Kinetics of sorption-desorption of benfuracarb insecticide in mollisols

BACKGROUND: Sorption‐desorption processes govern the movement of pesticides in soil. These processes determine the potential hazard of the pesticide in a given environment for groundwater contamination and need to be investigated. RESULTS: In the present study, sorption‐desorption processes of benfuracarb were investigated using a batch method in two mollisols. The kinetics of benfuracarb sorption in mollisols conformed to two‐compartment (1 + 1) first‐order kinetics. The fast sorption rate constant was about 3 times higher for silt loam than for loam soil. However, the slow sorption rate constants were statistically similar for both soils. The concentration‐dependent sorption‐desorption isotherms of benfuracarb could not closely conform to the Freundlich isotherm in mollisols of high organic C content. The computed values of both the sorption (log K) and desorption (log K′) capacities were higher for silt loam than for loam soil. The desorption index (n′/n) values in the range 30.0–41.3 indicated poor reversibility of sorbed benfuracarb in mollisols. CONCLUSION: In view of the strong sorption of benfuracarb in mollisols with only partial desorption, the possibility of the leaching of soil‐applied benfuracarb to contaminate groundwaters appears to be low. Copyright © 2010 Society of Chemical Industry     

Leaching behaviour of azoxystrobin and metabolites in soil columns

BACKGROUND: Azoxystrobin [methyl (E)‐2‐{2‐[6‐(2‐cyanophenoxy)pyrimidin‐4‐yloxy]phenyl}‐3‐methoxyacrylate], a strobilurin fungicide, is a broad‐spectrum, systemic and soil‐applied fungicide. Azoxystrobin has been registered for rice cultivation in India, but no information is available on its leaching behaviour in Indian soils. Therefore, leaching behaviour of azoxystrobin was studied in packed and intact soil columns under different irrigation regimes. RESULTS: Azoxystrobin did not leach out of the 300 mm long columns after 126 and 362 mm rainfall. After percolating water equivalent to 362 mm rainfall, azoxystrobin leached down to 10–15 cm (packed columns) and 15–20 cm (intact columns) depth. Azoxystrobin was not detected in the leachate from the packed column leached with 94.5 mL water every week (140 mm rainfall per month) during the 28 weeks of the study period. However, azoxystrobin acid, formed by azoxystrobin degradation, was detected in the leachate after 18 weeks. At the end of the study, azoxystrobin had leached down to 5–10 cm depth, and only 60% of initially applied azoxystrobin was recovered from the soil. CONCLUSION: The results indicate that azoxystrobin is fairly immobile in sandy loam soil, but azoxystrobin acid, a major metabolite of azoxystrobin, is quite mobile and may pose a threat of soil and groundwater contamination. Copyright © 2009 Society of Chemical Industry     

Influence of surfactants on the leaching of bentazone in a sandy loam soil

BACKGROUND: Surfactants are very often used for more efficient pesticide spraying, but knowledge about their influence on the leaching potential for pesticides is very limited. In the present study, the leaching of the herbicide bentazone [3‐isopropyl‐1H‐2, 1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide] was measured in columns with sandy loam soil with or without the addition of a non‐ionic surfactant, octylphenol ethylene oxide condensate (Triton X‐100, Triton), and an anionic surfactant, sodium dodecylbenzenesulfonate (SDBS), and in the presence of both surfactants (SDBS + Triton). RESULTS: The mobility of bentazone (B) increased in the following order: B + Triton (slowest) < B + SDBS + Triton < B < B + SDBS (fastest). When Triton X‐100 was applied to the soil together with bentazone, the leaching of bentazone in the soil decreased significantly compared with leaching of bentazone without the addition of surfactant. SDBS and Triton X‐100 neutralised their influence on the leaching speed of bentazone in the soil columns when both surfactants were applied with bentazone. CONCLUSION: From the study it can be concluded that, depending on their properties, surfactants can enhance or reduce the mobility of bentazone. By choosing a non‐ionic surfactant, bentazone mobility can be reduced, giving time for degradation and thereby reducing the risk of groundwater pollution. Copyright © 2009 Society of Chemical Industry     

Sensitivity of Podosphaera aphanis isolates to DMI fungicides: distribution and reduced cross‐sensitivity

