Environmental Levels And Human Exposure


Environmental levels

Limited data are available on the concentration of asphalt in environmental media. Asphalt fractions, including polars, aromatics, and saturates, were characterized in airborne particles and air samples collected 2.0–83.6 m from a highway in Denmark and in plant samples (grass, leaves, and wheat straw) collected 2.0–10.0 m from the highway (Kebin et al., 1996). The percentage of asphalt in these airborne particles was 1.61–11.02%. Concentrations of asphalt fractions in air samples were 0.54–3.96 × 10–3 mg polars/m3 air, 1.77–9.50 × 10–4 mg aromatics/m3 air, and 0.21–1.23 × 10–4 mg saturates/m3 air. Concentrations of asphalt fractions for polars, aromatics, and saturates in mg/g dry plant material were: 0.96, 0.89, and 0.37 for grass; 0.93 and 3.07, 2.91 and 3.89, and 1.28 and 1.53 for leaves; and 1.19 and 0.29, 1.38 and 1.30, and 0.63 and 0.56 for wheat straw (at 5 m and 10 m, respectively), respectively. However, diesel and gasoline exhaust from nearby traffic may have contributed to the composition of these fractions. An assessment was made of the effects of runoff from asphalt pavement on streams in California, USA (Cooper & Kratz, 1997). Concentrations of PAHs and selected heavy metals (lead, zinc, cadmium) were determined in water samples collected from water draining road surfaces and from waters upstream and downstream from the point where water discharged from road surfaces into stream sites. Results of analyses indicate that concentrations of all PAH analytes in all stream and road runoff samples were below the detection limit of 0.5 μg/litre. Although detectable levels of heavy metals were present in stream and runoff water, the authors concluded that no significant upstream versus downstream differences existed in the concentrations of any heavy metal across all streams. Furthermore, concentrations of metals were elevated in runoff waters from the road surfaces relative to upstream samples.

Elevated metal concentrations could be due to sources other than asphalt (i.e., vehicle emissions, crankcase oil drippings, industrial operations, etc.). Kriech et al. (2002b) conducted a laboratory study to determine 29 PACs in leachate water of six paving asphalt and four roofing asphalt samples. Samples were leached according to US Environmental Protection Agency (EPA) method SW846-1311. Results indicated that none of the roofing samples tested leached any of the 29 PACs. While four of the paving samples did not leach any of the 29 PACs, leachate of two paving samples contained detectable amounts of naphthalene and phenanthrene; however, the levels were well below drinking-water limits (0.015 mg/litre) in the USA. Similarly, Brantley & Townsend (1999) performed a series of leaching tests on samples of reclaimed asphalt from facilities in Florida, USA. None of 16 EPA priority pollutant PAHs were detected in the water leachates of any of these samples. The authors pointed out that during normal use of pavement, the asphalt may come in contact with vehicle exhaust, lube oils, gasoline, and metals from brake pads. In addition, Brandt & DeGroot(2001)  demonstrated that PAH concentrations in leachate water from 10 asphalts were well below the European maximum tolerable concentration for potable water (0.1 μg/litre).


Human exposure

Quantitative information on levels of asphalt in drinking-water and foodstuffs has not been identified. However, experiments conducted to determine whether the use of asphalt seal coating in ductile-iron pipe would contribute significant concentrations of PACs in drinking-water indicated that the highest concentration found in three experiments was 5 ng/litre (Miller et al.,

1982). The significance of these experiments is unclear, since they represented a worst-case scenario and the pipes were aged for only 1 month in a laboratory setting.

In the USA, approximately 300 000 workers are employed at hot-mix asphalt facilities and paving sites (APEC, 1999); an estimated 50 000 workers are employed in asphalt roofing operations; and about 15002000 workers are employed in approximately 100 roofing manufacturing plants (AREC, 1999). In Western Europe, there are approximately 4000 asphalt mixing plants employing 5–10 individuals per plant. Approximately 100 000 members of paving crews apply these asphalt mixes to road surfaces across Western Europe (Burstyn, 2001).

Data collected between 1994 and 1997 during seven paving surveys conducted in the USA by NIOSH (2000) indicated that, in general, most TWA PBZ air concentrations for both TP and BSP were below 0.5 mg/m3.

Geometric mean (GM) full-shift PBZ samples for TP and BSP ranged from 0.041 to 0.48 mg/m3 and from 0.073 to 0.12 mg/m3, respectively. However, GM data collected during paving operations in a tunnel in Boston, Massachusetts, USA (Sylvain & Miller, 1996), indicated that PBZ exposures to TP and BSP were about 3 times higher than exposures measured during the seven

NIOSH surveys at open-air roadway paving sites (NIOSH, 2000). Personal exposures to TP and BSP ranged from 1.09 to 2.17 mg/m3 and from 0.30 to 1.26 mg/m3, respectively (Sylvain & Miller, 1996).

