Preliminary study on persistence in soil and residues in maize of imidacloprid

The aim of this work was to study the distribution of imidacloprid in soil and its translocation to roots and aerial parts of maize plant. The main objective was to assess imidacloprid residues in field environment, in order to provide data on honeybees exposure level to such an active substance. Imidacloprid has been detected and quantified by Triple Quadrupole HPLC-MS-MS. Pesticide persistence in the soil and its residues in pollen and in maize plants have been evaluated during the growing of maize plants developed from seeds dressed with Gaucho 350 FS (imidacloprid: 1.0 mg/seed). The sowing has been performed by means of a pneumatic precision drill. Samples have been collected at 30, 45, 60, 80, 130 days after the sowing, as pollen samples have been collected at the tasseling. Imidacloprid presence in aerial part of maize plant declined to 2-3 μg/kg 80 days after the sowing, while concentration in kernel at harvest was <1 μg/kg. Maize pollen represents an important part of protein supply of beehives, and it is of critical importance to bee foraging. The values detected (imidacloprid residues <1 μg/kg) showed that maize pollen source should not be relevant for acute toxicity impact on honey bees.     

Wind tunnel simulation of environmental controls on fugitive dust emissions from mine tailings

The development of techniques for determining fugitive dust emissions presents numerous challenges and remains the subject of much investigation. Past approaches have included field based monitoring stations and wind tunnel studies, while more recently, highly portable field units (e.g., PI-SWERL) have been added to our toolkit of instruments and methodologies. In the case of the investigation reported herein, a laboratory wind tunnel study was designed to systematically simulate PM₁₀ emissions from mine tailings for a range of surface treatments. Unique challenges were associated with the project in the sense that the proposed mine and tailings did not exist at the time of the investigation, so that it was impossible to work on-site. Only a small amount of slurry from a milled drill core was available to work with, and there were no established test protocols and few experimental precedents to work from. The slurry formed highly cohesive bricks when dried, similar to crusted playas investigated in field experiments. The PM₁₀ emissions demonstrated strong temporal variation with particle supply limitation. A small amount of vertical dust dispersion was observed, with PM₁₀ concentrations decaying exponentially away from the source. The emission rates obtained are similar in magnitude to those obtained in field analogues. The highly controlled experiment allowed for separation and analysis of several physical controls on PM₁₀ emissions from tailings; namely, the study addressed the degree of disturbance, shrinkage and cracking, and the effects of spigotting, particle settling and re-wetting.     

Soil distribution of fipronil and its metabolites originating from a seed-coated formulation

Seed-coating with the insecticide fipronil has been intensively used in sunflower cultivation to control soil pests such as wireworms. A research project was undertaken to determine the soil distribution of fipronil and of its main phenylpyrazole metabolites. Under agronomic conditions, the quantity of fipronil in the seed-coat (437 microg/seed) decreased continuously during the cultivation period (3.9 microg day(-1) during the first two months; 0.3 microg day(-1) during the next four months). At the end of the cultivation period, 42% of all phenylpyrazole compounds remained in the seed-coat. Fipro nil was poorly mobile in soil, and at the end of the cultivation period it was mostly concentrated in the soil layer close to the seed (3240 microg kg(-1) soil). Starting from the seed-coating, a fipronil concentration gradient was measured in the soil, up to a distance of 11 cm from the seed. Degradation in the soil occurred at a moderate rate, probably due to the fact that water solubilization of the solid active ingredient present in the seed coating was rate limiting. Indeed, after 6 months of cultivation, only 51% of the fipronil seed-coating was found in the soil, about 7% having been absorbed by the sunflower plant, and 42% remaining in the seed coat. The predominant metabolites produced in the soil were sulfone-fipronil, sulfide-fipronil and amide-fipronil, which were produced at average rates of 5 microg kg(-1) soil day(-1), 3 microg kg(-1) soil day(-1), and 0.4 microg kg(-1) soil day(-1), respectively. In contrast, the photoproduct, desulfinyl-fipronil, was barely detected. All phenylpyrazole compounds were poorly mobile, except for the amide derivative, which is devoid of insecticidal activity in marked contrast to the other metabolites. Furthermore, detectable soil contamination was limited to a zone of about 11 cm around the seed.     