BACKGROUND: Management of strawberry powdery mildew, Podopshaera aphanis (Wallr.), requires numerous fungicide treatments. Limiting epidemics is heavily dependent on sterol demethylation inhibitors (DMIs) such as myclobutanil or penconazole. Recently, a noticeable reduction in the efficacy of these triazole fungicides was reported by strawberry growers in France. The goal of this study was to investigate the state of DMI sensitivity of French P. aphanis and provide tools for improved pest management. RESULTS: Using leaf disc sporulation assays, sensitivity to myclobutanil and penconazole of 23 isolates of P. aphanis was monitored. Myclobutanil EC₅₀ ranged from less than 0.1 to 14.67 mg L^?1 and for penconazole from 0.04 to 4.2 mg L^?1. A cross‐analysis and a Venn diagram showed that there was reduced sensitivity and a positive correlation between the less sensitive myclobutanil and penconazole isolates; 73.9% of isolates were less sensitive to a DMI and 47.8% exhibited less sensitivity to both fungicides. CONCLUSION: The results show that sensitivity to myclobutanil and, to a lesser extent, penconazole has become less efficient in strawberry powdery mildew in France. Therefore, urgent action is required in order to document its appearance and optimise methods of control. Copyright © 2009 Society of Chemical Industry     

Pedotransfer functions for isoproturon sorption on soils and vadose zone materials

BACKGROUND: Sorption coefficients (the linear K_D or the non‐linear K_F and N_F) are critical parameters in models of pesticide transport to groundwater or surface water. In this work, a dataset of isoproturon sorption coefficients and corresponding soil properties (264 K_D and 55 K_F) was compiled, and pedotransfer functions were built for predicting isoproturon sorption in soils and vadose zone materials. These were benchmarked against various other prediction methods. RESULTS: The results show that the organic carbon content (OC) and pH are the two main soil properties influencing isoproturon K_D. The pedotransfer function is K_D = 1.7822 + 0.0162 OC^1.5 ? 0.1958 pH (K_D in L kg^?1 and OC in g kg^?1). For low‐OC soils (OC < 6.15 g kg^?1), clay and pH are most influential. The pedotransfer function is then K_D = 0.9980 + 0.0002 clay ? 0.0990 pH (clay in g kg^?1). Benchmarking K_D estimations showed that functions calibrated on more specific subsets of the data perform better on these subsets than functions calibrated on larger subsets. CONCLUSION: Predicting isoproturon sorption in soils in unsampled locations should rely, whenever possible, and by order of preference, on (a) site‐ or soil‐specific pedotransfer functions, (b) pedotransfer functions calibrated on a large dataset, (c) K_OC values calculated on a large dataset or (d) K_OC values taken from existing pesticide properties databases. Copyright © 2011 Society of Chemical Industry     

Comparative systemic translocation of several xenobiotics and sucrose

The systemic movement of several xenobiotics was compared in soybean and barley. The more symplastic compounds were also compared to the movement of sucrose. The uptake and efflux from potato tuber tissue was studied and related to the in vivo translocation patterns. The patterns of translocation ranged from primarily apoplastic to ambimobile to symplastic. When the percentage of xenobiotic available for translocation was evaluated there were major differences in patterns of translocation, between plant genera. In barley fenapanil, fenarimol, and oxamyl exhibited primarily apoplastic transport while all three were more ambimobile in soybean. Basipetal transport of oxamyl was 4.2% in barley compared to 30.8% in soybean. Basipetal translocation of benomyl remained very low at 3.0 and 4.1% in barley and soybean, respectively, while sucrose was about 60% in both species. Glyphosate and sucrose were translocated in a similar pattern. The transport of 2,4-D was primarily symplastic, however, retention in the tissue appeared to limit the rate of movement when compared to sucrose. Uptake and efflux of fenapanil, fenarimol, and 2,4-D illustrated the possible role that cellular binding or partitioning may play in systemic translocation. In conjunction with the uptake and efflux, and systemic movement in plants, the octanol/water partition coefficients, log P, for fenarimol and fenapanil, 0.67 and ?0.03, respectively, are correlated with the possible role of cellular binding or partitioning in the systemic movement of xenobiotics.     

