Dust, surface

The name dust , is used in a variety of ways, and with different meanings. These range from the material that accumulates on the earth s surface, such as on streets and in living and working environments, to the particulate material suspended in the atmosphere. In this paper I wish to consider these two materials in terms of their chemical composition, sources and relationship between them. The names used for the two materials will be surface dust and atmospheric dust . The word aerosol may also be used for atmospheric dust but it more properly applies to the finer particles of atmospheric dust and includes liquid aerosol (i). Botfi surface and atmospheric dusts are increasingly seen to be a hazard to human beings as they are a source of intake of toxic materials such as heavy metals. For this reason study is important of the composition and sources of the dusts. 

The contribution of atmospheric dust to surface dust depends on the dust falling to the earth. This occurs either as dry dust fall or wet washout with rain, snow or hail (1-6,8-10). Dry dust fall occurs by s imentation, impaction, interception or diffusion. Sedimentation, the fall under gravity, may be estimated using Stoke s law which relates the density and diameter of particles to their falling velocity. A particle of density 1.0 g cm"3 and diameter around 0.1 pm would fall with a velocity of around 9 x 10" cm s" ... 

It is clear that both atmospheric and surface dusts are complex materials and not all that easy to describe. A summary is given in Fig. 2 of the sources of atmospheric and surface dusts and their inter-connection. Both natural and anthropogenic sources contribute to both dusts. The inter-connection between the two dusts is wet and dry deposition from the atmosphere to the ground, and the re-entrainment of surface dust through wind and human activity into the atmosphere. Dust is an important global component of our earth, and impinges on the wellbeing of people. 

Fig. 2. The sources and inter-connection between atmospheric and surface dusts.

Diverse techniques have been employed to identify the sources of elements in atmospheric dust (and surface dust) (Table V). Some involve considering trends in concentration and others use various statistical methods. The degree of sophistication and detail obtained from the analyses increases from top left to bottom right of the Table. The sources identified as contributing the elements in rural and urban atmospheric dusts are detailed in Table VI. The principal sources are crustal material, soil, coal and oil combustion emissions, incinerated refuse emissions, motor vehicle emissions, marine spray, cement and concrete weathering, mining and metal working emissions. Many elements occur in more than one source, and they are classified in the... 

The two surface dusts most studied are street and house dusts. As with atmospheric dust there is a remarkable agreement in the concentrations of the elements in either street or house dusts taken from a wide variety of sources (73). Therefore it is possible to estimate median concentrations for each element in the two dusts. The estimates are listed in columns 8 and 9 in Table H. One feature is that the concentrations of the elements in the two dusts are of the same order of magnitude as in soil (column 11, Table n). 

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. 

Table V Methods of Identifying Sources of Elements in Aerosols and Surface Dust...

House dust. Houses are enclosed spaces and tend to accumulate dust from the outside. There are also internal sources of house dust. The concentration ratio [MJhouse dust/[M]soil has a mean of 0.33 (standard deviation = 0.09) for the ten elements Mn, Fe, La, Sm, Hf, Th, V, Al, Sc and Ce suggesting that around 33% of house dust is soil (93). The concentration ratio for the two surface dusts, [M]house dust/[M]street dust is >1 for the elements Cu, Co, As, Sb, Zn, Cd, Au, Cl and C suggesting these elements also have an internal component. All of these elements, as well as Pb and Br, are enriched in house dust relative to their concentrations in soil. Lead and bromine originate mainly from outside the house, and probably from street dust and motor vehicle emissions and, in the case of lead, from paint. When the concentrations of lead in house dust are very high this generally signifies an internal source of lead paint, especially in older houses. 

Guinea pig and rat, adult 241 Am in three surface dust samples, single dose applied to tongue (GP, 5-15 ng/kg) or fed (rat, 12-49 ng/kg) GP 0.002 0.005 Rat 0.0003 0.001 0.001 Absorption estimate based on comparisons with liver and carcass 241 Am after an intraperitoneal dose, with adjustment for excretion Harrison et al. 1994... 