裸土风蚀型开放源起尘机制研究进展

中国北方多个城市空气颗粒物来源解析结果表明,开放源是空气颗粒物污染的主要来源,裸土风蚀型开放源是主要的排放源类.对裸土风蚀型开放源起尘机制进行了诠释,提出了裸土风蚀型开放源、裸土风蚀起尘、裸土风蚀尘的概念,并对裸土风蚀型开放源的风蚀影响因素进行了研究,为城市空气质量达标及空气颗粒物污染防治提供科学参考.     

Implementation of a windblown dust parameterization into MODELS-3/CMAQ: Application to episodic PM events in the US/Mexico border

Windblown dust is known to impede visibility, deteriorate air quality and modify the radiation budget. Arid and semiarid areas with unpaved and unvegetated land cover are particularly prone to windblown dust, which is often attributed to high particulate matter (PM) pollution in such areas. Yet, windblown dust is poorly represented in existing regulatory air quality models. In a study by the authors on modeling episodic high PM events along the US/Mexico border using the state-of-the-art CMAQ/MM5/SMOKE air quality modeling system [Choi, Y.-J., Hyde, P., Fernando, H.J.S., 2006. Modeling of episodic particulate matter events using a 3D air quality model with fine grid: applications to a pair of cities in the US/Mexico border. Atmospheric Environment 40, 5181–5201], some of the observed PM₁₀ NAAQS exceedances were inferred as due to windblown dust, but the modeling system was incapable of dealing with time-dependent episodic dust entrainment during high wind periods. In this paper, a time-dependent entrainment parameterization for windblown dust is implemented in the CMAQ/MM5/SMOKE modeling system with the hope of improving PM predictions. An approach for realizing windblown dust emission flux for each grid cell over the study domain on an hourly basis, which accounts for the influence of factors such as soil moisture content, atmospheric stability and wind speed, is presented in detail. Comparison of model predictions with observational data taken at a pair of US/Mexico border towns shows a clear improvement of model performance upon implementation of the dust emission flux parameterization.     

Spatial variations in the aeolian deposition of dust – the effect of a city: a case study in Be'er-Sheva,Israel

The effect of buildings on the dry deposition of dust particles was investigated in Be'er-Sheva, a desert city with about 140,000 inhabitants in southern Israel, and at two reference points in the surrounding rural area. The mineral and chemical composition of dust sampled at all sites was similar, reflecting the composition of the local loess soil, its likely origin. However, dust deposited in the traps set up in the vicinity of buildings in the city was significantly coarser than the dust which accumulated in similar traps at exposed sites in the countryside. The amount of dust (by weight) in the urban dust traps was on an average more than twice the amount deposited in the rural area. The differences in grain-size distribution and quantity of dust are attributed to the properties of the urban wind field and to various effects of human activity in the city.     

Behavior of particulate matter during high concentration episodes in Seoul

The behavior of particulate matter (PM) during high-concentration episodes was investigated using monitoring data from Guui station, a comprehensive air monitoring station in Seoul, Korea, from January 2008 to March 2010. Five non-Asian dust (ND) episodes and two Asian dust (AD) episodes of high PM concentrations were selected for the study. During the ND episode, primary air pollutants accumulated due to low wind speeds, and PM_2.5 increased along with most other air pollutants. Particles larger than PM_2.5 were also high since these particles were generated by vehicular traffic rather than wind erosion. During strong AD episodes, PM_10–2.5 primarily increased and gaseous primary air pollutants decreased under high wind speeds. However, even during the AD episode, PM_2.5 and gaseous primary air pollutants increased when the effects of AD were weak and wind speeds were low. This study corroborates that accumulation of air pollutants due to a drop in surface wind speed plays an important role in short-term high-concentration occurrences. However, low wind speeds could not be directly linked to local emissions because a significant portion of accumulated air pollutants resulted from long-range transport.     