Characterization of new photosynthesis-inhibiting imidazolidine derivatives. 1. Interpretation of post-emergence herbicidal performance from photosynthesis-inhibiting activity and systemicity

An attempt was made to account for quantitatively measured herbicidal performance of foliage-applied 5-hydroxy-3-methyl-2–oxo-imidazolidine-1-carboxamide derivatives by their photosynthesis-inhibiting activity and systemicity. Photosynthesis-inhibiting activity was estimated from the increase of chlorophyll fluorescence intensity in Chlorella vulgaris Beijer cells measured by a microplate scanner, and systemicity was also evaluated by computer-aided chlorophyll fluorescence imaging. The highest herbicidal performance was recorded for N-cyclohexyl-5-hydroxy-3-methyl-2-oxo-imidazo～idine-l-carboxamide, a compound with the second strongest photosynthesis-inhibiting activity and intermediate systemicity. Though neither photosynthesis-inhibiting activity nor systemicity showed significant correlation with the actual herbicidal performance in simple regression analyses, a high predictability was found for a multiple regression on both parameters as two independent variables, suggesting that these two factors work cooperatively in the field performance.     

Variability of retention process of isoxaflutole and its diketonitrile metabolite in soil under conventional and conservation tillage

BACKGROUND: Sorption largely controls pesticide fate in soils because it influences its availability for biodegradation or transport in the soil water. In this study, variability of sorption and desorption of isoxaflutole (IFT) and its active metabolite diketonitrile (DKN) was investigated under conventional and conservation tillage. RESULTS: According to soil samples, IFT K_D values ranged from 1.4 to 3.2 L kg^?1 and DKN K_D values ranged from 0.02 to 0.17 L kg^?1. Positive correlations were found between organic carbon content and IFT and DKN sorption. IFT and DKN sorption was higher under conservation than under conventional tillage owing to higher organic carbon content. Under conservation tillage, measurements on maize and oat residues collected from the soil surface showed a greater sorption of IFT on plant residues than on soil samples, with the highest sorbed quantities measured on maize residues (K_D ≈ 45 L kg^?1). Desorption of IFT was hysteretic, and, after five consecutive desorptions, between 72 and 89% of the sorbed IFT was desorbed from soil samples. For maize residues, desorption was weak (<50% of the sorbed IFT), but, after two complementary desorptions allowing for IFT hydrolysis, DKN was released from maize residues. CONCLUSION: Owing to an increase in organic carbon in topsoil layers, sorption of IFT and DKN was enhanced under conservation tillage. Greater sorption capacities under conservation tillage could help in decreasing DKN leaching to groundwater. Copyright © 2012 Society of Chemical Industry     

Aminocyclopyrachlor sorption–desorption and leaching in soil amended with organic materials from sugar cane cultivation

The correct application of a new herbicide depends on knowledge concerning its behaviour within the cultivation system. The objective of this study was to evaluate the sorption–desorption process of aminocyclopyrachlor in soils with the addition of three aged organic materials from sugar cane and their transport via leaching. Sugar cane straw (12 t/ha), filter cake (90 t/ha) and vinasse (200 m³/ha) were added to a clayey soil 15, 30 and 60 days before herbicide application. Sorption and desorption were evaluated by the batch equilibrium method. For leaching assessments, the materials were applied to the soil surface. Sorption was relatively low in all treatments (K_d = 0.17–0.41 L/kg), although significantly higher in soil without organic material addition. A negative correlation between herbicide sorption and increased soil base saturation was observed, indicating competition for sorption sites. With the addition of vinasse, 71% of the herbicide reached the leachate, while <50% reached the leachate in the other treatments. Aminocyclopyrachlor availability was not reduced with organic material addition to the soil, which may be favourable for weed control. However, the presence of vinasse leads to the risk of leaching to deeper soil layers than the seed bank.     

Influence of topsoil tilth and soil moisture status on losses of pesticide to drains from a heavy clay soil

Twelve lysimeters with a surface area of 0.5 m² and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural tilth or a finer topsoil tilth. The influence of topsoil tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h^?1 over a 4‐week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4‐week period. Leaching losses of the three herbicides were monitored for a subsequent drainage event. Analysis of covariance showed a significant effect of topsoil tilth and total flow on both the maximum concentrations (P = 0.034) and total losses (P = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer tilth. However, generation of the fine tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains. © 2001 Society of Chemical Industry     

Factors influencing rates of degradation of an arylamide and a benzoic acid in subsoils

