氯胺嘧草醚在土壤中的吸附行为研究

为评价氯胺嘧草醚的环境安全性,采用批量平衡法测定了氯胺嘧草醚在5种土壤中的吸附-解吸行为,并运用数学模型对其吸附-解吸特性及移动性能进行了分析。结果表明:氯胺嘧草醚在5种土壤中的等温吸附-解吸曲线符合Freundlich模型,吸附常数（Kf值）范围在6.991~18.49之间;不同土壤对其的吸附作用强弱依次为:黑土 > 水稻土 > 褐土 > 潮土 > 红土。氯胺嘧草醚在5种土壤中的有机碳吸附常数（KOC）范围在704.4~1 579之间,推测其在土壤中具有低移动性;薄层层析试验也表明,氯胺嘧草醚在土壤中的移动性较弱。氯胺嘧草醚在5种土壤中的吸附自由能绝对值均小于40 kJ/mol,表明其吸附机理主要是物理吸附。其Kf值与土壤有机质含量、黏粒含量呈正相关,而与土壤pH值呈负相关。解吸试验表明,氯胺醚在其中3种土壤中的解吸过程存在滞后现象。研究表明,在正常使用情况下,氯胺嘧草醚不易对地表水或地下水造成污染风险。     

环丙酰草胺在土壤中的迁移特性

为研究环丙酰草胺在土壤中的吸附迁移规律，分别采用批平衡法和柱淋溶法测定了环丙酰草胺在江西红壤、太湖水稻土、常熟乌杉土、陕西潮土和东北黑土5种土壤中的吸附和淋溶特性，并运用数学模型对其在土壤中的吸附及迁移特性进行了分析。结果表明:环丙酰草胺在5种土壤中的等温吸附曲线符合线性吸附方程，吸附常数K_d在1.41~7.08之间；环丙酰草胺在5种土壤中的淋溶性大小依次为:东北黑土>陕西潮土>常熟乌杉土>太湖水稻土>江西红壤。通过对吸附常数K_d与土壤有机质含量和pH值的关系进行分析，发现土壤pH值在吸附过程中属主要因素，K_d与土壤pH值呈负相关。上述结果表明，环丙酰草胺在供试的5种土壤中比较容易迁移，影响其迁移的主要因素是土壤pH值。环丙酰草胺在使用过程中应关注其对地表水和地下水造成的风险。     

烟嘧磺隆在土壤中的吸附及与土壤性质的相关性研究

采用平衡振荡法研究了烟嘧磺隆在8种不同类型土壤中的吸附,结果表明,其吸附过程均符合经典的Freundlich模型,最大吸附常数为6.891,最小吸附常数为0.798。根据土壤有机吸附常数和吸附自由能的大小对该除草剂的移动性能进行了评价,认为其在8种土壤中均以物理吸附为主,且具有中等或较高的移动性能。通过对吸附常数Kf与土壤有机质含量、粘土含量和pH值的关系进行分析,发现土壤有机质含量、粘土含量和pH值在吸附过程中均属支配因素,Kf与土壤有机质含量、粘土含量呈正相关,而与土壤pH值呈负相关。     

精异丙甲草胺在土壤中的吸附行为及环境影响因素研究

采用平衡振荡法研究了精异丙甲草胺在粘壤土、粘土及砂壤土中的吸附和解吸附行为。结果表明,3种土壤的吸附等温线均属L型并符合Freundlich模型,吸附常数(Kf)分别为4.01、6.15及8.62,且Kf 和1/n(n为经验常数)的乘积与土壤有机质含量呈正相关性。解吸附实验结果表明,精异丙甲草胺在土壤中的解吸附与吸附并不一致,显示出明显的滞后性。温度及pH值等环境因素对吸附影响的结果显示,随温度升高精异丙甲草胺在土壤中的吸附量有所减少,中性环境下土壤吸附量较低。     