Application of back-trajectory techniques to the delimitation of urban clean air zones

Following a request by environmental authorities in New Zealand, atmospheric modelling has been applied to delimitation of clean air zones for urban areas. This approach involved the integration of a kinematic trajectory model with an atmospheric mesoscale model to identify the spatial extent of the catchment of air affecting air pollution concentrations in Christchurch on nights of high air pollution. The Regional Atmospheric Modelling System (RAMS) was configured for the region and idealised simulations performed to obtain predicted wind fields for synoptic situations typical of winter smog events. The predicted surface wind fields on two grids, with horizontal resolutions of 1.5 and 0.5 km, respectively, were then used to derive back-trajectories from the late evening peak of pollution over the central city (around 2200 NZST) to the time at which people tend to first light their domestic fires (around 1800 NZST). The results indicate that although winds are often light, the air tends to travel from a significant distance outside the city boundary over this time period. In particular, cold air typically travels up to 20 km from the Canterbury Plains to the west into the city during these air pollution events, as well as from small valleys in the Port Hills to the south of the city. This research illustrates the significance of upstream sources of air for providing relatively clean air to the city, and acting as buffer zones. It is, therefore, possible to identify the area around the city to which urban air quality is particularly sensitive. This area could either be designated as a buffer zone, or included within the clean air zone of the city. This technique also provides a useful tool for identifying the role of different components of the local wind field responsible for air pollution dispersion and transport in different parts of the area.     

Control of particle re-entrainment by wetting the exposed surface of dust samples

Experiments have been conducted in a wind tunnel to measure the emission factor of re-entrained particles from a dry or wetted dust sample with a smooth or rough surface. Effects of wind velocities and water contents in the sample on the emission factor also were investigated. The results show that re-entrainment of particles can be controlled efficiently in a certain period of time when the surface watering density is between 60 and 80 g/m2 at a wind velocity from 7 to 15 m/sec for both smooth and rough surfaces. After the effective period is elapsed, which depends on wind speeds and environmental conditions, water will eventually evaporate, and re-entrainment starts to occur again. The experimental water evaporation rates at different wind speeds are in good agreement with theoretical values. After watering for 210, 130, and 110 min at average wind velocities of 0, 2, and 4 m/sec, respectively, the dust sample must be replenished with water to avoid dust re-entrainment.     

Weed interference on maize (Zea mays) under no tillage system

A field trial was carried out in Brazil in March 2002 with the aim to evaluate the effects of different timing and extension of weedy period on maize productivity. The hybrid Pioneer 30K75 was sowed under 7 t ha(-1) mulching promoted by glyphosate spraying. The treatments were divided in two groups: In the first group, weeds were maintained since the maize sowing until different periods in the crop cycle: 0, 14, 28, 42, 56, 70, and 150 days (harvesting time). In the second group, the maize crop was kept weed free for the same periods of the first group. Weed control was done through hand hoeing. A complete randomized blocks experimental design with five replications was used for plots distribution in the field. Nonlinear regression model was used to study the effects of weedy or weedfree periods on maize productivity. Weed community included 13 families and 31 species. Asteraceae, Poaceae, and Euphorbiaceae were the most abundant families. Results showed that under no tillage condition with 7 t ha(-1) mulching at sowing time, the maize crop could cohabit with weed community for 54 days without any yield lost. On the other hand, if the crop was kept weed free for 27 days, the weed interference was not enable to reduce maize production. According to these results one weed control measure between 27 and 54 days after crop emergence could be enough to avoid any reduction in maize productivity.     

