditions at 60 days after treatment. Fractionation of the nonextractable soil residues indicated that bound radioactivity was associated mainly with humin fraction. No significant volatile products or [14C]carbon dioxide was observed during the study. On the basis of these results, pyribenzoxim is considered to undergo rapid degradation in soil by microbial and chemical reactions, mainly hydrolysis, which limits its transfer to and accumulation in lower soil layers and groundwater. Therefore, the possibility of environmental contamination from the use of pyribenzoxim is expected to be very low.     

Aerobic soil metabolism of a new herbicide,LGC-42153

To elucidate the fate of a new sulfonylurea herbicide, LGC-42153 [N-((4,6-dimethoxypyrimidin-2-yl)aminocarbonyl)-2-(1-methoxyacetoxy-2-fluoropropyl)-3-pyridinesulfonamide], in soil, an aerobic soil metabolism study was carried out for 120 days with [(14)C]LGC-42153 applied to a loamy soil. The material balance ranged from 90.7 to 101.5% of applied herbicide. The half-life of [(14)C]LGC-42153 was calculated to be approximately 9.0 days. The degradation products resulted from the cleavage of the sulfonylurea bridge. The metabolites identified during the study were N-((4,6-dimethoxypyrimidin-2-yl)aminocarbonyl)-2-(1-hydroxy-2-fluoropropyl)-3-pyridinesulfonamide, 2-(1-hydroxy-2-fluoropropyl)-3-pyridinesulfonamide, and 4,6-dimethoxy-2-aminopyrimidine. No significant volatile products or [(14)C]carbon dioxide was observed during the study. Nonextractable (14)C-residue reached 14.4-30.5% of applied material at 120 days after treatment, and radioactivity was distributed mostly in the humin and fulvic acid fractions.     

土石混合介质导气率变化特征试验

土壤中碎石的存在改变了土壤结构和孔隙分布,进而影响土壤通气性能。该文通过对碎石单粒径土石混合介质导气率变化特征研究,旨在探讨单粒径土石混合介质导气内在机理,为进一步研究复杂的野外土石混合介质的导气特性提供基础。为了研究土石混合介质中碎石对导气率的影响,该文通过试验研究,分析土壤颗粒小于2mm的样本(砂土、砂壤土、黏壤土)、碎石质量分数(10%、20%、30%、40%、50%)和碎石粒径(2～3、>3～5mm)对土石混合介质导气率的影响。结果表明:在土壤颗粒小于2mm的样本条件下,土壤导气率呈砂土>砂壤土>黏壤土;在相同碎石质量分数的土石混合介质中导气率呈砂壤土>砂土>黏壤土;碎石的存在改善黏壤土的导气性能,使黏壤土碎石混合介质的导气率大于黏壤土的导气率;降低了砂壤土和砂土的导气性能,且砂土的降低幅度远大于砂壤土;在砂壤土中碎石粒径2～3mm的导气率大于>3～5mm的导气率;在砂土中碎石质量分数30%之内,碎石粒径>3～5mm的导气率稍大于2～3mm的导气率,在40%则相反,但两种粒径下混合介质导气率差异不是很明显。     

深松耕作和秸秆还田对农田土壤物理特性的影响

[目的]为了增加中国干旱半干旱地区农田土壤蓄水保墒能力。[方法]采用野外试验和室内分析相结合的方法研究了深松和深松结合秸秆还田耕作技术对晋中北部地区两种主要类型土壤物理特性的影响。[结果]深松可以打破土壤犁底层,显著降低黏土和壤土10—30cm土层范围内的土壤容重;调节土壤孔隙度,增加了黏土10—30cm土层范围内的土壤总孔隙度、毛管孔隙度和非毛管孔隙度,同时增加壤土10—30cm土层土壤总孔隙度、毛管孔隙度和20—30cm土层土壤非毛管孔隙度;改善黏土和壤土20—30cm土层土壤固、液、气3相状况;深松结合连年秸秆还田进一步优化了壤土耕层环境,同时显著降低了玉米拔节期土壤地表结皮的厚度和紧实度。[结论]深松结合连年秸秆还田和深松耕作技术可以缓解土壤板结状况,增加降雨入渗。     

