Metal transport, atmosphere

Bismuth, considered a potential tracer of volcanic activity, has been extensively studied thanks to the exceptional sensitivity of LEAFS. So far, little attention has been paid to this metal whose atmospheric cycle is likely to be still undisturbed by man. This element can be of extraordinary importance, since it can represent untransformed tracers of specific natural sources and of atmospheric transport pathways. Although data on the occurrence of Bi in the environment are still very scarce, it is indeed likely that this metal is an excellent tracer of volcanic emission into atmosphere, since concomitant emissions from other natural sources are of little importance (84-86). Investigations of the occurrence of this metal in polar archives could produce very valuable time series of volcanic activity in both hemispheres and relevant data on the transport patterns of volcanic aerosols in the atmosphere (87). 

With few exceptions, metallothioneins consist of relatively simple amino acids, aromatic amino acids and histidine only being found in a small number of species [329]. This amino acid composition suggests that metallothioneins evolved early in the evolution of life, probably even before the oxygenation of the atmosphere. A further clue is one of their functions. As metal-transport and storage proteins, thioneins are capable of binding metal ions but release them relatively easily as well. Metallothioneins can therefore be considered a transition from non-metal to metalloproteins. It is improbable, however, that the known copper proteins evolved from copper metallothioneins as there are no homologies between them and other copper proteins or enzymes. 

Pollution plume trajectories in the Southern Hemisphere have received less attention in comparison with the Northern Hemisphere. There are few studies of long-range metal transport from Africa or South America despite the fact that these continents are known to be significant emitters of metals to the atmosphere (Fig. 4). A number of studies have been undertaken examining metal pollution accumulation in Antarctica, which being the most remote landmass from urban... 

Table 6.1 shows fluxes for metals from mines, emission to atmosphere, transportation by rivers, and removal by rainwater. Most of anthropogenic metals transported to atmosphere are taken up by rainwater. However, this is unclear because fluxes to the atmosphere are not only by human activity but also by namral process such as volcanic activity and estimated proportion of these two processes has large uncertainty. Riverine fluxes to ocean are mostly larger than anthropogenic fluxes to atmosphere and fluxes by rainwater, but anthropogenic fluxes to atmosphere for toxic metals (Pb, Hg, Se, As, and Sb) are considerably large. 

Chemical Reactivity - Reactivity with Water. Reacts violently with water, liberating hydrogen chloride gas and heat Reactivity with Common Materials None if dry. If wet it attacks metals because of hydrochloric acid formed flammable hydrogen is formed Stability During Transport Stable if kept dry and protected from atmospheric moisture Neutralizing Agents for Acids and Caustics Hydrochloric acid formed by reaction with water can be flushed away with water. Rinse with sodium bicarbonate or lime solution Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Before electron transfer can occur the oxygen in the atmosphere must be transported to the metal/solution interface, and this involves the following steps... 

The atmosphere may be an important transport medium for many other trace elements. Lead and other metals associated with industrial activity are found in remote ice caps and sediments. The transport of iron in wind-blown soil may provide this nutrient to remote marine areas. There may be phosphorus in the form of phosphine, PH3, although the detection of volatile phosphorus has not been convincingly or extensively reported to date. 

Natural mobilization includes chemical, mechanical, and biological weathering and volcanic activity. In chemical weathering, the elements are altered to forms that are more easily transported. For example, when basic rocks are neutralized by acidic fluids (such as rainwater acidified by absorption of CO2), the minerals contained in the rocks can dissolve, releasing metals to aqueous solution. Several examples are listed below of chemical reactions that involve atmospheric gases and that lead to the mobilization of metals ... 

Volcanic activity has a significant effect on the mobilization of metals, particularly the more volatile ones, e.g., Pb, Cd, As, and FFg. Effects of volcanism are qualitatively different from those of the weathering and other near-surface mobilization processes mentioned above, in that volcanism transports materials from much deeper in the crust and may inject elements into the atmospheric reservoir. 

Despite the difficulties, there have been many efforts in recent years to evaluate trace metal concentrations in natural systems and to compare trace metal release and transport rates from natural and anthropogenic sources. There is no single parameter that can summarize such comparisons. Frequently, a comparison is made between the composition of atmospheric particles and that of average crustal material to indicate whether certain elements are enriched in the atmospheric particulates. If so, some explanation is sought for the enrichment. Usually, the contribution of seaspray to the enrichment is estimated, and any enrichment unaccounted for is attributed to other natural inputs (volcanoes, low-temperature volatilization processes, etc.) or anthropogenic sources. 

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