毒死蜱和氰戊菊酯在土壤中的吸附与迁移

为评估被用作白蚁预防药剂的毒死蜱和氰戊菊酯在土壤中的移动性,采用平衡吸附法和薄层层析法分别测定了两种农药在浙江宁波地区的东钱湖土(粉砂质壤土)、青岭土(粉砂质壤土)和象山土(粉砂质黏壤土)3种土壤中的吸附常数(Kd)和迁移率(Rf)。结果表明,两种供试药剂在东钱湖土中的吸附等温线线性化程度均较高,而在青岭土和象山土中的吸附等温线均近似于 "L"型。从Kd和有机质吸附常数Koc的数值看,氰戊菊酯在土壤中的吸附作用主要受土壤有机质因素影响,而毒死蜱的吸附并非只受土壤有机质因素的影响。毒死蜱在3种供试土壤中的Kd和Rf值均高于氰戊菊酯。这表明由Kd值推测不同农药在土壤中的相对移动性可能会存在一定偏差。毒死蜱和氰戊菊酯在3种土壤中的Rf值由大到小的顺序为:东钱湖土>青岭土>象山土;而Kd值由大到小顺序为象山土>青岭土>东钱湖土。对Kd和Rf值与土壤理化性质的多元线性回归分析表明:1)土壤有机质含量和阳离子代换量在决定Kd和Rf值中所起的作用相互重叠;2)土壤有机质含量(或土壤阳离子代换量)和土壤黏粒含量是影响Kd和Rf值的关键因素,而土壤pH值对于Kd和Rf值无决定性影响。     

双氟磺草胺在不同类型土壤中的吸附与淋溶特性研究

农药在土壤中的吸附和淋溶特性是评价其环境行为的重要指标。采用批量平衡法和土柱淋溶法,研究了双氟磺草胺在小麦种植区3种代表性土壤中的吸附和淋溶特性。结果表明:双氟磺草胺在安徽黏土、山东砂质壤土和河南砂质黏壤土中的吸附规律均可以较好地用Freundlich方程描述,其吸附系数(Kf)在0.39~0.62之间;土壤有机碳归一化吸附系数(Koc)在66.91~81.35之间,表明双氟磺草胺在3种土壤中均属于难吸附型;吸附自由能(ΔG)在-10.90~-10.42kJ/mol之间,均属于物理吸附。双氟磺草胺在3种土壤中的淋出率在71.7%~74.1%之间,说明其在3种土壤中的淋溶性均较强。双氟磺草胺初始添加量和腐殖酸对淋出率具有一定影响。综合试验结果,认为双氟磺草胺在3种土壤中的吸附和淋溶可能受土壤有机质含量、黏粒含量、阳离子交换量和土壤pH值等多个因素的综合影响,其对地下水的污染风险较大,因此应引起高度重视。     

七种农药在3种不同类型土壤中的吸附及淋溶特性

采用振荡平衡法和土柱淋溶法研究了2,4-滴酸、丁噻隆、毒草胺、炔草酸、氟环唑、甲基磺草酮和烯啶虫胺7种农药在江西红壤、太湖水稻土及东北黑土3种不同理化性质土壤中的吸附及淋溶特性,探讨了农药性质及土壤理化性质对供试农药在土壤中吸附、淋溶行为的影响。结果表明:农药的水溶性越大,其在土壤中的吸附性越弱,淋溶性越强;农药在土壤中的吸附性与土壤pH值、有机质含量以及阳离子交换量之间有较好的相关性。土壤pH值、有机质含量以及农药性质是影响农药在土壤中淋溶及迁移的主要因素。     

环酰菌胺在土壤中的吸附及降解特性

为评价环酰菌胺在土壤中的生态风险,采用超高效液相色谱-串联质谱(UPLC-MS/MS)方法测定了土壤和水中环酰菌胺的残留量,研究了该农药在红壤和水稻土中的吸附及降解特性,并对其淋溶特性进行了分析,评估了该农药对地下水的污染风险。结果表明:环酰菌胺在红壤和水稻土中的吸附符合Freundlich吸附等温线方程,KOC值分别为373.69和726.86 mL/g,水稻土对环酰菌胺的吸附能力强于红壤。好氧条件下,环酰菌胺在红壤和水稻土中的降解半衰期分别为0.63和5.06 d,积水厌氧条件下的降解半衰期分别为6.80和9.24 d,表明环酰菌胺在好氧条件下降解较快。环酰菌胺在红壤和水稻土中的地下水污染指数(groundwater ubiquity score)分别为1.19和1.10,表明其对地下水的污染风险较低。结果可为环酰菌胺的生态风险评估提供参考。     

24%咪鲜胺·噻呋酰胺SC防治水稻纹枯病试验

对24%咪鲜胺·噻呋酰胺SC防治水稻纹枯病的田间药效进行了试验。结果表明,24%咪鲜胺·噻呋酰胺SC 450g/hm2处理后对水稻纹枯病的防效达到87.44%,高于对照药剂240g/L噻呋酰胺SC 187.5g/hm2防效80.37%和对照药剂25%咪鲜胺EC 750g/hm2防效77.37%。说明24%咪鲜胺·噻呋酰胺是一种防治水稻纹枯病的优良制剂,可在生产上大面积推广和应用。     

