Air, lead concentrations

Extrapolation of the data obtained In this study to the situation world-wide leads to a tentative estimate that people living In about one third of the cities of the world may be exposed to air lead concentrations which are either marginal or unacceptable. The problem Is probably most acute In large urban areas In developing countries with dense automobile traffic. This problem could be easily mitigated through a world-wide effort to eliminate lead In fuels. 

Abulfaraj WH, Ahmed M, Mousli KM, et al. 1990. Measurement of ambient air lead concentrations in the city of Jeddah, Saudi Arabia. Environ Inter 16 85-88. 

Pbs=soil lead concentration PbD=dust lead concentration Pbw=water lead concentration PbA0=outside air lead concentration PbAI = inside air concentration PbF=food lead concentration T=relative time spent... 

Values of AAF are plant dependent, due to differences in surface characteristics, but values of 5 0 are typical.Thus, a plant grown on an agricultural soil with 50 mg kg lead will derive 0.25 mg kg dry weight lead from the soil (CF = 5 x 10 ), while airborne lead of 0.1 pg m will contribute 2.0 pg g (=mg kg ) of lead (AAF = 20 m g ). Thus, in this instance airborne lead deposition is dominant. The air lead concentration of 0.1 pg m was typical of rural areas of the UK until 1985. Since that time, the drastic reduction of lead in gasoline has led to appreciably reduced lead-in-air concentrations in both urban and rural localities. 

Commission of European Communities, Air Lead Concentration in the European Community, Yearly Report April 1971-March-1971, Luxemburg 1973. 

TABLE 1-3 Lead Exposure on US Air Force Firing Ranges (2007-2012)—Air Lead Concentrations on Weapons and... 

The OSHA lead standard set the PEL at 50 pg/m as an 8-hour TWA, which was technically feasible for industry. In OSHA s opinion, a lower air lead concentration of 40 pg/m would not offer a substantial benefit compared with 50 pg/m. ... 

At the time, the OSHA proposal was for an action level of 50 pg/m, which NIOSH endorsed in its criteria document as a future goal to provide greater assurances of safety (NIOSH 1978, p. XII-19). That air level would keep BLLs at about 40 pg/dL or lower in virtually all workers, protecting against subclinical effects of lead. NIOSH also endorsed a vigorous medical surveillance program for workers exposed above the action level but below the proposed maximum air lead concentration of 100 pg/m. NIOSH estimated that even at the proposed air standard of 100 pg/m less than half of the workers will have blood lead levels above 40 [pg/dL] (NIOSH 1978, p. XII-19). 

Derivation of the appropriate air lead concentration used the steepest slope (0.19 pg/dL of blood per pg/m of air) found in the literamre (slopes ranged from 0.03 to 0.19 pg/dL of blood per pg/m of air). A TLV-TWA of 50 pg/m would be expected to result in a BLL of about 9.5 pg/dL. ACGIH proposes that this air concentration will be sufficient to prevent a BLL of 30 pg/dL (the BEI) if other sources (community or noninhalation workplace exposures) are adequately controlled. 

The relationship between air lead concentration and BLL is complex. Exposure to lead can occur through multiple pathways. BLL is the exposure metric most commonly described in association with health effects in humans, and lead exposure is typically assessed by using a pharmacokinetic model to relate air (or dietary) exposure concentratiorrs to BLLs. The committee s goal was not to review in depth the various dosimetry models available for lead but to explore how dosimetry models were used in the development of the OSHA generd industry lead standard and to evalirate the models and their assumptions (see Table 3-1). 

FIGURE 3-3 Time-dependent relationship between BLL and air lead concentration as estimated with the CPA model used by OSHA to develop the permissible exposure level. Estimated DLLs for lead workers exposed to airborne lead at 50 pg/m. ... 

Snee (1982) provides equations based on the best fit to the Williams dataset. When it is apphed to an air lead concentration of 50 pg/m, the resulting... 

The ability to predict BLLs on the basis of air lead concentrations is central to the development of the OSHA standard s PEL. The OSHA PEL of 50 pg/m was set to resirlt in the average lead worker s having a BLL under 40 pg/dL. That BLL was judged by the committee to be inadeqrrate for protecting personnel who had repeated lead exposirres on firing ranges (see response to the first question above) thus, the OSHA PEL for lead woirld also be insufficiently protective. 

The CPA model used in the OSHA standard to predict BLLs from air lead concentrations may not be appropriate for direct application to firing-range personnel, so physiologically based pharmacokinetic or other dosimetry models may need to be developed for this purpose. Those models could consider other biometrics of exposure, such as bone and semen lead levels. 

Later, with data provided by the manual air monitoring system operated by SEDUE, Jauregui and Sanchez (1987) studied the distribution of atmospheric lead in Mexico City during the period 1978-1985. In 1978, the maximum lead concentration found was 2.5 pg/m and corresponded to downtown Mexico City (centro) and the industrial area of Vallejo-Villa (see Fig. 4). In January 1978, a large area of the city had an air lead concentration of 1.5 pg/m, which has been accepted by SEDUE as the limit. In later years, the highest average was 7 pg/m and corresponded to the station located at the industrial area known as Xalostoc. 

In that period, air lead concentrations in the city frequently exceeded the limit of 1.5 pg/m for example, during 1985 this limit was exceeded more than 50% of the time in the central and northern zones of the city (Stations Museo, Xalostoc and La Villa) as well as in one of the southern areas (Taxquena) which, from the data available, is generally considered one of the least polluted in this period the accepted limit was exceeded up to 12% of the time, even for one of the suburban regions located in the northeast of the city (Nezahualcoyotl). This area has consistently shown the lower values of air pollutants and this is attributed by the authors to its being frequently swept by the predominant winds. These data are presented in Table 6. 

Meterological factors may affect the air lead concentrations for example, during the years 1978 to 1984, in the rainy season at the La Villa sampling station, in the northern part of the city, lead levels were below the limit but they exceeded it during the dry season (Jauregui and Sanchez, 1987). 

Fig. 2.3 Annual ambient air lead concentrations, by area, prior to the August 1974 and August 1975 surveys [8].

Since soils are strong accumulators of lead, the analysis of lead in soil is an excellent indicator of accumulated deposition in the vicinity of a source of the metal. In one survey around a secondary smelter [12], concentrations of lead up to 21 000 mg kg" (dry weight) were found in the upper 5 cm of soil adjacent to the smelter with the levels decreasing exponentially with distance from the source. Mean concentrations of lead in soil around the Silver Valley lead smelter [13] (air lead concentrations in Fig. 2.3) are shown in Fig. 4.2. Changes in soil lead between the 1974 and 1975 surveys presumably arise mainly from random errors introduced by minor spatial variability in the lead concentration. 

Of these three pathways, there is at present no available information to assess the magnitude of the contribution of deposited atmospheric lead to the third pathway. There is on the other hand considerable information upon the incremental change in blood lead (dPbB) caused by a small increase in air lead concentration (dPbA) i.e. the ratio dPbB/dPbA (Table 7.8). It is important to remember when examining these data that the ratio dPbB/dPbA is likely to decrease as the exposure to lead increases. There is, furthermore, some evidence that the ratio dPbB/dPbA is higher in children than adults [6]. 

Air lead concentrations for purposes of determining dispersion data can be found by actual measurement over some unit of selected time, e.g., 24-hour high-volume sampling or with various dispersion models. A major factor in either air lead measurement or modehng is the type of lead emission source. Mobile sources or mixes of mobile and point lead sources when modeled within relatively broad geographic areas such as urban zones require quite different quantification approaches than modeling particular point source emissions, i.e., from a primary or secondary lead smelter. 

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