Geoscience Reference
In-Depth Information
Fig. 4.7 Simplified conceptual model for light nonaqueous-phase liquid (LNAPL) release and
migration. Reprinted from Mercer and Cohen (
1990
). Copyright 1990 with permission from
Elsevier
The direct exposure pathways of humans to PH following a leak are described
in Fig.
4.8
. Once released to the surface and subsurface environment, PHs can
reach humans directly as vapors, solutes, or adsorbed on particles.
Here, we briefly discuss several individual compounds that are common con-
stituents of different PH mixtures, the main groups being (1) small aromatic
compounds, mostly benzene derivatives (e.g., benzene, toluene, ethylbenzene, and
xylenes), which are considered slightly soluble (150-1,800 mg/L); (2) branched
and linear aliphatics (e.g., n-dodecane and n-heptane), which are characterized by
relatively low water solubility; and (3) polar hydrocarbons and petroleum additives
(e.g., methyl tertiary-butyl ether (MTBE) and alcohols), which are highly soluble.
The
weight
percentage
of
three
selected
compounds
in
various
commercial
petroleum products is given in Table
4.1
.
Benzene is important from an environmental point of view, as it is an important
component of various petroleum products. Its weight fraction ranges from prac-
tically zero for the heavy distillates to 3.5 % for gasoline, as shown in Table
4.1
.
Its solubility is 1,780 mg/L, and it is very volatile (vapor pressure 100 torr at
26.1 C). The acute (short-term) effects of benzene toxicity include dizziness,
headache, nausea, vomiting, and drowsiness; with higher levels of benzene toxicity
come the threat of convulsions, coma, and death. The long-term or chronic results
of
benzene
toxicity
include
reproductive
damage,
chromosomal
aberrations,
immunodeficiencies, and several types of leukemia (ATSDR
2006b
).
Xylene belongs to the group of small aromatic compounds with relatively higher
solubility, like benzene. Exposure to toluene causes CNS depression (Faust
1994
).
Short-term exposure effects include fatigue, confusion, lack of coordination,
impaired reaction time, perception, and motor control and function (NTP
1990
).
Exposure to high concentrations results in narcosis and death (WHO
1985
). Pro-
longed abuse of toluene or solvent mixtures containing toluene has led to permanent
