Chemicals factors affecting concentrations

Progress in quality control and in basic understanding of the physical and chemical factors affecting formaldehyde emission processes have made it possible to predict formaldehyde indoor air levels for most use conditions. Progress in manufacturing techniques and implementation of new technology have reduced formaldehyde emission so much that UF-bonded wood products can now be used in almost all applications without indoor air concentrations exceeding 0.I pp. 

A second chemical factor affecting mineral weatherability is the position of ions in the structure. The tetrahedra of Ca feldspars contain half Al3+ and half Si4+. At room temperature, Al3+ is more stable in octahedral coordination, The charge deficit created by the Al3+ substitution is made up by Ca2+ ions between the tetrahedra. The structural strain, the charge deficit in the tetrahedra, and concentrated Ca2+ counter charge weaken the anorthite feldspar structure with respect to weathering relative to Na and K feldspars. In Na and K feldspars, only one-quarter of the tetrahedral positions are occupied by A1 and that charge deficit can be locally neutralized by Na+ or K+. Calcium feldspars are, therefore, the least stable feldspars under soil conditions. Potassium feldspars are more stable than Na feldspars, because K fits better between adjacent tetrahedra. 

Figure 5.9 Root concentration factor in barley roots for substituted phenoxyacetic acids as a function of pH. The lines represent predictions based on the ion-trap mechanism. O, 2,4-D ( ), 3,5-D. [Reproduced from G. G. Briggs, R. L. O. Rigitano, and R. H. Bromilow, Physico-chemical factors affecting uptake by roots and translocation of weak acids in barley Pesticid. Sci. 19, 101. Copyright 1987, Society of Chemical Industry. Reproduced with permission granted by John Wiley and Sons, Ltd on hehalf of the S.C.I.]...

Adsorption — An important physico-chemical phenomenon used in treatment of hazardous wastes or in predicting the behavior of hazardous materials in natural systems is adsorption. Adsorption is the concentration or accumulation of substances at a surface or interface between media. Hazardous materials are often removed from water or air by adsorption onto activated carbon. Adsorption of organic hazardous materials onto soils or sediments is an important factor affecting their mobility in the environment. Adsorption may be predicted by use of a number of equations most commonly relating the concentration of a chemical at the surface or interface to the concentration in air or in solution, at equilibrium. These equations may be solved graphically using laboratory data to plot "isotherms." The most common application of adsorption is for the removal of organic compounds from water by activated carbon. 

Several factors can influence metal uptake by stream autotrophic biofllms in fluvial systems. These include chemical factors (pH, saUnity, phosphate concentration) which affect metal bioavailabiHty by either altering the speciation of the metal or by complexing it at the biotilm s matrix and cell surfaces [18, 40], and also other biological and physical factors. 

Factors affecting the size of the mesoglobules include polymer concentration, i.e. the size increases with solution concentration and, more importantly, heating rate (Fig. 34). Thus, a fast increase in temperature (nonequilibrium heating) leads to mesoglobules of smaller size than those formed upon slow heating through the sample LCST [ 141 -145,147]. The chemical composition of... 

Host plant preferences of insect pests are often Influenced by environmental conditions. The effects of plant stress on susceptibility to Insect attack have been obseirved in many crop plants. Stress factors affecting the physiological state of the plant Include drought, disease, chemical pollutants, and high salt concentrations. Profound... 

Howat, G. R. and Wright, N. C. 1937. Factors affecting the solubility of milk powders. III. Some physico-chemical properties of concentrated solutions of milk solids. J. Dairy Res. 5, 236-244. 

The formation of complexes is affected by many physical and chemical factors. Such environmental factors as solvent, temperature and pressure are often important. Concentration factors sometimes markedly influence the stabilities of the complexed species in solution. The role of the donor atoms of the ligand in forming complexes has already been mentioned. 

A second important factor affecting the kidneys sensitivity to chemicals is its ability to concentrate the tubular fluid and, as a consequence, as water and salts are removed, to concentrate any chemicals it contains. Thus a nontoxic concentration in the plasma may be converted to one that is toxic in the tubular fluid. The transport characteristics of the renal tubules also contribute to the delivery of potentially toxic concentrations of chemicals to the cells. If a chemical is actively secreted from the blood into the tubular fluid, it will accumulate initially within the cells of the proximal tubule or, if it is reabsorbed from the tubular fluid, it will pass into the cells in relatively high concentration. 

Many factors potentially can affect the distribution of an organic chemical between an aqueous and solid phase. These include environmental variables, such as temperature, ionic strength, dissolved organic matter concentration, and the presence of colloidal material, and surfactants and cosolvents. In addition, factors related specifically to the experimental determination of sorption coefficients, such as sorbent and solid concentrations, equilibration time, and phase separation technique, can also be important. A brief discussion of several of the more important factors affecting sorption coefficients follows. 

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