Remote atmospheric dust

Fig. 3. Relationships between the concentrations of the elements in remote atmospheric dusts (a) continental vs Antarctic atmospheric dust, (b) island vs Arctic atmospheric dust. [M] is the concentration of element M.

A summary is given in Table III of the results of the elucidation of the sources of the elements in remote atmospheric dusts. Four main sources are identified silicate o dust, marine spray, high temperature natural emissions (e.g. volcanic, plant and rock... 

It is remarkable that, except for local hot-spots such as around industrial sites, mining areas and volcanoes, the elemental compositions of atmospheric dust in similar locations, such as remote or rural or urban are relatively constant over the world. This suggests either common sources, or a dominant source, or good mixing and transport of the dust around the globe. In fact all three factors have a role in determining the uniformity. Because of the consistent composition it is possible to estimate the median concentrations of the elements in atmospheric dusts in similar, but widely separated, locations. These estimates are given in columns 2 to 7 in Table n. The concentrations of the elements in the atmospheric dust are expressed as mass per volume of air. For remote locations (columns 2 to 5) the concentrations are in ng m 3, whereas for rural and urban areas (columns 6 and 7) the elemental concentrations are in xg m-3. 

Since the majority of the elements in surface dust arise from deposited aerosol and added soil it is not surprising to find strong linear relationships between the concentrations of the elements in an atmospheric dust and street or house dust. This is illustrated by the two examples given in Fig. 8 for remote house dust vs urban atmospheric dust and street dust vs rural atmospheric dust. As discussed above crustal/soil material is a major component of atmospheric dust and the soil based elements in the atmospheric dust are Al, Ca, Fe, Mg, Mn, Ni, K, Si and Ti. The elements As, Br, Cd, Cl, Co, Cu, Pb, Rb, Se, V, and Zn are, on the other hand, enriched in atmospheric dust. The same elemental distribution applies to surface dust, but in this case their concentrations (compared on a mass basis) are reduced presumably due to dilution with soil. However, the elements enriched in the atmosphere remain enriched in the surface dusts. 

There is increasing evidence that pesticides have contaminated extensive areas of the world not directly treated with pesticides. In many instances, the translocation can be attributed to food or water as the transmission vehicle. Another medium of dispersal of pesticides is the atmosphere. Analyses of rainwater and dust have revealed the presence of chloro-organic substances in all samples examined. Identification of specific pesticides has demonstrated that at least some of the chloro-organic compounds are pesticidal in origin. An analysis of dust, whose distant origin was documented by meteorological evidence, proved that pesticide-laden dust can be transported over great distances via the atmosphere and can be deposited over land surfaces remote from the point of application. 

Pesticide residues in humans, animals, and fish in areas remote from pesticide application can, in many cases, be attributed to an intermediate such as the food chain. Thus, migratory fish and birds can easily accumulate pesticide residues from foods directly contaminated by pesticide application. In those instances where the food chain cannot serve as a reasonable explanation, then, clearly, the atmosphere, including dust and rainfall, offers an alternative solution to pesticides translocation. 

By itself, the discovery of pesticides in rainfall, however, provides no evidence that the origin of the pesticides was local or distant. The analysis of dust, whose origin has been documented by meteorological evidence, does prove that pesticides can be transported over great distances via the atmosphere, that the pesticides can survive the photochemical processes of high altitude, and, finally, that these pesticides can be deposited over land surfaces remote from their application. 

Mineral dust also has important effects on the amounts of nutrients supplied to the oceans, thereby affecting biological productivity and amounts of CO2 released into the atmosphere (Martin and Gordon, 1988 Watson, 1997). Iron is thought to be a limiting factor for phytoplankton productivity in remote marine areas (Falkowski et al., 1998 Fung et al., 2000 Gao et al., 2001). 

Off-gas purification. As a high-temperature process, any type of vitrification process will have to have a very effective off-gas cleaning system. In fact, besides the remote operation and maintenance technique, off-gas treatment will be among the most important waste-processing problems to be solved. The off-gas may contain volatile fission products, such as ruthenium and cesium, as well as aerosols and dust. Multistage systems will be required with wet and dry cleaning procedures to obtain an off-gas sufficiently clean for release to the atmosphere. 

Natural emissions include lead released from volcanoes, seawater sprays, forest fires, and wind-bome soil particles in remote areas. These releases are typically to the atmosphere and are set forth in Table 4.2. Cumulative atmospheric releases in the natural source category average 19,000 MT/year and a median of 12,000 MT/year (Nriagu, 1989). It should be noted that one has to distinguish between tme natural sources and emissions and those which are more inclusive, i.e., background lead estimates. Such background levels can represent releases to the atmosphere and subsequent deposition of reentrained dusts contaminated with lead from past anthropogenic activities. 

Where atmospheric Pb levels are high, this pathway is significant in terms of PbB contribution. Note that in this modeled depiction, a causality chain and pathway flow within that chain are implicitly required and explicitly depicted. For example, environmental Pb input to the human receptor goes from remote sources to proximate pathway. Hand Pb is proximate to the intake and uptake of Pb by children and lead workers with dusty Pb conditions in the workplace. This approach provides considerable mechanistic information on the specifics of how Pb exposures occur. Cross-sectional SEM models, the more typical form of this approach, probe the relationships among several environmental pathways simultaneously, as would be the case above linking soil and dust Pb to Pb via soil to dust, dust to blood, and the direct path of soil Pb to blood Pb. 

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