Geoscience Reference
In-Depth Information
MTBE is an octane enhancer; that is, it promotes more complete burning of
gasoline and thereby reduces carbon monoxide and ozone levels. MTBE is very
soluble, and once released, it moves through soil and into water more rapidly than
other chemical compounds present in gasoline. In groundwater, it is slow to
biodegrade and more persistent than other gasoline-related compounds. Exposure
to vapors may result in several health effects including dizziness, nausea, sore
eyes, and respiratory irritation (McCarthy and Tiemann
2001
). The US EPA
concluded that MTBE poses a potential for carcinogenicity to humans at high
doses; however, because of uncertainties and limitations in available data, the EPA
has been unable to reliably estimate the risk at low exposure levels (EPA
1997
).
Based on this, several wells contaminated with MTBE have been closed, but
because MTBE is an additive, its effect should be considered against other alter-
natives, which usually are more problematic.
In general, because of the combination of solubility and toxicity characteristics,
aromatic compounds are the major group of PH contaminants in groundwater.
However, due to the large amounts of PH released to the environment and lack of
information, much more research is needed to understand the behavior and toxicity
of
these
complex
mixtures
and
their
potential
effect
on
the
subsurface
environment.
4.4 Pharmaceuticals and Personal Care Products
A large class of chemicals gaining attention in recent years comprises pharma-
ceutical, veterinary, and illicit (''recreational'') drugs and the ingredients in cos-
metics, food supplements, and other personal care products, together with their
respective metabolites and transformation products; they are collectively referred
to as pharmaceuticals and personal care products (PPCPs). PPCPs are used in
large amounts throughout the world, and some studies demonstrated their occur-
rence in aquatic environments in Austria, Brazil, Canada, Croatia, Denmark,
England, Germany, Greece, Italy, Spain, Switzerland, the Netherlands, and the
USA (Heberer et al.
2002
; Daughton and Ternes
1999
; Erickson
2002
).
Most PPCPs are disposed of or discharged into the environment on a continuous
basis via domestic and industrial sewage systems and wet weather runoff. In many
instances, untreated sewage is discharged into receiving waters (e.g., flood over-
load events, domestic ''straight piping,'' or sewage waters lacking municipal
treatment). A scheme of possible pathways for the occurrence of PPCP residues in
aquatic environments is depicted in Fig.
4.9
. The bioactive ingredients are first
subjected to metabolism by the dosed user; the excreted metabolites and unaltered
parent compounds then can be subjected to further transformations in sewage
treatment facilities. The literature shows, however, that many of these compounds
survive biodegradation, eventually being discharged into receiving waters. Many
of these PPCPs and their metabolites are ubiquitous and display persistence in, and
bioconcentration
from,
surface
waters.
Additionally,
by
way
of
continuous