Other studies examined exposures to asphalt not only at road paving sites, but also at hot-mix plants, refineries and terminals, roofing manufacturing plants, and roofing application sites in the USA (Hicks, 1995; Exxon, 1997; Gamble et al., 1999). GM exposures for TP and BSP at these sites are presented in Table 5. GM exposures for TP and BSP varied across all industry types: TP ranged from 0.18 to 1.40 mg/m3, and BSP ranged from 0.05 to 0.27 mg/m3. Heikkilä et al. (2002)

reported GM exposures for TP from asphalt (described by the author as bitumen fume) of 0.4, 0.5, and 4.1 mg/m3 for paving operator, screed operator, and manual mastic paver, respectively. Similarly, Burstyn et al. (2000) reported higher GM asphalt fume exposures (described by the author as bitumen) during mastic laying operations (2.29 mg/m3) compared with exposures during paving operations (0.28 mg/m3). These values indicate that exposures may be higher in situations such as mastic laying.


Several investigators have attempted to assess asphalt exposure by the dermal route. Wolff et al. (1989) collected dermal wipe samples by wiping a 3 × 3 cm area of the forehead of workers exposed to asphalt during the application of hot asphalt to roofs in order to evaluate the extent to which dermal absorption of PAHs may contribute to the total body burden. These dermal wipe samples were analysed for specific PAHs. In the Wolff et al. (1989) study, PAH residues per square centimetre of skin were higher in postshift samples (6.131 ng/cm2) than in preshift samples (0.44–2.2 ng/cm2).



Geometric mean of personal exposures (mg/m3)

Type of industry





Road paving





Hot-mix plants





Refineries and terminals





Roofing manufacturing





Roofing application





a Adapted from Hicks (1995).

b Adapted from Exxon (1997) and Gamble et al. (1999).


Table1. Geometric mean of personal exposures for total particulates (TP) and benzene-soluble particulates (BSP).


However, workers monitored during the entire roofing application were potentially exposed to PAHs during both the removal of the old coal tar pitch roof and the application of hot asphalt for the new roof. Hicks (1995) collected dermal wipe samples by wiping a 4 × 8 cm area from the back of the hand or forehead of workers at the various asphalt sectors described in Table 5. The

PAH concentrations determined from these postshift samples ranged from 2.2 to 520 ng/cm2. Workers in paving operations produced the largest number of PAHs detected (12 of 16), while refinery and roofing workers had the fewest (2 of 16). However, the HPLC/fluorescence technique used by these authors cannot reliably identify and quantify components of asphalt; their results are presented for completeness only. Toraason et al. (2001, 2002) examined urinary 1-OHP concentrations at the beginning and end of the same work week (4 days later) in seven roofers who applied hot asphalt products but had no coal tar exposure during the preceding 3 months. All seven workers were smokers at the time of the study. Urinary 1-OHP concentrations were statistically significantly increased (P<0.05) at the end of the work week start of work week) 0.26 ± 0.13 μmol/mol creatinine; end of work week 0.58 ± 0.29 μmol/mol creatinine). The average weekly TWA exposure for TP and BSP for a crew of six asphalt-only roofers was 0.24 ± 0.10 mg/m3 and 0.08 ± 0.02 mg/m3, respectively. The TWA exposures for TP and BSP for a seventh roofer in another crew were 0.31 mg/m3 and 0.18 mg/m3, respectively.

Heikkilä et al. (2002) measured preshift and postshift urinary 1-OHP concentrations in 32 road pavers participating in a study to evaluate asphalt fume exposures of workers employed at 13 paving sites where 11 different asphalt mixtures were applied. The mean TP exposure for the 11 asphalt mixtures ranged from 0.2 to 4.2 mg/m3 (AM [arithmetic mean] = 0.6 mg/m3; GM =0.5 mg/m3). The mean TP exposure for all mixtures was below 0.5 mg/m3, with the exception of manual mastic paving (4.2 mg/m3) and stone mastic asphalt (2.0 mg/m3). The control group consisted of 78 smoking and non-smoking unexposed office workers obtained from a national reference group for 1-OHP in Finland.

The authors reported that mean 1-OHP concentrations were statistically significantly higher (P < 0.05) among pavers (AM = 6.6 nmol/litre, standard deviation [SD=9.8]) than in controls (AM = 1.6 nmol/litre, SD = 2.6) and twice as high among pavers who were smokers (preshift: AM = 8.5 nmol/litre, SD = 10.5) as among pavers who were non-smokers (preshift: AM = 4.0 nmol/litre, SD =8.0) (P < 0.05) (P. Heikkilä, personal communication, Finnish Institute of Occupational Health, Helsinki, 2003. (A similar trend was observed in postshift data (data not shown). There was no difference between nonsmoking road pavers or non-smoking referents (data not shown), suggesting that smoking strongly influences urinary 1-OHP concentrations and may not be a sensitive measure of occupational asphalt fume exposure. No studies that report exposures to cutback asphalts, emulsified asphalts, or asphalt-based paints (products applied at or near ambient temperatures) have been found. Because these products are liquids, workers may be exposed via inhalation and dermal contact.

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