Concentration over time

Provides information on the plume size, motion, and concentration over time and predicts toxic corridors. 

Another study found that trichloroethylene can be absorbed from the atmosphere by foods and concentrated over time, so that acceptable ambient air levels may still result in food levels which exceed acceptable limits (Grob et al. 1990). The authors estimated that in order to limit food concentrations of trichloroethylene to 50 pg/kg (the maximum tolerated limit for food halocarbons in Switzerland), the level in surrounding air should not exceed 38.5 pg/m (0.007 ppm). Since the accepted levels found near emission sources are often far above this limit, foods processed or sold near these sources may routinely exceed the tolerated trichloroethylene concentration, thus making the setting of air emission standards problematic. It is also noteworthy that the limits recommended by Grob et al. (1990) exceed acceptable ambient air concentrations for many regions of the United States (see Chapter 7). 

Fish are often the focal point of interest for methylmercury contamination, representing the main exposure pathway for humans and wildlife. Unfortunately, longterm data sets with records of both mercury deposition and fish mercury concentrations over time are limited. In Sweden, Johansson etal. (2001) estimated that... 

Monitoring the change in serum PSA concentration over time (PSA rate, PSA velocity, or rising PSA values) and... 

The actual movement of a specific deep-well-injected hazardous substance depends on the types of processes that act on the waste and on the ways in which different processes interact. Figure 20.3 shows the expected change in concentration over time of a deep-well-injected organic compound in an observation well at an unspecified distance from the original point of injection. 

Placental tissue incubated for as long as 24 h in media containing 145 mg Ni/L MONKEYS When compared to controls, treated tissues had increased permeability, lipid peroxidation, and nickel concentration over time. Treatment with ascorbic acid or zinc decreased nickel-induced placental lipid peroxidation and permeability, but had no effect on nickel tissue concentrations 43... 

Kinetics is the study of the speed of reactions. The speed of reaction is affected by the nature of the reactants, the temperature, the concentration of reactants, the physical state of the reactants, and catalysts. A rate law relates the speed of reaction to the reactant concentrations and the orders of reaction. Integrated rate laws relate the rate of reaction to a change in reactant or product concentration over time. We may use the Arrhenius equation to calculate the activation... 

With respect to the detection of C-odd-SPC in the present test solution, their occurrence can be explained by the fact that the C12-LAS used contained an impurity of some 0.5% of C-odd-LAS. The concentration profile of the C-odd SPC is displayed in Fig. 5.1.6. The long-chain Cu SPC is not detectable, while the levels of C9- and C7-SPC are below 0.3 pmol L-1. The change in C5- and C7-SPC concentrations over time qualitatively resembles that of C6- and C -SPC, respectively. C5-SPC is accumulated in the test liquor up to about 5 pmolL-1, but upon addition of the nutrient solution, the concentration drops rapidly. This is reduced to a certain level, but is not completely eliminated, with... 

Equation (5) describes the variation of a metabolite concentration over time as proportional to the rates in which a metabolite is synthesized minus the rates at which it is consumed. A stationary and time-invariant state of metabolite concentrations S° (steady state) is characterized by the steady-state condition... 

Three approaches have been recommended to obtain evidence for in situ biodegradation [71,343,344], including (1) quantitative determination of the pollutant of interest in samples collected at different times to show a decrease in its concentration over time, (2) lab oratory-based microbial degradation studies under conditions that mimic the environment to show the potential of biodegradation in the field, and (3) searching for a particular metabolite of biodegradation in samples collected from the field. Thus, without knowing the amount and nature of PAH inputs, it is impossible to estimate any biotic loss of PAHs. 

The last paper in this category describes monitoring of a submerged filamentous bacterial cultivation.38 Arnold et al. studied a 12-1 stirred tank where a strain of Streptomyces fradiae was used for fermentation. They followed ammonium, methyl oleate, glucose, and glutamate concentrations over time in the production of tylosin. 

Pharmacokinetic concentration-time curves for a drug and ifs mefabolifes are used to identify primary exposure metrics such as AUC, or which are not time-dependent unlike the sequential measurements of concentration over time. A peak plasma concentration of a drug is often associated with a PD response, especially with an adverse event. There can be large inter-individual variability in the time-to-peak concentration, and closely spaced sampling times are often critical to determining the peak plasma concentration accurately in individual patients because of differences in demographics, disease states, and food effects, if any. All these elements are clearly spelled out in the protocols written to conduct these studies. 

The area under the plasma-concentration time curve, the AUC, is a useful parameter in defining fhe overall body exposure to a drug this parameter integrates the concentration-over-time fimction ... 

To learn more about reaction rates expressed as changes in concentration over time, go to the Chemistry 12 Electronic Learning Partner. 

Starting materials can be defined as the raw materials that form the basis of a chemical reaction as a part of the synthesis of an intermediate in the production of a drug substance. Catalysts typically include any material added to a mixture to accelerate, control, or otherwise modify a chemical reaction. Intermediates are those products of a synthesis scheme that will undergo further reaction. By-products are the side-products of a chemical reaction, and may include conjugates, dimers, enantiomers, unintended salts or free-bases, over-substitution, others. These types of impurities are usually considered to be process impurities and are not expected to increase in concentration over time. 

The concentration over time of the initiating carcinogenic chemical (typically a metabolite) at the cellular target. 

Oceanographers follow three basic approaches to collecting data for the study of biogeo-chemical processes (1) they measure concentrations over time and space, (2) they make direct measurements of chemical fluxes, and (3) they perform laboratory experiments... 

Turbulent mixing coefficient Constant of porportionality used in Pick s First and Second Laws to predict changes in solute concentration over time or fluxes from solute gradients that arise from turbulent mixing. The constant is a function of length scales and the degree of density stratification and hence is termed a coefficient . 

II.a.3. Repeated Oral Dosing with Measurements of Blood Plasma Concentration over Time... 

Table E6.12.1 Estimated concentration over time and space with transport through a uniformly porous sandstone...

Solve the tanker truck spill problem of Example 2.2 using explicit, central differences to predict concentrations over time in the groundwater table. Compare these with those of the analytical solution. The mass spilled is 3,000 kg of ammonia over 100 nf, and the effective dispersion coefficient through the groundwater matrix is 10 m2/s. 

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