咪鲜胺在冬枣中的残留及消解动态

为评价咪鲜胺在冬枣上使用的安全性,开展了咪鲜胺在冬枣中的残留量及消解动态研究,进行了1年4地田间试验。消解动态试验按咪鲜胺667倍液(675mg/kg,1.5倍推荐最高制剂量)施药;最终残留试验按咪鲜胺1 000倍液(450mg/kg),高剂量按制剂量667倍液(675mg/kg,1.5倍推荐最高制剂量)施药,施药3~4次,施药间隔7d,施药后7、14、21、28d采集冬枣样品。利用GC-ECD定量分析检测。检测结果表明:咪鲜胺在冬枣中的半衰期为5.7d,咪鲜胺在距离最后施药28d采样时冬枣中残留量为0.16?4.57mg/kg。     

INFLUENCE OF SOIL PROPERTIES ON PHYTOTOXICITY OF 4–AMlNO-3,5,6–TRICHLOROPICOLINIC ACID (PICLORAM)

Summary. Effective dosages of picloram (4–amino-3,5,6–trichloropicolinic acid) required to reduce fresh weight of sunflowers ( Helianthus annuus L. var. Menonite) were determined for seven Saskatchewan soils under controlled environmental conditions. The relationships between ED₅₀ value and clay content, organic matter content and cation exchange capacity were evaluated by correlation and regression analysis for possible usefulness in predicting dose requirements. ED₅₀ values were also determined for Weyburn loam and in culture solutions adjusted to various pH levels.
There Was no significant correlation between ED₅₀ values of picloram and soil clay content or cation exchange capacity. ED₅₀ values were highly correlated with soil organic matter content, and they increased as the soil pH was lowered or raised from pH 6.5. The increase in ED₅₀ values in the acidic range was attributed to adsorption of the unionized molecules of picloram on the organic matter in the soil. The increase in ED₅₀ values in the alkaline range may be mainly due to reduced uptake of the ionized acid by plant roots.     

Interactions between organophosphorus compounds and soil materials I. Adsorption of ethyl methylphosphonofluoridate by clay and organic matter preparations and by soils

Data for the adsorption of ethyl methylphosphonofluoridate from aqueous and the vapour phases onto montmorillonite and kaolinite clays, onto soil organic matter preparations, and onto a limited number of soils are reported. These show that the phosphonofluoridate was absorbed from the vapour phase onto the dry clay preparations by physical-chemical forces but was not adsorbed by the organic soil materials. In a general way adsorption onto dry soils could be related to their clay contents when the organic matter contents were low. Water was found to compete effectively with the phosphonofluoridate for adsorption sites, and it is concluded that this molecule will be most effectively retained by dry soils low in organic matter and rich in clay. Mechanisms for its adsorption onto clays are discussed.     

Adsorption-desorption behaviour of flufenacet in five different soils of India

Adsorption-desorption of the herbicide flufenacet (FOE 5043) has been studied in five soils from different locations in India (Delhi, Ranchi, Nagpur, Kerala and Assam) varying in their physicochemical properties. The organic matter (OM) content varied from 0.072 to 0.864%, clay content from 2.5 to 43.7% and pH from 4.45 to 8.35. The adsorption studies were carried out using a batch equilibration technique. Ten grams of soil were equilibrated with 20 ml of aqueous 0.01 M CaCl2 solution containing different concentrations (0-30 mg litre-1) of flufenacet. After equilibration, an aliquot of supernatant was taken out for analysis. During desorption, the amount withdrawn for analysis was replenished with fresh 0.01 M CaCl2 solution and further equilibrated. Desorption studies were carried out with the 30 mg litre-1 concentration of flufenacet only. The adsorption studies revealed that there was moderate to high adsorption of flufenacet considering the comparatively low organic carbon content in the five test soils. Average Kd values ranged from 0.77 to 4.52 and Freundlich KF values from 0.76 to 4.39. The highest adsorption was observed in Kerala soil (OM 0.786%; clay 25%; pH 4.45) followed by Ranchi, Nagpur and Delhi soils, and the lowest in Assam soil (OM 0.553%; clay 2.5%; pH 6.87). The trend in adsorption could be attributed to the chemical nature of flufenacet and the physicochemical properties of the soil such as pH, OM and clay contents. OM and clay contents were positively correlated whereas pH was negatively correlated. Soils having low pH, high OM and high clay contents showed higher adsorption. Desorption studies revealed that there was a hysteresis effect in all the soils. Hysteresis coefficient values (ratio of n(ad) and n(des)) varied from 0.09 to 0.45. The study implies that, because of its moderate to high adsorption, flufenacet is likely to persist in soil for some time. However, the possibility of its movement by leaching or surface run off is less.     