基于HYDRUS-2D模型的玉米高出苗率地下滴灌开沟播种参数优选

开沟播种是一种可显著提高地下滴灌春玉米出苗率的新型播种方式,为了优化该技术模式,该文通过两年田间试验分析了地下滴灌玉米出苗率与灌水后种子处土壤有效饱和度(effective saturation)的关系,并基于HYDRUS-2D构建了地下滴灌开沟播种土壤水分运动模型,以90%玉米出苗率为前提,研究了不同土质和土壤初始含水率条件下3个技术参数——开沟深度、滴灌带埋深和灌水量对种子处土壤有效饱和度的影响.结果表明:1)出苗率随土壤有效饱和度线性递增,土壤有效饱和度不小于0.77时,出苗率超过90%;2)地下滴灌开沟播种HYDRUS-2D模型模拟精度较高,模拟得到的土壤有效饱和度随开沟深度增大而增大,随滴灌带埋深增大而减小;3)满足土壤有效饱和度为0.77所需的出苗水灌水量随土壤黏粒含量、土壤初始含水率和开沟深度增大而减小,随滴灌带埋深增大而增大.当表层土壤初始含水率为40%田持~60%田持时,开沟深度每增加5cm,砂壤土的出苗水灌水量减小15~20mm,粉壤和粉黏土的出苗水灌水量减小6~18mm;滴灌带埋深由30cm增大到35cm时,砂壤土的出苗水灌水量增大16~21mm,粉壤和粉黏土的出苗水灌水量增大4~14mm.不同埋深和开沟深度下,当表层土壤初始含水率由40%田持增大到60%田持时,砂壤土的出苗水灌水量减小9~14mm,粉壤和粉黏土的出苗水灌水量减小9~19mm;4)综合考虑土壤质地、玉米根系分布、机械作业、耗能、耕作深度和土壤水深层渗漏以及土壤初始含水率,玉米地下滴灌适宜的滴灌带埋深为30~35cm,开沟深度为10~15cm,灌水量范围为25~67mm.农业生产者可以根据当地实际情况对以上3个技术参数进行合理配置.     

Efficiency of wheat straw mulching in reducing soil and water losses from three typical soils of the Loess Plateau,China

Mulching the soil surface with a layer of plant residue is considered an effective method of conserving water and soil because it increases water infiltration into the soil, reduces surface runoff and the soil erosion, and reduces flow velocity and the sediment carrying capacity of overland flow. However, application of plant residues increases operational costs and so optimal levels of mulch in order to prevent soil and/or water losses should be used according to the soil type and rainfall and slope conditions. In this study, the effect of wheat straw mulch rate on the total runoff and total soil losses from 60-mm simulated rainstorms was assessed for two intensive rainfalls (90 and 180 mm h⁻¹) on three slope gradients typical conditions on the Loess Plateau of China and elsewhere. For short slopes (1 m), the optimal mulch rate to save water for a silt loam and a loam soil was 0.4 kg m⁻². However, for a clay loam soil the mulch rate of 0.4 kg m⁻² would be optimal only under the 90 mm h⁻¹ rainfall; 0.8 kg m⁻² was required for the 180 mm h⁻¹. In order to save soil, a mulch rate of 0.2 kg m⁻² on the silt loam slopes prevented 60%–80% of the soil losses. For the loam soil, mulch at the rate of 0.4 kg m⁻² was essential in most cases in order to reduce soil losses substantially. For the clay loam, 0.4 kg m⁻² may be optimal under the 90 mm h⁻¹ rain, but 0.8 kg m⁻² may be required for the 180 mm h⁻¹ rainstorm. These optimal values would also need to be considered alongside other factors since the mulch may have value if used elsewhere. Hence doubling the optimal mulch rate for the silt loam soil from 0.2 kg m⁻² or the clay loam soil under 90 mm h⁻¹ rainfall from 0.4 kg m⁻² in order to achieve a further 10% reduction in soil loss needs to be assessed in that context. Therefore, Optimal mulch rate can be an effective approach to virtually reduce costs or to maximize the area that can be treated. Meantime, soil conservationist should be aware that levels of mulch for short slopes might not be suitable for long slopes.     