In the Cincinnati prospective lead study of public and private low- and moderate-income housing, the lead concentration ranges were painted interior walls, 0.1-35 mg/cm2 interior home surface dust, 0.04-39 mg/m2 and 72-16,200 pg/g interior home dustfall, 0.0040-60 mg/m2/30 days exterior dust scrapings, 20-108,000 pg/g and dust on children s hands, 1-191 pg. The lead levels in older private deteriorating or dilapidated housing were higher than the levels in newer public and rehabilitated housing (Clark etal. 1985). 

Bomschein RL, Succop PA, Krafft KM, et al. 1986. Exterior surface dust lead, interior house dust lead and childhood lead exposure in an urban environment. In Hemphil DD, ed. Trace substances in environmental health. Vol. 20. Columbia, MO University of Missouri 322-332. 

DugganMJ. Inskip MJ. 1985. Childhood exposure to lead in surface dust and soil A community health problem. Public Health Rev 13 1-54. 

Surface dust from e-waste sites also contained enriched metals. Elevated mean concentrations of heavy metals, such as Pb (52,770 mg/kg), Cu (13,400 mg/kg), Zn (5,080 mg/kg), and Ni (605 mg/kg), were found in surface dust collected from e-waste recycling workshops in Guiyu (Table 2) [14]. The mean concentration of Pb (52,770 mg/kg) was 29 times higher than that in floor dust samples from printer circuit board component separation workshops in East Delhi, India. This may indicate that Pb pollution in e-waste sites of China was much more serious than... 

Leung AOW, Duzgoren-Aydin NS, Cheung KC, Wong MH (2008) Heavy metals concentrations of surface dust from e-waste recycling and its human health implications in southeast China Environ Sci Technol 42(7) 2674—2680. doi 10.1021/es071873x... 

Windblown Surface Dust Quartz Calcite Oxides of iron Clay minerals Montmorillonite Illite 1-10 pm 30% globally... 

The most frequently used methods for sampling indoor surface dust for SVOC/ POM analysis is simply to use dust from a vacuum cleaner dust bag, see for example, Krause, Chutsch and Englert (1989), or a special vacuum cleaner mouthpiece containing a filter, see for example, 0ie, Hersoug and Madsen (1997). Both the mouth-piece and the filter should be cleaned prior to use. It must be assured that the SVOCs and POMs of interest are quantitatively captured by the filter (e.g., phthalates are quantitatively captured by quartz fiber filters (Clausen and Wolkoffi 1997b)) and that the vacuum cleaner exhaust does not contaminate the samples with for example, phthalates. However, the vacuum cleaner sampling method is probably very dependent on the sampling conditions (e.g., carpet or hard floor... 

To avoid the problems with vacuum cleaner surface dust sampling a special surface dust sampler, HVS-3, was developed (Roberts et al, 1991). The sampler consists of a nozzle that can be adjusted to a well defined distance to the surface, a cyclone that collects the dust particles, an air pump, and an exhaust filter to capture particles that are not retained in the cyclone. SVOCs may break through the cyclone as vapors and a PUF plug can be inserted after the cyclone. HVS-3 has been modified to ensure a more constant suction pressure and volume, and a known sampled area (Gyntelberg et al, 1994). The design and use of the HSV3 has now been standardized (ASTM, 1997, D 5438-94). 

No association was found for BaP in house dust and the indoor air by Dieckow, Ullrich and Seifert (1999). Nor did Fromme et al. (2004b) find an association between concentrations of polycyclic aromatic hydrocarbons in household dust and indoor air. But for fluoranthene, phenanthrene, and pyrene, statistically significant correlations of surface dust loadings (ngcnf2) with personal air and indoor air concentrations were noted (Clayton et al., 2003). As stated by Hansen and Volland (2002), there seems to be no simple relation between PAHs in air and in dust. 

Absorption and Adsorption are not the sam e Absorption is the incorporation (sometimes even consumption) of a matter into a medium (light is absorbed/consumed by a pigment, gas is ab-sorbed/dissolves into a liquid), whereas Adsorption is the adhesion of matter onto a—usually solid—surface (dust on furniture, steam on windscreen, vapours on any solid surface...) Adsorption is further subdivided in chemisorption, in which the matter is bound to a surface by chemical bonds, and phy si sorption, in which the bonding is only a physical effect. The transition between both is fluent. 

The sanded panel is brushed and vacuumed to remove surface dust and debris. Minute wood particles remaining on the surface through subsequent finishing steps will result in defective filling and printing operations. 

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