Common Contaminants in Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 233

Health effects from exposure to benzene include headaches, dizziness, drowsiness,
rapid heart rate, tremors, and unconsciousness. Exposure to high levels can result in
death (ATSDR 2007a). Health effects from exposure to toluene include tiredness, confu-
sion, loss of appetite, memory loss, loss of color vision, and nausea (ATSDR 2001); whereas
exposure to ethyl benzene may cause irreversible damage to the inner ear and hearing
loss, dizziness, and kidney damage (ATSDR 2007b). You are not safe around xylenes
either, as exposure to them can result in headaches, lack of muscle coordination, dizzi-
ness, and confusion. Exposure to very high levels of xylenes can cause unconsciousness
(ATSDR 2007c).
Methyl-tert-butyl ether (MTBE) is a LNAPL compound produced exclusively as a gaso-
line additive, and it belongs to a group of chemicals known as “oxygenates” because they
raise the oxygen content of gasoline and thereby raise the octane level. MTBE is a colorless
liquid at room temperature, and is very volatile and flammable (USEPA 2007). The pur-
pose of adding MTBE to gasoline was to increase the efficiency of combustion in automo-
biles enabling them to run cleaner and emit fewer pollutants, thus improving air quality
in urban areas. However, the use of MTBE has declined recently because (1) of health
concerns and (2) MTBE has been detected in many groundwater aquifers used as drinking
water sources in the United States (USEPA 2007). Many states now ban MTBE because of
its propensity to contaminate groundwater and the high costs incurred to remove it from
groundwater (United States Department of Energy 2009).
MTBE is also used to dissolve gallstones. Patients treated for gallstones using MTBE
have MTBE delivered directly to the gall bladder through surgically inserted tubes. Health
effects from exposure to MTBE may include nose and throat irritation, headaches, nausea,
dizziness, and mental confusion. Currently, evidence suggesting that MTBE may cause
cancer is lacking (ATSDR 1997; USEPA 2009b).
7.3.2 Dense Nonaqueous Phase Liquids
DNAPLs are liquids denser than water, that do not mix or dissolve readily in water (USGS
2006). DNAPL compounds include many common solvents and coal tar (Suthersan and
Payne 2005). They are also commonly referred to as chlorinated solvents or haloge-
nated VOCs because chlorine is in the atomic structure, and the most common uses of
these compounds are for cleaning and degreasing (USGS 2006). Chlorinated solvents
have been in use for nearly 100 years. They are still widely used by industry, and many
household products contain them (Figure 7.3) (USGS 2006).
Halogenated VOCs are a group of organic compounds with a halogen atom as part of its
molecular structure. Halogens include the elements Fluorine (F), Chlorine (Cl), Bromine
(Br), or Iodine (I). Part of the uniqueness of halogenated VOCs is they tend to have a very
weak tendency to form hydrogen bonds with water. This lack of affinity for water means
the halogenated VOCs—especially those with fluorine or chlorine—tend to be hydropho-
bic and have low solubility (Suthersan and Payne 2005).
Common halogenated VOCs include the following:
• Tetrachloroethene (PCE)
• Trichloroethene (TCE)
• cis -1,2-Dichloroethene (DCE)