建筑物对高架点源大气污染物扩散影响的模拟研究

运用数值方法对城市中高架点源排放大气污染物的扩散规律进行了模拟研究,在计算区域内建立了三维数学模型,并将拉格朗日法描述的颗粒轨道模型耦合到风场。本研究计算了地面风速为3 m/s时的大气流场,并模拟研究了该风场条件下气体污染物的扩散和固体颗粒污染物的运动轨迹。通过分析模拟结果,给出了高架点源中排放的气体污染物的扩散区域和固体颗粒污染物运动轨迹的变化规律。     

钢铁厂露天堆料场挡风抑尘墙效果的数值模拟

对某钢铁厂露天堆料场设置挡风抑尘墙进行数值模拟研究,通过对动力阴影区覆盖面积的考察,分析了自然风速、墙高、墙开孔率及墙后建构筑物对挡风抑尘墙的挡风抑尘效果的影响.该钢铁厂露天堆料场设置防风抑尘墙的最佳几何尺寸是:墙长(L)为500 m,墙厚(d)为5 mm,墙高(H)为15～20 m,墙开孔率(k)为0.2～0.3,在主导风风速达到10 m/s以上的大风天气能够形成有效覆盖整个料场的动力阴影区,再配以合适的喷雾洒水或喷洒化学抑尘剂等其他抑尘手段就能够非常有效地抑制料场扬尘.     

干旱区地表石油污染物风蚀作用大气传输量估算研究

通过焉耆盆地石油开发区石油污染物水环境污染途径特点的分析 ,认为落地油将通过风蚀作用由大气传输以降尘的形式落入水体 ,对水环境产生影响。本文以土壤侵蚀的风洞实验求得污染源源强 ,采用高斯模式对地表风蚀作用的传输量进行估算 ,进而对石油开发区落地油通过大气传输途径对区域水环境 (博斯腾湖 )的影响进行了预测 ,建立了相应的模型。为人们了解干旱区石油污染物风蚀作用水环境污染影响提供了初步依据 ,对干旱区湖泊石油污染的全面防治提供了科学范式     

Weed Interference on Maize (Zea mays) Under No Tillage System

Abstract

A field trial was carried out in Brazil in March 2002 with the aim to evaluate the effects of different timing and extension of weedy period on maize productivity. The hybrid Pioneer 30K75 was sowed under 7 t ha^?1 mulching promoted by glyphosate spraying. The treatments were divided in two groups: In the first group, weeds were maintained since the maize sowing until different periods in the crop cycle: 0, 14, 28, 42, 56, 70, and 150 days (harvesting time). In the second group, the maize crop was kept weed free for the same periods of the first group. Weed control was done through hand hoeing. A complete randomized blocks experimental design with five replications was used for plots distribution in the field. Nonlinear regression model was used to study the effects of weedy or weedfree periods on maize productivity. Weed community included 13 families and 31 species. Asteraceae, Poaceae, and Euphorbiaceae were the most abundant families. Results showed that under no tillage condition with 7 t ha^?1 mulching at sowing time, the maize crop could cohabit with weed community for 54 days without any yield lost. On the other hand, if the crop was kept weed free for 27 days, the weed interference was not enable to reduce maize production. According to these results one weed control measure between 27 and 54 days after crop emergence could be enough to avoid any reduction in maize productivity.     

The Portable In Situ Wind Erosion Laboratory (PI-SWERL): A new method to measure PM10 windblown dust properties and potential for emissions

A new device—the Portable In Situ Wind ERosion Lab (PI-SWERL)—for measuring the potential for wind erosion and dust emission from soil surfaces is described. The device uses an annular ring (inner diameter=39 cm, outer diameter=51 cm) that rotates 6 cm above the soil test surface. Dust and sand are mobilized by the shear created by the rotating ring. Dust concentrations within the chamber that encloses the annular ring are measured by light scattering, used as a surrogate for particulate matter mass concentrations. While the PI-SWERL does not realistically simulate natural wind erosion processes that are often driven by saltation, measurements with the device provide a robust index of wind erosion/dust emission potential. Compared to traditional field wind tunnels used for the same purpose, the PI-SWERL offers significant economy in size, portability, and ease of use.     