Adsorption-desorption studies of alachlor, metolachlor, EPTC, chlorothalonil and pirimiphos-methyl in contrasting soils

Five soils with different organic matter contents ranging from 0.48 to 10.4% were used to study the adsorption and desorption of alachlor, metolachor, EPTC, chlorothalonil and pirimiphos-methyl in batch experiments. The isotherm shapes according to Giles classification were S-type for alachlor, metolachlor and chlorothalonil, changing to L-type for the latter as the level of soil organic matter increased, and L-type for EPTC and pirimiphos-methyl. The adsorption isotherms fitted the Freundlich equation x/m = KfCe1/n. The Kf values increased with the increase of organic matter content. The amounts of pesticides adsorbed over a range of concentrations of 0.1-20 mg litre-1 reached 63.1% for alachlor, 69.2% for metolachlor, 89.3% for EPTC, 98.4% for chlorothalonil and 96.3% for pirimiphos-methyl. The increase of the amounts desorbed with acetone indicated that the sorption of organic compounds onto organic matter occurred principally via weak London-type induction forces, or dispersion forces which are characteristics of the physical adsorption process.     

Adsorption and degradation of four acidic herbicides in soils from southern Spain

BACKGROUND: Pesticide degradation and adsorption in soils are key processes determining whether pesticide use will have any impact on environmental quality. Pesticide degradation in soil generally results in a reduction in toxicity, but some pesticides have breakdown products that are more toxic than the parent compound. Adsorption to soil particles ensures that herbicide is retained in the place where its biological activity is expressed and also determines potential for transportation away from the site of action. Degradation and adsorption are complex processes, and shortcomings in understanding them still restrict the ability to predict the fate and behaviour of ionisable pesticides. This paper reports the sorption and degradation behaviour of four acidic pesticides in five soils from southern Spain. Results are used to investigate the influence of soil and pesticide properties on adsorption and degradation as well as the potential link between the two processes. RESULTS: Adsorption and degradation of four acidic pesticides were measured in four soils from Spain characterised by small organic matter (OM) contents (0.3-1.0%) and varying clay contents (3-66%). In general, sorption increased in the order dicamba < metsulfuron-methyl < 2,4-D < flupyrsulfuron-methyl-sodium. Both OM and clay content were found to be important in determining adsorption, but relative differences in clay content between soils were much larger than those in OM content, and therefore clay content was the main property determining the extent of herbicide adsorption for these soils. pH was negatively correlated with adsorption for all compounds apart from metsulfuron-methyl. A clear positive correlation was observed for degradation rate with clay and OM content (P < 0.01), and a negative correlation was observed with pH (P < 0.01). The exception was metsulfuron-methyl, for which degradation was found to be significantly correlated only with soil bioactivity (P < 0.05). CONCLUSIONS: Both OM and clay content were found to be important in determining adsorption, but relative differences in clay content between soils were much larger than those in OM content, and therefore clay content was the main property determining the extent of herbicide adsorption for soils of this type. pH was negatively correlated with adsorption for all compounds apart from metsulfuron-methyl. The contrasting behaviour shown for these four acidic pesticides indicates that chemical degradation in soil is more difficult to predict than adsorption. Most of the variables measured were interrelated, and different behaviours were observed even for compounds from the same chemical class and with similar structures.     

Adsorption,decomposition and movement of oxamyl in soil

A study was conducted of the behaviour of oxamyl in Israeli soils of varying clay and organic matter contents. The adsorption isotherms for oxamyl were linear, and the adsorption coefficient (K_d) could be correlated to the clay content of the soils, as well as to the organic matter content of the soil. Oxamyl adsorption was underestimated by using published correlations between the adsorption and the chemical properties of pesticides, such as their solubility or octan-1-ol-water partition coefficient. The decomposition of oxamyl in soils followed first-order kinetics. The half-life ranged from 4 to 33 days in a Bet Dagan soil. The reaction rate increased with increasing moisture content of the soil until field capacity was reached, at which point it levelled off. The Arrhenius relationship was followed, with degradation proceeding more rapidly at higher temperatures. In several soils of varying composition, which were kept at field capacity, no difference in the degradation rates was observed. Oxamyl was applied to a Bet Dagan soil from a point source in a single pulse, as a split application, and on a continuous basis. The distribution patterns of oxamyl under the various treatments differed significantly. After the single-pulse application, oxamyl was leached out of the emitter zone. While the split application decreased the oxamyl-free zone, the best results were obtained by continuous application, which gave a nearly uniform distribution of oxamyl in the soil.