Lead in street dusts

Al-Chalabi, A.S. and Hawker, D. (1996) Retention and exchange behaviour of vehicular lead in street dusts from major roads. Sci. Total Environ., 187, 105-119. 

Table 4.6 Concentrations of total lead in street dusts in Lancaster, England (mg kg" as collected) [20].

Harrison, R. M. Organic lead in street dusts. J. Environ. Sci. Health A 11, 417... 

A method for analysis of Pb(C2Hs)4 and other alkyllead compounds in street dust was developed. From measured values between 0.4 and 7.4 ppm and at least two orders of magnitude less than the inorganic lead content, it was concluded that if there is a health hazard associated with lead in street dust, it is due to the inorganic lead rather than to the organolead compounds present [330]. 

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. 

Biggins, P.D.E. and Harrison, R.M. (1980) Chemical speciation of lead compounds in street dusts. Environ. Sci. TechnoL, 14, 336-339. 

Copper, lead, cadmium and zinc have been found predominantly in potentially mobile forms by sequential extraction of material collected during road cleaning (Colandini et al, 1995). Cadmium and zinc were found to be more labile than lead and copper. A study of street dust and gully pot sediments confirmed this order of potential availability (Striebel and Gruber, 1997) and also suggested that lead levels in material of the types studied had decreased since the introduction of unleaded fuel in Germany. Lead has also been studied in street dusts from Brisbane, Australia. The element was found mainly in the carbonate phase and in the smaller particle size fraction (Al-Chalabi and Hawker, 1996) except where resuspension caused particle aggregation. 

Larssen S, ROYSETOand VadsetM (1997) Origin and patterns of distribution of trace elements in street dust unleaded petrol and urban lead. Atmos Environ 31 2733-2740. 

Harrison, R.M., Laxe, D.P.H., Wilson, S.J., 1981. Chemical associations of lead, cadmium, copper and zinc in street dusts aud road side soils. Euvirou. Sci. Techuol. 15, 1378-1383. 

Levels of tetra-, tri-, and dialkyllead were measured in street dust samples collected in 1976 in Lancaster (UK), and the concentrations ranged between 0.4 and 7.4pgPbg. With regards to the study carried out in Sibenik (Croatia), in contrast to the total lead (19.8 +17ng per g), organolead compovmds were not found to be accumulated in sediments (0.2 +0.2 ng per g). 

Highly elevated concentrations of lead may be found in deposited dust and in street dusts close to lead works. Concentrations of up to 300000 mg kg (30%) lead have been reported, but typical values are of the order of 1000-50 000 mg kg" [11]. 

When viewing theie concentrations, one point worthy of note is that lead levels in deposited urban dusts sampled in 1928, before the widespread use of leaded petrol, showed concentrations very similar to those found today in street dusts [11]. Presumably the far greater emissions of smoke from coal combustion and the use of high-lead paints had a substantial influence upon lead deposition. 

Concentrations of lead in household dusts are of a similar order to those in street dusts, although it is not clear whether the prime source of lead is within or without the house [20]. 

Table 4.7 Crystalline compounds of lead identified in street dusts [22].

There is less certainty about the magnitude of the effect of the direct ingestion of lead in deposited dust (street dust or dust incorporated in soil). The possible magnitude of this intake by young children, who are particularly susceptible, has already been discussed (Section 7.2.5). There are in addition some epidemiological data which are summarized in Table 7.9. These data show a remarkable consistency when analysed as a log-log relationship and when applied at comparable exposure levels. They would suggest an increase in PbB for children of ca. 3 Mg (100 ml) when the soil lead (PbS) increases from 200 to 1200 mg kg"L It must be noted however that these studies do not prove that the soil lead was the sole cause of the increase in blood lead levels. 

Dusts containing lead have been shown to be a significant pathway for childhood Pb exposures, notably dusts with which children readily and frequently come in contact. Dusts are composed of much smaller particles in more mobilizable form than soils and are also more readUy transportable by various means within children s Pb environments. In the case of street dusts, in vitro testings show that simulated gastric acidity conditions in children as a solubilization surrogate for ingestion of leaded dusts by children readily mobilize street dusts. Across various studies, up to 90% Pb in street dusts can be dissolved (Table 8.5). 

