Herbicide dispersal

Stable activable tracers are powerful tools for the study of many environmental problems. Compared with fluorescent dyes or radiotracers, they offer many advantages that are reviewed herein. Our research group has emphasized the use of rare earth nuclides with short-lived activation products as stable activable tracers. Use of rare earth nuclides is cost-competitive with conventional tracers and allows rare earth "fingerprints to mark individual sources with subsequent simultaneous tracing of effluents from several sources. We present results from the application of these tracers to monitor pollutant dispersal from multiple industrial stacks, monitor fluid-bound pollutant dispersal in estuarine and fresh-water systems, monitor herbicide dispersal, and trace toxic organic chemicals in the marine environment. 

Biospheric Applications. The current controversies about the dispersal of herbicides used in forestry have demanded the immediate implementation of tracer techniques that can be used in connection vsdth herbicide dispersal. As a result, we have developed a quick and dirty tracer technology. The success of our eflFort has certain consequences concerning strategies for monitoring herbicide dispersal and for establishing legal responsibility for its consequences. 

It is true that to trace the movement of the herbicides studied in this work in the environment, one would need only to measure the As content of various samples. However, the results do have potential usefulness in monitoring herbicide dispersal. Quite frequently, the problem is not to establish whether or not herbicides were present but to establish who was responsible for the herbicide. Thus, drawing on this work and previous work involving multiple source tracing in fresh water (17), one should be able simply to mark a given application of herbicide wdth a... 

I wish to acknowledge the cooperation and assistance of a number of my graduate students, past and present, whose experimental work forms the basis of this report. They include Y. S. Shum (air-pollutant tracers) S. W. K. Chick, K. M. Keasler (fiuid-bound pollutants) A. Borovik (herbicide dispersal) and L. Ghannam (toxic organic chemicals). I would gratefully acknowledge financial support for these eflForts... 

Frisch, Gerhard, "Aqueous Herbicidal Dispersion Concentrate Containing Linuron And Monolinuron As Active Substances", United States Patent 5,226,945, issued July 13, 1993. 

Uses Matched emulsif er pair with Toximul R-HF for herbicides dispersant, stabilizer, hydrophilic agent Regulatory EPA cleared Properties Dk. brn. liq. sol. in xylene HLB 13.0 TOXIMUL SF Series [Stepan]... 

Volatilization. The susceptibility of a herbicide to loss through volatilization has received much attention, due in part to the realization that herbicides in the vapor phase may be transported large distances from the point of application. Volatilization losses can be as high as 80—90% of the total applied herbicide within several days of application. The processes that control the amount of herbicide volatilized are the evaporation of the herbicide from the solution or soHd phase into the air, and dispersal and dilution of the resulting vapor into the atmosphere (250). These processes are influenced by many factors including herbicide application rate, wind velocity, temperature, soil moisture content, and the compound s sorption to soil organic and mineral surfaces. Properties of the herbicide that influence volatility include vapor pressure, water solubility, and chemical stmcture (251). 

Sorbed pesticides are not available for transport, but if water having lower pesticide concentration moves through the soil layer, pesticide is desorbed from the soil surface until a new equiUbrium is reached. Thus, the kinetics of sorption and desorption relative to the water conductivity rates determine the actual rate of pesticide transport. At high rates of water flow, chances are greater that sorption and desorption reactions may not reach equihbrium (64). NonequiUbrium models may describe sorption and desorption better under these circumstances. The prediction of herbicide concentration in the soil solution is further compHcated by hysteresis in the sorption—desorption isotherms. Both sorption and dispersion contribute to the substantial retention of herbicide found behind the initial front in typical breakthrough curves and to the depth distribution of residues. 

Agricultural Products. Pesticides are frequendy appHed as emulsiftable concentrates. The active insecticide or herbicide is dissolved in a hydrocarbon solvent which also contains an emulsifier. Hydrocarbon solvent selection is critical for this appHcation. It can seriously impact the efficacy of the formulation. The solvent should have adequate solvency for the pesticide, promote good dispersion when diluted with water, and have a dash point high enough to minimise dammabiUty ha2ards. When used in herbicide formulas, low solvent phytotoxicity is important to avoid crop damage. Hydrocarbon solvents used in post-harvest appHcation require special testing to ensure that polycycHc aromatics are absent. 

The two examples of sample preparation for the analysis of trace material in liquid matrixes are typical of those met in the analytical laboratory. They are dealt with in two quite different ways one uses the now well established cartridge extraction technique which is the most common the other uses a unique type of stationary phase which separates simultaneously on two different principles. Firstly, due to its design it can exclude large molecules from the interacting surface secondly, small molecules that can penetrate to the retentive surface can be separated by dispersive interactions. The two examples given will be the determination of trimethoprim in blood serum and the determination of herbicides in pond water. 

The solutes were separated by standard reverse phase processes where differential interactions occur between the dispersive centers of the solute molecules and the hydrocarbon chains of the reversed phase. The concentration of the herbicides in the pond water was 10 ppb. 

Nonpoint source sampling occurs where the analyte of interest is dispersed over a large area such that a specific point of origin cannot be ascertained. The innate occurrence of analytes of interest would be an example of a nonpoint source. The occurrence of plant nutrients, either naturally occurring or from fertilization, is an example of a nonpoint source of agricultural analytes. Herbicides, insecticides, and pest-control agents are, once applied on a field scale, also potential nonpoint sources of analytes. It is common to think of crop... 

Wauchope and Myers [116] studied the adsorption-dispersion kinetics of Atrazine and Linuron in sediment-aqueous slurries. The resulting adsorption or desorption was very rapid, approaching 75% of equilibrium values within 3-6min. Chlorinated adsorption of the herbicide on the sediment was completely reversible after 2h of adsorption. 

During the late spring and summer of 1990 and 1991, a USGS study focused on herbicide transport into the atmosphere by various processes. This study was conducted prior to significant label rate reductions for atrazine-containing products. Once in the atmosphere, these compounds can be dispersed by air currents and redeposited by precipitation, snow, and dry deposition on the land surface, lakes, and streams. 

The distribution of body weights was assumed to be a normal distribution with mean 70 kg and a 20% coefficient of variation (i.e., a standard deviation equal to 14kg). The amount of exposure for a body part was a PHED-based distribution, depending on the body part and the type of user, as well as the type of herbicide formulation used. The herbicide formulations were granule (G) formulated with fertilizer and used by homeowners for residential lawn care flowable formulation (FF), which is among the formulations classified as emulsifiable concentrate (EC) in PHED and water-dispersible granule (WDG). 

Many industrial and consumer products are formulated as emulsions including numerous surface coatings (Chapter 12), foods, pesticides and herbicides (Chapter 13), pharmaceutical products (Chapter 14), and personal care products such as creams and lotions (Chapter 15). Some emulsions are made to reduce viscosity so that an oil can be made to flow. Emulsions of asphalt, a semi-solid variety of bitumen dispersed in water, are formulated to be both less viscous than the original... 

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