Kinetics of nitrification under upland and flooded soils of varying texture

Abstract

Higher rates of nitrification often reported in fine than in coarse textured soils may not be a direct effect of soil texture because in most of the earlier studies, soil water content has been usually expressed as gravimetric, volumetric or soil's water‐holding capacity without consideration of differences in density/ porosity for soils of varying texture. The same water content in texturally different soils could provide very different conditions of soil aeration and associated nitrifying activity. Effects of soil texture on nitrification was studied by incubating three semiarid subtropical soils having sandy loam, loam, and silty clay textures at 35°C for 30 days using water‐filled pore space (WFPS) as the criterion of soil aeration. Upland or aerobic soil conditions, simulated by incubating soil at 60% WFPS, exhibited very fast nitrification of added fertilizer nitrogen (N) and most of the applied 100 mg of ammonium‐nitrogen (NH₄+‐N/kg soil) was nitrified within 10 days of incubation in all three soils irrespective of the differences in texture. Under flooded soil conditions (120% WFPS), nitrification was slow and only 84 to 92% of the applied NH₄+‐N was nitrified even after 30 days. Nitrification could be described by first‐order kinetics for both the upland and flooded moisture regimes, thus nitrification rate depended upon NH₄+ concentration. At similar gravimetric water contents, rates of nitrification differed greatly in soils of varying texture, but when varying water‐holding capacity and bulk density were accounted for using WFPS, all the soils behaved similarly at 60% WFPS. Under impeded aeration (flooded conditions), however, substantial differences were observed in nitrification in soils of varying texture, the largest in fine‐textured Chamror silty clay followed by Habowal loam and the smallest in Tolewal sandy loam soil. These results illustrate the utility of WFPS, compared with soil water content, and its reliability as an indicator of aeration dependent nitrification for soils of varying texture.     

吡啶硫酮锌(ZPT)与土壤颗粒的吸附和解吸研究

吡啶硫酮锌作为一种有效的抗头皮屑剂广泛应用于洗护发产品中。在没有下水处理设施的地区,去屑洗发香波中所含有的吡啶硫酮锌随着生活排水被直接排放到河里。本文通过试验对吡啶硫酮锌在不同土质上的吸附及在黏质壤土土样的解吸进行了研究。在避光条件下,通过用紫外分光光度法测得水相中吡啶硫酮锌的质量浓度,推算出土壤中吡啶硫酮锌的含量。吸附试验结果显示:在加入有机质较高的黏质壤土样5 min、10 min、20 min和30 min后,所测得的水相吡啶硫酮锌浓度分别下降77.8%、70.9%、68.6%和82.5%;加入有机质含量低的砂质土,分别下降39.1%、52.2%、50.6%和52.1%。不论是有机碳含量高的黏质壤土,还是有机碳含量低的砂质土,吡啶硫酮锌均极易被吸附。解吸试验结果显示:经过3次水洗,ZPT的解吸量在8%~10%;在冷暗条件下,分别放置3、5、7 d后,ZPT的解吸量少于5%。试验结果说明有机碳含量高的黏质壤土土样对ZPT的解吸作用较弱。     

