Scavenging trace elements

The influence of river water inputs on trace metal distributions is illustrated in Figure 11.17c, which shows that the surface-water concentration of dissolved Mn in the Pacific Ocean decreases with increasing distance from the California coast. The vertical profile measured in the coastal zone (Figme 11.17b) exhibits a strong surface enrichment characteristic of scavenged trace elements. A similar vertical gradient is seen in the... 

They scavenge a variety of materials (e.g. nutrients and trace elements) from the air... 

Pippenger, C.E., Meng, X., Stolfi, V, McGonagle, B. and Fazio, V.W. (1991). Free radical scavenging activities and trace element concentrations in erythrocytes and plasma of adult patients with inflammatory bowel disease. In Inflammatory Bowel Diseases. Progress in Basic Research and Clinical Implications (eds. H. Gocbell, K. Ewe, H. Malchow and Ch. Koelbel) p. 33. Kluwer Academic Publishers, Lancaster. 

Craig, H. (1974). A scavenging model for trace elements in the deep sea. Earth Planet. Sci. Letters, 23, 149-59. 

As shown in Table 11.3, the concentrations of trace elements in the water column is - despite anthropogenic pollution - extremely small (10 11 - 10 7 M) illustrating the remarkable efficiency of the continuous "conveyor belt" of the settling adsorbing and scavenging particles. The sedimentary record reflects the accumulation of trace elements in sediments and a profile of concentration vs sediment-depth (or age) gives a "memory record" on the loading in the past (Fig. 11.9). 

Table 11.3 Ocean. Deepwater Scavenging Residence Times of Some Trace Elements in the ...

Trace elements that undergo scavenging are characterized by vertical profiles in which dissolved concentrations decrease with increasing depth. These include Al, Mn, Pb, Ce,... 

Th, Co, and, in some locations, Fe. Surfece-water enrichments are usually caused by rapid rates of supply to the mixed layer via atmospheric deposition or river runoff. Removal usually occurs through relatively rapid precipitation into or adsorption onto sinking particles. Trace elements controlled by scavenging tend to have short (100 to lOOOy) residence times. Since these residence times are less than the mixing time of the ocean, significant geographic gradients are common. 

Trace elements, as exemplified by Pb (Fig. 10), frequently exhibit an increase in concentration between 1 and 3 days of corrosion, followed by a decrease between 3 and 10 days, but absolute values vaiy strongly from sample to sample and from element to element. This observation supports the hypothesis that crystalline secondary phases forming at the surface of corroded HT materials act as trace metal scavengers. 

J. P. Hu and co-workers, Structure-Activity Relationship ofFlavonoids with Superoxide Scavenging Activity, Biological Trace Element Research, Vol. 47, The Humana Press Inc., Clifton, N.J., pp. 327—331,1995. 

Assuming that particle-reactive radionuclides and many other trace elements are scavenged by particles settling through the water column, and that these fluxes of sediment and the associated radionuclide have remained constant over time, an accumulation rate (A) can be calculated using the following equation ... 

The availability of other sample media at a drainage site has been briefly mentioned previously. The dirty water filters with the >45 im suspended sediment captured on the filter discs could be very useful in studies of the suspended-sediment load. The Fe and Mn coatings on pebbles and other chemical precipitates (e.g., insoluble Fe hydroxides) could also be collected as these are known to have good scavenging properties for certain trace elements. 

Formation of Biogenic Manganese Oxides and Their Influence on the Scavenging of Toxic Trace Elements... 

Table 10 The deepwater scavenging residence times of some trace elements in the oceans...

Finally, we must somehow resolve the vexing problem of the chemical speciation of trace elements in seawater what is the chemical nature of the various metal chelators whose existence has been demonstrated by electrochemistry Is the chemistry of several metals in surface seawater really controlled by metallophores released by prokaryotes Or are dissolved metals chiefly present as parts of metalloproteins in the process of remineralization How do metal chelators affect the residence times of metals (in particular, scavenged elements such as iron and cobalt) and in turn how do those chelators influence the global carbon cycle via changes in marine primary productivity ... 

German C. R., Campbell A. C., and Edmond J. M. (1991b) Hydrothermal scavenging at the Mid-Atlantic Ridge modification of trace element dissolved fluxes. Earth Planet. Sci. Lett. 107, 101-114. 

Particles represent important agents of transport in global ocean cycles of many trace elements, of carbon, and of other substances. Once introduced into the oceans, many trace elements are removed from seawater by scavenging (sorption, com-plexation, and other forms of surface reactions) to particles (Goldberg, 1954 Turekian, 1977). Scavenging and burial in marine sediments represents the principal loss process influencing the biogeochemical cycle of many trace elements in the ocean (Li, 1981). 

It is well established that selenium is an essential trace element and selenium dietary supplements are commonly available, especially in countries such as France and New Zealand, where soils are selenium deficient. The principal role of selenium in vivo is to prevent free-radical damage either through incorporation into radical scavengers, or indirectly through reduction of the byproducts of oxidative damage. 

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