Acetylcholinesterase in honey bees (Apis mellifera) exposed to neonicotinoids, atrazine and glyphosate: laboratory and field experiments

In Québec, as observed globally, abnormally high honey bee mortality rates have been reported recently. Several potential contributing factors have been identified, and exposure to pesticides is of increasing concern. In maize fields, foraging bees are exposed to residual concentrations of insecticides such as neonicotinoids used for seed coating. Highly toxic to bees, neonicotinoids are also reported to increase AChE activity in other invertebrates exposed to sub-lethal doses. The purpose of this study was therefore to test if the honey bee’s AChE activity could be altered by neonicotinoid compounds and to explore possible effects of other common products used in maize fields: atrazine and glyphosate. One week prior to pollen shedding, beehives were placed near three different field types: certified organically grown maize, conventionally grown maize or non-cultivated. At the same time, caged bees were exposed to increasing sub-lethal doses of neonicotinoid insecticides (imidacloprid and clothianidin) and herbicides (atrazine and glyphosate) under controlled conditions. While increased AChE activity was found in all fields after 2 weeks of exposure, bees close to conventional maize crops showed values higher than those in both organic maize fields and non-cultivated areas. In caged bees, AChE activity increased in response to neonicotinoids, and a slight decrease was observed by glyphosate. These results are discussed with regard to AChE activity as a potential biomarker of exposure for neonicotinoids.     

A directional passive air sampler for monitoring polycyclic aromatic hydrocarbons (PAHs) in air mass

A passive air sampler was developed for collecting polycyclic aromatic hydrocarbons (PAHs) in air mass from various directions. The airflow velocity within the sampler was assessed for its responses to ambient wind speed and direction. The sampler was examined for trapped particles, evaluated quantitatively for influence of airflow velocity and temperature on PAH uptake, examined for PAH uptake kinetics, calibrated against active sampling, and finally tested in the field. The airflow volume passing the sampler was linearly proportional to ambient wind speed and sensitive to wind direction. The uptake rate for an individual PAH was a function of airflow velocity, temperature and the octanol-air partitioning coefficient of the PAH. For all PAHs with more than two rings, the passive sampler operated in a linear uptake phase for three weeks. Different PAH concentrations were obtained in air masses from different directions in the field test.     

Correlation of Dust Scrubber Efficiency

The grid-type electrostatic precipitator¹ evolved from some basic research into the collection of airborne charged dust particles in the wake of a flat, metallic, perforated plate under the action of an externally applied electric field. In the earliest experiments in the laboratory² a flat grounded perforated plate (or grid) was placed at right angles to an air stream moving at 6 ft/sec and an electric field was created on its downstream side by the placement of a second grid, bearing high negative potential, just downstream of the first. Negatively charged dust particles, carried along by the air stream through the openings in the first of the two grids, collected on the downstream face of the upstream grid as a result of the electric force acting on them in the direction opposing the air flow. Measured values of dust collection efficiency could not be accounted for simply by resolving the directly opposing mainstream air flow and electrostatic forces. The concept of vortex-enhanced precipitation was therefore proposed in order to explain the experimental results.     

Cohesion of Precipitated Dust Layer in Electrostatic Precipitators

One of the important cohesive forces acting on the precipitated layer in an electrostatic precipitator Is that due to the effect of the electric field established in the air gaps between adjacent particles by the corona current as it flows through the layer. A theoretical expression for this force is developed for an idealized dust layer which takes into account the increase in effective contact area between adjacent particles due to elastic deformation and the limiting of the electric field in the airgap to a maximum allowable value. It is shown that the cohesive force is approximately proportional to the electric field established across the layer. This relationship is in general agreement with measurements made in the laboratory using industrially produced dust samples.