Common Contaminants in Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 236

TABLE 7.4
Chemical Formula and Carcinogenicity for Common THMs

Compound CAS Registry Number Carcinogenicity Rating Chemical Formula

Chloroform 67-66-3 Group: A2 CHCl 3

Bromodichloromethane 75-27-4 Group: A2 CHBrCl 2

Dibromodichloromethane 124-48-1 Under Review CHBr 2 Cl

Bromoform 75-47-8 Under Review CHBr 3

Source: United States Environmental Protection Agency, Integrated Risk Information System (IRIS),

http://www.epa.gov/ncea/iris/intro.htm (accessed October 21, 2009), 2009b.

disinfect water for drinking or recreational use; they form from a
reaction between chlorine and/or bromine with organic matter (EPA
2006). Chloroform, a common THM, has also been used as an anes-
thetic and is often used in swimming pools as a disinfectant (ATSDR
1997b). The most common THMs, CAS registry numbers, carcinoge-
nicity rating, and chemical formula are listed in Table 7.4 (ATSDR
1989, 1997b). The structure of chloroform and bromodichlorometh-
ane are shown in Figures 7.5 and 7.6.
According to USEPA (2009b), THMs may cause adverse health effects
at high concentrations. Exposure to high concentrations of bromo-
form may interfere with normal brain function and cause sleepiness
(ATSDR 2005). USEPA has established maximum allowable concen-
tration of THMs in drinking water at 80 μg/L for the combined con-
centration of chloroform, bromoform, bromodichloromethane, and
dibromochloromethane.

H

C

Cl Cl

Cl

FIGURE 7.5
Molecular structure
of chloroform.

H

C

Cl Br

Cl

FIGURE 7.6
Molecular structure
of bromodichloro-
methane.

7.4 Polynuclear Aromatic Hydrocarbons
PNAs or PAHs are a group of compounds formed synthetically or naturally during
the incomplete combustion of coal, oil, tar, gas, wood, garbage, and may also be pres-
ent in tobacco, medicines, dyes, plastics, pesticides, and charbroiled meat (United States
Department of Health and Human Services [USDHH] 1995). Other sources of PAHs include
heavy petroleum, including diesel fuels, kerosene, aviation fuels, heavy home-heating oils,
oils, waste oil, and many lubricants (Missouri Department of Natural Resources 2006).
Overall, there are more than 100 distinct PAH compounds.
Chemically, PAHs are composed of multiple benzene rings (Figure 7.7), are lighter than
water, and are generally not very soluble in water. In addition, PAHs strongly attach them-
selves or sorb to soil grains, especially organic soils and clay (USEPA 1989). Because PAHs
are not very soluble and are lighter than water, they are considered LNAPLs.
With two rings, naphthalene is the smallest of the PAHs. Naphthalene is a common PAH
compound, and is characterized by its distinctive odor and common use in mothballs.
Anthracene and phenanthrene are composed of three rings. Phenanthrene is an isomer of
anthracene and they share many physical properties except boiling point and water solu-
bility (Fetzer 2000). With its five rings, benzo(a)pyrene is the largest PAH molecule, and is
the only known human carcinogen of the four compounds shown in Figure 7.7 (Group:A1).