The kinetics of fundamental reactions (hydrolytic, oxidative and reductive) involved in the degradation of organic compounds such as pesticides in subsoils were investigated using the model compounds N‐(4‐nitrophenyl)propanamide and 4‐nitrobenzoic acid. The rates of hydrolysis of N‐(4‐nitrophenyl)propanamide were also measured in aqueous buffers, hydrolysis being extremely slow at neutral pH; its degradation in three soils was by microbially mediated hydrolysis, being very much faster than aqueous hydrolysis at the same pH. Rates of degradation of N‐(4‐nitrophenyl)propanamide in subsoils were initially up to thirty times slower than those in topsoil, and in some subsoils degradation showed a marked lag‐phase of between 72–144 h. For 4‐nitrobenzoic acid, a similar lag‐phase of slow degradation, followed by a phase of rapid degradation, was observed in both topsoils and subsoils. Remarkably, the rapid phases of degradation in subsoils often approached rates occurring in the corresponding topsoil. No reduction of the nitro group on either compound was observed, even in a water‐saturated subsoil. Sometimes there were differences in the length of the lag‐phases measured for replicate samples of subsoils; also, application of lower concentrations of 4‐nitrobenzoic acid generally gave rise to shorter lag‐phases. Partial sterilization of soils by azide greatly slowed breakdown of both compounds, confirming the important role of microbial degradation. Such behaviour is consistent with the variable build‐up of populations of micro‐organisms able to degrade the compound, smaller populations being able to deal rapidly with the lower concentrations. After applying a second dose of 4‐nitrobenzoic acid to soil, degradation was rapid but initially not as fast as the final rates during breakdown of the first treatment. Hence, soil may only partially retain the ability to degrade previously applied xenobiotics. Nonetheless it is noteworthy that, even in deep subsoils, indigenous microbial populations can rapidly adapt to degrade certain small organic molecules. © 2000 Society of Chemical Industry     

磺草酮在土壤中的淋溶特性研究

基于所建立的土壤中磺草酮残留的超高效液相色谱-串联质谱分析方法,通过土壤薄层层析试验研究了磺草酮在中国3种典型土壤中的淋溶特性。结果表明:添加水平为1和10 mg/kg时,磺草酮在土壤中的添加回收率为80%~104%,相对标准偏差为1.2%~8.1%,最低检测浓度为0.1 mg/kg。磺草酮在河北潮土、湖南红土和吉林黑土中的比移值(Rf)分别为0.563、0.101和0.422,其在潮土和黑土中的移动性为中等,在红土中为不易移动;磺草酮在土壤中的淋溶特性与土壤理化性质密切相关,主要影响因素是土壤p H值及黏粒组分含量。     

Dormancy,germination and emergence of Urochloa panicoides regulated by temperature

Urochloa panicoides is an annual weed of summer crops. In Argentina, in subhumid areas with monsoon rainfall, it germinates and establishes in a single flush. To (i) identify the environmental factors that modify its seed dormancy level and germination and (ii) quantify the parameters describing the thermal behaviour of the germination and emergence dynamics of this weed under non‐limiting water conditions, we established a set of germination experiments performed (i) under controlled conditions using seeds after ripened for 3 or 6 months in different thermal and hydric conditions and (ii) under field conditions, where the soil temperature was modified by applying different shading levels. Seed dormancy level remained high with 3 months after ripening in all treatments. After 6 months, seeds stored at 4°C in dry conditions did not germinate at any temperature, while seeds stored at 25°C in dry conditions and in situ germinated c. 20% and 60% respectively. Germination percentage was higher in seeds harvested before their natural dispersal. The base, optimum and maximum temperatures for seed germination were 6, 35 and 45°C respectively. Shading reduced the number of emerged seedlings, possibly by reducing the soil thermal amplitude. The results explained the dormancy‐breaking mechanism of U. panicoides that allows a high germination rate in the field when rainfall occurs.     

In situ bioremediation of organochlorine‐pesticide‐contaminated microcosm soil and evaluation by gene probe

BACKGROUND: Pesticide‐formulating industries are contaminating the environment through various activities. Bioremediation is the best method for decontamination, as chemical and physical methods are not only costly but also not very effective in open field systems. In the present study, in situ bioremediation of organochlorine‐contaminated soil was demonstrated by combined biostimulation and bioaugmentation strategies, followed by evaluation using a molecular method. RESULTS: Three parameters were monitored: microbial biomass (colony‐forming units (CFU) g^?1 soil), residual pesticides after treatment and catabolic genes from microcosm soil. Both the biostimulation and the bioaugmentation treatments showed an initial lag phase of 80 days towards colony‐forming units. Gas chromatography of soil samples showed that concentrations of residual pesticides in the soil declined by up to 85–90% after 80 days, indicating their utilisation with time. On dot‐blot hybridisation of the total DNA from the same soil samples, it was observed that catabolic genes tfdC (catechol 1,2‐dioxygenase) and cm genes (chlorophenol monoxygenase) were predominant, whereas other catabolic genes such as catechol 2,3‐dioxygenase (xylE) were negligible. CONCLUSION: The strategy of in situ bioremediation and its evaluation by gene probe and also by conventional methods was demonstrated for organochlorine‐pesticide‐contaminated soil in open microcosms. It showed that bioaugmentation along with biostimulation was effective, although initial acclimatisation for a period of almost 2–3 months was required in the open field systems. Copyright © 2009 Society of Chemical Industry     