It has been demonstrated that a small part of the lead content of street dust (mean three ppm, 0.1% of total lead) (Harrison 1976, Harrison and Laxen 1978) and airborne particles (mean 0.02 /xg/m, 0.5% ) (Harrison and Laxen 1977 and 1978) is organic. Potter et al. (1977) could not find RsPb or RaPbXz in roadside dust above the detection limit of two ppm. Further, I Pb levels were below 0.02 ppm (Potter et al. 1977), indicating that most of the organolead found in street dust is probably alkyUead salts. 

Pb(CH3)4 in street dust is extracted with ammoniacal methanol and reacted with I2 the extracted lead is determined by atomic absorption spectroscopy [596] see also [597]. 

Very low levels of organic lead were found in street dust [39]. According to other studies, Pb(C2H5)4 was absent in street dust or soil [106]. 

Nageotte, S. M., and Day, J. P. (1998). Lead concentrations and isotope ratios in street dust determined by electrothermal atomic absorption spectrometry and inductively coupled plasma mass spectrometry. Analyst (London) 123(1), 59. 

While lead in soil does not appreciably dissipate over time, some lead in soil and especially lead in street and sidewalk dust can be washed away by rain. It is likely that the lead concentrations in street and curbside dust were greater in the early 1970s during the peak use of leaded gasoline than it is today (Rolfeeta/., 1975 Wheeler eta/., 1979 Hamilton eta/., 1984 and Brunekreef eta/., 1983). 

ICP-MS isotope ratio measurements of house dust samples were used to assess potential sources of Pb [342]. Street dust and soil outside the house showed similar Pb isotope ratios, but lead paint in the house had a different isotopic pattern. Sources of lead outside the home were found to contribute as much to lead in most of the house dusts as did lead from lead-based paints inside the house. 

In busy avenues, the street dust has a lead content ranging from 500 ppm to 2 500 ppm and plant screens are effective to reduce the lead burden in gardens. Some similar results were obtained in British cities (Davies 1978). 

Duggan MJ and Williams S (1977) Lead in dust in city streets. Sci Total Environ 7 91-97. 

Thus, we conclude that the likely sources of Pb in this house dust originate from both indoor (Pb-based paint) and outdoor (soil) sources. These conclusions are similar to those of Adgate et al. (1998a, b) who used Pb isotopes to study the contributions from indoor versus outdoor Pb sources in New Jersey homes. Adgate et al. (1998a) estimated that around 35% of total Pb in house dust originated from lead-based paints compared to 50% coming from soil and street dust in an urban area. 

A large part of the lead deposited in the street surface from vehicle exhausts becomes incorporated in the street dust. It is then transported during a runoff event as a suspended solid. Street sweeping, often vacuum assisted, removes solids from the street surface and thus reduces the lead available for runoff. There remains, nevertheless, the problem of disposal of the contaminated street dust. 

Duggan MJ, Williams S (1977) Lead-in-dust in city streets. Sci Total Environ 7 91-97 Dyson SE, Jones DG (1976) Some effect of undernutrition on synaptic development -a quantitative ultudastructural study. Brain Res 167 363-371 Fomon SJ (1974) Infant nutrition, 2nd ed. W.B. Saunders Company, Philadelphia London, p 24... 

Dusts resuspended in localized atmospheres reflect both the distribution of lead species and particulate sizes in the dusts or soils serving as the source and the main mechanisms producing the resuspension. Street dusts have a bimodal distribution, the fine particle sizes arising from the tailpipes directly and the coarse materials from such mechanisms as smaller particle distribution. Al-Chalabi and Hawker (1997) reported that with increasing resuspension, the lead levels decreased, consistent with either coalescing small and coarser particles or increasing dispersion from the source. Similarly, Abu-Allaban et al. (2003) reported that road dust had most of its lead content in the coarse fraction. 

Leaded dusts can occur in soils, in the household, on hard exterior surfaces such as streets, and as occupational dusts in the specific context noted above. The ability of lead in dusts to rapidly accumulate on hard surfaces produces both a problem for quantification and a potent potential factor in human lead exposure assessments (U.S. EPA, 1986, Ch. 7). The physical and chemical compositions of dusts as well as the levels of lead are determined in large measure by their origin. It is also typical of dusts that they can deposit onto an almost infinite array of hard surfaces, and as a consequence can accumulate to quite high levels over time. This accumulation can be depicted quantitatively as either concentration or as dust lead loadings. 

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