Surrogate particles

Until now, toxicological studies have failed to adequately address the issue of inhaled particle toxicity relative to the foregoing mechanisms. Most studies have been limited by exposure protocols and the lack of clear-cut pathways for toxic effects. The best currently available studies have employed surrogate particles (26) or limited combinations of ambient pollutants to take into account atmo-... 

The solubihty of hydrophobic substances in, or their absorbabiUty on suspended particles, on sediments, on biota, or on soil particles can be related to the solubihty of these substances in organic solvents. The solvent -octanol, CH2(CH2)yOH, is a kind of surrogate for many kinds of environmental and physiological organic substances and has become a reference phase for organic phase water partitioning of organic solutes. 

As a generalization, to be orally well absorbed a compound must be soluble in the contents of the gastrointestinal lumen [4]. Solubility in aqueous buffer is commonly used as a simpHfying surrogate for intestinal content solubility. There are rare exceptions to the principle that to be absorbed a compound must be soluble. SoHd particles, e.g. starch, can be absorbed. Absorption of very small quantities of even biologically very large compounds can occur via lymphoid tissue, e.g. orally active vaccines. Very hpophihc basic compounds, e.g. certain antimalarials, can be absorbed via the intestinal lymphatics and dehvered directly to the heart... 

The presence of particles in the brains of experimental rats and humans exposed to asbestos has been reported (Pontefiart and Cunningham, 1973 Auerbach et al., 1980). In experimental studies, particles of Teflon, a reflux paste, enter the brain via intravascular transport when injected into the bladder (Aaronson et al., 1993). Encephalitic reactions to accumulated calcium oxalate crystals in the brain as a result of infusions of glucose surrogate polyol solutions have been described (PciflPcr etal., 1984). Such studies indicate the capacity of particulates to enter the brain and thus pose a potential pathological threat to the functioning of the central nervous system (CNS). 

NoV are readily transferred from hands to fomites and vice versa (Bidawid et al., 2004 D Souza et al., 2006). The pronoimced environmental stability of NoV particles also contributes to the spread of outbreaks from point sources of surface contamination. All stability studies have made use of surrogate organisms to model NoV response to conditions, since the human virus is not easily grown in cell culture (Duizer et al., 2004b Straub et al., 2007). The murine norovirus (MNV) and the feline calicivirus (FCV) have both been used, with the mouse virus providing more... 

A critical requirement for the success of receptor models for atmospheric particles Is that the compositions of particles from all major sources in an area be accurately known. Chemical element balances (CEBs) of 130 samples taken In Washington, D.C. and analyzed for 40 elements yielded nearly the same source strengths when 28 elements are used In the least-squares fit as when only nine carefully chosen elements are used. Certain elements are important to the stability of CEB fits (Na, Ca, V, Mn, As and Pb) and should be measured carefully In particles from sources. For three of the nine elements (Al, Fe and Zn), other elements can serve as surrogates (many lithophlles for Al and Fe, Sb and Cd for Zn). Measurements on many more sources of each Important type should be done In order that trends can be observed that will allow one to predict compositions of particles from unmeasured sources. Instack measurements should Include collections of at least two size fractions of particles plus vapor-phase species. Measurements of at least 20 elements plus some classes of carbonaceous material should be made. 

Implications for Source Studies. The results discussed above Indicate the need for measurements of a number of elements In studies of particles both from sources and In ambient air. Measurements of Na, Pb, Ca, As, Mn and V are very Important for use In receptor models. Aluminum and Fe are quite useful, but not essential If many other llthophlle elements are measured (e.g., SI, Tl, Sc). Likewise, Zn Is useful, but could be replaced by elements such as Sb and Cd. However, AI, Fe and Zn can usually be measured more easily than their surrogates. Iron and elements such as Cr, Mn, Co and N1 will be Important In areas that have Iron and steel Industries and elements such as Cu, Zn, Pb and other chalcophlles In areas that have non-ferrous metal Industries. Sources of the unexplained Mn, Cr, Cu, Nl, K and Mg In Washington need to be Identified. Thus, we have a set of about 15 elements that should be measured as a minimum, plus others that may provide additional useful Information, e.g., Br, Ba, Cd, Sb. Note that It Is not sufficient to measure a given element only In particles from the dominant source of the element. For example, motor vehicles are the major source of Pb In most areas however, significant amounts are released by refuse Incinerators and non-ferrous smelters. Thus, If the CEB Is to determine the correct source strength for the motor—vehicle component, Pb contributions from the other, less Important sources must be known. 

More recently, Chung introduced a combination of a well-designed GO surrogate 30 and ruthenium colloidal particles (RuCNC) (Equation (12)). =... 

The key parameter for any drug product is its efficacy as demonstrated in controlled clinical trials. The time and expense associated with such trials make them unsuitable as routine quality control methods. Therefore, in vitro surrogate tests are often used to assure that product quality and performance are maintained over time and in the presence of change. A variety of physical and chemical tests commonly performed on semisolid products and their components (e.g., solubility, particle size and crystalline form of the active component, viscosity, and homogeneity of the product) have historically provided reasonable evidence of consistent performance. More recently, in vitro release testing has shown promise as a means to comprehensively assure consistent delivery of the active component(s) from semisolid products. 

Particle deposition velocities depend on a number of factors, including wind speed, atmospheric stability, relative humidity, particle characteristics (diameter, shape, and density), and receptor surface characteristics. Recent studies on dry particle deposition to surrogate surfaces and derived from atmospheric particle size distributions and micrometeorology suggest that a V equal to about 0.5 cm s 1 is applicable to urban/industrial regions [116-120]. 

Validation of the methodology used for components that could not be detected in extracts of particle samples was obtained by extraction of surrogate samples. The surrogate sample for PAHs was soot generated from an air-starved methane flame. The positive results obtained from this soot sample have been reported elsewhere (13). The surrogate sample for dioxins was an incinerator ash obtained from Dow Chemical Company. Results obtained from analysis of extracts of this ash sample were 50% of the published values for the tetra-, hexa-, hepta- and octachloro- isomers (14). This agreement substantiated the validity of the analytical protocol used to screen the effluent samples for dioxin compounds. 

As an application, in Figure 1 we compare the prediction Z t) of the surrogate theory and the result of nonequilibrium MD simulation. The solute is a spherical particle with Lennard-Jones (LJ) parameters e/kg =2668 K, a =6.975 A, which undergoes ionization from = 0 to = 1 e (where e is the proton charge). The simulation results are... 

In some situations where one or more of the latex properties are measured either directly or indirectly through their correlation with surrogate variables and where extreme nonlinearities such as the periodic generation of polymer particles does not occur, one can use much simpler modehng and control techniques. Linear transfer function-type models can he identified directly from the plant reactor data. Conventional control devices such as PID controllers or PID controllers with dead-time compensation can then be designed. If process data is also used to identify... 

In mashing, the next step in the process, the dried malt and the starch adjunct (malt surrogate, 25-30% of the total starch) are ground up to coarse particles. Some of the ground malt and the whole of the adjunct are then mixed with water and boiled for half an hour in a cereal cooker to convert insoluble to soluble starch (Eqs. 16.3 and 16.4). 

---