排土场平台-边坡系统沟蚀形态演变与产沙特征

排土场是露天采矿区主要泥沙来源的人造地貌之一,控制排土场土壤侵蚀对矿区高质量发展具有重要意义。该研究采用野外放水冲刷试验,研究排土场平台-边坡系统沟蚀演变及产沙特征。结果表明：1）沟蚀演变中的主导侵蚀方式存在阶段性转变,侵蚀沟形态发育特征也呈阶段性差异,平台侵蚀沟分为沟头形成阶段,溯源-拓宽阶段和稳定阶段3个发育演变阶段;边坡侵蚀沟依次经历覆土层下切阶段,覆土层拓宽阶段,红土层下切阶段和侵蚀减缓阶段。2）边坡是平台-边坡系统主要沙源,其累积产沙量占平台-边坡系统的88.15%～90.16%;覆土层下切阶段和红土层下切阶段是边坡的主要产沙阶段,其累积产沙量分别占边坡的29.72%～53.36%和19.06%～48.88%。3）平台和边坡侵蚀速率均与径流功率的响应关系较优,在平台沟蚀的溯源-拓宽阶段和稳定阶段为线性响应;在边坡沟蚀的覆土层下切阶段和红土层下切阶段为指数响应,拓宽阶段和侵蚀减缓阶段为线性响应。模型建立中需进一步考虑此种响应规律随沟蚀发育演变产生的变化,研究结果可为排土场水土保持措施布设和科学认识沟蚀过程与特征提供参考。     

Der Einfluß des Wassergehaltes auf den Atrazin-Abbau im Boden

The influence of water-content on atrazine degradation in soil In samples of the standard soil 2.2 (loamy sand, 3 % C, pH 7,0) and of a Luvisol (Ap-horizon, loam 1,4 % C, pH 5,2), the degradation of [ethyl-1-¹⁴C]atrazine was investigated in dependence of the soil water content. The experimental conditions were choosen in accordance with the methods proposed by the Biologische Bundesanstalt to study the degradation of pesticides in the soil. The soil water content was varied to simulate the moisture conditions observed in a soil during plant growth. Therefore, besides a steady water content of 20, 40, 60, and 80 % of the maximum water holding capacity of the soils, the soil water contents were fluctuated by 20 to 60 % of the maximum water holding capacity by passing dry air through the soil. At a concentration of 10mg atrazin/kg of soil between 4 and 6 % of the ethyl-1-carbonatom of the atrazine molecule was mineralized to CO₂ within 71 days at a constant soil temperature of 22°C. In the standard soil 2.2 the mineralization in total was reduced to 2/3 compared to the degradation in the Luvisol. With decreasing water content increasing hydroxilated metabolites were formed. About 30–40 % of the applied radioactivity was determined as non-extractable residue in the soil. In general the degradation processes were more enhanced and more intense in the Luvisol as compared to the Standard soil 2.2 which again unterlines that for this type of experiments a fresh soil should be used. In conclusion, the variation of the soil water content did not have a pronounced influence on the mineralization rates of atrazine, but did influence the metabolism and the formation of certain metabolite fractions.     

Organic carbon mineralization responses to temperature increases in subtropical paddy soils

Purpose

Understanding organic carbon mineralization and its temperature response in subtropical paddy soils is important for the regional carbon balance. There is a growing interest in factors controlling soil organic carbon (SOC) mineralization because of the potential for climate change. This study aims to test the hypothesis that soil clay content impedes SOC mineralization in subtropical paddy soils.

Materials and methods

A 160-day laboratory incubation at temperatures from 10 to 30 °C and 90% water content was conducted to examine the dynamics of SOC mineralization and its temperature response in three subtropical paddy soils with different clay contents (sandy loam, clay loam, and silty clay soils). A three-pool SOC model (active, slow, and resistant) was used to fit SOC mineralization.

