Factors influencing concentration effect

Due to the movement of the pesticides to the bed surface, air samples were taken to determine any volatilization and subsequent concentration In the air along the berm on the downwind side of the bed. In most Instances, the top of the berm was only about 12 vertical Inches above the bed surface. Spencer and Farmer ( ) have reviewed the literature on the transfer of pesticides Into the atmosphere. Even though pesticide volatility Is related to vapor pressure of the chemical, there are many factors Influencing the effective vapor pressure from soil and water surfaces. 

White phosphorus exposure to plants results in a variety of deleterious effects which are based upon the species of plant, the smoke concentration, the duration of exposure, the relative humidity, and the wind speed. These effects can include leaf tip bum, leaf curl, leaf abscission and drop, floral abortion, chlorosis, neucrotic spotting, wilting, dessication, and dieback. Other factors influencing the effects of white phosphorus upon plants are whether or not there is a post-exposure rainfall and whether the exposure is a large acute dose or several lower chronic doses (Van Voris et al. 1987). 

Another factor influencing the effectiveness of inhibitors is the anion concentration. At concentrations on the order of 10,000 ppm, some anions (e.g., sulfate) interfere with the inhibitor film formation. Again, the supplier of the specific inhibitor should be consulted. 

Gulden M, Morchel S, Seibert H (2001) Factors influencing nominal effective concentrations of chemical compounds in vitro cell concentration. Toxicol In Vitro 15 233-243... 

Several factors influence toxic effects, one of which is the concentration of a material (see Eigure 8.5). Concentrations may be expressed in terms of percentage or parts per million or billion per milligram or kilogram the higher the concentration, the more serious the effect. Eigure 8.6 illustrates some parts-per-million approximations. Some materials can also have an anesthetic effect. This may range from loss... 

When testing dispersant effectiveness in the field, it is very difficult to measure the concentration of oil in the water colnmn over large areas and at frequent enough time periods. It is also difficult to determine how much oil is left on the water surface as there are no methods available for measuring the thickness of an oil shck and the oil at the subsurface often moves differently than the oil on the surface. Field effectiveness trials, laboratory effectiveness tests, and factors influencing the effectiveness of a dispersant will be discussed in the following sections. 

Barrier properties of materials indicate their resistance to diffusion and sorption of molecules. A good barrier polymer has low values of both diffusion (D) and solubUity (S) coefficients. Since the permeabUity coefficient P is a derived function of D and S, a high-barrier polymer has low values of P. The diffusion coefficient is a measure of how fast a penetrant will move within the polymer in a particular direction, while the solubility coefficient gives the amount of the penetrant taken (or sorbed) per unit mass of polymer from a contacting phase per unit of sorbate concentration. Both diffusion and solubility can be applied to the reverse process of sorption, that is, the migration of compounds from the polymer to a surrounding media. Several factors influence the effective value of diffusion and solubility coefficients in polymers. 

An effective buffer neutralizes small to moderate amounts of added acid or base. Recall from the opening section of this chapter, however, that a buffer can be destroyed by the addition of too much acid or too much base. What factors influence the effectiveness of a buffer In this section, we examine two such factors the relative amounts of the acid and conjugate base and the absolute concentrations of the acid and conjugate base. We then define the capacity of a buffer (how much added acid or base it can effectively neutralize) and the range of a buffer (the pH range over which a particular acid and its conjugate base can be effective). 

Considerable studies have been done on the effects of the most important chemical and physical factors involved in the degradation of anthocyanins (temperature, light, pH, SO2, metal, sugar, and oxygen) in model systems and food extracts. In addition, anthocyanin concentrations, its chemical structures, and media compositions are fundamental factors influencing stability. 

Establishing the process sensitivity with respect to the above-mentioned factors is crucial for further scale-up considerations. If the sensitivity is low, a direct volume scale-up is allowed and the use of standard batch reactor configurations is permitted. However, many reactions are characterized by a large thermal effect and many molecules are very sensitive to process conditions on molecular scale (pH, temperature, concentrations, etc.). Such processes are much more difficult to scale up. Mixing can then become a very important factor influencing reactor performance for reactions where mixing times and reaction times are comparable, micromixing also becomes important. 

From the coverage made thus far, it may be of interest to record in one place the different factors which influence the rate of chemical reactions. The rate of chemical reaction depends essentially on four factors. The nature of reactants and products is one. For example, certain physical properties of the reactants and products govern the rate. As a specific example in this context mention may be of oxidation of metals. The volume ratio of metallic oxide to metal may indicate that a given oxidation reaction will be fast when the oxide is porous, or slow when the oxide is nonporous, thus presenting a diffusion barrier to the metal or to oxygen. The other two factors are concentration and temperature effects, which are detailed in Sections. The fourth factor is the presence of catalysts. 

Dose levels in vitro As for in vivo studies, it is necessary to establish a concentration-effect relationship. The upper limit of concentrations tested may be influenced by physicochemical properties of the test substance and other factors such as cytotoxicity. 

---