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EC number: 295-518-9
CAS number: 92062-05-0
A complex combination of hydrocarbons obtained from the vacuum distillation of the products from a thermal cracking process. It consists predominantly of hydrocarbons having carbon numbers predominantly greater than C34 and boiling above approximately 495°C (923°F).
substances such as bitumen do not lend themselves to toxicokinetic
analysis as the properties and interactions of the individual
constituents will influence the toxicokinetic behaviour. Toxicokinetics
of some individual constituents, such as specific volatile organic
compound and polyaromatic hydrocarbon (PAH) species have however been
studied in more detail (Syracuse Research Corporation, 1985). The main
routes for bitumen exposure in humans are inhalation and dermal. The
major sites of potential uptake of constituents of bitumen in humans are
the lungs and respiratory tract, after inhalation exposure to emissions
from bitumen, and the skin, as a result of contact with neat bitumen,
cutback bitumen or condensed fumes from bitumen. In general, the
individual constituents of bitumen and fumes from bitumen undergo
oxidative metabolism, which may lead to bioactivation. Whole body
distribution of PAHs has been studied in rodents. These studies have
demonstrated that low but detectable levels of PAHs may be found in
internal organs, especially adipose tissue which may serve as a storage
depot. In general, PAH are eliminated by urinary or biliary excretion of
metabolites (ATSDR, 1999; IPCS, 2005).
limited number of laboratory studies have been done with bitumen
solutions, condensed fumes and fumes from bitumens. Also a limited
number of studies have been performed in humans, either in volunteers or
in workers. From these studies it is clear that some constituents,
including PAH, can be absorbed through the skin and be taken up via the
lungs. Dermal uptake was shown to be a function of viscosity and the
bioavailability of neat bitumen is deemed to be negligible. The
bioavailability of PAH from cutback bitumens is expected to be higher,
but based on experimental data the amounts of PAH becoming available
from the bitumen itself are too low to pose a carcinogenic hazard
(Potter et al., 1999; Brandt et al., 1999; Potter et al., 1995).
Experiments also show that PAHs in condensed fume from bitumen are
bioavailable when the condensate is directly applied to the skin (Roy et
al., 2007). Studies in human volunteers showed that under rather extreme
experimental conditions, the uptake through the skin of 3- and 4-ring
PAH from fumes from bitumen could account for about half of the total
exposure (Knecht et al., 2001; Walter and Knecht, 2007). Studies in
workers, under normal conditions as they occur during paving, gave
evidence of dermal absorption and subsequent systemic availability of 2-
to 4-ring PAH through the determination of urinary metabolites.
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