Results and discussion

Total CO₂ evolved during incubation following the order of clay loam > silty clay > sandy loam. The temperature response coefficients (Q ₁₀) were 1.92?±?0.39, 2.36?±?0.22, and 2.10?±?0.70, respectively, for the sandy loam soil, clay loam soil, and silty clay soil. But the soil clay content followed the order of silty clay > clay loam > sandy loam. The sandy loam soil neither released larger amounts of CO₂ nor showed higher temperature sensitivity, as expected, even though it contains lower soil clay content among the three soils. It seems that soil clay content did not have a dominant effect which results in the difference in SOC mineralization and its temperature response in the selected three paddy soils. However, dissolved organic carbon (DOC; representing substrate availability) had a great effect. The size of the active C pool ranged from 0.11 to 3.55% of initial SOC, and it increased with increasing temperature. The silty clay soil had the smallest active C pool (1.40%) and the largest Q ₁₀ value (6.33) in the active C pool as compared with the other two soils. The mineralizable SOC protected in the silty clay soil, therefore, had even greater temperature sensitivity than the other two soils that had less SOC stabilization.

Conclusions

Our study suggests that SOC mineralization and its temperature response in subtropical paddy soils were probably not dominantly controlled by soil clay content, but the substrate availability (represented as DOC) and the specific stabilization mechanisms of SOC may have great effects.     

基于农作物长势信息的三种主要土壤属性预测——以江苏北部平原区为例

土壤属性空间分异研究是土壤调查、土壤资源利用与保护的重要依据。结合现有土壤资料和剖面数据,利用农作物长势信息探测稻—麦轮作种植的平原农区土壤属性的空间变化状况。结果表明:A1和A2区成土母质为湖相沉积物,A3区为黄淮冲积—海相沉积物,B区为黄泛冲积物。A1、A2、B2和A2与B2的过渡区土壤质地为黏土,A3和A1与B1的过渡区为黏壤土,B1区为壤土,B1与B2的过渡区为上壤下黏。A1和B1及其过渡区的地下水埋藏深度大于120 cm,A2区约70 cm,A3区约60 cm,B1与B2的过渡区约80~90 cm,B2和A2与B2的过渡区约55~70 cm。农作物长势信息可以指导中尺度平原区土壤属性空间分异规律研究,如成土母质、地下水埋藏深度和土壤质地等,将有利于提高平原区土壤调查的效率与精度。     

甘肃省不同气候类型区土壤水分特性

为揭示甘肃省不同气候区不同质地土壤的容重、田间持水量和凋萎湿度的差异,对观测资料的适用性和推广价值进行评价。通过对77个站点10—100 cm土壤水分资料的分析,结果表明:甘肃省全省的土壤容重范围为0.89～1.79 g/cm~3,平均值为1.36 g/cm~3,表层土壤容重与深层土壤容重差异显著(P0.05),半湿润区、半干旱区浅层土壤容重更易受到外界环境及人为活动的干扰。甘肃省大部田间持水量由西北向东南呈增加趋势,田间持水量的最大值为36%～40%,分布在高寒湿润区10—50 cm土层,全省10 cm与20 cm土层田间持水量差异较小,相关系数为0.96,与其他层次差异较大,50 cm土层很可能是甘肃地区土壤田间持水量的分界层。各土层凋萎湿度最大值均出现在冷温带干旱区、高寒半干旱半湿润区中部,不同层次间田间持水量与凋萎湿度呈极显著相关。甘肃省全省大部分地区主要以壤土为主,除此之外干旱区主要以砂壤土为主,半干旱区主要以砂壤土与黏壤土为主,半湿润区主要以粉壤土与黏壤土为主。探讨不同气候区不同层次间土壤容重、田间持水量和凋萎湿度的差异,以期为保障地上生产力、提高水分利用效率提供数据支撑。     

