Particle concentration effect , trace

Figure 14.5 Particle concentration effect showing negative relationship between particle/solution partition coefficient (X,j) of selected trace metal ions and suspended particulate matter (SPM). Data are from six Texas estuaries (USA). (Modified from Benoit et al., 1994.)...

Benoit G. and Rozan T. F. (1998) The influence of size distribution on the particle concentration effect and trace metal partitioning in rivers. Geochim. Cosmochim. Acta 63(1), 113-127. 

The solid-water interface, mostly established by the particles in natural waters and soils, plays a commanding role in regulating the concentrations of most dissolved reactive trace elements in soil and natural water systems and in the coupling of various hydrogeochemical cycles (Fig. 1.1). Usually the concentrations of most trace elements (M or mol kg-1) are much larger in solid or surface phases than in the water phase. Thus, the capacity of particles to bind trace elements (ion exchange, adsorption) must be considered in addition to the effect of solute complex formers in influencing the speciation of the trace metals. 

Tsai WT, Lai CW, Hsien KJ (2003) Effect of particle size of activated clay on the adsorption of paraquat from aqueous solution. J Coll Interface Sci 263 29-34 Turner A (1996) Trace-metal partitioning in estuaries Importance of salinity and particle concentration. Marine Chemistry 54 27-39... 

One of the constant concerns of numerous industries where either aerosols or toxic vapors are produced is the effects of these upon workers. A variety of health problems arise because of the workers inhaling gases and aerosols of irritant or toxic fibers which are produced in the normal course of activities. A less obvious hazard arises from the attachment of trace molecular species to particles. If these trace species are radioactive or chemically toxic, the particles, which effectively concentrate them, provide a vehicle for delivery deep within the body causing a health hazard far beyond that suggested by their gross molecular concentration in the air [1.31,32]. Kinetic theory, thermodynamics, and interaction forces, all enter into descriptions of the attachment process. 

To have an intuitive understanding of the concentration effect, we consider a suspension of hard spheres. Suppose that a portion of the suspension acquires temporarily a higher concentration than the surrounding, as shown in Pigure 3.25a. The particles in the locally concentrated region tend to move away from each other, resulting in the collision of black particles with white particles (Pig. 3.25b). Upon collision, the particles bounce back, although the motion is overdamped in a viscous environment (Pig. 3.25c). When we trace the motion of each black particle, the collision makes the square displacement smaller compared with the one in the absence of collisions. The effect of the local concentration fluctuation is, however. 

The chemistry of carbon, and radiocarbon, in the atmosphere represents one of the most important areas of environmental research today. The primary practical reason for this is the increasing attention which must be paid to the critical balance between energy and the environment, especially from the viewpoint of man s perturbations of natural processes and his need to maintain control. Probably more than other species, carbonaceous molecules play a central role in this balance. Some of the deleterious effects of carbonaceous gases and particles in the atmosphere are set down in Table 3. The potential effects of increased local or global concentrations of these species on health and climate have led to renewed interest in the carbon cycle and the "C02 Problem". It should be evident from the table, however, that carbon dioxide is not the only problem. In fact, the so-called "trace gases and particles" in the atmosphere present an important challenge to our interpretation of the climatic effects of carbon dioxide, itself [20]. 

Most of the trace elements are present in concentrations well below those that should result from the maintenance of simple equilibria with mineral phases. Clearly some other processes are effectively removing these elements from seawater. As it turns out, all of these processes involve incorporation of the trace metals into sinking particles. 

During controlled exposures of human subjects to specific compounds like ozone, the concentrations of suspended particles and trace gases must be known and minimized to ensure that health effects can be attributed solely to ozone. The air purification units for the environmental chambers are designed to remove most of the particles and pollutant gases from the ambient air. Prefilters and efficient absolute filters are used to remove 99% of the particles with diameters of 0.3 nin... 

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