Model Predictions and Field Measurements of Chlorsulfuron Leaching under Non-steady-state Flow Conditions

Model simulations of chlorsulfuron (1-(2-chlorophenylsulfonyl)-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea) leaching in a loamy soil were made with the mechanistic dual-porosity model MACRO. Comparisons were made with a data set obtained in a lysimeter experiment in which leaching was measured during an 11-month period after applying chlorsulfuron at two rates (4 and 8 g ha⁻¹). In this experiment, peak concentrations appeared c.6 months after pesticide application, reaching levels of 14 and 21 ng litre⁻¹ in the low- and high-dose treatments, respectively. These peak concentrations appeared after c.70 mm of accumulated leachate, implying that some of the herbicide was displaced through the soil columns by non-equilibrium flow processes. Model calibration was limited to parameters related to evapotranspiration, water uptake by roots and degradation rates in the subsoil. With this minimum amount of calibration, the model successfully described the leaching pattern of chlorsulfuron, provided that the two-flow domain option in the model was used. Running the model in one-flow domain resulted in considerable underestimates of leaching of chlorsulfuron over the short-term (<1 year). The degradation rate in the subsoil was also found to be critical. It had to be increased about fivefold to match measured chlorsulfuron concentrations in leachate. At such concentrations, 0·012 g ha⁻¹ of chlorsulfuron (0·3% of that applied) was predicted to leach through the soil profile during the 11-month simulation period when the lower dose of the compound was applied.     

基于Sentinel-1/2的土壤盐分含量反演研究

本试验利用Gram-Schmidt（GS）变换将Sentinel-1A雷达影像与Sentinel-2A多光谱影像进行融合,并分析雷达影像、多光谱影像及融合影像各波段与吉林省白城市表层土壤含盐量的相关性,建立研究区土壤含盐量的反演模型,对研究区土壤含盐量进行制图。研究结果表明：Sentinel-1A 的VH、VV波段后向散射系数与研究区土壤含盐量均呈显著正相关,可用作土壤盐碱化监测的遥感数据源;合适的数学变换可以提升Sentinel-1A、Sentinel-2A及融合影像与土壤含盐量的相关性,其中,Sentinel-1A的VV波段与Sentinel-2A第5 波段融合后,其二次方变换与土壤含盐量的相关系数达到0.820;引入合适的盐分指数可以有效改善Sentinel-2A及融合影像与土壤含盐量的相关性,其中,融合影像的盐分指数(D₂D₄)/D₃与土壤含盐量相关系数达到0.889;利用融合影像及盐分指数(D₂D₄)/D₃建立的研究区土壤含盐量反演模型Y=86.260X-66.206X²-5.312,模型决定系数达到0.791,均方根误差为1.884 g·kg^-1,表明将Sentinel-1A雷达影像与Sentinel-2A多光谱影像进行融合来提升土壤含盐量反演精度的方法切实可行。     

异噁唑草酮在土壤表面光解及在土壤中的降解和淋溶特性

为合理评估除草剂异唑草酮的环境风险,在实验室模拟条件下,研究了异唑草酮在土壤 (红壤土)表面光解以及在不同质地土壤 (潮土、水稻土和红壤土) 中的降解和淋溶特性。结果表明:异唑草酮在土壤表面的光解遵循一级反应动力学方程c_t = 4.23e–0.008t (r = 0.937),半衰期为82.5 h;其在潮土、水稻土和红壤土中的降解均符合一级动力学方程,好氧条件下,异唑草酮在3种土壤中的降解半衰期分别为10.5、43.3和139 h,厌氧条件下的降解半衰期分别为19.4、18.4和158 h;其在潮土、水稻土和红壤土中的淋溶系数 (R_f) 分别为0.417 0、0.083 3和0.083 3。研究表明:异唑草酮在土壤表面光解速率较慢,而在土壤中好氧及厌氧条件下降解速率均较快,残留期短;其在土壤中淋溶性较弱,不易对周围环境及地下水造成污染风险。     