Degradation of flumioxazin in illuminated water-sediment systems

The aerobic aquatic metabolism of flumioxazin was studied in two water-sediment systems under illumination and in darkness to investigate its degradation profiles. (14)C-Flumioxazin separately labeled at the 1- and 2-positions of the tetrahydrophthalimide moiety or uniformly labeled at the phenyl ring was applied to a overlying water at a rate equivalent to 600 g ai/ha by assuming uniform distribution in the water layer to a depth of 100 cm. Flumioxazin was rapidly degraded at 20 °C in the overlying waters irrespective of irradiation with half-lives of 0.1-0.4 day. Both various modes of liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy analyses showed four major degradates under irradiation. Two of them were formed via successive hydrolysis of the cyclic imide ring, and the others were 2-arizidinone derivatives via photoinduced rearrangement. The presence of sediment under illumination greatly reduced the formation of these degradates and accelerated their degradation. The partitions of flumioxazin and its degradates to the bottom sediment not only reduced their fractions in the water layer subjected to hydrolysis and photolysis but also enhanced their microbial degradation in the sediment. The illuminated water-sediment systems were considered to more adequately represent the behavior of flumioxazin and its degradates in the environment than the corresponding studies of aqueous photolysis and water-sediment in darkness.     

Effects of soil pH and soil water content on prosulfuron dissipation

The sulfonylurea herbicide prosulfuron, 1-(4-methoxy-6-methyltriazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)phenylsulfonyl]urea, is used for the selective control of broadleaf weeds in corn, sorghum, and cereal grains. To investigate its fate in soils, this study examined the effects of soil pH and water content on the rates of dissipation processes and the products formed under aerobic conditions. Radiometry and chromatography analyses were used to quantify the degradation products and bound residues formed in incubations of 10 different soils. The pH-dependent hydrolysis of the sulfonylurea bridge to form phenyl sulfonamide was the primary transformation process. Significant microbial degradation of prosulfuron occurred in 2 of the 10 soils, yielding (14)CO(2) and desmethyl prosulfuron among the major products. The time required for 50% dissipation of the herbicide (DT(50)) was determined for each soil and water content treatment. At equivalent water contents, prosulfuron DT(50) values were positively correlated with soil pH (P < 0.0001), varying from 6.5 days at pH 5.4 to 122.9 days at pH 7.9. Soil pH and water content strongly influence the fate of sulfonylurea herbicides in agricultural fields. Differences in the effect of soil water content on dissipation kinetics in a comparison of two soils were attributed to differences in soil pH, texture, and the ability of indigenous microorganisms to transform the herbicide.     

壤和堆肥中四环素类抗生素的检测方法优化及其在土壤中的降解研究

在对土霉素（OTC）、四环素（TC）和金霉素（CTC）3 种四环素类抗生素的高效液相色谱（HPLC）检测分析方法以及在土壤和堆肥中的提取方法进行改进和优化的基础上,采用该方法进行了 3 种抗生素在土壤中的降解试验。结果表明,选用 Agilent Eclipse XDB-C8（4.6150 mm,5 m）色谱柱,以 0.01 mol/L草酸/乙腈/甲醇（79/10.5/10.5,v/v/v）为流动相,紫外检测波长 268 nm,流速 1.0 mL/min,进样量 5 L,采用外标法定量,可使 3 种四环素类抗生素在 20 min 内全部洗脱并达到基线分离; 在 0~10 mg/L 范围内,抗生素浓度与峰面积呈显著的线性关系,相关系数（r）均 0.999。土壤和堆肥样品中的 OTC、TC 和 CTC可用1 mol/L NaCl/0.5 mol/L 草酸/乙醇（25/25/50,v/v/v）混合溶液提取,其回收率在 76.0%~92.5% 之间。加入到土壤中的抗生素在 25℃下避光培养 49 d 后,在壤土和红土中的降解率分别是 67%~72% 和 36%~46%,对应的半衰期分别为 2630 d 和 4675 d,说明抗生素在壤土中比红土中容易降解。此外,3种抗生素在壤土中的半衰期没有显著性差异,而在红土中 CTC 和 TC 的降解速率显著高于 OTC。