[14C]Glyphosate transport in undisturbed topsoil columns

Although glyphosate (N‐(phosphonomethyl)glycine) is one of the most frequently used herbicides, few controlled transport experiments in undisturbed soils have been carried out to date. The aim of this work was to study the influence of the sorption coefficient, soil‐glyphosate contact time, pH, phosphorus concentration and colloid‐facilitated transport on the transport of [¹⁴C]glyphosate in undisturbed top‐soil columns (20 cm height × 20 cm diameter) of a sandy loam soil and a sandy soil. Batch sorption experiments showed strong Freundlich‐type sorption to both soil materials. The mobility of glyphosate in the soil columns was strongly governed by macropore flow. Consequently, amounts of glyphosate leached from the macroporous sandy loam soil were 50–150 times larger than from the sandy soil. Leaching rates from the sandy soil were not affected by soil‐glyphosate contact time, whereas a contact time of 96 h strongly reduced the leaching rates from the sandy loam soil. The role of pH and phosphorus concentration in solution was relatively unimportant with respect to total glyphosate leaching. The contribution of colloid‐facilitated transport was <1 to 27% for the sandy loam and <1 to 52% for the sandy soil, depending on soil treatment. The risk for glyphosate leaching from the top‐soils seems to be limited to conditions where pronounced macropore flow occurs shortly after application. © 2000 Society of Chemical Industry     

Persistence of pyrazosulfuron in rice-field and laboratory soil under Indian tropical conditions

BACKGROUND: Pyrazosulfuron ethyl, a new rice herbicide belonging to the sulfonylurea group, has recently been registered in India for weed control in rice crops. Many field experiments revealed the bioefficacy of this herbicide; however, no information is available on the persistence of this herbicide in paddy soil under Indian tropical conditions. Therefore, a field experiment was undertaken to investigate the fate of pyrazosulfuron ethyl in soil and water of rice fields. Persistence studies were also carried out under laboratory conditions in sterile and non‐sterile soil to evaluate the microbial contribution to degradation. RESULTS: High‐performance liquid chromatography (HPLC) of pyrazosulfuron ethyl gave a single sharp peak at 3.41 min. The instrument detection limit (IDL) for pyrazosulfuron ethyl by HPLC was 0.1 µg mL^?1, with a sensitivity of 2 ng. The estimated method detection limit (EMDL) was 0.001 µg mL^?1 and 0.002 µg g^?1 for water and soil respectively. Two applications at an interval of 10 days gave good weed control. The herbicide residues dissipated faster in water than in soil. In the present study, with a field‐soil pH of 8.2 and an organic matter content of 0.5%, the pyrazosulfuron ethyl residues dissipated with a half‐life of 5.4 and 0.9 days in soil and water respectively. Dissipation followed first‐order kinetics. Under laboratory conditions, degradation of pyrazosulfuron ethyl was faster in non‐sterile soil (t_1/2 = 9.7 days) than in sterile soil (t_1/2 = 16.9 days). CONCLUSION: Pyrazosulfuron ethyl is a short‐lived molecule, and it dissipated rapidly in field soil and water. The faster degradation of pyrazosulfuron in non‐sterile soil than in sterile soil indicated microbial degradation of this herbicide. Copyright © 2012 Society of Chemical Industry     

Adsorption, transport and degradation of fipronil termiticide in three Hawaii soils

BACKGROUND: The behavior of the termiticide fipronil in soils was studied to assess its potential to contaminate ground and surface water. This study characterizes (1) adsorption of fipronil in three different soils, (2) transport of fipronil through leaching and runoff under simulated rainfall in these soils and (3) degradation of fipronil to fipronil sulfide and fipronil sulfone in these soils. RESULTS: The adsorption experiments showed a Freundlich isotherm for fipronil with K_oc equal to 1184 L kg^?1. In the leaching experiments, the concentration of fipronil and its metabolites in leachate and runoff decreased asymptotically with time. The concentration of fipronil in the leachate from the three soils correlated inversely with soil organic carbon content. The degradation experiment showed that the half‐life of fipronil in the soils ranged from 28 to 34 days when soil moisture content was 75% of field capacities, and that 10.7–23.5% of the degraded fipronil was transformed into the two metabolites (fipronil sulfide and fipronil sulfone). CONCLUSION: Fipronil showed large losses through leaching but small losses via runoff owing to low volumes of runoff water generated and/or negligible particle‐facilitated transport of fipronil. The half‐life values of fipronil in all three soils were similar. Copyright © 2011 Society of Chemical Industry